Circulation of blood around the body

Question 1

Structure and function of the aorta

Answer 1

Expands during contraction phase of cardiac cycle and contracts elastically between contractions - allow continuous flow (like a balloon)

• reduces pressure fluctuations between beats
• helps propel blood into the aorta and prevent back-flow

Question 2

Structure and function of arteries and arterioles

Answer 2

• Adjust their diameter (therefore resistance to blood flow) so change the amount of blood flowing through them
• called resistance vessels because they control blood flow to specific tissues.

Question 3

What is the structure of arteries and arterioles?

Answer 3

Tunica adventitia
• connective tissue (OUTERMOST)
• external elastic lamina

Tunica media
• smooth muscle

Tunica intima
•internal elastic lamina
•endothelium (INNERMOST)

Question 4

What structure allows arteries and arterioles to withstand high pressure?

Answer 4

• Many collagen and elastin fibers in the tunica adventitia

* this strengthens the vessel wall

Question 5

What allows the aorta to expand and recoil?

Answer 5

Elastin

Question 6

What allows the artery/arterioles to adjust diameter?

Answer 6

• Smooth muscle in the tunica media contracts • causes vasoconstriction (narrowing of artery diameter)
• Endothelial cells in tunica intima produce factors that cause vasodilation or vasoconstriction

Question 7

What is the function of veins?

Answer 7

Drains blood from capillary beds under very low pressure (not sufficient to propel blood to the heart)

Smooth muscle contracts to help blood return to the heart under low pressure
• thin smooth muscle layer, but large volume in veins and a small contraction pushes a lot of blood towards the heart

Question 8

Why are venules and veins called capacitance vessels?

Answer 8

Because of their ability to stretch and store blood

Question 9

Describe the structure of a vein

Answer 9

Outermost:
Tunica Adventitia
• loose connective tissue

Tunica media (smooth muscle)

Tunica intima
• internal elastic lamina
• endothelium

Valve - innermost

Question 10

How are veins expandable?

Answer 10

They have little muscle or less collagen in the adventitia

Question 11

Outline the main structural difference between arteries and veins

Answer 11

Arteries
• more elastin
• more smooth muscle
• more fibrous collagen in tunica adventitia

Veins
• less elastin
• less smooth muscles and valves
• less collagen

Question 12

What factors influence venous return?

Answer 12

venous return - returning blood to the heart
• Gravity affects venous return
• larger veins have some smooth muscle which contracts to assist venous return
• skeletal muscles contract in surrounding muscles
• valves in veins prevent back-flow

Question 13

What is Deep Vein Thrombosis (DVT) and what causes it?

Answer 13

Formation of a blood clot (“thrombus”) in a deep vein
• in a person sitting upright, gravity causes blood to accumulate in the veins of the lower body
• decreased flow rate of blood due to immobility can lead to venous thrombosis

Question 14

Venous return in aviators and astronauts

Answer 14

• invention of anti-gravity suit

* prevented blood pooling in the lower part of the body during acceleration which deprives the brain of blood

Question 15

What do capillaries do?

Answer 15

• Receives high pressure blood from arterioles

* allow exchange of materials and interstitial fluid

Question 16

What materials are exchanged by capillaries?

Answer 16

1. Gas exchange: O2 delivered to tissues and CO2 removed
2. Nutrient delivery: glucose, ions, water etc to tissue
3. waste removal: Metabolites removed from tissue
4. production of tissue fluid: extracellular/interstitial fluid

1-3 rely on diffusion

Question 17

Brielfly describe the structures of capillaries, related to its function

Answer 17

• very narrow (5-10 microns)
• single layer of endothelial cells endothelium - improves diffusion and osmosis
• have tiny holes - allows water, some ions, solutes like glucose and very small proteins to leak out

Question 18

Fenestrations

Answer 18

Small holes in capillaries which allow water, some ions, solutes like glucose and very small proteins to leak out

Question 19

How is surface area of capillaries increased, and how does this affect the pressure?

Answer 19

• arterioles branch into extensive networks of capillaries - hugely increases the overall cross-sectional area (CSA)
• this reduces pressure and flow
• enough pressure remains for water and small solutes to be squeezed through capillaries and into interstitial spaces

Question 20

Starling’s forces

Answer 20

Two opposing forces that maintain water balance in capillaries

Question 21

How is blood volume maintained if fluid is continuously leaking out of the capillaries?

Answer 21

Starling’s forces
• Blood pressure (Hydrostatic) - tends to force water and small solutes out

• Osmotic pressure: Tends to draw water back into capillaries

Question 22

What creates osmotic pressure in capillaries?

Answer 22

Large protein molecules that cannot leave the capillaries - causes water to be drawn back into capillaries

Question 23

Describe the starling’s forces along a capillary. (Venular and arteriolar end)

Answer 23

Arteriolar end - carrying oxygenated blood
• higher blood pressure than osmotic pressure
• net driving force for fluid to leave capillary

Venular blood - carry deoxygenated blood back to the heart
• osmotic pressure higher than blood pressure
• net driving force for fluid to reenter the capillary

Question 24

What changes in starling’s forces lead to oedema?

Answer 24

• Tissue fluid drains into the lymphatic system and is returned to the Cardiovascular system (CVS)
• An imbalance between blood pressure, osmotic pressure and lymphatic draining lead to oedema

Question 25

Coronary Heart Disease (CHD)

Answer 25

Narrowing of the small blood vessels that supply the blood and oxygen to the heart
• can lead to heart attacks and strokes

Question 26

What is atherosclerosis?

Answer 26

1. Begins with damage smooth endothelial lining found in healthy arteries
2. Inflammatory response occurs - deposits form (plaque)
3. smooth muscle cells migrate towards the lumen and attract lipids so plaque becomes fatty
4. Fibrous connective tissue produced causing ‘hardening’ of artery
   Artery narrowed

Question 27

What arteries provide blood supply to the heart?

Answer 27

Left and right coronary arteries
• branch off base of the aorta
• if they become blocked heart muscle can become damaged or stop beating (heart attack)

Question 28

How does aspirin treat chronic heart disease?

Answer 28

• prevent the blood clots from forming in the arteries - reducing the risk of having a heart attack

Question 29

What does the tunica adventitia consist of?

Answer 29

• connective tissue

* external elastic lamina

Question 30

What does the tunica intima consist of?

Answer 30

• Internal elastic lamina, connective tissue

* endothelium

Question 31

What does the tunica media consist of?

Answer 31

Smooth muscle

Question 32

What best describe the differences in blood pressure along a capillary?

Answer 32

• Blood pressure is highest at the arterial end

* osmotic pressure remains constant throughout the capillary

Question 33

What do the endothelial cells in the tunica intima do?

Answer 33

• They produce factors that cause vasodilation or vasoconstriction (widening or narrowing of artery diameter)

Question 34

What is the name and function of the small openings at the base of the aorta?

Answer 34

Coronary arteries

• supply oxygen-rich blood to the entire heart muscle

Question 35

What is the function of the septomarginal trabecula?

Answer 35

• right atrium
• string that prevents the ventricle from overstretching
• also acts as an electrical conductor pathway