Topic 6: Human Physiology

6.1 Outline the sequence of events that occur in order for food to be digested and absorbed.

mouth -\> stomach (with liver and gall bladder) -\> small intestine (pancreas) -\> large intestine -\> anus

mechanical digestion -\> chemical digestion

-food is physically broken down into smaller fragments via the acts of chewing (mouth), churning (stomach) and segmentation (small intestine)

**Absorption occurs in small and large intestine

-pancreas secretes enzymes into the lumen of the small intestine.
-digested food monomers must pass from the lumen into the epithelial lining of the small intestine

6.1 Explain how the muscles in the digestive system aid in digestion.

The contraction of circular and longitudinal muscle of the small intestine mixes the food with enzymes (churning) and moves it along the gut.

Peristalsis:
-peristalsis is the involuntary, wave-like contraction of muscle layers of the small intestine.
-the principal mechanism of movement in the oesophagus, although it also occurs in both the stomach and gut
-continuous segments of longitudinal smooth muscle rhythmically contract and relax
-contraction of longitudinal muscle «layers»/peristalsis helps move food along the gut
-food is moved unidirectionally along the alimentary canal in a caudal direction (mouth to anus)

Segmentation:
-involves the contraction and relaxation of non-adjacent segments of circular smooth muscle in the intestines
-circular muscle contraction prevents backward movement of food
-segmentation contractions move chyme in both directions, allowing for a greater mixing of food with digestive juices
-while it helps to physically digest food particles, its bidirectional propulsion of chyme can slow overall movement

6.1 Explain the source of enzymes, stomach acid, and bile, and how it aids in overall digestion along with associated organs.

Enzymes
-allow digestive processes to therefore occur at body temperatures and at sufficient speeds for survival requirements
-specific for a substrate and so can allow digestion of certain molecules to occur independently in distinct locations

Stomach Acids
-contains gastric glands which release digestive acids to create a low pH environment (pH ~2)
-acidic environment denatures proteins and other macromolecules, aiding in their overall digestion
-stomach epithelium contains a mucous membrane which prevents the acids from damaging the gastric lining
**pancreas releases alkaline compounds (e.g. bicarbonate ions), which neutralise the acids as they enter the intestine

Bile
-liver produces a fluid called bile which is stored and concentrated within the gall bladder prior to release into the intestine
-contains bile salts which interact with fat globules and divide them into smaller droplets (emulsification)
-emulsification of fats increases the total surface area available for enzyme activity (lipase)
-bile/bicarbonate secreted into the small intestine creates favorable pH for enzymes

6.1 Explain the function of the pancreas in digestion.

The pancreas secretes digestive enzymes (e.g. amylase, lipase and an endopeptidase) into the lumen of the small intestine depending on the specific macromolecule required for hydrolysis.
-digestive enzymes are secreted in ribosomes on the rER, processed in the Golgi A. and secreted by exocytosis.

Enzymes digest most macromolecules in food into monomers in the small intestine.

**cellulose remains undigested.
**pancreas also releases alkaline compounds (e.g. bicarbonate ions), which neutralise the acids as they enter the intestine

6.1 Describe and explain one specific feature of the small intestine that aids in the absorption of food.

The inner epithelial lining of the intestine is highly folded into finger-like projections called villi (singular: villus)
-villi increase the surface area of epithelium over which absorption is carried out.
-villi absorb monomers formed by digestion as well as mineral ions and vitamins.
**villi are part of the mucosa layer of the small intestine

rich blood supply (part of submucosa layer):
-each villus has a capillary bed that absorbs sugars and amino acids from the small intestine
-dense capillary network rapidly transports absorbed products

single layer epithelium:
-minimises diffusion distance between lumen and blood
-increases surface area for absorption

lacteals (part of submucosa layer)
-absorbs lipids from the intestine into the lymphatic system

**intestinal glands:
-exocrine pits (crypts of Lieberkuhn) release digestive juices

membrane proteins:
-facilitates transport of digested materials into epithelial cells

tight junctions:
-keep digestive fluids separated from tissues and maintain a concentration gradient by ensuring one-way movement
-gives the sheet mechanical strength
-makes it impermeable to small molecules

mitochondria :
-epithelial cells of intestinal villi will possess large numbers of mitochondria to provide ATP
-required for primary active transport (against gradient), secondary active transport (co-transport) or pinocytosis

absorptive cells:
-have many pinocytic vesicles (does endocytosis)
-creating vesicles that contain liquid and nutrients taken in from the lumen of the small intestine.

6.1 Outline the different methods of membrane transport are required to absorb different nutrients.

**glucose is hydrophilic, therefore needs to be transported via active transport

Secondary Active Transport:
-glucose and amino acids are co-transported across the epithelial membrane by the active translocation of sodium ions (Na+)
-can only work on glucose and amino acids because they are positively charged (like Na+)

Facilitated Diffusion
-help hydrophilic food molecules pass through the hydrophobic portion of the plasma membrane
-situated near specific membrane-bound enzymes (creates a localised concentration gradient)
-certain monosaccharides (e.g. fructose), vitamins and some minerals are transported by facilitated diffusion

Osmosis
-movement in response to the ions and hydrophilic monomers (solutes)
**the absorption of water and dissolved ions occurs in both the small and large intestine


Simple Diffusion
-fatty acids and lipoprotein are hydrophobic, therefore can diffuse through membrane passively
-once absorbed, lipids will often pass first into the lacteals rather than being transported via the blood
-e.g. fatty acids and monoglycerides

Endocytosis
-small droplets of the fluid are passed through the membrane by means of vesicles.
-e.g. triglycerides and cholesterol in lipoprotein particles.

6.1 List out the organs in the digestive system and their functions.

alimentary canal: organs through which food actually passes
-oesophagus, stomach, small & large intestine

accessory organs: aid in digestion but do not actually transfer food
-salivary glands, pancreas, liver, gall bladder

Oesophagus
• A hollow tube connecting the oral cavity to the stomach (separated from the trachea by the epiglottis)
• Food is mixed with saliva and then is moved in a bolus via the action of peristalsis

Stomach
• A temporary storage tank where food is mixed by churning and protein digestion begins
• It is lined by gastric pits that release digestive juices, which create an acidic environment (pH ~2)

Small Intestine
• A long, highly folded tube where usable food substances (nutrients) are absorbed
• Consists of three sections - the duodenum, jejunum and ileum

Large Intestine
• The final section of the alimentary canal, where water and dissolved minerals (i.e. ions) are absorbed
• Consists of the ascending / transverse / descending / sigmoidal colon, as well as the rectum

**Salivary Glands
• Release saliva to moisten food and contains enzymes (e.g. amylase) to initiate starch breakdown
• Salivary glands include the parotid gland, submandibular gland and sublingual gland

Pancreas
• Produces a broad spectrum of enzymes that are released into the small intestine via the duodenum
• Also secretes certain hormones (insulin, glucagon), which regulate blood sugar concentrations

**Liver
• Takes the raw materials absorbed by the small intestine and uses them to make key chemicals
• Its role includes detoxification, storage, metabolism, bile production and haemoglobin breakdown

Gall Bladder
• The gall bladder stores the bile produced by the liver (bile salts are used to emulsify fats)
• Bile stored in the gall bladder is released into the small intestine via the common bile duct

6.1 Application: Explain the use of dialysis tubing to model absorption of digested food in the intestine.

Dialysis tubing models the size-specific permeability of cell membranes.
-large molecules (e.g. starch) cannot pass through the tubing
-smaller molecules (such as maltose) can cross
-these properties mimic the wall of the gut, which is also more permeable to small rather then large particles.
**dialysis tubing is not selectively permeable based on charge (ions can freely cross)

Dialysis tubing can be used to model absorption by passive diffusion and by osmosis.

Experiment to measure:

-meniscus levels in the tube
-amylase digests starch into maltose -\> increase in concentration
-water will move into the tubing via osmosis (towards the solute) causing the meniscus level to rise

-measuring maltose diffusion (without the use of tubes)
-amylase digests the starch into maltose
-make it small enough to diffuse out of the tubing and into the beaker
-presence of maltose can be detected using Benedict's reagent or glucose indicator strips

6.1 Skill: Produce an annotated diagram of the digestive system.

Look in notes!

6.1 Skill: Identification of tissue layers in transverse sections of the small intestine viewed with a microscope or in a micrograph.
Outline the function of the four layers of tissue found in the wall of the small intestine.

