Renal Physiology Flashcards
HP = hydrostatic pressure is due to what? 2
Describe it in the capillary? (where does the fluid go and at what pressure?) 3
IN the intersitial fluid? 2
- Due to fluid pressing against a wall
- “Pushes”
In capillary (HPc) 1. Pushes fluid out of capillary 2. 35 mm Hg at arterial end and 3. 17 mm Hg at venous end of capillary in this example
In interstitial fluid (HPif)
- Pushes fluid into capillary
- 0 mm Hg in this example
OP = osmotic pressure is due to what? 1
In capillary (OPc) where does the fluid go and at what pressure? 2
In interstitial fluid (OPif) where does the fluid go and at what pressure? 2
- Due to presence of nondiffusible
solutes (e.g., plasma proteins) - Pulls fluid into capillary
- 26 mm Hg in this example
- Pulls fluid out of capillary
- 1 mm Hg in this example
FP (net filtration pressure) in the arteriole is ___ mm Hg; fluid moves ____?
10
out
NFP in the venule side is __ mm Hg;
fluid moves___?
~8
in
Abnormalities of Extracellular
Fluid Na+ Concentration:
1. Hypernatremia affects Na+ levels and water levels how?
- Hyponatremia affects Na+ and water levels how?
- What is normal plasma Na?
- water loss, Na+ excess
- Water excess, Na+ loss
- 140-145 mmol / L
Consequences of Hyponatremia and Hypernatremia: Water moves in or out of cells → cells swell or shrink. This has profound effects on the brain.
- Rapid shrinking?
- Rapid swelling? (Why does the brain herniate so easily?)
- Rapid shrinking can tear vessels and cause hemorrhage
- Rapid swelling can cause herniation
- Because the skull is rigid, the brain cannot increase its volume by more than 10% without herniation.
Extracellular hypertonicity 1._______ expression of gene encoding proteins that 2.________ intracellular osmoles.
What are these encoding proteins? 2
What is the clinical significance of this?
-rapid changes vs slow changes
- increases
- increase
- Membrane transporters (Na+-H+- exchanger)
- Enzymes (e.g. aldose reductase that synthesize intacellular solutes e.g. sorbital)
Clinical significance: Rapid changes in extracellular fluid tonicity alter cell volume and cause neurologic complications, while slow changes have much less effect on cell volume and much less clinical effect.
- Normal plasma volume?
- Normal interstitial fluid volume?
- Intracellular fluid volume?
- plasma 3 L
- IF 11 L (so extracellular is 14 L)
- Intracellular 28L
- What is fluid intake regulated by? 2
- What is electrolyte intake governed by? 1
- What is fluid output regulated by? 1
- What is electrlyte output regulated by? 1
- Fluid Intake: regulated by thirst mechanism, habits
- Electrolyte intake: governed by dietary habits
- Fluid Output: regulated mainly by kidneys
- Electrolyte output: regulated mainly by kidneys
What does the posterior pituatary release that signals water reabsorption in the collecting ducts of the kidneys?
ADH
What signals the posterior pituitary to release ADH?
increased osmolarity and Na+ concentration in the plasma stimulates osmoreceptors in the hypothalamus. This stimulates the pituitary
Describe the flow of blood flow from the heart to the kidney’s
15
- Aorta
- renal artery
- segmental artery
- interlobar artery
- arculate artery
- cortical radiate artery
- afferent artiole
- Glomerulus (capillaries)
- efferent artioles
- peritubular capillaries and vasa recta
- cortical radiate vein
- arcuate vein
- Interlobar vein
- renal vein
- IVC
Which part of the nephron has intercalated cells?
collecting duct
What is the formula for excretion?
Excretion = filtration - reabsorption + secretion
The kidney produces urine through 4 steps
- Glomerular filtration
- Tubular reabsorption
- Tubular secretion
- Concentration
- WHat does glomerular filtration create?
- What does tubular reabsorption remove?
- What does tubular secretion remove?
- What does the concentration remove?
- creates a plasmalike filtrate in the blood
- removes useful solutes from the filtrate, returns them to the blood
- removes additional wastes from the blood and adds them to the filtrate
- removes water from the urine, concentrates wastes
What happens at the proximal convoluted tubule?
reabsorption of water, ions, and all organic nutrients
What happens at the distal convoluted tubule? 2
Secretion of ions, acids, drugs and toxins.
