Week 6, Lec 1 Flashcards
what are the 3 layers of the walls of arteries and veins
▪ Tunica intima
▪ Tunica media
▪ Tunica externa
in general what’s in the 3 layers of walls of blood vessels
▪ Tunica intima : endothelium, sub endothelial layer
▪ Tunica media: smooth muscle, connective tissue, collagen
▪ Tunica externa: collagen, elastic tissue, vasa vasorum
JUST ROUGHLY
what do veins have that arteries dont
valves
what types of cells is tunica intimata
simple squamous
continuous sheet of simple squamous endothelial cells (endothelium) lining the lumen
what are the general parts of the tunica intima
- continuous sheet of simple squamous endothelial cells (endothelium) lining the lumen
- various amounts of subendothelial connective tissue (CT)
- Internal elastic lamina, a thin layer of elastic fibers, forms the outermost boundary of the tunica intima
what is the thickest layer of the wall in arteries?
what is the thickness layer of the wall in veins?
tunica media
tunica adventitia
what is the thickest layer of the wall in arteries?
tunica media
what is the thickness layer of the wall in veins?
tunica adventitia
what type of cells in the tunica media
muscle cells
what are the general parts of tunica media
- Circularly arranged smooth muscle cells and fibroelastic CT
▪ elastic content increases greatly with the size of the vessel - External elastic lamina, an elastic fiber-rich layer, forms the outermost boundary of the tunica media
what is generally in tunica adventitia (2 things)
connective tissue and vasa vasorum
what does vasa vasorum do
small blood vessels that supply the tunica adventitia and media
general parts of tunica adventitia
outermost layer of the vessel wall, consisting of dense irregular CT
- In larger vessels, the tunica adventitia houses vasa vasorum
▪ small blood vessels that supply the tunica adventitia and media
why do elastic arteries (i.e. aorta, pulmonary trunk) have a a greater number of elastic membranes
to deal with high pressure blood flow from the heart
what do muscular arteries have to help regulate blood flow in various regions of the body
smooth muscle layers
what do arterioles do
control the flow into capillary beds and regulate blood pressure through constriction or dilation.
which vessel is responsible for regulating blood pressure and how?
arterioles
via constriction and dilation
what are metarterioles? where are they found
act as transitional vessels between arterioles and capillaries, controlling blood flow into capillaries.
what type of arteries are major pressure reservoirs of circulation
elastic arteries
elastic arteries vs msuclular arteries
elastic: more elastic fibers
muscular: more smooth musclea
elastic arteries characteristic
▪ relatively thin external elastic lamina
▪ Very pulsatile, and are the major pressure reservoirs of the circulation
▪ Designed to handle high-pressure blood flow near the heart
muscular arteries characteristic
▪ Still pulsatile, but do not serve a major pressure reservoir function
▪ Although a large layer of smooth muscle, cannot completely vasoconstrict and “cut off” blood flow, and not the major source of peripheral resistance
▪ Distribute blood to various organs and tissues, controlling flow through smooth muscle contraction
what are the majority of arteries throughout the body
muscular arteries
what are the 5 elastic arteries (conducting arteries)
- Aorta
- Pulmonary arteries (pulmonary trunk)
- Common carotid arteries
- Subclavian arteries
- Common iliac arteries
what are the 5 muscular arteries (distributing arteries)
- Radial artery
- Femoral artery
- Brachial artery
- Coronary arteries
- Popliteal artery
what is the main controller of blood pressure
arterioles
- Control systemic blood pressure and direct blood flow into capillary beds through smooth muscle constriction and dilation.
what is the microvascular control point that regulates blood flow into individual capillaries through pre capillary sphincters, fine tuning the supply to meet local tissue demands
metarterioles
what are the major sites of regulation in the CV system
arterioles and metarterioles
▪ Arterioles can constrict significantly and restrict blood flow to a capillary bed
▪ Pre-capillary sphincters at the junction of metarterioles and capillaries can greatly reduce flow to a capillary bed AND metarterioles can shunt blood directly to venules
what are the 3 types of capillaries
- continuous capillaries
- fenestrated capillaries
- sinusoidal capillaries
which capillary is least permeable and what is most permeable
continuous- least
sinusoidal- most
continuous capillaries
Least permeable, found in tissues that need tight control over what passes through
fenestrated capillaries ? what type of organs are they found in? what do they allow the passage of?
