deck_16304278 Flashcards
blood vessels function
deliver blood to the organs and tissues in your body
help maintain homeostasis via vasoconstriction/vasodilation
note that many capillary sphincters are often constricted to make blood’s delivery of oxygen/nutrients efficient for tissues that require it most
..
how many km of blood vessel does left side pump through?
The left side of the heart pumps blood through an estimated 100,000 km of blood vessels
major types of BV
Arteries (efferent vessels)
Blood vessels that carry blood AWAY from the heart
Arterioles
Smaller than arteries, carries blood AWAY from the heart
Capillaries
Smallest blood vessels where O2 & CO2 can be exchanged
Venules
Smaller than veins, carries blood TOWARDS the heart
Veins (afferent vessels)
Blood vessels that carry blood TOWARDS the heart
arteries about
Also called efferent vessels
carry blood away from the heart to other tissues
High pressure/low volume reservoir
Have thick elastic walls.
characteristic of wall of arteries
thick elastic walls.
arterioles about
Small arteries that are less elastic
Have more smooth muscles
Provide the greatest resistance to the blood flow that help to regulate blood pressure
Regulate flow into capillary beds
arterioles vs arteries
arterioles less elastic
arterioles have more smooth muscle
which vessels contribute most to regulating BP
arterioles
Provide the greatest resistance to the blood flow that help to regulate blood pressure
capillaries about
The site of exchange with tissues
Exchange of gases and nutrients between blood and tissue cells
Compose of single layer of the endothelial cells, (thin flattened cells that line the inner wall of all vessels)
+
and basal membrane
venules and veins, about
Also called afferent vessels
carry blood away from the tissues to the heart
Low pressure/High volume reservoir
Regulate cardiac filling (how much blood is returning to the heart)
what is known as low pressure / high volume reservoire
veins / venules
how do veins regulate cardiac filling?
Neurohumoral mechanisms can mobilize the blood in veins to maintain filling pressure in the right heart when required.
3 layers of wall of blood vessel
Tunica interna
Innermost layer, adjacent to lumen
Tunica media
Middle layer of smooth muscle and elastic CT
Tunica externa
Outermost layer, CT outer covering
tunica interna aka
TUNICA INTIMA
more commonly known as “
tunica externa aka
tunica adventitia
we will refer to it as tunica externa
how are the 5 vessels structurally different?
some structural variations correlate to the different functions of the 5 major blood vessel types
about Tunica Intima (tunica interna)
Forms the inner lining of the blood vessel and is in direct contact with the blood
3 components of tunica intima
3 components:
Endothelium (simple squamous epithelium)
Basement membrane (reticular fibers)
Internal elastic lamina forming the boundary between the tunica interna and tunica media
—> (contributes to distensibility & stretch of vessel)
basement membranes function (general function – maybe not applicable here?)
Functionally, the BM is important for providing physical and biochemical cues to the overlying cells, sculpting the tissue into its correct size and shape.
tunica media – about
Muscular and CT layer that displays the greatest variation among the different vessel types
Composed of smooth muscle and elastic fibers
External elastic lamina separating the tunica externa from tunica media
which component of vessels has the greatest variation b/w the different types?
TUNICA MEDIA (esp because some vessels require more smooth muscle than others, depending on function)
Note external elastic lamina
shown as part of tunica externa in diagram, but notes include it as part of tunica MEDIA
more about role of tunica media
Regulates the diameter of the lumen, ultimately effecting the rate of blood flow and pressure
Helps limit blood loss with injury (VASOCONSTRICTION)
Allows stretch and recoil of the blood vessel
note hemostasis (vascular phase & tunica media)
(Helps limit blood loss with injury)
recall:
1) vascular phase
2) platelet phase
3) coagulation phase
tunica media contributes to vasoconstriction (during vascular phase)
tunica media and stretch/recoil
“Allows stretch and recoil of the blood vessel”
tunica externa (adventitia) – about
Consists of elastin and collagen fibers, numerous nerves and blood vessels (VASA VASORUM)
Contains the vasa vasorum
Small blood vessels that supply blood to the tissues of the vessels
Helps anchor vessel to surrounding tissues
vasa vasorum
Vasa vasorum are defined as small blood vessels that supply or drain the walls of the larger arteries and veins, and connect with a branch of the same vessel or a neighboring vessel to form a network of small blood vessels
Supply the vessel tissue with blood (oxygen and nutrients)
small arteries and veins in the tunica externa
NOTE diagram cmoparing vein vs artery
may not always be the case, but —>
in diagram shows that vein does not have internal/external ELASTIC LAMINA
otherwise, both have all the same components in diagram
SMOOTH MUSCLE (tunica media) layer is esp THICKER in artery
and Tunica externa is also considerably thicker in artery
tunica interna is roughly same
(all according to this diagram, in slides)
also note LUMEN
also note that LUMEN is much LARGER in vein
Seems that both are roughly same size externally, but due to increased mass of TUNICA MEDIA (smooth muscle layer) in ARTERY –> lumen size is relatively smaller
note differences
Arteries: thickest walls
Veins: largest lumens
Movement in vessel:
—> Arteries: pressure from heart
—> Veins: have valves and use skeletal muscle actions to move blood
vein valves
esp lower extremity
prevent backflow
as skeletal muscles assist in pushing blood upward, past valves, back to heart
arteries – HIGH COMPLIANCE
somewhat similar in concept to “plasticity”
Compliance:
“the ability of an organ to distend in response to applied pressure.”
