3.4-Mass transport in animals 1

what do arteries do?

carry blood at high pressure, travelling fast, and pulsing- that is, the pressure fluctuates with the heartbeat

what is the structure of arteries?

relatively small lumen

walls are:

very thick

have an inner coat of a single layer of endothelium

have lots of elastic tissues and muscle fibre

Why is the endothelium smooth?

To reduce friction between blood and blood vessel wall

when do the elastic fibres stretch?

when high pressure blood is pumped out by the heart

makes the artery wider and reduces the pressure a little

when do elastic fibres recoil?

when the pressure falls during diastole

elastic recoil keeps the blood under pressure and pushes it along

reduces fluctuations in pressure and helps smooth out blood flow as the blood moves along

Why do arteries close to the heart have more elastic fibres in their walls than arteries further away from the heart?

Greater blood pressure closer to the heart- elastic fibres allow artery walls to stretch to accommodate surges in pressure

Elastic recoil of arteries helps to smooth out blood flow- keeps blood under some pressure and moving during diastole

what are arterioles and what is their function?

Smaller vessels which arteries branch into when they reach the tissues to which they are transporting blood and they control blood flow to the capillaries of different organs

what is the structure of arteriole walls?

• have lots of muscle tissue

• Are thinner than arteries

• Have an inner coat of a single layer of endothelium

what is vasoconstriction?

When the muscles contract, narrowing the lumen diameter

This reduces blood flow to the capillaries they serve

what is vasodilation?

When the muscle relaxes, to widen the lumen diameter

This increases the blood flow to the capillaries they serve

What happens during exercise?

Arterioles supplying blood to the muscles in the legs would be dilated ( wide), whilst those carrying blood to the gut would be constricted ( narrower )

What is the advantage of arterioles in the skin dilating when we are too hot?

Allows blood to flow to surface of the skin for heat to be lost by radiation

what is the function of veins?

return blood to the heart

why don’t veins have thick walls?

by the time blood enters a vein, pressure has dropped to a very low level

what is the structure of the walls of veins?

• very thin

• Have valves

why do veins contain semi-lunar valves?

to keep blood flowing in the right direction

these valves only open to allow blood to flow towards the heart and close to stop it falling back down again

what are adaptations of capillaries?

Same diameter as red blood cell- blood flow reduced- allows more time for diffusion/ exchange

All red blood cells close to capillary wall- reduces diffusion pathway for oxygen

walls- consist of single layer of squamous endothelial cells, providing a short diffusion pathway between the body and blood tissues

tiny pores between the cells in the wall- making them highly permeable- water and many dissolved substances can be forced out of the capillary, forming tissue fluid

Small size and large number- provides large sa:v ratio

What is the importance of capillary beds?

It is in the networks of capillaries penetrating the body’s tissues that exchange of materials between the blood and the cells of the body occurs

Capillaries exchange nutrients and dissolved gases with the tissue fluid

How is tissue fluid formed?

High hydrostatic pressure at the arterial end (caused by ventricular contraction)

Causes water and small soluble substances to be forced out through the capillary wall

Plasma proteins are too large and remain in the capillary

There is a decrease in water potential

Water at the venous end re enters by osmosis

Remaining fluid is absorbed by the lymphatic capillary + transported around the body by the lymphatic system

What causes a drop in blood pressure in the capillary?

Loss of fluid from the capillary to the tissue fluid

Resistance as blood flows thru narrow lumen

What causes the water potential to decrease in the capillary?

Large plasma proteins remain in capillary + loss of fluid

what is the heart made of?

cardiac muscle

what is pulmonary circulation?

pulmonary artery carries deoxy blood from the heart to lungs, then pulmonary vein carries oxy blood back to heart

what is systematic circulation?

aorta carries oxy blood from the heart to the body, then vena cava carries deoxy blood to the heart

what is the pathway of blood from the body, back to the body?

vena cava carries deoxy blood from the body, to the right atrium, right ventricle, pulmonary vein to the lungs where it becomes oxygenated

pulmonary artery, left atrium, left ventricle, aorta to the rest of the body, back to the vena cava

what is the advantage for the human heart to have two separate pumps rather than one?

RHS generates pressure to send blood thru the lungs where pressure drops

returned to the LHS of the heart, generates more pressure so blood can travel around the body- fast enough to generate high HR

what do the coronary arteries do?

delivery oxy blood to the cardiac muscle that makes up the walls of the heart

why does the cardiac muscle need a rich supply of blood?

needs good supply of O2 and glucose for high rates of aerobic respiration to produce lots of ATP for muscle contraction

what does the septum do?

separate the oxy blood on the left and the deoxy blood on the right- makes gas exchange in lungs and body tissues more efficient

why are the left ventricle walls thicker than the right ventricle walls?

left ventricles need to contract with more force and pump blood all round the body, whereas the right ventricle only pumps blood to the lungs

What is the function of the AV and SL valves?

Prevent backflow of blood when they close

AV- allow blood to be pumped from atrium to ventricles

SL- allow blood to be pumped from ventricles to artery

what is a cardiac cycle?

one complete sequence of contraction and relaxation

what is atrial systole, ventricular systole and diastole?

atrial systole- atria contract

ventricular systole- ventricles contract

diastole- relaxation of heart muscle

where does blood flow from?

region of high pressure to low pressure

what happens during atrial systole?

atrial contraction

atrial pressure increases (higher than ventricular pressure)

AV valves open

blood pumped from atria to ventricles

blood stays in ventricles

what happens during ventricular systole?

ventricular contraction

ventricular pressure increases (higher than atria)

AV valves close (prevent blood going back to atria)

SL valves open- ventricular pressure higher than arteries

blood pumped from ventricles to arteries

what happens during diastole?

relaxation of heart muscle i.e atria and ventricles

SL valves close- pressure higher in arteries than ventricles- prevent blood going back to ventricles

meanwhile, blood is being pumped from the veins to the atria to start the process again

why is the cardiac muscle myogenic?

contracts on its own without needing nervous stimulation

how is a heartbeat initiated and co-ordinated?

SAN- acts as a pacemaker and sends a wave of impulse across the atria, causing them to contract

non-conducting tissue prevents immediate contraction of ventricles

AVN delays impulse whilst blood leaves atria

AVN sends wave of impulse down Bundle of His/Purkyne fibres

causes ventricles to contract from base up

where is elastic tissue found?

in the arteries

what is a pulse?

the stretch and subsequent recoil of the arteries travels as a wave known as the pulse

Pulse rate also known as heart rate

Measured in bpm

what is stroke volume and what is it determined by?

volume of blood pumped out from one ventricle during each contraction

the fuller the ventricles, the greater the force of contraction

what is cardiac output?

total volume pumped out from one ventricle per minute

how to calculate cardiac output (dm3 min-1)

stroke volume (cm3) multiplied by heart rate (bpm)

if a trained athlete’s heart gets bigger over time, what happens to the stroke volume and heart rate?

resting stroke volume will be bigger, resting heart rate will drop

more capacity to increase cardiac output during exercise

what does an increase in cardiac output allow?

more oxygen and glucose to be delivered to working muscles

what does the renal vein do?

carry deoxy blood from kidneys to heart (vena cava)

what does the renal artery do?

carry oxy blood from heart (aorta) to kidneys