Variable reabsorption of water, Na ions, and calcium ion (underhormonal control)
What is the function of the renal corpuscle?
production of filtrate
What is the purpose of the loop of henle?
Further reabsorption of water (descending limb) and both sodium and chloride ions (ascending limb)
Collecting System:
What is the purpose of the collecting duct?
What is the purpose of the papillary duct?
- Variable reabsorption of water and reabsorptionor secretion of sodium, potassium, hydrogen, and bicarbonate ions
- Delivery of urine to the minor calyx
What is clearance?
Renal clearance specifically?
is a general concept that describes the rate at which substances are removed (cleared) from the plasma.
of a substance is the volume of plasma completely cleared of a substance per min by the kidneys.
Cs x Ps = Us x V
What does each mean?
Cs = clearance of substance S Ps = plasma conc. of substance S Us = urine conc. of substance S V = urine flow rate
Cs = Us x V
Ps
For a substance that is freely filtered, but not reabsorbed or
secreted (inulin, 125 I-iothalamate, creatinine), renal clearance
is equal to what?
GFR
What is the equation for GFR?
GFR = (Uin x V)/Pin
WHat does Ccr = ?
GFR
Theoretically, if a substance is completely cleared from
the plasma, its clearance rate would equal what?
renal plasma flow
Cx = renal plasma flow
1._____________ _____ is freely filtered and secreted
and is almost completely cleared from the renal plasma
- Whats the equation?
- To Calculate Actual RPF , One Must Correct for what?
- Paraminohippuric acid (PAH)
- ERPF = Upah x V/Ppah
- Incomplete Extraction of PAH
HOw do we calulate Epah?
How do we calculate RPF?
Apah- Vpah/Apah
RPF = ERPF/Epah
The Filtration Membrane
From the plasma to the capsular space, fluid passes through three barriers. What are they?
- foot processes
- fenestrated epithelium
- Basement membrane
Almost any molecule smaller than __ nm can pass freely through the filtration membrane into the capsular space.
This includes? 7
Kidney infections and trauma commonly damage the filtration membrane and allow _____ ______ or ______ _____ to pass through
3
- Water,
- electrolytes,
- glucose,
- amino acids,
- lipids,
- vitamins, and
- nitrogenous wastes
plasma proteins or blood cells
Net filtration pressure (10mm Hg) is a combination of what?
glomerular hydrostatic pressure (60) - Bowman’s capsule pressure (18) - glomerular oncotic pressure (32)
Glomerular hydrostatic pressure is also called?
capillary blood pressure
Normal GFR?
125 ml/min = 180 liters/day
- Plasma volume is filtered ___times per day
- Glomerular filtrate composition is about the same as plasma, except for what?
- Filtration fraction is what?
- 60
- large proteins
- (GFR/Renal Plasma Flow) = 0.2 (i.e., 20% of plasma is filtered)
- Glomerular Filtration Rate (GFR)
is what? - An average of ___% of the filtrate is reabsorbed, so that only ____ L of urine per day is excreted.
- is the amount of filtrate formed per minute by the two kidneys combined.
- 99
1-2
Renal Autoregulation is what?
the ability of the kidneys to maintain a relatively stable GFR in spite of the changes (75 - 175 mmHg) in arterial blood pressure.
The nephron has two ways to prevent drastic changes in GFR when blood pressure rises. Describe them.
1) Constriction of the afferent arteriole to reduce blood flow into the glomerulus
2) Dilation of the efferent arteriole to allow the blood to flow out more easily.
Change in an opposite direction if blood pressure falls
What is a myogenic response?
muscle in the arteriole respond to pressure changes
Increased constriction of the afferent arteriole leads to what?
2
decrease in GFR
Decrease in renal blood flow
Increased constriction of the efferent arteriole leads to what?
2
increased GFR
decrease in renal blood flow
What is tubuloglomerular feedback?
It involves the concept of purinergic signaling, in which an increased distal tubular sodium chloride concentration causes a basolateral release of ATP from the macula densa cells. This initiates a cascade of events that ultimately brings GFR to an appropriate level.
