Kidney (K1-K9) Flashcards
these are firm, reddish brown glands, located close to the dorsal body wall high in the abdomen at the level of the thoracolumbar junction
kidneys
this kidney is usually more cranial (except the pig)
right
the right kidney is embedded in this of the liver, which secures its position
renal fossa
this is tough and fibrous covering of the kidneys that restricts their ability to expand
capsule
within the kidney, the parenchyma can be visually divided into these two sections
outer cortex and inner medulla
this part of the kidneys contains the renal corpuscles and convoluted parts of renal tubules; it is light in color and granular in appearance
cortex
this part of the kidney is characterized by its striated appearance and contains collecting ducts and nephric loops
inner medulla
these are the functional units of the kidney, the structures that are apparent within the cortex and medulla
nephrons (corpuscle, tubules, loops, and ducts)
these are paired tubes that form as the internal ducts within the kidneys join to form a common expansion (renal pelvis); exit the kidney at the hilus and follow a saggital course towards the pelvis
ureters
the ureter bends medially to enter this in the male
genital fold
the ureter bends medially to enter this in the female
broad ligament
what are the three regions of the bladder
apex, the neck, body
this region of the bladder is a cranial blind end
apex
this region of the bladder is a funnel-shaped region between ureter openings and urethra
the neck
this region of the bladder is situated between the neck and apex
the body
this is the duct through which urine is discharged from the bladder
urethra
the male urethra consists of these two components
pelvic and penile
each kidney is supplied by this artery arising from the abdominal aorta
renal artery
veins that correspond with the arteries of the kidney join to form this single vein that enters the vena cava
renal vein
efferent arterioles arising from juxtamedullary nephrons descend into the medulla and give rise to this, which descend and re-ascend close to the Loops of Henle
vasa recta
this is the functional unit of the kidney and consists of the renal corpuscles and renal tubules
nephron
what are the two major parts of the nephron
renal corpuscles and renal tubules
these are responsible for the filtration of blood and are made up of Bowman’s capsule and the glomerulus
renal corpuscles
this part of the renal corpuscles consists of a single layer of flattened cells resting on a basement membrane
Bowman’s capsule
this is a network of capillaries that arise from the afferent arteriole, and invaginate Bowman’s capsule
glomerulus
the renal cortex is easily identified at low magnification due to the presence of these, which are not found in the renal medulla
renal corpuscles
the capillary loops of the glomerulus are supported by specialized connective tissue called this
glomerular mesangium
these cells are contractile and can modify the diameter of glomerular capillaries (secrete vasoactive substances and other factors)
mesangial
this is the first part of the renal tubule which drains Bowman’s capsule and is made up of a coiled section and a shorter straight segment
proximal tubule
this is the coiled section of the proximal tubule; it is lined by simple, cuboidal epithelium with a prominent brush border which increases surface area for absorption; it is the longest and most convoluted part of the nephron
proximal convoluted tubule (PCT)
this is the shorter straight segment of the proximal tubule; it is lined by low cuboidal epithelium with no brush border and leads onto the loop of Henle
proximal straight tubule (PST)
name the three parts of the loop of Henle
descending thin limb, ascending thin limb, thick ascending limb
the cells in th thick ascending limb of loop of Henle that lie closest to Bowman’s capsule are specialized cells known as this; they mark the end of the thick ascending limb and start of distal convoluted tubule
macula densa
this is a group of specialized cells that regulate renal blood blow comprised of 3 cell types
juxtaglomerular apparatus
what are the 3 cell type that comprise the juxtaglomerular apparatus?
