Chapter 6: Transport systems Part 1: Mammals Flashcards
Closed circulatory system
-blood always moves within blood vessels which allows pressure to be maintained
Double circulatory system
-blood passes through the heart twice per complete circuit round the body
Pulmonary circuit
-blood travels from Right ventricle=lungs=left atrium
Systemic circuit
-blood travels from LV=body=ight atrium
Advantages of double circulatory system
-blood pressure can be maintained (BP will naturally fall as distance from heart increases due to surface of blood vessels generating resistance to blood flow)
-oxygenated blood is not mixed with deoxygenated blood which increases the efficiency of oxygen uptake at alveoli
-increased efficency in delivery oxygen and glucose to tissues
-Blood pressure in sytemic and pulmonary circuits can be maintained at different levels (if there was only a single circuit than a high BP would cause alveoli walls to rupture whereas a low BP would not be high enough to enable oxygen to be delivered at a rate that would not meet demand)
Advantages of closed system
-BP can be maintained all though body
-BP in PC and SC can be different
-Blood supply can be varied between organs to match their specific metabolic demands e.g increase delivery to skeletal muscles during exercise, increase delivery to small intenstine during digestion.
-lower volumes of blood required (compared to if blood was allowed to bathe all cells)
Blood vessels-Artery
-2cm in diameter
-narrow lumen to maintain high blood pressure
-smaller lumen to wall thickness
-tunica externa: collagen fibres and elastic fibres
-tunica media: smooth muscle and elastic fibres
-tunica intima-single layer of endothelial cells
-large quantity of smooth muscle in TM: maintains blood flow and redistributes blood via vasoconstriction and vasodilation
-large number of elastic fibres in TM=enables blood vessel to stretch during ventricular systole and recoil during ventricular diastole
-smooth inner endothelial lining= reduces friction and resistance for smooth flow
-high blood pressure
-carries blood away from the heart
-generally transports oxygenated blood (except pulmonary artery)
-no semi lunar valves present
pulse
Arterioles
-approx 200 micrometres in diameter
-narrower lumen than artery but wider than capillary
-thin wall
-mainly smooth muscle (less than arteries)
-some elastic fibres (less than arteries)
-relative blood pressure is less than arteries but still high
-carries oxygenated blood from arteries to capillaries
-regulates flow and distribution (contraction and relaxation of smooth muscle by vasoconstriction or vasodilation)
-no semi lunar valves present
-yes there is a pulse but it is less pronounced
Capillary
-diameter is 8 micrometres
-size of lumen is same as diameter of red blood cell which reduces diffusion distance for loading and unloading of oxygen
-single layer of squamous endothelial cells (thin and flat)
-pores between cells called fenestrations which enable formation of tissue fluid and for white blood cells to squeeze through to form macrophages
-“leaky walls =” to allow constant exchange of materials
-low blood pressure
-smallest blood vessel
-site of exchange between plasma and cells
-very large combined surface area for exchange of materials
-no semilunar valves
-no pulse
Venules
-very thin wall
-some smooth muscle
-some elastic fibres
-very low blood pressure
-carries deoxygenated blood from capillaries to veins
-no semi lunar valves
-no pulse
Vein
-13mm diameter
-size of lumen varies but much wider than artery (large to decrease resistance)
-thin wall
-tunica externa: collagen fibres
-tunica media: connective tissue and elastic fibres
-Tunica intima: single layer of endothelial cells
-small quantity of smooth muscle in tunica media
-small quantity of elastic tissue in tunica media
-low blood pressure (contraction of skeletal muscles applies pressure onto veins which compresses veins and raises blood pressure within vein)
-veins return blood to the heart
-generally transport deoxygenated blood except pulmonary vein
-slow blood flow due to low pressure
-semi lunar valves present to ensure blood flows in one direction
-no pulse
Function of valves in veins
-stops backflow of blood due to low pressure
-allows one way flow back to the heart
