6 - Physiology and Function

6.1 - Digestion 6.2 - Heart 6.3 - Immune System 6.4 - Lungs & Respiration 6.5 - Neurons & Synapses 6.6 - Homeostasis

Understandings

6.1

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

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

3. The pancreas secretes enzymes into the lumen of the small intestine

4. Villi increase the surface area of epithelium over which absorption is carried out

5. Villi absorb monomers formed by digestion as well as mineral ions and vitamins

6. Different methods of membrane transport are required to absorb different nutrients

6.2

1. Arteries convey blood at high pressure from the ventricles to the tissues of the body

2. Arteries have muscle cells and elastic fibres in their walls

3. The muscle and elastic fibres assist in maintaining blood pressure between pump cycles

4. Blood flows through tissues in capillaries

5. Capillaries have permeable walls that allow exchange of material between cells in the tissue and the blood in the capillary

6. Veins collect blood at low pressure from the tissues of the body and return it to the atria of the heart

7. Valves in veins and the heart ensure circulation of blood by preventing backflow

8. There is a separate circulation for the lungs

9. The heart beat is initiated by a group of specialised muscle cells in the right atrium called the sinoatrial node

10. The sinoatrial node acts as a pacemaker

11. The sinoatrial node sends out an electrical signal that stimulates contraction as it is propagated through the walls of the atria and then the walls of the ventricles

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

13. Epinephrine increases the heart rate to prepare for vigorous physical activity

6.3

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

2. Cuts in the skin are sealed by blood clotting

3. Clotting factors are released from platelets

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

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

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

7. Antibiotics block processes that occur in prokaryotic cells but not in eukaryotic cells

8. Viruses lack a metabolism and cannot therefore be treated with antibiotics

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

6.4

1. Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries

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

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

4. 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

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

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

6.5

1. Neurons transmit electrical impulses

2. The myelination of nerve fibres allows for saltatory conduction

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

4. An action potential consists of depolarization and repolarization of the neuron

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

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

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

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

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

6.6

1. Insulin and glucagon are secreted by β and α cells of the pancreas respectively to control blood glucose concentration

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

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

4. Melatonin is secreted by the pineal gland to control circadian rhythms

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

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

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

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

The Digestive System

Three main functions: Digestion, breaks down food into absorbable nutrients; Absorption, absorbs the nutrients; Elimination, expels remaining solid waste.

Digestive System Structure

alimentary canal, organs which food passes through: esophagus, stomach, small and large intestines.

accessory organs, help in digestion but do not transfer food: salivary glands, pancreas, liver, gall bladder.

Esophagus

The first alimentary canal organ composed of a hollow tube that connects the oral cavity to the stomach separating the trachea by the epiglottis, bolus is moved via peristalsis.

Epiglottis

a flap of cartilage that covers the windpipe and larynx while swallowing

Bolus

chewed food mixed with saliva

Peristalsis

the involuntary contraction and relaxation of longitudinal and circular muscles throughout the digestive tract, beginning in your throat and ending in the anus.

Trachea

a long, U-shaped tube that connect the larynx/voice box to your lungs, the epiglottis protects the larynx and helps to swallow.

Stomach

The second alimentary canal organ lined by gastric pits which release acidic digestive juices, approx. pH 2, it temporarily stores food where its mixed via churning and protein digestions starts

Small Intestine

The third alimentary canal organ composed of a long, highly folded tube and three sections: the duodenum, jejunum, ileum, where nutrients are absorbed

Large intestine

The final alimentary canal organ consisting of ascending, transverse, descending, sigmoidal colon and rectum; where water and dissolved minerals as ions are absorbed.

Salivary glands

The first accessory organ consisting of the parotid, submandibular, sublingual glands, that release saliva to moisten food and contain enzymes, like amylase to start starch breakdown

Pancreas

The second accessory organ which produces various enzymes releasing them into the small intestine via the duodenum, and secretes certain hormones like insulin to regulate blood sugar

Liver

The third accessory organ which takes raw nutrients absorbed via the small intestine and makes them into key chemicals, the liver plays a role in detoxification, storage, metabolism, bile production, hemoglobin breakdown

Gall bladder

The last accessory organ which stores liver-produced bile which is release into the small intestine via the common bile duct.

Digestive System Summary

1. Salivary glands

2. Esophagus

3. Stomach

4. Small intestine

5. Pancreas

6. Liver

7. Gallbladder

8. Large Intestine

9. Anus/Rectum

Stomach - J-shaped bag connecting to esophagus and small intestine

Liver - upside down triangle on the right points left

bile duct connects to gall bladder and with pancreatic ducts connects to U-shaped bend of the small intestine, small intestine thinner than large intestine

Mechanical Digestion

The physical breakdown of food into smaller pieces.