why arteries high compliance
High compliance due to numerous elastic fibers
smooth muscle innervation in arteries
Smooth muscle innervated by autonomic nervous system
smooth muscle innervation vs VASOCONSTRICTION
Vasoconstriction:
—> sympathetics cause a decrease in the diameter of an artery or arteriole
—> increases BP or restricts blood flow to a damaged area
smooth muscle innervation vs VASODILATION
Vasodilation:
—> The process by which a decrease in sympathetics causes an increase in the diameter of the artery or arteriole.
—> via an increased need for blood supply or changes to body metabolism
(E.g. via effect of drugs)
are parasympathetics involved in vasodilation?
No
reduced sympathetic nervous signals is responsibly for vasodilation
also
what about effect of drugs?
E.g.
NO as mediator of vasodilation
medication vs vasodilation (E.g. NO)
NO and Vasodilation Mechanism
NO diffuses into the smooth muscle cells of blood vessels and activates an enzyme called guanylate cyclase,
which in turn increases the production of cyclic guanosine monophosphate (cGMP).
Elevated levels of cGMP cause the relaxation of smooth muscle cells, leading to vasodilation.
types of arteries
Elastic arteries (aka conducting arteries)
Muscular arteries (aka distributing arteries)
elastic arteries (aka conducting arteries)
LARGE DIAMETER
More elastic fibers, less smooth muscle
Function as pressure reservoirs
E.g. of elastic arteries
aorta and pulmonary arteries
contain much more elastic tissue in the tunica media than muscular arteries
high compliance of aorta
also note DICROTIC NOTCH and elasticity of AORTA
Muscular arteries (aka distributing arteries)
Medium diameter
More smooth muscle, fewer elastic fibers
smooth muscles allow vessels to regulate blood supply constricting or dilating.
Distribute blood to various parts of the body
more about elastic arteries
Largest diameter arteries in the body
Their walls are relatively THIN compared to their large DIAMETER.
internal and external lamina of ELASTIC ARTERIES
Well defined internal and external elastic lamina
(Elastic arteries)
thick tunica media, but primarily of which composition?
Thick tunica media made primarily of ELASTIC FIBRES called ELASTIC LAMELLAE
more about function of elastic arteries
they stretch & expand to accommodate a surge of blood during ventricular systole (E.g. Aorta)
Store mechanical energy – functioning as a “pressure reservoir”
When the ventricles of the heart are relaxed, these arteries may still propel the blood forward
—> VIA ELASTIC “recoil” (??)
again, E.g.
Examples: aorta, pulmonary trunk, aorta’s major initial branches
more about structure of muscular arteries (distributing arteries)
Medium-sized arteries
Tunica media contains more smooth muscle and fewer elastics fibers than elastic arteries
Well defined internal elastic lamina, thin external elastic lamina
—> external lamina that is part of tunica media does not need to be as thick
more about function of muscular arteries
Branch and ultimately distribute blood to each of the various organs
Capable of greater vasoconstriction and vasodilation
—> Responsible for control of blood flow rate
muscular arteries and “VASCULAR TONE”
Vascular tone
—> The ability of the smooth muscle to contract and maintain a state of partial contraction
—> Important in maintaining pressure and efficient blood flow
arterioles
Not much bigger than capillaries
Thin tunica interna
—> Thin fenestrated internal elastic lamina (disappears at terminal end)
Tunica media
—> consists of 1 to 2 layers of smooth muscle
Tunica externa
—> loose CT containing sympathetic nerves
(these impact blood flow and resistance via diameter changes)
more about important features related to function of arterioles
These vessels regulate the flow of blood into the capillary networks
METARTERIOLE & “Thoroughfare Channel”
Metarteriole (initial segment?) connects arteriole w/ venule —> VIA THOROUGHFARE CHANNEL (latter segment?)
the channels extending from metarteriole are capillaries
—> forming CAPILLARY BED(s)
a sphincter is at junctions of capillaries @ the metarteriole / thoroughfare channel
Precapillary-sphincters
at junction of arteriole and capillary
precapillary sphincter constriction?
