Human nutrition

Question 1

Explain Circulatory systems in mammals

Answer 1

Mammals have a four-chambered heart and a double circulation
This means that for every one circuit of the body, the blood passes through the heart twice
The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs (the pulmonary circulation)
The left side of the heart receives oxygenated blood from the lungs and pumps it to the body (the systemic circulation)

Question 2

Advantages of double circulation

Answer 2

Blood travelling through the small capillaries in the lungs loses a lot of pressure that was given to it by the pumping of the heart, meaning it cannot travel as fast
By returning the blood to the heart after going through the lungs its pressure can be raised again before sending it to the body, meaning cells can be supplied with the oxygen and glucose they need for respiration faster and more frequently

Question 3

How do people get affected with coronary heart disease

Answer 3

If a coronary artery becomes partially or completely blocked by fatty deposits called ‘plaques’ (mainly formed from cholesterol), the arteries are not as elastic as they should be and therefore cannot stretch to accommodate the blood which is being forced through them - leading to coronary heart disease

Question 4

Difference between partial blockage and complete blockage

Answer 4

Partial blockage of the coronary arteries creates a restricted blood flow to the cardiac muscle cells and results in severe chest pains called angina
Complete blockage means cells in that area of the heart will not be able to respire and can no longer contract, leading to a heart attack

Question 5

Explain the structure of heart

Answer 5

The ventricles have thicker muscle walls than the atria as they are pumping blood out of the heart and so need to generate a higher pressure
The left ventricle has a thicker muscle wall than the right ventricle as it has to pump blood at high pressure around the entire body, whereas the right ventricle is pumping blood at lower pressure to the lungs
The septum separates the two sides of the heart and so prevents mixing of oxygenated and deoxygenated blood

Question 6

What are the two sets of valves

Answer 6

There are two sets of valves in the heart:

The atrioventricular valves separate the atria from the ventricles

The valve on the right side of the heart is called the TRICUSPID and the valve on the left side is called the BICUSPID

These valves are pushed open when the atria contract but when the ventricles contract they are pushed shut to prevent blood from flowing back into the atria

The semilunar valves are found in the two blood arteries that come out of the top of the heart

They are unusual in that they are the only two arteries in the body that contain valves

These valves open when the ventricles contract so blood squeezes past them out of the heart, but then shut to avoid blood flowing back into the heart

Question 7

Explain the function of heart

Answer 7

Deoxygenated blood coming from the body flows into the right atrium via the vena cava

Once the right atrium has filled with blood the heart gives a little beat and the blood is pushed through the tricuspid (atrioventricular) valve into the right ventricle

The walls of the ventricle contract and the blood is pushed into the pulmonary artery through the semilunar valve which prevents blood flowing backwards into the heart

The blood travels to the lungs and moves through the capillaries past the alveoli where gas exchange takes place (this is why there has to be low pressure on this side of the heart – blood is going directly to capillaries which would burst under higher pressure)

Oxygen-rich blood returns to the left atrium via the pulmonary vein
It passes through the bicuspid (atrioventricular) valve into the left ventricle

The thicker muscle walls of the ventricle contract strongly to push the blood forcefully into the aorta and all the way around the body
The semilunar valve in the aorta prevents the blood flowing back down into the heart

Question 8

What are the effects of physical activity on heart

Answer 8

So that sufficient blood is taken to the working muscles to provide them with enough nutrients and oxygen for increased respiration

An increase in heart rate also allows for waste products to be removed at a faster rate

Following exercise, the heart continues to beat faster for a while to ensure that all excess waste products are removed from muscle cells

It is also likely that muscle cells have been respiring anaerobically during exercise and so have built up an oxygen debt

This needs to be ‘repaid’ following exercise and so the heart continues to beat faster to ensure that extra oxygen is still being delivered to muscle cells

The extra oxygen is used to break down the lactic acid that has been built up in cells as a result of anaerobic respiration

Question 9

Describe the structure of arteries

Answer 9

Arteries
Carry blood at high pressure away from the heart
Carry oxygenated blood (other than the pulmonary artery)
Have thick muscular walls containing elastic fibres
Have a narrow lumen
Speed of flow is fast

Question 10

Describe the structure of veins

Answer 10

Veins
Carry blood at low pressure towards the heart
Carry deoxygenated blood (other than the pulmonary vein)
Have thin walls
Have a large lumen
Contain valves
Speed of flow is slow

Question 11

Describe the structure of capillaries

Answer 11

Capillaries
Carry blood at low pressure within tissues
Carry both oxygenated and deoxygenated blood
Have walls that are one cell thick
Have ‘leaky’ walls
Speed of flow is slow

Question 12

Difference between arterioles and venules

Answer 12

As arteries divide more as they get further away from the heart, they get narrower
The narrow vessels that connect arteries to capillaries are called arterioles
Veins also get narrower the further away they are from the heart
The narrow vessels that connect capillaries to veins are called venules

Question 13

What are the main blood vessel of liver

Answer 13

The hepatic artery brings oxygenated blood from the heart to the liver
The hepatic vein brings deoxygenated blood from the liver back to the heart
The hepatic portal vein transports deoxygenated blood from the gut to the liver

Question 14

What is the structure of Red blood cells

Answer 14

Biconcave disk containing no nucleus but plenty of the protein haemoglobin

Question 15

What is the structure of White Blood cell

Answer 15

Large cells containing Big nucleus, different types have slightly different structures and functions

White blood cells defend the body against infection by pathogens by carrying out phagocytosis and antibody production
Platelets are involved in helping th

Question 16

What is platelets

Answer 16

Fragments of cells
Platelets are involved in helping the blood to clot

Question 17

Define plasma

Answer 17

Stray coloured liquid
Plasma is important for the transport of carbon dioxide, digested food (nutrients), urea, mineral ions, hormones and heat energy

Question 18

Describe the structure of Phagocytes

Answer 18

Phagocytes
Carry out phagocytosis by engulfing and digesting pathogens

Phagocytes have a sensitive cell surface membrane that can detect chemicals produced by pathogenic cells

Once they encounter the pathogenic cell, they will engulf it and release digestive enzymes to digest it

They can be easily recognised under the microscope by their multi-lobed nucleus and their granular cytoplasm

Question 19

Describe the lymphocytes

Answer 19

Lymphocytes
Produce antibodies to destroy pathogenic cells and antitoxins to neutralise toxins released by pathogens

They can easily be recognised under the microscope by their large round nucleus which takes up nearly the whole cell and their clear, non-granular cytoplasm

Question 20

Explain the conversion of Fibrinogen

Answer 20

Platelets are fragments of cells which are involved in blood clotting and forming scabs where the skin has been cut or punctured
Blood clotting prevents continued / significant blood loss from wounds

Scab formation seals the wound with an insoluble patch that prevents entry of microorganisms that could cause infection
It remains in place until new skin has grown underneath it, sealing the skin again

When the skin is broken (i.e. there is a wound) platelets arrive to stop the bleeding

A series of reactions occur within the blood plasma

Platelets release chemicals that cause soluble fibrinogen proteins to convert into insoluble fibrin and form an insoluble mesh across the wound, trapping red blood cells and therefore forming a clot

The clot eventually dries and develops into a scab to protect the wound from bacteria entering