Lecture: Blood Vessels and Circulation Flashcards
What are the 3 layers of a blood vessel?
from inside to outside:
tunica interna (tunica intima)
tunica media
tunica externa (tunica adventitia)
Describe the composition of the tunica interna (tunica intima).
endothelium: simple squamous epithelium
- continuous layer of cells throughout system
- layer in contact with the blood
What are the 4 functions of the tunica interna (tunica intima)?
1) selectively permeable barrier
2) secretion of chemicals
3) repels blood cells and platelets
4) inflammation
Describe the composition of the tunica media.
smooth muscle (amount varies)
elastic tissue
collagen
What are the 2 functions of the tunica media?
1) strengthens vessels / prevents rupture
2) vasomotion (vasoconstriction / vasodilation)
Describe the composition of the tunica externa (tunica adventitia).
loose CT
What are the 3 functions of the tunica externa (tunica adeventitia)?
1) protects and anchors blood vessel
2) passage for nerves & lymphatic vessels
3) smalls vessels called vaso vasorum supply blood to outer walls of larger vessels
What are the 3 categories of arteries?
1) conducting arteries (elastic, large)
2) distributing arteries (muscular, medium)
3) resistance arteries (arterioles, small)
Comment on the composition of conducting arteries. Give some examples of conducting arteries.
largest diameter
elastic tunica media
ex. aorta, pulmonary trunk, common carotid, subclavian, common illiac
What is the function of conducting arteries?
reduce effects of BP surgers
- expand during systole, recoil during diastole
- helps maintain blood flow
Comment on the composition of distributing arteries. Give some examples of distributing arteries.
thicket smooth muscle
ex. brachial, femoral, renal, splenic
What is the function of distributing arteries?
distribute blood to specific organs and adjust flow based on demand
Describe the composition of resistance arteries.
smooth muscles layers variable;
little elastic tissue
Define: arterioles.
smallest resistance vessels
lead into capillary bed
Define: metarterioles.
link arterioles to capillaries
What is the function of resistance arteries? What vital signs does it influence?
primary control of blood flow
most responsible for PR
significantly affects BP
Describe the composition of capillaries.
single layer of endothelial cells
small lumen
What is the function of capillaries?
to exchange materials, accomplished by their close proximity to nearly all cells
What are the 3 types of capillaries?
1) continuous
2) fenestrated
3) sinusoid
Describe the composition of continuous capillaries.
present in most tissues, such as skeletal muscle;
tight junctions hold endothelial cells together
intracellular clefts
pericytes
Define: intracellular clefts
spaces between endothelial cells in continuos capillaries;
allow small molecules (ex. glucose) to pass through;
retrain larger molecules such as plasma proteins and formed elements
Define: perictyes
contractile proteins in continuous capillaries
Describe the composition of fenestrated capillaries.
endothelial cells covered in filtration pores (fenestrations);
greater permeability
allow rapid passage of small molecules but retain formed elements
What are some examples of organs/tissues perfused by fenestrated capillaries?
kidneys
endocrine glands
small intestine
choroid plexus
Describe the composition of sinusoids.
a.k.a. discontinuous capillaries;
irregular, blood-filled spaces;
endothelial cells have large filtration pores (fenestrations) through which formed elements can pass
What are some examples of organs/tissues perfused by sinusoids?
liver
bone marrow
spleen
Define: capillary beds.
networks of capillaries;
not all are perfused at any given time;
they drain into a distal continuation of the metarteriole called a thoroughfare channel, which then leads to a venule
Define: capillary sphincter.
smooth muscle cell that wraps around the opening to each capillary and regulates blood flow
Describe the composition of postcapillary venules.
smallest veins
only tunica intima
often have pericytes
extremely porous
Describe the composition of muscular venules.
thin tunica media
thin tunica externa
Describe the composition of medium veins.
have all 3 tunics -thin tunica media -thick tunica externa -large lumen -tunica intima folds inward, forming valves; relatively thin wall vessel -BP much lower, collapses when empty; blood "reservoirs" (large % of total blood supply)
Where are venous valves found/ not found in the body?
abundant where upward flow opposed by gravity;
not present in small/large veins, abdominal/thoracic cavities, and the brain
Describe the composition of large veins. Name some examples of large veins.
v. thin tunica intima, v. thick tunica externa;
ex. venae cavae, pulmonary, internal jugular, renal
Describe the 5 different types of circulatory routes.
