A&P2 Lecture 2 part 2 Capillaries

winniesmith1's version from 2017-03-11 23:33

Section 1

Question Answer
What are capillaries Smallest blood vessels connect arterial outflow and venous return
How do capillaries form part of the microcirculationAs blood flows from metarteriole through capillaries and into postcapillary venule
What is the primary function of capillariesExchange vessels. exchange between blood and interstitial fluid
What is the structure of capillary bedsFunction as an interconnected network (capillary bed). Entrance to each capillary is guarded by a precapillary sphincter (band of smooth muscle at arteriole-capillary junction). Arise from single metarteriole.
What do precapillary sphincters doContraction=reduces flow. Dilation = increases flow. Cyclical activity (-12 minutes). Vasomotion. Results in intermittent flow, responding to local changes in milieu (autoregulation)

Section 2

Question Answer
What is the structure of capillariesLack tunic media and tunic externa (one layer of endothelial cells and basement membrane)
What are the 3 types of capillaries1. Continuous. 2. Fenestrated. 3. Sinusoids
Describe continous capillariesEndothelial cell membranes form a continuous tube
Describe fenestrated capillariesHave fenestrations or pores
Describe sinusoid capillariesWider and more winding. Unusually large fenestrations.
By what processes do capillaries exchange material Diffusion, filtration, osmosis

Section 3

Question Answer
Compare the structure of veins to arteriesStructural changes not as distinct. Tunica interna- thinner than arteries. Tunica media- thinner with little smooth muscle. Tunica externa- thickest layer. Has valves
Describe the structure of veinsVery thin walls in relation to total diameter. Not designed to withstand high pressure, thin layer of smooth muscle cells and elastic fibres. Has valves- aid venous return by preventing backflow. Large lumen.
Why do veins need valves?Low BP in veins (too low to push blood back toward heart). Help blood return to heart (aid venous return) by preventing backflow.
Describe venulesVery small blood vessel in the microcirculation. Collect blood from capillaries. Venules feed blood to veins.
What are veins innervated bySympathetic nerve activity (Vasconstriction, aids in return of blood to the heart). Skeletal muscle pump (aids in return of blood to the heart)
What does vaso vasorum meanvessels of the vessles
What are vaso vasorumssmall arteries and veins in the walls of large arteries and veins. Eg. Aorta and vena cava. Supply cells of the tunica media and externa with oxygen and nutrients.

Section 4

Question Answer
What is blood pressurethe force exerted by the blood on the vessel wall
Why is blood pressure neededto overcome friction (resistance) to sustain blood flow
What is the average blood pressure120(SBP) /80 (DBP)
What is pulse pressure (PP) average?SBP- DBP= PP = 40
What is mean arterial blood pressure (MAP) average?DBP + 1.3 (PP) += 93

Section 5

Question Answer
What is venous return The amount of blood arriving at right atrium each minute
What is venous pressure2-30mmHg. The average BP within the venous compartment.
What is venous return assisted byCompression of skeletal muscles. Respiration – inhaling decreases pressure in thoracic cavity, leading to expansion of inferior vena cava and right atrium
What is the pressure at the arterial end of capillaryhydrostatic pressure (35mmHg)
What is the pressure at the venous end of capillaryosmotic pressure (caused by plasma proteins in blood)(10-15mmHg)

Section 6

Question Answer
What is blood flowthe volume of blood that flows through any tissue in a give time period (ml/min)
What is cardiac output (L/min)Total blood flow
How do you work our cardiac outoutCO= SV*HR
What is the average resting CO?70ml x 70ml =4900 ml/min or 5L/min
Distribution of CO depends on what The pressure differences that drive blood through tissue ‚ Flows from higher to lower pressure. - Resistance to blood flow in specific tissues ‚ Higher resistance means lower blood flow
Describe arterial pressure difference throughout circulationà Ventricle ‚ Contraction generates ‚ BP à Aorta - distribute ‚ Dampener à Arteriole – reistance ‚ Steep pressure drop à Capillary – exchange à Veins – capacitance ‚ 70-80% of blood vol. à MAP falls progressively with distance from LV

Section 7

Question Answer
What is vascular resistanceOpposition to blood flow due to friction between blood and vessel walls
What factors influence resistance (R)à Blood viscosity (Ș) à Vessel length (L) à Vessel diameter (r = radius) ‚ Most important factor R = 8LȘ/(ʌr4)
How does the size of lumen affect vascular resistanceVasoconstriction makes lumen smaller meaning greater resistance.
How does blood viscosity affect vascular resistanceratio of RBCs to plasma and protein concentration, higher viscosity means higher resistance
How does total blood vessel length affect vascular resistanceresistance directly proportional to length of vessel. 400 miles of additional blood vessels for each 2.2lb of fat
How much does doubling vessel diameter increase flow16x
Describe velocity of blood flowà Speed in cm/sec in inversely related to crosssectional area à Velocity is slowest where total cross sectional area is greatest ‚ Aorta à Blood flow becomes slower farther from the heart ‚ Slowest in capillaries ‚ Aids in exchange

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