Blood Vessels Flashcards
vascular pathway of blood flow
-arteries leave the heart and branch into:
-arterioles feed parts of organs and branch into:
-capillaries, where chemical and gaseous exchange occurs, and which drain into:
-venules, the smallest vessels of the venous system, which drain into:
-veins, which return blood to the atria of the heart
three layers of vessel walls are
tunica intima (or tunica interna), tunica media, tunica externa (or tunica adventitia)
tunica intima (or tunica interna)
has endothelial lining and elastic connective tissue
tunica media
has smooth muscle with collagen and elastic fibers
controls diameter of vessel
tunica externa (or tunica adventitia)
sheath of connective tissue may anchor to other tissues
capillaries
-tunica interna only
-endothelial cells with basement membrane
-ideal for diffusion between plasma and IF
-thin walls provide short diffusion distance
-small diameter slows flow to increase diffusion rate
-enormous number of capillaries provide huge surface area for increased diffusion
capillary beds are
an interconnected network of capillaries
entrance to bed is regulated by
precapillary sphincter, a band of smooth muscle
relaxation of sphincter allows for
increased flow
constriction of sphincter
decreases flow
the relaxation and constriction is referred to as
vasomotion
control is local through
autoregulation
veins
collect blood from tissues and organs and return it to the heart
venules
are the smallest and some lack tunica media
medium sized veins
tunica media has several smooth muscle layers
in limbs, contain valves
valves
prevent backflow of blood toward the distal ends
increase venous return
large veins
thin tunica media and thick collagenous tunica externa
thinner walls than arteries because of low pressure
maintaining adequate blood flow
flow maintain adequate perfusion of tissues
normally, blood flow equals cardiac output (CO)
increased CO leads to increased flow through capillaries
decreased CO leads to reduce flow
capillary flow influenced by pressure and resistance
increased pressure increases flow
increased resistance decreases flow
liquids exert ______ pressure in all directions
hydrostatic
a pressure gradient
exists between high and low pressures at different points
circulatory pressure
high in aorta vs. low in venae cavae
(arterial pressure is blood pressure
capillary pressure
venous pressure)
flow is proportional to
pressure gradients
resistance
any force that opposes movement
circulatory pressure must be high enough to overcome total peripheral resistance
the highest pressure gradient exists in
arterioles due to high peripheral resistance
vascular resistance
largest component of peripheral resistance
-caused mostly by friction between blood and vessel walls
-amount of friction due to length and diameter of vessel
-length doesn’t normally change
-the longer the vessel, the higher the resistance
-arteriolar diameter is primary source of vascular resistance
-the smaller the diameter, the greater the resistance
blood pressure
arterial pressures fluctuate
recorded as systolic over diastolic (e.g., 120/80 mm Hg)
pulse is alternating changes in pressures
systolic pressure (SP)
is peak and occurs during ventricular contraction
diastolic pressure (DP)
is the minimum and occurs at the end of ventricular relaxation
pulse pressure
the difference between systolic and diastolic pressures
pulse pressure =
SP - DP
pulse pressure diminishes over distance,
eliminated at the capillary level
arterial recoil or elastic rebound occurs during diastole
adds additional push or squeeze on blood
results in fluctuation of pressures
capillary pressures
drops from 35 to 18 mmHg along capillary length
capillaries are permeable to
ions, nutrients, wastes, gases, and water
capillary pressures cause filtration out of bloodstream and into tissues
some materials are reabsorbed into blood
some materials are picked up by lymphatic vessels
four functions of capillary exchange
- maintains constant communication between plasma and IF
- speeds distribution of nutrients, hormones, and gases
- assists movement of insoluble molecules
- flushes bacterial toxins and other chemicals to lymphatic tissues for immune response
mechanisms of capillary exchange
-diffusion of solutes down concentration gradients
-filtration down fluid pressure gradients
-osmosis down osmotic gradient
-water is filtered out of capillary by fluid or hydrostatic pressures
-water is reabsorbed into capillary due to osmotic pressure
capillary hydrostatic pressure (CHP)
is high at arteriolar end, low at venous end
(CHP) tends to push water out of plasma
into tissues at arteriolar end, favoring filtration
blood osmotic pressure (BOP)
is higher than in interstitial fluid
(BOP) as CHP drops over length of capillary,
BOP remains the same, favoring reabsorption
venous pressure
gradient is low compared to arterial side
large veins provide low resistance ensuring
increase in flow despite low pressure
when standing,
blood flow must overcome gravity
muscular compression
pushes on outside of veins