- Moderately permeable, allowing larger molecules to pass, found in organs involved in filtration and absorption
sinusoidal capillaries- what do they allow to pass? found in?
- Highly permeable, allowing large particles like proteins and cells to pass, found in specialized organs
what type of capillary are the majority?
continuous capillaries
what do continuous capillaries allow to pass
▪ Intercellular junctions allow movement of water-soluble substances
where are fenestrated capillaries found? for what purpose?
or areas that require higher filtration or increased delivery of soluble substances
▪ Glomerulus in the kidney
▪ Endocrine glands, lamina
propria of the intestines
▪ Fenestrae are covered/altered by proteins that form a sort of diaphragm whose properties can be altered
where to find fenestrated capillaries
ie. absorb and filter = kidneys, endocrine glands, intestines
where are sinusoidal capillaries found (let large molecules pass through)
- liver, spleen, lymph
nodes - bone marrow
what makes sinusoidal capillaries so permeable?
gaps btw intercellular junctions and discontinuous basal lamina
sinusoidal capillaries
▪ Discontinuous basal lamina
▪ Larger diameter
▪ Massive gaps between the intercellular junctions
▪ Specialized for allowing cells to move in and out of them
which capillaries have fenestrae (pores through the endothelial cells)
sinusoidal capillaires
where are continuous capillaries found
CT, muscle, neural tissue; modified in brain tissue
what has largest and smallest diameter of capillaries
smallest is continous
largest is sinusoidal
which capillaries form tight junctions at marginal fold with itself or adjacent cells vs which have endothelial and basal lamina that are discontinous
tight junctions= continuous and fenestrated capillaries
discontinous= sinusoidal capillaries
examples of large veins
Vena cava, pulmonary veins, portal vein.
overall 3 layer structure of large veins
- Tunica Intima: Well-developed, with endothelium and a prominent subendothelial layer.
- Tunica Media: Thin, containing relatively fewer smooth muscle cells compared to arteries.
- Tunica Adventitia: Thickest layer, composed of dense connective tissue, collagen, and elastic fibers. Contains vasa vasorum (small blood vessels) to nourish the vein wall.
what is the thickest layer in large and medium veins
tunica adventitia
which veins; large, medium, small have vasa vasorum (small blood vessels) in their tunica adventitia
large- yes
medium- sometimes
small- no
how much smooth muscle cells do veins have in the tunica media
less than arteries
what is the function of large veins
Large veins return deoxygenated blood to the heart from systemic circulation. They are able to accommodate large blood volumes.
examples of medium veins
Femoral vein, renal vein, brachial vein.
what is the 3 layer structure of medium veins
- Tunica Intima: Thin, with endothelium and a thin subendothelial layer.
- Tunica Media: Thinner than arteries, with scattered smooth muscle cells.
- Tunica Adventitia: The thickest layer, with collagen and elastic fibers. May have some vasa vasorum.
what is present in medium veins? what is the purpose of this structure?
valves
Present, especially in the limbs, to prevent backflow of blood due to low pressure.
what is the function of medium veins
These veins drain blood from organs and limbs, using valves to direct blood flow toward the heart.
what are examples of small veins (venules)
Postcapillary venules, collecting venules.
what are the 3 layers of small veins (venules)
- Tunica Intima: Endothelial cells with a thin basal lamina.
- Tunica Media: Very few layers of smooth muscle cells or absent in the smallest venules.
- Tunica Adventitia: Thin layer of connective tissue.
what is the function of small veins
Venules collect blood from capillaries and begin the process of returning it to larger veins. Postcapillary venules also play a role in inflammatory responses, allowing white blood cells to exit the bloodstream and enter tissues.
how are valves formed? where are they found (type of vessel)? where in body?
forms from reflections of tunica intima
found in large and medium veins
more in lower extremities than upper
lumen of veins is _____ than artery
Lumen of veins is much larger and much less likely to be constricted than that of an artery
how much of the body blood volume do systemic veins carry
2/3
which types of veins can somewhat constrict and in response to the secretion of what
Large and medium veins can constrict somewhat in response to increased secretion of catecholamines
what is hemodynamics
study of how blood moves in the vascular compartments
what impacts hemodynamics
Impacted by properties of the vessels, properties of the blood, activity of the heart, and the presence of gravity (and position of the patient)
if the patient is recumbent vs standing what is the difference in venous pressure
when standing way more pressure in legs and less near head
way less and more evenly spread pressure when laying
poiseuilles law if for
flow rate
poiseuilles law
▪ Describes the flow of an incompressible and Newtonian fluid (like blood in small vessels) through a cylindrical pipe or tube.
