Ch 20 Blood Vessels and Circulation

EXAM II

direction of bloodflow, starting in heart/ending in veins

heart → arteries → arterioles → capillaries → venules → veins → heart

3 layers of blood vessels

tunica externa

tunica media

tunica intima

tunica externa composition and role (arteries)

made up of collagen and elastic fiber

anchors vessels to adjacent tissues in arteries

tunica externa composition (veins)

contains elastic fibers and smooth muscle cells

vasa vasorum

small arteries and veins that supply the tunica media and externa

what types of vessels have vasa vasorum

large arteries and large veins

makeup of the tunica media

smooth muscle

external elastic membrane

separates tunica media and externa

two layers of the tunica media

inner: circular sheets

outer: longitudinal

role of tunica media

vasoconstriction and vasodilation

how is the tunica media regulated

sympathetic fibers via the nervi vasorum

makeup of the tunica intima

connective tissue

endothelium layer

internal elastic membrane

part of tunica intima

only in arteries

what factor allows arteries to absorb pressure

elasticity

contractility (diameter can change)

what regulates the elasticity and contractility of vessels

sympathetic division of the ANS

vasoconstriction

arterial smooth muscle contraction by ANS

vasodilation

relaxation of arterial smooth muscle

lumen is enlarged

conducting arteries

elastic arteries

large size

tunica media is more elastic fibers than muscle fibers

distribution arteries

muscular arteries

medium size

arterioles

very small

thin or incomplete tunica media

little to no tunica externa

aneurysm

bulge in arterial wall

weak spot in elastic fiber

pressure can rupture vessel

structure of capillaries

endothelial tube

similar diameter to red blood cell

no tunica media and no tunica externa

continuous capillaries

complete endothelium

in all tissues except epithelia and cartilage

diffusion of water, small solutes, lipid-soluble materials

block plasma proteins and blood

CNS capillaries

restrict permeability using tight junctions, a thick basement membrane, and astrocyte extensions

makes blood brain barrier

fenestrated capillaries

pores in the endothelial lining

rapid exchange of water and large solutes

where are fenestrated capillaries found

choroid plexus to protect the CSF

endocrine organs for hormone exchange

kidneys to filter blood

intestinal tract for nutrient absorption

sinusoids

gaps between adjacent endothelial cells

free exchange

phagocytes present to monitor blood

where are sinusoids present

liver to filter blood from hepatic portal and such

spleen to filter systemic blood

bone marrow for new RBCs

endocrine organs to filter lymph

capillary beds

capillary plexus

connects one arteriole and one venule

precapillary sphincter

guard capillary entrance

causes capillary blood to flow in pulses by opening/closing valves

thoroughfare channels

direct connections between arterioles and venules

how are thoroughfare channels controlled

smooth muscle segments called metarterioles

vasomotion

contraction and relaxation of capillaries that causes blood flow to constantly change routes

bulk flow

mass movement of fluids through capillary beds that flows from areas of high to low pressure

filtration

fluid in capillaries pushed out of arterial end

reabsorption

fluid pulled into venous end of capillary

hydrostatic pressure

pressure exerted by blood from the heart pumping against an enclosed space

osmotic pressure

water is drawn into the venous end due to high solute pressure

size comparison between arteries and veins

veins are larger than arteries but have thinner walls

blood pressure comparison between veins and arteries

veins have lower blood pressure

venules

small veins that collect blood from capillaries

describe the tunica media of medium-sized veins

few smooth muscle cells

tunica externa of medium sized veins

longitudinal bundles of elastic fiber

describe each layer of a large vein

all three layers

thick tunica externa

thin tunica media

venous valves composition and function

folds of the tunica intima

prevents backflow and compresses to push blood toward the heart

what percent of blood volume is heart, arteries, and capillaries

30% - 35%

what percent if the body’s blood volume is the venous system

60% - 65%

1/3 in venous networks of liver, bone marrow, and skin

what signal indicates to the body to redistribute blood

vasomotor center in the medulla sends sympathetic stimulation to smooth muscle in veins

resistance

factors that slow blood flow

blood pressure

force exerted on the walls of vessels and the heart chambers

systolic

pressure on the arterial chambers when blood is ejected via ventricular contraction

diastolic

arterial pressure when the ventricles are relaxed

sphygomanometer

instrument that listens to the sound of bloodflow to measure blood pressure

korotkoff sounds

ticking sound created by turbulent blood flow

normal blood pressure

120/80

hypertension

abnormally high blood pressure

>140/90

hypotension

abnormally low blood pressure

pulse

caused by expansion and recoiling of elastic fibers in the arteries

mean arterial pressure

mean arterial pressure

average blood pressure in the arteries

difficult to quantify

70-110 mm Hg

MAP formula

MAP = diastole BP + ((systolic-diastolic BP)/3)

5 examples of things that affect blood flow and blood pressure

cardiac output

compliance (elasticity of vessels)

volume of blood

viscosity of blood

vessel length and diameter

cardiac volume formula

stroke volume x heart rate

stroke volume

amount of blood pumped out by the left ventricle during systole

compliance

blood vessels expanding to accommodate more blood

veins > arteries

healthy vessels > atherosclerotic vessels

Poiseuille’s equation

uses blood viscosity, length of blood vessel, and radius of vessel to descrive the blood flow

pressure (P)

pressure generated to overcome resistance

pressure gradiant (∆P)

difference between pressure at heart and at capillary beds

blood flow (F)

pressure difference (∆P) divided by resistance (R)

blood volume

usually stays roughly constant but can change due to various conditions

hypovolemia

reduction in blood volume

hypervolemia

excessive fluid volume

caused by sodium and water retention

what conditions put one at risk for hypervolemia

heart failure

liver cirrhosis

blood viscosity

also does not change quickly

due to formed elements and plasma proteins

vessel length vs resistance

longer vessels = greater resistance

how many vessels do adults have

60,000 miles

dynamics of the blood vessels diameter

routinely changes throughout the day

examine these

this one too!

vessel diameter would be a parabola

venous system

blood in the veins are continually moving toward the atria

vascular tone of the venous system creates a pressure gradient

pressure difference between veins and atria

pressure in the veins is higher than the atria

skeletal muscle pump

helps vessels overcome gravity

valve system

respiratory pump

promotes blood flow through veins of abdomen and thorax

respiratory pump during inhalation

thorax volume increases and compresses the abdominal cavity

blood is forced back into the atria