blood vessels

the delivery system of dynamic structures that begins and ends at the heart

ateries

carry blood away from the heart - the blood is oxygenated except for pulmonary circulation and umbilical vessels of a fetus

capillaries

contact tissue cells and directly serve cellular needs - endothelium with sparse lamina

veins

carry blood towards the heart

venous system

heart - large veins (capacitance vessels) - small veins (capacitance vessels) - postcapillary venule - thoroughfare channel - capillaries

arterial system

- elastic arteries (conducting vessles) - muscular arteries (distributing vessels)-

layers of the blood vessel wall are in order from the inside out

lumen
layer one -tunica intima: endothelium - subendothelial layer -internal elastic lamina
layer two - tunica media: smooth muscle and elastic fibers - external elastic lamina
layer three- tunica externa; collagen fibers

lumen

central blood containing space, which is surrounded by three distinct layers or tunics.

tunica intima

the innermost tunic - it is in intimate contact with the blood in the lumen
simple squamous endothelium lines the lumen of all vessels, in vessels larger than 1 mm a subendothelial connective tissue basement membrane is present

tunica media

smooth muscle and sheets of elastin, sympathetic vasometer nerve fibers control vasoconstriction and vasodialation of vessels

vasoconsctriction

reduction in lumen diameter as the smooth muscle contracts

vasodialation

increase in lumen diameter as the snooth muscle relaxes

tunica externa (also known as tunica adventitia)

collagen fibers protect and reinforce, large vessels contain vasa vasorum to nourish the external layer

vasa vasorum

a system of tiny blood vessels theat nourish the more external tissues of the blood vessel wall -its own blood supply

Arteries:

•Arteries have three layers: a smooth inner layer, a muscular layer, and a thin outer layer.
•Arteries, with the exception of the pulmonary artery, carry oxygenated blood from the heart to the body.
•Arteries are of greater size, thickness and elasticity than veins.
•Blood in arteries is under significant pressure.
•Arteries do not contain valves; valves would be unnecessary considering the force that is already applied to the blood in arteries.

Veins:

•Veins, like arteries, have three layers: a smooth inner layer, a muscular layer, and a thin outer layer.
•Veins, with the exception of the pulmonary vein, carry deoxygenated blood that has been used by body tissue back to the heart. Veins, as well as carrying deoxygenated blood, carry waste products.
•Veins are smaller, thinner and much less elastic than arteries.
•Blood in veins does not experience as much pressure as blood in arteries.
•Veins contain valves to prevent back flow of blood.

atery and vein

label

A. Tunica intima
C. Tunica media
D. External elastic lamina
E. Tunica externa
B. Internal elastic lamina

elastic ateries

large thick walled arteries with elastin in all three tunics, near the heart the aorta and its major branches, large lumen offers low resistance sometimes referred to as conducting arteries, act as pressure resevoirs - expand and recoil as blood is ejected from the heart
average lumen diameter 1.5 cm
average wall thickness 1.0 mm

lumen

central blood containing space

capillaries

endothelium with sparse basal lamina

tunica intima

simple squamous endothelium, lines the lumen of all vessels in vessels larger than 1 mm a subendothelial connective tissue basement membrane is present

tunica media

smooth muscle and sheets of elastin, sympathetic vasomotor nerve fibers control vasoconstriction and vasodialation of vessels

tunica externa (tunica adventitia)

collagen fibers protect and reinforce, larger vessels contain vasa vasorum to nourish the external layer

elastic conducting ateries

large thick walled arteries with elastin in all three tunics, the aorta and its major branches, large lumen offers low resistance, acts as pressure reservoirs - expand and recoil as blood is ejected from the heart

lumen

internak hollow space

muscular(distributing) arteries and arterioles

distal to elastic arteries, deliver blood to body organs, have a thick tunica media with more smotth muscle, active in vasocontriction, controls blood flow through tissues

arterioles

smallest arteries, lead to capillary beds, control flow into capillary beds via vasodialation and vasoconstriction

vasodialation

relaxation of the smooth muscles of the blood vessels, producing dialation

vasoconstriction

narrowing of blood vessels

capillaries

microscopic blood vessels, walls of thin tunica intima, one cell thick, pericytes help stablize their walls and control permeability, size allows only a single RBC to pass at a time, inall tissues except for cartilage, epithelia, cornea and lens of eye.

