Module 2 Introductory Anatomy and Physiology of Blood Vessels Flashcards
Compare and contrast the three tunics that make up the walls of most blood vessels
a
Distinguish between elastic arteries, muscular arteries, and arterioles on the basis of structure, location, and function
a
Explain the structure and function of venous valves in the large veins of the extremities
a
Identify the major structures and subdivisions of the renal corpuscles, renal tubules, and renal capillaries
a
What is the tunica intima
- Innermost layer of a blood vessel
- > direct contact with blood as it flows through lumen
- Includes
- > Endothelial lining
- > -> Active participant in regulating vessel tone, coagulation, inflammation…
- > Basement membrane
- > In many vessels, an internal elastic lamina
What is the tunica media
- Middle layer containing concentric sheets of smooth muscle tissue in a framework of loose CT
- Collagen fibers bind all layers together
- Greatest variation among different vessel types
What is the tunica externa
- Outermost layer forming a CT sheath around the vessel
- Very thick and composed mostly of collagen fibers and some elastic fibers
- Contain numerous nerves and tiny blood vessels (vasa vasorum)
What is the sub-layers in the 3 layers in a blood vessel from internal to external
- Tunica intima (endothelium -> basement membrane -> internal elastic lamina)
- Tunica media (smooth muscle -> external elastic lamina)
- Tunica externa (loose fibrous CT -> epithelial cells)
In traveling from the heart to peripheral capillaries, blood passes through:
- Elastic/conducting
- > Large vessels, diameter up to 2.5 cm
- > Pressure reservoir - Muscular/distributing
- > Medium vessels, diameter around 0.4 cm - Arterioles
- > Smaller vessels, diameter around 30 µm
Fill in the blanks about elastic arteries:
Help ____ blood onward while the ventricles are _______
As blood is ejected from the heart into the elastic _____, their walls ______, easily accommodating the surge of blood.
As they stretch, the elastic fibers momentarily _______ mechanical energy functioning as a ______ reservoir.
Then, the elastic fibers ______ and convert stored (potential energy) in the vessel into _____ energy of the blood. Thus, blood continues to move through the arteries even when the ventricles are ______.
Help PROPEL blood onward while the ventricles are RELAXING
As blood is ejected from the heart into the elastic ARTERIES, their walls STRETCH, easily accommodating the surge of blood.
As they stretch, the elastic fibers momentarily STORE mechanical energy functioning as a PRESSURE reservoir.
Then, the elastic fibers recoil and convert stored (potential energy) in the vessel into kinetic energy of the blood. Thus, blood continues to move through the arteries even when the ventricles are RELAXED.
In Muscular Arteries, the
- > Tunica intima very thin and consists of:
1. _______
2. _________
3. ___________ - > Tunica media is major identifying characteristic:
1. ______________
2. _____________ - > (Thin/thick?) external elastic lamina
- > Tunica adventitia is (not/well?) developed
In Muscular Arteries, the:
- > Tunica intima very thin and consists of:
1. Endothelium
2. Flattened subendothelial layer of COLLAGEN and ELASTIC fibres
3. Internal ELASTIC LAMINA - > Tunica media is major identifying characteristic:
1. THICK SMOOTH MUSCULAR layer
2. very FEW ELASTIC fibres - > THIN external elastic lamina
- > Tunica adventitia is WELL developed
Where is the major site of systemic vascular resistance?
Arterioles
Terminal end (metarteriole) tapers towards capillary junction and forms _____
precapillary sphincter
Describe the 3 layers in arterioles:
- Tunica intima
- > Endothelium, no sub-endothelial layer - Tunica media
- > Composed of 1-3 layers of smooth muscle - Tunica adventitia
-> Fairly prominent
Lots of nerves
Describe venules:
- (Thinner/thicker?) walls than arterial counterparts
- ______ venule
- > Smallest venule - Form part of microcirculatory exchange unit with _____
- Muscular venules have thicker walls with _____ layers of smooth muscle
- THINNER walls than arterial counterparts
- POSTCAPILLARY venule
- > Smallest venule - Form part of microcirculatory exchange unit with CAPILLARIES
- Muscular venules have thicker walls with 1 OR 2 layers of smooth muscle
Fxn of veins
Collect blood from all tissues and organs and return it to the heart
How are veins classified?