Other Factors That Influence GFR
5
- Prostaglandins
- Fever, pyrogens
- Glucocorticoids
- Aging
- Increased dietary protein
Hypergylcemia
How do the following affect GFR: 1. Prostaglandins? 2. Fever, pyrogens? 3. Glucocorticoids? 4. Aging? 5. Increased dietary protein Hypergylcemia?
- : increase GFR; non-steroidal anti-inflammatory agents can decrease GFR, especially in volume depleted states
- increase
- increase
- decrease
- increase
Renal blood flow = 1._____ mls/min or
2.____%of cardiac output (7x flow to brain) needed to deliver enough 3.______ to kidneys for
glomerular filtration
- To deliver ______ to kidney so that the renal cells can perform their functions (only about 20% of renal blood flow needed for this function)
- 1100
- 22
- plasma
- nutrients
MACULA DENSA FEEDBACK:
- Decreased GFR leads to?
- what does this lead to?
- Which leads to what?
- Finally what results?
- Decreased Distal NaCl Delivery
- decreased macula densa NaCl
- decreased afferent arteriolar resistance
- increase in GFR
An increase in GFR inhibits what?
a decrease in distal NaCl delivery
Describe the return to homeostasis after GFR is decreased.
4
- renin release
- angiotensin activation
- Elevation of blood pressure and volume
- increased GFR
Where does most of Na+ reabsorption take place?
Proximal Convoluted Tubules
- The proximal convoluted tubule (PCT) is formed by what?
2. PCT reabsorbs about ___% of the glomerular filtrate and return it to the blood.
- one layer of epithelial cells with long apical microvilli.
- 65
Mechanisms of Proximal Tubular Reabsorption
6
1) Solvent drag
2) Active transport of sodium.
3) Secondary active transport of glucose, amino acids, and other nutrients.
4) Secondary water reabsorption via osmosis
5) Secondary ion reabsorption via electrostatic attraction
6) Endocytosis of large solutes
Sodium pumps (Na-K ATPase) in basolateral membranes transport sodium where and how?
This gives us a net negative or positive charge in the tubule?
sodium out of the cells against its concentration gradient using ATP.
negative
Secondary active transport of what? How are they transported in?
3
Various cotransporters can carry both Na+ and other solutes. Give an example?
- glucose,
- amino acids, and
- other nutrients
cotransport
the sodium-dependent glucose transporter (SDGT) can carry both Na+ and glucose.
Secondary water reabsorption via osmosis: Sodium reabsorption makes both intracellular and extracellular fluid 1._________ to the tubular fluid. Water follows sodium into the 2.__________capillaries.
- hypertonic
2. peritubular
Secondary ion reabsorption via electrostatic attraction: _______ions tend to follow the ________ sodium ions by electrostatic attraction.
Negative
positive
Endocytosis of large solutes: The glomerulus filters a small amount of protein from the blood. The PCT reclaims it by doing what? 3
- endocytosis
- hydrolzes it to amino acids
- and releases these to the ECF by facilitated diffusion.
How does Na reabsorption affect lumen? 3
This all leads to what? 2
- increase in lumen negative potential
- increase in luminal Cl- concentration
- increase luminal urea concentration
- passive Cl- reabsorption
- passive urea reabsorption
- Whats transport maximum?
- How does it relate to threshold?
- What are examples of this? 4
- There is a limit to the amount of solute that the renal tubule can reabsorb because there are limited numbers of transport proteins in the plasma membranes.
- If all the transporters are occupied as solute molecules pass through, some solute will remain in the tubular fluid and appear in the urine.
- glucose,
- amino acids,
- phosphate,
- sulphate
Summary of Proximal Tubule Transport
- What goes back out of the proximal tubule and is reabsorbed? 7
- What goes back in and is excreted? 3
- Na+
- Cl-
- HCO3
- K+
- H2O
- Glucose
- Amino Acids
- H+
- Organic Acids
- Bases
What reabsorption happens in the nephron loop:
- Thin loop? 1
- Thick loop? 8
- What are the three main electrolytes we are concerned with that loop diuretics target in the loop of Henle?
- very permeable to water, which leaves the descending loop
- not permeable to water.