capillaries - function

exchange gases, nutrients, wastes, hormones, etc.

the three structural types of capillaries

continuous capillaries
fenestrated capillaries
sinusoidal capillaries (sinusoids)

continuous capillaries are abundant where

in the skin and muscles
held together by tight junctions connect endothelial cells and intercellular clefts allow the passage of fluids and small solutes

continuous capillaries of the brain - junctions

tight junctions are complete, forming the *blood brain barrier*

fenestrated capillaries

some endothelial cells contain pores (fenestrations) more permeable then continuous capillaries - function in absorption or filtrate formation (small intestines, endocrine glands, and kidneys)

sinusoidal capillaries

fewer tight junctions, larger intercellular clefts, large lumen, usually fenestrated, allow large molecules and blood cells to pass between the blood abd surrounding tissues

where are sinusoidal capillaries found

in the liver, bone marrow and spleen

where do the clefts sit

in between the cells

capillary beds

are interwoven networks of capillaries form the microcirculation between arterioles and venules

capillary beds consist of two types of vessels what are they

1. vascular shunt (metarteroile - thoroughfare channel) directly connects the terminal arteriole and a postcapillary venule
2. true capillaries - 10 - 100 exchange vessels per capillary bed - they branch off the metarteriole or terminal arteriole

precapillary sphincters do what

regulate blood flow into true capillaries; regulated by local chemical conditions and vasomotor nerves

when are venules formed

when capillary beds unite, they are very porous and allow fluids and WBC's into tissues - post capillary venules consist of endothelium and a few pericytes, larger venules have on or two layers of smooth muscle cells

which are bigger veins or capillaries

veins

When are veins formed

when venules converge, have thinner walls, larger lumens compared with corresponding arteries, blood pressure is lower than in arteries, thin tunica media and a thick externa consisting of collagen fibers and elastic networks - called capacitance vessels (blood reservoirs) contain up to 65% of the blood supply, are adaptations that ensure return of blood to the heart

pericyte

adventitial cell or mural cell, is a connective tissue cell that occurs about small blood vessels.[

what purpose do large diameter lumens offer in the veins

they offer little resistance

what purpose do valves offer in the veins

prevent the backflow of blood - most abundant in veins of the limbs

what are venous sinuses

they are flattened veins with extremely thin walls (coronary sinus of the heart and dural sinuses of the brain)

vascular anastomoses are

interconnections of blood vessels - arterial anastomoses provide alternate pathways (collateral channels) to a given body region - they are common at joints, in abdominal organs, brain and heart
vascular shunts of capillaries are example of arteriovenous anastomoses - venous anastomoses are common

blood flow -

volume of blood flowing through a vessel, an organ, or the entire circulation in a given period
- it is measured in ml/min
- equivilant to cardiac output (CO) for entire vascular system - it is relatively constant when at rest, varies widely through individual organs, based on needs

blood pressure

force per unit area exerted on the wall of a blood vessel by the blood, expressed in mm Hg
measured as systemic arterial BP in large arteries near the heart -
the pressure gradient provides the driving force that keeps blood moving from higher to lower pressure areas

resistance (peripheral resistance)

opposition of flow
measure of the amount of friction blood encounters
generally encountered in the peripheral systemic circulation

three important sources of resistance are

blood viscosity - thickness of the blood
total blood vessel length
blood vessel diameter

factors that remain relatively constant in regards to resistance are

blood viscosity - the stickiness of the blood due to formed elements and plasma proteins
and
blood vessel length - the longer the vessel the greater the resistance encountered

frequent changes that alter peripheral resistance are

blood vessel diameter - it is always changing
small diameter arterioles are the major determinants of peripheral resistance
abrupt changes in diameter or fatty plaques form atherosclerosis dramatically increase resistance * distrupt laminar flow and cause terbulance

blood flow (F) is directly proportional to what

the blood (hydrostatic) pressure gradient (delta P) if the pressure gradient increases then the blood flow speeds up

blood flow is inversely proportional to what

peripheral resistance (R)
if the resitance increases blood flow decreases

flow =

pressure gradient divided by peripheral resistance

peripheral resitance is more important in influencing local blood flow because of what

