Lecture 32 - Cardiovascular System: Control of Blood Flow Within Tissue

Question 1

Where are the 2 key points where blood flow through capillary beds can be controlled. What are their characteristics?

Answer 1

Arterioles and pre-capillary sphincters

Key characteristics:
- Smooth muscle
- Relatively narrow lumen = larger proportional changes in diameter

Question 2

What is the function of vasoconstriction and vasodilation in smooth muscle?

Answer 2

They related to the amount of tension produced in the smooth muscle of the tunica media

Question 3

How does intrinsic regulation (autoregulation) affect blood flow?

Answer 3

Through regulation by factors occurring within the local environment of that vessel. Can be direct or indirect

Ex. Metabolic regulation, immune regulation, myogenic regulation

Question 4

How does extrinsic regulation affect blood flow?

Answer 4

Regulation by mechanisms involving integrative organ systems (outside the local environment)

Ex. Neuronal regulation (ANS), hormonal regulation

Question 5

How can vasodilation through autoregulation occur DIRECTLY?

Answer 5

It occurs directly through changes in gases, ions, or metabolites in the surrounding tissue

Question 6

Name 4 stimuli that would directly trigger muscle relaxation in peripheral tissue

Answer 6

1. Dec. O2
2. Inc. CO2
3. Inc. H+
4. Inc. K+

Question 7

How can vasodilation through autoregulation occur INDIRECTLY?

Answer 7

Paracrine signalling pathways

Question 8

Name 3 paracrine signalling pathways

Answer 8

1. Paracrine factors - chemical messengers that remain within their local environment
2. Vasoactive paracrine factors - can be generated in surrounding tissues or by endothelial cells
3. Nitric oxide (NO) - soluble gas; causes smooth muscle relaxation by reducing Ca2+ entry into smooth muscle

Question 9

How can vasoconstriction through autoregulation occur?

Answer 9

It can occur through:

Myogenic mechanism - stretching vascular smooth muscle triggers increases in its contraction, returning vessel diameter to original value

Paracrine mechanism - endothelins are paracrine factors which are constantly secreted at low levels, helping to maintain a baseline state of slight vasoconstriction

Question 10

Role of a1 adrenergic receptors in changes to vessel diameter

Answer 10

They elevate intracellular calcium, enhancing smooth muscle contraction (vasoconstriction)

Very sensitive to NE (ie. ANS activity)

Question 11

Role of b adrenergic receptors in changes to vessel diameter

Answer 11

They elevate intracellular cAMP, reducing smooth muscle contraction (vasodilation)

Very sensitive to E (ie. hormonal release)

Question 12

How does epinephrine and other hormones affect blood vessel diameter?

Answer 12

It can lead to vasoconstriction or dilation depending on the type of intracellular biochemistry triggered by its receptors and its location

Question 13

What reflexes are triggered during exercise when metabolic activity increases?

Answer 13

Global chemoreceptor reflexes are triggered, including general vasoconstriction across all peripheral arterioles