blood vessels and circulation

efferent vessels that carry blood away from the heart: not all carry oxygenated blood

arteries

small arteries right before capillary bed that control the flow into the capillary

arterioles

connection between the smallest arteries and veins and is the site of substance exchange

capillaries

afferent vessels that carry blood toward the heart; not all carry oxygenated blood

veins

small veins right after the capillary

venules

what is the path of the vessels in the circulatory system

arteries→venules→capillaries→venules→veins

what are the layers of the vessel walls in the circulatory system

tunica interna, tunica media, and tunica externa

innermost layer of simple squamous epithelium and is a selectively permeable barrier that secretes chemicals to stimulate contraction or dilation

tunica interna (intima)

middle and thickest layer of smooth muscle, collagen, and elastin tissue to allow for constriction; found more in arteries

tunica media

outermost layer of loose CT and may contain vaso vasorum that supply blood to the vessel itself

tunica externa (tunica adventitia)

referred to as resistance vessels due to strength and the ability to handle high pressure because they are more muscular than veins with a thicker tunica media and have three types

arteries

elastic or large artery that moves a high amount of blood with a thick tunica media

conducting arteries

arteries that are muscular or medium that distribute blood to specific organs

distributing arteries

arteries that are small smooth muscle with little elastic tissue; arterioles are a sub type

resistance arteries

what type of receptor is a baroreceptor

pressure sensor

baroreceptors that are located at the proximal internal carotid artery with sensory innervation via the glossopharyngeal nerve (CNIX) and motor to the circulatory system via the vagus nerve (CNX)

carotid sinuses

what happens when the carotid sinuses (baroreceptors) are stretched

parasympathetic increases to decrease HR

chemoreceptors that detect pH and are located near the carotid sinus

carotid body

what happens when the chemoreceptors detect low pH

stimulate glossopharyngeal nerve to increase respiratory rate from medulla

site of gas, nutrient, waste, fluid exchange between the bloodstream and tissue and is possible dir to the very thin walls

capillaries

what are the three types of capillaries

continuous, fenestrated, and sinusoids

endothelial cells are held together with tight junctions and are separated by intercellular clefts; allow smaller solutes like glucose to diffuse but not plasma proteins or cells

continuous capillaries

endothelial cells with filtration pores to allow rapid passage of small molecules but still retain cells and proteins in blood (kidneys and small intestine)

fenestrated capillaries

endothelial cells with large gaps and irregular fenestrations to allow proteins and RBCs to pass through; typically found in the liver, bone marrow, and spleen

sinusoid capillaries

organization of capillary network

capillary beds

short arteries that link arterioles to capillaries and have precapillary sphincters that encircle the entrance the capillary; constriction of these shuts off blood to the capillary

metaarterioles

what does it mean if the precapillary sphincter is open in the capillary beds

it is perfused and blood passes through

what happens if the precapillary sphincters are closed in the capillary beds

no capillary bed perfusion and blood goes straight through the metarteriole to the venule

why are ¾ of the capillary beds are closed at a given time

there is not enough blood to fill the entire capillary system at once

capacitance vessels that expand to accommodate increasing volume easily and so hold the majority of blood during the cardiac cycle and contains a steady flow of blood

veins

blood goes through two capillary systems

portal system

what is the typical circulatory route of blood before returning back to the heart

only goes through one capillary system

multiple connection between vessels to allow for collateral flow

anastomosis

can completely bypass a capillary network and is often found in areas to reduce heat loss like fingers, toes, and ears

AV anastomosis

amount of blood moving through a vessel over time (mL/min)

flow

delivery of blood to a tissue (mL/min/g); how well a tissue is being supplied with blood

perfusion

what are the physical principles of blood flow mainly based on

pressure difference over resistance

the force of blood exerted against vessel wall

blood pressure

peak arterial pressure during contraction

systolic arterial pressure (120)

minimum pressure during relaxation

diastolic arterial pressure (80mmHg)

systolic-diastolic pressure and reveals how well blood flows

pulse pressure (40mmHg)

average bp during the cardiac cycle; needs to be greater than 60mmHg to maintain adequate perfusion