▪ It relates fluid flow rate to the vessel’s dimensions and pressure differences.
what variables effect poiseuilles law
pressure gradient
radius of vessel
viscosity
length of vessel
according to poiseuilles law a smaller radius causes
higher resistance
according to poiseuilles law and increased length and viscosity causes (i.e. dehydration)
higher resistance
what increases and decreases flow (poiseuilles law)
- Flow increases with increased pressure and vessel radius.
- Flow decreases with increased viscosity and vessel length.
when does poiseuilles law work
ONLY WITH LAMINAR FLOW
not turbulent!!!
when does poiseulles law not apply
in turbulent flow
what is laminar flow
where fluid moves in parallel layers, and each layer flows smoothly without mixing with adjacent layers.
what happens to poisolles law if flow is turbulent
no longer applies
- If flow becomes turbulent, then flow is proportional to the square root of the pressure gradient
▪ turbulent flow is less “energy efficient”
what is more energy efficient; laminar or turbulent flow
laminar
what things occur in turbulent flow? what areas does turbulent flow occur at?
In turbulent flow, fluid movement is irregular, with eddies, vortices, and chaotic mixing between layers
.
▪ This typically occurs at high flow velocities or in areas with sharp changes in vessel diameter (e.g., bifurcations, atherosclerotic plaques).
what is the assumption of poiselles law
constant resistance
In turbulent flow, Poiseuille’s law does not apply because the law assumes a constant resistance to flow. However, in turbulent flow, the resistance increases unpredictably due to chaotic fluid motion and energy dissipation.
which number to predict when turbulent flow will occur
Reynolds number
what is Reynolds number for
to predict when turbulent flow will occur
what is the # for Reynolds number that says flow will be turbulent
> 2300
what is reynolds number calculated by
fluid density
diameter of vessel
velocity of fluid
viscosity
What are pathological situations that could increase the likelihood of turbulent flow?
- Atherosclerosis
- Stenosis
- Hypertension
- Aneurysms
- Valvular heart disease,
when is turbulent flow more likely to occur
Turbulent flow is more likely when blood velocity increases, vessel diameter is irregular or constricted, or viscosity decreases.
if viscosity decrease what type of flow is more likely
turbulent flow
if blood velocity increases what type of flow is more elikely
turbulent flow
what is poiseuilles law
Q= (P1-P2) pi r^4/ 8nl
Q= flow
(p1-p2)= pressure gradient
r= radius of vessel
n= viscosity
l= length of vessel
what is Bernoullis principle assume
pressure is constant in a system, regardless of velocity
according to Bernoulli
If forward velocity increases in a blood vessel, that increases “forward pressure”
▪ What is the impact on the force that is exerted against the wall of the vessel?
As forward velocity increases, while the dynamic pressure may increase, if the static pressure decreases due to the conservation of energy in the system, the overall impact on the force against the vessel wall can vary. (chat gpt)
Bernoulli says pressure is constant, regardless of veloctiy
what happens to pressure and velocity when you go from arteries to capillaries
- Pressure: Decreases significantly.
- Velocity: Decreases significantly (slowest in capillaries).
what happens to pressure and velocity when you go from capillaries to veins
- Pressure: Continues to decrease but at a slower rate.
- Velocity: Increases as blood moves back toward the heart.
where is pressure and velocity the highest
aorta and large arteries
arteries and pressure
- Blood pressure is highest in the aorta and large arteries (around 120 mm Hg during systole).
- As blood travels through smaller arteries, the pressure gradually decreases but remains relatively high compared to other vessels.
arteries and velocity
- Blood velocity is high in the aorta due to the forceful contraction of the heart.
- As blood moves into smaller arteries and arterioles, the velocity starts to decrease slightly due to the increased cross-sectional area.
capillaries and pressure- why is it low
for nutrient and waste exhange
capillaries and pressure
- Pressure drops significantly in the capillaries, usually around 30 mm Hg or lower.
- This reduction in pressure is crucial for facilitating the exchange of nutrients and waste between the blood and surrounding tissues.
where is blood velocity lowest
capillaries
capillaries and velocity
- Blood velocity is lowest in the capillaries. This is essential because slower flow allows more time for the exchange processes to occur.