Increase resistance:
—> Decrease diameter & vasoconstrict
—> Decreases blood flow into capillaries (E.g. when not needed)
Decrease resistance:
—> Increase diameter & vasodilate
—> Increases blood flow into capillaries
About Capillaries
Aka “exchange vessels”
Smallest of all vessels, but large total surface area
capillaries contact all body cells
—> The more metabolically active the cell the more capillaries serving it
primary function @ capillaries
Exchange of gases and nutrients between the blood and interstitial fluid
No metabolically active tissue is more than a few hundred micrometers from a capillary
capillaries structural characteristics
Lack both a tunica media and a tunica externa
Capillary walls are composed of only
—> a single layer of endothelial cells and
—> a basement membrane
average diameter of capillary
Average diameter = 8 µm
About the same as a single RBC
sometimes smaller –> requiring RBC to bend
capillary beds
interwoven network of many capillaries that supplies an organ or tissue
arises from a single arteriole
the more metabolically active the cells, the more capillaries in the capillary bed
metarterioles (AKA PRECAPILLARY ARTERIOLE)
Initial segment of the connection passageway
Contains smooth muscle that can change the vessel’s diameter and adjust flow rate through capillary bed
“Can be bypassed by arteriovenous shunt that directly connects arteriole to venule”
—> “Regulated by sympathetic innervation”
shunt define
SURGERY
an alternative path for the passage of the blood or other body fluid.
“shunt surgery”
what about arteriovenous shunt (???)
—> nothing found regarding surgery
—> *** MAY BE REFERRING TO THE METARTERIOLE “[serving] as vascular shunt when precapillary sphincters are closed”
Thoroughfare channel (?)
Most direct passageway through capillary bed (bypass)
Contains NO smooth muscle
thoroughfare channel vs metarteriole
Note that metarteriole and thoroughfare channel are continuous and connect arteriole with venule
—> however thoroughfare channel me be referring to the latter portion (venous portion?) which does NOT contain smooth muscle
precapillary sphincters
Precapillary sphincters:
Bands of smooth muscle that contract and relax to control flow into the capillary bed
more about capillary beds (Arterial collaterals)
Capillary bed may be supplied by more than one artery
Multiple arteries called COLLATERALS
—> (ARTERIAL COLLATERALS (via arterial anastomosis?) leading to arteriole?)
—> (collaterals?) fuse before giving rise to arterioles
fusion / arterial anastomosis
Fusion is an example of arterial anastomosis
Anastomosis is joining of blood vessels
why arterial anastomosis?
Allows continuous delivery of blood to capillary bed even if one artery is blocked or compressed
(note also arteriovenous anastomosis)
firectly b/w arteriole and venule
—> possibly also function as backup channels, in this case directly between arterioles and venules
(instead of from small arteries leading into an arteriole)
what about an artery that is the ONLY blood supply to a tissue/organ
An artery that is the only blood supply to a tissue or organ is called a terminal artery or an end artery
TERMINAL ARTERY / END ARTERY
Three types of capillaries
Continuous capillaries
Fenestrated capillaries
Sinusoids (sinusoidal capillaries)
Continuous capillaries
Continuous endothelium with intermittent breaks called intercellular clefts
where continuous capillaries?
Found in the brain, lungs, skeletal and smooth mm, CT
why continuous capillaries
Permits diffusion of water, small solutes, and lipid-soluble materials
Prevents loss of blood cells and plasma proteins
Some selective vesicular transport
specialized continuous capillaries –> where are they, and what do they do?
Specialized continuous capillaries in CNS and thymus have endothelial tight junctions
E.g.
Blood Brain Barrier (?)
Enables restricted and regulated permeability
Esp via vesciles (?)
Fenesterated capillaries
Contains “windows,” or pores, penetrating endothelial lining
Permits rapid exchange of
water and larger solutes
where found?
Capillaries of hypothalamus,
pituitary, pineal, and
thyroid glands
Absorptive areas of
intestinal tract
Kidney filtration sites
sinusoidal capillaries (aka sinusoids or “Discontinuous” capillaries)
Wider and more winding
Unusually large fenestrations
Missing a basement membrane
(OR INCOMPLETE BM w/ very large caps)
Large intercellular clefts
sinusoid etymology
sinus (q.v.) + -oid
sinusoidal capillaries – where?
Found in RBM, spleen, liver, anterior pituitary, parathyroid glands
Portal system?
Portal systems allow passage of blood from one capillary network to another through a portal vein
where are portal systems found?
There are 2 locations found in the body:
—> Liver (hepatic portal system)
—> Pituitary gland (hypophyseal portal system)
hepatic portal system
the venous system that returns blood from the digestive tract and spleen to the liver
why?
It supplies veins with metabolic substrates.
It also ensures that food ingested is processed by the liver first before entering the systemic circulation.
This way, ingested toxins are detoxified by hepatocytes
hypophyseal portal system
Capillary beds in the hypothalamus and the anterior pituitary are connected
(Important structures in the endocrine system)
why hypophyseal portal system?
Its main function is to quickly transport and exchange hormones between the hypothalamus arcuate nucleus and anterior pituitary gland
3rd example?
google says renal portal system
venules
Small veins
Drain capillary blood and begins the return flow of blood back to the heart
about POSTCAPILLARY VEINS
Postcapillary venules:
Initially receive blood from capillaries
lack a tunica media and resemble expanded capillaries
Are very porous and therefore function as a site for exchange and WBC emigration
common site for WBC emigration (Diapedesis / extravasation)
POSTCAPILLARY VEINS
Microcirculation
The blood flow through the smallest vessels in the circulatory system
—> arterioles,
venules,
shunts (referring to metarteriole/thoroughfare channel)
and capillaries
which organs don’t have microcirculation?
exists in all tissues and organs except for the
cornea and epidermis
veins
Veins are formed from the union of several venules
Contain the characteristic 3 layers that make up arteries
how are layers different?