The small intestine is composed of four main tissue layers, which are (from outside to centre):

serosa:
-outermost protective layer covering composed of a layer of cells reinforced by fibrous connective tissue

muscle layer:
-outer layer of longitudinal muscle (peristalsis)
-inner layer of circular muscle (segmentation)

submucosa:
-contains blood and lymph vessels that carry away absorbed materials
-composed of connective tissue separating the muscle layer from the innermost mucosa

mucosa:
-lines the lumen of the small intestine
-a highly folded inner layer which absorbs material through its surface epithelium from the intestinal lumen

6.2 Explain the structure of arteries in relation to its function.

• Arteries convey blood at high pressure from the ventricles -\> tissues of the body

• Arteries have muscle cells and elastic fibres in their walls to accomplish blood transfer

-thick walls to withstand high pressure/maintain blood flow/pressure;
-collagen fibres/elastic fibres/connective tissue (in outer layer) give wall strength/flexibility/ability to STRETCH and RECOIL;
-(smooth) muscle layer (contracts) to maintain pressure;
-narrow lumen maintains high pressure;
-many muscle fibres to help pump blood;
many elastic fibres to stretch and pump blood after each heart beat;
-no valves as pressure is high enough to prevent backflow;
-endothelium/smooth inner lining to reduce friction for efficient transport;Their recoil helps propel the blood down the artery.

6.2 Explain how the muscle and elastic fibres assist in maintaining blood pressure between pump cycles.

-blood: heart -\> ventricular contraction -\> arteries
-muscle and elastic fibres assist in maintaining the high pressure between pumps

Muscle fibres:
-form a rigid arterial wall that is capable of withstanding the high blood pressure
-contract to narrow the lumen -\> increases the pressure between pumps and helps to maintain blood pressure throughout the cardiac cycle

Elastic fibres:
-allow the arterial wall to stretch and expand upon the flow of a pulse through the lumen
-the pressure exerted on the arterial wall is returned to the blood when the artery returns to its normal size (elastic recoil)
-their recoil helps propel the blood down the artery.
-elastic recoil helps to push the blood forward through the artery as well as maintain arterial pressure between pump cycles

6.2 Explain the function of capillaries and their features.

-the function of capillaries is to exchange materials between the cells in tissues and blood travelling at low pressure
-artery -\> arterioles -\> capillaries
**ensures blood is moving slowly and all cells are located near a blood supply; maximizes material exchange
-higher hydrostatic pressure at the arteriole end of the capillary forces material from the bloodstream into the tissue fluid
-lower hydrostatic pressure at the venule end of the capillary allows materials from the tissues to enter the bloodstream
-capillaries -\> venules -\> larger veins

Features:
-capillaries' walls thin/one cell thick for better diffusion; (do not accept membranes)
-small diameter/narrow lumen to fit into small places/between cells;
-small diameter for greater surface area for molecular exchange;
-pores between cells of the walls so plasma can leak out;
-pores between cells of the walls allow phagocytes/immune components to enter tissues;
-only one red blood cell allowed to pass at a time for efficient oxygen uptake;
-extensive branching increases surface area for exchange of materials;

6.2 Explain the function of veins and its features.

-function of veins is to collect the blood from the tissues and convey it at low pressure to the atria of the heart

-arteries -\> capillaries -\> veins -\> heart -\> begin another pumping cyles
-high pressure -\> low pressure

Features:
-thin walls allow (skeletal) muscles to exert pressure on veins;
-thin outer layer of collagen/elastic/muscle fibres provide structural support;
-wide lumen allows great volume of blood to pass; to maximise blood flow for more effective return;
-valves prevent backflow;

6.2 Skill: Identification of blood vessels as arteries, capillaries or veins from the diameter, thickness of wall, muscles, and the number of layers.

Diameter:
veins \> arteries \> capillaries

Thickness of wall:
arteries \> veins \> capillaries

Muscles & Elastic Fibres:
arteries \> veins \> capillaires (none)

Number of layers
arteries \= veins (3 layers) \> capillaries (only 1)

6.2 Explain the blood circulation of lungs.

There is a separate circulation for the lungs.

-there are two sets of atria and ventricles in heart because there are two distinct locations for blood transport

-left side of the heart pumps oxygenated blood around the body (systemic circulation)
-right side of the heart pumps deoxygenated blood to the lungs (pulmonary circulation)

-the left side of the heart will have a much thicker muscular wall (myocardium) as it must pump blood much further

6.2 Skill: Recognition of the chambers and valves of the heart and the blood vessels connected to it in dissected hearts or in diagrams of heart structure.

Chambers:
-two atria (singular \= atrium) - smaller chambers near top of heart that collect blood from body and lungs
-two ventricles - larger chambers near bottom of heart that pump blood to body and lungs

Heart Valves:
-atrioventricular valves (between atria and ventricles) - bicuspid valve on left side ; tricuspid valve on right side -semilunar valves (between ventricles and arteries) - aortic valve on left side ; pulmonary valve on right side

Blood Vessels:
-vena cava (inferior and superior) feeds into the right atrium and returns deoxygenated blood from the body
-pulmonary artery connects to the right ventricle and sends deoxygenated blood to the lungs
-pulmonary vein feeds into the left atrium and returns oxygenated blood from the lungs
-aorta extends from the left ventricle and sends oxygenated blood around the body

6.2 Explain the presence of heart beat.

-the sinoatrial node acts like a pace maker (cardiac cells act in unison)
-the signal for a heart beat is initiated by the heart muscle cells (cardiomyocytes) rather than from brain signals
-sends out an electrical signal that stimulates contraction
-it is propagated through the walls of the atria and then the walls of the ventricles.

-a specialised cluster of cardiomyocytes which direct the contraction of heart muscle tissue \-- sinoatrial node (SA)

-stimulates atria to contract;
-stimulates another node at the junction between the atrium and ventricle
-the atrioventricular node (AV node) sends signals down the septum via a nerve bundle (Bundle of His)
-Bundle of His innervates nerve fibres in the ventricular wall, causing ventricular contraction
-(autonomic) nerves can alter the pace;
-(by secretion of) epinephrine/adrenaline/norepinephrine/noradrenaline increase the pace;
-(by secretion of) acetylcholine reduces the pace;
-adrenal glands release epinephrine/adrenaline; carried by blood to heart; to increase pace;

-sequence of events ensures there is a delay between atrial and ventricular contractions, resulting in two heart sounds
-delay allows time for the ventricles to fill with blood following atrial contractions so as to maximise blood flow

6.2 Explain the changes in heart rate.

The heart rate can be increased or decreased by impulses brought to the heart through two nerves from the medulla of the brain.

**nerve signals from the brain can trigger rapid changes, while endocrine signals can trigger more sustained changes

blood pressure levels/[CO2] (blood pH) -\> changes in heart rate:
-when exercising, more CO2 is present in the blood a nerve signal is sent to the sinoatrial node to speed up the heart rate.
-when CO2 levels fall the vagus nerve reduces heart rate.

Two nerves connected to the medulla regulate heart rate by either speeding it up or slowing it down:
-the sympathetic nerve releases the neurotransmitter noradrenaline (a.k.a. norepinephrine) to increase heart rate
-the parasympathetic nerve (vagus nerve) releases the neurotransmitter acetylcholine to decrease heart rate

6.2 Explain the function of epinephrine.

Epinephrine (or adrenaline) is a hormone increases the heart rate to prepare for vigorous physical activity.

-released from adrenal glands
-increases heart rate by activating the same chemical pathways as the neurotransmitter noradrenaline

6.2 Application: Explain the pressure changes in different areas of the heart during the cardiac cycle.

-cardiac cycle is comprised of a period of contraction (systole) and relaxation (diastole)

Systole:
-blood returning -\> atria and ventricles (because) the pressure in them is lower due to low volume of blood)
-atriums are ~70% full -\> atrial systole -\> increasing pressure in the atria -\> forcing blood into ventricles
-ventricles systole -\> ventricular pressure exceeds atrial pressure -\> AV valves close to prevent back flow (first heart sound)
-both sets of heart valves closed, pressure rapidly builds in the contracting ventricles
-ventricular pressure exceeds blood pressure in the aorta -\> aortic valve opens -\> blood is released into the aorta

Diastole
-blood exits the ventricle and travels down the aorta, ventricular pressure falls
-ventricular pressure drops below aortic pressure -\> aortic valve closes to prevent back flow (second heart sound)
-ventricular pressure drops below the atrial pressure -\> the AV valve opens -\> blood can flow from atria to ventricle
-aortic pressure remains quite high as muscle and elastic fibres in the artery wall maintain blood pressure

6.2 Application: Explain the causes and consequences of occlusion of the coronary arteries.

Atherosclerosis is the hardening and narrowing of the arteries due to the deposition of cholesterol.

