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Biology > Exchange between Organisms (Mass Transport) - Blood Vessels > Flashcards

Exchange between Organisms (Mass Transport) - Blood Vessels Flashcards

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1
Q

What are coronary vessels?

A
  • The heart is supplied by its own blood vessels, called coronary arteries.
  • Supply the heart tissue with oxygen, glucose etc.
  • Responsible for gas/nutrients/waste exchange in the cardiac muscle.
  • Branch off the aorta shortly after it leaves the heart.
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2
Q

What are arteries?

A

Arteries are large vessels that carry blood away from the heart and into arterioles.

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3
Q

What are arterioles?

A

Arterioles are smaller arteries that control blood flow from arteries to capillaries.

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4
Q

What are capillaries?

A

Capillaries are tiny vessels which deliver blood as close as possible to the cells. They link the arterioles to venules, which link to veins.

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5
Q

What are veins?

A

Veins carry blood from capillaries and venules back to the heart.

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6
Q

What is the layered structure of arteries, arterioles and veins, from the outside inwards?

A
  • tough fibrous outer layer (collagen) that resists pressure changes from both within and outside
  • muscle layer that contract and so control the flow of blood
  • elastic layer that helps to maintain blood pressure by stretching and springing back (recoiling)
  • thin inner lining (endothelium) that is smooth to reduce friction and thin to allow diffusion
  • lumen that is not actually a layer but the central cavity of the blood vessel through which the blood flows
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7
Q

Which vessels carry out transport and which vessels carry out exchange?

A

Arteries, arterioles and veins carry out transport. Only capillaries carry out exchange.

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8
Q

What differs between each type of blood vessel?

A

The relative proportions of each layer. Arterioles are similar to arteries but they differ in being smaller in diameter and having a relatively larger muscle layer and lumen. The differences in structure are related to the differences in the function that each type of vessel performs.

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9
Q

What do the elastic tissue of arteries do?

A

The elastic tissue of arteries will stretch and recoil. It is not muscle and will not contract and relax.

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10
Q

What is the function of arteries?

A

The function of arteries is to transport blood rapidly under high pressure from the heart to the tissues.

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11
Q

How is the structure of arteries adapted to its function?

A
  • the muscle layer is thick compared to veins
  • the elastic layer is relatively thick compared to veins
  • the overall thickness of the wall is great
  • there are no valves (except in the arteries leaving the heart)
  • small lumen because blood is pumped at high pressure
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12
Q

Why is the muscle layer of arteries thick compared to veins?

A

This means smaller arteries can be constricted and dilated in order to control the volume of blood passing through them.

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13
Q

Why is the elastic layer of arteries relatively thick compared to veins?

A

Because it is important that blood pressure in arteries is kept high if blood is to reach the extremities of the body. The elastic wall is stretched at each beat of the heart (systole). It then springs back when the heart relaxes (diastole) in the same way as a stretched elastic band. This stretching and recoil action helps to maintain high pressure and smooth pressure surges created by the beating of the heart.

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14
Q

Why do arteries have thick walls overall?

A

This resists the vessel bursting under pressure.

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15
Q

Why do arteries have no valves (except in the arteries leaving the heart)?

A

Because blood is under constant high pressure due to the heart pumping blood into the arteries. It therefore tends not to flow backwards.

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16
Q

What is the function of arterioles?

A

Arterioles carry blood, under lower pressure than arteries, from arteries to capillaries. They also control the flow of blood between the two.

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17
Q

How is the structure of arterioles adapted to its function?

A
  • the muscle layer is relatively thicker than in arteries to adjust diameter
  • the elastic layer is relatively thinner than in arteries
  • no valves
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18
Q

Why is the muscle layer of arterioles relatively thicker than in arteries?

A

The contraction of this muscle layer allows constriction of the lumen of the arteriole. This restricts the flow of blood and so controls its movement into the capillaries that supply the tissues with blood.

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19
Q

Why is the elastic layer of arterioles relatively thinner than in arteries?

A

Because blood pressure is lower.

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20
Q

What is the function of veins?

A

Veins transport blood slowly, under low pressure, from the capillaries in tissues to the heart.

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21
Q

How is the structure of veins adapted to its function?

A
  • the muscle layer is relatively thin compared to arteries
  • the elastic layer is relatively thin compared to arteries
  • the overall thickness of the wall is small
  • there are valves at intervals throughout
  • bigger lumen because blood is pumped at low pressure
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22
Q

Why is the muscle layer of veins relatively thin compared to arteries?

A

Because veins carry blood away from tissues and therefore their constriction and dilation cannot control the flow of blood to the tissues.

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23
Q

Why is the elastic layer of veins relatively thin compared to arteries?

A

Because the low pressure of blood within the veins will not cause them to burst and pressure is too low to create a recoil action.

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24
Q

Why do veins have thin walls overall?

A

Because there is no need for a thick wall as the pressure within the veins is too low to create any risk of bursting. It also allows them to be flattened easily, aiding the flow of blood within them.

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25
Q

Why do veins have valves at intervals throughout?

