The Heart & Circulatory System

Question 1

What diameter do arteries have to be before they are classified as arterioles?

Answer 1

0.1 mm

Question 2

Describe the layers of a capillary.

Answer 2

Simply an endothelium and its underlying basement membrane

Question 3

What is the average volume of blood in the human body? How is this further divided?

Answer 3

There are on average 5 litres of blood within the human body - 3 litres of plasma and 2 litres of erythrocytes

Question 4

Where is the majority of blood held at any one time within the circulatory system? How many litres of blood is that?

Answer 4

In the peripheral veins (65%) - 5 x 0.65 = 3.25 litres

Question 5

What happens in pulmonary circulation?

Answer 5

Blood passes through the heart and is oxygenated, releasing CO2 for it to be exhaled

Question 6

Which side of the heart is more muscular? Why?

Answer 6

The left side of the heart is more muscular - it pumps blood through systemic circulation so has to contract at a greater force

Question 7

Where is the tricuspid valve found? Where is the mitral valve found?

Answer 7

The tricuspid valve is found between the right atrium and right ventricle - the mitral valve is found between the left atrium and left ventricle

Question 8

What is an end artery? What can happen if these are somehow occluded?

Answer 8

An end artery is an artery that supplies all the blood to a specific part of the body - if these are occluded then insufficient blood will reach the tissue, causing complications

Question 9

Give 4 examples of functional end arteries.

Answer 9

Renal end arteries
Splenic end arteries
coronary arteries
Cerebral end arteries

Question 10

Where is the atrioventricular node located?

Answer 10

Between the right atrium and right ventricle

Question 11

What is collateral circulation?

Answer 11

In response to vessel occlusion, smaller vessels branching off the artery may join, bypassing the occlusion and providing an alternative blood flow route around the blockage

Question 12

How long is the delay between the first signal from the sinoatrial node and initiation of contraction by the most distal purkinje fibres on the left and right ventricles?

Answer 12

0.21 seconds pass before the most distal purkinje fibres cause contraction of the right ventricle, while 0.23 seconds pass before the most distal purkinje fibres of the left ventricle initiate contraction

Question 13

What 2 arteries does the brachiocephalic trunk branch into?

Answer 13

The common carotid artery and subclavian artery

Question 14

Describe is systolic pressure.

Answer 14

Systolic pressure is the pressure of the aorta upon contraction of the venues of the heart, where the aorta is being filled - systolic pressure is generally around 120 mm/Hg

Question 15

Describe diastolic pressure.

Answer 15

Diastolic pressure is the pressure of the aorta when the ventricles of the heart are refilling - the aorta is relaxed, and so diastolic pressure is less than systolic pressure, at around 80 mm/Hg

Question 16

What is an aneurysm? Where is it most common and why?

Answer 16

An aneurysm is the dilation of a blood vessel - it is most common in the infrarenal abdominal aorta, as this vessel has few elastic fibres, meaning it struggles to recoil

Question 17

How many layers of smooth muscle may be apparent in the interna media of a muscular artery? How does this compare to an average arteriole?

Answer 17

There may be 40 layers of smooth muscle in a muscular artery - in comparison, there are usually around 3 layers of smooth muscle in a typical arteriole

Question 18

What are precapillary sphincters?

Answer 18

Regions of smooth muscle preceding capillaries, encircling their endothelium, which can regulate blood flow and pressure within arterioles and metarterioles

Question 19

What are metarterioles?

Answer 19

A division of arteriole that directly precedes the capillary bed

Question 20

What is the velocity of blood within a capillary? What does this allow?

Answer 20

Around 0.3 mm/s - this permits time for gasometer and nutrient exchange to occur

Question 21

What is capacitance?

Answer 21

The ability of a vessel to increase its volume without a reflectional increase in pressure - it is inversely proportional to elasticity

Question 22

What are the proportions of blood volume in any one structure at any one time?

Answer 22

65% in veins
10 % in arteries
20% in the lungs & heart
5% in capillaries

Question 23

How do veins resist gravity and manage to transport blood back to the heart?

Answer 23

Valves within veins prevent backflow of blood, while smooth muscle contraction and relaxation is used to pump blood in the direction of the heart

Question 24

Why does fluid filtrate out of the capillary at the arteriole end?