Tunica interna & tunica media is thinner in veins
much less smooth muscle and elastic fibers
—> veins look collapsed when dissected
veins vs elastic laminae?
vs recoil dynamics
Veins lack the internal and external elastic laminae
(They can increase and decrease in size to adapt to changes in volume & pressure but without the recoil dynamics of arteries.)
veins / venules pressure
Veins & venules are under very low pressure
blood tends to stop or even pool
veins and one-way valves (esp @ lower extremity)
One-way valves prevent backflow and keep blood moving forward
Extensions of the tunica interna form valves
point towards the heart and prevent back flow
venous system –> pressure and blood flow
Blood pressure in peripheral venules is <10 percent of that in ascending aorta (largest artery)
Mechanisms are needed to maintain flow of blood in veins against force of gravity
what are the mechanisms used to maintain blood flow against gravity?
Valves
Contraction of skeletal muscles
Respiratory pump
Gravity
respiratory pump (effect?)
The respiratory pump is a mechanism to pump blood back to the heart using inspiration. It aids blood flow through the veins of the thorax and abdomen
vascular (venous) sinus
A vein with a thin endothelial wall and no smooth muscle to alter its diameter
“DCT replaces the tunica media and externa in providing support”
DCT?????
“Dense Connective Tissue” (?)
E.g.
Coronary sinus, dural venous sinuses
vein paths vs arteries
Veins follow the same path as arteries, but are more numerous
Double veins connect via venous channels called ANASTOMOTIC VEINS
—> Superficial veins
—> Deep veins
varicose veins
If valves do not work properly, blood can pool in veins, causing distention and a range of effects
Mild discomfort and cosmetic problems, as with varicose veins (in thighs and legs)
Painful distortion of adjacent tissues, as in hemorrhoids (form in the venous networks of the anal canal)
where varicose veins most common
Most common in lower extremities & esophagus
varicose veins of rectum?
hemorrhoids?
why varicose veins?
Varicose veins in the extremities are usually a result of mechanical stress, repetitive stress, pregnancy (worsen existing), age
Varicose veins in the esophagus are suspected due to eating habits & repetitive reflux/regurgitations
varicose veins SSx
SSx
Pain & tenderness locally, hardened nodules due to dead cells, localized edema, altered blood flow and itchiness
Varicose veins risk factors
Genetics, age, smoking, drugs, obesity, inactivity & trauma
varicose veins Tx
Range from diet & exercise, compression stockings, surgery, laser therapy & light massage
CAREFUL**** – deep stripping NOT recommended for moderate to severe varicose veins
hemorrhoids?
Hemorrhoids varicose veins in the anal canal
Caused by excessive straining, constipation
Angiogenesis
Refers to the growth of new blood vessels from existing vasculature
Functions
Wound healing
Uterine lining
Tumour angeiogenesis factors (TAFs)
Tumor cells secrete proteins called tumor angiogenesis factors (TAFs)
Stimulate blood vessel growth to provide nourishment for the tumor cells
Research to inhibit this and thus inhibit the growth of tumors
Blood reservoires
Total blood volume distribution
Uneven distribution among arteries, veins, and capillaries
Systemic venous system contains 64% of total blood volume (~3.5 L)
Of that , ~1 L is in venous networks carrying blood from digestive organs to liver (Hepatic portal system??)
Act as blood reservoirs
how much blood in systemic arteries?
Systemic arteries contain 13 percent total blood volume
remaining blood?
The remaining blood is in the systemic capillaries, heart, and pulmonary circuit
(23%)
Blood reservoires (Venoconstriction)
Venoconstriction:
Contraction of smooth muscle fibers in veins
—> Reduces diameter of the veins and the amount of blood in the venous system
Why?
Method of maintaining blood volume in the arterial system even with a significant blood loss
venoconstriction via?
Controlled by the vasomotor center in the medulla oblongata
Sympathetic nerves stimulate smooth muscles in medium-sized veins
…
…
Capillary exchange
The movement of substances between capillaries/blood & interstitial fluid
Involves a combination of diffusion, transcytosis, and filtration
combination of 3 processes
1) diffusion,
2) transcytosis,
3) filtration
Diffusion
Net movement of substances from an area of higher concentration to lower concentration
Transcytosis
Large, lipid-insoluble (HYDROPHILIC?) substances cross the capillary membranes via exocytosis and endocytosis
Filtration
Net movement of water from an area of higher pressure to lower pressure
(Vs osmosis???)
DIffusion
Net movement of substances from an area of higher concentration to lower concentration
when is diffusion most rapid (what variables)?
1) Distances are short
2) Concentration gradient is large
3) Ions or molecules involved are small
DISTANCE,
concentration,
size
which part of capillary wall, diffusion ?
Occurs continuously across capillary walls
what types of subtssances, diffusion?
