chapter 20 - the cardiovascular system: blood vessels

form a closed delivery system transporting blood to and from all body tissues; deliver oxygen to tissues, deliver nutrients, deliver hormones, remove carbon dioxide

blood vessels

the 3 major types are

arteries, capillaries, and veins

carry blood away from the heart

arteries

carry blood toward heart

veins

the exchange sites between blood and tissues

capillaries

innermost layer; composed of endothelium (simple sq.), subendothelial con. tissue; regulates diffusion, permeability; smooth surface to minimize resistance to blood flow

tunica intima

middle layer; contains smooth muscle and elastic fibers; controls vessel diameter and responsible for vasoconstriction and vasodilation; thickest layer in arteries, less developed in veins

tunica media

outermost layer, composed of collagen fibers, connective tissue; provide structural support and anchors vessels; contains vasa vasorum (in large vessels) which supply vessel walls

tunica externa (adventitia)

carry blood away from heart, high-pressure vessels, contain thick walls, transport blood under pressure, maintain flow during cardiac cycle

arteries

largest arteries (ex/aorta), high elastic fiber content allows them to stretch and recoil, smoothing out pressure fluctuations

elastic arteries

medium-sized arteries, smooth muscle, distribute blood to organs, control blood flow via contraction

muscular arteries

smallest arteries, most important for regulating blood pressure via systemic blood pressure via vasoconstriction and dilation, controlling blood flow into capillary beds, site of peripheral resistance

arterioles

smallest vessels, connect arterioles to venules, single endothelial layer and a basement membrane, function= oxygen, carbon dioxide, nutrients, wastes

capillaries

most common, tight junctions limit but do not prevent fluid movement

continuous capillaries

have pores (fenestrations) for increased permeability, found in kidneys, small intestine

fenestrated capillaries

large gaps for passage of cells and large molecules, incomplete basement membrane (ex/liver, bone marrow, spleen)

sinusoid capillaries

network between arteriole and venule, regulates blood distribution, exchange efficiency; starts with arteriole and ends with a venule

capillary beds

regulate the flow of blood entering the capillary bed

pre-capillary sphincters; open → blood enters caps closed → blood bypasses cap bed

channel that connects arteriole directly with venule (metarteriole-thoroughfare channel)

vascular shunt

actual vessels involved in exchange

true capillaries

carry blood toward the heart under low pressure, have thinner walls and larger lumens than arteries, contain valves (especially in limbs) to prevent backflow

veins and venules

collect blood from capillaries and merge into larger veins

venules

act as blood reservoirs

vein functions

prevent backflow, especially important in lower limbs, failure leads to varicose veins (enlarged veins)

valves

deliver oxygen, nutrients, hormones, and removes wastes through coordinated blood flow

circulatory system

refers to the volume of blood moving through a vessel, tissue, or organ per unit time (cardiac output)

blood flow

blood flows from areas of __ pressure to _ , driven by pumping of the heart and pressure gradients

higher, lower

volume pumped per minute

cardiac output

force on vessel walls

blood pressure

opposition to flow, mainly due to vessel diameter

resistance

thickness of blood, depends on RBC count and plasma proteins; increases resistance

blood viscosity

as resistance increases, what decreases?

blood flow

measurement of amount of friction blood encounters with vessel walls, generally in peripheral circulation

blood flow resistance

the thickness or “stickiness” of blood due to formed elements (RBC) and plasma proteins; greater viscosity, less easily molecules can move

blood viscosity

longer vessels, more resistance

vessel length

greatest influence on resistance, small changes = LARGE effects, main regulatory factor, frequent changes alter peripheral resistance; resistance varies inversely (one up, other down) between radius and resistance

blood vessel diameter

decreases lumen diameter, increasing resistance and blood pressure

vasoconstriction

increases lumen diameter, reducing resistance and blood pressure

vasodilation

controlled by smooth muscle in vessel walls, influenced by the ANS and chemical signals

vessel diameter

measured in millimeters of mercury as systolic/diastolic

blood pressure

pressure during ventricular contraction; normal is less than 120 mmhg

systolic pressure

pressure during ventricular relaxation; normal is less than 80 mmhg

diastolic pressure

provides an average pressure driving blood flow to tissues

mean arterial pressure (MAP)

difference between systolic and diastolic pressure

pulse pressure

throbbing of arteries due to difference in pulse pressures (systolic and diastolic), pressure wave from heart contraction

pulse

pulse and blood pressure, along with respiratory rate and body temperature

vital signs

taken at the wrist, most routinely used for taking a pulse, count number of beats per minute to get heart rate

radial pulse

measured indirectly by auscultatory methods using a sphygmomanometer; location is in the brachial artery

blood pressure measurement

inflate cuff, stops flow, slowly release pressure until flow returns, listen for korotkoff sounds

procedure for BP measurement

first sound is? sound disappears?

