11. Transport in humans (11.1, 11.2, 11.3, & 11.4)

Main circulation - heart - lungs - back to the heart again - main circulation
Double circulation = pulmonary + systemic
Pulmonary - pulmonary arteries carry the deoxygenated blood from the heart to the lungs, and pulmonary veins carry oxygenated blood from the lungs to the heart
Systemic - oxygenated blood from the left side of the heart to all parts of the body [except lungs], deoxygenated blood from all parts of the body brought to the right side of the heart by the veins

3. Understand that a double circulation provides a low-pressure circulation to the lungs and a high-pressure circulation to the body tissues

11.2 Heart

1. Identify the structures of the mammalian heart, limited to: the muscular wall, the septum, the left and right ventricles and atria, atrioventricular and semilunar valves and coronary arteries

2. Explain the relative thickness:

(a) of the muscle walls of the left and right ventricles

The wall of the left ventricle is made of cardiac muscle. This is about three times thicker than the wall of the right ventricle.
The reason for the difference is that the right ventricle only needs to produce enough pressure to pump blood to one organ, the lungs, which are next to the heart. However, the left ventricle needs to pump blood to all the main organs of the body

(b) of the muscle walls of theatriacompared to those of the ventricles

The ventricles need to pump blood at a higher pressure to pump it around the body and to the lungs, whereas the atria only need to pump the blood to a short distance - the ventricles, so they do not need such a high pressure

3. Describe the functioning of the heart in terms of the contraction of the muscles of the atria and ventricles and the action of the valves in a heartbeat

The mammalian heart has 4 chambers - 2 atria and 2 ventricles. The right side of the heart is completely separated from the left side of the heart by a muscle known as the median septum to prevent the mixing of oxygenated and deoxygenated blood.
Blood from various parts of the body is returned through the two venae cavae to the right side of the heart. The aorta receives deoxygenated blood. The heartbeat is started by the“pacemaker”, which is a group of specialised muscle cells at the top of the right atrium. These fire an impulse. The impulses spread through the wall of the right and left atria, causing them to contract and pump blood to the right ventricle. Between the right atrium and the right ventricle is the tricuspid valve, which consists of3 flaps attached to the walls of the ventricle by cord-like tendons. These chordae tendineae help in the easy flow of blood.
When therightventriclecontracts these flaps shut, preventing the backwards flow of blood to the atria. The blood is pumped to the lungs through the pulmonary arteries. Semilunar valves between the arteries and the ventricle prevent the backwards flow of blood in the ventricle.
Oxygenated blood is returned from the lungs to the heart by the pulmonary veins. Blood is pumped into the left side of the heart. The atria contract and pump blood to the left ventricle. Similar to the right ventricle, the left ventricle has a bicuspid valve to prevent the backwards flow of blood. The right ventricle pumps blood to the aorta, which supplies blood to all parts of the body. Like the pulmonary arteries, it also contains semilunar valves to prevent the backwards flow of blood. Blood entering theaortaisvery high pressure.
Two small coronary arteries originate from the aorta and supply oxygen and food substances to the heart muscles.

4. State that blood is pumped away from the heart in arteries and returns to the heart in veins

5. State that the activity of the heart may be monitored by an electrocardiogram (ECG), pulse rate, and listening to the sounds of the valves closing

In ECG electrodes, which are attached to ECG recording machines, are connected to the skin on the chest, legsand arms. The trace of a heartbeat can then be viewed on the monitor.
A stethoscope amplifies the sound of the heart valves opening and closing. A healthy heart produces first a "lub" and then a"dub" sound. The“lub” sound caused the atrioventricular valves to close. The dub sound is caused by the semilunar valves closing.

6. Investigate and explain the effect of physical activity on heart rate

When a person is exercising, the muscles need more energy
As a result, the heart has to deliver more oxygen and glucose for respiration, which causes the heart to rapidly beat and provide oxygen, trying to keep up with the demands of the muscles
The heartbeat gradually returns to normal when a person stops exercising
In a fit person, the heartbeat returns to normal quickly. In an unhealthy person, it may take quite some time for the heartbeat to return to normal

7. Describe coronary heart disease in terms of the blockage of coronary arteries and state the possible risk factors, including diet, sedentary lifestyle, stress, smoking, genetic predisposition, age, and gender

The heart is made of muscle cells that need their own supply of blood to deliver oxygen, glucoseand other nutrients remove carbon dioxide and other waste products. The blood is supplied by the coronary arteries.
If a coronary artery becomes partially or completely blocked by fatty deposits called atheroma(mainly formed from cholesterol). These patches may join up to make a bigger area, which reduces the internal diameter of the vessel.
Partial blockage of the coronary arteries creates 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.
Diet: If a person takes a diet with too much fat or calories, it can lead to obesity
Being overweight puts extra strain on the heart, causing it to work harder to pump blood around the body, making it difficult for them to exercise
Sometimes fats can be deposited in the interior lining of the artery, restricting the flow of blood. This can cause blood clots to form, leading to a heart attack
Sedentary lifestyle: When a person does not exercise regularly, it leads to a slower blood flow, allowing atheroma to form in the interior lining of the artery.
Stress: High levels of emotional stress can cause raised blood pressure
High blood pressure can increase the rate of formation of atheroma in the arteries
Smoking: The risk of a person having a heart attack increases by 2 or 3 times if a person smokes as compared to a non-smoker of a similar age. Chemicals present in the cigarette may damage the interior lining of the artery, allowing atheroma to form.
Genetics: There is evidence that coronary heart disease is passed down from one generation to the next
Age and gender: As a person grows older, the risk of coronary heart disease increases
Males are generally at higher risk than females [this might be because females have a healthier lifestyle than males]. In females, the hormone oestrogen prevents heart disease until later on in life when its production stops