Food is chewed, tongue pushes it to throat, goes down the esophagus as bolus where epiglottis blocks the trachea and uvula blocks the nasal cavity.

Churning, the stomach is lined with muscles that squeeze and mix the food with acidic digestive juices. Food is digested in several hours into chyme, later enters the duodenum where absorption occurs.

Peristalsis, the rhythmic contraction and relaxion of continuous segments of longitudinal smooth muscle causing movement of the esophagus and stomach. Food is moved unidirectionally along the alimentary canal from mouth the anus.

Segmentation, the contraction and relaxion of non-adjacent intestinal segments of circular smooth muscle, moving chyme bidirectionally for better mixing, helps digest food particles but overall slow.

Chemical Digestion

The chemical breakdown of food into small molecules via chemical agents, like enzymes, acids and bile.

Acids: Gastric stomach glands release digestive acids around pH 2, creating an acidic environment which denatures proteins and other macromolecules for digestion. The stomach epithelium has a mucous membrane that protects the gastric lining from acid damage. The pancreas releases alkaline compounds, like bicarbonate ions that neutralize acids before entering the intestine.

The liver produces bile concentrations stored in the gall bladder before release into the intestine. Bile contains bile salts that interact and divide fat globules into smaller droplets via emulsification, increasing the surface area for lipase enzyme activity.

Enzymes speed up reaction rates by lowering activation energy and allow digestive processes to occur at body temperature at sufficient speeds for survival. Enzymes are specific for substrates and digest molecules independently in separate locations.

Digestive Enzymes

Proteins secreted into the lumen of the small intestine by the pancreas or others for digestion. Type and location of enzyme secreted depends on the macromolecule required for hydrolysis.

Carbohydrate digestion

starts in the mouth with amylase from salivary glands converting polysaccharides to disaccharides, continues with pancreatic amylase within the small intestine converting disaccharides to monosaccharides, enzymes for disaccharide hydrolysis are often embedded within the epithelial lining of the small intestine near channel proteins, humans cannot digest cellulose.

Protein digestion

begins in stomach with protease that functions best in acidic environments, smaller polypeptides chains are broken down by endopeptidases in the small intestine which function best in neutral environments, pancreas neutralizes the acids in the intestine

Lipid digestion

Begins in the intestines where bile from the gall bladder emulsifies fat globules, smaller fat droplets are digested by lipase from the pancreas

Nucleic acid digestion

The pancreases releases nuclease which digest nucleic acids like DNA into smaller nucleosides.

Small Intestine Structure

Four main tissue layers from outside to center: Serosa - protective outer covering reinforced by fibrous connective tissue. Muscle layer - outer layer of longitudinal muscle for peristalsis, inner layer of circular muscle for segmentation. Submucosa - connective tissues separating the muscle layer from the innermost mucosa. Mucosa - highly folded inner layer which absorbs material through the surface epithelium from the intestinal lumen. Cross-section of small intestine is called the ileum.

Absorption

The transport of digested food monomers from the lumen into the epithelial lining of the small intestine. Tight junctions between epithelial cells block any gaps between cells and different monomers cross the apical and basolateral membranes differently. Absorption mechanisms: Secondary active transport, facilitated diffusion, osmosis, endocytosis/bulk transport.

Absorption Membrane Transport Mechanisms

In secondary active transport, a protein joins the active translocation of one molecule to the passive movement of another and co-transport. Co-transport across the epithelial membrane by active translocation of Na+ is used for glucose and amino acids.

In facilitated diffusion, channel proteins near specific-membrane bound enzymes create a localized concentration gradient and help hydrophilic food molecules pass through hydrophobic portions of the membrane. Facilitated diffusion is used for some monosaccharides, vitamins, minerals.

Osmosis in the small and large intestine diffuses water across the membrane in response to ion and hydrophilic monomer movement.

In simple diffusion, hydrophobic materials like lipids cross the hydrophobic portion of the membrane freely. Once absorbed lipids move into lacteals, NOT blood transported.

For bulk transport, endocytosis forms a cavity in the membrane to create an internal vesicle holding extracellular material, this requires energy due to breaking and reforming the phospholipid bilayer. In the intestines via pinocytosis, vesicles form around fluid containing dissolved materials allowing fast and bulk transport.

Starch digestion

Begins in the mouth with salivary amylase, continues with pancreatic intestine amylase as optimal pH is 7. Amylase digests amylose into maltose disaccharides and amylopectin into branched chains of dextrin, further broken down by maltase within the epithelial small intestine lining. Hydrolysis of sugars form glucose, if hydrolyzed further produces ATP or is stored as glycogen in animals.

Starch digestion and Pancreas

The pancreas releases the enzyme amylase from the exocrine glands into the intestinal tract.