- Classified on the basis of their size (3):
- Venules
- > Average diameter 20 µm - Medium sized
- > Diameter of 2 to 9 mm
- > Tunica media thin, thick tunica externa with longitudinal bundles of elastic and collagen fibers - Large
- > Diameter of 10 mm to 3 cm
- > Slender tunica media surrounded by thick tunic externa
Pressure in venules and medium sized veins is too ___ to oppose the force of ____
- LOW
2. GRAVITY
Veins contain ____ to prevent backflow of blood
one way valves
Venous valves fxn to
Compartmentalize the blood within the veins
Describe how pressure changes throughout Systemic system:
- From aorta (____ mmHg) to right atrium (_____mmHg)
- Pressure _____ as does velocity of flow
- Friction on walls (converted to _____, and decreasing pressure) is represented by _____
- Resistance and pressure drop is increased with ____ flow
- From aorta (95 mmHg) to right atrium (0-3 mmHg)
- Pressure DECREASES as does velocity of flow
- Friction on walls (converted to HEAT, and decreasing pressure) is represented by RESISTANCE
- Resistance and pressure drop is increased with TURBULENT flow
Describe how pressure changes throughout CAPILLARY BEDS:
- High as ___ at arteriole end, low as ___ at venous end
- Functional average is __mmHg
- High as 35 at arteriole end, low as 10 at venous end
- Functional average is 17mmHg
In the Theory of Circulatory Function, what are the 3 basic principles that underlie all functions of the system
- Blood flow to each tissue of body is almost always precisely controlled in relation to tissue needs
- CO is controlled mainly by the SUM of all the local tissue flows
- Arterial pressure is controlled independently of either local blood flow control or CO
Discuss the principle “The rate of blood flow to each tissue of the body is almost always precisely controlled in relation to the tissue need.”
- Active tissues can need as much as _____x the amount of blood flow compared to at rest BUT heart can only increase output ______x the resting levels
- Therefore, (it is/it is not?) possible simply to increase blood flow everywhere in the body when a particular tissue demands increased flow
- Instead, the microvessels of each tissue continuously monitor tissue needs, (e.g. availability of ______ and ______ and the accumulation of ____ and other waste products)
- These in turn act directly on the ________, dilating or constricting them, to control local blood flow precisely to that level required for the tissue _____.
- Active tissues can need as much as 20-30x the amount of blood flow compared to at rest BUT heart can only increase output 4-7x the resting levels
- Therefore, IT IS NOT possible simply to increase blood flow everywhere in the body when a particular tissue demands increased flow
- Instead, the microvessels of each tissue continuously monitor tissue needs, (e.g. availability of OXYGEN and NUTRIENTS and the accumulation of CO2 and other waste products)
- These in turn act directly on the LOCAL BLOOD VESSELS, dilating or constricting them, to control local blood flow precisely to that level required for the tissue ACTIVITY.
Discuss the principle “The CO is controlled mainly by the sum of all the local tissue flows.”
- When blood flows through a tissue, it immediately returns by way of the ____ to the heart.
- The heart responds automatically to this increased inflow of blood by pumping it immediately into the ____ from whence it had originally come.
- Thus, the heart responds to the ____ of the tissues.
- When blood flows through a tissue, it immediately returns by way of the VEINS to the heart.
- The heart responds automatically to this increased inflow of blood by pumping it immediately into the ARTERIES from whence it had originally come.
- Thus, the heart responds to the DEMANDS of the tissues.
Discuss the principle “In general the arterial pressure is controlled independently of either local blood flow control or cardiac output control.”
- The circulatory system has an extensive system that controls the ______ BP.
- g. if at any time the pressure falls significantly below the normal level of about ____mmHg, within seconds _____ reflexes will raise the pressure back toward normal.
- The circulatory system has an extensive system that controls the ARTERIAL BP.