venous valves
prevent backflow
respiratory pump
due to thoracic pressures
short-term hormonal control of cardiovascular performance
E and
short-term hormonal control of cardiovascular performance
E and NE trigger rapid increase of cardiac output and vasoconstriction
long-term hormonal control of cardiovascular performance
antidiuretic hormone (ADH), antigiotensin II, EPO
-raise BP when too low
atrial natriuretic peptide (ANP)
-lowers BP when too high
ADH(antidiuretic hormone) is released from posterior in response to
decrease in blood volume
increase in blood osmolarity
presence of angiotensin II
results of ADH (antidiuretic)
vasoconstriction
conserving water by kidneys, increasing blood volume
angiotensin II and cardiovascular regulation
when BP decreases, kidney secrets renin
cascade of reactions forms angiotensin II
angiotensin II
stimulates CO, arteriolar constriction
immediately increase BP
stimulates release of ADH and aldosterone
stimulates thirst center
erythropoietin is release by kidney when
BP drops and plasma oxygen drops
erythropoietin stimulates
RBC production and increases blood volume
atrial natriuretic peptide is released by atrial walls when BP increases
from stretch of atrial wall due to more venous return
effects of atrial natriuretic peptide
increases sodium (and therefore water) loss by kidneys
reduces thirst
blocks release of ADH, aldosterone, E, NE
stimulates arteriolar dilation
short-term cardiovascular response to hemorrhage
loss of blood causes decrease in BP
loss of blood causes decrease in BP
-carotid and aortic reflexes increase cardiac output and peripheral resistance
-vasoconstriction accesses venous reserve
-sympathetic activation triggers arteriolar constriction
-all mechanisms function to elevate BP
long-term cardiovascular response to hemorrhage
may take several days to restore blood volume to normal
long-term cardiovascular response to hemorrhage
-fluids are accessed from interstitial space
-ADH and aldosterone promote fluid retention
-thirst increases
-EPO triggers RBC production
-all mechanisms lead to increase in volume and BP
three functional patterns of the cardiovascular system
- distribution of arteries and veins nearly identical except near heart
- single vessel may undergo name changes as it crosses anatomical boundaries
- anastomoses of arteries and veins reduce threat of temporary blockage of vessel to organ
the pulmonary circuit (lungs)
-blood exists right ventricle through pulmonary trunk
-branches into left and right pulmonary arteries
-enter lungs, arterial branching nearly parallels branching of respiratory airways
-smallest arteriole feeds capillary surrounding alveolus
-oxygenated blood returns to left atrium through left and right, superior and inferior pulmonary veins
the systemic circuit (body)
-supplies oxygenated blood to all non-pulmonary tissues
-oxygenated blood leaves left ventricle through aorta
-returns deoxygenated blood to right atrium through superior and inferior venae cavae, and coronary sinus
-contains about 84 percent of total blood volume
the aorta
-ascending aorta is first systemic vessel
-begins at aortic semilunar valve
-left and right coronary arteries branch off near base of aorta
-aortic arch curves across top of heart
-descending aorta drops down through mediastinum
three elastic arteries of the aortic arch
- brachiocephalic
- left common carotid
- left subclavian
the brachiocephalic trunk
branches to form right common carotid artery and right subclavian artery
an example of non-mirror-image arrangement
-from here on, arteries are the same on both sides of the body
-designation of right and left not necessary
the blood supply to the brain two pathways
vertebral arteries and cerebral arterial circle
vertebral arteries enter skull and fuse
posterior cerebral artery
posterior communicating artery
cerebral arterial circle
ring-shaped anastomosis encircling the infundibulum of the pituitary
systemic veins
venous network returns blood to heart
arteries and veins run parallel, often similar names
major veins in neck and limbs different than arteries
arteries are located
deep
veins usually a set of two
one deep and the other superficial
aids in body temperature control
hepatic portal system
The portal venous system is responsible for directing blood from parts of the gastrointestinal tract to the liver. Substances absorbed in the small intestine travel first to the liver for processing before continuing to the heart.
portal system
is two capillary beds in series connected by portal vessel
blood going through capillaries of digestive organs
absorbs nutrients, some wastes, some toxins
blood is processed by
liver before entering general circulation
hepatic portal system pathway
Capillaries from:
-Lower large intestine —> inferior mesenteric vein
-Spleen, stomach, pancreas —> splenic vein
-Stomach, small and large intestines —> superior mesenteric vein
All three —> hepatic portal vein
-Blood from gastric vein and cystic vein added
Blood enters liver capillaries —> hepatic vein —-> IVC