It produces the hormone insulin and glucagon from the endocrine glands into the blood, they regulate blood sugar concentrations in the bloodstream. Insulin lowers blood sugar by increasing glycogen synthesis and storage in the liver and adipose tissue, whereas glucagon increases blood sugar by inhibiting the synthesis and storage of glycogen by the liver and adipose tissue.

Digestion Experiment

Dialysis Tubing: Digestion and absorption requires impermeable membranes to transport molecules via proteins. Size-specific permeability of membranes is modelled via dialysis tubing. It contains pores ranging from 1-10 nanometer diameter and is semi-permeable according to molecular size. Large molecules cannot pass, and the tubing is not ion selective. Impermeable to amylase and starch, but permeable to maltose.

1: For control condition, some dialysis tubing is connected to a thistle funnel and filled with starch solution. For experimental, some tubing is connected to a thistle funnel and filled with starch and amylase. Both placed in a beaker with water which will move into the tubing through osmosis towards the solute causing the meniscus to rise and the tube with amylase will have less solute as starch is digested, not rising as much.

2: Tubing filled with starch is suspended in a beaker with water, control. The other filled with starch and amylase, experimental. Amylase digests the starch into maltose which diffuses out the tubing into beaker, maltose is detected using Benedict's reagent or glucose indicators.

William Harvey’s Discovery of circulation

Harvey proposed that arteries and veins were separate blood networks, that veins pumped “natural“ blood produced via liver, whereas arteries pumped heat produced by the heart via lungs. After experiments he concluded: Arteries and veins were part of a single connected blood network, arteries pumped blood from heart to lungs and tissues, veins returned blood from lungs and tissues back to heart, he did not predict capillaries.

Myocardium

heart muscle tissue

Arteries

Arteries transport large volumes of blood at high pressure from the ventricles upon ventricular contraction to tissues and lungs in repeated pulses, blood carried in the lumen. They withstand high pressure and high volume due to ventricle contraction, consist of three layers, muscle and elastin maintain pressure between pumps.

Structure:

1. Narrow lumen - Maintains high blood pressure of 80-120 mmHg

2. Thick wall with outer collagen layer - Prevents rupturing under high pressure.

3. Thick arterial wall - consists of the inner layer of muscles and elastic fibers to maintain pulse flow by contracting or stretching. Muscle fibers contract to narrow the lumen and increase pump pressure to maintain pressure.

4. Elastin fibers - Allow the arterial wall to stretch and expand when blood flows through the lumen that exerts pressure on the wall, resulting in elastic recoil when artery returns to normal size and propels blood even further, maintaining arterial pressure

Artery wall tissues:

1. Tunica intima - The innermost layer composed of endothelial cells that provide a smooth surface for blood flow and help regulate vessel diameter.

2. Tunica media - The thicker middle layer composed of smooth muscle cells and elastin fibers, it provides structural support and regulates vessel tone and diameter.

3. Tunica adventitia -The outer layer consisting of connective tissue that provides strength and support to the artery.

Capillaries

Capillaries are tiny blood vessels that exchange materials between the cells in tissues and blood traveling at low pressure (<10mmHg).

Arteries split into arterioles which split into capillaries, decreasing arterial pressure as total vessel volume increases, artery branching ensures blood moves slowly and all cells are close to a blood supply, after exchanging materials capillaries pool into venules which gather into larger veins.

Structure: To efficiently exchange materials capillaries have a very small diameter of 5 micrometers and only one red blood cell passes at a time. Single-layer cell wall to minimize diffusion distance for permeable materials. Surrounded by outer layer basement membrane permeable to needed materials. Capillaries may be porous to help transport materials between tissue fluid and blood.

Structure varies upon location and role: Continuous - to limit the permeability of large molecules capillary walls can be continuous with endothelial cells held together by tight junctions; Fenestrated - for absorption, capillary walls can be porous; Sinusoid - some capillaries are sinusoidal with open spaces between cells and permeable to large molecules and cells.

Capillary blood flow: Very slow at very low pressure for maximum material exchange. High blood pressure in arteries is slowed by extensive branching and narrowing of the lumen. Higher hydrostatic pressure at the arteriole end of the capillary forces material from the bloodstream into the tissue fluid, oxygen and nutrients exits capillaries at tissues for cell respiration. Lower hydrostatic pressure at the venule end of the capillary allows materials from tissues to enter bloodstream, CO2 and urea enter capillaries at body tissues as waste.

Veins

Veins transport blood at low pressure from tissue to atria.

