[361] Physiology - Regional Circulations Flashcards
Is brain O2 consumption//atriovenous O2 difference//blood flow low, middle or high in comparison to other organs?
Cerebral circulation
* Brain O2 consumption: 3.3 ml/(100g tissue * minute)
-Somewhere in middle
* Brain blood flow: 54 ml/(100g tissue * minute
-Somewhere in middle
* Arteriovenous O2 difference: 62 ml O2/L blood
-Pretty high
* Total O2 consumption
-20% of O2
What is range of BP where brain can compensate for changes by autoregulation? Is brain//skeletal muscle blood flow controlled mainly by the myogenic or metabolic pathway?
Autoregulation of cerebral blood flow
* Brain heavily autoregulates
-Changing PP in brain from between 60- 160 mmHg has minimal effect on the brain
-Main control of blood flow to brain & skeletal muscle is metabolic (not myogenic)
* What happens when MAP falls below ~60 mm Hg?
-It drops
Does brain perform a lot of “mechanical work”? What “type” of work does brain do? Give 1-2 examples of physiochemical work performed by the brain? What is active hyperemia? How is active hyperemia different from autoregulation?
Local Metabolic Control
* Flow adjusts flow to metabolic need
-Called local/metabolic control
* Mechanical work: cardiac and skeletal muscle
* “Physio-chemical” work: brain, kidney
-Brain: Making neurotransmitters, Na-K pump needing ATP
-Kidney: pulling ions against concentration gradients
* [active] hyperaemia
-Increased blood flow to an organ due to increased metabolic demands of tissue
-Same mechanism as in autoregulation, but different goal
-Autoregulation is to regulate blood flow after change in BP
-Here we have the mechanism in order to meet metabolic demands of the tissue
-I.e. triggering event changed
What effect does increasing//decreasing PCO2a have on cerebral blood flow? Explain why we breathe into brown paper bag when hyperventilating?
Local or metabolic control of cerebral blood flow by CO2
* Arterial pCO2 is normally well buffered
-Increasing CO2a (arterial) → rise in blood flow
-Decreasing CO2a → vasoconstriction (decrease in cerebral blood flow)
* Same true in other organs (except lungs
* Hyperventilation → brown paper bag treatmentIncrease in pCO2 → decrease in cerebral blood flow (oxygen tent for preemies)
** 1-2 examples of things that cause increase in intracranial pressure? Effect of increased intracranial pressure on cerebral blood flow?** Explain the general mechanism of how this occurs? What is this phenomenon called (high cranial pressure → reduced blood flow)?
Skull - essentially a closed box
* Intracranial haemorrhage (trauma, stroke), tumours, increased CSF volume,…
- These things (increasing pressure) cause decrease in cerebral (brain) blood flow
- Venous pressure will increase due to high cerebral pressure and therefore decreases PP (arterial pressure is high, so now high venous pressure minimises the difference between the 2).
- This is called CNS ischemic response
Another name for CNS ischemic response?
In CNS ischemic response, what happens to vessel diameter//BP//cerebral blood flow//SNS activity?
What is the goal of BP & SNS activity increase (read purple)? What 3 irregularities make up Cushing’s triad?
The central nervous system (CNS) Ischemic reflex
* Also called the Cushing response or reflex
- If intracranial pressure increases, there is fall in the flow and so you get massive vasoconstriction in order to increase (restore) BP
- Decreasing flow of blood to brain causes BP increase & SNS activation
-This is so brain can get enough blood flow
-In this case I think its because the brain pressure is high, so it cant just vasodilate to increase flow, the most effective method at that point is to vasoconstrict to try and up BP so arterial BP overcomes venous BP
* Cushing’s triad: hypertension, bradycardia, irregular respiration
What happens to brain//organ urea levels if urea is injected into veins?
Drugs: e.g., antibiotics; chemotherapeutic agents
* Inject urea into veins
-Leaves vessels and goes to organs - But injecting into vessels of brain, we dont see this increase in brain tissue - Due to blood brain barrier [BBB]
Is blood flow to kidneys//O2 consumption by the kidneys relatively low, middle or high? How much fo CO (_%) does kidney take? **Explain blood flow through glomerulus (which vessels have low//high P; is there filtration or absorption)? **What is total urine production every day (L)?