- extraglomerular mesangial cells
- granular cells
- macula densa cells
once the fluid has been deposited into the calyx it is known as this and no longer changes
urine
this is an area of the urinary bladder and is a dorsal triangular area connecting the ureteral openings and urethral exit; has a smooth mucosa and originates from mesoderm
trigone
the male urethra is lined by this type of epithelium
stratified or psuedostratified columnar epithelium
the female urethra is predominately lined by this type of epithelium (but changes to stratified squamous epithelium near the external urethral orifice)
urinary epithelium
this species kidney has obvious external demarcation of the cortex and separation of the medulla into lobes/pyramids
bovine
what is the classification of the bovine kidney
multilobar or multipyramidal
this species kidney is multilobar, however has a single cortex with a smooth outer surface and has a flattened appearance
pig
these species (5) kidney is unilobar, the cortex and medulla fuse into a single unit and the linearly fused papillae form a renal crest
cat, dog, horse, rodent, and sheep
these 2 species have the standard smooth, bean-shaped kidneys that are reddish brown and cannot be distinguished from each other
dog and sheep
this species has a unilobular kidney with a fused cortex and is heart-shaped/triangle-shaped
horse
approximately 2/3 of total body water (40% total body weight) is located within cells and known as this
intracellular fluid (ICF)
one third (20% total body weight) is located outside of cells and known as this
extracellular fluid (ECF)
what are the two subcategories of extracellular fluid
interstitial or intravascular
what percent of total lean bodyweight is made up of water
60%
what is the ratio of fluid percentages in the body? (total lean bodyweight made of water:intracellular fluid:extracellular fluid)
60:40:20
the intracellular and extracellular fluid compartments are separated by this
cell membrane
the interstitial and intravascular fluid compartments are divided by this
vascular endothelium
what are the three main colloid particles within plasma?
vascular endothelium is not permeable to them
albumin, globulins, and fibrinogen
the particles within a particular fluid compartment exert this meaning they can cause fluid to move by osmosis to one or other side of the membrane, towards the area of higher solute concentration (higher osmolarity)
osmotic pressure (tonicity)
this is a measure of all particles dissolved within a fluid compartment , whether or not they can cross the semi-permeable membrane
total fluid osmolarity
particles that can cross the semi-permeable membrane contribute to this but not to this
osmolarity but not osmotic pressure
what is the average plasma osmolarity in a dog
300 mOsm/kg
this pressure is the contribution of colloid particles and their associated electrolytes towards plasma oncotic pressure
oncotic pressure (aka colloid osmotic pressure, COP)
this is the only difference between intravascular and interstitial fluid
the concentration of proteins
standard biochemical tests measure solutes within this fluid and may not reflect changes in total body solute levels
extracellular fluid
fluid flux across the capillary endothelium is described by this equation
Starling’s equation
what are the Starling forces in Starling’s equation
the oncotic and hydrostatic pressure gradient’s between the capillary and interstitium
along the length of the capillary, this pressure increases and this pressure decreases
oncotic pressure increases, hydrostatic pressure decreases
fluid moves (into or out of?) the capillary at the arteriolar end/beginning
out of (into the interstitium)
fluid moves (into or out of?) the capillary at the end ?
into the capillary
why is plasma COP essential to prevent excessive fluid efflux into the the interstitium?
intravascular and interstitial osmolality would be identical and fluid would move freely out of capillaries causing oedema and potential loss of blood volume
this is a gel-like matrix on the luminal surface of endothelial cells now thought to determine transcapillary fluid flux
glycocalyx
these are fluids containing electrolytes and other solutes that can freely cross the capillary endothelium to pass between the intravascular and interstitial space
crystalloids
crystalloids are classified according to this
their osmolarity relative to that of plasma
fluids with osmolarity greater than plasma (300 mOsm/kg) are termed this
ex: 7.2% NaCl
hypertonic
fluids with osmolarity lower than plasma (300 mOsm/kg) are termed this
ex: 0.45% NaCl
hypotonic
fluids with osmolarity similar to plasma (300 mOsm/kg) are termed this
ex: 0.9% NaCl
isotonic
this type of saline is very effective for resuscitating patients in severe shock because water is pulled rapidly out of the intracellular space and redistributes between the interstitial and intravascular spaces
hypertonic saline
these losses of water are easy to measure, i.e. urine
sensible losses
these losses of water are difficult to measure, i.e. feces, saliva, evaporation from respiratory tract, skin
insensible losses
this component of urinary water loss is the amount of water required for the kidney to excrete solutes such as urea
obligatory loss
this component of urinary water loss is the removal of any water excess to body requirements
free loss
healthy dogs drink about this much water per day
50-60 mL/day
if a dog drinks more than 100 mL of water per day it is defined as this
polydipsia
what is the normal urine output of a healthy dog?