Structure:

1. Thin wall with less muscle and elastic fibers as blood flows at very low pressure of 80-120 mmHg

2. Veins have valves to prevent backflow and stop the blood from pooling at the lowest end as pressure is low

3. Very wide lumen for maximum blood flow and effective return

Vein blood flow: Veins consist of unidirectional valves to ensure circulation by preventing backflow and transporting blood against gravity despite low pressure. Veins run across skeletal muscle groups that facilitate vein blood flow via periodic contractions. Skeletal muscles contract, squeeze the vein, and cause blood to flow from the compression site. Veins run parallel to arteries and a similar effect can be caused by rhythmic arterial bulges created by a pulse.

Identification of blood vessels

Arteries: Transport blood from heart, thick walls, narrow lumen, high blood pressure, three layers, a lot of muscle and elastin, no valves.

Veins: Transport blood to heart, thin walls, wide lumen, low blood pressure, three layers, some muscle and elastic, valves.

Capillaries: Exchange materials with tissues, extremely thin single-cell wall, low blood pressure, one layer, no muscle or elastic, no valves.

Circulation separation from the lungs

The heart has four chambered organs, two sets of atria, and ventricles… in order to transport blood to two different locations. The left side is for systemic circulation pumping oxygenated blood around the body and has a thicker muscular wall/myocardium to pump blood further, whereas the right side is for pulmonary circulation pumping deoxygenated blood to the lungs.

Atrium

Reservoir chambers at the top of the heart which collect returning blood from lungs and body via veins and then pass blood to ventricles

Ventricles

Chambers at the bottom of the heart which expel blood from heart to lungs and body at high pressure via arteries, thick muscular walls and left ventricle is thicker.

Pulmonary

referring to the lungs

Systemic circulation

carries oxygenated blood from the left ventricle to the body via arteries and to tissues via capillaries, returning to the right atrium.

Pulmonary circulation

carries deoxygenated blood from the right ventricle to the lungs, returning to the left atrium.

Heart structure

Left side represents the right side, 4 chambers of those 2 atria near top that collect blood from body and lungs, as well as 2 ventricles near bottom that pump blood to body and lungs.

4 valves, 2 atrioventricular valves between atria and ventricles the bicuspid valve on left and tricuspid valve on right, 2 semilunar valves between ventricles and arteries with aortic valve on left, pulmonary valve on right.

4 blood vessels, vena cava inferior and superior which feed into right atrium returning deoxygenated blood from the body. Pulmonary artery feeds into right ventricle sending deoxygenated blood to lungs. Pulmonary vein feeds into left atrium returning oxygenated blood from lung. Aorta extends from left ventricle sending oxygenated blood around the body.

Sinoatrial node

The sinoatrial node is a specialized cluster of cardiomyocytes in the right atrium wall that control the contraction of heart muscle tissue. It acts as a primary pacemaker as it controls a normal heart rate or sinus rhytm of 60 to 100 bpm.

Atrioventricular node

The atrioventricular node is a small structure in the heart, that acts as a secondary pacemaker if the SA node fails maintaining 40 to 60 bpm.

Bundle of His

The Bundle of His is a cluster of cardiomyocytes that act as a final pacemaker maintaining 30 to 40 bpm.

Myogenic Contractions

Heart contractions are myogenic as the signals for cardiac compression or for a heart beat come from the heart muscle cells, cardiomyocytes within the heart itself rather than the brain.

Heart Beat

The sinoatrial node initiates and controls one’s heartbeat at around 60 to 100 cardiac contractions per minute, if it fails AV maintains 40 to 60 bpm, and if that fails the Bundle of His maintains. Interference of the pacemakers leads to fibrillation, and irregular and uncoordinated contractions though it is possible to restore a normal sinus rhythm via controlled electrical current, defibrilation.

The sinoatrial node sends out an electrical impulse that stimulates myocardium contraction, the impulse causes atria to contract and stimulates the atrioventricular node that sends signals down the septum via Bundle of His which innervates Purkinje fibers in the ventricular wall and causes ventricular contraction. The sequence of these events creates a delay between atrial and ventricular contractions resulting in two heart sounds, this lets the ventricles fill with blood then atrial contractions occur to maximize blood flow.

Heart rate

the number of times your heart beats per minute. Nerve signaling, hormone signaling, changes in blood pressure, and changes in CO2 concentrations which affect blood pH cause changes in one’s heart rate.

Nerve Signals and Heart Rate

The pacemaker is under autonomic control from the brain, namely the medulla oblongata or brain stem. There are two nerves connected to the medulla cause rapid changes in heart rate, the sympathetic nerve releases neurotransmitter noradrenaline increasing heart rate, parasympathetic nerve releases acetylcholine to decrease heart rate.