- g. if at any time the pressure falls significantly below the normal level of about 40mmHg, within seconds NERVOUS reflexes will raise the pressure back toward normal.
Carotid sinus baroreceptors respond in the range of ____
~40-240mmHg??
Aortic arch baroreceptors are stimulated in the same manner, but tend to fire at about ____mm Hg higher than the carotid sinus receptors
30 mmHg
Baroreceptor response is important for ____-term correction of BP
Short-term
A decrease in arterial pressure _____ the baroreceptors - the terminals of afferent fibers of the _______ and ______ nerves - that are situated in the ______ and ______. This leads to a ______ in the afferent impulses that are relayed from these mechanoreceptors through the glossopharyngeal and vagus nerves to the ______ in the dorsomedial medulla. The reduced baroreceptor afferent activity produces a ______ in vagal nerve input to the sinus node that is mediated by the neuroanatomical connections of the NTS to the _________. There is an _____ in sympathetic efferent activity that is mediated by the NTS projections to the _________ (an excitatory pathway) and from there to the __________ (an inhibitory pathway). The activation of RVLM presympathetic neurons in response to hypotension is thus predominantly due to ________. In response to a sustained fall in blood pressure, _______ release is mediated by projections from the ______ cell group in the ventrolateral medulla. This projection activates vasopressin-synthesizing neurons in the magnocellular portion of the _______ and the ________ of the hypothalamus. Blue denotes sympathetic neurons and green parasympathetic neurons.)
A decrease in arterial pressure UNLOADS the baroreceptors - the terminals of afferent fibers of the GLOSSOPHARYNGEAL and VAGUS nerves - that are situated in the AORTIC ARCH and CAROTID SINUS. This leads to a REDUCTION in the afferent impulses that are relayed from these mechanoreceptors through the glossopharyngeal and vagus nerves to the NUCLEUS OF THE TRACTUS SOLITARIUS (NTS) in the dorsomedial medulla. The reduced baroreceptor afferent activity produces a DECREASE in vagal nerve input to the sinus node that is mediated by the neuroanatomical connections of the NTS to the NUCLEUS AMBIGUUS (NA). There is an INCREASE in sympathetic efferent activity that is mediated by the NTS projections to the CAUDAL VENTROLATERAL MEDULLA (an excitatory pathway) and from there to the ROSTRAL VENTROLATERAL MEDULLA (an inhibitory pathway). The activation of RVLM presympathetic neurons in response to hypotension is thus predominantly due to DISINHIBITION. In response to a sustained fall in blood pressure, VASOPRESSIN release is mediated by projections from the A1 NORADRENERGIC cell group in the ventrolateral medulla. This projection activates vasopressin-synthesizing neurons in the magnocellular portion of the PARAVENTRICULAR NUCLEUS (PVN) and the SUPRAOPTIC NUCLEUS (SON) of the hypothalamus. Blue denotes sympathetic neurons and green parasympathetic neurons.)
What is the myogenic hypothesis?
- Maintains constancy
- Smooth muscle stretching → constriction
- ↓ stretch → dilation
Likely has very little physiologic significance – metabolic autoregulation seems to be much more important
What is the metabolic hypothesis?
O2, CO2, H+, K+, lactate, adenosine, K+ accumulate and lead to vasodilation
How do metabolic byproducts act in neg feedback
- metabolic byproducts leads to vasodilation -> increased blood flow leads to washout of the same metabolites
How can metabolic byproduct lead to REACTIVE HYPEREMIA?
after a period of vasoconstriction, metabolites build up and lead to a period of vasodilation and greatly increased PERFUSION
What hormones cause vasodilation?
