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
Describe interstitial fluid oncotic pressure (piif).
-force favoring filtration
-determined by the interstitial fluid protein concentrations
-low bc little loss of protein in intersitial fluid
Describe albumin molecules.
-carry charged amino acid residues (net charge = -17) at normal ph -> strong attraction of Na ions & water is pulled into vasculature as a result -> each gram of albumin is capable of holding 10mL of H2O within the intravascular space
Describe the arterial end VS the venous end.
ARTERIAL END:
-BP higher than osmotic pressure. Water moves out.
VENOUS END:
Osmotic pressure is higher than BP. Water moves in.
*if the result of all forces (net filtration pressure) is positive = net fluid filtration across the capillaries
*if the result of the starling forces is negative = net fluid reabsorption from the interstitial fluid into the capillaries
Describe the hydrostatic pressure VS osmotic pressure.
Hydrostatic pressure: BP
-pushes the fluid out of the capillaries
Osmotic pressure: proteins
-holds fluid inside of capillaries
Describe the permeability of the capillary wall.
-influences fluid movement in capillaries
-hydraulic conductance (Kf) = water permeability of the capillary wall
-varies among diff types of tissue
>size of cleft between cells
>whether capillaries are fenestrated
-permeability is increased in capillary injury
>ex. Toxins, burns, inflammation
>increase permeability to water
Describe the fluid exchange.
-amount of fluid filtering outward from the arterial ends of capillaries equals exact fluid returned to the circulation by absorption
-slight disequilibrium that occurs (favors filtration) accounts for the fluid that’s eventually returned to the circulation by way of the lymphatics
1. Arteriole = 20 L per day filtered
2. Venule = 17 L pet day reabsorped
remaining 3 L = returns to circulation through lymphatic capillaries
Describe the lymphatic system.
-accessory route through which fluid can flow from the interstitial spaces into the blood
-lymphatics carry proteins & lg particle matter away from the tissue space
>neither can be removed by absorption directly into the blood capillaries
-lymphatic capillaries lie in the interstitial fluid close to the vascular capillaries
key role in controlling interstitial fluid protein concentration, volume, pressure
Describe the lymphatic capillaries.
-possess one way flap valves which permit interstitial fluid & protein to enter but not to leave
-tissues have special lymph channels that drain excess fluid directly from intersitial spaces
-lympatic capillaries merge into larger lymphatic vessels/thoracic duct
>lymph flow depends on contraction of smooth muscle in the lymph vessel & compression of the lymph vessels by activity of the surrounding skeletal muscle
Describe the lymphatic system functions.
- Fluid balance
- Fat transport
-absorbed fats from the intestines & transports to the blood stream - Immune system
-transports foreign material to lymph nodes
-involved in development of immune cells
Describe changes in starling forces.
influences direction & magnitude of fluid movement
1. Edema = increase in interstitial fluid volume
2. Effusion = abnormal collection of fluid in a hollow space or between tissues (ex. Pleural effusion)
Describe congestive heart failure.
R side failure
Blood can’t be properly pumped -> ‘accumulates’ backwards -> increase in capillary hydrostatic pressure -> fluid moves out of vessel -> oncotic/hydrostatic pressure -> causes edema or effusion
Describe the lymphangiectasia.
Protein losing enteropathy -> decrease in plasma proteins concentration -> decrease in capillary oncotic pressure -> hydrostatic/oncotic pressure -> fluid moves out of vessel -> causing edema/effusion
Describe a snake bite.
Local inflammation -> release vasoactive mediators -> increase permeability of capillary wall -> fluid moves out of vessel -> causing edema/effusion
Describe lymphoma.
Neoplasia impairing normal drainage of fluid from tissue -> fluid from filtration accumulates -> cause edema/effusion