Hormone Signals and Heart Rate

Hormones are chemical messengers released into the bloodstream that act on distant target sites like the heart. Hormonal signaling by adrenaline released from adrenal glands above the kidneys causes a sustained increase of heartbeat to prepare one for physical activity. Adrenaline activates the same chemical pathway as neurotransmitter noradrenaline.

Cardiac Cycle

The series of events within the heart over a single hear beat consisting of a period of contraction, systole, and relaxation, diastole.

Systole

A period of contraction where blood returns to the heart flowing into the atria and ventricles as pressure in them is lower due to a low volume of blood.

Once ventricles are about 70% full the atria contract and atrial pressure increases which forces blood into the ventricles.

As ventricles contract the ventricular pressure becomes greater than atrial pressure and the atrioventricular valves shut close to prevent back flow, creating the first heart sound.

With both sets of heart valves closed, pressure rapidly build in the contracting ventricles, isovolumetric contraction.

Ventricular pressure becomes greater than blood pressure in the aorta, the aortic valve opens and blood releases into the aorta.

Diastole

Blood exits ventricle travels down aorta and ventricular pressure decreases.

When ventricular pressure is lower than aortic pressure, the aortic valve shuts to prevent back flow, resulting in second heart sound.

Ventricular pressures is lower than atrial pressure, the atrioventricular valve opens and bloods flows from atria to ventricle.

Throughout the cycle, aortic pressure is relative high as muscle and elastic fibers in the artery wall maintain blood pressure.

Coronary Artery Occlusion

Coronary arteries are blood vessels surrounding the heart which nourish cardiac tissue to keep the heart working. Coronary artery occlusion refers to a heart disease where blood is pumped through the heart at high pressure and cannot supply the heart muscle with oxygen and nutrients. If coronary arteries are occluded, the region of heart tissue with the blocked artery dies and stops function. Coronary thrombosis is the formation of clots within the coronary arteries.

Causes:

Atherosclerosis is the hardening and narrowing of arteries due to high cholesterol. Fatty deposits develop in the arteries reducing lumen diameter. Blood flow is restricted and increases artery pressure damaging the arterial wall. Damaged area is repaired with fibrous tissue which significantly reduces elasticity and as smooth lining degrades lesions form - atherosclerotic plaques. If plaque ruptures blood clotting begins and forms a thrombus that restricts blood flow, thrombus can become dislodged and become an embolus which causes a blockage in smaller arteriole.

Consequences:

If atherosclerosis causes blood clots in coronary arteries it causes coronary heart disease. Myocardial tissue cannot function without oxygen and nutrients and an acute myocardial infarction is caused. Blockages of coronary arteries are treater via by-pass surgery or creating a stent.

Risk factors for Coronary Heart Disease

Mnemonic, a goddess:

Age - blood vessels less flexible with age.

Genetics - hypertension predispose people to getting CHD.

Obesity - overweight strains the heart

Diseases - Some diseases increase risk of CHD, like diabetes.

Diet - extra saturated fats, salt, alcohol

Exercise - Not enough exercise

Sex - Lower oestrogen in males

Smoking - Nicotine causes vasoconstriction and raises blood pressure

6.3 - Immune System

Pathogen

An organism that causes disease and disrupts normal physiology of the infection organism. Cellular pathogens are bacteria, parasites and protozoa, acellular are viruses and prions

Primary Defense against Pathogens

There are two surface barriers that prevent pathogens from entering the body in the first place. The skin protects our external structures, it consists of a dry, thick and tough region of mostly dead surface cells. Sebaceous glands secrete chemicals and enzymes preventing microbial growth. Also secretes lactic acid and fatty acids to lower the pH, ranging from 5.6 to 6.4.

Mucous Membranes protect internal structures which are accessible through holes or tubes, like nostrils or urethra. It has a thin region of living surface cells that release fluids, like saliva to wash away pathogens. They can secrete lysozymes that destroy cell walls and cause cell lysis. Mucous membranes can have cilia, hair-like projections that help remove pathogens, as well as coughing or sneezing.

Clotting

Clotting or hemostasis is the repair process of broken or damaged blood vessels. The function of clotting prevent bleeding and pathogens from entering the bloodstream.

Blood clots

Primary hemostasis consists of platelets that undergo a structural change when activated to form a sticky plug at damaged regions. Platelets and damaged cells, extrinsic and intrinsic pathways release clotting factors needed for the coagulation cascade.

Secondary hemostasis consists of insoluble mesh of fibrin strands that trap blood cell at damage site.

Coagulation Cascade

A complex set of reactions facilitated by clotting factors released by extrinsic and intrinsic pathways that result in the formation of blood clots.