- NO (produced by endothelial cells). Shear stress (↑ P) leads to its release → arteriole dilation
- Ach → NO production (erectile tissue)
- Histamine: vasodilates arterioles, constricts venules → edema
- Bradykinin: circulating protein, activated by inflammatory signals
- > Potent vasodilator - Prostaglandin E2 and I2
- ANP (atrial natriuretic protein) – dilates
- Epinephrine, norepinephrine through beta-2 receptors
What hormones cause vasoconstriction
- Epinephrine, norepinephrine through alpha-1 receptors
- Serotonin – released in tissue damage → local vasoconstriction
- > When released by platelets or GI tract, sometimes results in vasodilation - Prostaglandins A2 and F constrict
- Angiotensin II
- ADH constrict (long term water regulation)
- Reaction to damage (platelet plug formation)
Does epinephrine or norepinephrine have a greater effect on a1, a2, b1, and b2 receptors
- Epinephrine has greater effect on B2 receptors than norepinephrine
- they’re ~equal for a1, a2, and b1
Fxn of B2?
causes vasodilation in skeletal muscle, cardiac muscle and liver
Fxn of alpha receptors
cause vasoconstriction in all tissues including muscle
Describe the renin-angiotensin aldosterone system (not examable?)
- a hormone system that regulates blood pressure and fluid balance.
When renal blood flow is reduced, juxtaglomerular cells in the kidneys convert the precursor prorenin (already present in the blood) into renin and secrete it directly into the circulation. Plasma renin then carries out the conversion of angiotensinogen, released by the liver, to angiotensin I.[2] Angiotensin I is subsequently converted to angiotensin II by the angiotensin-converting enzyme (ACE) found on the surface of vascular endothelial cells, predominantly those of the lungs.[3] Angiotensin II is a potent vasoconstrictive peptide that causes blood vessels to narrow, resulting in increased blood pressure.[4] Angiotensin II also stimulates the secretion of the hormone aldosterone[4] from the adrenal cortex. Aldosterone causes the renal tubules to increase the reabsorption of sodium and water into the blood, while at the same time causing the excretion of potassium (to maintain electrolyte balance). This increases the volume of extracellular fluid in the body, which also increases blood pressure.
The rate at which different substances are excreted in the urine represent the sum of WHAT three renal processes
- Glomerular filtration
- Reabsorption of substances from renal tubules into the blood
- Secretion of substances from the blood into the renal tubules
What is the equation for urinary excretion
Excretion = Filtration - Reabsorption + Secretion
What does the renal corpuscle consist of
- Bowman’s capsule (parietal and visceral layers)
- Bowman’s space (between the parietal and visceral layers)
- Glomerular capillary loop
What are 3 key histologic and physiologic features:
- shared basement membrane of the glomerulus and pedicel
- filtration slit
- fenestrations
Blood enters the glomerular capillary via the ______
afferent arteriole
What determines the rate and amount of fluids and small solutes that filter through the fenestrations in the glomerular capillary,
The hydrostatic and osmotic pressure in the glomerular capillary
Fxn of The basement membrane, the fenestrations, and the filtration slits formed by the pedicels
regulate the filtration of larger, charged molecules,
Where does The fluid that collects in Bowman’s space flow
into the proximal convoluted tubule.
What is the fxn of mesangial cell that is located on the “inside” of the glomerular tuft
- Serves to phagocytose old and “worn-out” basement membrane
- Likely also has a contractile function that changes the surface area of the glomerular capillary
The basil lamina is ____ nm thick consisting of ___ layers
- 300 nm
- 3 layers
What are the 3 layers of the basil lamina
- Lamina rarae interna
- Lamina densa (LD)
- Lamina rarae externa
Describe the Lamina rarae interna (what layer, what does it contain)
- Inner layer
- Contains laminin, fibronectin, heparin sulfate
- Between endothelial cells of capillary and LD
Describe the Lamina densa (LD)
- Middle layer
- Consists of type IV collagen
Describe the Lamina rarae externa
- Same composition as LRI
- Between LD and visceral layer of Bowman’s capsule
What is Visceral Layer of Bowman’s Capsule composed of
Composed of PODOCYTES (epithelial cells) highly modified to AID FILTRATION
In podocytes, primary processes branch to form _______
secondary processes
the secondary processes are known as _____ and form the filtration slits
pedicels
What are filtration slits? Width?