systolic, diastolic

neural and hormonal mechanisms adjust vessel diameter and heart rate to meet immediate demands (sympathetic and parasymp. stimulation)

short term regulation

epinephrine, norepinephrine, ADH, RAAS increase BP; ANP decreases BP

hormonal influences

renal mechanisms adjust blood volume via urine output

long-term regulation

chronically elevated BP increases risk for heart disease, stroke, and kidney failure

hypertension

abnormally low BP can lead to inadequate tissue perfusion and shock

hypotension

atherosclerosis and arteriosclerosis alter

resistance and impair flow

venous pressure=low, factors include muscular pump, respiratory pump, and sympathetic venoconstriction

venous return

contraction of skeletal muscles “milks” blood back toward heart; valves prevent backflow

muscular pump

pressure changes during breathing move blood toward heart by squeezing abdominal veins as thoracic veins
expand

respiratory pump

under sympathetic control, smooth muscles constrict,
pushing blood back toward heart

sympathetic venoconstriction

contraction __ veins, propelling blood _ heart

squeezes, toward

prevent retrograde flow

one way valves

essential during upright posture and exercise

skeletal muscle pump

distributing blood from the heart to tissues

arterial system is high pressure

returning blood to heart, aided by valves and skeletal muscle pumps

venous system is low pressure

alternate pathways for blood flow; important for maintaining perfusion if a vessel is blocked

anastomoses

carries blood between the heart and lungs for gas exchange

pulmonary circulation

delivers oxygenated blood to tissues and returns deoxygenated blood to the heart

systemic circulation

blood flows in a closed loop: name pathway

heart → arteries → capillaries → veins → heart

left ventricle → aorta → systemic arteries → systemic capillaries → systemic veins → right atrium; supplies oxygen, nutrients, and hormones to all body tissues

systemic circulation

includes coronary circulation (heart muscle), cerebral circulation (brain), and hepatic portal circulation (GI tract to liver)

systemic circulation

deliver oxygenated blood from aorta to all tissues, organized into major branches serving head, neck, thorax, abdomen, and limbs

systemic arteries

right ventricle → pulmonary trunk → pulmonary arteries → lungs → pulmonary veins → left atrium

pulmonary circulation

exchange of gases, oxygenates blood and removes carbon dioxide

pulmonary circulation

carry deoxygenated blood; pulmonary veins carry oxygenated blood (opposite of systemic pattern)

pulmonary arteries

supplies myocardium, blockage can lead to myocardial infarction

coronary circulation

brain blood supply, including the Circle of Willis for redundancy

cerebral circulation

directs nutrient-rich blood from digestive organs to the liver for
processing before entering systemic circulation

hepatic portal circulation

special structures (ductus arteriosus, foramen ovale, ductus venosus); allow blood to bypass fetal lungs and liver; these close after birth.

fetal circulation

ductus arteriosus and foramen ovale shunt blood away from the lungs

fetal shunts

between pulmonary trunk and aorta

ductus arteriosus

between left and right atrium

foramen ovale

brings blood from umbilical vein to inferior vena cava and bypasses the liver since the fetus is not processing food yet from
the digestive system

ductus venosus

largest artery in the body; ALL arteries branch off this

aorta

R/L coronary arteries

ascending aorta

supplies right side of the head and neck, and right upper extremity (ARCH OF AORTA)

brachiocephalic trunk

supplies left side of the head and neck (ARCH OF AORTA)

left common carotid artery

supplies left upper extremity (ARCH OF AORTA)

left subclavian

supplies stomach, liver, spleen (DESCENDING AORTA)

celiac trunk

supplies kidneys (DESCENDING AORTA)

R/L renal artery

supplies the colon/intenstines (DESCENDING AORTA)

superior and inferior mesenteric arteries

supplies lower extremities (DESCENDING AORTA)

R/L common iliac arteries

anastomotic ring at base of brain; supplies the brain; internal carotid arteries (anterior) and vertebral arteries (posterior)

circle of Willis

drains upper body, formed by merging of the r/l brachiocephalic veins

superior vena cava

drains lower body; formed by merging of the r/l common iliac veins

inferior vena cava

drain blood from kidneys to IVC

r/l renal veins

drains lower extremities towards IVC

common iliac veins

buildup of plaque in arterial walls, reducing blood flow

artherosclerosis

incompetent venous valves leading to pooling of blood; common in lower limbs under high hydrostatic pressure; risk factors= pregnancy, prolonged standing

varicose veins

localized dilation of an artery due to wall weakness, risk of rupture and hemorrhaging

aneurysm