Renal circulation
* Blood flow to kidneys adjusted for organ weight: 420 ml/100gmin
-Highest in body
* O2 consumption in kidneys: 6 ml/100gmin
-Very high
-Second only to heart
* CO: ~20% of cardiac output
* Blood flow to kidneys:
-Glomerulus
-af=afferent arteriole
-High pressure: causing fluid to leave the capillaries
-ef=efferent arteriole
-Second set of capillaries (going to vasa recta)
-Vasa recta after ef
-Low pressure: Reabsorbs large amount of fluid and brings it back to veins
* Portal system
-Glomerular filtration rate: ~ 100 mL/min
-Urine output: ~ 1-2 L/day
-What fraction of fluid is reabsorbed? (Do the calculation)
-{[100ml(#min in a day)] - Urine output}/[100ml(#min in a day)]
-Renal blood flow: ~1200 mL/min
2 blood supplies to liver? Which supplies oxygenated//deoxygenated blood? **How much(#/4) of liver blood flow is received through each blood supply? **Is liver blood flow//O2 consumption (not adjusted for organ weight) low, middle or high relative to other organs? How much of CO is sent to liver (_%)?
Splanchnic circulation
* Stomach, small intestine, large intestine, spleen, pancreas, liver
* Liver has 2 supplies
1.Portal vein: deoxygenated blood
2. Hepatic artery: oxygenated blood
* Liver blood flow (not adjusted for organ weight): 1500 ml/min
-Highest in the body
* Liver O2 consumption (not adjusted for organ weight): 51 ml/min
-Highest in the body
* CO: ~25% of CO used by liver
Is there autoregulation in portal blood supply of liver?
Portal system
* Little or no autoregulation of the portal supply
Is blood flow//R to skeletal muscle (at rest) low, middle or high?
Skeletal muscle circulation
* Blood flow to skeletal muscle: 2.7 ml/100g*min
-Smallest per 100g tissue
-At rest, not much blood needed by skeletal muscle
* R to flow (at rest): 198.4
-Very high!
* O2 consumption
-Not adjusted for weight: high
-Adjusted for weight: low (½ of body weight is muscle! And it doesnt really need the O2 unless exercising, only needs to work Na-K pump, thats it)
What happens to blood flow if SNS going to skeletal muscle is stimulated//cut?
Vascular tone in skeletal muscle
* SNS activation in skeletal muscle: Decrease blood flow
-Bind a1 → vasoconstriction
* Exercise: can increase blood flow by up to 30x
-Local metabolic control is stronger than any neural or hormonal response
* Cut sympathetic nerves going to skeletal muscle: tiny rise in blood flow
3 ways heat is transferred to environment through skin?
Heat transfer
1. Conduction
-Heat moves from skin to air touching it
2. Convection
-Heated air moves up and cold air comes down (near skin) to take away heat (constant “refreshing” of cold air)
3. Radiation
What happens to core temperature of people if exposed to cold for long time (fluctuates a lot or relatively stable)? **2 ways core temperature is maintained? **
Exposure to cold
* Exposure of naked subject to ambient temperature of 8°C for three days
* Core temperature relatively unchanged
* How is core temp maintained?
-Cutaneous vasoconstriction, shivering:
1.Vasoconstriction: Less blood flow going to skin surface and you dont lose as much heat
2.Shiver generates heat
Explain countercurrent heat exchanger in the body? This mechanism requires blood flow to be int he same or opposite direction? How do many aquatic mammals conserve heat using countercurrent exchanger mechanism?
Countercurrent exchanger
* Large veins & arteries next to one another
-Heat moves from artery to veins (because artery is warmer than vein)
-Only works if flow in arteries and veins are opposite in direction
* **In mammals that swim **(ocean is cold water), they have an arrangement such that arteries going to skin are surrounded by veins, so that the heat in the artery is transferred to the venous blood, and is not lost at skin surface.
