Circulatory 1 Flashcards
Mastery
Blood Flow
what drives blood fow?
inversely proportional to…
F = ΔP / R
F =
ΔP =
R =
From higher to lower pressure
directly proportional to pressure gradient
inversely proportional to vascular resistance
F = ΔP / R
The bigger the gradient greater the flow. DIF BETWEEN HIGH AND LOW
F = flow rate of blood through a vessel
ΔP = pressure gradient
R = resistance of blood vessels
Blood Flow
Resistance
measure of opposition to blood flow
Depends on
* ρ
* l
* r (major)
TEST
Eg. If vessel radius decreases by a factor of 2,
Flow would decrease by
Thus -
Depends on
* Blood viscosity, ρ
* vessel length, l
* vessel radius , r (major determinant – biggest effect)
AFTER
Eg. If vessel radius decreases by a factor of 2,
Flow would decrease by a factor of 16 (r4)
Thus - Vessel vasoconstriction and dilation controls flow
Variance in Blood vessels
Arterioles
Capillaries
Arteries
PICTURE:
As area goes up…
Velocity …
Pressure…
AFTER
Vasculature has Layers
Tunica Externa
Tunica Intima
Tunica Media
Arterioles
Highest proportion of smooth muscle
Capillaries
single layer of endothelium
Arteries
Reinforced with collagen and elastin
AFTER
Tunica Intima
* Endothelium
* Areolar CT
Tunica Media
* Smooth muscle
* Elastin
Tunica Externa
* Connective tissue
⬧ Collagen, elastin, and areolar connective tissue
Arteries
flow rate and pressure
* radius
when heart is relaxing…
what composes it
…. flow
Systolic pressure of
Diastolic pressure of
`Arteries
High flow rate / High pressure
* Large radius (low resistance)
Pressure reservoir when heart is relaxing
Collagen fibers
* tensile strength
Elastin fibers
* Stretch / Recoil
of walls
Pulsatile flow
Systolic pressure of ~120
Diastolic pressure of ~80 mmHg
….. Is caused by the buildup of cholesterol within arteries
TEST. * Only blood supply to …. remains constant
- to other organs?
atherosclerosis
- Only blood supply to brain remains constant
- Blood supply to other organs alter via arteriole radius
Factors affecting Vascular Tone
Local influences
Local physical influences
Local influences
- Local metabolite changes
- Histamine release
- Endothelial factors
* Nitric oxide, EDRF, Endothelin
Local physical influences
- heat (dilates) or cold (constricts)
- Myogenic response to stretch
* Reflex contraction
Arterioles
main function…
radius and why…
regulate…
PULSATILE FLOW?
Vasoconstriction
Vasodilation
vessel radius, contraction, resistance and flow?
smooth muscle
- Major resistance vessels
- Radius can be adjusted to: Distribute cardiac output among organs, depending on body’s needs
- Help regulate arterial blood pressure
SMOOTH OUT FLOW, DONT DESTROY CAPILLARY
Vasoconstriction
* narrowing of vessel (↑ resistance)
* Contraction of smooth muscle
* Reduced flow
Vasodilation
* enlargement (↑ radius) of vessel
* relaxation of smooth muscle
* ↓ resistance and ↑ flow
Triggered by several factors (local and central
Vasodilation occurs with
… O2
… CO2
… acid
… K+
… osmolarity
… release
Nitric Oxide
… Heat
AFTER
Extrinsic control
Alpha 1 Receptors
Beta 2 Receptors
Angiotensin II
- Decreased O2 , exercise, need more O2
- Increased CO2
- Increased acid, exercise, lactic acid
- Increased K+
- Increased osmolarity
- Adenosine release
- Nitric Oxide
- Heat
AFTER
Extrinsic control
- Sympathetic input
- Hormones
Alpha 1 Receptors
* Norepinephrine
* Vasoconstrict vessels
Beta 2 Receptors
* Epinephrine
* Heart / skeletal muscle
* Vasodilate
Angiotensin II
* vasoconstricts
Pre-capillary Sphincters
functions? at rest? if relaxed?
Metarteriole
Pre-capillary Sphincters
Constrict sphincter – close capillary bed
At rest, many capillaries are not open
Relax sphincter – opens capillary bed
Metarteriole
Runs between an arteriole and a venule
Capillaries
Main function
type of walls, diffusion distance, radius, velocity, time, SA?
AFTER
What makes up the capillary bed
site of gas exchange
Thin-walled
↓ diffusion distance
Small radius
Velocity of blood flow is slow
* gas exchange time ↑
Extensively branched ↑ surface area
AFTER
Arteriole, pre-capillary sphincter, smooth muscle, meta arteriole, venule
Capillary Types
types of holes, where?
CFS
Continuous
* most common
* Least permeable
* Muscle, lungs, brain, CT
Fenestrated
* have pores
* Kidneys, Small intestine
Sinusoids
* Large clefts for RBCS, proteins
* Liver, bone marrow, spleen
Capillary Bulk Flow
Starling forces that determine fluid flow between tissue and capillary
Capillary blood pressure
Interstitial fluid hydrostatic pressure (PIF)
Plasma colloid osmotic pressure (πCAP)
Interstitial fluid colloid osmotic pressure (π IF)
BALANCE OF THE 2
Hydrostatic pressure and osmotic pressure regulate bulk flow
hydro goes down, then fluid comes in
Capillary blood pressure
* hydrostatic pressure
* Encourages fluid flow into tissue, out of cappulary
Interstitial fluid hydrostatic pressure (PIF)
* Opposes hydrostatic pressure
wants to push fluid into capillary
Plasma colloid osmotic pressure (πCAP)
* Encourages movement of fluid into capillary
Interstitial fluid colloid osmotic pressure (π IF)
* Opposes plasma colloid osmotic pressure
Wants to pull water out of capillary and into tissue
Lymphatic System
Structure? Function? TEST-Similar to veins? How?
Network of open-ended vessels
- Helps drain fluid from tissues
- Return of excess filtered fluid
- Defence against disease
- Lymph nodes - phagocytes
- Transport of absorbed fat
- Return of filtered protein
Lymph vessels
Similar in structure to veins
Low pressure
Have valves
Edema
What is it? Occurs when? Causes?
- Swelling of tissues
- Occurs when too much interstitial fluid accumulates
- Reduced concentration of plasma proteins
- Increased permeability of the capillary wall
- Increased venous pressure
- Blockage of lymph vessels
Venules
Formed when? Leaky? Allows? Made of?
Veins
Return to? Pressure? Resistance? Flow? radius? Serves as?
AFTER
Venous Return
Decreased by:
Increased by:
Formed when capillary beds unite
Very porous allow fluids and WBCs into tissues
Larger venules have one or two layers of smooth muscle cells
Veins
Return to heart. Low pressure. Low resistance. Slow flow. Large radius
Serves as blood reservoir
AFTER
Venous Return
Decreased by:
- Venous compliance, stretch of vessel
Increased by:
- Driving pressure from cardiac contraction
- Sympathetically induced venoconstriction
- Skeletal muscle activity
- Effect of venous valves
- Respiratory activity
- Effect of cardiac suction
Venous Valves?
Varicose Veins
Venous Valves Prevent backflow, chambers
Varicose Veins
Weak valve – allows back-flow
Blood stagnates and clots