- The vast network of capillaries (huge total cross-sectional area) contributes to this reduction in velocity.
what happens to velocity and pressure when go from capillaries to veinsq
pressure continues to drop
velocity increases
pressure in veins
- After passing through the capillaries, pressure continues to drop as blood enters the venules and larger veins, eventually reaching around 5-10 mm Hg near the vena cava.
- The pressure in veins is significantly lower than in arteries.
velocity in veins
- Blood velocity begins to increase as it returns to the heart through the venules and larger veins, even though the pressure is low.
- The cumulative effect of the return flow through the veins results in a higher velocity as it approaches the heart, despite the low pressure.
what are the 2 types of vascular systems for circulation
parallel and series
what is series circulation
In a series arrangement, blood flows through one vessel, then directly into the next, one after the other. This is less common in the body.
Example: The arrangement of blood flow from the heart through the aorta and then through various arteries to a single capillary bed is somewhat sequential but isn’t truly series in a broad physiological sense.
which has lower resistance; series or parallel circulation
parallel
implication of series circuit on resistance
In a series circuit, the total resistance to blood flow is the sum of the resistances of each individual vessel. This can lead to higher overall resistance and potentially less efficient blood flow.
parallel circulation and example
In a parallel arrangement, blood can flow through multiple vessels simultaneously. This is the predominant arrangement in the body.
- Example: The systemic circulation is characterized by many capillary beds in parallel. For instance, when blood reaches an organ, it can be distributed through multiple arterioles leading into many capillaries, allowing different tissues to receive blood concurrently.
what is the predominant arrangement of vascular system in the body
parallel circulation
what is the implication of parallel circuit
In a parallel circuit, the total resistance is less than the resistance of any individual vessel. This is because each additional pathway provides an alternative route for blood flow, which reduces the overall resistance and enhances perfusion. This allows for efficient distribution of blood to various tissues and organs
series circuits:
why the cumulative resistance of the systemic capillary beds are so low, even though the radius of the vessels are so small (Poiseuille’s law says small vessel = higher resistance)?
- Despite individual capillaries having high resistance due to their small radius
- their parallel arrangement results in low cumulative resistance, enabling effective blood flow and nutrient exchange in the systemic circulation.
what is total blood volume in adults;
where is the majority of the blood in systemic circulation found
5 L
majority in veins
how much total blood in systemic circulation? veins? arteries and capillaries?
▪ 80% in the systemic circulation
▪ 60% in systemic veins
▪ Small arteries and capillaries – 20% of blood volume
are veins compliant or non compliant
Veins are very compliant – they’re “floppy” and are easy to distend (up to a point)
▪ If you give someone 500 mL of normal saline, 80% of that stays in the systemic circulation, and most of it (95%) locates in the veins…
what effect do veins have on arterial blood pressure
very little- very floppy
what is compliance
describes how much pressure is required to change the diameter (volume) of a structure
the ability of a blood vessel to expand and accommodate changes in blood volume or pressure.
high compliance ? are veins or arteries compliant?
small amount of pressure ! large change in volume
▪ In general, veins are more compliant than arteries
what does compliance decrease with
▪ Compliance of a vessel – especially larger arteries -decreases with age; vessels become “stiffer”
* Atherosclerosis
* Calcification
- Compliance decreases with contraction of smooth muscle within blood vessels
arterial compliance
Arterial compliance is the ability of arteries to stretch and expand when blood pressure increases during systole (heart contraction).
what type of compliance do arteries have
Arteries have relatively low compliance, meaning they do not stretch easily. This is due to their thick muscular walls and elastic fibers, which allow them to withstand high pressure from the blood being pumped by the heart.
why do arteries have low compliance
The low compliance helps maintain high blood pressure, ensuring efficient blood flow to various organs. Arteries can also dampen the pressure fluctuations caused by the heartbeat.
what compliance do veins have
High Compliance: Veins have high compliance, allowing them to accommodate larger volumes of blood at lower pressures. Their walls are thinner and less muscular compared to arteries.
venous compliance
Venous compliance is the ability of veins to expand and hold more blood without a significant increase in pressure.
why do veins have high compliance
bc act as blood reservoir
This high compliance serves as a blood reservoir. During periods of rest or when blood volume increases, veins can expand to store extra blood without a drastic increase in pressure, which helps regulate blood flow and maintain venous return to the heart.