1-2 mL/kg/hour
name some causes of abnormal fluid loss
vomiting, diarrhea, polyuria, high body temp, excessive panting, hemorrhage, exudation/transudation into a body category, ongoing physiological losses due to reduced water intake
fluid is often lost first from here
extracellular fluid
a loss of hypotonic fluid will have this effect on ECF tonicity resulting in this shift of fluid
hypertonic, water moves out of ICF
a loss of hypertonic fluid will have this effect on ECF tonicity resulting in this shift of fluid
hypotonic, water moves into ICF
this type of fluid loss is loss of water in excess of solute
hypotonic
this type of fluid loss is loss of water and solute in equal proportions
isotonic
this type of fluid loss is loss of solute in excess of water
hypertonic
perfusion of tissue with blood depends on this fluid compartment
intravascular fluid compartment
hydration depends on these 2 fluid compartments
interstitial and intracellular fluid compartments
this is the process by which water and solutes leave the vascular system through the filtration barrier of the glomerular capillaries and enter the Bowman’s space
glomerular filtration
the volume of filtrate formed per unit of time by glomerular filtration is known as this
Glomerular Filtration Rate (GFR)
this is a network of capillaries between the afferent and efferent arterioles, encased within the Bowman’s capsule
glomerular filter
what are the three major layers of the glomerular capillary membrane which make up the filtration barrier
- glomerular endothelium
- basement membrane
- podocytes
this layer of the glomerular capillary membrane prevents filtration of plasma proteins because of the strong negative electrical charges associated with the proteoglycan molecules
basement membrane
what 3 layers is the basement membrane of the glomerular capillary membrane made up of
- lamina rara interna: fused to endothelium
- lamina densa: middle
- lamina rara externa: fused to epithelium
which is the most significant filtration barrier of the glomerular capillary?
basement membrane
this is a layer of intricate interlocking cells that make up the visceral epithelium of the glomerular capillary membrane
podocytes
this is the resulting product of glomerular filtration
an ultrafiltrate of plasma
solutes pass through the 3 layers of glomerular capillary membrane to form an ultra filtrate which enters this
proximal tubule
the glomerular filtration barrier restricts the filtration of molecules on the basis of these 3 things
size, weight, and electrical charge
all surfaces of the glomerular filtration barrier contained fixed polyanions, which repel macromolecules with this charge (prevents protein loss with urine since many proteins in the blood have this charge)
negative
which Starling’s forces favor glomerular capillary filtration
hydrostatic pressure in glomerular capillary (oncotic pressure in Bowman’s capsule is near zero so doesn’t really favor filtration)
which Starling’s forces oppose glomerular capillary filtration
oncotic pressure in glomerular capillary bed and hydrostatic pressure in Bowman’s space
for glomerular capillaries, the net ultrafiltration pressure always (favors or opposes?) filtration
so, the direction of fluid movement is always (into or out of?) capillaries
favors filtration, out of capillaries
GFR is regulated by changes in the hydrostatic pressure within the glomerular capillary which is mediated by changes in this
resistance of the afferent and efferent arteriole
afferent arteriolar resistance is (positively or negatively?) correlated with the hydrostatic pressure in the glomerular capillary and therefore GFR?
negatively (decrease in resistance increases hydrostatic pressure and GFR)
efferent arteriolar resistance is (positively or negatively?) correlated with the hydrostatic pressure in the glomerular capillary and therefore GFR?
positively (decrease in resistance decreases hydrostatic pressure and GFR)
what is the equation for renal blood flow (RBF)?
