exam 4- circulatory 2 Flashcards by Lindsey Kuipers

arteries are composed of 3 layers of tissue:

1- internal layer called tunica intima (made of single layer of endothelial cells which contact blood)

2- middle layer called tunica media (made of collagen, elastic fibers, and smooth muscle - the proportions depend on the type of artery) - tunica media is very thick & well-developed

3- outer layer called tunica adventitia (made of connective tissue)

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name 3 classes of arteries

1- elastic artery
2- muscular artery
3- arteriole

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describe properties of elastic arteries

1- the largest arteries- closest to the heart
2- ex: aorta, pulmonary artery, common carotid, subclavian, and common iliac
3- very thick tunica media made primarily of elastic fibers (proportion of smooth muscle is low)
4- very thin tunica adventitia - very flexible, when blood pumped in, can expand like a spring
5- very poorly innervated, not a lot of NS control – contract mainly due to heart –> so called conducting arteries (conduct blood from heart to other arteries

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what controls arterial smooth muscle tone?

sympathetic NS

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which arteries are called the conducting arteries and why

elastic arteries
contract mainly due to heart (not NS control) - conduct blood from heart to other arteries

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describe properties of muscular arteries

1- medium-sized
2- ex: superior mesenteric, radial artery (most of the smaller unnamed arteries)
3- tunica media made primarily of smooth muscle- 25-40 layers (low proportion of elastic fibers)
4- primarily innervated by the sympathetic NS, have abundance of alpha1 receptors on them –> called the distributive arteries (responsible for distributing blood to major organ systems of the body by opening or closing diameter
5- smaller muscular arteries are adapted for vasodilation & vasoconstriction

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describe properties of arterioles

1- smallest diameter arteries & have the thinnest walls
2- tunica intima has single layer of endothelial cells
3- tunica media has only 1 or 2 surrounding layers of smooth muscle
4- feed blood to individual capillary beds
5- what sets them apart= circular rings of smooth muscle around each capillary –> creates a pre-capillary sphincter (this opens or closes the capillary bed, controls blood flow to capillary beds within tissues)
6- typically not innervated, they respond to diff signals

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list the 4 functions of arteries

1- route of distribution of blood from heart to major organ systems of body

2- pressure reservoir

3- dampen pressure oscillations of the heart

4- regulates distribution of blood to systemic organs

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describe the arterial function of pressure reservoir

when LV contracts, it generates large pressure (120 mmHg) –> this gets pushed into elastic arteries which stretch & expand –> when heart relaxes, pressure drops to 0 –> elastic arteries then spring back and apply inward pressure on the blood in them (stores pressure when heart contracts & releases it when heart relaxes)

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describe the arterial function of dampening pressure oscillations of the heart

ventricle contracts (systole- 120 mmHg), ventricle relaxes (diastole- 0 mmHg)

huge change/pressure oscillation, the diff b/w systolic & diastolic pressure is called the pulse pressure –> in the ventricle, results in a pulsatile flow (flow in discrete individual pulses) - not good for supplying metabolically active tissue with blood (gets blood, then no blood; gets oxygen, then no oxygen)

–> so what happens is when the heart/ventricle contracts, the systolic pressure in aorta is 120 mmHg, but when heart relaxes, the aorta releases stored pressure, its diastolic pressure only drops to 80 mmHg (so pulse pressure is only 40 mmHg, much less of a fluctuation) – by storing & releasing pressure of the heart, the arteries dampen the pressure oscillation (arteries convert pulsatile flow to laminar flow- continuous flow in smooth lines)

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describe the arterial function of regulating distribution of blood to systemic organs

regulates distribution by opening or closing pre-capillary sphincters – not every capillary bed in body is open at one time

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what is the major feature of veins structurally

they still have the 3 layers (tunica intima, media & adventitia), but the tunica media is much less developed
–> very little smooth muscle in veins

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describe the 2 major functions of veins

1- route of return of blood to the heart

2- volume reservoir: means that at rest, about 60% of total blood volume is in your veins (blood volume not evenly distributed throughout circulatory system)
- reservoir for when you need extra blood, for example, during exercise- drawn into arteries to feed active metabolizing tissue, or, if you are injured and are losing blood, the blood lost from artery will be replaced by draining down reserve in the veins
- veins are considered high volume, low pressure component of the system (but if low pressure, how does blood flow thru the veins…?)

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___% of blood volume is in arteries % arterioles at a given time

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how is blood able to flow through veins since veins have low pressure?

veins run through major skeletal muscle systems of the body (whenever you move and contract skeletal muscle, skeletal muscle squeezes down on veins, putting external pressure on the veins, moving blood thru them)

one way direction thru pocket valves (when blood moves toward heart, pocket valves relax- when moving backward, pocket valves close & prevent backflow

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what happens if pocket valves of veins are damaged?