central blood volume (25%) includes:
▪ vena cavae
▪ heart
▪ pulmonary circulation
what is central blood volume important for
▪ determining preload of the heart (optimal ventricular
stretch–>optimal force of contraction)
▪ pathologic situations like pulmonary edema due to
congestion
how to acutely shift large volumes of blood into or out of central compartments
by varying the amount in the peripheral compartments
▪ Peripheral compartments – veins in the abdominal cavity or limbs
what is elasticity
the tendency for a structure to resume it’s original shape once a distending force (pressure) is removed
what decreases cardiac work
compliant yet elastic arteries
what effect does increasing venous filling pressure have on cardiac out? why?
increases cardiac output due to improve actin-myosin overlap at optimal preload
- … but at the same time, as cardiac output increases, the central venous blood volume is removed more quickly
▪ due to increased movement of fluid
what solution to the venous return to central blood when in an upright position?
valves in leg veins or lower body
surround leg veins with skeletal muscle (contracts with standing)
▪ Breathing in decreases intrathoracic pressure…
* Which draws blood upwards
how much of the cardiac cycle is spent in systole
1/3
what is the mean arterial pressure (MAP) formula
Pulse pressure (PP) = systolic pressure (SP) – diastolic pressure (DP)
MAP = DP + PP/3
OR
MAP = Diastolic Pressure + 1/3(Systolic Pressure - Diastolic Pressure)
what are distributing arteries
When an artery enters an organ, it undergoes multiple branches (six to eight times). These arteries are known as distributing arteries, as they distribute blood to different regions of the organ.
what are arterioles
the distributing arteries branch into arterioles, which are smaller
blood vessels with a diameter of about 10 to 15 microns.
artery –> distributing arteries –> arterioles –> metarterioles –> pre-capillary sphincters –> capillaries
:)
what is the function of arterioles
arterioles typically branch two to five times and serve as the primary site for regulating blood flow into the capillaries. They play a key role in controlling resistance and blood pressure.
arterioles play a key role in
regulating blood flow, controlling resistance and blood pressure
what are metarterioles
As arterioles continue to branch, they lead to metarterioles, which are transitional vessels between arterioles and capillaries.
what is the difference in musculature between arterioles and metarterioles
- Muscle Layer: Muscular arterioles (the larger arterioles) usually have a single layer of smooth muscle that helps regulate blood flow
. - Discontinuous Muscle: Metarterioles have a discontinuous layer of smooth muscle along their length, which is not uniform like in the larger arterioles.
metarterioles have ____ muscle
discontinuous layer of smooth
what is before capillaries;
Metarterioles lead directly to capillaries, which have an internal diameter
ranging from 3 to 9 microns.
what occurs in capillaries
site of nutrient and gas exhange
capillaries function
Capillaries are the sites of nutrient and gas exchange between the blood and surrounding tissues. Their small diameter allows red blood cells to pass through in single file, facilitating this exchange.
where are pre capillary sphincters found
At the junction of metarterioles and capillaries are pre-capillary sphincters. These are small bands of smooth muscle that regulate blood flow into the capillary beds.
what is the function of pre-capillary sphincters
When the sphincters are contracted, blood flow into the capillaries is reduced or halted, directing blood flow to other areas or minimizing flow when tissues are not active. When relaxed, they allow more blood to flow into the capillaries for exchange.
what is the basement membrane of capillaries made of
type IV collagen
why collagen in basement membrane of capillaries
The basement membrane of capillaries is primarily formed by Type IV collagen. This structure supports the capillary walls and provides a scaffold for endothelial cells, ensuring the integrity and functionality of the capillaries.
what are continuous capillaries? what do they allow the movement of?
Continuous capillaries are characterized by an uninterrupted endothelial lining, which allows them to maintain a relatively tight barrier between the blood and surrounding tissues. Most continuous capillaries are considered “leaky,” permitting the free movement of small, water-soluble substances (like ions, glucose, and amino acids) while restricting larger molecules and cells.
what are the exceptions to the continuous capillaries
- Blood-Brain Barrier (BBB)
- Blood-Testes Barrier
they have tight junctions and are less permeable
what do the * Blood-Brain Barrier (BBB) and * Blood-Testes Barrier have in them
continuous capillaries with tight junctions formed by proteins called occludins and claudins.
