objective 4 Flashcards
what are the 2 main neural mechanisms control peripheral resistance?
MAP is maintained by altering blood vessel
diameter, which alters resistance
Example: If blood volume drops, all vessels constrict (except those to
heart and brain)
2. Can alter blood distribution to organs in
response to specific demands
Example: during exercise blood is shunted temporarily from
digestive organs to skeletal muscles.
what do neural controls operate via reflex arcs that involve what?
Cardiovascular center (medulla)
◦ Baroreceptors (changes in pressure)
◦ Chemoreceptors (changes in chemical messengers)
◦ Higher brain centers (hypothalamus)
composed of sympathetic neurons in medulla
cardiovascular center
cardioinhibitory and cardioacceleratory
centers
cardiac centers
cause continuous moderate constriction called vasomotor tone
vasomotor center
what happens if MAP is high?
Increased blood pressure stimulates baroreceptors to
increase input to vasomotor center
Inhibits vasomotor and cardio-acceleratory centers
Stimulates cardio-inhibitory center
Results in decreased blood pressure
what are the 2 mechanisms that result in decrease in BP?
vasodilation
decreased cardiac output
Decreased output form vasomotor center causes
dilation
vasodilation
reduces peripheral
resistance, MAP falls
arteriolar vasodilation
shifts blood to venous reservoirs, decreasing
venous return and CO
venodilation
impulses to cardiac
centers inhibit sympathetic activity and stimulate
parasympathetic
Reduces heart rate and contractility; CO decrease causes
decrease in MAP
decreased cardiac output
what happens if MAP is low?
vasoconstriction is initiated that increases CO and
blood pressure
baroreceptors that monitor BP to ensure enough blood to brain
maintains BP in systemic circuit
Baroreceptors are ineffective if altered blood pressure
is sustained (i.e chronic HTN)
Become adapted to hypertension, so not triggered by
elevated BP levels
Aortic arch and large arteries of neck detect
increase in CO 2 , or drop in pH or O2
chemoreceptor reflexes
how does chemoreceptor reflexes increase BP?
Signaling cardio-acceleratory center to increase
Cardiac output
Signaling vasomotor center to increase
vasoconstriction ( so more resistance)
This causes increase in BP that speeds return of blood
to heart and lungs
Reflexes that regulate BP are found in medulla
oblongata
◦ Hypothalamus and cerebral cortex are not involved
in routine control of BP
◦ Hypothalamus increases blood pressure during
stress
◦ Hypothalamus mediates redistribution of blood flow
during exercise and changes in body temperature
◦ Allows modification of neural controls of BP
influence of higher brain centers
how do hormones regulate BP?
short-term via changes in peripheral resistance
◦ long-term via changes in blood volume
increase CO and vasoconstriction
Epinephrine and norepinephrine
stimulates vasoconstriction
Angiotensin II
cause vasoconstriction
ADH
causes vasodilation
and promotes a decline in blood volume and
therefore BP
atrial natriuretic peptide
how do kidneys regulate arterial BP?
Direct renal mechanism
2. Indirect renal mechanism (renin-angiotensin-
aldosterone)
Alters blood volume independently of hormones
Increased BP or blood volume causes elimination of
more urine, therefore reducing blood volume, thus
reducing BP
Decreased BP or blood volume causes kidneys to retain
more water, increasing blood volume and BP rises
direct renal mechanism
The renin-angiotensin-aldosterone mechanism:
Decreased blood pressure causes release of renin from
kidneys
Triggers formation of angiotensin II
indirect mechanism
what do angiotensin II cause?
Release of aldosterone stimulating salt and water retention
Vasoconstriction
Release of ADH
Thirst
* all of these will lead to increased blood volume and BP
Determines the distribution of fluids between the bloodstream and
the interstitial space
} Fluid flows out capillary bed at arteriolar end and re-enters the
capillary blood at the venous end
Extremely important in determining relative fluid volumes in
blood and interstitial space
} Bulk fluid flows across capillary walls causes continuous mixing of
fluid between plasma and interstitial fluid; maintains interstitial
environment
bulk flow
what does direction and amount of fluid flow depend on?
Hydrostatic pressure
Colloid osmotic pressure
force exerted by blood
pressing against vessel wall/chamber
◦ Primary source driving fluid transport
hydrostatic pressure
BP in capillaries that forces
fluids through capillary walls; greater at arterial end
capillary hydrostatic pressure
pressure pushing
fluid back into vessel; usually aim to be 0 as lymphatic
vessels drain interstitial fluid
interstitial fluid hydrostatic pressure
sucking pressure created by
non-diffusible plasma proteins pulling water back into capillary
capillary colloid osmotic pressure
opposes hydrostatic pressure
colloid osmotic pressures
pressure is
inconsequential because interstitial fluid has very low protein
content
interstitial fluid colloid osmotic pressure
Net filtration pressure (NFP) comprises all forces acting on
capillary bed
◦ Net fluid flow out at arterial end
◦ Net fluid flow in at venous end
◦ More fluid leaves at arterial end than is returned at venous end
◦ Excess interstitial fluid is returned to blood via lymphatic
system
hydrostatic-osmotic pressure interactions
runs from heart to lungs and
back to heart
pulmonary circulation
to all parts of body and back
to heart
systemic circulation
share same name with corresponding artery
deep veins
do not correspond to names of any arteries
superficial veins
Veins can have more than one name, making venous
pathways harder to follow
venous pathways are more interconnected
contains dural venous sinuses
brain
drains into hepatic portal system, which perfuses through liver
before returning to heart
venous system of the digestive system
runs behind and to right of pulmonary
trunk before becoming the aortic arch
ascending aorta
branches of ascending aorta that
supply the mediastinum
Rt. & Lt coronary arteries
deep to sternum. Has 3 branches that provide
arterial supply to head, neck, upper limbs, and part of
thorax:
aortic arch
runs along anterior spine. Called thoracic
aorta from T5 – T12. Supplies the thorax and viscera, it enters
the abdominal cavity to become the abdominal aorta.
descending aorta
supplies abdominal walls and ends at L4
where it splits into Rt. & Lt. common iliac arteries
abdominal aorta
supply pelvis and lower limbs
Rt. and Lt common iliac arteries