-atheromas develop in the arteries and significantly reduce the diameter of the lumen
-restricted blood flow increases pressure in the artery, leading to damage to the arterial wall (from shear stress)
**blood pumped through the heart is at high pressure and cannot be used to supply the heart muscle with oxygen and nutrients

-damaged region is repaired with fibrous tissue -\> reduces the elasticity of the vessel wall
-smooth lining of the artery is progressively degraded, lesions form called atherosclerotic plaques
-plaque ruptures -\> blood clotting -\> thrombus -\> restricts blood flow
-thrombus is dislodged it becomes an embolus and can cause a blockage in a smaller arteriole

-if a coronary artery becomes completely blocked, an acute myocardial infarction (heart attack) will result
-typically treated by by-pass surgery or creating a stent (e.g. balloon angioplasty)

Risk Factors:
Age - Blood vessels become less flexible with advancing age
Genetics - Having hypertension predispose individuals to developing CHD
Obesity - Being overweight places an additional strain on the heart
Diseases - Certain diseases increase the risk of CHD (e.g. diabetes)
Diet - Diets rich in saturated fats, salts and alcohol increases the risk
Exercise - Sedentary lifestyles increase the risk of developing CHD
Sex - Males are at a greater risk due to lower oestrogen levels
Smoking - Nicotine causes vasoconstriction, raising blood pressure

6.2 Application: Explain William Harvey's discovery of the circulation of the blood with the heart acting as the pump.

-our modern understanding of circulatory system is based upon the discoveries of 17th century English physician, William Harvey

Based on some simple experiments and observations, Harvey instead proposed that:
-blood flow through large vessels is unidirectional, with valves to prevent backflow.
-arteries and veins were part of a single connected blood network
**he did not predict the existence of capillaries however
-arteries pumped blood from the heart (to the lungs and body tissues)
-veins returned blood to the heart (from the lungs and body tissues)
- also showed that the rate of flow through major vessels was far too high for blood to be consumed in the body after being pumped our by the heart, as earlier theories proposed.
-it must therefore return to the heart and be recycled.

Some of the experiments include:

-fish hearts having their veins tied. The hearts emptied of blood, then refilled when the tie was removed.
-blood was shown flowing towards the heart in veins of a human arm.
-calculations of blood volume and pulse rates showed that huge volumes of blood were leaving the heart

6.3 Describe the first line of defense.

The skin and mucous membranes form a primary defence against pathogens that cause infectious disease.

Skin:
-protects external structures when intact (outer body areas)
-dry, thick and tough region composed predominantly of dead surface cells
-(skin/stomach) acid prevents growth of many pathogens;

Sebaceous glands (on skin):
-associated with hair follicles
-secrete sebum and enzymes which inhibit microbial growth on skin (by lowering pH level)
-secretes lactic acid and fatty acids to lower the pH (skin pH is roughly ~ 5.6 - 6.4 depending on body region); inhibits growth of bacteria and fungi

Mucous Membranes:
-protects internal structures (i.e. externally accessible cavities and tubes - such as the trachea, oesophagus and urethra)
-can be found in nasal passages and other airways, the head of the penis and foreskin and the vagina.
-a thin region of living surface cells that release fluids to wash away pathogens (mucus, saliva, tears, etc.)
-secretes a sticky solution of glycoproteins, which traps pathogens and harmful particles and either swallow or expels it
-lysozyme in mucus can kill bacteria;
-ciliated to aid in the removal of pathogens (along with physical actions such as coughing / sneezing)

-inflammatory response/inflammation can cause swelling/redness/fever (to inhibit the pathogen);

6.3 Explain the cascade of events that occur in blood clotting.

Cuts in the skin are sealed by blood clotting; clotting factors are released from platelets.

-prevent blood loss
-limit pathogenic access to the bloodstream when the skin is broken

-clotting factors cause platelets to become sticky and adhere to the damaged region to form a solid plug
-localised vasoconstriction reduces blood flow through the damaged region

The cascade results in the rapid conversion of fibrinogen to fibrin by thrombin.

-clotting factors trigger the conversion of the inactive zymogen prothrombin into the activated enzyme thrombin
-thrombin catalyses the conversion of the soluble plasma protein fibrinogen into an insolube fibrous form called fibrin
-fibrin strands form a mesh of fibres around the platelet plug and traps blood cells to form a temporary clot

6.3 Application: Explain the causes and consequences of blood clot formation in coronary arteries.

Consequences:
the occlusion of a coronary artery by a blood clot may lead to an acute myocardial infarction (heart attack)

Causes:
-blood clots form when the vessels are damaged as a result of the deposition of cholesterol
-aheromas (fatty deposits) develop in the arteries and significantly reduce the diameter of the lumen \-- atherosclerosis
-restricted blood flow increases pressure in the artery, leading to damage to the arterial wall (from shear stress)
-damaged region is repaired with fibrous tissue which significantly reduces the elasticity of the vessel wall
-smooth lining of the artery is progressively degraded, lesions form \-- atherosclerotic plaques
-plaque ruptures -\> blood clotting -\> forms thrombus -\> restricts blood flow
-thrombus is dislodged it becomes an embolus and can cause a blockage in a smaller arteriole

-coronary occlusion
-damage to the capillary epithelium
-hardening of arteries
-rupture of atheroma

Factors that are correlated with an increased risk of coronary thrombosis:

-smoking
-high blood cholesterol concentration
-high blood pressure
-diabetes
-obesity
-lack of exercise

6.3 Explain the second line of defence against infectious disease.

It is the innate immune system: non-specific in its response.
-non-specific
-non-adaptive

-main component: phagocytic white blood cells that engulf and digest foreign bodies
-other components: inflammation, fever and antimicrobial chemicals

Ingestion of pathogens by phagocytic white blood cells gives non-specific immunity to disease.

Phagocytes
-solid materials (such as pathogens) are ingested by a cell (i.e. cell 'eating' via endocytosis)
-phagocytic leukocytes (WBC) circulate in the blood and move into the body tissue freely in response to infection
-damaged tissues release chemicals (e.g. histamine) which draw white blood cells to the site of infection
-extensions surround the pathogen and then fuse to form an internal vesicle
-vesicle is then fused to a lysosome and the pathogen is digested
-antigens (fragments from pathogens) may be presented on the surface of the phagocyte in order to stimulate the third line of defence

6.3 Explain how the immune system can be adaptive.

Production of antibodies by lymphocytes in response to particular pathogens gives specific immunity

-differentiate between particular pathogens and target a response that is specific to a given pathogen
-respond rapidly upon re-exposure to a specific pathogen, preventing symptoms from developing (immunological memory)

Lymphocytes
-when phagocytic leukocytes engulf a pathogen, some will present the digested fragments (antigens) on their surface
-these antigen-presenting cells (dendritic cells) migrate to the lymph nodes and activate specific helper T lymphocytes
-helper T cells then release cytokines to activate the particular B cell capable of producing antibodies specific to the antigen
-activated B cell will divide and differentiate to form short-lived plasma cells that produce high amounts of specific antibody
-antibodies will target their specific antigen, enhancing the capacity of the immune system to recognise and destroy the pathogen
-a small proportion of activated B cell (and activated TH cell) will develop into memory cells to provide long-lasting immunity

6.3 Describe what cells antibiotics target and explain why.

• Antibiotics block processes that occur in prokaryotic cells but not in eukaryotic cells

-kill or inhibit the growth of microbes (specifically bacteria) by targeting prokaryotic metabolism including:

-key enzymes
-70S ribosomes
-components of the cell wall

-eukaryotic cells do not possess these features
-antibiotics will target the pathogenic bacteria and not the infected host
-either kill the invading bacteria (bactericidal) or suppress its potential to reproduce (bacteriostatic)

• Viruses lack a metabolism and cannot therefore be treated with antibiotics

-do not possess a metabolism and instead take over the cellular machinery of infected host cells
-they cannot be treated with antibiotics and must instead be treated with specific antiviral agents

6.3 Explain antibiotics resistance, its causes, and solutions.

• Some strains of bacteria have evolved with genes that confer resistance to antibiotics and some strains of bacteria have multiple resistance.