Clotting factors cause platelets to be sticky and they stick to damaged regions as solid plugs, they start localized vasoconstriction which reduces blood flow through damaged regions, and trigger conversion of inactive zymogen prothrombin into activated enzyme thrombin which catalyzes the conversion of soluble plasma protein fibrinogen into an insoluble fibrin. Fibrin strands form a mesh around the platelet plug and trap blood cells forming a temporary clots, when damaged region is repaired, plasmin dissolves the clot.

Antigens

Membrane proteins specific to each pathogen that are found on their outside, allows for recognition by macrophages and other cells.

Secondary Defense against Pathogens

The innate immune system is non-specific in its response or does not differentiate between different pathogens, and non-adaptive meaning it responds the same way every time.

Damaged tissues release chemicals to signal leukocytes to the infection site via chemotaxis, and phagocytic leukocytes circulating in the blood move into tissues via extravasation in response to infection, pathogens are engulfed with cellular extensions and fuse into an internal vesicle via phagocytosis, vesicle fuses to a lysosome and pathogen is digested. Pathogen fragments, antigens, can be present on phagocyte surfaces to stimulate third-line defense. Other secondary defenses include inflammation, fever, and antimicrobial chemicals.

Antibodies

Free, Y-shaped proteins made up of 4 polypeptide chains joined by disuplhide bonds, produced by B lymphocytes and plasma cells, they float around in the cytoplasm, recognize and attach themselves to a specific antigen acting like a lock and key to eliminate it.

The ends of the Y arms, variable regions bind to the antigen, differ between antibodies, the rest of the antibody is the same across them and is a recognition site.

Immunological memory

The ability of the third / adaptive immune system to remember and recognize pathogens it has encountered before.

Tertiary Defense against Pathogens

The adaptive immune system is specific in its response so it differentiates between specific pathogens and targets a specific response for it, responds quickly when exposed to previously encountered pathogens and prevents symptoms from developing. Lymphocytes coordinate this system.

B lymphocytes or B cells produce antibodies which recognize and target particular antigens. Helper T lymphocytes or Th cells regulate the release of cytokines which active specific B lymphocytes.

In secondary defense phagocytic leukocytes engulf pathogens and sometimes antigens are presented on the surface, these antigen-presenting cells move to the lymph nodes and activate specific helper T lymphocytes. The helper T cells release cytokines to activate specific B cell to produce antibodies for antigen. The activated B cell divides and differentiates into short-lived plasma cells that produce a lot of antibodies which target the specific antigen. A small amount of activated B cells and activated Th cells develop into memory cells and provide long-lasting immunity.

Antibiotics

Antibiotics are compound that kill or prevent the growth of microbes like bacteria by targeting prokaryotic metabolism. They block processes that occur in prokaryotic cells , like key enzymes, 70S ribosomes, and cell wall components, eukaryotes do not have these features and are not targeted.

Antibiotics do not work on viruses as they are not alive, do not posses a metabolism, and are treated with antivirals agents instead.

Antibiotic Resistance

Some strains of bacteria evolved genes that degrade the antibiotic, block its entry, increase its removal or alter the target, bacteria reproduce fast and resistance can proliferate easily, resistant strains can pass resistance genes to other straits via bacterial conjugation or horizontal gene transfer.

Factors increasing antibiotic resistance: Antibiotic over prescription or misuse, some antibiotic are in animal food, drug resistant bacteria is high in hospital where antibiotic use is high.

Florey and Chain’s Experiment

Alexander Fleming found the first antibiotic, penicillin in 1928 by contaminating a dish of S. aureus, penicillin mold grew and an area of prevent bacterial growth was seen around the mol.

In 1940 Florey and Chained tested penicillin on infected mice, 8 mice injected with a disease and then with penicillin, mice that weren’t treated with penicillin died.

HIV

The Human Immunodeficiency Virus is a virus that infects helper T cells hence disables the body’s third line of defense, the adaptive immune system. It causes a symptom called AIDS.

After targetting the helper T lymphocytes, the virus remains inactive and infected T cells reproduce, the virus reactivates and spreads destroying the T helper cells. Antibodies are unable to be made and the body is easily susceptible to infections resulting in eventual death.

HIV is transmitted via exchange of body fluids, some people are immune due to the lack of a CD4+ receptor on Th cells that HIV needs for docking.

Physiological Respiration

The physiological process of gas exchange, or the transport of oxygen from outside to the cells within tissues where energy is produced and the removal of CO2. Physiological respiration consists of ventilation, gas exchange, and cell respiration.

Ventilation System

The passive exchange of air between the outside and the lungs through breathing. A ventilation system maintains a concentration gradient in the alveoli. Oxygen is constantly being consumed in cellular respiration and removed from the alveoli into the bloodstream, and CO2 waste is constantly being released.

