Lecture 29: Capillaries and Veins Flashcards
What are Capillaries ?
Tubes of endothelial cells that branch from the arterioles-sites of O2,CO2 and nutrient exchange between the blood and cells.
How much volume of blood is found in the capillary beds?
Only 250ml of 5000ml total blood volume is found in the capillary beds
What does the decrease in velocity help with once blood reaches the capillaries?
the velocity slowing down allows for nutrient exchange or dropping O2 and picking CO2. flow remains the same but the velocity slows down
what are capillary pores and what do they do?
-Water filled cleft
-enable passage of K,Na,and amino acids
-pores are present at cellular junctions between endothelial cells
-pore size differs with tissue type: liver capillary pores are large and brain capillary pores are non-existent .
What is a precapillary sphincter and a metarteriole?
Precapillary sphincters surround capillaries.
Metarterioles is a thoroughfare channel from an arteriole to a venule
What happens during passive exchange?
Passive exchange of glucose,CO2 and O2 between IF and plasma membranes of cells
What happens during bulk flow?
Movement of water and solutes across the capillary wall via pores of things like Na, K, glucose and amino acids .
What is Ultrafiltration?
Fluid moves from the capillary lumen to the low pressure IF outside the capillary
How does the hydrostatic pressure change across the capillary ?
It starts at arteriole side Pc(37) and when it goes to the venue side the pressure drops to Pc(17)
What is reabsorption?
Reverse bulk flow: inward driving pressure exceeds an outward opposing pressure across the capillary wall.and this happens at the venule side
What forces drive bulk flow?
Capillary blood(hydrostatic fluid) pressure
Colloid osmotic pressure (oncotic pressure): product of the dissolved proteins within the plasma blood
What does the term Pc mean?
Capillary blood pressure is the hydrostatic pressure exerted on the inside of capillary walls by the blood
What does the term PI.p mean?
Plasma colloid osmotic pressure(oncotic pressure) exerted by dispersed plasma proteins .Encourages fluid movement into the capillary lumen (inward pressure ). More protein in plasma compared to IF. Plasma proteins attract water
What does the term P.IF mean?
Interstital fluid hydrostatic pressure=1 mmHg
What does the term Pi.IF mean?
Interstitial oncotic pressure =due to proteins in the IF-this is usually negligible. This is usually 0 but if unhealthy it could change
What is the significance of bulk flow?
It regulates the distribution of ECF between plasma and IF.
It can also help maintain BP
At the arteriolar end of the capillary what is the outward pressure?
The outward pressure is high
At the venular end of the capillary, what is the inward and outward pressure comparison?
The inward pressure is greater than the outward pressure
what is lymph?
It is a IF that enters a lymphatic vessel and contains plasma proteins that are not reclaimed by the blood plasma and fats. Wherever you have regular capillaries you will have lymph capillaries as well
What are the functions of the lymphatic system?
-Defense against disease by the lymph nodes
-Transport of absorbed fat from thew digestive tract
When does edema occur?
Occurs when there is excessive interstitial fluid in tissues
What causes Edmea?
Reduced concentration of plasma proteins(starvation)
Increased permeability of the capillary walls
Increased venous pressure
Blockage of lymph vessels
What is the velocity in veins compared to capillaries ?
Blood velocity is higher than the capillaries and veins have very thin walls unlike arteries that have very thick walls.
Veins have ______ radii and offer _____ resistance to flow
Large,Low
How much of the blood do the veins hold?
60% of the blood is stored in veins
What is venous return ?
It is the volume of blood entering each atrium per minute
What is another name for veins?
Capciatan vessels
review the five factors for enhanced venous return