Na+
Cl-
K+
Ca++
HCO3-
MG++
all leave
H+ in
- Na+
2Cl-
K+
What is the primary purposeof the nephron loop?
How does it do this?
establish a high extracellular osmotic concentration.
The thick ascending limb reabsorbs solutes but is impermeable to water. Thus, the tubular fluid becomes very diluted while extracellular fluid becomes very concentrated with solutes.
The high osmolarity enables the collecting duct to do what?
concentrate the urine later
What is reabsorbed in the distal convoluted tubule:
Early? (4 out, Whats not permeable? 2)
Late? (6 out, 2 in, not permeable to what? 1)
- NA+, Cl-, Ca++, Mg++ out
- not permeable to water, not very permeable to urea
- out: Na, Cl, ADH, water, K, bicarb,
in: H+, K
not very permable to urea
Fluid arriving in the DCT still contains about 1.__% of the water and 2.__% of the salts of the glomerular filtrate.
A distinguishing feature of these parts of the renal tubule is that they are subject to 3. ________ control.
- 20
- 10
- hormonal
- Where is aldosterone secreted from and in response to what?
- What effects does it have? 2
- What does it help maintain? 2
- secreted from adrenal gland in response to a ⇓ Na+ or a ⇑ K+ in blood
- to increase Na+ absorption and K+ secretion in the DCT and cortical portion of the collecting duct.
- helps to maintain blood volume and pressure.
Angiotensin II Increases Na+ and Water Reabsorption:
- Stimulates what?
- Directly increases what?
- Constricts what?
- what does this lead to? 2
- Stimulates aldosterone
- Directly increases Na+ reabsorption (proximal, loop, distal, collecting tubules)
- Constricts efferent arterioles
- decreases peritubular capillary
hydrostatic pressure
- increases filtration fraction, which increases peritubular colloid osmotic pressure)
What dose increased angio II do to efferent arterioles?
increases resistence
ACE inhibitors (captopril, benazipril, ramipril)
Ang II antagonists (losartan, candesartin, irbesartan)
MOA? 3
This all leads to what? 2
- decrease aldosterone
- directly inhibit Na+ reabsorption
- decrease efferent arteriolar resistance
Natriuresis and Diuresis + Blood Pressure
- What is atrial natriuretic factor secreted by and in response to what?
- What does it inhibit?
- Increases what?
- This all leads to?
- secreted by the atrial myocardium in response to high blood pressure.
- It inhibits
-sodium and water reabsorption, - increases the output of both in the urine,
- and thus reduces blood volume and pressure.
ANP affects each of the following how:
- Renin release?
- Aldosterone?
- GFR?
- WHat does this all lead to?
- decrease
- decrease
- Increase
- Increased Na+ and H2O excretion
Tubular Secretion:
Renal tubule extracts chemicals from the 1._____ and secretes them into the 2.______.
What are all poorly reabsorbed here? 4
What Purpose does it serve? 2
- blood
- tubular fluid
- Bile salts,
- oxalate,
- urate creatinine and
- catecholamines.
All poorly reabsorbed.
serves the purposes of
- waste removal and
- acid-base balance.
- Where does the collecting duct begin? And what does it recieve there?
- What does it reabsorb?
- The collecting duct (CD) begins in the cortex, where it receives tubular fluid from numerous nephrons.
- CD reabsorbs water.
What is the driving force of reabsorption/urine concentration in the collecting duct?
The high osmolarity of extracellular fluid generated by NaCl and urea, provides the driving force for water reabsorption.
What regulates reaborption/urine concentration in the collecting duct?
The medullary portion of the CD is not permeable to NaCl but permeable to water, depending on ADH.
Control of Urine Concentration depends on the body’s state of what?
hydration
In a state of full hydration, WHAT? is not secreted and the CD permeability to water is____, leaving the water to be excreted.
In a state of dehydration, WHAT? is secreted; the CD permeability to water ______?. With the increased reabsorption of water by osmosis, the urine becomes more concentrated.
antidiuretic hormone (ADH) low
ADH
increases
ADH synthesis happens where?
Released by what?
Action on what?
in the magnocellular neurons of hypothalamus,
release by the posterior pituitary,
and action on the kidneys
