IB Biology Topic 6

Glucagon

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

Insulin

A hormone that lowers blood glucose levels

Dialysis tubing

Plastic-like cellulose tubing with tiny holes to allow small molecules to pass through, it models absorption of food in the intestine

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

pulmoary 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

Cappliaries absorb

cell waste e.g. carbon dioxide and urea

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

Spirometery

measuring the volume and / or flow at which air can be inhaled or exhaled

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

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

resting potential

the state of the neuron when not firing a neural impulse

How do neurons reach a resting potential

through pumping sodium and potassium ions across their membrame

sodium-potassium pump in neurons

is important for maintaining the resting membrane potential

The resting potential is maintaned by

the Na+/K+ pump

How does the NaK pump work? in neurons

it exchanges 3 sodium ions (3 out) and 2 potassium ion (2 in) so that the membrane mecomes slightly negative

the unequal distribution of ions on different sides of the membrane is called

a membrane potential

Depolirization of a neuron

- The sudden change in membrane potential from a negative to the positive internal charge

- In response to a signal at a dendrite the sodium channels in the axon's membrane open

- As there are more sodium concentrated outside of the neuron the opening of sodium channels causes a passive influx of sodium

- The sodium causes the neuron to be more positive

SODIUM CHANNEL OPENS

Repolarization of a neuron

- The restoration of membrane potential following depolarisation

- Following the sodium influx, potassium channels open

- As K ions are more concentrated in the neuron, a passive removal of potassium is caused

- This means we return to resting potential with a negative interior

POTASSIUM CHANNEL OPENS

refractory period

- the time following an action potential during which a new action potential cannot be initiated

- after re and de polarisation the ionic distribution is reversed using NA K pumps and active transport

- this readies the neuron for the next action potential

NA K PUMP OPENS

Nerve impulses are

action potentials propagated along the axons of neurons

Action potentials are generated within the axon according to the

all or none principal

all-or-none principle

The principle that when a neuron fires, it fires with the same potency each time; a neuron either fires or not—it cannot partially fire.

- An action potential of the same magnitude will always occur provided a minimum electrical stimulus is generated

- This minimum stimulus - known as the threshold potential (-55 mV) - 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

Local currents in an axon cause

each successive part of the axon to reach the threshold potential

Oscilloscope traces

Measure the changes in membrane potential in axons during action potential

Myelination of the nerve fibres allows

for saltatory conduction

saltatory conduction

Rapid transmission of a nerve impulse along an axon, resulting from the action potential jumping from one node of Ranvier to another, skipping the myelin-sheathed regions of membrane.

Synapses

tiny gaps between neurons and receptor/effector cells

Chemical Transfer Across Synapses

- When an action potential reaches the axon terminal, it triggers the opening of voltage-gated calcium channels

- Calcium ions diffuse into the cell and promote the fusion of vesicles with the cell membrane

- The neurotransmitters are released from the axon terminal (exocytosis) and cross the synaptic cleft

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

- The opening of ion channels generates an electrical impulse in the post-synaptic neuron, propagating the pre-synaptic signal

- The neurotransmitters released into the synapse are either recycled (by reuptake pumps) or degraded (by enzymatic activity)

How are neurotransmitters released?

calcium opens voltage gated channels and allows synaptic vesicle to bind to receptors and exocytosis occurs

When presynaptic neurons are depolarized they release

a neurotransmitter into the synapse

Depolarization in axon terminals causes

Calcium channels to open

centeral nervous system

brain and spinal cord

peripheral nervous system

the sensory and motor neurons that connect the central nervous system to the rest of the body

Acetylcholine

A neurotransmitter that enables learning and memory and also triggers muscle contraction

Acetylcholine must be removed from the synapse as

overstimulation can leas to fatal stuff and paralysis

Acetylcholine is broken down by

acetylcholinesterase

Acetylcholine is made from

choline and acetyl CoA

When Acetycholine is broken down by acetycholinesterase...

choline returns to the axon terminal

Neonicotinoid pesticides

Bind to ACh receptors in the post-synaptic membranes of cholinergic synapses in insects. Cholinesterase does not break down these pesticides, so they remain bound to the receptors, preventing ACh from binding. Thus, they block synaptic transmission, killing the insect.