Answer 24

The capillary hydrostatic pressure (35 mm/Hg) is greater than the blood colloidal oncotic pressure (25 mm/Hg) - fluid flows from high to low pressure, som over out of the capillaries and into the interstitial fluid

Question 25

Why is fluid reabsorbed back into the capillaries at the venous end?

Answer 25

As fluid filtrated out at the arteriole end, the capillary hydrostatic pressure has dropped (15 mm/Hg) below that of blood colloidal oncotic pressure (25 mm/Hg), and so fluid moves back into the capillary

Question 26

How much fluid is taken back to the heart by the lymphatic system each day? Where abouts does this fluid re-enter circulation?

Answer 26

Around 3 litres of fluid is returned back to circulation every day by the lymphatic system, at the subclavian and internal jugular veins

Question 27

What are the names of the main arteries that supply the lower limbs?

Answer 27

The right and left common iliac arteries

Question 28

What are the names of the major arteries that supply blood to the brain?

Answer 28

The right and left common carotid artery

Question 29

What 2 veins carry all the blood to the heart?

Answer 29

The inferior and superior vena cava

Question 30

What veins collect blood from the head and upper limbs before forming the vena cava? What veins join to form these veins?

Answer 30

The left and right innominate (brachiocephalic) veins - these form from the corresponding left and right jugular and subclavian veins

Question 31

How may layers are there in the wall of an artery? List them.

Answer 31

• tunica intima
• tunica media
• tunica adventitia

Question 32

What is an aneurysm?

Answer 32

The dilation of a blood vessel

Question 33

How are the layers of an artery wall comprised?

Answer 33

• tunica intima - comprising of endothelium, and separated from the tunica media by the internal elastic membrane
• tunica media - contains concentric sheets of smooth muscle, surrounded by loose connective tissue, separated from the tunica adventitia by the external elastic membrane
• tunica adventitia - connective tissue and some elastic fibres, innervated by sympathetic nerve fibres

Question 34

How many sheets of smooth muscle does the tunica media layer contain?

Answer 34

Up to 40 sheets of smooth muscle

Question 35

How does stimulation of the sympathetic nerve fibres in the tunica adventitia affect an artery?

Answer 35

Sympathetic stimulation leads to the release of noradrenaline, which diffuses to the edges of the tunica media, causing vasoconstriction of its 40 layers of smooth muscle

Question 36

What is the role of precapillary sphincters? What type of muscle is associated with this structure?

Answer 36

They regulate blood flow through arteriole and metarterioles, using smooth muscle contractions

Question 37

What advantage do precapillary sphincters give during periods of strenuous activity?

Answer 37

They can direct blood flow away from peripheral vessels and towards vessels that flow to areas under significant stress eg skeletal muscles during exercise or during the fight or flight response

Question 38

What vessels are known as capacitance vessels?

Answer 38

Veins

Question 39

How does the wall of a vein differ to an artery?

Answer 39

Veins generally have a larger diameter than corresponding arteries, and thinner walls that have more connective tissue and less elastic and muscle tissue

Question 40

Why do veins in the legs have comparatively thicker layers of smooth muscle than veins elsewhere in the body?

Answer 40

To resist distension caused by gravity

Question 41

How does venous blood get back to the heart from the legs in a standing human?

Answer 41

Through a combination of muscle contraction which encourages blood flow and valves that prevent backflow

Question 42

In terms of the blood, what can happen in calf muscle pump failure?

Answer 42

Venous hypertension in the leg

Question 43

Specifically, where are valves in veins found? Where are they not found? Why?

Answer 43

• there are valves in the lower limbs, upper limbs, and the heart
• there are no valves in the intra-abdominal, intra-thoracic, and neck veins, as pressure/gravity/muscle contraction is enough to return the blood to the heart

Question 44

How do the layers of the vessel wall differ in small/intermediate and large vessels?

Answer 44

• small/intermediate vessels have a well developed tunica adventitia, but poorly developed tunica intima and tunica media (2-3 layers of smooth muscle)
• large veins also have a well developed tunica adventitia, the tunica intima is thicker, though they do not have a prominent tunica media