CH 2 Blood Vessels and Circulation

unique feature of capillaries

they have “leaky” walls via either clefts or fenestrations

cleft

incomplete tight junction

pulmonary circuit

moves blood from the right side of the heart to the lungs and back to the heart.

systemic circuit

moves blood from left side of the heart to the head and body and returns it to the right side of the heart to repeat the cycle.

walls arteries vs veins

thicker walls, smaller lumen, and elastic membrane

types of arteries

elastic, muscular, arteriole

arteriole

very small artery that leads to a capillary. have the same three tunics as larger vessels but way thinner

perfusion

distribution of blood into the capillaries so they can supply tissues with blood

flow through capillaries is often described as

microcirculation

types of capillaries

continuous, fenestrated, sinusoid

sinusoid capillary

the most leaky, allowing for the largest molecules to pass through. has incomplete basement membrane and intercellular gaps

fenestrated capillary structure

has pores (fenestrations) along with tight juncs allowing for large molecules to pass through

continuous capillaries

least leaky, have complete endothelial lining with incomplete tight junctions between cells allowing for small molecules to pass through

fenestrated capillary locations

small intestine, kidneys, choroid plexus of the brain, and endocrine structures

sinusoid capillary locations

lymph nodes, liver, bone marrow, spleen, pituitary gland + other endo glands

continuous capillary locations

everywhere (all vascularized tissue)

metarteriole function

serve as thoroughfare channels to the venules which bypass the capillary bed, or as conduits to supply the capillary bed with blood

metarteriole

a short vessel arising from a terminal arteriole that branches towards the capillary bed

capillary bed

network of 10–100 capillaries connecting arterioles to venules

precapillary sphincters

smooth muscle sphincters surrounding the entrance to a capillary that can open or close to regulate blood flow

where does blood go if precapillary sphincters are closed

flows directly from the metarteriole to the thoroughfare channel

thoroughfare channel

tube from the metarteriole that bypasses the capillary bed and directly connects to venules

why do pre capillary sphincters need to close? what would happen if all of them stayed open

they would collectively hold all of the blood in the body leaving the veins and arteries empty

when do precap sphincters open

when the surrouding tissue needs oxygen and have excess waste products

vascular shunt

the continuation of metarteriole and thoroughfare channel that allows blood to skip the capillary beds and go straight to venule

arteriovenous anastomosis

short vessel connecting an arteriole directly to a venule and bypassing the capillary beds

is blood flow through capillary beds smooth or pulsating

pulsating

vasomotion

irregular, pulsating flow of blood through capillaries and related structures

where does blood go if precap sphincters are open

through the capillary bed

veins vs venule

veins are larger and have valves to prevent back flow of blood. venules are basically mini veins without valves

venule

an small vessel leading from the capillaries to veins

skeletal muscle pump

a system promoting venous return of blood during locomotory activity, is done via peripheral veins

peripheral veins

veins in your limbs with one-way valves that direct flow away from the limb and toward the heart

how does the skeletal muscle pump work

when body is in motion skeletal muscles contract, peripheral veins in between them undergo compression causing their valves to open and push blood upwards. when body is relaxed, peripheral veins become decompressed and the blood remains.

variations in circulatory pathways

1. simple pathway: one capillary bed

2. portal system: 2 cap beds

3. arteriovenous anastomosis (shunt/highway)

4. venous anastomoses

5. arterial anastomoses

blood flow

refers to blood movement through vessel/organ/tissue, is measured in volume of blood per unit of time

resistance

any factors that slow or counteract blood flow

blood pressure

the force blood exerts on the walls of a vessel or heart chamber

hydrostatic pressure

the force exerted by a fluid due to gravitational pull, usually against the wall of the container its in

systemic arterial blood pressure

blood pressure without any specific descriptors, follows the pressure of blood flowing in systemic arteries

clinical measure of blood pressure

mm/Hg “milimeters of mercury”