it is easily changed by altering blood vessel diameter

what generates blood flow

the pumping action of the heart

pressure results when what

when flow is opposed by resistance

systemic pressure is

highest in the aorta
declines throughout the pathway
is 0 mm Hg in the right atrium

the steepest drop occurs where

in the arterioles

arterial blood pressure reflects what

two factors of the arteries close to the heart - elasticity (compliance or distensibility) volume of blood forced into them at any time
30

pulse near the heart is what

pulsatle

systolic pressure

pressure exerted during ventricular contraction

diastolic pressure

lowest level of arterial pressure

pulse pressure

difference between systolic and diastolic pressure

mean arterial pressure

pressure that propels the blood to the tissues

MAP =

diastolic pressure = 1/3 pilse pressure

when do pulse pressure and MAP both decline

with increasing distance from the heart

what is the range of capillary blood pressure

ranges from 15 to 35 mm Hg, low capillary pressure is desirable - high blood pressure would rupture fragile, thin- walled capillaries, most are very permemable, so low pressure forces filtrate into interstitial spaces

when pressure is low how does the blood move

more slowly

does venous pressure change during the cardiac cycle

very little
small pressure gradian, about 15 mm Hg
low pressure due to cumulative effects of peripheral resistance

one of the factors aiding venous return is the respiratory pump - explain

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

one of the factors aiding venous return is the muscular pump - explain

contraction of skeletal muscles "milk" blood toward the heart and valves prevent backflow

one of the factors aiding venous return is the vasoconstriction - explain

vasoconstiction of veins under sympathetic control - because of the smooth muscle

maintaining blood pressure requires what

cooperation of the heart blood vessels and kidneys
supervision of the brain

what are the main factors influencing blood pressure

cardiac output (CO)
peripheral resistance (PR)
blood volume
•F = P/PR and CO = P/PR

Blood pressure =

= CO x PR (and CO depends on blood volume)
•Blood pressure varies directly with CO, PR, and blood volume
•Changes in one variable are quickly compensated for by changes in the other variables

how is the cardiac output determined

by venous return and neural and hormonal controls

resting heartrate is maintinaed by what

the cardioinhibitory center via the parasympathetic vagus nerve

stroke volume is controled by what

venous return (EDV)

during stress the heart cardioaccelertory center increases heart rate and stroke volum via what

sympathetic stimulation

if the ESV decreases what happens to MAP

it increases

what are the short term controls of blood pressure

neural and hormonal controls
they counteract fluctuations in blood pressure by altering peripheral resistance

what are the long term controls of blood pressure

long term renal regulation
conteracts fluctuations in blood pressure by altering the blood volume

neural controls of peripheral resistance do what

maintain MAP by altering blood vessel diameter
alter blood distribution in response to specific demands

neural controls operate via reflex arcs tha tinvolve what

baroreceptors
vasomotor centers and vasomotor fibers
vacular smooth muscle

the vasomotor center is what

a cluster of sympathetic neurons in the medula that oversee changes in blood vessel diameter
part of the cardiovascular center along with the cardiac center

the vasomotor center does what

maintains vasomotor tone (moderate constriction of the arterioles)
receives inputs from baroreceptors, chemoreceptors, and higher brain centers

where are barorecptors located

in carotid sinuses, aortic arch, walls of large arteries of the neck and thorax

what happens to the baroreceptors when blood pressure increases

increased blood pressure stimulates the baroreceptors to increase input to the vasomotor center
inhibits the vasomotor center, causing arteriole dialation and venodialation
stimulates the cardioinhibitory center

what protects the blood supply to the brain

Baroreceptors taking part in the carotid sinus reflex protect the blood supply to the brain

what helps maintain adequate blood pressure in the systemic circuit

Baroreceptors taking part in the aortic reflex help maintain adequate blood pressure in the systemic circuit

what happens if the blood pressure rises above a normal range

1. blood pressure (arterial blood pressure rises above normal range)
2. baroreceptors in carotid sinuses and aortic arch are stimulated
3. impulses from baroreceptors stimalte cardioinhibitory center (and inhibit cardioacceleratory center) and inhibit vasomotor center
4a sympathetic impulses to the heart cause a decrease in HR, a decrease in contractility and a decrease in cardiac output
4b decrease rate of vasomotor impulses allows vasodialation causing a decrease in peripheral resistance

