Lecture 32 - Cardiovascular System: Control of Blood Flow Within Tissue Flashcards
Where are the 2 key points where blood flow through capillary beds can be controlled. What are their characteristics?
Arterioles and pre-capillary sphincters
Key characteristics:
- Smooth muscle
- Relatively narrow lumen = larger proportional changes in diameter
What is the function of vasoconstriction and vasodilation in smooth muscle?
They related to the amount of tension produced in the smooth muscle of the tunica media
How does intrinsic regulation (autoregulation) affect blood flow?
Through regulation by factors occurring within the local environment of that vessel. Can be direct or indirect
Ex. Metabolic regulation, immune regulation, myogenic regulation
How does extrinsic regulation affect blood flow?
Regulation by mechanisms involving integrative organ systems (outside the local environment)
Ex. Neuronal regulation (ANS), hormonal regulation
How can vasodilation through autoregulation occur DIRECTLY?
It occurs directly through changes in gases, ions, or metabolites in the surrounding tissue
Name 4 stimuli that would directly trigger muscle relaxation in peripheral tissue
- Dec. O2
- Inc. CO2
- Inc. H+
- Inc. K+
How can vasodilation through autoregulation occur INDIRECTLY?
Paracrine signalling pathways
Name 3 paracrine signalling pathways
- Paracrine factors - chemical messengers that remain within their local environment
- Vasoactive paracrine factors - can be generated in surrounding tissues or by endothelial cells
- Nitric oxide (NO) - soluble gas; causes smooth muscle relaxation by reducing Ca2+ entry into smooth muscle
How can vasoconstriction through autoregulation occur?
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
Role of a1 adrenergic receptors in changes to vessel diameter
They elevate intracellular calcium, enhancing smooth muscle contraction (vasoconstriction)
Very sensitive to NE (ie. ANS activity)
Role of b adrenergic receptors in changes to vessel diameter
They elevate intracellular cAMP, reducing smooth muscle contraction (vasodilation)
Very sensitive to E (ie. hormonal release)
How does epinephrine and other hormones affect blood vessel diameter?
It can lead to vasoconstriction or dilation depending on the type of intracellular biochemistry triggered by its receptors and its location
What reflexes are triggered during exercise when metabolic activity increases?
Global chemoreceptor reflexes are triggered, including general vasoconstriction across all peripheral arterioles