-confer resistance by encoding traits that:
-degrade the antibiotic
-block its entry
-increase its removal
-alter the target

-resistant strains of bacteria can proliferate very quickly following the initial mutation
-can be passed to susceptible strains via bacterial conjugation (horizontal gene transfer)

The prevalance of resistant bacterial strains is increasing rapidly with human populations due to a number of factors:
-over-prescribed (particularly broad-spectrum drugs) or misused (e.g. given to treat a viral infection)
-many are freely available without a prescription and certain antibiotics
-commonly included in livestock feed
-multi-drug resistant bacteria are especially common in hospitals

-an example of an antibiotic resistant strain of bacteria is Golden Staph (MRSA - Methicillin Resistant Staphylococcus aureus)

Solutions:

-doctors prescribing antibiotics only for serious bacterial infections
-patients completing courses of antibiotics to eliminate infections completely
-hospital staff maintaining high standards of hygiene to prevent cross-infection
-farmers not using antibiotics in animal feeds to stimulate growth
Pharmaceutical companies developing new types of antibiotics - no new types have been introduced since the 1980s

6.3 Application: Describe Florey and Chain's experiments.

-Florey and Chain's team developed a method of growing the fungus Penicillium in liquid culture
-also developed methods for producing reasonably pure samples of penicillin from the cultures
-the penicillin killed bacteria on agar plates, but they needed to test whether it would control bacterial infections in humans.

Florey and Chain conducted experiments to test penicillin on bacterial infections in mice.

-8 mice were injected with hemolytic streptococci and four of these mice were subsequently injected with doses of penicillin
-untreated mice died of bacterial infection
-those treated with penicillin all survived - demonstrating its antibiotic potential

-Florey and Chain decided that they should next do tests on human patients, which required much larger quantities.
-when enough penicillin had been produced, a 43-year-old policeman was chosen for the first human test.
-he had an acute and life-threatening bacterial infection causes by a scratch on the face from a thorn on a rose bush.
-he was given penicillin for four days and his condition improved considerably, but supplies of penicillin ran out and he suffered a relapse and died from the infection.
-larger quantities of penicillin were produced and five more patients with acute infections were tested.

All were cured of their infections, but sadly one of them died.

6.3 Application: Explain the effects of HIV on the immune system and methods of transmission.

HIV infects helper T cells, disabling the body's adaptive immune system
-causes a variety of symptoms and infections collectively classed AIDS

Effects of HIV:
-infection -\> virus undergoes a period of inactivity (clinical latency) during which infected helper T cells reproduce
-the virus becomes active again and begins to spread, destroying the T lymphocytes in the process
-reduction in the number of helper T cells -\> antibodies are unable to be produced -\> lowered immunity
-body becomes susceptible to opportunistic infections, eventually resulting in death if the condition is not managed

Transmission of HIV:
-through the exchange of body fluids (including unprotected sex, blood transfusions, breastfeeding, etc.)
-HIV through sexual contact can be minimised by using latex protection (i.e. condoms)
-HIV is a global issue, but is particularly prevalent in poorer nations with poor education and health systems

6.4 Explain the purpose of ventilation.

• Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries.
**because gas exchange is actually passive!

-O2 consumed by cells during cellular respiration
-carbon dioxide produced as a waste product

-O2 is constantly being removed from the alveoli into the bloodstream (and CO2 is continually being released)
-lungs function continually cycles fresh air into the alveoli from the atmosphere
-O2 levels must stay high in alveoli (and diffuse into the blood) and CO2 levels stay low (and diffuse from the blood)
-the lungs are also structured to have a very large surface area, so as to increase the overall rate of gas exchange

6.4 Identify and explain the structure and function of cells that line the alveoli in relation to how it aids in ventilation.

There are two types of alveolar cells - type I pneumocytes and type II pneumocytes

• Type I pneumocytes are extremely thin alveolar cells that are adapted to carry out gas exchange.

Function:
-involved in the process of gas exchange between the alveoli and the capillaries

Structure:
-flattened in shape to minimise diffusion distance for respiratory gases
-connected by occluding junctions, which prevents the leakage of tissue fluid into the alveolar air space
-amitotic and unable to replicate
-type I pneumocytes are amitotic and unable to replicate, however type II cells can differentiate into type I cells if required

• Type II pneumocytes secrete a solution containing surfactant that creates a moist surface inside the alveoli to prevent the sides of the alveolus adhering to each other by reducing surface tension

Structure:
-cuboidal in shape and possess many granules (for storing surfactant components)
-provides an area from which carbon dioxide can evaporate into the air and be exhaled.

Function:
-responsible for the secretion of pulmonary surfactant
-create a moist surface -\> easier for oxygen to diffuse across the alveolar and capillary membranes when dissolved in liquid -\> reduces surface tension

-type II pneumocytes secrete a liquid known as pulmonary surfactant which reduces the surface tension in alveoli
-surface tension is the elastic force created by a fluid surface that minimises the surface area (via cohesion of liquid molecules)
-as an alveoli expands with gas intake, the surfactant becomes more spread out across the moist alveolar lining
-this increases surface tension and slows the rate of expansion, ensuring all alveoli inflate at roughly the same rate

6.4 Explain how air travels in the respiratory system.

• Air is carried to the lungs in the trachea and bronchi and then to the alveoli in bronchioles

-enters the respiratory system through the nose or mouth and passes through the pharynx to the trachea
-trachea -\> divides into two bronchi (singular: bronchus) -\> connect to the lungs

-right lung is composed of three lobes, while the left lung is only comprised of two (smaller due to position of heart)
-bronchi divide into many smaller airways called bronchioles, greatly increasing surface area
-bronchiole terminates with a cluster of air sacs called alveoli, where gas exchange with the bloodstream occurs

nostrils → nasal cavity → pharynx → larynx → trachea →
bronchi (with cartilaginous rings) → bronchioles (without cartilage) → alveoli.

6.4 Skill: Draw an annotated diagram showing the structure of an alveolus and an adjacent capillary.

-have a very thin epithelial layer (one cell thick) to minimise diffusion distances for respiratory gases

-surrounded by a rich capillary network to increase the capacity for gas exchange with the blood

-roughly spherical in shape, in order to maximise the available surface area for gas exchange

-internal surface is covered with a layer of fluid, as dissolved gases are better able to diffuse into the bloodstream

6.4 Explain how muscle contractions play a role in ventilation.

• Muscle contractions cause the pressure changes inside the thorax that force air in and out of the lungs to ventilate them.

-external intercostal contract -\> rise in ribcage
-diaphragm contracts to make space in thorax
-pressure in the chest < atmospheric pressure, air will move into the lungs (inspiration)

-internal intercostal contract -\> lower in ribcage
-diaphragm relaxes
-abdominal muscles contract to force air out
-when the pressure in the chest \> atmospheric pressure, air will move out of the lungs (expiration)

• Different muscles are required for inspiration and expiration because muscles only do work when they contract.

-muscles that increase the volume of the chest cause inspiration (as chest pressure is less than atmospheric pressure)
-muscles the decrease the volume of the chest cause expiration (as chest pressure is greater than atmospheric pressure)

6.4 Application: Explain the causes and consequences (symptoms) of lung cancer.

Lung cancer describes the uncontrolled proliferation of lung cells, leading to the abnormal growth of lung tissue (tumour)

-the tumours can remain in place (benign) or spread to other regions of the body (malignant)
-lungs possess a very rich blood supply, increasing the likelihood of the cancer spreading (metastasis) to other body regions

Symptoms:
-difficulties with breathing
-persistent coughing
-include coughing up blood, wheezing, respiratory distress and weight loss
-loss of appetite, weight loss
-general fatigue
-if the cancer mass compresses adjacent organs it can cause:
-chest pain, difficulty swallowing and heart complications

Causes:
-smoking: contains many mutagenic chemicals. As every cigarette carries a risk, the incidence of lung cancer increases with the number smoked per day
-air pollution: sources of air pollution that are most significant are diesel exhaust fumes, nitrogen oxides from all vehicle exhaust fumes and smoke from fossil fuels
-radon gas causes (a radioactive gas that leaks out of certain rocks such as granite). It accumulates in badly ventilated buildings and people then inhale it.
-certain infections
-genetic predispositions

6.4 Explain the causes and consequences of emphysema.

-degradation of the alveolar walls can cause holes to develop and alveoli to merge into huge air spaces (pulmonary bullae)
-damage to lung tissue leads to the recruitment of phagocytes to the region, which produce an enzyme called elastase
-this elastase, released as part of an inflammatory response, breaks down the elastic fibres in the alveolar wall
-loss of elasticity results in the abnormal enlargement of the alveoli -\> lower total surface area for gas exchange

Cause:
-smoking: the chemical irritants in cigarette smoke damage the alveolar walls
-a small proportion of emphysema cases are due to a hereditary deficiency in this enzyme inhibitor due to a gene mutation

Symptoms:
-shortness of breath
-expansion of the ribcage
-cyanosis and
-increased susceptibility to chest infections
-fatigue
-weezing
-chest tightness
-anxiety

6.4 Application: Explain how inspiration (inhaling) and expiration (exhaling) are controlled by muscle groups.

• External and internal intercostal muscles, and diaphragm and abdominal muscles are examples of antagonistic muscle action.