The lungs function as a ventilation system by cycling fresh air into the alveoli from the atmosphere, so O2 levels stay high in the alveoli and diffuse into the blood, CO2 levels stay loow and diffuse from blood. Lungs have a very large surface area to increase overall rate of gas exchange.

Gas Exchange

The exchange of oxygen and CO2 between the alveoli and bloodstream via passive diffusion.

Lung Structure / The Respiratory System

Air enters the respiratory system through the nose or mouth and passes through pharynx to the trachea.

Air travels down the trachea and divides into two bronchi which connect to the lungs.

The right lung made up of three lobes, left only two due to the heart.

Inside each lung, the bronchi divide into smaller airways or bronchioles to increase SA.

Each bronchiole ends with alveoli where gas exchange with the bloodstream occur.

Alveolus Structure

Alveoli are very small air sacs where the exchange of oxygen and CO2 with the bloodstream occur. Alveoli have a one-cell thick epithelial layer that minimizes diffusion distance for respiratory gases, they are surrounded by a rich capillary network to increase capacity for gas exchange with blood, they are roughly spherical in shape to maximize available surface area for gas exchange, internal surface is covered with fluid layer as dissolved gases diffuse better.

Pneumocytes

Pneumocytes are alveolar cells which line the alveoli and make up most of the inner surface of the lungs.

Type I pneumocytes are flattened and extremely thin about 0.15 micrometers to carry out gas exchange between the alveoli and the capillaries while minimizing diffusion distance. They’re connected by occluding junctions which prevent leakages of tissue fluid into alveolar air space. They’re amitotic and unable to replicate.

Type II pneumocytes are cuboidal in shape and possess many granules for storing surfactant components and responsible for secretion of pulmonary surfactant that reduces surface tension in the alveoli. Only 5% of f Type II pneumocytes are present on the alveolar surface, but 60% of total cells.

Surfactant (UNFINISHED)

Type II pneumocytes secrete a solution containing surfactant that creates a moist surface inside the alveoli to prevent the alveoli from sticking to each other by reducing surface tension.

Breathing Mechanism

Breathing is the active movement of respiratory muscles that pass air into and out of the lungs. Contractions of these muscles change the volume of the thoracic cavity, volume increase decreases pressure, volume decrease increases pressure. Gases move from high pressure to low pressure, pressure in chest less than atmospheric air moves into lungs, pressure in chest greater than atmospheric air moves out lungs.

Contractions of Respiratory Muscles

Respiratory muscles contract to change the volume and thus pressure in the thoracic cavity. Muscles only work via contraction and require different muscles. Muscle increasing volume causes inspiration or inhaling, and decreasing causes expiration or exhaling. Respiratory muscles are controlled by antagonistic muscle groups, inspiratory muscles contract and expiratory muscles relax.

Why is it hard to breathe at higher altitudes?

Atmospheric pressure is lower at high altitudes and greater increases in chest volume are required for a pressure difference, hence hard to breath at high altitudes. The body adapts to this.

Inspiration

1. The diaphragm muscles contract causing it to flatted and increase the volume of the thoracic cavity.

2. External intercostals contract pulling ribs upwards and outwards.

3. Other muscle groups help ribs up and out

Expiration

1. Diaphragm muscles relax and the diaphragm curves up hence reducing the volume.

2. Internal intercostal muscles contract pulling ribs in and down

3. Abdominal muscles contract and push the diaphragm up during forced exhalation

4. Other muscle groups help pull ribs down.

Lung Cancer

Lung cancer refers to the uncontrolled proliferation of lung cells resulting in the growth of a tumor in the lungs, impacts tissue function, causes symptoms depending on size and location of tumor. Lungs are vital to body function and hold a very rich blood supply increasing the chance of metastasizing.

Symptoms: Coughing blood, wheezing, respiratory distress, weight loss, cancer mass may compress adjacent organs causing chest pain, difficulty swallowing, heart complications.

Causes mnemonics - raped goats: Radiation, ageing, pollution, environment, diseases, genetics, occupation, asbestos, tobacco, smoke.

Emphysema (Unfinished)

Lung condition where the alveoli walls lose elasticity due to damage to alveolar walls. The loss of elasticity results in abnormal enlargement of the alveoli lowering total SA for gas exchange, degradation of alveolar walls causes holes and alveoli merge into big air spaces.

Causes: smoking as irritants in smoke damage the alveolar walls.

Symptoms: Shortness of breath, phlegm production, expansion of ribcage, increased susceptibility to chest infections.

Spirometry

A method of diagnosis and monitoring of lung conditions, measures how much air you breathe out.

Ventilation and Activity

Ventilations changes in response to physical activity as the body produces more ATP creating more CO2 waste and taking in more oxygen. CO2 blood levels change and chemosensors within artery walls send signals to brainstem. Exercise increases either ventilation rate, more breaths for continuous gas exchange or tidal volume, higher volume of air taken in and out allows more air to be exchanged.

