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blood must circulate so that it can…
deliver nutrients and remove waste, provide immune protection and clotting functions, maintain homeostasis
rank hydrostatic pressure in arteries, capillaries, and veins
arteries (80-120 mmHg) > capillaries (15-35 mmHg) > veins (0-20 mmHg)
coronary arteries
deliver oxygenated blood to heart cells
coronary veins
drain into coronary sinus, which opens into right atrium; return deoxygenated blood from the heart cells back to the general circulation
functional classification of vessels
distribution, exchange, collection
characteristics of arteries
hold ~13% blood volume, need to withstand high pressure during ventricular systole
types of arteries
elastic, muscular, arteriole
elastic artery
large diameter, buffer changes in blood pressure because of pressure-storing ability due to lots of elastic tissue, conducting
muscular artery
medium diameter, most common type, distribution
arteriole
small diameter, no tunica externa (smooth muscle tunica media is on the outside instead), can alter peripheral resistance and effect blood pressure
how is diameter controlled in arterioles?
because there is no tunica externa, diameter can be controlled by local, autonomic, and hormonal factors
capillary characteristics
holds ~9% of blood volume, permit bi-directional flow, have thin walls made up of a single layer of endothelium cells and a connective basement membrane essential for exchange
capillary bed
large surface area, thin-walled vessels, mesh like network, contains thoroughfare channels and metarterioles
thoroughfare channels
within the capillary bed, direct flow between arteries and veins
metarterioles
small vessels with precapillary schincters (individal smooth-muscle cells in place of tunica media to regulate flow within and between beds)
Arteriovenous anastomosis
proximal to the capillary bed, allow alternate route of bloodflow in event of blockage
types of capillaries
continuous, fenestrated (window), sinusoid (large holes)
continuous capillaries
exchange small molecules without loss of RBCs or plasma protein, found in most tissue, thin continuous walls
fenestrated (window) capillaries
exchange small peptides; fenestrations = windows; found in hypothalamus, pituitary, intestine, kidneys
sinusoid (large holes) capillaries
exchange blood proteins and blood cells; like fenestrated but with larger windows and 5 times larger diameter; found in liver, marrow, spleen
characteristics of veins
accommodate low pressure on return to heart, hold ~64% of blood volume, thin walls allow veins to expand without rupture
how to veins deal with low pressure
skeletal muscle pump and respiratory pump
skeletal muscle pump for veins
Veins pass through skeletal muscles → when skeletal muscles contract, they push on the veins and move the blood; valves in the veins keep this flow unidirectional and prevent backflow during diastole
respiratory pump for veins
The drop in pressure in the chest cavity during inhalation reduces pressure on the veins; allows blood to flow back towards the heart
types of veins
venule, medium-diameter vein, large vein
venule
small diameter, no muscle (no real tunica media)
medium-diameter vein
medium diameter, some have valves (made of in-folding of the tunica intima), expand easily to accommodate volume changes (high compliance)
large veins
large diameter, can hold large blood volume, has three layers, but the layers are relatively thin
vein functions
low-resistance conduit of blood back to right atrium, venous blood reserve (central reflexes can decrease compliance to increase arterial blood volume)
the layers of arteries are ___ than the layers of veins
thicker
3 layers of arteries and veins
tunica externa, tunica media, tunica intima
tunica externa
outer layer, support, connective tissue made of collagen and elastic fibers, some smooth muscle
tunica media
middle layer, contraction, primarily smooth muscle surrounded and contained by internal/external elastic membranes, transverse elastic fibers
tunica intima
inner layer, lining, endothelial cells, longitudinal elastic fibers running the length of the vessel, subendothelial connective tissue
blood pressure =
cardiac output * total peripheral resistance
total peripheral resistance is also called
systemic vascular resistance
flow =
change in pressure/resistance = (P arterial - P venous)/resistance
flow occurs when system circulatory pressure is ___ total peripheral resistance
greater than
resistance
friction between blood and vessel wall
L = length
n = viscosity
r = radius
arrangement of vessels affects resistance…parallel arrangement has ___ resistance than series arrangement
lower
example of parallel arrangement of vessels
capillaries
flow =
velocity * area
with a constant flow, velocity and area are ___ proportional
inversely
how does surface area play a role in capillaries?
