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Ch. 13 The Cardiovascular System: Blood Vessels and Circulation (13.7…
Ch. 13 The Cardiovascular System: Blood Vessels and Circulation
13.1 Blood Vessels
arteries
from the heart to the capillaries
elastic (aorta 100mHg)
muscular (distribution)
arteriole
distribute blood to body organs
elastic arteries
large and resiliant
examples: pulmonary trunk and aorta
walls contain a tunica media dominated by elastic muscle cells rather than smooth muscle cells
are able to absorb the pressure changes that occur during he cardiac cycle
during ventricular systole blood pressure rises and additional blood is pushed into the systemic circuit
elastic arteries are stretched and their diameter increases
during ventricular diastole blood presure decreases and the blood vessels return to their normal size
muscular arteries
medium sized, distribution arteries
distribute blood to the skeletal muscles and internal organs
example: external carotid arteries of the neck
contains more smooth muscle cells and fewer elastic fibers than elastic arteries
arterioles
provide blood to capillaries
branches of arteries
larger than muscular arteries
tunica media has 2 layers which enable muscular arteries and arterioles to change the diameter of the lumen, altering blood pressure and the rate of flow
layers of blood vessels
tunica media
muscle tissue, collagen, elastic fibers
tunica intima
endothelial lining
tunica Externa (aventitia)
connective tissue
stabilizes and anchoring blood vessels
capillaries
form extensive branching networks that are 25,000 miles long
chemical and gaseous exchange between the blood and interstitial fluid occurs across capillary walls
tissue cells rely on this to get nutrients and oxygen and to remove wastes like CO2 and urea
venules
smallest vessels of the venous system
merge to form small veins
veins
blood passes through to the venae cavae or the pulmonary veins
13.2 Blood Pressure
factors affecting blood flow
vascular resistance
the largest component of peripheral resistance
most important part is friction between the blood and vessel walls
amount of friction depends on
length of the vessel
diameter of the vessel
small changes can make a big difference
occurs mostly in arterioles, extremely muscular
viscosity
resistance to flow resulting from interactions among molecules and suspended materials in a liquid
liquids with low viscosity only flow under high pressure
blood's viscosity is 5x that of water
pressure
flows from higher pressure to lower pressure
the greater the difference in pressure, the faster the flow
largest pressure difference = pressure gradient
found in the systemic circuit between the base of the aorta and the entrance to the right atrium
circulatory pressure is the difference and averages 100mmHg
high pressure is needed to force the blood through the arterioles into the capillaries
three components
capillary pressure
capillary pressure is just like regular blood pressure but the capillary walls are more permeable to small ions, nutrients, organic wastes, dissolved gases, and water, which are absorbed by the capillaries.
water and solutes flow through the peripheral tissues and enter the lymphatic vessels and empty into the bloodstream
plays a role in homeostasis
2 more items...
venous pressure
pressures are low and veins offer resistance, once entered, pressure drops slowly
as blood travels, veins become larger, resistance drops more, and flow rate increases
two factors to help overcome gravity
2 more items...
arterial pressure
turbulence
blood flowing smoothly through the vessels affected by disorders that change the vessel and interrupt the smooth flow
slows flow and increases resistence (generates the third and fourth heart sounds)
turbulent flow across damaged vessels produces the sound of heart murmers
resistance
opposes movement of blood
circulatory pressure must be great enough to overcome the total peripheral resistance (resistance of the entire cardiovascular system)
sources of the peripheral resistance
vascular resistane
turbulence
viscosity
interplay between pressure and resistance
cardiovascular pressures within the systemic circuit
venous pressure
blood pressure (arterial pressure)
capillary pressure and capillary exchange
13.3 Cardiovascular Regulation
Autoregulation
changes in tissue conditions act directly on precapillary sphincters to alter peripheral resistance
produces local changes in the pattern of blood flow in capillary beds
causes immediate localized homeostatic adjustments
neutral regulation
baroreceptors
monitors the degree of stretch in the walls of expandable organs
located in
aortic sinuses
carotid sinuses
wall of right atrium
baroreceptor reflexes
autonomic reflexes that adjust cardiac output and peripheral resistance to maintain normal arterial pressures
chemoreceptors
respond to changes in CO2, O2, or pH in blood and cerebrospinal fluid
sensory neurons found in the carotid bodies and aortic bodies
monitor the chemical compostion of the arterial blood
stimulation fo the cardioacceleratory and vasomotor centers which elevated arterial pressure and increases blood flow through peripheral tissues
output affects the respriatory centers in the medulla oblongata which increases blood flow and blood pressure (associated with an elevated respiratory rate)
Hormones / Endocrine regulation
antidiuretic hormone
released at the posterior pituitary gland in response to
increase in osmotic concentration of plasma
presence of angiotensin II
decrease in blood volume
the immideate result is peripheral vasoconstriction which elevates blood pressure
angiotension II
formed in the blood following the release of the enzyme renin by kidney cells in response to a fall in blood pressure
stimulates cardiac output and triggers arteriole constriction which elevates systemic blood pressure
stimulates secretion of ADH by the pituitary gland and aldosterone by the suprarenal cortex
ADH stimulates water conservation at the kidneys
aldosterone stimulates the reabsorption of sodium ions and water from the urine
