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45 Cards in this Set

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Mean Arterial Pressure (MAP)
of the aorta is approximately 85mmHg.
Central Venous Pressure (CVP)
of the large veins emptying into the R. Atrium isabout 2-8mmHg. Since the CVP is sosmall, it is usually ignored and the ΔP is 85mmHg.
Resistance– determined by 3 factors:
Vessel radius

Vessel length


Blood viscosity

Vessel radius
as radius decreases (vasoconstriction), resistance increases and as radius increases (vasodilation) the resistance decreases
Vessel length
as the vessel length increases, resistanceincreases (and vice versa.
Blood viscosity
as viscosity (thickness) increases, resistanceincreases

What is the flow of the blood vessels

BloodVessels = Vasculature: heart - arterioles - capillaries - venules - veins - heart
Arteries
conduct blood away from the heart
Large Arteries
In large arteries, the wall contains smooth muscle and lots of elastinfibers. The large arteries actas pressure reservoirs(storage sites for pressure to ensure continual, smooth flow ofblood).

a.Asthe arterial walls are expanding due to increased volume duringsystole, the elastin fibers are like a spring being stretched. b.Theelastic force is stored such thatduring diastole, when no moreblood is entering the arteries, the walls passively recoil inward, propelling blood forward.

Arterioles
we go from large arteries to arterioles

What happens once the large arteries go to arterioles

(1) the amount of elastinfibers decrease;

(2) the smooth muscle of the wall becomes thepredominant feature; and


(3) the pressure drops.

What happens to the arterioles

The arterioles provide the greatest resistance to blood flow (~60%)– 2 reasons: i. thevessel radius decreases ii. vasoconstriction and vasodilation(contract or relaxmuscle)

* This resistance determines (1) amount ofblood flow to capillaries and (2) blood pressure.

The vasoconstriction and vasodilation iscontrolled by

Intrinsic and extrinsic control mechanisms
Intrinsic control mechanisms
these are controls occurring in the organitself. 4 examples:

What are the 4 examples of Intrinsic control mechanism

Active Hyperemia


Reactive Hyperemia


Myogenic Response


Chemical Messengers

Active Hyperemia
a vasodilation or vasoconstriction based onmetabolic activity
Reactive Hyperemia
a vasodilation based on a decrease in blood flow.
Myogenic Response
arteriole smooth muscle contains stretch-sensitivefibers. Thus, as the MAP increases, the arteriolar wall isstretched. The response is vasoconstrictionand vice versa!
Chemical Messengers
the cells lining the blood vessel (in theendothelium) can release chemicals, which relax or contract arteriolar muscle:Exs

-nitricoxide = vasodilator


-endothelin-1= vasoconstrictor

There are 3 types of Extrinsic Control Mechanisms, what are they

Sympathetic Nervous System


Vasopressin


Angiotensin II

Sympathetic Nervous System
under stress the neurons of this system areactivated.norepinephrine is released, which binds to the alpha adrenergicreceptors on the smooth muscle cells causing vasoconstriction,increased R, and increased MAP.

Where is Epinephrine released from

adrenal gland

what binds to epinephrine

Like norepinephrine it will bind to the alphaadrenergic receptors and cause vasoconstriction

It can also bind to beta 2 adrenergicreceptors. At low levels it has ahigher affinity for beta 2 adrenergic receptors (= vasodilation), butat high levels it can bind to either. Since most arteriolar muscle contains alphas the effect is primarily vasoconstriction,but in the arteriolar muscle of heart and skeletal muscle, betas predominate = vasodilation.

Vasopressin
(AntidiureticHormone, ADH) – increases MAP; vasoconstricts,
Angiotensin II
increases MAP; vasoconstricts
Capillaries
smallest blood vessels (10-40 billion in thebody); exchanges between the blood and the tissue cells occur through theirthin walls by diffusion

What are the two types of capillaries

Continuous


Fenestrated

Continuous (Capillaries)

most common,they have small gaps between the cells which allows for permeability of smallsized molecules and/or lipid soluble molecules (oxygen, carbon dioxide, steroidhormones, etc.). Permeability of largemolecules (proteins) is low.

Fenestrated

the cells havepores (= fenestrations). The pores allow for rapid movement of water-soluble molecules (sodium,potassium, glucose, etc), large proteins and even cells. Found in organs (kidneys, liver, and bonemarrow) which depend on rapid movement of materials.

how is the flow into capillary beds (networks)

regulated by themetarterioles and precapillary sphincters.

how does the bulk flow across capillary wall

from blood tointerstitial fluid = filtration; from interstitialfluid to blood = absorption. The forces driving the movement into andout of the capillaries = Starling’sforces (4 of them).

What are the 4 Starling forces

1. Capillary hydrostatic pressure


2. Interstitial fluid pressure


3. Capillary osmotic pressure


4. Interstitial fluid osmotic pressure

Capillary hydrostatic pressure
the pressureexerted by the fluid in the capillary = blood pressure. This favors filtration. This pressure decreases as you move down thecapillary (from arteriolar end to venule end).
Interstitial fluid pressure
this forceopposes Capillary hydrostatic pressure At the venule end, when CHP. decreases, the interstitial fluid pressure is greater and absorptionis favored.
capillary osmotic pressure
NOTE: thepresence of a nonpermeating solute exerts an osmotic pressure that tends todraw water to the side where it is present in greater concentration. The most prevalent of these solutes in theblood are large proteins. These generatethe capillary osmotic pressure. Thisfavors absorption.
interstitial fluid osmotic pressure
interstitial fluid osmotic pressure
Net Filtration Pressure (NFP)
filtration pressure– absorption pressure NFP= (Capillary hydrostatic pressure + interstitial fluid osmotic pressure) – (interstitial fluid pressure + capillary osmotic pressure)
Arteriolar end
NFP = (38 + 0) – (25 + 1) NFP = 12mm Hg (filtration)
· Venuleend:
NFP = (16 + 0) – (25 + 1)NFP = - 10mm Hg (absorption)
Venules
vessels slightlylarger than the capillaries. They fusetogether to form veins.
Veins
these have thinwalls compared to arteries (considerably less pressure here) and have muchlarger lumens. The larger veins have one-way valves. They are high compliance vessels (thatis, a relatively small increase in the pressure within veins causes a relativelylarge degree of expansion [increase in volume]). Thus, at any givenpressure, veins can hold more blood than arteries = volume reservoir. At anygiven time ~ 60% of the blood is in the veins. 4 factors affect the flow of blood through the veins:
skeletal muscle pump
when musclescontract venous pressure increases and return increases
respiratory pump
when we take abreath the chest pressure drops (no valves in chest veins), the diaphragmflattens, and abdominal pressure increases (abdominal veins have valves); bloodis pushed upward into chest.
blood volume
as blood volumedecreases, venous pressure falls, venous return to heart falls, end-systolicvolume drops, cardiac output falls and thus MAP drops and vice versa.
vasomotor tone
when thesympathetic nervous sys. is activated, the veins constrict, venous pressurerises, venous return increases, CO increases, and MAP increases.