what happens if the blood pressure drops below a normal range

1. blood pressure decreases (arterial blood pressure falls below a normal range)
2.baroreceptors on carotid sinus and aortic arch are inhibited
3. impulses from baroreceptors stimulate cardioacceleratory center (and inhibit cardioinhibitory center) and stimulate vasomotor center
4a an increase of sympathetic impulses to the heart cause an increase in heart rate an increase in contractility and an increase in cardiac output
4b vasomotor fibers stimulate vasoconstriction causing an increase in preipheral resistance

Short-Term Mechanisms: Chemoreceptor-Initiated Reflexes where are the Chemoreceptors located

in the Carotid sinus, aortic arch, large arteries of the neck
same location as the baroreceptors

what do the chemoreceptor sin the carotid sinus respond to

to rise in CO2, drop in pH or O2
Increase blood pressure via the vasomotor center and the cardioacceleratory center
Are more important in the regulationof respiratory rate

where are the relexes that regulate blood pressure integrated from

the medulla
higher brain centers (cortex and hypothalamus) can modify BP via relays to medullary centers

which hormone causes blood pressure to decline

ANP atrial natriuretic peptide
causes blood volume and blood pressure to decline, causes generalized vasodialation

influence of selected hormones on variables affecting blood pressure: epinepherine and norepinephrine

cause generalized vasoconstriction and increase cardiac output

influence of selected hormones on variables affecting blood pressure: angiotensin II

generated by kidney release of renin causes vasoconstriction

influence of selected hormones on variables affecting blood pressure: ADH (antidiurectic hormone - vasopressin)

causes intense vasoconstriction in cases of extremely low BP

influence of selected hormones on variables affecting blood pressure: aldosterone

increase in blood volume, decrease in water loss - occurs in the kidneys

influence of selected hormones on variables affecting blood pressure: cortisol

increase in blood volume, decrease in water loss - occurs in the kidneys

kidneys act directly to regulate arterial blood pressure by doing what

direct renal mechanism
alters bllod volume independantly of hormones
*increased blood pressure or blood volume causes the kidneys to eliminate more urine, thus reducing blood pressure
*decreased blood pressure or blood volume causes the kidneys to conserve water and blood pressure rises

kidneys act indirectly to regulate arterial blood pressure by doing what

indirect renal (renin- angiotensin) mechanism
a decrease in arterial blood pressure releases renin which produces angiotensinII which is a potent vasoconstrictor - angiotensin then leads to aldosterone secretion , which causes renal absorption of sodium and decreases urine formation

Angitensin II stimultes the release of what

ADH

what are vital signs

pulse and blood pressure along with rsepiratory rate and body temperature

pulse

pressure wave caused by the expansion and recoil of ateries - rarial pulse Taken at the wrist) routinely used

how do you measure blood pressure

with a sphygmomanometer
*pressure is increase in the cuff until it exceeds systolic pressure in the brachial artery
*pressure is then slowly release and the examiner listens for sounds of KORTIKOFF with a stehoscope
* sound first occcur as blood starts to spurt through the artery (systolic pressure) (normally 110-140 mmHg)
*sounds disappear when the artery is no longer constricted and blood is flowing freely (diastolic pressure) (normally 70-80 mmHg)

what are some variations in blood pressure

blood pressure cuclye over a 24 hour period
blood presure peaks in the mornig due to levels of hormones
age, sex, weight, race, mood, and posture may vary BP

hypotension

low blood pressure
systolic pressur ebelow 100 mm Hg
often associated with long life and lack of cardiovascular illness

orthostatic hypotension

temporary low blood pressure and dizziness when suddenly rising from a sitting or reclining position

chronic hypotension

hint of poor nutrition and warning signs for addisons disease (hyposecretion of aldosterone) or hypothyroidism

acute hypotension

important sign of circulatory shock

hypertension

high blood pressure
Sustained elevated arterial pressure of 140/90 or higher
May be transient adaptations during fever, physical exertion, and emotional upset
Often persistent in obese people
Prolonged hypertension is a major cause of heart failure, vascular disease, renal failure, and stroke