1) simple pathway: 1 network of capillaries
2) portal system: 2 networks of capillaries (ex. kidneys, hypophyseal portal system)
3) arteriovenous anastomosis (a.k.a. shunt): artery directly to vein
4) venous anastomosis: alternative drainage
5) arterial anastomosis: collateral supply
Define: anastomosis.
point of convergence between 2 blood vessels other then capillaries
Define: flow.
vol. of blood through an organ, tissue, or vessel in a given amt. of time;
expressed in ml/min
Define: perfusion.
flow per given volume or mass of tissue;
expressed in ml/min/g
Define: pressure.
force of blood exerted on vessel wall;
expressed in mmHg
Define: hemodynamics.
study of physical principles of blood flow; based on pressure and resistance
F ≈ ΔP / R
where F = blood flow, ΔP = difference in pressure, R = resistance to flow
How does blood pressure vary throughout the body / circulatory system?
highest pressure immediately after systole;
highest pressure proximal to heart;
arteries > capillaries > veins
What 3 factors is blood pressure influenced by?
elasticity of arteries: recoil maintains pressure and facilitates flow;
blood volume;
kinetic energy of blood stretching the aorta
Define: pulse pressure (PP).
measure of pressure surges
PP = SBP - DBP
Define: mean arterial pressure (MAP).
avg. of pressures
MAP = DBP + 1/3 (PP)
BP depends on what 3 organs coordinated by what 1 organ?
brain
- heart
- blood vessels
- kidneys
What are the 3 main variables determining blood pressure?
1) cardiac output
2) blood volume
3) resistance to flow
Define: resistance.
measure of friction encountered by blood through vessels;
opposition to flow
Define: peripheral resistance.
opposition to blood flow encountered away from the heart, generally from smaller vessels and arterioles
What are 3 sources of resistance?
1) blood viscosity
2) blood vessel length
3) blood vessel diameter (most dynamic)
Define: blood viscosity. What contributes to it? What is its relationship to resistance and flow?
“thickness” of blood;
results from RBC and albumin;
directly proportional to resistance (which is usually constant);
inversely proportional to flow
What effect does blood vessel length have on friction, resistance, and flow?
longer distance = more cumulative friction;
directly proportional to resistance;
inversely proportional to flow
What are the terms for blood vessel diameter changes? What effect does this have on peripheral resistance?
vasoreflexes: vasodilation & vasoconstriction;
constantly alters peripheral resistance
Differentiate laminar and turbulent flow.
laminar flow: layered flow, faster in center and slower near the walls;
turbulent flow: at higher velocities, flow becomes rougher and lateral mixing occurs
What is the most significant variable of Poiseuille’s Law?
vessel radius (to the fourth power!)
What are the 3 reasons that arterioles are the most significant point of control over peripheral resistance and blood flow?
1) location proximal to capillary beds makes them best positioned to regulate flow into the capillaries
2) greatly outnumber any other class of arteries
3) more muscular in proportion to their diameters than any other class of blood vessel, and are highly capable of changing radius
Name the 3 mechanisms for regulating pressure and flow.
1) local control
2) neural control
3) hormonal control
Explain local control.
autoregulation;
myogenic control: vasoreflexes
metabolic control;
-CO2, H+, K+, lactic acid
-vasoactive chemicals: histamine, prostaglandins, bradykinin;
angiogenesis: growth of new blood vessels
Define: autoregulation.
ability of tissues to regulate their own blood supply;
corresponds to local control
Define: angiogenesis.
growth of new blood vessels;
corresponds to local control
Explain neural control.
vasomotor center in medulla sends sympathetic impulses to smooth muscle, constricting most vessels, but dilating some cardiac and skeletal muscles; regulated by 3 autonomic reflexes 1) baroreflex 2) chemoreflex 3) medullary ischemic reflex
Define: baroreflex.
autonomic, negative feedback response in response to BP (detected by baroreceptors); BP increase inhibits SNS, including cardiac and vasomotor centers; BP increase excites vagal fiber; effects: -reduce HR -reduce cardiac output -dilates vessels -reduces BP
Define: chemoreflex.
autonomic response to chemical changes;
chemoreceptors activated by low pH, low O2, and high CO2;
primary role of chemoreceptors = adjust respiration;
secondary role = vasomotor
-vasoconstriction
-increases perfusion
Define: medullary ischemic reflex.
autonomic response to brain hypoperfusion;
cardiac and vasomotor centers increase HR & contractile force and cause widespread vasoconstriction;
these centers also receive input from higher brain centers: stress, arousal, anger can stimulate them and raise BP
Name 6 hormones and their effects on vascular smooth muscle.
1) Angiotensin II: vasoconstriction
2) Aldosterone: sodium retention by kidneys
3) Atrial natriuretic peptide: increases sodium excretion
4) Antidiuretic hormone: water retention
5 & 6) epinephrine and norepinephrine: vasoconstriction in most vessels; vasodilation in coronary and skeletal muscle blood vessels
Explain how blood flow can be redirected.
local vasoconstriction of an artery;
downstream of site of constriction, pressure decreases;
upstream of site of constriction, pressure increases;
blood takes path of least resistance