Important for solute exchange (ie. Oxygen, CO2, glucose, aa)
what about water-soluble substances (?) –> hydrophilic
Water soluble (glucose, aa) move through intercellular clefts or fenestrations
FENSTRATED CAPILLARIES
fenestrations are on cell itself, not just between
what about lipid-soluble (hydrophobic) substances?
Lipid soluble (oxygen, CO2, steroids) move through endothelial cells
can RBC or plasma protein exit?
No
except
can not pass through continuous or fenestrated capillaries but can pass through sinusoids
sinusoids:
liver, spleen, lymph nodes, bone marrow and endocrine glands
liver break down RBC
bone marrow create blood cell
endocrine? hormones???
spleen / lymph nodes (LYMPHOCYTES)
2) transcytosis
Enters on one side, transported through the cell via a pinocytic vesicle, then exits on the other side
Hormones (E.g. insulin) & certain large proteins (ABs)
3) Filtration —> BULK FLOW
A passive process in which large numbers of ions, molecules or fluid moves together in the same direction
via what type of gradient (Bulk flow)
Occurs from an area of high pressure to low pressure
what is bulk flow / filtration important for
Important for regulation of the relative volumes of blood and interstitial fluid
what are two processes involved in bulk flow (?)
Depending on the pressure differences, can be either:
1) Filtration
Movement from capillaries —> interstitial fluid
2) Re-absorption
Movement from interstitial fluid —> capillaries
a) Filtration is via BHP
1) Blood hydrostatic pressure (BHP) or capillary hydrostatic pressure (CHP)
—> The pressure of the blood against vessel walls
—> 35 mmHg at arteriole end, 18 mmHg at venous end
a) Filtration is via ISFCOP (oncotic pressure)
2) Interstitial fluid colloid osmotic pressure (IFCOP)
—> Pressure that “pulls” fluid from capillaries into interstitial fluid
—> Very low (close to 0 mmHg), few proteins present in interstitial fluid
b) Reabsorption is via BCOP
3) Blood colloid osmotic pressure (BCOP)
—> Colloid pressure in capillaries caused by large protein molecules that “pulls” fluid from interstitial into blood (mainly albumin)
—> 25 mmHg
b) Reabsorption is via ISFHP
4) Interstitial Fluid Hydrostatic Pressure (IFHP)
—> The pressure that “pushes” fluid from interstitial space back into the capillaries.
—> It varies from a value of -1mmHg to +1mmHg therefore, for our discussion, it’s 0 mmHg.
So net pressure???
35mmHg OUT @ ARTERIAL END
18mmHg OUT @ VENOUS END
25mmHg IN via blood proteins (I.e. albumin)
what about remaining 15% that doesn’t get re-absorbed?
THE REMAINING 15% that doesn’t get re-absorbed returns to blood VIA LYMPH vessels
Starling’s law of capillaries
States that the movement of fluid between the capillaries and interstitial fluid is due to the net effect of all pressures across the capillary (Starling Forces)
what forces are MAIN DETERMINANTS OF NET fluid movement
Because IFHP and IFOP are so low, movement across capillary is largely dependent on the balance of
****hydrostatic and osmotic pressure of the blood
NFP
NET FILTRATION PRESSURE
the balance of these pressures which determines the direction of fluid flow
NFP = (BHP + IFOP) – (BCOP + IFHP)
NFP @ ARTERIAL VS VENOUS ENDS
@ arterial end, NFP = (35) – (25) = 10 mmHg
—-> MORE EXITING
@ venous end, NFP = (18) – (25) = -7 mmHg
—-> MORE RETURNING
In total, more still exits than returns via capillaries/ISF
what about amount that doesn’t return
On average, 85 % of fluid filtered out of the capillaries is reabsorbed.
The other 15 % enters the lymphatic circulation to eventually return back to the heart.
NFP positive vs negative number
+10 mmHg (a positive # indicates filtration)
–> exit
-7 mmHg (a negative # indicates re-absorption)
–> enter
Edema
an abnormal increase in interstitial fluid volume
Usually noticeable after interstitial volume has risen to 30% above normal
Is the result of either excess filtration or inadequate reabsorption
edema causes
Causes include liver disease and damage to the lymphatic system
hemodynamics
Hemodynamics refers to the factors affecting blood flow
Blood Flow:
—> Volume of blood flowing through tissues in a period of time
—> Measured in mL/min
Blood flow 2 key factors
1) Pressure Difference
2) Peripheral Resistance
1) Pressure difference (and blood flow)
Pressure difference (Blood Pressure)
Systolic Blood Pressure: the HIGHEST pressure attained in arteries during systolic contraction
Diastolic Blood Pressure: the LOWEST pressure attained in arteries during diastolic relaxation
Mean Arterial Pressure (MAP): the average BP in the arteries (more later)
arterial pressure
Blood pressure:
Pressure within the cardiovascular system as a whole
Arterial pressure is much higher than venous pressure
—> Receives blood from the heart
—> Have greater degree of contractile capability
Capillary pressure
Capillary pressure is lower than artery and arteriole pressure
Increased overall surface area of total capillaries
Blood spreads throughout capillary network
capillary pressure vs blood flow speed
Drop in capillary pressure causes blood flow in capillaries to be very slow
Allows plenty of time for capillary exchange
Diffusion between blood and interstitial fluid
Venous pressure
Blood pressure in veins is maintained by:
a) Valves
(prevent backflow, keep even pressure along length)
b) Muscular compression of peripheral veins
blood closer to heart vs venous pressure
As blood moves toward the heart, vessels get larger, and resistance decreases
VENOUS RETURN =
Amount of blood arriving at the right atrium each minute
On average, equal to the cardiac output
Changes in blood pressure
Highest pressure at the aorta
—> Heart generates pressure of about 120 mm Hg
—> Aorta cross-sectional area 4.5 cm2
where does pressure drop from the aorta (???
