A&P Ch. 19: Circulation and Short-Term Regulation of Blood Pressure

layers of blood vessels (outermost to innnermost)

tunica externa

tunica media

tunica intima

what is tunica media responsible for?

vasoconstriction

which blood vessel layer is present in arteries but absent in veins?

internal elastic lamina

between externa & media

why do arteries need to be elastic?

to handle larger amounts of pressure from the heart

types of arteries

elastic & muscular

elastic arteries

close to the heart (aorta, pulmonary artery)

large lumens to collect large amounts of blood from heart

pressure reservoirs

muscular arteries

largest tunica media

great ability to vasoconstrict

deliver blood to arterioles throughout body

arterioles

smallest artery type

largest contain all three tunics
tiniest only endothelium

resistance vessels

arterioles that change their diameter to allow more or less blood flow

metabolic response to regulate blood flow into capillary beds

adjust blood flow based on specific demands of local tissue

myogenic response to regulate blood flow into capillary beds

occurs reflexively within tunica media

(increased pressure causes contraction)

capillaries structure and function

smallest bv type

erythrocytes flow in single file

gas and nutrient exchange

only tunica intima

permeable

types of capillaries

continuous, fenestrated, sinusoid

continuous capillary

most common

no pores

exchange through intercellular clefts and pinocytic vessels

examples of where you would find continuous capillaries

skin, muscle, blood-brain barrier

fenestrated capillaries

endothelial cells with pores

allows passage of fluid and larger molecules

examples of where you would find fenestrated capillaries

kidney, small intestine, endocrine glands

sinusoid capillary

large fenestrations and a discontinuous basement membrane (hole/patchy looking)

allows movement of entire cells through barrier

examples of where you would find sinusoid capillaries

liver, bone marrow, spleen, lymph nodes

vascular shunt

directly connects terminal arteriole to the postcapillary venule

“H”

Metarteriole + Throughfare Channel

precapillary sphincters

bands of smooth muscle around origin of capillary from metarteriole

venules

smallest of vessels carrying blood back to heart

venules converge to form:

veins

veins

large lumens

blood reservoirs

contain valves

why do veins contain valves?

they ensure unidirectional flow

blood flow equation

F= delta P/ R

variables that influence resistance:

viscosity, length, radius

Poiesuille’s Equation

delta P = 8nLF/pi*r⁴

^{n is viscosity}

Total Peripheral Resistance

forces impeding blood flow throughout the entire circulation

mainly veins because of weaker pressure

what happens to flow with abrupt changes to diameter?

flow is normally laminar, but the diameter change can lead to turbulent flow, increasing resistance

How are blood vessels compliant?

they are able to change structure in response to changes in pressure

Mean Arterial Pressure equation

MAP = Diastolic BP + Pulse Pressure/3

or CO * TPR

what pumps assist venous return?

muscular & respiratory

muscular pump

during contraction, muscles compress veins, forcing blood back toward heart

baroreceptors

detect blood pressure changes

send signals to brain to active sympathetic or parasympathetic system to either increase or decrease bp

what hormones cause vasoconstriction?

ADH/vasopressin

thromboxane and serotonin

epinephrine and norepinephrine

renin-angiotensin-aldosterone system (RAAS) result in:

Na+ (aldosterone) and H₂O (vasopressin) reabsorption

what happens to circulation as we age?

blood vessels stiffen and narrow due to loss of elasticity

vessels accumulate plaque

stiff vessels cause high MAP, further stiffening vessels