Cardiovascular System—Systemic Circulation

measurement unit of perfusion

mL/min/g

capillaries

sites of exchange between arteries and veins

tunica intima is made up of

endothelium (simple squamous epithelium) and subendothelial layer (areolar connective tissue)

tunica media is made up of

smooth muscles in circularly arranged layers

tunica media is responsible for

vasoconstriction and vasodilation

vasa vasorum

small arteries supplying blood to very large vessel walls

arteries have a thicker ____ and a narrower ____

tunica media, lumen

capillaries contain only

tunica intima, made up of endothelium and basement membrane with intercellular clefts

thin capillary walls allow for rapid exchange of

gas and nutrients

as arteries branch into smaller vessels extending from the heart, they

decrease in lumen diameter, decrease in elastic fibers, increase in relative amount of smooth muscle

elastic arteries

largest arteries, conduction of blood from heart to medium arteries

muscular arteries

medium arteries, external elastic lamina and internal elastic lamina

arterioles

smallest arteries

vasomotor tone

smooth muscle somewhat constricted to regulate systemic blood pressure and blood flow, regulated by vasomotor center in brainstem

continuous capillaries

intercellular clefts, most common, found in CNS lungs muscle and skin

fenestrated capillaries

pores (fenestrations) allow for movement of smaller plasma proteins and fluid, found in intestine and glomerulus

sinusoid capillaries

endothelial cells form incomplete lining with large gaps, basement membrane incomplete or absent, allows for large substances to be transported, found in liver spleen bone marrow

capillary bed structure

arterioles → met arterioles → true capillaries → thoroughfare channels → venules

precapillary sphincter relaxation

permits blood flow to flow into true capillaries to meet tissue nutrition needs

precapillary sphincter contraction

causes blood to bypass true capillary bed when tissue needs have been met

venule diameter

8-100 um

post capillary venues

drain the capillary bed

venules become veins when

diameter > 100 um

most large veins contain

valves

venous valves are made up of

tunica intima, elastic and collagen fibers

at rest, __% of blood is in systemic circulation

70

at rest, __% of blood is in systemic veins

55

vaso/venoconstriction of veins

shifts blood from systemic venous reservoir to systemic circulation

vaso/venodilation of veins

shifts blood from systemic circulation to systemic venous reservoir

vasodilation of arteries causes

increase in local blood flow at capillary bed

simple pathway

arterial anastomosis

venous anastomosis

arteriovenous anastomosis

portal system

simple pathway examples

splenic artery and splenic vein

arterial anastomosis examples

superior and inferior epigastric arteries

venous anastomosis example

most common, brachial and cephalic veins

blood flow velocity and total cross-sectional area are

inversely related

diffusion

concentration gradient (high to low)

route of diffusion depends on

particle size

vesicular transport

endothelial cells use pinocytosis and exocytosis to transport hormones and fatty acids

bulk flow

fluids flow down a pressure gradient

filtration

fluid and small solutes flow easily through capillary openings, away from blood (occurs at arterial end)

reabsorption

fluid moves back into blood (occurs on venous end of capillary)

blood hydrostatic pressure

force exerted per unit area by blood on vessels wall; promotes filtration from capillary

interstitial fluid hydrostatic pressure

force of interstitial fluid on outside of blood vessel, close to 0 in most tissues

in systemic capillary, blood hydrostatic pressure ___ interstitial fluid hydrostatic pressure

greater than

high blood pressure causes

high net hydrostatic pressure of capillary and increased net filtration pressure

low blood pressure causes

low net hydrostatic pressure of capillary and decreased net filtration pressure

colloid osmotic pressure

pull on water due to the presence of proteins in the blood

net filtration pressure (NFP)