-antagonistic means working oppositely - when the inspiratory muscles contract, the expiratory muscles relax (and vice versa)

Inspiration
-the diaphragm and external intercostals (plus some accessory muscles)
-diaphragm muscles contract -\> diaphragm flatten
-\>increase the volume of the thoracic cavity
-External intercostals contract -\> pulling ribs upwards and outwards (expanding chest)

Expiration
-abdominal muscles and internal intercostals (plus some accessory muscles)
-diaphragm relax -\> diaphragm curves upwards -\> reduce the volume of the thoracic cavity
-Internal intercostal muscles contract, pulling ribs inwards and downwards (reducing breadth of chest)
-abdominal muscles contract and push the diaphragm upwards during forced exhalation

6.4 Skill: Explain the monitoring of ventilation in humans at rest and after mild and vigorous exercise. (Practical 6)

Ventilation can either be monitored by:
-simple observation (counting number of breaths per minute)
-simple apparatus
-data logging with a spirometer (recording the volume of gas expelled per breath)
- chest belt and pressure meter (recording the rise and fall of the chest)

Ventilation rate and tidal volume can be measured by spirometer:

-involves measuring the amount (volume) and / or speed (flow) at which air can be inhaled or exhaled
-a device that detects the changes in ventilation and presents the data on a digital display

-simplistic method is breathing into a balloon and measuring the volume of air in a single breath
-volume of air can be determined by submerging the balloon in water and measuring the volume displaced (1ml \= 1cm3)

6.5 Explain the function of neurons and its structure.

• Neurons are specialised cells that function to transmit electrical impulses within the nervous system.

Neurons contain:
-dendrites: short-branched fibres that convert chemical information from other neurons or receptor cells into electrical signals
-axon: an elongated fibre that transmits electrical signals to terminal regions for communication with other neurons or effectors
-soma: a cell body containing the nucleus and organelles, where essential metabolic processes occur to maintain cell survival
-myelin sheath: improves the conduction speed of electrical impulses along the axon, but require additional space and energy

-nervous system converts sensory information into electrical impulses in order to rapidly detect and respond to stimuli

6.5 Explain the function for the myelination of nerve fibres.

• The myelination of nerve fibres allows for saltatory conduction.

-myelin functions as an insulating layer

-the main purpose of the myelin sheath is to increase the speed of electrical transmissions via saltatory conduction
-allows nerve impulse to jump across gaps in the myelin sheath called the nodes of Ranvier and jump from node to node

6.5 Explain how neurons generate a resting potential.

• Neurons pump sodium and potassium ions across their membranes to generate a resting potential.

-resting potential is the difference in charge across the membrane when a neuron is not firing
-the inside of the neuron is more negative relative to the outside in resting potential

The maintenance of a resting potential is controlled by sodium-potassium pumps \-- active process:
-expels 3 Na+ ions for every 2 K+ ions admitted (additionally, some K+ ions will then leak back out of the cell)
-as there are more positively charged ions outside of the cell and more negatively charged ions inside the cell \-- electrochemical gradient
-requires hydrolysis of ATP

6.5 Describe an action potential.

-action potentials are the rapid changes in charge across the membrane that occur when a neuron is firing

• An action potential consists of depolarization and repolarization of the neuron (in between has a refractory period)

Depolarisation
-a sudden change in membrane potential - usually from a (relatively) negative to positive internal charge
-in response to a signal initiated at a dendrite, sodium channels open within the membrane of the axon
-as Na+ ions are more concentrated outside of the neuron, the opening of sodium channels causes a passive influx of sodium
-the influx of sodium causes the membrane potential to become more positive (depolarisation)

Repolarisation
-the restoration of a membrane potential following depolarisation (i.e. restoring a negative internal charge)
-influx of sodium, potassium channels open within the membrane of the axon
-K+ ions are more concentrated inside the neuron, opening potassium channels causes a passive efflux of potassium
-efflux of potassium causes the membrane potential to return to a more negative internal differential (repolarisation)

Refractory Period
-the period of time following a nerve impulse before the neuron is able to fire again
-normal resting state: sodium ions are predominantly outside the neuron and potassium ions mainly inside (resting potential)
-ionic distribution is largely reversed (in de and repolarization) so the resting potential must be restored via the antiport action of the sodium-potassium pump

6.5 Describe what nerve impulses are.

• Nerve impulses are action potentials propagated along the axons of neurons.

-nerve impulses are action potentials that move along the length of an axon as a wave of depolarisation
-depolarisation occurs when ion channels open and cause a change in membrane potential
-ion channels that occupy the length of the axon are voltage-gated (open in response to changes in membrane potential)

-depolarisation at one point of the axon triggers the opening of ion channels in the next segment of the axon
-causes depolarisation to spread along the length of the axon as a unidirectional 'wave'

• Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to reach the threshold potential.

-an action potential of the same magnitude will always occur provided a minimum electrical stimulus is generated
- threshold potential is the level required to open voltage-gated ion channels
-if the threshold potential is not reached, an action potential cannot be generated and hence the neuron will not fire

• A nerve impulse is only initiated if the threshold potential is reached.

-threshold potentials are triggered when the combined stimulation from the dendrites exceeds a minimum level of depolarisation
-if the overall depolarisation from the dendrites is sufficient to activate voltage-gated ion channels in one section of the axon, the resulting displacement of ions should be sufficient to trigger the activation of voltage-gated ion channels in the next axon section

6.5 Define synapses.

• Synapses are junctions between neurons and between neurons and receptor or effector cells.

-neurons transmit information across synapses by converting the electrical signal into a chemical signal

6.5 Outline the release of chemical signals in synaptic cleft.

• When presynaptic neurons are depolarized they release a neurotransmitter into the synapse

-neurotransmitters are released in response to the depolarisation of the axon terminal of a presynaptic neuron
-bind to receptors on post-synaptic cells and can either trigger (excitatory) or prevent (inhibitory) a response

6.5 Application: Explain the secretion and reabsorption of acetylcholine by neurons at synapses

Acetylcholine: neurotransmitter

-released at neuromuscular junctions and binds to receptors on muscle fibres to trigger muscle contraction
-released within the autonomic nervous system to promote parasympathetic responses ('rest and digest')

-created in the axon terminal by combining choline with an acetyl group (at cholinergic synapses)
-stored in vesicles within the axon terminal until released via exocytosis in response to a nerve impulse
-activates a post-synaptic cell by binding to one of two classes of specific receptor (nicotinic or muscarinic)
-must be continually removed from the synapse, as overstimulation can lead to fatal convulsions and paralysis

-acetylcholine -\> two component parts by the synaptic enzyme acetylcholinesterase (AChE)
-either released into the synapse from the presynaptic neuron or embedded on the membrane of the post-synaptic cell
-liberated choline is returned to the presynaptic neuron where it is coupled with another acetate to reform acetylcholine

6.5 Application: Explain the blocking of synaptic transmission at cholinergic synapses in insects and its disadvantages.

-blocking of acetylcholine by the binding of neonicotinoid pesticides to acetylcholine receptors

-neonicotinoid pesticides cannot be broken down by acetylcholinesterase -\> permanent overstimulation of target cells
-overstimulation results in fatal convulsions and paralysis

-insects have a different composition of acetylcholine receptors which bind to neonicotinoids much more strongly
-more toxic to insects than mammals -\> highly effective pesticide

Disadvantages:
-linked to a reduction in honey bee populations (bees are important pollinators within ecosystems)
-linked to a reduction in bird populations (due to the loss of insects as a food source)

6.5 Skill: Analysis of oscilloscope traces showing resting potentials and action potentials.

-oscilloscopes are scientific instruments that are used to measure the membrane potential across a neuronal membrane

X axis: time (ms)
Y axis: membrane potential (mV)

A typical action potential will last for roughly 3 - 5 milliseconds and contain 4 key stages:

Resting potential: Before the action potential occurs, the neuron should be in a state of rest (approx. -70 mV)

Depolarisation: A rising spike corresponds to the depolarisation of the membrane via sodium influx (up to roughly +30 mV)

Repolarisation: A falling spike corresponds to repolarisation via potassium efflux (undershoots to approx. -80 mV)

Refractory period: The oscilloscope trace returns to the level of the resting potential (due to the action of the Na+/K+ pump)

**an action potential will only occur if the initial depolarisation exceeds a threshold potential of approximately -55 mV

6.6. Explain how blood glucose concentration is controlled.

• Insulin and glucagon are released by β and α cells of the pancreas to control blood glucose concentration.

