IB BIOLOGY TOPIC 6

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)

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

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

Small Intestine

A long, highly folded tube where usable food substances (nutrients) are absorbed

Large intestine

Final section of alimentary canal, where water and dissolved minerals are absorbed

Consists of the ascending / transverse / descending / sigmoidal colon, as well as the rectum

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

Peristalsis

the process of wave-like muscle contractions of the longitudinal muscles that moves food along

How does food move through the gut?

contraction of circular longitudinal musces of the small intestine

Chemical digestion : stomach acids

- Contain gastric glands which release digestive acids \= low pH environment
- Acidic environment denatures proteins and other macromolecules
- Stomach epithelium \= mucous membrane \= prevents acids damaging gastric lining
- Pancreas releases alkaline compounds \= neutralises the acids as they enter the intestine

Chemical digestion : bile

- Liver produces
- Stored and concentrated in gall bladder
- Released into the intestine
-Contains bile salts \= emulsification of fat
- The emulsification of fats increases the total surface area available for enzyme activity (lipase)

Enzymes digest most...

macromolecules in food into monomers in the small intestine e.g. lipase breaks down fat

Digestion of Carbohydrates

- Begins in the mouth with the release of amylase from the salivary glands
- Amylase is also 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

digestion of proteins

-Begins in the stomach with the release of proteases
- Smaller polypeptide chains enter the small intestine where they are broken down by endopeptidases released by the pancreas
- These endopeptidases work optimally in neutral environments as the pancreas neutralises the acids in the intestine

digestion of lipids

- Occurs in the intestines, beginning with emulsification of fat by bile
- The smaller fat droplets are digested by lipases released from the pancreas

digestion of nucleic acids

Pancreas releases nucleases \= digest nucleic acids (DNA, RNA) into smaller nucleosides

What secretes enzymes into the lumen of the small intestine?

the pancreas

how many layers in the small intestine structure?

4 (serosa, muscle layer, submucosa, mucosa)

Serosa

protective outer layer

Muscle layer

outer layer of longitudinal muscle (peristalsis) and inner layer of circular muscle (segmentation)

Submucosa

connective tissue seperating the inner mucosa and the muscles

mucosa

a highly folded inner layer which absorbs through its surface epithelium

Villi

Fingerlike extensions of the intestinal mucosa that increase the surface area for absorption

Villi absorb

monomers formed by digestion and mineral ions and vitamins

Features of Villi

Mnemonic: MR SLIM
- Microvilli
- Rich blood supply
- Single layer epithelium
- Lacteals
- Intestinal glands
- Membrane proteins

Different types of membrane transport for digestion:

Endocytosis, Simple Diffusion, Osmosis, Facilitated Diffusion, Co-Transport/Active transport

Glucuoe and amino diffuse through...

co-transport

monosaccarides and hydrophillic diffuse through...

facilitated diffsuion

water diffuses through...

osmosis

hydrophopic substances transport through...

simple diffusion

Pinocytosis

A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes.

Process of the digestion of starch in small intestine:

1. salivary amylase and pancreatic amylase are the enzymes which digest
2. Ammylose into maltose subunits
3. Amylopectin into dextrins
4. The hydrolysis of dextrins and maltose \= production of glucose
5. This can be used to make ATP or stored as glycogen
6. The hormone insulin and glucagon regulate the concentration of glucose

Insulin

A hormone which lowers blood glucose levels

Glucagon

A protein hormone secreted by pancreatic endocrine cells that raises blood glucose levels

WIlliam Harvey discovered the blood system

were a combined network, blood flows continusouly, the heart is the pump (arteries from hear) (veins to heart), Blood flow is unidirectional

pulmonary circuit

on the right side of the heart

systemic circulation

on the left side of the heart

Arteries

Blood vessels that carry blood away from the heart

Characteristics of arteries

blood at high pressure, walls are thick, wales stretch or contract with a pulse, walls contain muscles cells and elastic fibres

Capillaries

Microscopic vessel through which exchanges take place between the blood and cells of the body