filtration slits are narrow clefts, 20 to 40 nm in width
Podocytes are covered by thin ________ extending between neighboring pedicels – the diaphragm can be dynamically altered to change the ________ of the glomerulus
Podocytes are covered by thin FILTRATION DIAPHRAGM extending between neighboring pedicels – the diaphragm can be dynamically altered to change the FILTRATION CHARACTERISTICS of the glomerulus
Pedicels express ______ sialoproteins on their surface
negatively-charged
What are the 2 types of sialoproteins on the surface of pedicels
- Podocalyxin
2. Podoendin
Where do podocytes rest on
Rest on the lamina rara externa of the basal lamina
What is the Glomerular Filtration Barrier composed of (3)
- Fenestrations in the glomerular capillary
- Layers of the basement membraneq
- The spaces between the pedicels (filtration slits)
What is filtration slit diaphragm composed of
The slit and the proteins that bridge them
How does the spaces btwn pedicels (filtration slits) change
- proteins bridge these slits, and can be altered dynamically to affect filtration
- the size of the slits can also change dynamically
What is the Glomerular Filtration Rate
Volume of FLUID filtered from the RENAL (kidney) GLOMERULAR CAPILLARIES into the BOWMAN’S CAPSULE per unit time
In a healthy adult, what is the GFL per min and per day
- 125 ml/min
2. 180 liters/day
about ____% of plasma flowing through kidneys is filtered by glomerular capillaries
20%
Like other capillaries, GFR is determined by: (2)
- The balance of hydrostatic and colloid osmotic pressure acting across the capillary membrane
- Capillary filtration co-efficient
What is the Capillary Filtration Co-efficient (Kf)
Measure of the PRODUCT of the HYDRAULIC CONDUCTIVITY and the SURFACE AREA of the glomerular capillaries
Can the capillary filtration co-efficient (Kf) be measured directly? If not, how?
Cannot be measured directly, but estimated experimentally by DIVIDING GFR by NET FILTRATION PRESSURE
What is the value of Kf in the kidney in comparison to other capillary systems of the body
Shows a value about 400 times as high as Kf of most other capillary systems of the body (due to fenestrations)
What is the Net Filtration Pressure
Sum of hydrostatic and colloid osmotic forces that either favor or oppose filtration across glomerular capillaries
What are the forces favouring filtration
- Capillary hydrostatic pressure (PG )
2. Bowman’s colloid osmotic pressure (πB)
What are the forces opposing filtration
- Bowman’s hydrostatic pressure (PB )
2. Capillary colloid osmotic pressure (πG)
What is the NET glomerular filtration rate (give number)
= total pressure that promotes filtration
= glomerular blood hydrostatic pressure (55mmHg) - [(capsular hydrostatic pressure 15 mmHg) + (blood colloid osmotic pressure 30mmHg)]
= GBHP - (CHP + BCOP)
= 55 - (15+30)
= 10 mmHg going INTO the capsule
Does the Glomerular Capillary Hydrostatic Pressure (PG ) favour or oppose filtration
Force favoring filtration
What does Increased (PG) vs. Decreased (PG) mean for GFR
- Increased (PG ) = increased GFR
2. Decreased (PG ) = decreased GFR
What is the Primary means for physiological regulation of GFR
Glomerular Capillary Hydrostatic Pressure (PG)
What 2 variables determine the Glomerular Capillary Hydrostatic Pressure (PG )
- Afferent arteriolar pressure
- Efferent arteriolar resistance
- > Biphasic action
Does the Glomerular Capillary Colloid Osmotic Pressure (πG) favor or oppose filtration
Force opposing filtration
Increased Glomerular Capillary Colloid Osmotic Pressure (πG) = _______ GFR
Decreased GFR
As blood passes from afferent arteriole through glomerular capillaries to the efferent arterioles, plasma protein concentration (increase/decrease) about _____%
- Increase
2. 20%
What are the 2 factors affecting Glomerular Capillary Colloid Osmotic Pressure (πG)
- Arterial plasma colloid osmotic pressure
2. Fraction of fluid filtered by glomerular capillaries (filtration fraction)
What is the eqn for filtration fraction (FF)
FF = GFR / Renal plasma flow
What does filtration fraction represent
Fraction of plasma filtered by glomerular capillaries
Increasing filtration fraction = ______ GFR. Why?