stimulates thirst and the ADH and aldosterone retains the water, elevating blood volume
erythropoietin
released by the kidneys when blood pressure falls or the oxygen content of the blood becomes abnormally low
stimulates red blood cell production which elevates blood volume and improves the oxygen carrying capacity of blood
Arterial Natriuretuc Peptide
stimulated by increase in blood pressure
produced by cardiac muscle cells in the wall of the right atrium when they are stretched by excessive venous return
reduces blood volume and blood pressure
increases the loss of sodium ions and water at the kidneys
promotes water loss by increasing the volume of urine produced
reduces thirst
blocks the release of ADH, aldosterone, E, NE
stimulates peripheral vasodialation
13.7 Systemic Circuit
ascending aorta
arteries of the aortic arch
subclavian arteries
carotid artery and blood to the brain
descending aorta
superior vena cava
venous return from the head and neck
venous return from the upper limbs and chest
inferior vena cava
hepatic portal system
13.9 Aging
the capabilities of the cardiovascular system gradully decline with age, changes effect: blood, heart, and vessels
blood changes
decreased hematocrit
constriction or blockage of peripheral veins by formation of thrombus
pooling of blood in the veins of the legs because valves are not efficent
heart changes
reduction in maximum cardiac output
changes in activities of the nodal and conducting cells
reduction in the elasticity of the fiberous skeleton
progressive atherosclerosis, restricting coronary circulation
the replacement of damages cardiac muscle cells by scar tissue
vessel changes
calcium salts can be deposited on weakened vascular walls, increasing risk of heart attack or stroke
thrombi can form atherosclerotic plaques
the inelastic walls of arteries become less tolerant of sudden pressure increases (leads to aneurysm, stroke, or heart attack)
13.4 physiological stress
hemorrhage
short term
appear almost as soon as the blood pressure starts to decline
when the carotid and aortic reflexes increase cardiac output and cause peripheral vasoconstriction
when blood is lost, cardiac output drops, vasometer center improves venous return and restores cardiac output
with a more substantial blood loss, cardiac output is maintained by increasing the heart rate and activating sympathetic which elevates blood pressure
long term
may take a few days to return to normal blood volume
when short term methods dont work, ADH and aldosterone retain fluid and prevent further reductions in blood volume
exercise
venous return increases
cardiac output rises
extensive vasodialation occurs
13.6 pulmonary circuit
L & R pulmonary arteries
enter the lungs before branching repeatedly, giving rise to smaller and smaller arteries
the smallest branches, the pulmonary arterioles provide blood to capillary networks that surround small air pockets,
alveoli of the lungs
the walls of the alveoli are thin enough for gas exchange to occur between the capillary blood and inspired air
pulmonary trunk
start of the pulmonary circuit, carbon dioxide is released, oxygen stores are replenished, and the oxygenated blood is returned to the heart for distribution in the systemic circuit
L & R pulmonary veins
venules lead to these arteries, these arteries empty into the left atrium and complete the pulmonary circuit
blood entering the right atrium, after returning from peripheral capillary beds where oxygen is released and carbon dioxide is absorbed. after traveling through the right atrium and ventricle
13.8 Fetal Circulation
fetal circulation
lungs are collapsed during fetal life and the interatrial part is functionally incomplete until birth
foramen ovale acts as a valve and blood can flow freely from the right atrium to the left; any backflow will close the valve and isolate the chambers
between the pulmonary and aortic trunks is the ductus arteriosus
the lungs are not a part of fetal circulation, the blood flows from the right atrium to the right ventricle to the foramen ovale into the left atrium then into the right ventricle, ductus arteriosus, and enters the systemic circuit
changes at birth
lungs and pulmonary vessels expand with the baby's first breath
smooth muscles in the ductus arteriosus contract and isolate the pulmonary and aortic trunk and blood begins flowing the pulmonary circuit
pressures rise in the left atrium and close the foramen ovale
fossa ovalis marks where the foramen ovale used to be in adults
remannts of the ductus arteriosus persist as a fiberous chord, ligamentum arteriosum
if proper changes do not take place, problems will develop because of the heart working too hard
treatment may include: surgical closure of the foramen ovale, the ductus arteriosus, or both
placental blood supply
reaches the placenta through umbilical arteries, rise from the internal iliac arteries before entering the umbilcal cord, at the placenta, blood picks up oxygen and gives away carbon dioxide
umbilical vein is what the blood flows through before reaching the developing liver, some blood flows through capillaries within the liver adn the rest bypasses and reaches the ductus venosus with the inferior vena cava
13.5 pulmonary & systemic circuits
systemic circuit
composed of arteries that transport oxygenated blood and nutrients to all other organs and tissues and veins that return deoxygenated blood to the heart
begins at left ventricle and ends at the right atrium
pulmonary circuit
composed of arteries and veins that transport blood between the heart and the lungs
begins at right ventricle and ends at the left atrium
the distribution of arteries and veins on the left and right sides of the body is usually identical, except near the heart where large vessels connect to the atria or ventricles
a single vessel may undergo several name changes as it crosses specific anatomical boundaries
tissues and organs are usually serviced by several arteries and veins, often anastomoses between adjacent arteries or veins reduce the impact of a temporary or permanent blockage of a single blood vessel