Transport In Mammals

Question 1

What is the systemic circulation?

Answer 1

Blood is pumped out of the left ventricle into the aorta and travels from there to all parts of the body except the lungs. It returns to the right side of the heart in the vena cava.

Question 2

What is the pulmonary circulation?

Answer 2

Blood is pumped out of the right ventricle into the pulmonary arteries which carry it to the lungs. The pulmonary veins return the blood to the left side of the heart.

Question 3

What is meant by double circulation?

Answer 3

A circulatory system in which the blood passes through the heart twice on one complete circuit of the body.

Question 4

State the role of the pulmonary artery, the pulmonary vein, the aorta and the vena cava.

Answer 4

Pulmonary artery: carries deoxygenated blood from the heart to the lungs
Pulmonary vein: carries oxygenated blood from the lungs to the right atrium
Aorta: carries oxygenated blood from the heart to the body
Vena cava: returns deoxygenated blood from the body to the heart

Question 5

What are elastic arteries, and what is their function?

Answer 5

Elastic arteries, like the aorta, have a lot of elastic tissue in their walls. They carry blood from the heart and help regulate pressure by expanding when blood pressure is high and recoiling when it is low.

Question 6

How do elastic arteries help maintain blood pressure?

Answer 6

When blood enters at high pressure, elastic arteries widen to reduce pressure. When blood pressure drops, they recoil inward, pushing blood forward and slightly raising the pressure.

Question 7

What are muscular arteries, and how do they function?

Answer 7

Muscular arteries transport blood from elastic arteries to tissues. Their smooth muscle can contract (vasoconstriction) to reduce blood flow or relax (vasodilation) to increase it.

Question 8

What is vasoconstriction, and how does it affect blood flow?

Answer 8

Vasoconstriction is the narrowing of arteries due to smooth muscle contraction, reducing blood flow to specific areas and directing it elsewhere.

Question 9

What is vasodilation, and how does it affect blood flow?

Answer 9

Vasodilation is the widening of arteries due to relaxation of smooth muscle, increasing blood flow to certain areas.

Question 10

What is the function of capillaries, and why are they important?

Answer 10

Capillaries bring blood close to all body cells, enabling rapid exchange of substances like oxygen and nutrients. Their small size allows them to reach every cell efficiently.

Question 11

What is tissue fluid, and how is it formed?

Answer 11

Tissue fluid is leaked plasma from capillaries that flows into spaces between cells in tissues. It forms when plasma passes through gaps in capillary walls.

Question 12

How does the composition of tissue fluid compare to blood plasma?

Answer 12

Tissue fluid is almost identical to blood plasma but contains far fewer protein molecules since they are too large to pass through capillary walls.

Question 13

Why does tissue fluid not contain red blood cells?

Answer 13

Red blood cells are too large to pass through the capillary endothelium, so they remain in the bloodstream and do not enter tissue fluid.

Question 14

Can white blood cells enter tissue fluid?

Answer 14

Yes, some white blood cells can squeeze through capillary walls and move freely within the tissue fluid.

Question 15

Explain the movement of fluid into and out of capillaries.

Answer 15

As blood moves through the tiny capillaries in tissues, some of the fluid (plasma) leaks out to surround the cells, forming tissue fluid. This happens because the pressure inside the capillaries is high at the arterial end, which pushes the fluid out. However, the blood still contains a lot of dissolved proteins that create a pulling force (water potential gradient) that tries to bring water back into the capillaries.

By the time the blood reaches the venule end of the capillary bed, the pressure has dropped, so less fluid is pushed out. However, the water potential gradient remains, so more water is pulled back into the capillaries. Since more fluid leaves the capillaries than returns, there is a net loss of fluid from the blood as it moves through the capillary bed. This lost fluid is later collected by the lymphatic system and returned to circulation.

Question 16

What happens at the arterial end of a capillary bed?

Answer 16

At the arterial end, high blood pressure pushes fluid out of the capillaries into the surrounding tissue, forming tissue fluid.

Question 17

Why does water move into the tissue fluid from the capillaries?

Answer 17

The higher blood pressure inside the capillaries forces fluid out, despite the water potential gradient that tries to pull water back into the blood.

Question 18

What happens at the venule end of a capillary bed?