Capillaries have very narrow diameters, so we would think the velocity is high → this would give them no time to exchange which is bad since that’s their main job
BUT when you combine many capillaries, there is an aggregate cross-sectional area that is VERY HIGH
High area results in very slow blood velocity → this gives enough time for gas/nutrient exchange
Poiseuille’s Law
predicts blood flow rate in a vessel
delta P: pressure gradient
r: radius
n = viscosity
L = length of vessel
methods of capillary exchange
diffusion, transcytosis, bulk exchange
what happens at the arterial end of the capillaries
forces water OUT of the capillaries, hydrostatic pressure is the driving force
net hydrostatic pressure (NHP) =
capillary hydrostatic pressure (CHP) - interstitial hydrostatic pressure (IHP)
what values of NHP show flow in/out of capillaries
NHP > 0 → fluid flows out of capillaries
NHP < 0 → fluid flows into capillaries
what happens at the venous end of the capillaries
reabsorption, draws water INTO the capillaries, oncotic pressure is the driving force
oncotic
colloid osmotic pressure (COP) = osmotic pressure for large solutes
oncotic pressure =
molarity * RT (high concentration = high oncotic pressure)
net colloid osmotic pressure (NCOP) =
blood COP - interstitial COP
equation for net filtration pressure =
NHP (net hydrostatic pressure) - NCOP (net colloid osmotic pressure)
positive net filtration pressure indicates
net flow out
negative net filtration pressure indicates
net flow in
exchange equation that incorporates filtration coefficient and reflection coefficient
NFR = Kf (Pc - Pi) - σ (πc - πi)
reflection coefficient (σ)
an adjustment for oncotic pressure
high σ = low protein permeability (ex. glomerulus, brain)
low σ = high protein permeability (ex. liver, spleen)
filtration coefficient (Kf)
high Kf = high H2O permeability (ex. kidneys)
low Kf = low H2O permeability
major functions of lymphatic system
homeostatic re-circulation: collects excess leaked fluid from the capillaries and returns it to the blood circulation
absorption: transport absorbed fat to blood via lacteals
immune: Production, maintenance, and distribution of lymphocytes (T-cells and B-cells); delivery of pathogens, antigens, and dendritic cells to lymph nodes
lacteals
specialized structures in intestinal villi that transport absorbed fat
how does lymphatic flow occur? what is the speed?
slow
occurs by skeletal muscle pump and peristaltic smooth muscle contraction
helped by valves
what happens when the lymphatic system doesn’t recover excess fluid?
edema
what could cause edema?
increased capillary pressure, decreased plasma proteins, increased capillary permeability, blockage of lymph return
Viagra → ___ PDE3 → does not allow conversion of cGMP and cAMP to GMP and AMP → more cGMP and cAMP → smooth muscle ___ → blood vessels ___ → more blood flow → PENILE ERECTION!!!
inhibits, relaxes, dilate
does smooth muscle have sarcomeres?
no
does smooth muscle have troponin?
no
Opening of IP3 receptors (and some RyR) on sarcoplasmic reticulum release ___ into the cytoplasm
Ca2+
what regulates contraction in smooth muscles
myosin light chain (MLC)
MLC is regulated by ___, which leads to ___
calmodulin/MLC kinase (MLCK), contraction
MLC phosphatase reverses ___ function, leading to ___
MLCK, relaxation
Smooth muscle activity constricts and dilates ___
blood vessels
epinephrine functions
increases cardiac output, heart rate, stroke volume, and contractile force
pathway for increased contractile force
epi → beta-1 adrenergic receptor → Gsa → cAMP → PKA
what receptor does epi bind to increase blood pressure?
alpha-1 adrenergic on smooth muscle of blood vessels
pathway for increasing blood pressure
thromboxane → Gq g-protein signaling → IP3 receptors on sarcoplasmic reticulum are activated → calcium is released into cytoplasm → increased contraction of smooth muscle → elevates BP
what does thyroid hormone do?
increases cardiac output, heart rate, stroke volume, and contractile force
how does TH increase contractile force
TH-receptor-mediated regulation of genes related to contractility; elevates Ca2+ ATPase pump and decreases phospholamban
how does TH effect blood pressure?
decreases it
what receptor does TH bind to to effect blood pressure
beta-2 adrenergic receptor
pathway of TH effect on blood pressure
TH increases expression of beta-2 adrenergic receptors → activates cAMP → inhibits MLCK → relaxes smooth muscle → dilation of blood vessels → decreased BP → elevated blood flow to skeletal muscles
hyperthyroidism
low systemic vascular resistance (dilation of BP), high heart rate, increased ejection fraction, increased cardiac output
nitric oxide
gasouse signaling molecule
where and in response to what is NO released
released by endothelial cells in response to shear force of blood flow (high BP)
NO activates guanylate cyclase (GC) → ___ → ___
increases cGMP; activates protein kinase G (PKG)
what does NO release do to blood pressure
decrease it
how does NO make blood pressure go down?
Increases MLC phosphatase → inactivates MLC → muscle relaxation → dilates blood vessels → blood pressure goes down
Inhibits IP3-R receptors on sarcoplasmic reticulum, so Ca+ is not released and can’t bind to calmodulin → MLCK does not get activates → inactivates MLC → muscle relaxation → dilates blood vessels → blood pressure goes down
compliance
how easily a heart chamber of blood vessel expands when filled with blood
change in volume over change in pressure
what is compliance on a curve of volume v.s. pressure
slope of the curve
veins have ___ compliance because they need to ___
high, have a large change in volume in response to a small change in pressure
veins have ___ elasticity
low (store very little pressure even with large volume changes)
arteries have ___ compliance because ___
low, a massive change in pressure is required for a small change in volume
arteries have ___ elasticity
high (a small volume change results in a large pressure change)
what are the 3 lines of defense in the immune system?
prevention of infection → targeted destruction of pathogens → specific targeting of pathogens/immunological memory
the first two line of defense of the immune system are ___
nonspecific
the third line of defense of the immune system is ___
specific
1st line: prevention of infection
Skin
Mucous membranes
Secretions of skin and mucous membranes
2nd line: targeted destruction of pathogens
Phagocytic white blood cells
Antimicrobial proteins
The inflammatory response
3rd line: specific targeting of pathogens; immunological memory
Lymphocytes
Antibodies
nonspecific lines of defense
first line: physical barriers, inflammatory response
second line: phagocytes, immunological surveillance, interferon, complement, fever
Note
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