When blood glucose levels are high (e.g. after feeding):
-insulin is released from beta (β) cells of the pancreas and cause a decrease in blood glucose concentration
May involve the following:
-(high blood glucose levels) detected by pancreas islet cells/beta cells;
-stimulating glycogen synthesis in the liver (glycogenesis) (glucose -\> glycogen)
-promoting glucose uptake by the liver and adipose tissue
-increasing the rate of glucose breakdown (by increasing cell respiration rates)
-glucose converted to fatty acids/triglycerides/fat;
-stimulates cells to absorb glucose;
**negative feedback process;

When blood glucose levels are low (e.g. after exercise):
-glucagon is released from alpha (α) cells of the pancreas and cause an increase in blood glucose concentration
May involve the following:
-stimulating glycogen breakdown in the liver (glycogenolysis)
-conversion of polysaccharides/glycogen (in the liver) to glucose
-promoting glucose release by the liver and adipose tissue
-decreasing the rate of glucose breakdown (by reducing cell respiration rates)

6.6 Application: Explain the causes and treatment of Type I and Type II diabetes.

Type 1 diabetes: unable to produce insulin
Type 2 diabetes: failing to respond to insulin production

Type 1:
-occurs during early childhood
-caused by the destruction of beta cells
-insulin injections

Type 2:
-usually occurs during adulthood
-caused by the down regulation of insulin receptors
-controlled by managing diet and lifestyle

6.6. Explain how metabolic rate and body temperature is controlled and regulated.

• Thyroxin is secreted by the thyroid gland to regulate the metabolic rate and help control body temperature

-primary role of thyroxin is to increase the basal metabolic rate (amount of energy the body uses at rest)
-achieved by stimulating carbohydrate and lipid metabolism via the oxidation of glucose and fatty acids
-increasing metabolic activity -\> production of heat
-hence thyroxin helps to control body temperature

-thyroxin is released in response to a decrease in body temperature in order to stimulate heat production
-partially composed of iodine; a deficiency of iodine in the diet -\> decreased production of thyroxin

-cold temp. -\> hypothalamus -\> thyroxin release -\> increased metabolic rate -\> generate heat -\> increase in body temp.

6.6 Explain how the inhibition of appetite is controlled by hormones.

• Leptin is secreted by cells in adipose tissue and act on the hypothalamus of the brain to inhibit appetite

-the concentration of leptin in the blood is controlled by food intake and the amount of adipose tissue in the body.
-regulates fat stores within the body by suppressing appetite
-leptin binds to receptors located within the hypothalamus -\> inhibit appetite

-overeating -\> more adipose cells to formed -\> more leptin is produced -\> suppressing further appetite
-starvation -\> reduction in adipose tissue -\> less leptin is released -\> hunger

-obese people are constantly producing higher levels of leptin -\> body becomes progressively desensitised to the hormone
-they are more likely to feel hungry, less likely to recognise when they are full and are hence more likely to overeat

-leptin resistance also develops with age, increasing the potential for weight gain later in life (e.g. the 'middle-age spread')

6.6 Applications: Explain the testing of leptin on patients with clinical obesity and reasons for the failure to control the disease.

-leptin was considered as a form of treatment for individuals with clinical obesity
-leptin injections -\> reduce hunger -\> limit food intake -\> weight loss

Experiment shows that:
-most cases of obesity are caused by an unresponsiveness to leptin and not a leptin deficiency
-hence, very few participants experienced significant weight loss in response to leptin injections
-many patients did experience adverse side effects from leptin injections, including skin irritations

-leptin treatments are not considered to be an effective way of controlling obesity

6.6 Explain how circadian rhythms are controlled by hormones.

• Melatonin is secreted by the pineal gland to control circadian rhythms

-secretion controlled by cells in the hypothalamus called the suprachiasmatic nuceli (SCN)
-retina detects light -\> sends signals to SCN -\> sends signals to the pineal gland
-controls circadian rhythms/biological clocks «in mammals»
-production is controlled by amount of light detected by the retina
-produced by the pineal gland of the brain in response to changes in light
-light exposure -\> hypothalamus -\> inhibits melatonin secretion
-melatonin is secreted in response to periods of darkness, resulting in higher concentrations at night

-circadian rhythms are driven by an internal circadian clock
-can also be modulated by external factors

-melatonin is responsible for synchronising circadian rhythms and regulates the body's sleep schedule
**production/secretion is directly proportional to night time duration

-melatonin secretion is suppressed by bright light (principally blue wavelengths)
-hence levels increase during the night
-melatonin secretion becomes entrained to anticipate the onset of darkness and the approach of day

-melatonin functions to promote activity in nocturnal animals and conversely promotes sleep in diurnal animals (like humans)
-affects «seasonal» reproduction/sleep-wake cycles/jet lag

-melatonin levels naturally decrease with age, leading to changes in sleeping patterns in the elderly

6.6 Applications: Explain the causes of jet lag and methods of alleviation.

-alteration of circadian rhythm caused by the body's inability to rapidly adjust to a new time zone following extended air travel ('jet' lag)

-pineal gland continues to secrete melatonin according to the old time zone -\> sleep schedule is not synchronised to the new timezone
-symptoms of jet lag include fatigue, headaches, lethargy, increased irritability and reduced cognitive function
-jet lag should resolve as the body resynchronises its circadian rhythm

-taking melatonin near the sleep time of the new time zone can help recalibrate the body
-artificially increasing melatonin levels at the new night time -\> body can respond quicker to the new day-night schedule

6.6 Explain the development of male characteristics.

• A gene on the Y chromosome causes embryonic gonads to develop as testes and secrete testosterone

XX \= female
XY \= male
Y chromosomes is shorter than X chromosome

-Y chromosome includes a gene called the SRY gene (Sex Determining Region Y) -\> male development
-SRY codes for a DNA-binding protein called TDF (testis determining factor)
-TDF stimulates the expression of other genes that cause testis development.
-SRY gene -\> testis-determining factor (TDF) -\> embryonic gonads form into testes (male gonads)
-the testes produce testosterone to promote the further development of male sex characteristics

-no TDF protein (i.e. no Y chromosome) -\> ovaries
-produce estrogen and progesterone to promote the development of female sex characteristics

6.6 Outline role of testosterone in prenatal development of male genitalia.

• Testosterone causes pre-natal development of male genitalia and both sperm production and development of male secondary sexual characteristics during puberty.

-testes develop testosterone-secreting cells at an early stage and these produce testosterone until about the 15th week of pregnancy.
-during the weeks of secretion, testosterone causes male genitalia to develop.
-testosterone \= male reproductive hormone
-secreted by the testes

Functions:
-pre-natal development of male genitalia
-involved in sperm production following the onset of puberty
-aids in the development of secondary sex characteristics (including body hair, muscle mass, deepening of voice, etc.)
-helps to maintain the male sex drive

6.6 Explain the development of female sexual characteristics.

• Estrogen and progesterone cause pre-natal development of female reproductive organs and female secondary sexual characteristics during puberty.

-main female reproductive hormones (secreted by the ovaries) are estrogen and progesterone

Functions:
-promote the pre-natal development of the female reproductive organs
-responsible for the development of secondary sex characteristics (including body hair and breast development)
-involved in monthly preparation of egg release following puberty (via the menstrual cycle)

-initially, estrogen and progesterone are secreted by the mother's ovaries and then the placenta

6.6 Explain how the menstrual cycle is controlled.
\****** finish this up

• The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and
pituitary hormones.