- decreased
- As filtration fraction increases, fluid loss from capillary concentrates the plasma proteins and raises πG
- > This ends ups reducing GFR
How to increase filtration fraction:
- Raising GFR
2. Reducing renal plasma flow
As in the blood flow, only about ___% of the plasma that flows through the renal artery actually reaches the nephrons. This figure represents the estimated amount of plasma that reaches the glomerulus.
- 90%
What is ERPF? Units?
Effective Renal Plasma Flow (ERPF in ml/min)
What is ERPF equal to
ERPF = 0.9(RPF)
ERPF = 0.9(660 ml/min) = 594 ml/min
ERPF ≈ 594 ml/min (Normal value used in lab)
Units for Glomerular Filtration Rate
GFR in ml/min
What is Glomerular Filtration Rate
Amount of plasma that is actually filtered into Bowman’s capsule.
3 ways GFR is regulated
- Neural Regulation
- > Sympathetic Nervous system - Hormonal Regulation
- > NE, E, Endothelin
- > Angiotensin II
- > Endothelin-derived NO
- > Prostaglandins and bradykinin - Renal Auto-regulation
- > Tubuloglomerular feedback
- > Myogenic theory
Importance of GFR Regulation?
Prevents large changes in GFR and renal excretion of water and solutes with changes in BP
What happens when no auto-regulation of GFR?
- Normally:
- GFR is 180 L/day
- Tubular reabsorption is 178.5 L/day - BUT Without auto-regulation:
- Increase of BP from 100 to 125 mm Hg would cause 25% increase in GFR to 225 L/day
- If tubular reabsorption remained constant, urine flow would increase to 46.5 L/day
- Plasma volume is only 3L and would quickly deplete blood volume
Describe the myogenic mechanism (an renal auto-regulation of GFR)
INHERENT tendency of SMOOTH MUSCLE CELLS:
- Muscle CONTRACTS or RELAXES in response to INC or DEC in vascular wall TENSION
- > BV respond to increased wall tension / stretch by CONTRACTION of smooth muscle
- > This reduces BF thru arteriole
- Operates in most arterioles thruout body
- > Prevents excessive inc in RBF and GFR when arterial pressure inc
- > Questioned by some physiologists cause mechanism has no means of directly detecting changes in RBF or GFR
Describe the tubuloglomerular feedback
- Juxtaglomerular apparatus MONITORS FLUID entering the DISTAL TUBULE and ADJUSTS the GFR as needed
- Helps to ensure relatively CONSTANT RATE of NaCl to DISTAL TUBULE
- Auto-regulates RBF and GFR in parallel
What are the 2 components of tubuloglomerular feedback that act together to control GFR
- > Afferent arteriolar feedback mechanism
- > Efferent arteriolar feedback mechanism
What is the Juxtaglomerular Apparatus
Microscopic structure in kidney that regulates the function of each nephron
Where is the Juxtaglomerular Apparatus located
Between vascular pole of renal corpuscle and returning DCT of same nephron
What are the 3 components of the Juxtaglomerular Apparatus
- Macula densa
- Juxtaglomerular cells
- Extraglomerular mesangial cells
Explain what happens when there is a DEC GFR, to tubuloglomerular feedback
- DEC GFR SLOWS the FLOW rate in loop of Henle
- Causes INC REABSORPTION of Na and Cl ions in ascending loop of Henle
- This reduces conc of NaCl at macula densa cells which initiates 2 effects:
- DEC afferent arteriolar RESISTANCE, which raises glomerular hydrostatic pressure to help return GFR to normal
- INC RENIN release from juxtaglomerular cells
- May be mediated by purinergic signalling, maybe by NO, still being characterized
What is renin
Enzyme that breaks down (hydrolyzes) ANGIOTENSINOGEN secreted from the liver into the peptide ANGIOTENSIN I
Fxn of ACE
Angiotensin I is further converted to angiotensin II by ACE
Fxn of angiotensin II
constricts the efferent arterioles (increases resistance) which increases glomerular hydrostatic pressure
How does the Autoregulation of renal blood flow and glomerular filtration rate compare to autoregulation of urine flow during changes in renal arterial pressure.