A

To ensure that blood does not flow backwards. which it might otherwise do because the pressure is so low. When body muscles contract, veins are compressed, pressurising the blood within them. The valves ensure that this pressure directs the blood in one direction only: towards the heart.

26
Q

What is the function of capillaries?

A

The function of capillaries is to exchange metabolic materials such as oxygen, carbon dioxide and glucose between the blood and the cells of the body. The flow of blood in capillaries is much slower. This allows more time for the exchange of materials.

27
Q

How is the structure of capillaries adapted to its function?

A
  • their walls consist mostly of the lining layer
  • they are numerous and highly branched
  • they have a narrow diameter
  • their lumen is narrow
  • there are spaces between the lining (endothelial) cells
  • they have no muscle/elastic layer and no valves
28
Q

Why do capillary walls consist mostly of the lining layer?

A

This makes them extremely thin, so the distance over which diffusion takes place is short. This allows for rapid diffusion of materials between the blood and the cells.

29
Q

Why are there so many capillaries and why are they highly branched?

A

This provides a large surface area for exchange and diffusion.

30
Q

Why do capillaries have a narrow diameter?

A

They have a narrow diameter and so permeate tissues, which means that no cell is far from a capillary and there is a short diffusion pathway.

31
Q

Why is the lumen of capillaries so narrow?

A

Their lumen is so narrow that red blood cells are squeezed flat against the side of a capillary. This brings them even closer to the cells to which they supply oxygen. This again reduces the diffusion distance.

32
Q

Why are there spaces between the lining (endothelial) cells in capillaries?

A

There are spaces between the lining cells that allow white blood cells to escape in order to deal with infections within tissues.

33
Q

Can capillaries serve every single cell directly?

A

Although capillaries are small, they cannot serve every single cell directly. Therefore the final journey of metabolic materials is made in a liquid solution that bathes the tissues. This liquid is called tissue fluid.

34
Q

What are venules?

A

Venules are small veins that collect blood from the capillaries and take it to the veins.

35
Q

What is the sinoatrial node?

A

The heart is myogenic (its contraction is initiated from within the muscle itself).

Within the wall of the right atrium are a group of pacemaker cells known as sinoatrial node (SAN).

SAN has an automatic rhythm of stimulation that determines the beat of the heart.

36
Q

What is an electrocardiogram?

A

The electrical activity of the heart can be monitored by using an electrocardiograph.

Several electrodes are attached to specific places on a person’s chest. These detect electrical changes in the heart by measuring current at the skin’s surface.

The leads are connected to a machine that draws an electrocardiogram (ECG).

37
Q

How is the cardiac cycle controlled?

A
  1. A wave of electrical activity spreads out from the sinoatrial node across both atria, and the atria contract.
  2. A layer of non-conductive tissue prevents the wave crossing to the ventricles.
  3. The wave passes through a second group of cells called the atrioventricular node, which is between the atria.
  4. The atrioventricular node conveys an electrical wave between ventricles along a series of specialised muscle fibres called the bundle of His.
  5. The bundle of His conducts the wave through the septum to the base of the ventricles where it branches into Purkinje fibres.
  6. The wave is released from these fibres, causing ventricles to contract from the base upwards.
38
Q

What is plasma?

A
  • transports substances around the body
  • CO2 from cells to lungs
  • urea from liver to kidneys
  • hormones, enzymes, antibodies, fibrinogen (protein for blood clotting)
  • distributes heat
39
Q

What are white blood cells?

A
  • leukocytes
  • defence
  • lymphocytes produce antibodies and antitoxins
  • phagocytes/neutrophils engulf and destroy pathogens (microbes)
40
Q

What are red blood cells?

A
  • erythrocytes
  • contains haemoglobin, formation requires iron
  • haemoglobin transports oxygen from lungs to cells
  • biconcave discs, large surface area for diffusion of oxygen
  • no nucleus, more space for haemoglobin
  • flexible, squeeze through capillaries in single file
41
Q

What are phagocytes?

A
  • defence: phagocytosis
  • contain enzymes
  • engulf (ingest) microbes and digest them
42
Q

What are lymphocytes?

A
  • defence: immune response
  • produce antibodies and antitoxins
  • killer cells, destroy cells infected with viruses
43
Q

What are platelets?

A
  • rupture and release enzymes at site of cut
  • initiates a cascade of reactions
  • converts insoluble blood protein fibrinogen to insoluble fibrin threads which trap blood cells and platelets to form a blood clot
44
Q

What does tissue fluid contain?

A
  • water
  • glucose
  • amino acids
  • fatty acids
  • dissolved ions
  • dissolved monomers and gases
  • some hormones
  • some white blood cells
45
Q

What does tissue fluid not contain?

A
  • red blood cells
  • platelets
  • large proteins
46
Q

What is tissue fluid?

A

Tissue fluid supplies all of the substances it contains to the tissues. In return, it receives carbon dioxide and other waste materials (e.g. urea) from the tissues.

Tissue fluid is therefore the means by which materials are exchanged between blood and cells and it bathes all the cells of the body.

47
Q

What kind of environment does tissue fluid provide for the cells it surrounds?