Answer 18

The blood pressure is lower, so less fluid is pushed out. Instead, the water potential gradient causes water to move from the tissue fluid back into the capillaries.

Question 19

Is there a net gain or loss of fluid from the blood in a capillary bed?

Answer 19

There is a net loss of fluid from the blood because more fluid leaves the capillaries than returns.

Question 20

What happens if blood pressure is too high?

Answer 20

Too much fluid is pushed out of the capillaries, leading to a buildup of fluid in the tissues, which is called oedema.

Question 21

What role do arterioles play in preventing oedema?

Answer 21

Arterioles help reduce the pressure of blood before it enters the capillaries, preventing excessive fluid loss and reducing the risk of oedema.

Question 22

State the functions of tissue fluid.

Answer 22

1. Exchange of materials between cells and the blood occur through the tissue fluid.
2. Delivers nutrients and oxygen to cells throughout the body.
3. Removes waste products from cells.
4. Helps regulate body temperature.
5. Provides a moist environment for cells and tissues.
6. Acts as a shock absorber to protect tissues.

Question 23

Describe the structure of a red blood cell.

Answer 23

1. Red blood cells are shaped like a biconcave disc - the dent in each side of the cell increases the surface area to volume ratio. This large surface area means that oxygen can diffuse quickly into or out of the cell.
2. Red blood cells are very small - the small size means that no haemoglobin molecule within the cell is very far from the cell surface membrane and the haemoglobin molecules can therefore quickly exchange oxygen with the fluid outside the cell.
3. Red blood cells are very flexible - this allows them to be squashed into different shapes but then spring back to produce the normal biconcave shape.
4. Red blood cells have no nucleus, no mitochondria and no endoplasmic reticulum - this means that there is more room for haemoglobin so maximising the amount of oxygen which can be carried by each red blood cell.

Question 24

How are white blood cells different from red blood cells?

Answer 24

• White blood cells all have a nucleus
• Most white blood cells are larger than red blood cells
• White blood cells are either spherical or irregular in shape

Question 25

What are the two main groups of white blood cells?

Answer 25

White blood cells are divided into phagocytes and lymphocytes.

Question 26

How do phagocytes destroy microorganisms?

Answer 26

Phagocytes destroy microorganisms by phagocytosis (engulfing and digesting them).

Question 27

What is the most common type of phagocyte, and how can it be recognized?

Answer 27

The neutrophil is the most common phagocyte. It has a lobed nucleus and granular cytoplasm.

Question 28

What is a monocyte, and what does it develop into?

Answer 28

A monocyte is a type of white blood cell that can develop into a macrophage, another type of phagocyte.

Question 29

How do lymphocytes destroy microorganisms?

Answer 29

Lymphocytes destroy microorganisms by secreting antibodies that attach to and destroy invading cells.

Question 30

How can lymphocytes be identified?

Answer 30

Lymphocytes are smaller than phagocytes, with a large round nucleus and very little cytoplasm.

Question 31

What does the haemoglobin dissociation curve show?

Answer 31

The curve shows that at low partial pressures of oxygen the percentage saturation of haemoglobin is very low. That is the haemoglobin is combined with only a very little oxygen. At high partial pressures of oxygen the percentage saturation of haemoglobin is very high; it is combined with large amounts of oxygen.

Question 32

What happens when an oxygen molecule combines with a haem group?

Answer 32

Oxygen molecules combine with the iron atoms in groups of a haemoglobin molecule. When an oxygen atom combines with one haem group the whole haemoglobin molecule is slightly distorted. The shape change makes it easier for a second oxygen molecule to combine with a second haem group. This in turn makes it easier for the third oxygen molecule to combine with a third haem group. It is then even easier for the fourth and final oxygen molecule to combine.

Question 33

What is the role of carbonic anhydrase?

Answer 33

Carbonic anhydrase catalyses the following reaction: - carbon dioxide + water = carbonic acid The carbonic acid dissociates: - carbonic acid = hydrogen ion + hydrogencarbonate ion Haemoglobin combines with the hydrogen ions forming haemoglobinic acid, HHb. When haemoglobin does this, it releases the oxygen which it is carrying.

Question 34

What is the result of the reaction of carbonic anhydrase?

