Cardio 7 Flashcards
Describe microcirculation.
functions of small blood vessels, capillaries & lymphatics
1. Small arteries & arterioles
-major site of resistance
-role in regulation of arterial BP & blood flow
2. Venules & small veins
-imp capacitance function
-role in distribution of blood volume
3. Capillaries
-site for exchange of nutrients
-physical structure, lg #, enormous SA
4. Lymphatics
-take up excess fluid from tissue
Describe the structure of microcirculation.
-each artery enters an organ branch 6-8x before becoming arterioles
-arterioles branch 2-5x until they become ‘terminal arterioles’ that supply blood to capillaries
>terminal arterioles = ‘metarterioles’
Describe metarterioles.
-dont have a continuous muscular coat
-smooth muscle fibers encircle vessel intermittently
-each true capillary originates from a metarteriole, a smooth muscle fiber usually encircle capillary
-precapillary sphincter = open/close entrance of capillary
=
not all capillaries are perfused with blood at all times, depends on metabolic needs
Describe venules VS arterioles.
-venules = larger & weaker muscular coat
>pressure is lower & allow constriction
Describe the capillary wall.
-simple layer of endothelial cells & thin BM
-lipid soluble substances cross capillary wall by dissolving in & diffusing across endothelial membrane
-water-soluble substances (ex. Ions) cross capillary wall through water filled clefts/through lg pores (fenestrated)
What are the special types of pores that occur in the capillaries of certain organs?
- Brain
-space between endothelial cells
-tight junctions allow small molecules to pass BBB - Liver
-sinusoidal capillaries
-clefts between cells are wide open to allow dissolved substances of plasma to pass from blood to liver - Kidney
-small oval fenestrations penetrate through middle of endothelial cells
-lg amounts of sm molecules & ionic substances can filter through glomeruli without passing through the clefts between endothelial cells
Describe blood flow through the capillaries.
-intermittent flow = turns off/on every few secs/min
-vasomotion = intermittent contraction of metarterioles & precapillary sphincters
-degree of constriction/relaxation affects blood flow
>determines total peripheral resistance
metarterioles = vascular shunt when precapillary sphincters are closed (throughfare channel)
What is the most important factor affecting the degree of opening & closing of metarterioles/precapillary sphincters?
-oxygen
-when rate of O2 usage by the tissue is great (O2 decreases) = the blood perfusion of capillaries increase
-part of local control of tissue blood flow
Describe fluid exchange across capillaries.
-diffusion is the most important way that substances are transferred between plasma & interstitial fluid
-concentration difference influences the net rate of diffusion through the membrane
-net rate of diffusion is proportional to the concentration difference of the substance between the 2 sides of the membrane
>lg quantities of O2 moves from blood to tissues
>CO2 moves into blood & carried away from tissues
Describe the interstitial fluid.
-filtration & diffusion from the capillaries forms the interstitial fluid = fluid present in interstitium
-1/6 of total volume of body is interstitium
>made up of collagen & proteoglycan filaments
>tensional strength
-interstitial fluid = entrapped within proteoglycans filaments forming a ‘tissue gel’
>small amounts of fluid “free fluid”
>EDEMA = lg amounts of free interstitial fluid
Describe the starling forces.
-fluid filtration across capillaries determined by hydrostatic & oncotic pressure
1. Filtration = movement of water from capillary plasma into the interstitial fluid
2. Reabsorption = movement of water into a capillary
Describe capillary hydrostatic pressure (Pc).
-pressure drives fluid out the capillaries into the intersitial space = favors filtration
-highest at the arteriolar end of the capillary & low at venular end
-equal to BP
-capillary arterial pressure = 35 mmHg
-capillary venous pressure = 17 mmHg
Describe interstitial fluid hydrostatic pressure (Pif).
-pressure that drives fluid out of the interstitial space into the capillaries
-opposes filtration
-normally is near zero/slightly negative
Describe capillary oncotic pressure (pip).
-colloid osmotic pressure
-pressure exerted by plasma proteins
-favors reabsorption
-arterial osmotic pressure = 26 mmHg
-venous osmotic pressure = 26 mmHg
Describe hydrostatic pressure.
-pressure that any fluid exerts in a confined space