2 groups of hormones:
-pituitary hormones: (FSH and LH); released from the anterior pituitary gland and act on the ovaries to develop follicles
-ovarian hormones (estrogen and progesterone); released from the ovaries and act on the uterus to prepare for pregnancy

Hormonal Actions During Menstrual Cycle:
-hypothalamus -\> anterior pituitary -\> FSH and LH -\> ovary -\> estrogen and progesterone -\> uterus

1. Follicular Phase
-anterior pituitary -\> follicle stimulating hormone (FSH)
-\> stimulates growth of ovarian follicles
-dominant follicle produces estrogen -\> inhibits FSH secretion (negative feedback) **prevent other follicles growing
-estrogen acts on the uterus -\> thickening of the endometrial layer

2. Ovulation: midway through the cycle (~ day 12)
-estrogen stimulates the anterior pituitary to secrete hormones (positive feedback)
-positive feedback -\> large surge of luteinizing hormone (LH) and lesser surge of FSH
-LH causes the dominant follicle to rupture and release an egg (secondary oocyte) - this is called ovulation

3. Luteal Phase
-ruptured follicle -\> degenerating corpus luteum
-corpus luteum -\> high levels of progesterone + lower levels of oestrogen
-estrogen and progesterone act on the uterus to thicken the endometrial lining (in preparation for pregnancy)
-estrogen and progesterone also inhibit secretion of FSH and LH, preventing any follicles from developing

4. Menstruation
-fertilisation: developing embryo will implant in the endometrium and release hormones to sustain the corpus luteum
-no fertilisation: the corpus luteum eventually degenerates (forming a corpus albicans after ~ 2 weeks)
-estrogen and progesteron levels drop as corpus luteum degenerates and the endometrium can no longer be maintained
-endometrial layer is sloughed away and eliminated from the body as menstrual blood (i.e. a woman's period)

-estrogen and progesterone levels are too now low to inhibit the anterior pituitary, the cycle can now begin again

6.6 Application: Explain the process of IVF including down-regulation, superovulation, harvesting, fertilization and implantation.

IVF drugs to suspend the normal secretion of hormones, followed by the use of artificial doses of hormones to induce superovulation and establish a pregnancy.

Down regulation
-drugs are used to halt the regular secretion of FSH and LH -\> stops the secretion of estrogen and progesterone
-doctors can take control of the timing and quantity of egg production by the ovaries
-typically delivered in the form of a nasal spray

Superovulation
-involves using artificial doses of hormones to develop and collect multiple eggs from the woman
-patient is firstly injected with large amounts of FSH to stimulate the development of many follicles
-follicles are then treated with hCG; a hormone usually produced by a developing embryo
-hCG stimulates the follicles to mature and the egg is then collected (via aspiration with a needle) prior to the follicles rupturing

Fertilisation
-extracted eggs are then incubated in the presence of a sperm sample from the male donor
-eggs are then analysed under a microscope for successful fertilisation

Implantation
-two weeks prior to implantation, the woman begins to take progesterone treatments to develop the endometrium
-healthy embryos are selected and transferred into the female uterus (or the uterus of a surrogate)
-multiple embryos are transferred to improve chances of successful implantation (hence multiple births are a possible outcome)
-roughly two weeks after the procedure, a pregnancy test is taken to determine if the process has been successful

6.6 Applications: Explain William Harvey's investigation of sexual reproduction in deer

Original soil and seed theory:
-male produces a 'seed' which forms an 'egg' when mixed with menstrual blood (the 'soil')

William Harvey tested Aristotle's theory using a natural experiment with deers:

-unable to detect a growing embryo until approximately 6 - 7 weeks after mating had occurred
-so concluded that Aristotle's theory was incorrect and that menstrual blood did not contribute to the development of a fetus
-unable to identify the correct mechanism of sexual reproduction and incorrectly asserted that the fetus did not develop from a mixture of male and female 'seeds'

-Harvey failed to solve the mystery of sexual reproduction because effective microscopes were not available when he was working
-so fusion of gametes and subsequent embryo development remained undiscovered at his time

6.6 Skill: Annotate diagrams of the male reproductive system to show names of structures and their functions.

Testis:
responsible for the production of sperm and testosterone (male sex hormone)

Epididymis:
site where sperm matures and develops the ability to be motile (i.e. 'swim') - mature sperm is stored here until ejaculation

Sperm Duct:
long tube which conducts sperm from the testes to the prostate gland (which connects to the urethra) during ejaculation

Seminal Vesicle:
secretes fluid containing fructose (to nourish sperm), mucus (to protect sperm) and prostaglandin (triggers uterine contractions)

Prostate Gland:
secretes an alkaline fluid to neutralise vaginal acids (necessary to maintain sperm viability)

Urethra:
conducts sperm / semen from the prostate gland to the outside of the body via the penis (also used to convey urine)

6.6 Skill: Annotate diagrams of the female reproductive system to show names of structures and their functions.

Ovary:
where oocytes mature prior to release (ovulation) - it also responsible for estrogen and progesterone secretion

Fimbria:
a fringe of tissue adjacent to an ovary that sweep an oocyte into the oviduct

Oviduct:
transports the oocyte to the uterus - it is also typically where fertilisation occurs

Uterus:
the organ where a fertilised egg will implant and develop (becoming an embryo)

Endometrium:
the mucous membrane lining of the uterus, it thickens in preparation for implantation or is otherwise lost (via menstruation)

Vagina:
passage leading to the uterus by which the penis can enter (uterus protected by a muscular opening called the cervix)

6.2 Blood is a liquid tissue containing glucose, urea, plasma proteins and other components. List the other components of blood.

plasma/water;
dissolved gases / CO2 / O2;
erythrocytes / red blood cells;
leucocytes / white blood cells;
lymphocytes and phagocytes;
platelets;
hormones / named hormone(s);
amino acids / albumin / antibodies;
salts / minerals / ions other named solute in plasma apart from glucose, urea and plasma proteins;

6.2 Explain the roles of the atria and ventricles in the pumping of blood.

-atria collect blood from veins (vena cava/pulmonary);collect blood while ventricles are contracting;
-atria pump blood into ventricles/ensure ventricles are full;
-ventricles pump blood into arteries/out of the heart;
-ventricles pump blood at high pressure because of their thicker, muscular walls;
-mention of heart valves working with atria and ventricles to keep blood moving;
-left ventricle pumps blood to systems and right ventricle pumps blood to lungs;

Both left and right ventricles with correct function required for mark to be awarded.

6.2 State molecules transported by the blood.

a. example of a nutrient e.g. glucose;
b. oxygen/O2;
c. carbon dioxide/CO2;
d. nitrogen/N2;
e. hormones;
f. antibodies;
g. urea;

6.1 List the name, substrate and product of four PANCREATIC enzymes that hydrolyze food in the small intestine.

Amylase - Carbs
-begins in the mouth with the release of amylase from the salivary glands (amylase \= starch digestion)
-secreted by the PANCREAS in order to continue carbohydrate digestion within the small intestine
-enzymes for disaccharide hydrolysis are often immobilised on the epithelial lining of the small intestine, near channel proteins
-substrate: starch - amylose and amylopectin
-amylose -\> amylase -\> maltose
-amylopectin -\> amylase -\> dextrins

Protease - Protein
-begins in the stomach with the release of proteases that function optimally in an acidic pH
**in the stomach, pepsin is the main digestive enzyme attacking proteins.
-secreted by the PANCREAS
-proteins/polypeptides -\> short peptides
-endopeptidases work optimally in neutral environments (pH ~ 7) as the pancreas neutralises the acids in the intestine

Lipase - Lipids
-breakdown occurs in the intestines, beginning with emulsification of fat globules by bile released from the gall bladder
-smaller fat droplets are then digested by lipases released from the PANCREAS
-triglycerides -\> glycerol/fatty acids + monoglycerides

Phospholipase - Phospholipids
-phospholipids -\> fatty acids, glycerol and phosphate

6.1 List the name, substrate and product of six enzymes produced by GLAND CELLS in the small intestine wall.

Nucleases:
-digests DNA and RNA into nucleotides.

Maltase:
-digests maltose into glucose.

Lactase:
-digests lactose into glucose and galactose.

Sucrase:
-digests sucrose into glucose and fructose.

Exopeptidases (a type of protease):
-digest peptides
-removes single amino acids either from the carboxyl or amino terminal of the chain until only a dipeptide is left.

Dipeptidases:
-digest dipeptides into amino acids.

6.1 State why enzymes produced by gland cells in the small intestine wall often remain immobilized in the cell membrane.

So it can be reused or be linked to secondary functions like membrane transport.

