cardiovascular - blood vessels and circulation

does smooth muscle have sarcomeres?

no, actin & myosin are not organized into sarcomeres in smooth muscle = non-striated appearance

approx actin:myosin in smooth muscle vs straiated muscle cells

smooth = ~15:1, far greater than striated = ~2:1

dense bodies

function like Z-lines of striated muscle cells

where actin is anchored

contraction speed of smooth muscle

slow

portal systems (parts of circulatory system)

large vessels otw to heart become

smaller vessels that supply tissues become

larger vessels that return to the heart

*breaks normal hierarchy of vessels becoming continuous smaller or larger

major example of portal systems in mammals - hepatic portal system

venous blood returning to the heart from the digestive tract via the hepatic portal vein first pass through a capillary network in the liver before entering the vena cava of the heart via the hepatic vein

lymphatic system - subsystem of the circulatory system

network of lymphatic vessels, lymph nodes, and associated organs/tissues (e.g. bone marrow, spleen, and thymus)

function of lymphatic system

drain interstitial fluids and returns leaked fluids (collected by lymph capillaries) and proteins back to the cardiovascular system via the subclavian vein

lymph

the fluid traveling in lymphatic vessels

*very similar in composition to interstitial fluid

endothelium

the inner lining of the entire circulatory system composed of a specialized type of simple squamous epithelium called endothelial cells

function of endothelium

to form the barrier between vessels and tissue to control the movement of substances, fluid, and white blood cells

vascular endothelial cells

line the interior of all blood vessels and the interior of the heart (endocardium)

lymphatic endothelial cells

line the interior of all lymphatic vessels

endothelial cells are a specialized type of

simple squamous epithelium

arteries carry

oxygenated blood away from the heart

*exceptions: pulmonary and umbilical arteries that carry deoxy blood to the organs that oxygenate it (the lungs and placenta, respectively)

artery sizes

elastic artery: largest, ex: aorta →

muscular arteries: can change in diameters via contracting & dilating due to smooth muscle →

arterioles →

capillaries →

function of capillaries

site of exchange of substances between vasculature and surrounding interstitial fluid

vein sizes

capillaries

venules →

medium veins →

large veins: return blood to the heart, ex: vena cava

veins carry

deoxygenated blood towards the heart

*exceptions: pulmonary and fetal veins that carry oxygenated blood

tunica intima

the innermost layer of an artery or vein consisting mainly of endothelial cells and a supporting internal elastic lamina

tunica media

the middlemost layer of an artery of vein made up of smooth muscle cells and elastic connective tissue

tunica externa

the outermost layer of an artery or vein made up of connective tissue comprised of collagen and elastin fibers

traits of artery walls vs veins

artery walls contain more smooth muscle, are more elastic, and often have a smaller diameter than veins

which part of circulatory system generally has higher blood pressure?

arteries

*highest during ventricular systole

what is special about veins?

they have one-way valves to prevent backflow of blood while the blood is moving back up toward the heart

skeletal muscle pump

skeletal muscle contraction that squeeze on intramuscular veins, pushing venous blood back toward the heart

microcirculation

blood circulation in the smallest blood vessels (pre-capillary aterioles, metarterioles, capillaries, and post capillary venules) present in most tissues of body

function of microcirculation

delivers O₂ & nutrients to tissue cells

removes CO₂ & waste products formed by cells

regulates local blood flow and tissue perfusion → affecting BP, edema, and thermoregulation

pre-capillary sphincters is composed of

smooth muscle cells

pre-capillary sphincters determines

amount of blood that enters capillary beds

pre-capillary sphincters react to

level of O₂/CO₂ in capillary bed

low O₂/high CO₂ = opens sphincters (dilates vessels coming in)

high O₂/low CO₂ = closes sphincters (constricts vessels coming in)

where is BP highest? lowest?

highest: in ascending aorta as blood leaves the left ventricle

lowest: in vena cava before returning blood into right atrium

systolic arterial blood pressure

highest blood pressure measured when ventricles contract (ventricular systole)

diastolic arterial blood pressure

lowest BP measured when ventricles relax (ventricular diastole)

pulse pressure =

difference between systolic and diastolic BP

autoregulation

process by which lack of tissue oxygen or increase in carbon dioxide creates local vasodilation of vascular smooth muscle thereby increasing local blood flow

when cardiac output is increased via sympathic neural stimulation of SA node, what happens to blood vessels?

skeletal muscle & heart: vasodilation

other organs (like intestines): vasocontriction

baroreflex - high BP

increased activation of cardioinhibitory center = decreased cardiac output

decreased activation of cardiostimulatory center = decreased cardiac output

decreased activation of vasomotor center = vasodilation

capillary hydrostatic pressure

pressure at capillary bed determined by ratio between pressure in artery and vein

high arterial BP = high capillary bed pressure

blockage in veins = high capillary bed pressure

can lead to edema

blood osmotic (colloid oncotic) pressure

osmotic pressure exerted by molecules too large to leave capillaries, such as proteins

large molecules are what draw fluid in