Regulation of blood flow to organs Flashcards
Radius of arterioles
Leads to diff parts of the body, can be adjusted independently of one another
This allows for specific changes in blood flow to specific organs
Arteriole smooth muscle:
Smooth muscle surrounding the arteriole can contract (vasoconstriction) or relax (vasodilation) to produce changes in resistance (and flow)
Rate of blood flow to each organ depends on…
The degree of contraction and relaxation (vasoconstriction/dilation) in the arterioles that supply blood to that organ
Pre capillary sphincters
Bands of smooth muscle at junctions between arterioles and capillaries
When sphincters open vs closed
- Relaxed, blood flows into capillary bed
- Constricted, blood flows directly from arteriole to venule through connecting vessels called metarterioles and does not enter capillaries
How is arteriole vasoconstriction/dilation modified: vascular tone
- Ca concentration (adds more tension)
- state of partiai contraction Independent of neural
signaling and
chemical effects (hormones)
Myogenic control
Ability of vascular smooth muscle within vital organs to regulate its
tone in response to changes in blood pressure
Increasing blood pressure=
stretches the smooth muscle in the
arteriole
Blood Flow to feet when standing up:
When standing, the increase in pressure in feet causes stretch, allows ca2+ in cell, smooth muscle contract so up tone, and reduce flow in feet
Local metabolic control
Tissue can control their own blood supply by releasing paracrine signalling molecules
Active Hyperemia (co2 and O levels)
Up blood flow to a tissue if high tissue activity (metabolism)
=down resistance
Tissue more active= Oxygen levels down, co2 up
Exercise
Down o2 levels and up co2, h,k, metabolic waste
Because of this Vascular endothelial cells will secrete NO2 which reduces ca entry- vasodilation
Results in
1) arterioles: increase blood flow to active tissues
2) precapillary sphincters: increase # of open capillaries in active tissues
Results in increase o2 levels and waste removal of blood
Endothelin-1 (released by and cause)
Released from arteriole cells in response to high pressure
= causes vasoconstriction by opening ca channels and increase ca release by SR
Histamin (released by & cause)
Released by mast cells of immune system
Cause vasodilation and inflammation
Usually happens during allergic reactions (quick onset) or injury/infection (2-8hr onset)
Serotonin (released by and cause)
In blood released from platelets due to wound
Cause vasoconstriction
Reactive hypermia
high blood flow after something limited your blood flow)
(Reduce flow= down stretch=vasodilation (relaxed)
What does total peripheral resistance change:
Blood pressure only (not flow)
So only the vasoconstriction/vasodilation changes
neural control (what it release and firing rate relationship)
synpathetic neurons mainly release NE
up firing rate= vasoconstriction= up TPR and also cause venoconstriction (constriction of veins)
decrease in firing rate is the opposite of this
hormonal control what/where it release
release epin
released from adrenal gland in response to sympathetic stimulation
binding to a1-receptors vs B2 receptors
- in skin (NE- vasoconstriction)
- in heart, liver, and skeletal muscle (E, vasodilation)
angiotensin II and vasopressin
- hormone that constricts blood vessels and increase blood pressure
- a hormone that helps regulate blood pressure and amount of water + salt in the body (ADH) up tpr
atrial natriuretic peptide (ANP)
causes relaxation of SM and vasodilation (down TPR)
local effect (brain/heart)
1) down arteriolar stretch
2) down [O2,] and up metabolic waste
results= dilation
problem= MAP down
4 important pressure: systolic pressure (sp)
max pressure in aorta (120mmhg)
reached halfway through ventricular ejection (ie during ventricular systole/contraction
Hypertension= over 140