mean arterial pressure

what is blood pressure physiologically determined by

cardiac output, blood volume, and resistance to flow

how do you calculate cardiac output

HR x SV

opposition to flow of blood that occurs in vessels and relies on three variables

peripheral resistance

what decreases flow if it increases and increases flow if it decreases

blood viscosity

how does vessel length affect the flow of blood

as it increases, the flow decreases due to encountering more friction the farther it goes

what does the principle of laminar flow state

blood flows in layers so it is faster near the center of the vessel due to less friction and slower near the vessel walls; explains why vasoconstriction decreases the flow of blood

how is vasomotion controlled

local, hormonal, or neural

ability of tissues to regulate blood supply

autoregulation

how is the pressure/flow of blood regulated locally

autoregulation, reactive hyperemia, and angiogenesis

increase in above normal flow after supply has been cut off or decreased for a period of time

reactive hyperemia

growth of new blood vessels stimulated by prolonged hypoxia

angiogenesis

how is the pressure/flow of blood regulated neurally

through sympathetic stimulation, baroreflex, chemoreflex, and medullary ischemic reflex

autonomic response when drop in perfusion to brain

medullary ischemic reflex

how is the pressure/flow of blood regulated hormonally

certain substances that are secreted act upon other areas

vasoconstrictor that increases BP

angiotension II

salt-retaining hormone that promotes Na+ retention by kidneys, water follows salt and so more blood volume and pressure

aldosterone

secreted by heart in response to stretch; increases Na+ excretion by kidneys and has generalized vasodilatory effect

atrial and brain natriuretic peptide

promotes water retention and at high levels can promote vasoconstriction

antidiuretic hormone

stimulate vasoconstriction for alpha-adrenergic receptors and vasodilation for beta-adrenergic receptors

epinephrine and norepinephrine

what is the purpose of vasomotion

to raise and lower BP throughtou the body in response to normal activity, selectively modify perfusion of a particular organ and reroute the blood, and it can reroute the blood to vital organs during hypoperfusion

two way movement of fluid and substances across the capillary wall

capillary exchange

what routes can chemicals pass through during capillary exchange

endothelial cell cytoplasm, intercellular clefts, and filtration pores (fenestrations)

for solutes than can permeate the plasma membrane or find passages large enough to pass through; proteins too large

diffusion

endothelial cells pick up material on one side and transport to the other

transcytosis

moves the fluid out of capillary

filtration

moves fluid into the capillary

reabsorption

due to hydrostatic and osmotic pressures, where do fluids tend to exit and re-enter the capillary

exit at arterial end and re-enter at venous

the physical force exerted by a liquid against a surface; the higher it is, the more fluid that wants to push out

hydrostatic pressure

the “pulling” pressure within the capillary due to proteins (albumins in plasma) within a compartment that exert pressure to help pull water into the capillary

colloid osmotic pressure

differences in COP of capillary from tissue

oncotic pressure

the opposing forces of hydrostatic and oncotic pressures that allow for fluid exchange

filtration pressures

the fluid going out of the capillary

net filtration pressure

the fluid going into the capillary

reabsorption pressure

how do you calculate the net filtration pressure

net hydrostatic pressure — oncotic pressure

if more fluid is filtered than gets reabsorbed by the venous end, where does the extra fluid in the interstitial space go

lymphatic system

what causes edema

accumulation of excess fluid within the interstitial space/tissue due to increased capillary filtration due to high hydrostatic pressure or low protein oncotic pressure, reduced capillary reabsorption, or obstructed lymphatic drainage

what causes venous return back to the heart

gravity in the right positions, skeletal muscle pump, respiratory/thoracic pump, cardiac suction/pump, and the pressure gradient slightly

when cardiac output is insufficient to meet the body’s metabolic needs

circulatory shock

poor pumping function of the heart and it can not keep up with demands

cardiogenic

loss of a lot of blood or fluid too fast with inadequate replacement typically due to dehydration, burns, or hemorrhage

hypovolemic

blood can not return to the heart to be pumped and lowers the preload

obstructed venous return

result from widespread inappropriate vasodilation; like during septic shock or neurogenic shock

venous pooling