Autoregulation of renal blood flow and glomerular filtration rate but LACK of autoregulation of urine flow during changes in renal arterial pressure.
All the blood vessels of the kidney, including afferent and efferent arterioles are richly innervated by ______
sympathetic nerve fibers
What occurs during MODERATE SYMPATHETIC STIMULATION
- Afferent and efferent constrict to same degree
2. Blood flow into and out restricted to same extent = decreased renal blood flow
What occurs during STRONG SYMPATHETIC STIMULATION
- Afferent vasoconstriction predominates
2. Decreased RBF and GFR
What 4 hormones influence GFR and renal blood flow
Epinephrine, endothelin, nitric oxide, prostaglandins
What 2 hormones REGULATE GFR
- Angiotensin II
2. Atrial natriuretic peptide (ANP)
How does epinephrine influence GFR and RBF
- Constrict afferent and efferent arterioles DEC RBF and GFR
- Blood lvls parallel activity of SNS so have influence under extreme conditions
How does endothelin influence GFR and RBF
- Powerful vasoconstrictor
- Released by damaged vascular endothelial cells of kidney
- > Contributes to hemostasis
How does ANGIOTENSIN II influence GFR and RBF
- Constricts efferent (stronger) & afferent (weaker) arterioles
- Raise glomerular hydrostatic pressure while reducing RBF
- Keep in mind: angiotensin II usually secreted in response to dec arterial pressure which tends to decrease GFR
- > In these cases, it helps prevent decreases in glomerular hydrostatic pressure and GFR
- > At the same time, the decreased RBF contributes to decreased flow through peritubular capillaries which increases reabsorption of sodium and water
What are the actions of Angiotensin II
- Potent vasoconstrictor of arterioles (efferent arterioles in kidney)
- Acts at PCT to increase sodium reabsorption
- Causes release of aldosterone from adrenal cortex
- Causes release of anti-diuretic hormone (ADH) from posterior pituitary gland
- Stimulates reabsorption of water in the kidneys
- Also acts on the CNS to increase an individual’s appetite for salt, and to stimulate the sensation of thirst
Action of NO? Released by? What happens when drugs inhibit it
- Decreases renal vascular resistance and increases GFR
- Released by the vascular endothelium throughout the body
- Basal level is important for maintaining vasodilation of kidneys
- Allows kidney to excrete normal amounts of sodium and water
- Drugs that inhibit normal formation of NO increases renal vascular resistance and decreases GFR and urinary sodium excretion leading to high BP
Actions of prostaglandins and bradykinin
- Cause vasodilation and increased RBF and GFR
- Not major in regulating RBF or GFR in normal conditions
- May dampen renal vasocontrictor effects of SNS or angiotensin II (especially constriction of afferent arterioles)
- Help prevent excessive reductions in GFR and RBF
How does High protein intake increase RBF and GFR
- Increases RBF and GFR (20 to 30% after high protein meal)
- Maybe due to increase release of amino acids into blood and their subsequent reabsorption in proximal tubule along with sodium
- Decrease sodium at macula densa which intiates tubuloglomerular feedback-mediated decrease in resistance of afferent arterioles, which increases GFR
Increased GFR allows sodium excretion to be maintained while increasing urea excretion - Increased blood glucose
- Increase glucose to tubules causes them to reabsorb excess sodium along with glucose
What makes ANP and fxn? Affect on GFR and RBF?
Secreted by cells in the atria of the heart due to increased stretching of the heart (increased blood pressure) – in general it antagonizes the effect of angiotensin II
- Dilates the afferent and efferent glomerular arteriole
- Increases GFR (a little) and RPF - Decreases sodium reabsorption in the PCT and cortical CD
- Decreased tubuloglomerular feedback
- Inhibits renin secretion, inhibits ADH
- Reduces aldosterone secretion by the adrenal cortex
- Relaxation of mesangial cells?
High concentrations tend to reduce blood volume
- Lower concentrations have a more complex effect on hemodynamics and renal function
