Lecture 23 : Blood Vessels - Part 2

Question 1

What mechanisms is vascular tone controlled by?

Answer 1

Intrinsic and extrinsic mechanisms

Question 2

What is the general location of vasodilator nerves?

Answer 2

In organs where brain needs to control and command a profound increase in blood flow

Question 3

What 2 transmitters are commonly released by parasympathetic fibres?

Answer 3

1. Acetyl choline (ACh)
2. Vasoactive intestinal peptide (VIP)

Question 4

What do parasympathetic vasodilator nerves innervate?

Answer 4

1. Salivary glands (ACh and VIP)
2. Pancreas and intestinal mucosa (VIP)
3. External genitals (NO and VIP)

Question 5

What do sympathetic vasodilator nerves innervate?

Answer 5

Skin - sweating (ACh and VIP)

Question 6

What hormone does the adrenal medulla secrete and what is the role of this hormone?

Answer 6

Epinephrine
- Increases plasma epinephrine
- Acts on α (vasoconstrictor) and β (vasodilator) receptors
- Acts on smooth muscle in skeletal muscle arterioles
- Alters arteriolar radius

Question 7

What hormone is released from sympathetic neurons to skeletal muscle arterioles and what is the role of this hormone?

Answer 7

Norepinephrine
- Increases norepinephrine in ECF
- Acts on α (vasoconstrictor) receptors
- Acts on smooth muscle in skeletal muscle arterioles
- Alters arteriolar radius

Question 8

What do β receptors cause?

Answer 8

Vasodilation

Question 9

What do α receptors cause?

Answer 9

Vasoconstriction

Question 10

What is adrenaline?

Answer 10

Main catecholamine secreted by adrenal medulla

Question 11

What is angiotensin ll?

Answer 11

Vasoconstrictor
- Responds to hypovolaemia (haemorrhage) and cardaic failure
- Raised in some hypertensives

Question 12

What is vasopressin (ADH)?

Answer 12

Vasoconstrictor
- Responds to hypovoleamia

Question 13

What is atrial natriuretic peptide?

Answer 13

Moderate vasodilator

Question 14

What is autoregulation?

Answer 14

When arterial pressure is altered, blood flow in many vascular beds remains constant

Question 15

What is myogenic autoregulation?

Answer 15

Resistance vessels respond directly to an increase in pressure by vasoconstriction or vasodilation

Question 16

Why is myogenic autoregulation important?

Answer 16

Protects organ perfusion against minute-minute fluctuation in arterial blood pressure

Question 17

What 3 places is myogenic autoregulation most developed in the body?

Answer 17

1. Brain - hypotension during spinal anaesthesia
2. Myocardium - blood flow downstream stenosed artery
3. Kidney - stabilises GFR

Question 18

What is metabolic regulation (active hyperemia)?

Answer 18

Intrinsic mechanism by which blood flow to organs is adjusted to match metabolic activity

Question 19

What are the vasodilators of metabolic regulation?

Answer 19

1. CO2
2. Lactate
3. H+
4. Adenosine

Question 20

What is the vasoconstrictor of metabolic regulation?

Answer 20

Oxygen

Question 21

What vasoconstrictors do endothelium produce?

Answer 21

1. Endothelin
2. Angiotensin ll

Question 22

What vasodilators do endothelium produce?

Answer 22

1. Nitric oxide
2. Prostacyclin (PGI2)
3. Endothelial derived hyperpolarizing factor (EDHF)

Question 23

Describe the structure of capillaries:

Answer 23

• Varies from organ to organ
• Thin walled tube of endothelial cells without smooth muscle cells
• Covered by basement membrane
• 500-1000µm long and 4-8µm wide
• Total thickness ~0.5µm

Question 24

What are the 3 types of capillaries?

Answer 24

1. Continuous capillary: have tight junctions
2. Fenestrated capillary: more permeable
3. Sinusoidal capillary: incomplete basement membrane

Question 25

What are the 2 functions of capillaries?

Answer 25

1. Fluid exchange - regulation of plasma & interstitial fluid volumes 2. Solute exchange - nutrition of tissue - hormone & drug delivery

Question 26

Describe the cross-sectional area and velocity of blood flow of capillaries:

Answer 26

Very large CSA Low velocity of blood flow

Question 27

How do small non-lipid soluble substances get across endothelial cells?

Answer 27

1. Fenestrations 2. Intercellular cleft

Question 28

How do lipid soluble substances get across endothelial cells?

Answer 28

Diffusion - O2, CO2

Question 29

How do large non-lipid soluble proteins get across endothelial cells?

Answer 29

1. Big gaps in inflammation 2. Transcellular channels 3. Vesicle transport

Question 30

What is the mechanism behind fluid exchange?

Answer 30

Bulk flow - due to pressure gradients across wall - obeys Starling principle

Question 31

How does size affect the diffusion of a substance across capillaries?

Answer 31

Low molecular weight = high permeability e.g. water, NaCl High molecular weight = low permeability e.g. albumin

Question 32

What is the mechanism behind solute exchange?

Answer 32

Diffusion (98% nutrients) - due to concentration gradients across wall

Question 33

What is the starling principle of fluid exchange?

Answer 33

Capillary blood flow is affected by plasma osmotic pressure (colloid osmotic pressure, COP) and hydrostatic pressure

Question 34

What 4 pressure determine filtration rate?

Answer 34

1. Capillary hydrostatic pressure (Pc) - outwards 2. Interstitial fluid hydrostatic pressure (PIF) - inward 3. Osmotic force due to plasma protein concentration (πc) - inward 4. Osmotic force due to interstitial fluid protein concentration (πIF) - Outward

Question 35

What is the value of interstitial fluid hydrostatic pressure?

Answer 35

0 mmHg

Question 36

What is the value of osmotic force due to interstitial fluid protein concentration?

Answer 36

3 mmHg

Question 37

What is the value of osmotic force due to plasma protein concentration?

Answer 37

28 mmHg

Question 38

How is net filtration pressure calculated?

Answer 38

Outward: Pc + π IF - PIF - πc

Question 39

What is favoured when net filtration is negative?

Answer 39

Absorption

Question 40

What is favoured when net filtration is positive?

Answer 40

Filtration

Question 41

What drives the movement of water across the capillary wall?

Answer 41

Sum of hydrostatic and colloid osmotic pressures of the blood and interstitial fluid

Question 42

What is colloid osmotic pressure of the blood generated by?

Answer 42

Oncotic pressure is driven by plasma proteins dissolved in the plasma

Question 43

What effect do hydrostatic forces have on water?

Answer 43

Move water out of the capillary - filtration

Question 44

What effect do osmotic forces have on water?

Answer 44

Draw water in - reabsorption

Question 45

What makes up the lymph system?

Answer 45

Lymph capillaries Lymphatic vessel Lymph node Valve

Question 46

What is the result of an imbalance in absorption and filtration?

Answer 46

1. Deep vein thrombosis: Pc raised 2. Cardiac failure, starvation, malabsorption, liver failure: πc reduced = Oedema: excess collection of fluid

Question 47

Describe the structure of veins compared to arteries:

Answer 47

* Walls are thinner than arteries * Less smooth muscle and elastin than arteries * Highly distensible; capacitance vessels that act as blood reservoirs

Question 48

What 4 factors increase venous pressure?

Answer 48

1. Sympathetic innervation 2. Skeletal muscle pump 3. Blood volume 4. Respiratory pump

Question 49

What are varicose veins?

Answer 49

Veins that have become dilated and tortuous because of incompetent (leaky) valves