Biology 🧬 Unit 8 - transport in mammals

Why do multicellular organisms/organisms with relatively small SA:V ratio need transport systems

Why do multicellular organisms/organisms with relatively small SA:V ratio need transport systems

1. Diffusion rate it too slow to supply their cells (because their surface area is too small to allow sufficient diffusion across it quickly enough)

2. The distance is too far for substances to travel by diffusion alone to reach all cells/tissues

3. Thus the time taken for substances to diffuse is too long

4. Level of activity is also important (plants don’t have a pump)

What is the cardiac cycle

1. The atria and ventricles are relaxed and empty

2. This phase is diastole

3. Blood at low pressure enters the atria

4. As they fill up with blood the pressure in the atria increases

5. When the pressure exceeds that in the ventricles blood flows through the atrioventricular valves into the ventricles

6. The atria contract

7. This contraction empties the atria

8. The sphincters where the vena cava and pulmonary veins enter the atria close to prevent back flow

9. The ventricles contract almost immediately

10. This phase is called systole

11. This increases the pressure in them above that in the pulmonary arteries and aorta

12. The elastic walls of the aorta stretch to accommodate the blood

13. The ventricles and atria relax

14. The pressure in the ventricles is now less than in the pulmonary arteries and the aorta

15. The back flow of blood is prevented by the semilunar valves and contraction of the aorta walls

What is the function of the pulmonary artery

Carries deoxygenated blood to the right and left lungs

What is the function of the Pulmonary vein

Carries oxygenated blood to the left atrium

What is the function of the Semi-lunar valve

Prevents back-flow of blood from arteries leaving the heart back into the ventricles

What is the function of the Left atrium

Receives oxygenated blood from the pulmonary veins pumps to the left ventricle

What is the function of the Bicuspid (mitral) valve (left atrium-ventricular valve)

prevents back-flow of blood between the left ventricle and left atrium

What is the function of the chordae tendinae (heart strings)

are attached to papillary muscles which prevent the valves from turning inside out (the muscles help the heart strings resist back-flow pressure)

What is the function of the left ventricle

Pumps oxygenated blood to the rest of the body (via the aorta)

What is the function of the cardiac muscle

Muscle tissue which contracts continuously

What is the function of the right ventricle

pumps deoxygenated blood to the lungs via the pulmonary artery

What is the function of the tricuspid valve (right atrio-ventricular valve)

valve preventing back-flow of blood from the right ventricle to the right atrium

What is the function of the right atrium

Receives deoxygenated blood from the vena cava and pumps to the right ventricle

What is the function of the inferior vena cava

Carries deoxygenated blood back to the right atrium from the lower body

What is the function of the superior vena cava

Carries deoxygenated blood back to the right atrium from the upper body

What is the function of the aorta

Carries oxygenated blood from the left ventricle out of the heart to the rest of the body

Why do we have a blood system

To transport substances such as nutrients (glucose, amino acids, fatty acids, glycerol) and oxygen around the body + remove waste products such as CO2, urea, excess water and slats

What does a ‘closed’ circulatory system mean

Blood is enclosed in vessels

What does ‘open systems’ mean in terms on circulatory systems (in terms of insects as an example)

Eg. In insects here the blood is pumped around the body by a heart and flows out of the heart in arteries, it is not then contained within the vessels but fills the body cavity called the haemocoel (blood space)

In insects the blood doesn’t transport oxygen as the gas exchange system is via Tracheae. These are tubes which carry air from the atmosphere directly to the tissues

describe a single circulatory system (using fish)

in fish the blood is pumped out of the heart to the gills where it picks up oxygen. The blood then continues to flow around the body

This system does result in the blood losing pressure as it travels (especially through the tine blood capillaries in the gills)

Humans have a double circulatory system what are the 2 ‘parts’ of this

pulmonary circulation - to the lungs

Systemic circulation - to the rest of the body

What is the cardiac cycle

The sequence of events that make up one heart beat

Describe what happens during atrial systole

Both atria contract, blood flows from the atria into the ventricles (via the a trio-ventricular valves). Backflow of blood into the vein is prevented by closure of the valves in the veins - sphincters at the junctions of the vein with the heart

How long roughly does ventricular systole last

0.3 seconds

Describe what happens during ventricular systole

Both ventricles contract. The atrio-ventricular valves are pushed shut by the pressurised blood in the ventricles. The semi-lunar valves in the aorta and pulmonary artery are pushed open. Blood flows from the ventricles into the arteries.

Describe what happens during ventricular diastole

Atria and ventricles relax. The semilunar valves in the aorta and pulmonary artery are pushed shut. Blood flows from the veins through the atria and into the ventricles

Systole =

contraction (of heart muscle)

Diastole =

relaxation (of heart muscle)

sound of the heart beat : lub(b) =

atrioventricular valves closing as ventricles contract

sound of the heart beat :

Dup(b/p) =

semilunar valves closing as ventricles relax

Around how long after the atria contract do the ventricles contract

0.1 seconds later

The heart muscle is myogenic what does this mean

It automatically contracts and relaxes without needing impulses from a nerve

What is the condition that can arise if the chambers are not synchronised

fibrillation

Why does the heart need controlling

The muscles from the atria and ventricles have their own frequency of contraction (atrial muscles tend to contract at higher frequency)

What. Is the hearts built-in coordinating system to prevent fibrillation

sinoatrial node (pacemaker)

What does the atrioventricular node do

Delays impulse of ventricle to allow atria to contract and empty fully

Where is the sinoatrial node situated

in the upper wall of the right atrium

Describe the ‘journey’ of the electrical impulse that goes through the heart ‘telling’ it when to contract/relax or open/close the valves

• the sinoatrial node initiates an impulse which flows over the left and right atria

• The electrical impulse is picked up by the atrioventricular node and flows down the central wall of the heart (the septum), between the 2 ventricles and into the left and right bundle branches (purkyne/purkinje fibres) via the electrical conductive tissue to carry the impulse over each of the ventricles

• The passage of this electrical conduction causes the muscle to contract, the valves to open and close and blood to empty into the lungs from the right side of the heart then back into the left side of the heart and around the body

• It is the pattern of electrical conduction or electrical wave that is picked up on the electrocardiogram (ECG), tracing the heart’s electrical activity

Where is the atrioventricular node located

The lower part of the right atrium close to the valves between the upper and lower chambers of the heart

What is the central wall of the heart called

The septum

What is the SAN (sinoatrial node)

a small patch of muscle in the wall of the atrium which sets the pace and rhythm for all the other cardiac muscle cells (the pacemaker)

The rhythm of contraction is slightly faster than the rest of the heart muscle and occurs 55-80 times a minute

Describe the contraction of the atria in terms of electrical activity

The wave of electrical activity spreads rapidly over the whole of the atrial walls

The cardiac muscle in the atrial walls respond by contracting in the same rhythm - all the muscle in both atria contracting almost simultaneously

Called atrial systole

A band of fibres between the atria and ventricles (inter-ventricular septum) does not conduct the excitation wave the route is through the AVN

Describe what the AVN (atrioventricular node) does in terms of when is receives the electrical impulse

the AVN picks up the excitation wave and after ~0.1 seconds passes it on to the purkyne tissue which runs down the inter-ventricular septum

This transmits the excitation wave very rapidly down to the base of the septum, from where it spreads outwards and passes upward through the ventricle walls

As it does so, it causes the cardiac muscle in these walls to contract, from the bottom up, squeezing blood upwards and into the arteries