RBF = (renal artery pressure - renal vein pressure) / total renal vascular resistance
the blood flow through the kidneys serves these 5 important functions
- indirectly determines GFR
- modifies rate of solute & water reabsorption by proximal tubule
- participates in concentration & dilution of urine
- delivers O2, nutrients, and hormones to cells of nephron and returns CO2 and reabsorbed fluid and solutes to general circulation
- delivers substrates for urinary excretion
what are the 3 major sites for renal resistance
- interlobular arteries
- afferent arterioles
- efferent arterioles
Vasodilation of the afferent arteriole (decreased resistance) will have this effect on RBF and GFR
increase both RBF and GFR
Vasoconstriction of the afferent arteriole (increased resistance) will have this effect on RBF and GFR
decrease both RBF and GFR
Vasodilation of the efferent arteriole (decreased resistance) will have this effect on RBF and GFR
increase RBF and decrease GFR
Vasoconstriction of the efferent arteriole (increased resistance) will have this effect on RBF and GFR
decrease RBF and increase GFR
what are the 2 autoregulation mechanisms that maintain constant RBF and GFR when the systemic blood pressure is between 80-200 mmHg
myogenic reflex and tubuloglomerular feedback
this reflex responds to changes in arterial blood pressure by constricting or dilating the afferent arteriole to maintain RBF and GFR at a constant level
myogenic
this reflex responds to changes in the NaCl concentration of tubular fluid and has a predominant effect on the afferent arteriole to regulate RBF and GFR
tubuloglomerular feedback
the NaCl concentration of tubular fluid is sensed by this part of the juxtaglomerular apparatus (JGA)
macula densa
what are the 3 components of the juxtaglomerular apparatus (JGA)?
- macula densa
- extraglomerular mesangial cells
- juxtaglomerular cells
this component of the juxtaglomerular apparatus (JGA) is the thick ascending limb of Loop of Henle
macula densa
this component of the juxtaglomerular apparatus (JGA) surround the capillary loop
extraglomerular mesagnial cells
this component of the juxtaglomerular apparatus (JGA) are specialized smooth muscle cells and make up the afferent and efferent arterioles
juxtaglomerular cells
when increased tubular fluid NaCl concentration is sensed by the macula densa, ATP and adenosine are released by the macula densa cells which has this effect on the afferent arteriole
vasoconstrictive effect (decreases RBF & GFR)
when decreased tubular fluid NaCl concentration is sensed by the macula densa, signals are initiated with these 2 effects
vasodilation of afferent arteriole and increased renin release from JGA cells
the ideal glomerular biomarker for measuring GFR must have these 3 characteristics
- be readily filtered across the glomerular capillaries, with no size or charge restrictions
- be secreted unchanged
- cannot effect GFR
this is the most tradition biomarker used for determining glomerular filtration; fructose polymer with 5000 Da molecular weight
inulin
this is an end-product of muscle catabolism and is an example of an endogenously produced biomarker for GFR
-it is freely filtered by the glomerulus at a constant rate but is a poor sensitive marker for GFR as blood serum levels do not increase until GFR decreases > 75%
creatinine
this is defined as the amount of substance filtered by the glomerulus into the Bowman’s space per unit time
filtered load
this is the movement of filtered solutes and water from tubular lumen back into the peritubular capillary
reabsorption
what are the 4 general mechanisms for reabsorption within the nephron
diffusion, facilitated diffusion, coupled transport, and active transport
this is when solutes dissolved in water are also carried along with the water when it is reabsorbed across tubule segments
solvent drag
if both solutes are transported via coupled transport in the same direction, the carrier protein is known as this
symporter
name 2 examples of symporters (one in the proximal tubule and one in the thick ascending limb of the loop of Henle)
- Na-glucose transporter
- Na-K-2Cl transporter
if each solute is transported via coupled transport in opposite directions, the carrier protein is known as this
antiporter
name an example of an antiporter in the proximal tubule
Na-H transporter (Na into cell, H+ out of the cell into the lumen)
what is the most prevalent example of active transport within the kidney (within the basolateral membrane)
Na-K-ATPase pump
this is when solutes cross the tubular epithelium by passing BETWEEN the cells (through tight junctions)
paracellular transport
this is when solutes cross the tubular epithelium by passing THROUGH cells
transcellular transport
this type of junction in tubular epithelium promotes the reabsorption of a large concentration of solutes and water; commonly seen within the proximal tubule
leaky junction
this type of junction in tubular epithelium have a low basal water permeability and effectively bar paracellular flow of water and solutes; typically found within the distal tubule
tight junctions
most reabsorption of water and solutes that have been filtered by the glomerulus occurs here
proximal convoluted tubule (PCT)
this is the longest and most convoluted part of nephron with a rich capillary network of peritubular capillaries surrounding it
proximal convoluted tubule (PCT)
in mammals, the peritubular capillary originates at this and subdivides, wrapping closely around the proximal tubule, allowing for the return of reabsorbed molecules back into the bloodstream
efferent arteriole
what are 4 reasons the proximal convoluted tubule has such a high efficacy for solute reabsorption
- rich peritubular capillary network
- brush border of microvilli
- lateral cellular interdigitations of basolateral cell membrane
- large numbers of mitochondria and protein carrier molecules
this accounts for almost half of the total solutes in the tubular fluid entering the PCT and most of the rest are anions that must accompany it to maintain electroneutrality
sodium
this is the first step in the process of solute reabsorption in the PCT
-achieved by the Na-K-ATPase pump
active transport of sodium out of tubular epithelial cell into interstitium
how is glucose reabsorbed across the tubular epithelium in the PCT?