why is it measured in milimeters of mercury

because the old historical machine they used to measure BP was a vertical tube of mercury (Hg) and they would measure how high it would get in mm to find BP

systolic and diastolic pressure

expressed as systolic pressure over diastolic pressure, the higher value is systolic and lower value is diastolic

normal adult blood pressure

120/80

systolic pressure

higher value, reflects arterial pressure resulting from the ejection of blood during ventricular contraction (systole)

diastolic pressure

lower value, represents arterial pressure of blood during ventricular relaxation (diastole)

pulse pressure

systolic pressure - diastolic pressure

mean arterial pressure (MAP)

represents the average pressure of blood in the arteries, formula is diastole + pulse pressure divided by 3

systole

contraction of ventricle muscles to release blood

diastole

ventricular relaxation

pulse sites of head and neck

temporal artery, facial artery, common carotid artery

pulse sites of the limbs

brachial artery, radial artery, popliteal artery, posterior tibial artery, dorsalis pedis artery, femoral artery

variables affecting blood flow and BP

cardiac output, compliance,volume of the blood, viscosity of the blood, blood vessel length and diameter

cardiac output

measurement of blood flow from the heart through the ventricles, usually measured in liters per minute

compliance

the ability of any compartment to expand to accomodate extra content (eg, heart and veins)

what is reduced when an artery is stiffened

compliance

there is a _____ correlation between blood volume, BP, and blood flow

positive

if blood volume decreases, BP and blood flow:

decrease

Hypovolemia

decrease in blood volume

Hyperlovenia

increased blood volume

viscocity of the blood is directly proportional to

resistance

viscocity is inversely proportional to

blood flow

The length of a blood vessel is directly proportional to its

resistance (bc gravity)

2 main determinants of blood viscocity

formed elements and plasma proteins

length of blood vessels during childhood vs adulthood

increase during childhood, stagnate during adulthood

the diameter of blood vessels _______ throughout the body depending on ___

changes, the type of vessel

the diameter of any given BV can _______ throughout the day

change

the diameter of BVs can quickly change in response to

neural and chemical signals that trigger vasoconstriction or vasodialtion

vascular tone

the contractile state of the smooth muscle and primary determinent of diameter

the effect of vessel diameter on resistance is

inverse (given the same volume of blood)

increased BV diameter means:

less blood contacting the walls, lower resistance, increased flow

decreased BV diameter

more blood contacting the walls, higher resistance, decreased flow

review: positive vs negative feedback mechanism

positive: when a product of a reaction leads to an increase in that reaction, strays from equillibrium

negative: when a product of a reaction leads to a decrease in that reaction, maintains equillibrium

example of positive feedback in cardiovascular system

blood clotting

example of negative feedback in cardiovascular system

blood pressure regulation

blood being pumped in the arteries goes from areas of _______ pressure to ______

higher, lower

transcytosis

transport of large molecules across capillary walls

mechanism of vasoconstriction and vasodilation

smooth muscles of the vessel walls either contract or relax to adjust their diameter, regulating blood flow

vasoconstriction/dialation is regulated by:

sympathetic nervous system and hormones

bulk flow

the mass movement of fluids into and out of capillary beds and tissue

bulk flow involves 2 pressure driven mechanisms:

filtration and reabsorption

filtration is driven by

hydrostatic pressure

reabsorption is driven by

osmotic pressure

what does osmotic pressure do

draws fluid back in

what does hydrostatic pressure do

push fluid out

hydrostatic pressure depends on __________ pressure

systolic blood pressure

osmotic pressure depends on

concentration of plasma proteins

elastic artery

arteries located close to the heart with a larger lumen and lots of elastic fibers

elastic artery functions

elasticity causes recoil during blood pumping which helps maintain the pressure gradient that circulates blood, large lumen allows it to accept large amounts of blood

Reabsorption: _____ → _______

tissues (interstital fluid) to capillaries

Filtration: _____ → _____

capillaries to tissue (intersital fluid)