The Circulatory System 4 Flashcards
what do blood vessels do?
direct flow of blood from heart to organs + tissues and back to the heart
what do blood vessels consist of?
- arteries
- arterioles
- capillaries
- venules
- veins
arteries
carry blood away from heart to tissues
arterioles
smaller branches of arteries with organs
capillaries
smaller branches of arterioles within organs; facilitate exchanges between blood and surrounding cells
venules
formed when capillaries re-join; return blood to heart
veins
formed when venues re-join; return blood to heart
the walls of blood vessels are composed of up to 3 tunics. what are these?
- tunic externa (adventitia)
- tunic media
- tunic interna (intima)
tunic externa (adventitia)
outer layer comprised of connective tissue elastin fibres
tunic media
middle layer composed of smooth muscle
tunic interna (intima)
- innermost lining of squamous endothelium
- basement membrane
- layer of elastin
what are the main functions of the arteries?
- serve as rapid-transit conduits for blood from heart to organs
- act as pressure reservoirs
- prov driving force for blood during diastole
what are the 2 main types of arteries?
- elastic arteries (aorta + p.artery)
- muscular arteries (femoral + coronary arteries)
elastic arteries
- numerous layers of elastin fibres in vessel wall
- expand when pressure of blood rises + recoils
muscular arteries
- less elastic but thicker layer of smooth muscle
- diameter changes slightly as BP rises + falls
what are arterioles?
smaller branches of arteries within organs
what do arterioles contain the highest % of?
smooth muscle
arterioles are the major ….. vessels
major
vessel radius supplying individual organs can be adjusted independently. give examples of this?
- distribute cardiac output among systemic organs
- depending on body momentary needs
- helps regulate arterial blood pressure
control of tone of arterioles is mediated through what…
nervous + chemical mechanisms
what does a large pressure drop facilitate blood flow to?
organs
what is vasoconstriction caused by?
- inc in myogenic activity
- inc in oxygen (O2)
- dec in CO2
- inc in endothelin
- inc in sympathetic stimulation vasopressin, angiotensin II
what is vasodilation caused by?
- dec in myogenic activity
- dec in O2
- inc in CO2
- inc in nitric oxide
- dec in sympathetic stimulation histamine release
what are capillaries?
smaller + dense branches off arterioles + metarterioles within organs
what do precapillary sphincters regulate?
blood flow
there are .. main types of capillaries depending on … of pores
3
size
exchange of materials largely occurs via what…
diffusion
what do the very thin walls of capillaries consist of?
single layer of flat endothelial cell + thin basement membrane
walls of capillaries are perforated by water filled pores. what does this permit?
passage of small water-soluble substances
what are the 3 main types of capillaries?
- continuous
- fenestrated
- discontinuous (sinusoidal)
continuous
- endothelial cells = continuous/closely joined
- narrow intercellular pores (~4nm) permit passage of molecules
- skeletal + cardiac muscle, lungs + adipose tissue
fenestrated
- have larger holes (20-100nm) in addition to narrow pores
- have greater permeability + rapid exchange
- kidneys, intestine + endocrine glands
discontinuous (sinusoidal)
- endothelial cells = discontinuous —> v large pores + leaky capillaries
- liver, spleen + bone marrow
what does transcytosis bring?
proteins and macromolecules across endothelium
what are the 2 mechanisms of capillary exchange between blood + surrounding tissues?
- passive diffusion
- bulk flow
what is passive diffusion?
movement of solutes down conc gradient
what is bulk flow?
ultrafiltration + reabsorption of protein-free plasma
what are the determinants of bulk flow?
- capillary blood pressure (Pc)
- plasma-colloid osmotic pressure (πp)
- interstitial fluid hydrostatic pressure (Pif)
- interstitial fluid colloid osmotic pressure (πif)
formula for net exchange pressure?
what is the venous system?
low resistance system that returns blood from tissue to the heart
what does the venous system comprise of?
- venules
- small veins
- large, systemic veins
systemic veins
- large radius –> low resistance to flow
- thing walls with little smooth muscle/elastin –> high distensibility + little elastic recoil
- serve as blood reservoir/capacitance vessels
- one-way valves ensure blood flow to heart
what does an increase in venous return lead to?
- inc in end-diastolic volume
- inc in stroke vol
- inc in cardiac output
what are the short term factors that facilitate an increase in venous return?
- inc in blood volume
- inc in sympathetic vasoconstrictor activity
- respiratory pump - dec pressure in chest veins –> inc in pressure gradient
- skeletal muscle pump - inc in venous pressure –> inc in pressure gradient
- cardiac suction effect - dec pressure in heart –> inc in pressure gradient
- pressure imparted to blood by cardiac contraction - inc in venous pressure –> inc in pressure gradient
what are the relative thickness layers in endothelium walls?
all blood vessels same thickness
what are the relative thickness layers in elastic fibre walls?
arteries have greatest thickness then veins
what are the relative thickness layers in smooth muscle walls?
arteries have greatest thickness followed by arterioles AND veins
what are the relative thickness layers of collagen fibre walls?
arteries have greatest thickness followed by veins and then arterioles