8. Discuss the role of diet and exercise in reducing the risk of coronary heart disease

Adopting a healthy diet low in saturated fats, cholesterol, and sodium, while high in fibre and nutrient-rich foods, combined with regular physical activity, plays a crucial role in reducing the risk of coronary heart disease

11.3 Blood vessels

1. Name the main blood vessels that carry blood to and from the heart, lungs, liver, and kidneys, limited to: aorta,venacava, pulmonary artery, pulmonary vein, hepatic vein, hepatic artery, hepatic portal vein, renal artery and renal vein

2. Describe, and identify on diagrams and photomicrographs, the structure of arteries, veins and capillaries, limited to:

(a) Relative thickness of the wall

Arteries have thick walls because they carry blood at high pressure, which prevents bursting and maintains pressure waves. The larger arteries, near the heart, have a greater proportion of elastic tissue, which allows these vessels to withstand the surges of high pressure caused by the heartbeat.
Veins have thin walls because they carry blood at low pressure

(b) Composition of the wall (muscle and elastic tissue).

Arteries have elastic fibres and fibrous tissue to have a thick wall and a smaller lumen
Veins do not have elastic fibres, and fibrous tissue has a thin wall and a larger lumen

(c) diameter of lumen

Lumen is small in the artery to maintain blood pressure
Lumen is large in the vein to reduce resistance to blood

(d) presence of valves

Valves are not present in arteries because high blood pressure prevents the backwards flow of blood.
Valves are present in veins to prevent backflow of blood. Contraction of body muscles, particularly in the limbs, squeezes the thin-walled veins. The valves in the veins prevent the blood from flowing backwards when the vessels are squeezed in this way. This helps the return of venous blood to the heart.

3. Explain how the structure of arteries, veins, and capillaries is related to the pressure of the blood that they transport

Arteries

thick muscular walls containing elastic fibres to withstand the high pressure of blood and maintain the blood pressure as it recoils after the blood has passed through.
Have a narrow lumen to maintain high pressure

Veins

Have a large lumen as blood pressure is low.
Contain valves to prevent the backflow of blood, as it is under low pressure

Capillaries

Have walls that are one cell thick so that substances can easily diffuse in and out of them.
Have ’ leaky’ walls so that blood plasma can leak out and form tissue fluid surrounding cells
Carry blood at low pressure within tissues.
Carry both oxygenated and deoxygenated blood
The speed of flow is slow to allow diffusion of materials to occur

11.4 Blood

1. Identify red and white blood cells(lymphocytes and phagocytes)as seen under the light microscope on prepared slides, and in diagrams and photomicrographs

2. List the components of blood as red blood cells, white blood cells, platelets and plasma

3. State the functions of the components of blood:

(a) Red blood cells – oxygen transport

Spherical biconcave disc
Depression in the centre due to the absence of the nucleus, which gives them the biconcave shape
Elastic in nature, so it can squeeze through capillaries smaller than itself
Spongy cytoplasm, which contains a red pigment - haemoglobin, which is an iron-containing protein
In places where there is a high concentration of oxygen, haemoglobin combines with oxygen. Oxygen is released in places where the oxygen concentration is low. This makes haemoglobin very useful in carrying oxygen from the lungs to the tissues.
Produced by the bone marrow and have a lifespan of 3- 4 months, they are destroyed in the liver.
The iron from the haemoglobin is stored in the liver.

(b) white blood cells – antibody production by lymphocytes and engulfing pathogens by phagocytes

Colourless [because they do not contain haemoglobin] - larger than red blood cells - fewer in number
Irregular in shape and can squeeze through blood capillaries - lifespan of only a few days
Two kinds of white blood cells: phagocytes and lymphocytes
Phagocytes carry out phagocytosis by engulfing and digesting pathogens.
They can be easily recognised under the microscope by their multi-lobed nucleus and their granular cytoplasm
The phagocytes can move about by a flowing action of their cytoplasm and can escape from the blood capillaries into the tissues by squeezing between the cells of the capillary walls. They collect at the site of an infection, engulfing and digesting harmful bacteria and cell debris – a process called phagocytosis.

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 larger, round nucleus, which takes up nearly the whole cell, and their clear, non-granular cytoplasm

(c) platelets – clotting by converting soluble fibrinogen to insoluble fibrin to prevent blood loss and the entry of pathogens

Special types of blood cells are formed in the bone marrow. Platelets are fragments of cells which are involved in blood clotting and forming scabs where skin has been cut. Blood clotting prevents continued/significant blood loss from wounds. Scab formation seals the wound with an insoluble patch that prevents the entry of microorganisms that could cause infection
When the skin is broken, platelets release an enzyme known as thrombokinase, which converts the enzyme prothrombin to thrombin (its active form). This process requires calcium ions. Thrombin catalyses the conversion of soluble fibrinogen proteins to convert into insoluble fibrin and forms 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.

(d) plasma – transport, limited to: blood cells, ions, glucose, amino acids, hormones, carbon dioxide, urea, vitamins and plasma proteins

4. Describe the transfer of substances between blood in capillaries, tissue fluid and body cells

The fluid that escapes from capillaries is not blood, nor plasma, but tissue fluid. Tissue fluid is like plasma but contains less protein because protein molecules are too large to pass through the walls of the capillaries. This fluid bathes all the living cells of the body. As it contains dissolved food and oxygen from the blood, it supplies the cells with their needs. Some of the tissue fluid eventually leaks back into the capillaries, having passed on its oxygen and dissolved food to the cells. However, it has now received the waste products of the cells, like carbon dioxide, which are carried away by the bloodstream.

Credits: Notes compiled by Manahil Naeem of Karachi Grammar School

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