6.2 The Transport System

Question 1

Outline the function of the coronary arteries

Answer 1

Coronary arteries supply the cardiac tissue with oxygen-rich blood and nutrients (i.e. glucose). These are required to produce the necessary energy via aerobic respiration. They are found on the outside muscle tissue of the heart.

Question 2

Outline the route of blood in the heart

Answer 2

Vena cava (superior and inferior) → Right Atrium → Right ventricle → Pulmonary artery → Lungs → Pulmonary vein → Left atrium → Left ventricle → Aorta → Body

Question 3

Explain how the heart valves maintain the one-way flow of blood

Answer 3

When the atria contract, atrioventricular (AV) valves open. Blood flows from the atria and into the ventricles. When the ventricles contract, the AV valves close and semilunar valves open. This forces blood out of the ventricles and into the arteries. As arterial pressure rises, the semilunar valves close, ensuring the one-way flow of blood.

Question 4

Explain the action of the heart in terms of collecting and pumping blood

Answer 4

The Superior and Inferiorvena cava bring deoxygenated blood returning from all parts of the body (except lungs) to theright atrium. The atria contract (lub) and the blood flows through the atrioventricular valves into the right ventricle. Semilunar valves are closed so that the ventricles can fill with blood. Atrioventricular valves close, preventing back flow; ventricles contract, increasing pressure in the chamber, causing the semilunar valves to open, allowing the blood to flow through thepulmonary arteryto the lungs (where blood is reoxygenated). Ventricles stop contracting (dub); pressure decreases; semilunar valves close, preventing back flow from arteries. Blood travels from the lungs, through the pulmonary vein to theleft atriumand passes through theleft ventricleto theaorta, where it is pumped around the body.

Question 5

Explain why the contraction of the heart muscle is a myogenic process

Answer 5

The signal arises from within the heart muscle itself, and does not require nerve impulses to stimulate it. It is an involuntary response, under autonomic control from the brain (medulla).

Question 6

Outline the function of the Sinoatrial node (SAN)

Answer 6

A specialised bundle of nerves located within the wall of the right atrium. Acts as a pacemaker, initiating contraction of the cardiace muscle. Regulates normal sinus rhythm (the normal beating of the heart). Stimulates the atria to contract; when the signal reaches the junction between atria and ventricles, stimulates the atrioventricular node (AVN).

Question 7

Outline the function of the Atrioventricular node (AVN)

Answer 7

When stimulated by the Sinoatrial node, sends signals via the Bundle of His to the Purkinje Fibres, which causes ventricular contraction.

Question 8

Explain why there is a delay between atrial and ventricular contractions, resulting in two heart sounds ‘lub dub’

Answer 8

The atria are electrically isolated from the ventricles, connected only via the AV node which briefly delays the signal. In order to maximize efficiency of contraction and cardiac output, the conduction system of the heart has substantial atrial to ventricular delay. This will allow the atria to completely empty their contents into the ventricles; simultaneous contraction would cause inefficient filling and back flow.

Question 9

State what happens to the heart following the contractions of the atriums and ventricles

Answer 9

There is a rest period while the heart refills with blood, where it becomes insensitive to stimulation.

Question 10

Outline the function of the medulla in myocardium

Answer 10

Can control the speed of a heart beat, speeding it up or slowing it down depending on the body’s needs.

Question 11

State 4 factors which affect heart rate

Answer 11

Blood pressure, Anticipation, Stress, Emotion (BASE)

Question 12

Outline the role of sympathetic nerves

Answer 12

Speed up heart rate by releasing a neurotransmitter called noradrenaline which increases the rate of myocardial contraction.

Question 13

Outline the role of parasympathetic nerves

Answer 13

Slows down the heart rate by releasing a neurotransmitter called acetylcholine which decreases the rate of myocardial contraction.

Question 14

Outline the function of a hormone which affects heart rate

Answer 14

Epinephrine (also known as adrenaline) increases heart rate when released into the blood from the adrenal gland

Question 15

State the three layers of veins and arteries

Answer 15

Tunica intima
Tunica media
Tunica adventitia

Question 16

Describe the Tunica intima

Answer 16

One layer of endothelial cells; elastic membrane lining (in Arteries); in direct contact with blood flow.

Question 17

Describe the Tunica media

Answer 17

Smooth muscles cells and elastic tissue. Can contract and stretch. Contains elastin.

Question 18

Describe the Tunica adventitia

Answer 18

Composed mainly of collagen, which anchors the vessel to nearby organs; prevent arteries from bursting under high pressure flow

Question 19

Outline the function of arteries

Answer 19

• Carry blood away from the heart at high pressure.
  
  • Narrow lumen (to maintain high pressure) surround by a thick wall made of three layers.
  • Thin tunica intima.
  • Tunica media contains muscle and elastin to help maintain pulse flow (it can contract and stretch).
  • Tunica adventitia contains collagen; prevents the artery rupturing due to the high pressure blood flow.

Question 20

Outline the function of veins

Answer 20

• Carry blood back to the heart under low pressure.
  
  • They have a very wide lumen (keeps pressure low and allows greater flow of blood).
  • The walls of tissue surrounding the vein are thin (blood is not travelling in rhythmic pulses).
  • They have valves to prevent blood pooling at extremities (arteries do not have valves).

Question 21

Outline the function of capileries

Answer 21

• Involved with material and gas exchange with the surrounding body tissue.
  
  • Branch out from arteries to bring blood closer to cells.
  • Blood pressure in the capillaries is relatively low and they have a very small diameter.
  • One cell thick endothelium layer, allowing for rapid diffusion.
  • Capillaries may contain pores to aid the transport of material, and the secretion of plasma and phagocytes.
  • Narrow lumen, allowing many to fit in a small space, and slowing down rate of blood flow as blood cells can only pass through single file.

Question 22

Outline the route of blood in the body

Answer 22

Aorta → Artery → Capillary → Vein → Vena cava

Question 23

State the four main components of blood

Answer 23

• Plasma - the fluid medium of the blood.
  
  • Erythrocytes - red blood cells (involved in oxygen transport).
  • Leukocytes - white blood cells, such as phagocytes (non-specific immunity) and lymphocytes (specific immunity).
  • Platelets - responsible for blood clotting (haemostasis).

Question 24

State seven things transported by the blood.

Answer 24

Nutrients (e.g. glucose)
Antibodies
Carbon dioxide
Hormones
Oxygen
Urea
Heat (not a molecules, unlike all the others)

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