glucose transporters (not paracellular transport)
why is glucose able to be almost completely reabsorbed in the PCT?
it is impermeable to the tight junctions
how are many of the solutes (including urea, potassium, calcium and magnesium) reabsorbed in the PCT?
paracellular transport via leaky tight junctions
this is responsible for concentrating or diluting the tubular fluid using concurrent multiplication
loop of Henle
this limb of the loop of Henle has low, simple squamous epithelium with few mitochondria so there is relatively little active transport of solutes here; however it is highly permeable to water with aquaporin 1 receptors and is responsible for 20% of water resorption
thin descending limb
the descending limb of the loop of Henle does not reabsorb solutes, so the tubular fluid tonicity (increases or decreases?) along its length and becomes this
increases, hypertonic
solutes are reabsorbed within this limb of the loop of Henle (impermeable to water)
ascending limb
the epithelial cells within this segment of the loop of Henle are relatively tall with many mitochondria and membrane in-foldings to allow for high capacity active solute transport
thick ascending limb
these segments of the renal tubule are commonly referred to as the ‘diluting segment’ of the nephron because there is resorption of solutes without water which dilutes the tubular fluid
ascending limb of the loop of Henle & distal tubule
this is known as the connecting segment and has properties of both the distal tubule and the collecting duct
late distal tubule
this is the site for final urine processing by regulated tubular resorption and secretion largely by the actions of aldosterone and vasopressin
late distal tubule and collecting ducts
what are the two distinct epithelial cells found in the late distal tubule and collecting ducts
principal cells and intercalated cells
these cells in the late distal tubule/collecting ducts act to resorb both water and sodium & secrete potassium
principal cells
this hormone acts to amplify the process of principal cells by up regulating and activating the basolateral Na-K-ATPase pumps, up regulating the apical sodium channels, and stimulating potassium secretion into the tubular lumen
aldosterone
the water permeability of principal cells is directly controlled by this hormone which binds to specific receptors on the basolateral membrane, resulting in the insertion of water specific channels into the luminal membrane
vasopressin
these cells found in the late distal tubule/collecting ducts are largely involved with regulation of acid base balance
intercalated cells
name the 2 types of intercalated cells
alpha and beta
this type of intercalated cells are the most important and function to secrete H+ ions and reabsorb HCO3 ions (key role in acid-base regulation)
-also resorb potassium into tubular fluid
alpha intercalated cells
this type of intercalated cell functions to secrete HCO3 and reabsorb H+
beta intercalated cells
where is the majority of sodium (65%) reabsorbed?