Answer 34

- Haemoglobin removes excess hydrogen ions from solution. When carbon dioxide dissolves and dissociates, a high concentration of hydrogen ions is formed. This produces a low pH. If the hydrogen ions were left in solution the blood would be very acidic. By removing the hydrogen ions from solution, haemoglobin helps to maintain the pH of the blood close to neutral. It is acting as a buffer. - The presence of a high partial pressure of carbon dioxide causes haemoglobin to release oxygen. This is called the Bohr shift. High concentrations of carbon dioxide are found in actively respiring issues which need oxygen. These high carbon dioxide concentrations cause haemoglobin to release its oxygen even more readily than it would otherwise do.

Question 35

What is the chloride shift?

Answer 35

The hydrogen carbonate ions that are produced inside red blood cells as a result of the action of carbonic anhydrase on carbon dioxide diffuse out of the cells and into the blood plasma. These ions have a negative charge and to balance their movement, chloride ions, which also have a negative charge, move from the blood plasma into the red blood cells.

Question 36

What would happen if the chloride shift did not happen?

Answer 36

If the chloride shift did not happen, the inside of the red blood cell would develop an overall positive charge because hydrogen ions (from the dissociation of carbonic acid) would accumulate. Hydrogen ions cannot leave the cell because its cell membrane is not permeable to them. The influx of chloride ions, therefore, helps to prevent the overall charge inside the cell from becoming too positive.

Question 37

How is carbon dioxide transported in the blood?

Answer 37

1. As hydrogencarbonate ions in the blood plasma - most of the hydrogencarbonate ions diffuse out of the red blood cell into the blood plasma where they are carried in solution. (85%) 2. As dissolved carbon dioxide molecules in the blood plasma - some carbon dioxide remains as carbon dioxide molecules and some of these are simply dissolved in the blood plasma. (5%) 3. As carbaminohaemoglobin - other carbon dioxide molecules diffuse into the red blood cells but do not undergo the reaction catalysed by carbonic anhydrase. Instead they combine directly with the terminal amine groups of some of the haemoglobin molecules. The compound formed is called carbaminohaemoglobin. (10%)

Question 38

What happens when blood reaches the lungs?

Answer 38

The reactions go into reverse. As there is a relatively low concentration of carbon dioxide in the alveoli compared with that in the blood, carbon dioxide diffuses from the blood into the air in the alveoli. In turn, this stimulates the carbon dioxide of carbaminohemoglobin to leave the red blood cell and hydrogen carbonate and hydrogen ions to recombine to form carbon dioxide molecules once more. This leaves the haemoglobin molecule free to combine with oxygen.

Question 39

What are the coronary arteries, and what is their function?

Answer 39

The coronary arteries branch from the aorta and deliver oxygenated blood to the walls of the heart.

Question 40

What is the function of the septum in the heart?

Answer 40

The septum is a wall of muscle that completely separates the left and right sides of the heart.

Question 41

What are the upper chambers of the heart called, and what is their function?

Answer 41

The upper chambers are called atria. They receive blood from veins—the right atrium from the vena cava and the left atrium from the pulmonary veins.

Question 42

What are the lower chambers of the heart called, and what is their function?

Answer 42

The lower chambers are called ventricles. They receive blood from the atria and pump it into the arteries—the left ventricle into the aorta and the right ventricle into the pulmonary arteries.

Question 43

What are the atrioventricular valves, and where are they located?

Answer 43

The atrioventricular valves are between the atria and ventricles. The left valve is the mitral (bicuspid) valve, and the right valve is the tricuspid valve.

Question 44

What is the sinoatrial node (SAN), and why is it important?

Answer 44

The sinoatrial node (SAN) is a small patch of muscle tissue in the right atrium wall. It automatically contracts and relaxes, generating electrical impulses that start the heartbeat.

Question 45

What is the function of the atrioventricular node (AVN)?

Answer 45

The AVN is the only pathway for electrical impulses to travel from the atria to the ventricles. It delays the impulse for a fraction of a second to ensure the ventricles contract after the atria.

Question 46

What is the Purkyne tissue, and what does it do?

Answer 46

The Purkyne tissue is a network of fibers in the septum that carries the excitation wave down to the ventricles, causing them to contract.