can get swelling veins called varicose veins

describe the size and amount of capillaries in the body

5-8 microns in diameter and 1 mm long (smallest type of blood vessel)
- billions of capillaries in the circulatory system feeding all tissues (any individual cell in the body is no more than 2 or 3 cells away from a capillary)
- for every pound of fat you gain, have to create 200 miles of capillary to supply blood to that tissue

name the 3 classes of capillaries and what determines their classification

1- continuous
2- fenestrated
3- sinusoid

classification depends on cellular structure & the permeability properties of each- in general, capillaries only have 1 layer (single layer of endothelial cells- no tunicas), how the endothelial cells are arranged determines the class

continuous capillaries: describe their permeability & where they are located

the least permeable

make up the capillary beds that act as barriers b/w blood and tissue (most common one is blood-brain barrier)

fenestrated capillaries: describe their permeability & where they are located

a little more permeable (middle)

make up capillary beds involved in filtration & absorption (predominantly in kidney for filtration and in intestines/GI for absorption)

sinusoid capillaries: describe their permeability & where they are located

the most permeable – can allows cellular components (RBCs) to cross b/w capillaries & tissues

involved in organ systems like the bone marrow & spleen that can store and release RBCs into the blood

describe the arrangement of endothelial cells in fenestrated capillaries

endothelial cells are perforated with a lot of window-like pores that increase the permeability of these capillaries; the adjacent endothelial cells are arranged so that there are spaces/clefts b/w them to increase permeability (strainer with a fine mesh)

describe the arrangement of endothelial cells in sinusoid capillaries

the spaces in b/w cells are really big, can allow cells to squish through them (incomplete membrane to hold capillary together- very flimsy and porous)

strainer with a large mesh

describe the arrangement of endothelial cells in continuous capillaries

no spaces, held together by tight junctions to not allow anything to cross (no fenestrations/clefts)

associated with the astrocytes (surrounding cells help regulate what crosses), transport b/w the capillary and cerebrospinal fluid across blood-brain barrier is very tightly controlled

for the blood vessels of the circ system, high surface area = __ diffusion barrier

small

how much total blood volume do capillaries contain at any one time?

only 5% b/c even tho there are so many capillaries, not all capillary beds are open at the same time- typically, more than 50% of capillary beds of the body are closed at any given time

name the 3 interacting mechanisms that regulate blood flow and controls which capillary beds get blood

1- sympathetic control: maintains high arterial pressure 2- reflex cardiovascular control (baroreceptor reflex) 3- local control

there are 3 interacting mechanisms that determine which capillary beds get blood, but the overriding theme is...

there is a hierarchy of importance- certain tissues need a constant supply of blood, will always get high flow, high distribution, their capillary beds will always be open --> these 2 tissues are the brain and the heart

describe 1st mechanism to regulate blood pressure and cap blood flow -- sympathetic control

body has to maintain high arterial pressure to keep blood going to the brain and heart - this is controlled by sympathetic NS (innervates ventricles of the heart & innervates smooth muscle of the muscular arteries) - helps with the baseline high BP necessary for constant supply to brain & heart - sympathetic stimulation is excitatory on ventricles of the heart by way of beta1 receptors --> increase heart rate & strength of contraction - symp stimulation on smooth muscle of muscular arteries - maintains constant flow to brain & heart

describe the 2nd mechanism to regulate BP and cap blood flow- reflex cardiovascular control, baroreceptor reflex

constant continuous monitoring of BP by baroreceptors (baroreceptors located in aortic arch, super impt ones in the carotid sinus) at the base of the internal carotid artery, there is a swelling that makes a sinus --> the wall of the sinus is much thinner than normal artery wall, so its more sensitive to pressure changes -- buried in the muscular wall of carotid sinus are the baroreceptors (these are very thin, finely-branched nerve endings that have ion channels that respond to the stretch of the membrane --> when membranes stretch, cause APs to generate in the nerve ending baroreceptors --> changes activity of the baroreceptors --> send their signals up NS to medulla oblongata to the cardiovascular regulatory center in the medulla stretch-activated receptors, mechanically-gated channels

how do the baroreceptors work to change blood flow?

if blood pressure goes up --> stretches the carotid sinus to activate baroreceptors --> receptors generate high frequency APs --> APs go to medulla oblongata regulatory center & activate parasympathetic NS --> para neurons inhibit sympathetic neurons --> sends signal to vagus nerve (inhibits pacemaker of heart & slows down heart) --> reduces cardiac output, which brings BP back down to normal if BP gets too low --> carotid sinus contracts & loses tension --> reduces firing rate of baroreceptors --> stimulates sympathetic excitatory neurons in medulla and shuts down parasympathetic --> sympathetic stimulates ventricles of the heart, increases cardiac output and stimulates vascular tone in muscular arteries --> brings BP back up to normal

what is the relationship b/w BP and heart rate

inverse relationship BP increases --> heart rate slows down

3rd mechanism to control capillary blow flow is local control, this is done at site of...

pre-capillary sphincters which feed individual capillary beds

___ is a temporary sensation for loss of blood flow to a tissue

ischemia

___ is an increase in blood flow to a certain tissue/capillary

hyperemia

what are the 2 diff types of hypereima

active & reactive

___ hyperemia = increase in blood flow to a tissue due to an increase in metabolic output to that tissue

active

___ hyperemia = increase in blood flow as a reaction and after an ischemic event (making up for the loss of blood flow)

reactive

describe local blood flow

local blood flow determined by the activity state of the tissue - when tissue changes activity state (from rest to active), the pre-capillary sphincters will open --> increases blood flow to that tissue (ex: skeletal muscle going from rest to active - these pre-capillary sphincters are not innervated, rather, they constrict or relax in response to changes in local chemical composition of the blood (when skeletal muscle active, contracting, it is using oxygen --> decrease in blood oxygen and local CO2 levels go up --> use a lot of glucose, so levels of blood glucose go down --> b/c CO2 going up, producing protons, so pH is going down --> electrical activity going on (as a result of repolarizations, capillary potassium goes up) --> this all acts on the ion channels in these muscles, muscle is inhibited and relaxes --> cap beds open up and blood flow increases when tissue goes back to rest, all these reverse (CO2 goes down, oxygen goes up, K goes down, pH goes up)