Pressure drops at each branching in arterial system
Smaller, more numerous vessels reduce pressure
At start of peripheral capillaries, pressure is
35 mm Hg
At the venules, pressure is 18 mm Hg
2) PERIPHERAL RESISTANCE
the opposition to blood flow due to friction b/w blood & the blood vessel walls.
must be overcome by sufficient pressure from the heart in order for circulation to occur
Can be altered due to needs
HOW IS PERIPHERAL RESISTANCE DETERMINED? 3 factors
a) Size of the lumen of the vessel (vessel diameter)
b) Blood vessel length
c) Blood viscosity
a) size of lumen
Friction occurs between moving fluid layers
Layer closest to vessel wall is slowed most because of friction with endothelial surface
Effect gradually diminishes away from wall
In smaller vessels, more fluid volume is near wall, so higher resistance
In larger vessels, central region unaffected, so lower resistance
size of lumen formula
Size of the lumen
Resistance (R) = 1/d4
If we increase diameter (d), there is a significant decrease in resistance (inverse relationship).
E.g.
R = 1/24 1/16 = 0.0625
R = 1/44 1/256 = 0.0039
b) total blood vessel length
the longer the pathway or blood vessel, the more the resistance
Friction occurs between vessel walls and moving blood
Increase in vessel length = increased surface area = increased in friction or resistance
E.g.
Capillaries total length longest (???)
c) blood viscosity
increased solutes, molecules, protein, & cells will increase the viscosity
Any condition that decreases fluid volume &/or increases viscosity will increase resistance
Systemic Vascular Resistance (SVR)
aka total peripheral resistance (TPR).
The total resistance of the entire vascular system (arteries, arterioles, capillaries, venules, veins) .
Veins & arteries have large diameters therefore don’t contribute very much to SVR.
Arterioles, capillaries, & venules are much smaller and therefore DO contribute to SVR.
Venules & capillaries have little to no smooth muscle, therefore their contribution to resistance is set and doesn’t change
WHAT CONTRIBUTES MOST TO SVR
The arterioles however DO contain smooth muscle and undergo vasoconstriction & vasodilation
and thus ARTERIOLES contribute the most to SVR
velocity of blood
According to the laws of physics, there is an inverse relationship of fluid velocity with cross sectional area of a closed tube.
The larger the total cross sectional area of the tube with associated liquid flow, the slower the velocity.
And conversely, the smaller the total cross sectional area, of the tube, the faster the velocity of flow.
We can see that aortas & arteries have smaller total cross sectional area than capillaries, and thus have a faster velocity. In contrast, capillaries with large cross- sectional area have a very slow the velocity.
REGULATION OF BP AND BLOOD FLOW
…
Homeostatic mechanisms
Ensure adequate tissue perfusion (blood flow through tissues)
Blood flow must match changes in demand for oxygen and nutrients
perfusion
the passage of blood, a blood substitute, or other fluid through the blood vessels or other natural channels in an organ or tissue.
Two regulatory pathways
1) Autoregulation
(LOCAL)
2) Central regulation
(Neural/endocrine)
—> esp if autoregulation ineffective
1) autoregulation
Involves local changes in blood flow within capillary beds
Regulated by precapillary sphincters in response to chemical changes in interstitial fluid
Examples of factors leading to autoregulation:
Changes to oxygen levels
Vasodilating and Vasoconstricting chemicals
Low oxygen in systemic tissues –> dilate
Low oxygen in pulmonary tissues –> constrict
WHY??
B/c not efficient to send blood to that area of pulmonary tissue, since there is no O2 to collect –> more efficient to stop sending blood to that part of lung tissue, and instead send it elsewhere where is it functional/useful
Vasodilating and Vasoconstricting chemicals
Dilation – potassium, H+, lactic acid, adenosine, NO
Constriction – thromboxane A2, serotonin, endothelins
2) CENTRAL REGULATION
Involves both neural and endocrine mechanisms
neural mechanism
Activation of cardioacceleratory center or cardioinhibitory center
Activation of vasomotor center (controls peripheral vasoconstriction)
Results:
Can increase cardiac output and reduce blood flow to nonessential or inactive tissues
endocrine mechanism
Release of vasoconstrictor (primarily NE), producing long-term increases in blood pressure
recall:
beta-blockers BLOCK epinephrine/noepinephrine
where do central regulators receive feedback/input from (??)
