Circulation Flashcards
Blood flow through the body
-heart to large arteries, to smaller arteries, arterioles, capillaries, venules to veins to the vena cava and back to the heart
Tunica intima
- endothelium
- subendothelial layer
- internal elastic membrane
tunica media
- (smooth muscle and elastic fibers)
- external elastic membrane
Tunica externa
- collagen fibers
- vasa vasorum
Arteries
- thick walls with elastic tissue and smooth muscle and collagen fibres
- inner surface of artery is lined with endothelial cells;
i) secrete substances that allow arteries to contract or dilate (ex. NO results in smooth muscles relaxation)
ii) regulate transport of nutrients and waste products
iii) hormone synthesis
Arterioles
- large amount of smooth muscle for walls; some elastic tissue; less collagen fibres
- inner surface lined with endothelial cells
- aerteriolar smooth muscle possess a large degree of spontaneous activity; myogenic tone
- myogenic tone sets a baseline level of contraction
- increase in contractile force above the vessel’s myogenic tone results in vasoconstriction while decrease results in vasodilation
- arterioles are the primary vessels involved in pressure flow/regulation*
Changes in myogenic tone
(i) local controls:
a) active (reactive) hyperaemia; increased metabilic activity causes a release of a variety of chemicals that result in vasodilation
b) flow autoregulation: decreased BP results in decreased oxygen delivery and decreased waste removal which stimulates the release of a variety of chemicals that produce vasodilation
(ii) extrinsic control:
- sympathetic nervous system is the primary neural regulator; sympathetic neurons release norepinephrine results in vasoconstriction: alpha-1-adrenegic, beta-2-adrenergic
- decreased sympathetic stimulation results in vasodilation
Alpha-1-adrenergic
receptors on the smooth muscle of arterioles when bound to norepinephrine= vasoconstriction
Beta-2-adrenergic
- receptors on the smooth muscle of arterioles that bind to norepinephrine result in vasodilation
- this effect is usually overwhelmed by the alpha-1 response
Parasympathetic NS regulation of vascular resistence
- plays a very minor role
- vasodilation can occur with the parasympathetic stimulation
- control is indirect
capillaries
- 0.006-0.010 mm in diameter
- thin-walled tube of endothelial cells, 1 layer thick resting on basement membrane
- arteriole drainage first goes through metarterioles and then per-capillary sphincters
- the structure of the capillaries is different depending on the location
types of capillaries
continuous: tight junctions (fat, muscle, NS)
fenestrated: pores (endocrine glands, liver)
discontinuous: Large gaps (liver, bone marrow, spleen)
- space between the endothelial cells can be altered through the release of Histamine
capillary regulation of nutrient exchange
- nutrients diffuse from the blood across capillary walls into cells
- metabolic end products move across cell membranes into capillaries
- capillary wall is a filter
- solute concentrations are higher inside the capillaries in the interstitial spaces and water tends to move into the capillaries
Starling hypothesis
-deals with the movement of water into or out of the capillaries
-plasma proteins are a key factor in preventing fluid loss from the capillaries= plasma protein oncotic pressure
Interstitial oncotic pressure; proteins/particles within the interstitium
capillary hydrostatic pressure: fluid pressure within the interstitium
-interstitial hydrostatic pressure: fluid pressure within the interstitium
Direction of water movement within arteries
1) high venous pressure: will result in back pressure into the capillaries, high capillary pressures will push H20 out of the capillaries into the interstitium
2) high arterial pressures:will increase blood delivery to the capillaries, increase blood volume in the capillaries will increase capillary pressures and push H20 into the interstitium
