The Vascular System Flashcards
How have blood vessels adapted to supplying nerves?
Blood vessels form long cables parallel to path of neurons to ensure efficient echange
How have blood vessels adapted to supplying Muscles?
Blood vessels corkscrew around so that during contraction, blood supply is not cut off
How have blood vessels adapted to supplying the Lungs?
Blood vessels are flat and wrap around alveolae to maximise gas exchange - has to be as efficient as possible
At the majority of time, where is the bulk of the blood held in the vascular system?
Venous system - veins & venules = 61%
- Allows vascular system to adjust for veinous return
Resistance blood vessels = arterioles - determine mean arterial blood pressure - 7% of blood storage
Regulation of blood pressure is determined by?
Blood vessel contractility = regulated by vascular smooth muscle cells length (shortening or relaxing)
- Having to continually change local blood pressure in order to meet demands - regulations general blood pressure
What are the 2 main components of blood vessels?
- Vascular smooth muscle cells - contracts and relaxes - sit in concentric circles around the endothelial cells - elasticity from the collagen and elastin which these cells produce and it surrounds them
- Endothelial cells - single layer with a tight junction between them - secrete mediators which can stimulate the vessel to contract/relax
How is the vascular smooth muscle contractility regulation by the Autonomic nervous system?
Mostly sympathetic innervation which regulates contractility
- Norephinephrine = contract (alpha-adrenergic receptors)
- Epinephrine = relax (beta-adrenergic receptors)
- Uneven distribution oof receptors for these compounds - more Beta-adrenergic receptors surrounding skeletal muscles
How is the vascular smooth muscle contractility regulation by the Endothelial-derived factors?
Nitric Oxide = relax
Endothelin = contract
How is the vascular smooth muscle contractility regulation by the Myogenic response?
Innate ability of vascular smooth muscle to respond to changes in pressure
What’s the regulation of vascular smooth muscle contractility?
2 enzymes
- Myosin light chain kinase = phosphorylates myosin light chains = contraction
- Myosin in smooth muscle has a regulatory light chain bound to it
- This phosphorylation allows it interact with actin and cause contraction - Myosin phosphatase = De-phosphorylates Myosin light chains with phosphate bound
- Prevents interaction between Myosin and Actin
What ion regulates Myosin light chain kinase?
Calcium
- Agonist (endothelin) binds to G-coupled protein receptor to get Phospholipase C
- Intacellularly, PIP2 reacts with Phospholipase C to create IP3
- IP3 causes Calcium ion release from stores which causes Myosin light chain kinase to phosphorylate Myosin light chains
- Actin-myosin interaction = contraction
How is the vascular smooth muscle contractility regulation by the Endothelial-derived factors - Nitiric Oxide?
- Produced in endothelial cells lining the lumen
- 2-5 sec half life in vivo = very localised effect
Production: L-arginine + Oxygen = NO
- Nitric oxide synthase (NOS) is a rate limiting compound
What are the activators of Nitric Oxide Synthase?
- Shear Stress*
- Thrombin
- Acetlycholine
How does Shear Stress cause eNOS activation?
When blood flow increases, endothelial cells detect the increase either by external receptors or by shear force on the cell structure
- This increase in force can damage the vessels/increase B.P if the lumen diameter doesn’t adapt
- Shear stress activates a kinase enzyme (AKt) which stimulates eNOS = causes the release of Nitric Oxide = Local relaxation of blood vesel
How does Nitric Oxide enter the vascular smooth muscle cells and cause them to relax?
- Due to the short-half life of NO it can pass rapidly through into vascular smooth muscle cells
- Activates Guanylate Cyclase in smooth muscles
- Converts GTP to cGMP
- cGMP and activates the Myosin Phosphatase
