Why would crying creat cyanotic periods in neonates but not normal 8-12 month old infants?
What physiologic feature of the aorta accomodates the systolic surge of blood flow and what sustains blood flow in the systemic and pulmonary circulations during diastole?
The distension of elastic fiber laminae in the tunica media of the aorta and pulmonary trunk accommodates the systolic surge and passive recoil of the elastic laminae sustains blood flow in the systemic and pulmonary circulations.
Where can smooth muscle fibers be found in muscular systemic arteries? What nerve fibers continuouslyt activate a few of these muscle fibers and why?
Smooth muscle fibers occupy the tunica media.
Post-synaptic sympathetic fibers continuously activate a few of these muscle fascicles to provide tonic contraction which will partially constrict the arterial lumen thus reducing blood pressure and flow velocity in the distal microcirculation.
Which vessels constitute the microcirculation and in which of these vessels can tonically contracted, helically arranged, smooth muscle fibers be found?
The microcirculation is made up of capillaries, venules, and arterioles.
Tonically contracted smooth muscle fibers can be found within the tunica media of arterioles.
What is the purpose of tight junctions inbetween adjacent capillary endothelial cells?
The purpose of these tight junctions is to permit only fluid and small solutes to enter interstitial fluid of the surrounding connective tissue.
What can be found within the lumen of veins of the extremities and what is the purpose of these structures?
Veins of the extremities contain valves with bicuspid leaflets formed by infoldings of the tunica intima.
The closure of these valves prevent backflow during venous return to the right atrium against gravity.