Baroreceptors
Respond to changes in blood pressure
Chemoreceptors
Respond to changes in O2, CO2, pH of blood and CSF
Proprioreceptors
Respond to body movement
Limbic system & higher brain centers
emotional & psychological stress/thoughts will descend from these centers directly onto the CV centers
baroceptor reflexes
Respond to changes in blood pressure
Receptors are located in walls of:
i) Carotid sinuses
ii) Aortic sinuses
iii) Right atrium
i) Carotid sinus
regulates pressure in the brain, in R/L internal carotid arteries, travel to the brain via glossopharyngeal (IX) nerve
ii) Aortic sinus
regulates systemic pressure in the rest of the body, in ascending and arch of aorta, travel to the brain via the vagus (X) nerve
iii) RA
.
WHAT ABOUT BV DIAMETER (??) (Motor output)
Vasomotor nerves (sympathetic NS) cause vasoconstriction of blood vessels
Sympathetic neurons that that run from the CV center, exit the spinal cord through all thoracic and L1/2 spinal nerves, pass into the sympathetic trunk ganglia to the blood vessels
Provide constant continuous moderate stimulation of smooth muscles
Motor output
Cardiac accelerator nerves from the thoracic spinal cord (sympathetic NS) increase HR and contractibility and therefore cardiac output (CO).
Vagus nerves (parasympathetic NS) decrease HR and therefore CO.
vasomotor tone
Vasomotor tone – the moderate state of vasoconstriction that sets the resting level of tone of most blood vessels (resting SVR)
Endocrine response
Provide short-term and long-term regulation of cardiovascular function
Utilize endocrine functions of:
The heart
The kidneys
The pituitary gland (antidiuretic hormone, or ADH)
HORMONAL RESPONSE TO LOW BP/volume
which homrone???
—> Immediate response:
Release of epinephrine (E) and norepinephrine (NE)
Released from the adrenal medullae
Caused increased CO and vasoconstriction = increased BP
Diverts blood to skeletal muscle and coronary circulation
other hormones during LOW BP
Antidiuretic hormone (ADH)
–> “Anti” + “urinate” –> less water/solutes (?) lost in urine = remain in blood = increase BP
Angiotensin II
Erythropoietin (EPO)
–> more RBC = more formed elements = more BCOP = more fluid = increase BP (?)
Aldosterone
Hormonal regulation
Renin – Angiotensin –Aldosterone system (RAAS)
juxtaglomerular cells of kidneys detect decrease in BP & volume & in turn secrete renin.
Renin activates angiotensin, angiotensin converting enzyme (ACE) in lungs converts it angiotensin II.
AG II will increase BP by:
1. Increase vasoconstriction
- Stimulates aldosterone which increases re-absorption of Na+ and therefore H2O by the kidneys.
hormonal regulation (ADH)
Anti-diuretic Hormone (ADH) aka “vasopressin”
released by the post pituitary gland in the brain
It is a powerful vasoconstrictor & helps the kidneys reabsorb H2O.
Hormonal regulation —-> DECREASE BP
Atrial Natriuretic Peptide (ANP)
released by atrial cells of the heart in response to heart stretch
powerful vasodilator & increase H2O loss in the kidneys (to decrease systemic BP).
SYNCOPE
together
cut off
MEDICINE
temporary loss of consciousness caused by a fall in blood pressure.
Sudden loss of consciousness due to lack of blood flow to the brain.
Can be related to medications, stress, or orthostatic hypotension (changes to body positions)
SHOCK and HOMEOSTASIS
What is shock?
Acute cardiovascular crisis marked by:
Low blood pressure (hypotension)
Inadequate peripheral blood flow
Normal homeostatic mechanisms cannot compensate
most common cause, shock
Most common causes are hemorrhage and heart damage (as in heart attack)
TYPES OF SHOCK
Hypovolemic Shock – decreased total volume of blood (ie. hemorrhaging or excessive dehydration)
Cardiogenic Shock – poor/lack of normal heart functioning (MI, arrythmias, fibrillations)
Obstructive Shock – blockage of blood flow (thrombus & embolus formations)
Anaphylactic Shock – massive vasodilation in response to an allergen
Neurogenic Shock – damage to nervous system interrupts normal neural BP regulation
Septic Shock – shock in response to sepsis
Hypovolemic Shock
Hypovolemic Shock – decreased total volume of blood (ie. hemorrhaging or excessive dehydration)
Cardiogenic Shock
Cardiogenic Shock – poor/lack of normal heart functioning (MI, arrythmias, fibrillations)
Obstructive Shock
Obstructive Shock – blockage of blood flow (thrombus & embolus formations)
Anaphylactic Shock
Anaphylactic Shock – massive vasodilation in response to an allergen
Neurogenic Shock
Neurogenic Shock – damage to nervous system interrupts normal neural BP regulation
Septic Shock
Septic Shock – shock in response to sepsis
..
.
SSx Shock (systemic drop in BP leads to…)
Muscles/brain
Decreased blood to the brain & systemic muscles –
fainting, cyanosis, pallor, changes to skin temp, altered mental state
SSx shock (CO, HR, pulse)
Pulse is weak and rapid due to decreased cardiac output and rapid heart rate
SSx shock, systolic pressure
Systole drops to below 90 mmHg
where vasoconstriction?
why?
