Lecture 14: The Vascular System

Question 0

What is the job of the pulmonary and systemic circuits?

Answer 0

Pulmonary circuit

• supplied by right heart
• blood vessels to and from heart and lungs

Systemic circuit:

• supplied by left heart
• blood vessels to and from heart and systemic tissues

Question 1

Fundamentals of vascular blood flow

Answer 1

• Vascular system is divided into 2 circulations, the pulmonary and systemic circulations
• each circulation is a closed system of blood vessels
• the circulations has both series and parallel components

Series circuit: components connected by a single path
Parallel circuit: components connected by multiple, alternative pathways

Question 2

Describe how there is parallel flow through the cardiovascular system

Answer 2

Blood flows in parallel through the different capillary beds of the systemic circuit
Advantages:
-each capillary bed receive fully oxygenated blood
-blood flow to different organs can be regulated independently
Exception: GI tract and liver are connected in series

Question 3

What to things determine blood flow through the body?

Answer 3

Pressure gradient/resistance

Question 4

What are the cellular components of a blood vessel?

Answer 4

• all blood vessels have a hollow interior, the lumen
• all blood vessels are lined by an endothelial cell layer
• some types of blood vessels also have
  
  • smooth muscle (➡contractile control of radius)
  • fibrous connective tissue (➡strength)
  • elastic connective tissue (➡stretch, recoil)

Question 5

Arteries and veins are names according to the direction of blood flow, NOT oxygenation.
True or false

Answer 5

True

Question 6

What is the properties and function of each of these vessels?

Answer 6

Arteries: 
P: large, elastic. Function: store pressure 
Arterioles: 
P: quite small, variable diameter. Function: resistance, regulate blood flow 
Capillaries: 
P: small, thin walled
F: blood- tissue exchange 
Venules: 
P: small, thin-walled
F: blood- tissue exchange 
Veins: 
P: large, variable diameter 
F: store blood

Question 7

Arteries. Describe

Answer 7

-Large branching vessels that conduct blood away from the heart
-rapid transport pathway: Large diameter➡little resistance
-store blood pressure:
➡Thick walls➡ low compliance➡ small increase in blood volume causes a large increase in pressure
-elastic walls ➡ stretch during systole, store energy, recoil during diastole, maintaining arterial BP

Question 8

Describe muscular arteries

Answer 8

Small arteries supplying tissues

• little elastin
• smooth muscle regulates radius
• structurally and functionally more like arterioles

Question 9

Describe arterioles

Answer 9

Small branching vessels that conduct blood away from heart.
High resistance (small and not many of them (compared with capillaries) 
Variable resistance (depends on contractile state of rings of smooth muscle in walls)

Question 10

Arterioles and total peripheral resistance.
What is peripheral resistance?
How do arterialise effect it?

Answer 10

TPR= combined resistance of all blood vessels in the systemic circuit. Arterioles provide greatest resistance to blood flow of all vessels >60% of TPR

Question 11

How do arterioles regulate blood flow?

Answer 11

The resistance of arterioles is regulated
Arterioles play important roles in
1) regulating mean arterial pressure
2) controlling flow to individual capillary beds
Both intrinsic (local) and extrinsic (neural, hormonal) control of arteriolar radius

Question 12

Capillaries
What are they
What’s their function?

Answer 12

Sit of exchange between blood and tissue
-single porous endothelial cell layer ➡minimal diffusion distance (most cells within 1mm of capillary)
-high cross sectional area, low velocity blood flow, allows exchange
Blood flow through capillary beds is highly regulated

Question 13

What are the 2 functions of movement of material across capillary walls

Answer 13

1) exchange of material
- waste, nutrients
- different mechanisms depending on solute (passive diffusion, mediated transport etc)
2) distribution of the extracellular fluid (bulk flow) = mass movement of water and dissolved solutes according to pressure gradients

Question 14

What is the purpose of bulk flow across capillary beds?

Answer 14

Bulk flow= mass movement of water and dissolved solutes according to pressure gradients
Purpose of bulk flow is to distribute the ECF
Filtration= movement out of capillary
Absorption= movement into capillary

Question 15

What is hydrostatic and osmotic pressures and how do they drive bulk flow (starling forces)

Answer 15

Fluid flow passively across capillaries according to 2 pressure gradients
Hydrostatic pressure:
-force due to fluid pressing on vessel walls
-water moves from high pressure to low pressure

Osmotic pressure:

• pressure exerted on the membrane by movement of water down its concentration gradient
• water moves from high concentration to low (osmosis)
• only non-penetrating solutes contribute to osmotic pressure
• plasma proteins are most important non-permeating solutes in capillaries

Question 16

Osmotic pressure ➡

How do penetrating solutes and non penetrating solutes contribute to osmotic pressure?

Answer 16

Penetrating solutes (move through separating membrane) don’t contribute to osmotic pressure. Ie solutes move so there is no nett water flow
If there is a higher concentration of non-penetrating solutes ➡ higher osmotic pressure
Water moves from low to high osmotic pressure
Slide 28

Question 17

How does hydrostatic and osmotic pressure gradients act on a capillary membrane?

Answer 17

Hydrostatic pressure:
-capillary hydrostatic pressure ➡filtration
-interstitial hydrostatic pressure ➡ absorption
HS pressure usually higher in capillary ➡ filtration

Osmotic pressure:
-capillary osmotic pressure ➡ absorption
-interstitial osmotic pressure ➡ filtration
Protein usually higher in capillary ➡absorption
Need to look at slide 29

Question 18

Haven’t finished this lecture, may require watching lecture, don’t really understand

Answer 18

H