Circulation Flashcards
explain the general path of blood through the body (not including gas diffusion in the lungs)
heart - > large arteries - > to smaller arteries - > arterioles - > capillaries - > venules - > veins to the vena cava - > back to heart
Anatomy of arteries, veins and capillaries
anatomy of an artery
thick walls with…
- > elastic tissue for stretch and recoil
- > smooth muscle
- > collagen fibres (prevents too much stretch)
- > inner surface is linned with endothelial cells
function of inner endothelial cells of arteries
i) secrete substances that allow arteries to contract and dialate (local control)
ii) regulate transport of nutrients and waste products to and from blood
iii) hormone synthesis
characteristics of arterioles
- > large amount of smooth muscle for walls but also some elastic tissue as well
- > less collagen fibres than arteries
- > inner surface lined with endothelial cells
- > arteriolar smooth muscle posses a large degree of “spontaneous activity”
i. e. contraction = myogenic tone
explain myogenic tone
- > sets a “baseline” level of contraction; resting force of contraction
- > an increase in contractile force above the vessels myogenic tone results in vasocontriction while a decrease in contractile force results in vasodilation
what are the primary blood vessels involved in pressure/flow regulation
arterioles
how do we change myogenic tones
- Local controls
- Extrinsic controls
explain how we change myogenic tones with local controls
a) with active/reactive hypernemia
- > increased metabolic activity causes a release of a variety of chemicals which results in vasodilation
vasodilation = increased BV diameter = increased BF + BV
b) flow autoregulation
- > decreased BP (through loss of pressure gradient) results in decreased oxygen delivery and decreases waste removal which stimulates the release of a variety of chemicals which produce vasodilation
explain how we change myogenic tone through extrinsic controls
- > the sympathetic nervous system is the primary neural regulator of systemic vascular resistance and BP (para symp.=minor role); symp. neurons release norepinephrine which results in vasocontriction
- > decreased symp. stimulation results in vasodilation
norepinepherine bind alpha-1-adrenergic receptors on SM of arterioles causing vasoconstriction
norepinepherine binds to beta-1-adrenergic receptors to cause vasodilation (this effect is usually overwhelmed by the a1-ardrenergic response)
functions of capillaries in arteriole drainage
- > 1 cell thick
- > arteriole drainage to the capillaries first goes through the metarterioles and then the pre-capillary sphincters
- > structure of the capillaries is different depending on the location and function of the capillaries with the primary difference being the size of pores on between endothelial cells that make up the walls of the capillary
explain how pore size changes the function of capillaries
- > capillaries with tightly regulated movement of fluids and molecules across the capillary walls tend to have small to non-existant pores (i.e. brain capillaries)
- > capillaries with greater molecular movement have larger pores and spaces between endotheial cells (i.e. liver capillaries)
types of capillary
How can the space between the endothelial cells of the capillaries be altered?
through the release of substances such as histamine (inflammatory/immune response) which results in “contraction” of the endothelial cells, opening up the space between individual cells making the endothelial barrier more “leaky”
How do capillaries regulate nutrient exchange
- > nutrients diffuse from blood across capillaries into cells
- > metabolic end products (waste) move across cell membranes into capillaries
- > capillary wall is a filter (i.e. protein free plasma moves across the wall) therefore solute concetrations are higher inside the capillaries than the interstitial spaces and water tends t move into capillaries
explain the different types of pressures in the Starling hypothesis
*states that the fluid movement due to filtration across the wall of a capillary is dependent on the balance between the hydrostatic pressure gradient and the oncotic pressure gradient across the capillary*
- > plasma proteins (produced by the liver) are a key factor in preventing fluid loss from the capillaries = plasma protein oncotic pressure
- > proteins/particles within intertitium = interstitial fluid oncotic pressure
- > fluid pressure within the capillaries = capillary hydorstatic pressre
- > fluid pressure within the interstitium = interstitial hydrostatic pressure
characteristics of veins and venules
- > thin walled and more complient than arteries
- > veins contain some some smooth muscle although not as much as arteries
- > veins contain some elastic tissue and some collagen fibres
- > large veins contain more smooth muscle (like large arteries) and the same amount of collagen fibres as lg art.
How are veins innervated
smooth muscle of veins are innervated by sympathetic NS…
- > stimulation of venous symp. neurons results in the release of norepinepherine, causing contractions of venous smooth muscle
- > this results in increased venous pressures and decreased compliance and more more blood is pushed out of the veins into the heart
peripheral veins
- > contain valves that close behind the blood to prevent backflow caused by the pull of gravity
how do veins return blood to the heart
- skeletal muscle contractions
- > compresses muscle embedded veins, forcing blood towards heart - respiration
- > inspiration causes an increase in abdominal pressure, compressing veins while a decrease in thorasic pressure occurs, lowering the pressures in the right atrium
- > this forms a vacuum that pulls blood back into the heart - sympathetic stimulation
- > venous contriction squeezes blood to heart
where is most of your blood stored
50% of your blood is located in the systemic venous compartment
- > veins are blood resevoirs
What are the valves found within the heart
- Right atrioventricular (tricuspid)
- Pulmonary semilunar
- Left atrioventricular (bicuspid or mitral)
- Aortic Semilunar
Semilunar valves
- > 2 of them: pulmonary and aortic
- > located in the roof of the right and left ventricles
- > each valve is made up of 3 semilunar cusps
shapes of the valves of the heart