6.1 List three adaptations that increase the surface area for absorption on the small intestine.

-villi look into the lumen
-microvilli are on top of villis
-small intestine wall has many folds.

6.1 Outline the role of peristalsis in the digestive process.

-peristalsis is the involuntary, wave-like contraction of muscle layers of the small intestine.
-contraction of circular muscles behind the food constricts the guy to prevent it from being pushed back towards the mouth
-contraction of longitudinal muscle where the food is located moves it on along the gut.
-swallowed food moves quickly down the esophagus to the stomach in one continuous peristaltic wave.
-peristalsis only occurs in one direction away from the mouth.

**main function of peristalsis in the intestine is churning of the semi-digested food to mix it with enzymes and thus speed up the process of digestion.

6.1 State the function of the following villi structures: capillary, epithelial cell, lacteal, and goblet cell.

capillary:
-maintain a concentration gradient for absorption by rapidly transporting absorbed products away.

epithelial cell:
-secretio
-selective absorption
-trans cellular transport
-tight junctions in between the epithelial cells \= maximum movement can occur because nothing can slip out
-brush border (where the microvilli) can increase the surface area

lacteal:
-absorb lipids from the intestine into the lymphatic system (which are later reabsorbed back into normal circulation)

goblet cell:
-secrete mucus to protect the mucous membranes where they are found

6.1 Label the following on a diagram of a villi: capillary, epithelial cell, lacteal, and goblet cell.

Check notes!

6.1 Define absorption.

Taking in substances through cell membranes or layers of cells in particular from the lumen of the gut into the blood or lymph capillaries

6.1 List materials absorbed by the villi cells of the small intestine.

-(carbohydrates) glucose, fructose, galactose and other monosaccharides
-(proteins) any of the twenty amino acids used to make proteins
-(lipids) fatty acids, monoglycerides and glycerol
-bases from digestion of nucleotides
-mineral ions such as calcium, potassium and sodium (no digestion required)
-vitamins such as ascorbic acid (vitamin C) (no digestion required)

6.1 Explain the absorption of triglycerides.

Products of lipase digestion: fatty acids and monoglycerides
-can be absorbed into villus epithelium cells by simple diffusion as they are hydrophobic
-also absorbed by facilitated diffusion as there are fatty acid transporters (proteins in the membrane of the microvilli)

-once inside the epithelium cells, fatty acids are combined with monoglycerides to produce triglycerides ( cannot diffuse back out in the lumen)
-triglycerides coalesce with cholesterol to form droplets with a diameter of about 0.2 (um), which become coated in phospholipids and protein.

-these lipoprotein particles are released by exocytosis through the plasma membrane on the inner side of the villus epithelium cells
-can either enter the lacteal and are carried away in the lymph or enter the blood capillaries in the villi.

6.1 Explain the absorption of glucose.

-glucoase cannot pass through the plasma membrane by simple diffusion because it is hydrophilic.
-sodium-glucose co-transporter proteins in the microvilli transfer a sodium ion and a glucose molecule together from the intestinal lumen to the cytoplasm of the epithelium cells.

This type of facilitated diffusion is passive but it depends on the concentration gradient of sodium ions created by active transport.

-glucose channels allow the glucose to move by facilitated diffusion from the cytoplasm to the interstitial spaces (in between) inside the villus and on into blood capillaries in the villus.

6.1 Application: Processes occurring in the small intestine that result in the digestion of starch and transport of the products of digestion to the liver.
Outline the source, function and specificity of amylase.
Outline the digestion of maltose, maltotriose and dextrins into glucose.

Source:
-saliva
-pancreas (secretes into small intestine)

Function:
-digestion of both forms of starch
-any 1,4 bonds in starch molecules can be broken by this enzyme as long as there is a chain of at least four glucose monomers.
-amylose -\> amylase -\> maltose
-amylopectin -\> amylase -\> dextrins

Specificity:
-because of the specificity of its active site, amylase cannot break 1,6 bonds in amylopectin
-fragments of the amyl-pectin molecule containing a 1,6 bond that amylase cannot ingest are called dextrins.

-dextrins -\> dextrinase -\> glucose
-maltose -\> maltase -\> glucose
**maltase are fixed to the epithelial lining of the small intestine
-maltotriose -\> glucosidase -\> glucose

6.1 State the role of the digestive system.

Break down the diverse mixture of large carbon compounds in food, to yield ions and smaller compounds that can be absorbed.

6.1 NoS Explain the use of models in physiology research.

A model can be used to represent a part of a living system and to investigate specific aspects of a process.

6.1 NoS State two examples of model systems used to study digestion.

Dynamic Gastric Model
Dialysis tubing made from cellulose

6.1 NoS State limitations of using model systems in physiology research.

Only model specific aspects of a process, not the whole process.
Oversimplified portrayal of the process

6.2 Describe the structure and function of the three layers of artery wall tissue.

Tunica externa:
a tough outer layer of connective tissue

Tunica media:
a thick layer containing smooth muscle and elastic fibres made of the protein elastin

Tunica intima:
a smooth endothelium forming the lining of the artery

6.2 Describe the mechanism used to maintain blood flow in arteries between heartbeats.

At the end of each heartbeat, the pressure in the arteries falls sufficiently for the stretched elastic fibres to squeeze the blood in the lumen.

6.2 Define systolic and diastolic blood pressure.

Systolic: the peak pressure reached in an artery is called the systolic pressure.

Diastolic: the minimum pressure inside the artery.

6.2 Describe the cause and effect of diffusion of blood plasma into and out of a capillary network.

Cause:
-the capillary wall consists of one layer of very thin endothelium cells
-coated by a filter-like protein gel
-contains pores between the cells

Effect:
-wall is thus very permeable and allows part of the plasma to leak out and form tissue fluid.
-the fluid flows between the cells in a tissue
-allowing the cells to absorb useful substances and excrete waste products.

6.2 Outline the roles of gravity and skeletal muscle pressure in maintaining flow of blood through a vein.

-blood flow in veins is assisted by gravity and by pressures exerted on them by other tissues especially skeletal muscles.

-veins typically pass between skeletal muscle groups, which facilitate venous blood flow via periodic contractions
-when the skeletal muscles contract, they squeeze the vein and cause the blood to flow from the site of compression
-contraction makes a muscle shorter and wider so it squeezes on adjacent veins like a pump.
-veins typically run parallel to arteries, and a similar effect can be caused by the rhythmic arterial bulge created by a pulse

6.2 Draw a diagram to illustrate the double circulation system in mammals.

Check notes!

6.2 Compare the circulation of blood in fish to that of mammals, and explain why the mammalian heart must function as a double pump.

Fish have a single circulation.
-blood is pumped at high pressure to their gills to be oxygenated
-after flowing through the gills the blood still has enough pressure to flow directly, but relatively slowly, to other organs of the body and then back to the heart.

In contrast, the lungs used by mammals for gas exchange are supplied with blood by a separate circulation.
**it is essential that blood flowing to and from the two circulations is not mixed.
-the heart is therefore a double pump, delivering blood under different pressures separately to the two circulations.

6.2 Define myogenic contraction.

The myocyte (muscle cell) itself is the origin of the contraction and is not controlled externally.

6.2 Outline the role of cells in the sinoatrial node.

The region of the heart with the fastest rate of spontaneous beating is a small group of special muscle cells in the wall of the right atrium, called the sinoatrial node.

-these cells have few of the proteins that cause contraction in other muscle cells
-but they have extensive membranes
-(therefore) the sinoatrial node initiates each heartbeat, because the membranes of its cells are the first to depolarise each cardiac cycle.

6.2 Identify the time of opening and closing of heart valves on a graph of pressure changes during the cardiac cycle.

Check Oxford textbook and study guide for practice questions?

6.3 Define pathogen.

Organism (or virus) that causes a disease.

6.3 Define the term passive immunity.

the acquisition of antibodies from another organism

6.3 Outline two roles of platelets in the blood clotting cascade.​

When a cut or other injury involving damage to blood vessels occurs:

1) plateletes aggregate at the site forming a temporary plug
2) release the clotting factors that trigger off the clotting process.

6.3 Define "specific immune response."

The production of antibodies in response to a particular pathogen.

6.3 Contrast antigen and antibody.

An antigen is a substance or molecule, often found on a cell or virus surface, that causes antibody formation.

An antibody is a globular protein which recognises a specific antigen and binds to it as part of an immune response.