difference between net hydrostatic pressure and net colloid osmotic pressure

NFP is higher at ____ and lower at ____

the arterial end; the venous end

tissues with high vascularity

are metabolically active; ie brain heart liver skeletal muscle

higher degree of vascular dilation means

greater potential for local blood flow

structures with little vascularity

are avascular; cornea and lens of eye, epithelia, cartilage, tendons, ligaments

angiogenesis increases

perfusion of a local tissue

angiogenesis occurs during

exercise, muscle conditioning, loss of adipose tissue

when metabolic activity increases

oxygen and nutrient levels decline, carbon dioxide lactic acid H+ and K+ increase, varied stimuli signal inadequate perfusion and act as vasodilators

nitric oxide

vasodilator

leukotrienes and thromboxane A2

vasoconstrictor

increased cardiac output will increase

blood pressure

blood pressure

force of blood against a vessel wall

blood pressure is highest in ____ and lowest in ____

arteries; veins

systolic pressure

when ventricle contracts, highest pressure generated

MAP (Mean Arterial Pressure) =

diastolic pressure + 1/3 (systolic - diastolic)

normal = 70-100

skeletal muscle pump

• as muscle contracts, veins are squeezed

• assists venous return from limbs

• blood is pushed and valves prevent back flow

• blood is moved more quickly during exercise

respiratory pump inspiration

diaphragm contracts, abdominal pressure increases, thoracic pressure decreases

respiratory pump expiration

diaphragm releases, thoracic pressure increases, abdominal pressure decreases

peripheral resistance

resistance of blood in blood vessels

in atherosclerosis, sustained increased levels of resistance lead to

increase in arterial pressure to maintain adequate blood flow

when vessels are longer, resistance is

greater

increased peripheral resistance results during

weight gain (= angiogenesis)

decreased peripheral resistance is associated with

weight loss (= vessel regression)

peripheral resistance is directly related to ____ and inversely related to ____

vessel length; vessel radius

as diameter increases, resistance ___ and flow ____

decreases; increases

flow is proportional to

radius of the fourth power

blood flow is directly related to ____ and inversely related to ____

pressure gradient; resistance

cardioacceleratory center

sympathetic nervous system, stimulates SA node and myocardium

vasomotor center

stimulates sympathetic neurons to release norepinephrine (NE) and adrenal medulla to release epinephrine (EPI)

epinephrine and norepinephrine cause

vasoconstriction

if blood pressure decreases

• baroreceptor firing rate decreases

• activates the cardioacceleratory center

• increases cardiac output

if blood pressure increases

• baroreceptor firing rate increases

• stimulates the cardioinhibitory center

• decreases cardiac output and heart rate

baroreceptor reflexes are best for ____, but are ineffective for ____

quick changes in blood pressure; long-term blood pressure regulation

chemoreceptors stimulate vasomotor center when

high carbon dioxide, low pH, very low oxygen

if chemoreceptors stimulate vasomotor center, then

increase in blood pressure and shift blood to the lungs

renin converts ____ to ____ in blood

angiotensinogen; angiotensin I

angiotensin II effects

• vasoconstrictor

• raises blood pressure

• stimulates thirst center

• acts on kidneys to decrease urine formation

why does angiotensin II decrease urine formation?

to ensure less fluid loss from the blood and maintain blood volume

aldosterone effects

• increases blood pressure

• decreases urine output

hormones that cause an increase in blood pressure

epinephrine, aldosterone, ADH

atrial natriuretic peptide (ANP) effects

• stimulates vasodilation

• decreases blood pressure

• increases urine output

hypertension

• may damage blood vessel walls, causing atherosclerosis

• may thicken arteriole walls, arteriosclerosis

essential hypertension

hypertension without any cause; starts between 30-50 years old

secondary hypertension

has an underlying cause; before age 30 or after age 50

labile hypertension

high blood pressure caused by stress (50% will end up with essential hypertension)

isolated systolic hypertension

seen in the elderly where systolic BP > 140 & diastolic < 90

pseudo hypertension

secondary to a stiff non-compressible blood vessel

during exercise

• total blood flow increases

• increased blood flow to coronary arteries, skeletal muscle, skin

• decreased blood flow to abdomen, kidney, GI and GU track