Vasoconstriction of abdominal, urinary, & reproduction organs
blood to brain/heart/lungs
helps conserve blood flow to the vital organs (“)
BLOOD VESSEL PATHOLOGIES
..
aging and BV
aging results in…
Loss of compliance of the aorta
Reduction in cardiac muscle fiber size
Progressive loss of cardiac muscular strength
Decline in maximum heart rate and CO
Increased systolic blood pressure
vasculitis
is inflammation of the vessel wall, due to autoimmune disease or infection
Phlebitis is inflammation of a vein,
arteritis is inflammation of an artery
phlebitis vs arteritis
Phlebitis is inflammation of a vein,
arteritis is inflammation of an artery
temporal arteritis
Inflammation of the temporal artery in the scalp. Pain in the jaw with chewing and pain over the scalp are common symptoms.
atherosclerosis
the formation of lipid lumps (atheromas) in the blood vessel wall, is the most common cardiovascular disease
most common cardiovascular disease
Atherosclerosis
coronary artery disease
Atherosclerosis with narrowing of the arteries supplying blood to the heart muscle. Coronary artery disease makes a heart attack more likely.
most likely cause of heart attack
coronary artery disease
Carotid artery disease
Atherosclerosis with narrowing of one or both of the carotid arteries in the neck. Disease of the carotid arteries makes stroke more likely.
Peripheral artery disease
Atherosclerosis that causes narrowing of the arteries in the legs or groin. The limitation in blood flow to the legs may cause pain or poor wound healing.
Peripheral artery disease
any disease of arteries that does not involve heart/brain
“Peripheral vascular disease is the reduced circulation of blood to a body part, other than the brain or heart, due to a narrowed or blocked blood vessel”
Chronic Venous Insufficiency
CVI damages veins causing blood to pool in your legs. This increases pressure in your leg veins and causes symptoms like swelling and ulcers.
discolouration of feet / lower legs (NECROSIS/gangrene)
arterial thrombosis
blood clot that develops in an artery. If it obstructs or stops the flow of blood to major organs, such as the heart or brain, it can cause damage.
thrombosis vs embolus
What is the difference between thrombosis and embolism? Thrombosis is when a blood clot, or thrombus, forms in a blood vessel. An embolus is when a clot, fat, air bubble, or other feature travels through blood vessels, with a risk of lodging elsewhere.
checking circulation
..
checking pulse
defined as the traveling pressure wave generated by systole & diastole of the ventricles.
generally which vessels can pulse be found?
Pulses can be measured in any artery especially the ones closest to the surface, and is too weak to measure in the arterioles, altogether non-existent in capillaries.
if vessel is farther from heart, what is the effect on pulse
The further away the artery from the heart, the weaker the pulse (generally); the closer the artery, the stronger.
(ie. carotid pulse is stronger than radial or dorsal pedis)
arteries that HCP reference for pulse measurement
Pulses can be measured at characteristic locations throughout the body that are used by EMS and health care professionals. These are arteries tend to be superficial and are easily accessible.
arteries for pulse
Superficial Temporal
Facial
Common Carotid
(common measuring point)
Brachial
(most common used to measure systemic BP)
Femoral: inferior to the inguinal ligament
Popliteal
Radial
(common measuring point)
Ulnar
Dorsal pedis
Abdominal: close to umbilicus
checking BP
a measure of the pressure in the arteries at left ventricular systole & left ventricular diastole.
Korotkoff sounds
sounds heard through the stethoscope when measuring the BP.
systolic vs diastolic BP
Systolic Blood Pressure (SBP) – the initial onset of the sounds created upon first release of the cuff
Diastolic Blood Pressure (DBP) – the point in which the sounds disappear
Pressure difference (BP)
Mean Arterial Pressure (MAP)
a. Systolic Blood Pressure: the HIGHEST pressure attained in arteries during systolic contraction
b. Diastolic Blood Pressure: the LOWEST pressure attained in arteries during diastolic relaxation
MEAN ARTERIAL PRESSURE:
the average BP in the arteries
MAP = diastolic BP + 1/3 (systolic BP –diastolic BP)
In a resting person, MAP = 80 + 1/3 (120 – 80)
MAP = 93 mmHg (using BP of 120/80)
Pulse pressure
the difference between systolic & diastolic pressures (normally about 40 mmHg)
Hypertension
any increase in the pulse pressures beyond the normal range. (ie. stress, atherosclerosis, aging, meds).
Current standards are >130 mmHg systolic BP or >80 mmHg diastolic BP.
Hypotension
any decrease in the pulse pressures beyond the normal range (ie. hemorrhaging, orthostatic changes, meds).
Current standards are <90 mmHg systolic BP or <60 mmHg diastolic BP.
vasomotor centre vs cardiovascular centre
The vasomotor center (VMC) is a portion of the medulla oblongata.
Together with the cardiovascular center and respiratory center, it regulates blood pressure.
It also has a more minor role in other homeostatic processes.