These proteins connect adjacent endothelial cells and form a more complete seal compared to regular continuous capillaries.
function of tight junctions in Blood-Brain Barrier (BBB) and * Blood-Testes Barrier
reduced paracellular permeabilty , ensuring that only specific substances can cross the endothelial barrier
what is pinocytosis
Continuous capillaries engage in a process known as pinocytosis, where they continuously endocytose (internalize) small pockets of extracellular fluid from the vascular space. This involves the formation of small vesicles that capture fluid and any dissolved substances.
what does pinocytosis allow for
ransport Across the Basement Membrane: Once internalized, these vesicles transport the fluid and its contents across the endothelial cells and release them into the surrounding tissue. This mechanism allows for the regulated exchange of substances between the bloodstream and the tissue, even in areas where tight junctions restrict other forms of transport.
what effect does inflammation have on pinocytosis
increases it in continuous capillaries –> increased fluid up to transport immune cells for infalmatory response (antibodies and nutrients)
what effect does inflammation have on permeability
increases it ; allow larger molecules and immune cells to pass to respond to injury or infection
what are caveolae in continuous capillaries?
Caveolae – “small caves”
▪ endocytosis and transcytosis of macromolecules across endothelial cells
▪ vesicles can move slowly through the endothelial cell
what is the purpose of caveolae in continuous capillaries?
acilitate the endocytosis and transcytosis of macromolecules.
allow for controlled transport across the endothelial barrier while intercellular clefts provide a selective pathway for small molecules.
what are vesicular channels formed by in continuous capillaries
pinocytic vesicles
what are intercellular clefts in continuous capillaries
just small enough so albumin doesn’t get through
which way do substances move
- Substances move down their concentration gradient (diffusion) except for water
▪ Water moves down its concentration gradient AND down its hydrostatic gradient
what is ricks law
speed of which substances diffuse down their gradient
what are starling forces
Starling forces govern fluid exchange in the body by balancing the hydrostatic pressure that pushes fluid out of capillaries and the oncotic pressure that pulls fluid back in.
what are the variables in starling forces
leakiness of capillary wall
hydrostatic pressure
osmotic pressure
fluid in capillary
fluid in interstitial space
how much protein leaks through capillary wall
what is Ficks law
describes the diffusion of substances, particularly the movement of gases or solutes across a barrier, such as cell membranes or capillary walls.
ricks law variables
flow/flux
concentration gradient
surface area
thickness of membrane
too much movement of substances across capillary walls causes what condition?
edema
what keeps water inside the capillary
▪ albumin and other plasma proteins
- a small amount leaks through ! a small oncotic pressure in the interstitial space
what helps to reduce excessive edema in tissue
GAGs and lymphs
▪ glycosaminoglycans that absorb water like a
“sponge” (lots of CHO moieties)
▪ lymphatics in most tissue
what is auto regulation
intrinsic ability of a capillary bed to regulate its own blood flow based on local tissue factors, rather than relying on systemic factors like overall blood pressure.
myogenic regulation
▪ Maintains a relatively constant rate of tissue flow despite
changes in MAP
- Higher pressures in the vessel (smaller vessels, i.e. arterioles)–> smooth muscle stretching → increased constriction (stretch-activated calcium channels)
- Decreased pressure!decreased stretch → dilation
what is the safe range for blood flow
80-125% of normal
arterial pressures of 60-160 mmHg
what happens when BP gets above and below 60-160 range (auto regulation)
- Atpressuresabove about 160 mm Hg, vascular resistance decreases because the pressure forces dilation to occur
- at pressures below 60 mm Hg, the vessels are fully dilated, and resistance cannot be appreciably decreased further.
what metabolic factors in auto regulation lead to vasodilation
O2, CO2, H+, lactate, adenosine, K+
mitochondria will produce H2S in hypoxic situations – may be the major metabolic autoregulatory mediator in some tissues
what is hyperaemia?
▪ increased blood flow leads to washout of the same metabolites
▪ Can lead to reactive hyperemia – after a period of vasoconstriction, metabolites build up and lead to a period of vasodilation and greatly increased perfusion
what does nitric oxide to do tissue flow
vasodilation
what causes release of nitric oxide
shear stress
NO is produced by endothelial cells - shear stress causes its release from the endothelium
what is shear stress
the force placed on a blood vessel along the axis of blood flow (increases with pressure, velocity of flow, turbulence)
what is shear stress detected by
Detected by mechanoreceptors that modulate nitric oxide synthase (which produces NO from L-arginine)
how does nitric oxide cause vasodilation?