A

Tissue fluid is formed from blood plasma (in capillaries), and the composition of blood plasma is controlled by various homeostatic systems. As a result, tissue fluid provides a mostly constant environment for the cells it surrounds.

48
Q

How is tissue fluid formed from blood plasma?

A

Blood pumped by the heart passes along arteries, then the narrower arterioles and, finally, the even narrower capillaries. Pumping by the heart creates a pressure, called hydrostatic pressure, at the arterial end of the capillaries. This hydrostatic pressure causes tissue fluid to move out of the blood plasma.

49
Q

What is hydrostatic pressure?

A

caused by an increased volume of fluid inside a vessel

50
Q

What two forces is the outward pressure opposed by?

A
  • hydrostatic pressure of the tissue fluid outside the capillaries, which resists outward movement of liquid
  • the lower water potential of the blood, due to the plasma proteins, that causes water to move back into the blood within the capillaries
51
Q

What is the combined effect of all these forces?

A

The combined effect is to create an overall pressure that pushes tissue fluid out of the capillaries at the arterial end.

This pressure is only enough to force small molecules out of the capillaries, leaving all cells and proteins in the blood because these are too large to cross the membrane. This type of filtration under pressure is called ultrafiltration.

52
Q

What prevents cells and proteins from leaking out of capillaries?

A

capillaries have a little fibrous tissue around them

53
Q

How is tissue fluid returned to the circulatory system?

A

Once tissue fluid has exchanged metabolic materials with the cells it bathes, it is returned to the circulatory system. Most tissue fluid returns to the blood plasma directly via the capillaries. This return occurs as follows:

  • The loss of the tissue fluid from the capillaries reduces the hydrostatic pressure inside them.
  • As a result, by the time the blood has reached the venous end of the capillary network, its hydrostatic pressure is usually lower than that of the tissue fluid outside it.
  • Therefore tissue fluid is forced back into the capillaries by the higher hydrostatic pressure outside them.
  • In addition, the plasma has lost water and still contains proteins. It therefore has a lower water potential than the tissue fluid.
  • As a result, water leaves the tissue by osmosis down a water potential gradient.
54
Q

What does tissue fluid lose and gain?

A

Tissue fluids loses much of its oxygen and nutrients by diffusion into the cells that it bathes, but it gains carbon dioxide and waste materials in return.

55
Q

What is the lymphatic system?

A

Not all the tissue fluid can return to the capillaries; the remainder is carried back via the lymphatic system. This is a system of vessels that begin in the tissues. Initially they resemble capillaries (except that they have dead ends), but they gradually merge into larger vessels that form a network throughout the body. These larger vessels drain their contents back into the bloodstream via two ducts that join veins close to the heart.

The lymphatic system contains lymph fluid, similar in content to tissue fluid. However, lymph fluid contains less oxygen and nutrients compared to tissue fluid, as its main purpose it to carry waste products. The lymph system also contains lymph nodes which filter out bacteria and foreign material from the fluid with the help of lymphocytes which destroy pathogens as part of the immune system defences.

56
Q

Why can’t large substances be components of the tissue fluid?

A

Hydrostatic pressure is created when blood is pumped along the arteries, into arterioles and then capillaries. This pressure forces blood fluid out of the capillaries. Only substances which are small enough to escape through the gap in a capillary are components of the tissue fluid.

57
Q

How does hydrostatic pressure cause water to move from the tissue fluid to the blood by osmosis?

A

The fluid is also acted on by hydrostatic pressure which pushes some of the fluid back into the capillaries. As both the tissue fluid and blood contain solutes, they have a negative water potential. Although the water potential of the tissue fluid is negative, it is less negative in comparison to the blood. This causes water to move down the water potential gradient from the tissue fluid to the blood by osmosis.

58
Q

How are the contents of the lymphatic system moved?

A

The contents of the lymphatic system (lymph) are not moved by the pumping of the heart. Instead they are moved by:

  • hydrostatic pressure of the tissue fluid that has left the capillaries
  • contraction of body muscles that squeeze the lymph vessels - valves in the lymph vessels ensure that the fluid inside them moves away from the tissues in the direction of the heart
59
Q

How are substances exchanged via tissue fluid?

A
  1. ULTRAFILTRATION
    Blood enters the arteriole end of capillaries at high hydrostatic pressure and is forced out through the gaps between endothelial cells. Blood cells and large proteins remain in the capillary.
  2. EXCHANGE OF SUBSTANCES
    Small dissolved substances (e.g. oxygen and glucose) move with the water and so can easily move into body cells.
  3. REABSORPTION
    As water leaves, the pressure is reduced so that at the venule end it is equal to the tissue fluid pressure, but since water has been lost from the capillary there is a reduction in water potential in the blood plasma. Some water re-enters the capillary by osmosis, and carbon dioxide by diffusion.
  4. LYMPHATIC SYSTEM
    Excess water is drained into the lymphatic system and re-enters the blood at the superior vena cava.
60
Q

Why does hydrostatic pressure build up?

A

because the capillaries are narrower than the arterioles, so the pressure builds up, forcing tissue fluid out of the blood plasma

Biology (67 decks)

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