PCT (proximal convoluted tubule)
these are channels for the transfer of water which are expressed in the luminal cell membranes in the descending limb of the loop of Henle
Aquaporins (AQP)
most of the nephrons in the kidney are short-loop nephrons, so they don’t have this section
ascending thin limbs of Henle’s loop
by what mechanism does the distal convoluted tubule reabsorb salt without water
Na-Cl symporter
what 3 types of baroreceptors are important in regulating sodium excretion
- arterial baroreceptors
- cardiopulmonary baroreceptors
- intrarenal baroreceptors
these stretch receptors detect low perfusion pressure, usually when intravascular volume is too low
high-pressure arterial stretch receptors
these stretch receptors detect whether intravascular volume is too high
low-pressure venous stretch receptors
these cells in the brain have sensory sodium channels that detect and respond to extracellular sodium concentrations and respond by modulating the activity of nearby neurons involved in the control of body sodium
glial cells
this is the most important controller of sodium excretion and volume sensing
RAAS
this is the most important peptide produced by the RAAS,
angiotensin II
this is produced in the kidneys by the juxtaglomerular apparatus and converts angiotensinogen to angiotensin I
renin
this is the rate limiting step of the formation of angiotensin II
amount of renin available to convert angiotensinogen to AI
these are the 3 key regulators of renin production
- sympathetic input
- aferent arteriole pressure
- macula densa response
this is released from postganglionic sympathetic nerve cells and activates the release of renin from the juxtaglomerular granular cells
norepinephrine
the granular cells respond directly to pressure in the afferent arteriole; when pressure decreases, renin production (increases or decreases?)
increases
what are the 4 key actions of angiotensin II via the RAAS?
- stimulates behavioral actions
- promotes sodium reabsorption
- controls the secretion of aldosterone
- vasoconstrictor
this is a key hormone secreted mainly by the heart; it inhibits the release of renin (and the actions of AII that promote sodium reabsorption), acts on the medullary collecting duct to inhibit sodium reabsorption, and relaxes the afferent arteriole promoting increased glomerular filtration
atrial natriuretic peptide (ANP)
these are agents that increase urine flow; their goal is to reduce ECF volume to correct or prevent edema and they work by increasing sodium excretion
diuretics
the most powerful diuretics act by blocking this in the thick ascending limb of the loop of Henle (called loop diuretics)
Na-K-Cl symporter
this group of diuretics block the Na-Cl symporter in the DCT
thiazide diuretics
what is the most dangerous unwanted side effect of many diuretics
increased secretion of potassium (hypokalemia)
the vast majority of body potassium is (intracellular or extracellular?)
intracellular
a patient with hypokalemia has a more (negative or positive?) resting potential than normal; this makes the cell (more or less?) excitable
negative (potassium ions diffuse faster out of cell); less excitable
this is the rapid homeostatic mechanism that prevents large post prandial swings in serum potassium
intracellular sequestration (extrarenal potassium homeostasis)
what are the two major factors that stimulate the Na-K-ATPase pump for potassium uptake?
insulin and adrenaline
what happens to potassium when extracellular hydrogen levels are high (acidosis) so H+ moves into the cells
potassium moves out of the cell to maintain electroneutrality
potassium can be both secreted and reabsorbed in this part of the kidney (reabsorption always but secretion only when the body needs to get rid of potassium)
distal nephron
Reabsorption of potassium always occurs at these 3 parts in the kidney
- proximal convoluted tubule (paracellular route)
- thick ascending limb of loop of Henle (Na-K-2Cl cotransporter)
- Collecting ducts (intercalated cells)
Secretion of potassium only occurs when the body needs to get rid of potassium in this location in the kidneys
collecting ducts (principal cells)
these cells in the collecting ducts reabsorb sodium and secrete potassium
principal cells
this is the dominant stimulus for renal potassium excretion; it is secreted by the adrenal glands in response to angiotensin II and by increased plasma potassium concentration
it acts on the principal cells to enhance sodium reabsorption and potassium secretion
aldosterone
which one inhibits the Na-K-ATPase pumps and which stimulates them: acidosis and alkalosis?