NO activates soluble guanylyl cyclase! cGMP production! activation of PK G ! relaxation (through dephosphorylation of myosin) of smooth muscle
net result of nitric oxide
shear stress increases –> nitric oxide production –> vasodilation in arterioles –> a decrease in shear stress
what makes nitric oxide
l arginine
histamine
bradykinin
prostaglandin E2 and I2
epi and NE via beta 2 receptors
all cause??
vasodilation
what is bradykinin acrtivated by
circulating protein, activated by inflammatory signals
▪ Potent vasodilator
what can histamine cause
vasodilates arterioles, constricts venules → edema
epi and NE via alpha 1
serotonin
thromboxane A2
prostaglandin F
angiotensin II
ADH
reaction to damage (platelets)
all cause?
vasocontriction
epi and noreipneuphrine different receptors causing vasoconstriction vs vasodilation
vasocontrict- alpha 1
vasodilate- beta 2
what effect does skeletal muscle have on capillaries adn veins
compresss capillaries to restrict blood flow
help veins pumo blood back to heart
Compression of Capillaries: During muscle contractions, the skeletal muscle fibers shorten and exert pressure on the capillaries that supply blood to the muscle. This compression can temporarily restrict blood flow within the capillary bed during contraction.
Emptying the Venous Tree: When skeletal muscles contract, they help pump blood back to the heart by compressing veins. This is particularly effective in emptying the venous tree, which can increase the pressure gradient driving blood flow from arteries to veins.
what happens to blood flow during exercise
increases
After the muscle contractions stop, there is a rapid increase in blood flow to the capillary beds. This increased flow delivers oxygen and nutrients necessary for recovery and continued activity.
what happens with lactate, K+ and adenosine in exercise; how does it effect tissue? what system does it override?
- Lactate: Produced during anaerobic metabolism, signaling the need for increased blood flow and oxygen delivery.
- Potassium (K+): Released by muscle cells during activity, causing local vasodilation to increase blood flow.
- Adenosine: Released as a result of ATP breakdown; acts as a potent vasodilator.
- These metabolites override the vasoconstrictive effects mediated by the ANS, leading to vasodilation and enhanced blood flow to active skeletal muscles.
at rest, how much oxygen do skeletal muscles take from the blood in capillaries? how does this change with exercise?
25-30%
blood flow increases up to 20 fold in exercise bc of vasodilation, capillaries need more gas and nutrient exchange
up to 90% oxygen need during exercise bc of heightened metabolic needs
what effects neural (cerebral) blood flow
ANS, intracranial pressure, ph, adenosine
how does ph and adenosine affect cerebral blood flow
▪ mostly mediated by local increases in H+/adenosine or
by carbon dioxide diffusing across the BBB
▪ Other vasomediators blocked by BBB, so it doesn’t really respond to circulating vasodilatory/constricting influences
what system does brain modulate and impact blood flow to other tissue?
- Brain is also capable of modulating ANS activity, thus it can control blood flow to other tissues
▪ wide range of mechanisms, including baroreceptor input, CO2 concentrations, endocrine feedback loops
an increase in intracranial pressure causses a
decreased perfusion
what is cushion reflex
↑ intracranial pressure → ↓ perfusion
▪ in response to this, the brain increases mean arterial pressure (Cushing reflex)
what receptors does skin have? what the effect of this?
alpha 1 receptors for constriction (sympathetic) - regualte body temperature
what is pulmonary controlled by
low oxygen concentraions = constriction
Pulmonary circulation is unique in that it constricts in response to low oxygen levels (hypoxia), whereas most other vascular beds in the body respond to low oxygen by dilating.
enhances gas exchange efficiency
coronary system is sensitive to
oxygen and adenosine
Mechanical compression during systole → poorer blood flow
what is renal system controlled by
myogenic and tubuloglomerular feedback, catecholamines, angiotensin II
cardiovascular impact of lower body negative presurre machine that stimulate hemorrhage by redistributing blood into lower extremities and mimic central hypovolemia
- Decreased Venous Return: Blood pools in lower extremities, reducing preload.
- Reduced Stroke Volume & Cardiac Output: Less blood fills the heart, decreasing output.
- Compensatory Tachycardia: Heart rate increases to maintain blood pressure.
- Peripheral Vasoconstriction: Sympathetic response causes vessel constriction to maintain pressure.
- Hypotension Risk: Prolonged LBNP can lead to a dangerous drop in blood pressure.
