TBL13 - Arteries, Arterioles, Venules and Veins Flashcards
What part of the aorta and pulmonary trunk accomodates the systolic surge? What do these structures allow for in the systemic and pulmonary circulations?
1) Distension of elastic fiber laminae in the tunica media of the aorta and pulmonary trunk accommodates the systolic surge
2) During diastole, passive recoil of the elastic laminae sustains blood flow in the systemic and pulmonary circulations
Why are systemic arteries designated muscular arteries? What do postsynaptic sympathetic fibers do to arteries? What does this result in?
1) Systemic arteries are designated muscular arteries. Multiple circular layers of smooth muscle fibers occupy the tunica media
2) Postsynaptic sympathetic fibers continuously activate a few muscle fascicles (i.e. tonic contraction) to partially constrict the arterial lumen
3) This tonic contraction reduces blood pressure and flow velocity in the distal microcirculation
What constitutes the microcirculation? What are terminal branches of arteries called? Describe the tunica media of arterioles.
1) Arterioles, capillaries, and venules constitute the microcirculation, which can be seen only with the aid of a microscope
2) Arterioles are terminal branches of the muscular arteries
3) The tunica media of arterioles consists of one or two layers of closely packed, helically arranged smooth muscle fibers, which are tonically contracted
How do arterioles maintain synchronized contraction? What does this result in?
1) Local activation of sympathetic fibers in the tunica media stimulates synchronized contraction of all the arteriolar smooth muscle fibers (i.e., vasoconstriction)
2) Blood flow into the capillaries is significantly reduced
What is the function of this vasoconstriction of arterioles?
This vasoconstriction regulates capillary blood flow based on local tissue needs (e.g., when jogging, arteriolar vasoconstriction occurs in the digestive tract and concomitant arteriolar vasodilation occurs in the extremities)
Compare pulmonary and systemic arterial pressures. Is tonic contraction of smooth muscle sufficient to reduce blood pressure and flow velocity in the pulmonary capillaries?
1) Pulmonary arterial pressure is significantly less than systemic arterial pressure
2) Despite relatively little smooth muscle in the tunica media of the pulmonary arteries and arterioles, tonic contraction of the smooth muscle is sufficient to reduce blood pressure and flow velocity in the pulmonary capillaries
What are capillary endothelial cells linked by? What does this permit? When excess filtrate exits capillaries, where will it go?
1) Adjacent capillary endothelial cells are linked by tight junctions, which permit only fluid and small solutes to enter interstitial fluid of the surrounding the connective tissue
2) Excess filtrate (aka lymph) is absorbed by resident lymphatic capillaries for drainage into local lymph nodes
What do capillaries drain into? What do venular walls consist of?
1) Capillaries drain into the venules (small tributaries of the veins)
2) The thin venular wall consists of endothelium surrounded by loose connective tissue
What characterizes the thick tunica media of muscular arteries? What characterizes the thin tunica media and thick tunica adventitia of veins? What does this allow for?
1) Circular layers of smooth muscle characterize the thick tunica media of muscular arteries
2) In the veins, the thin tunica media and thick tunica adventitia contain prominent bundles of type I collagen fibers and only scattered bundles of smooth muscle fibers
3) Tensile strength provided by the collagen fibers and tonic contraction of the smooth muscle restrict overdistension of the veins
What do veins of the extremities contain? What does this prevent?
1) Veins of the extremities contain valves with bicuspid leaflets formed by infoldings of the tunica intima
2) Closure of the leaflets prevents backflow during venous return to the right atrium against gravity