Characteristics of capllilaries

blood at low pressure, walls made of a single layer, extremly narrow lumen, facilatate material exhange

Veins

Blood vessels that carry blood back to the heart

Characterisitc of veins

blood at low pressure, wide lumen, have valves, walls are thin, small amounts of muscles

Role of valves in the blood system

prevent backwards blood flow

heart structure

Pathway of deoxygenated blood through the heart

-Vena Cava (veins) from body
-Right Atrium
-Tricuspid valve
-Right Ventricle
-Pulmonary valve
-Pulmonary (artery)
-Lungs

Pathway of oxygenated blood

-from lungs
-Pulmonary veins
-Left Atrium
-bicuspid valve
-Left ventricle
-aortic semilunar valve
-aorta
-body

Sinotorial node

pacemaker on right atrium of heart

Describe the electrical events that trigger the contraction of the heart muscle fibres

- The heart beat is myogenic
- Electrical signals are initiated by the sinoatrial (SA) node
- It stimulates the atria to contract and also relays signals to an atrioventricular node
- The atrioventricular node sends signals via the Bundle of His to Purkinje fibres
- These fibres innervate the ventricles and cause them to contract

how is heart rate increased and decreased?

by impulses brought to the heart through two nerves from the medulla of the brain.

Describe the role of the medulla and epinephrine (adrenaline) in regulating heart rate

- The SA node maintains the heart's normal sinus rhythm (60 - 100 bpm)
- The SA node may be regulated by the medulla, with sympathetic nerves increasing heart rate, by releasing noradrenaline and parasympathetic nerves decreasing the heart rate by releasing acetylcholine
- Heart rate may also be increased by the release of epinephrine (a.k.a. adrenaline) into the bloodstream

Outline the pressure changes in the heart during the cardiac cycle

Blood returning to the heart will flow into the atria and ventricles as the pressure in them is lower

As ventricles fill, atria contract (atrial systole), increasing pressure in atria and forcing blood into ventricles

As ventricles contract, ventricular pressure exceeds atrial pressure and AV valves close to prevent back flow

When ventricular pressure exceeds pressure in aorta, the aortic valve opens to release blood into the aorta

As blood exits the ventricle, ventricular pressure falls below aortic pressure, so the aortic valve closes

When ventricular pressure drops below atrial pressure, the AV valve opens and cycle begins again

Causes of Coronary Occlusion

- Fatty deposits develop in the arteries and reduce the lumen
- The restricted blood flow increases pressure in the artery, \= damage to the arterial wall
- The damaged region is repaired with fibrous tissue which significantly reduces the elasticity of the vessel wall
- As the smooth lining of the artery is degraded, lesions form called atherosclerotic plaques
- If the plaque ruptures, blood clotting is triggered, forming a thrombus that restricts blood flow
- If the thrombus is dislodged it becomes an embolus and can cause a blockage in a smaller arteriole

Risk Factors for Coronary Heart Disease

Age
Genetics
Obesity
Diseases
Diet
Exercise
Sex
Smoking

First line of defence

prevent the entry of pathogens into the body
- intact skin
- mucous membranes

Blood clots

1 - Platelets : form a sticky plug at the damaged region (primary haemostasis)
2 - Fibrin strands form an insoluble mesh of fibres that trap blood cells at the site of damage (secondary haemostasis)

Coagulation Cascade

1- Platelets to become sticky and adhere to the damaged region \= solid plug
2- Initiate localised vasoconstriction \= reduce blood flow. Triggers conversion of the inactive zymogen prothrombin into the activated enzyme thrombin
3 - Thrombin catalyses fibrinogen to fibrin
4 - The fibrin strands \= mesh of fibres around the platelet plug and traps blood cells to form a temporary clot
5- When the damaged region is completely repaired, an enzyme (plasmin) is activated to dissolve the clot