Primary or essential hypertension

90% of hypertensive conditions (no underlying cause), Due to several risk factors including heredity, diet, obesity, age, stress, diabetes mellitus, and smoking

Secondary hypertension

less common
Due to identifiable disorders, including kidney disease, arteriosclerosis, and endocrine disorders such as hyperthyroidism and Cushing’s syndrome (hypersecretion of glucocorticoids)

how many pulse points are there and where are they

nine
1. superficial temporal artery
2. facial artery
3. common carotid artery
4. brachial artey
5. radial artery
6. femoral artery
7. popliteal artery
8. posterior tibial artery
9. dorsalis pedis artery

blood flow tissue perfusion is involved in what

delivery of oxygen and nutrients to and removal of wastes from tissue cells
gas exchange in the lungs
absorption of nutrients in the digestive tract
urine formation in the kidneys
** the rate of flow is precisely yhe right amount to provide for proper function

properties of the velocity of blood flow

changes as it travels through the systemic circulation
is inversely related to the total cross sectional area
is fastest in teh aorta, slowest in the capillaries and increases again in the veins

what does slow capillary flow allow for

allows for adequate time for exchange between blood and tissues

autoregulation

automatic adjustment of blood flow to each tissue in proportion to its requirements at any given point in time

how is autoregulation controlled

intrinsically by modifying the diameter of local arterioles feeding the capillaries i ti is independant of MAP , which is controlled as needed to maintain constant pressure

what are the two types of autoregulation

1. metabolic
2. myogenic

describe metabolic autoregulation

•Vasodilation of arterioles and relaxation of precapillary sphincters occur in response to
•Declining tissue O2
•Substances from metabolically active tissues (H+, K+, adenosine, and prostaglandins) and inflammatory chemicals
•Effects
•Relaxation of vascular smooth muscle
•Release of NO from vascular endothelial cells
•NO is the major factor causing vasodilation
•Vasoconstriction is due to sympathetic stimulation and endothelins

describe myogenic autoregulation

•Myogenic responses of vascular smooth muscle keep tissue perfusion constant despite most fluctuations in systemic pressure

what is passive stretch

(increased intravascular pressure) promotes increased tone and vasoconstriction

what is reduced stretch

promotes vasodilation and increases blood flow to the tissue

Intrinsic mechanisms (autoregulation)

Distribute blood flow to individual organs and tissues as needed

what are the Metabolic controls involved in Intrinsic mechanisms (autoregulation)

decrease amounts of: pH and oxygen
increase
potassium
carbondioxide
Prostaglandins
Adenosine
Nitric oxide
Endothelins (constriction)

what are the Myogenic controls (muscular responses) involved in Intrinsic mechanisms (autoregulation)

Stretch

Extrinsic mechanisms

Maintain mean arterial pressure (MAP) Redistribute blood during exercise and thermoregulation

nerves involved in extrinsic control of anterior smooth muscle in the systemic circulation

sympathetic (constriction)

hormones involved in extrinsic control of anterior smooth muscle in the systemic circulation

epinephrine and norepinephrine (alpha receptors - constrict) (beta receptors - dilate)
angiotensin II constricts
antidiuretic hormone ADH - constricts
atrial natriuretic peptide (ANP) dilates

angiogenesis

occurs when short term autoregulation cannot meet tissue nutrient requirements
the number of vessels to a region increases and existing vessels enlarge

when does angiogenesis occur

common in the heart when a coronary vessel is occluded, or throughout the body in people in high aaltitude areas

what happens to blood flow to the skeletal muscles during rest

at rest myogenic and general neural mechanisms predominate

what happens with blood flow to muscles during activity

Blood flow increases in direct proportion to the metabolic activity (active or exercise hyperemia)
Local controls override sympathetic vasoconstriction
Muscle blood flow can increase 10 or more during physical activity

blood flow to the brain

Blood flow to the brain is constant, as neurons are intolerant of ischemia

what are the metabolic controls involved in blood flow to the brain

Declines in pH, and increased carbon dioxide cause marked vasodilation

what are the Myogenic controls involved in blood flow to the brain

Decreases in MAP cause cerebral vessels to dilate
Increases in MAP cause cerebral vessels to constrict
The brain is vulnerable under extreme systemic pressure changes
•MAP below 60 mm Hg can cause syncope (fainting)
•MAP above 160 can result in cerebral edema

syncope

fainting

cerebral edema

an excess accumulation of water in the intracellular and/or extracellular spaces of the brain.