Neurons

Neurons are specialized cells that transmit electrical impulses within the nervous system. They are responsible for communication and transmission of sensory information resulting in response.

Neuron Structure

Neurons differ according to role but all have:

Dendrites - short-branched fibers that convert chemical information from other neurons 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 - The axon may be surrounded by an insulating layer to improve conduction speed of electrical impulses along the axon, need more spade and energy.

Nervous system

The nervous system is a network that coordinates and controls the body via transmission of electrochemical signals by neurons. It consists of two parts: the central nervous system, CNS, and the peripheral nervous system, PNS.

Central Nervous System

The CNS integrates information received from peripheral nerves and coordinates bodily responses, mostly occurring in the brain, but sometimes regulated by the spinal cord. Contains brain, spinal cord, relay neurons.

Peripheral Nervous System

The PNS sends information to the CNS through sensory neurons and activates effectors (certain muscles or glands that respond to nervous impulses) via motor neurons. Contains of spinal, cranial, peripheral nerves, sensory and motor neurons.

Division of the Nervous System

Nervous System → PNS or CNS;

PNS → Sensory or Motor Division;

Motor → Somatic or Autonomic;

Autonomic → Sympathetic or Parasympathetic

How do neurons generate and conduct singals?

Neurons generate and conduct electrical signals by pumping NA+ and K+ across their membrane, unequal distribution of ions creates charge differences or membrane potentials.

Resting Potential

Resting potential refers to the charge difference across the membrane when a neuron is not firing, inside is more negative than outside ~ - 70mV. Maintaining a resting potential is an active process controlled by Na/K pumps.

Na/K pump is a transmembrane protein that actively exchanges Na and K ions, it needs ATP via ATP hydrolysis. 3 Na+ ions out for every 2 K+ ions in, creating an electrochemical gradient where inside is negative,

Action Potential

Action potential refers to quick charge changes across the membrane when a neuron fires consisting of depolarization, repolarization and a refractory period.

Depolarization - sudden change in membrane potential from negative to positive inside the membrane. A signal initiates at a dendrite, Na channels open within membrane of axon and with higher Na+ concentration outside causes a passive influx. The Na+ influx causes membrane to become more positive or depolarized ~30mV.

Repolarization - restoring membrane potential or negative internal charge. After Na+ influx, K channels open within axon membrane and with higher K+ concentration inside causes a passive efflux of K+, thus membrane potential returns back or is repolarized ~ -80mV.

Refractory period - time before a nerve impulse can fire again. During resting potential, Na+ are outside and K+ are inside. After depolarization with Na+ influx and repolarization K+ efflux, the distribution is greatly reversed, and resting potential needs to be restored via antiport action of Na/K pump.

Nerve Impulses

Nerve impulses are action potentials and move along an axon as a wave of depolarization. Depolarization happens when ion channels open and change the membrane potential, ion channels along an axon are voltage-gated and respond to such change where depolarization at one axon point triggers opening of ion channels in the next segment.

Nerve impulses are caused via local currents where each successive part of the axon reaches threshold potential ~55 mV. If threshold potential is reach an action potential can be generated. Combined dendrite stimulate exceeds minimum depolarization and triggers threshold potentials.

Oscilloscopes

Oscilloscopes measure membrane potentials across a neuronal membrane by graph where X-axis shows time in milliseconds and Y-axis shows membrane potential in millivolts. 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)

Myelination and saltatory conduction

Myelin is a mixture of protein and phospholipids, a fatty white substance made by glial cells that sometimes insulates axons.

Myelin sheaths increase electrical transmission speeds via saltatory conduction. In neurons without myelin, action potentials along axons propagate in a continuous wave of depolarization, whereas in myelinated neurons they hop between gaps in the myelin sheath called nodes of Ranvier. Speed increases up to 100-fold.

However, myelination needs space. NS regions made up of myelinated axons appear as white matter.

Synapses

Synapses are separating gaps between neurons, receptors, and effector cells. Neurons transmit info across synapse by converting electrical signals into chemical.

Synapse Transmission

Action potential arrives at axon terminal.

Voltage-gated Ca2+ channels open.

Ca2+ diffuses into the presynaptic neuron.

Ca2+ promotes neurotransmitter vesicle fusion.

Vesicles move to the membrane and dock.

Neurotransmitters are released from the axon terminal via exocytosis and cross synaptic cleft.

Neurotransmitters bind to receptors on post-synaptic membrane and open ligand-gated ion channels.

Opening of ion channels generates impulse in post-synaptic neuron and pre-synaptic signal is propagated.

Neurotransmitter released into synpase and either recycled or degraded.