Second line of defence

Innate immune system
- non-specific
- non-adaptive

Phagocytosis process

- Phagocytic leukocytes circulate in the blood and move into the body tissue in response to infection
- Histamine released which draw white blood cells to the site of infection via chemotaxis
- Pathogens engulfed when pseudopodia surround the pathogen and then fuse to form an internal vesicle
- The vesicle is then fused to a lysosome forming a phagolysosome and the pathogen is digested
- Antigens may be presented on the surface of the phagocyte in order to stimulate the third line of defence

Third line of defence

Adaptive immune system, which is specific in its response

B lymphocytes

are antibody producing cells that recognize and target particular antigens

T lymphocytes

are regulator cells that reslease chemicals to activate specfic B cells

Antibodies

Proteins produced by B cells that attach to antigens, keeping them from harming the body

Antigen

A protein that, when introduced in the blood, triggers the production of an antibody

Antigens are specific

to a antibody

Antibiotics can only work on

prokaryotic cells

Antibiotics targets

prokaryotic metabolism

Viruses lack a metabolsim and hence

can not be treated with antibiotics

Antibiotic resistance happens by ..

Genes degrade the antibiotic, block its entry, increase its removal or alter the target

Resistance increases due to....

Antibiotics are :
- Over-prescribed
- Misused
- Freely available

Penicillin

the first discovered antibiotic

Florey and Chain experiment

mice made sick with bacteria, half were given penicillin and teh other hald nothing, those who ingestied penicillin lived

Effects of HIV on the immune system

- HIV targets t cells
- the virus is inactive during when the t cells reproduce
- eventually, the virus is active and has spread
- antibodies can't be produced
- one is extremely susceptible to infection

ventialtion maintains

concentration gradients of oxygen and carbon dioxide between air in the alveoli and blood flowing in adjacent capllicaires

Ventilation

movement of air in and out of the lungs

gas exchange

the process of obtaining oxygen from the environment and releasing carbon dioxide

Gas exchange by pressure in lungs:

Occurs via diffusion
O2 concentration is higher in the lungs than in the blood, so O2 diffuses into blood.
CO2 concentration in the blood is higher than in the lungs, so CO2 diffuses out of blood.

cell respiration

the process in cells in which oxygen is used to release stored energy by breaking down sugar molecules

Lung structure

trachea, bronchi, bronchioles, alveoli

Alveoli structure

- Thin epithelial layer
- Rich capillary network
- Spherical
- Internal surface is covered with a layer of fluid

Type I pneumocytes

extremely thin alveolar cells that are adapted to carry out gas exchange

Type II pneumocytes

cuboidal cells that's produce surfactant which reduces surface tension in the alveoli

What does surfactant do?

It reduces surface tension inside the alveolar or respiratory membrane.

Muscle contrations in the lungs cause

pressure changes in the thorax that force air in and out of the lungs

When the volume of the thoracic cavity increases

pressure in the thorax decreases

When the volume of the thoracic cavity decreases

pressure in the thorax increases

When pressure in the chest is less than atmospheric pressure

inspiration will occur

When pressure in the chest is greater than atmospheric pressure

expiration will occur

Muscular process of inhalation:

1. diaphragm contracts
2. external intercostal muscles pull ribs up
3. this increases pressure in the thoracic cavity
4. pressure in the lungs decreases below atmospheric pressure
5. Air flows in the equalise

Muscular process of exhalation:

1. diaphragm muscles relax
2. internal intercostal muscles pull ribs down
3. abdominal muscles contract
4. decreases volume of thoratic cavity
5. pressure in lungs increases above atmospheric pressure
6. air flows out

Causes of lung cancer:

smoking, passive smoking, air pollution, radon gas, asbestos and silica

Consequence of lung cancer

death, metastasis, blood, wheezing etc.

Emphysema

a condition in which the air sacs of the lungs are damaged and enlarged, causing breathlessness.

causes of emphysema

smoking or second hand smoking

consequences of emphysema

reduced surface area in alveoli, difficulty breathing, volume of alveoli increases

Neuron

a specialized cell transmitting nerve electrical impulses; a nerve cell.

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

Cell body of nerve

site of metabolic reactions and dendrite input relay to axon

Myelin sheath

Improves the conduction speed of electrical impulses along the axon