blood flow to the skin does what (through the skin)

Blood flow through the skin
Supplies nutrients to cells (autoregulation in response to O2 need)
Helps maintain body temperature (neurally controlled)
Provides a blood reservoir (neurally controlled)

blood flow to the skin does what (below the skin surface)

Blood flow to venous plexuses below the skin surface
Varies from 50 ml/min to 2500 ml/min, depending on body temperature
Is controlled by sympathetic nervous system reflexes initiated by temperature receptors and the central nervous system

as temperature rises what occurs
(heat expossure, fever, vigorous exercise)

Hypothalamic signals reduce vasomotor stimulation of the skin vessels thus producing vasodilation
Heat radiates from the skin
Sweat also causes vasodilation via bradykinin in perspiration
Bradykinin stimulates the release of NO

Bradykinin

Bradykinin is a peptide that causes blood vessels to dilate (enlarge), and therefore causes blood pressure to lower

NO

nitric oxide

as temperature decreases what occurs

As temperature decreases, blood is shunted to deeper, more vital organs

blood flow to the lungs

Pulmonary circuit is unusual in that
The pathway is short
Arteries/arterioles are more like veins/venules (thin walled, with large lumens)
Arterial resistance and pressure are low (24/8 mm Hg)
Autoregulatory mechanism is opposite of that in most tissues
Low O2 levels cause vasoconstriction; high levels promote vasodilation
Allows for proper O2 loading in the lungs

blood flow to the heart - during ventricular systole

Coronary vessels are compressed
Myocardial blood flow ceases
Stored myoglobin supplies sufficient oxygen

blood flow to the heart - during ventricular diastole

At rest, control is probably myogenic

blood flow to the heart during the strenuous exercise

Coronary vessels dilate in response to local accumulation of vasodilators
Blood flow may increase three to four times

blood flow through the capillaries vasomotion

slow and intermittent flow
reflects the on/off openining and closing of precapillary sphincters

capillary exchange of respiratory gases and nutrients

Diffusion of
O2 and nutrients from the blood to tissues
CO2 and metabolic wastes from tissues to the blood
Lipid-soluble molecules diffuse directly through endothelial membranes
Water-soluble solutes pass through clefts and fenestrations
Larger molecules, such as proteins, are actively transported in pinocytotic vesicles or caveolae

what are the four possible pathways or routes of transport across the endothelial cell wall of a fenestrated capillary

1 Diffusion through membrane (lipid-soluble substances)
2 Movement through intercellular clefts (water-soluble substances
3 Movement through fenestrations (water-soluble substances)
4 Transport via vesicles or caveolae (large substances)

Fluid Movements: Bulk Flow

•Extremely important in determining relative fluid volumes in the blood and interstitial space
•Direction and amount of fluid flow depends on two opposing forces: hydrostatic and colloid osmotic pressures
•Capillary hydrostatic pressure (HPc) (capillary blood pressure)
•Tends to force fluids through the capillary walls
•Is greater at the arterial end (35 mm Hg) of a bed than at the venule end (17 mm Hg)
•Capillary colloid osmotic pressure (OPc)
•Created by nondiffusible plasma proteins, which draw water toward themselves (~26 mm Hg)

Net Filtration Pressure (NFP)

•NFP—comprises all the forces acting on a capillary bed
•NFP = hydrostatic pressure – osmotic pressure
•At the arterial end of a bed, hydrostatic forces dominate
•At the venous end, osmotic forces dominate
•Excess fluid is returned to the blood via the lymphatic system

Circulatory Shock

Any condition in which Blood vessels are inadequately filled, Blood cannot circulate normally and Results in inadequate blood flow to meet tissue needs

Hypovolemic shock:

results from large-scale blood loss

Vascular shock:

results from extreme vasodilation and decreased peripheral resistance

Cardiogenic shock

results when an inefficient heart cannot sustain adequate circulation

artery side (arteriole)

fluid goes out - pushes out

vein side (venule)

fluid goes in - pulls in