acidosis inhibits, alkalosis stimulates
this is the most commonly used K+ wasting diuretic; it acts on the thick ascending limb of loop of Henle where it inhibits the luminal Na-K-Cl cotransporter, exacerbating potassium loss
furosemide
what are the 2 classes of potassium-sparing diuretics
- aldosterone receptor antagonists
- aldosterone independent mechanisms
this is an aldosterone receptor antagonist diuretic which blocks the aldosterone receptor located on basolateral side of the cortical collecting duct principal cells (causing lack of potassium excretion)
spironolactone
the production of either concentrated or dilute urine by the kidney is regulated via these 3 main mechanisms
- dilution of tubule fluid by TAL and DCT
- generation of hypertonic medullary interstitium
- variability of water permeability of collecting duct in response to vasopressin
a change in this is the major determinant of the volume of water lost by the kidney
change in plasma osmolality
this is defined as 1 mole of any fully dissociated substance dissolved in water
osmole
this is defined as the concentration of osmoles in a mass of solvent (kg)
osmolality
this is defined as the concentration of osmoles in a volume of solvent (L)
osmolarity
this is the major determinant of plasma osmolality
serum sodium concentration
these are located within the hypothalamus and sense changes in plasma osmolality
osmoreceptors
an increase in plasma osmolality sensed by osmoreceptors in the hypothalamus results in increased production and release of this into circulation
vasopressin
name 3 effects of vasopressin that have a direct effect on both the volume of urine produced and the urine concentration/osmolality
- net absorption of water from tubule lumen
- stimulates reabsorption of urea
- enhances reabsorption of NaCl
the formation of a dilute or concentrated urine is achieved via a countercurrent mechanism within the nephron including these 3 structures
- loop of Henle
- cortical and medullary collecting ducts
- blood supply to these segments
what are the 2 countercurrent systems present within the nephron?
- loop of Henle
- vasa recta
this limb of the loop of Henle is permeable to water and impermeable to solutes
descending limb
this limb of the loop of Henle is permeable to solute and impermeable to water
ascending limb
at any point along the loop of Henle, the fluid in the ascending limb has (higher or lower?) osmolality than the fluid in the descending limb
lower
osmolality of the tubular fluid and interstitium at the tip of the hairpin turn of the loop of Henle is much (greater or lesser?) compared to those at the corticomedullary junction
greater
these are the most abundant solutes within the interstitial medulla
NaCl and urea
this is generated by the liver as a product of protein metabolism and is freely filtered by the glomerulus
urea
what are the 2 basic steps for the formation of dilute urine
- NaCl reabsorption w/o water in the thick ascending limb of loop of Henle
- absence of vasopressin causing no water reabsorption in collecting tubules
what are the two major steps for the excretion of a concentrated urine
- medullary interstitium is made hyperosmotic by reabsorption of NaCl without water in ascending limb of loop of Henle
- vasopressin increases permeability of collecting duct to water to be reabsorbed passively
this is a capillary network derived from efferent arterioles that form a parallel set of hairpin loops with the loop of Henle within the medulla;
highly permeable to solute and water & return NaCl and H2O back into systemic circulation; plays integral role in maintenance of medullary osmotic gradient
vasa recta
what percent of the total body calcium is distributed in the extracellular and intracellular fluid?
1%
what are the 3 forms of calcium present in the total extracellular calcium?
- free (55%)
- Protein bound (35%)
- complexed to other anions (10%)
this is the biologically active form of calcium and is the most important for physiological control of calcium concentrations
ionized form
what form of extracellular Ca is favored with acidemia (increased acid w/in the blood)?
ionized Ca (free)
what form of extracellular Ca is favored with alkalemia (acid deficit w/in the blood)?
protein bound (albumin-bound)
what happens to the total calcium concentration when there is decreased albumin concentration?
decreases (decr. protein bound fraction of Ca)
what is the distribution of phosphorus in the body? (3 locations)
- bone (80-85%)
- soft tissues (15%)
- extracellular space (1%)
where is the majority of filtered calcium reabsorbed?
proximal tubule
what percent of phosphorous is excreted with the urine
20% (bc it only reabsorbed in proximal tubule)
where is PTH synthesized?
parathyroid gland (by chief cells)
what is the major and principal stimulus for PTH release?
decreased plasma calcium concentration
what is responsible for the minut-to-minute control of serum [iCa]?
PTH
what effect does PTH have on serum [Ca] and serum [phosphorous] ?
increases serum [Ca], decreases serum [phosphorus]
what are the 3 mechanisms by which PTH increases serum [Ca] and decreases serum [phosphorus]
- effect on nephron (incr. Ca reabsorption and Phosphorus excretion in urine)
- effect on bone (activates osteoclasts to release Ca and phosphorous into circulation)
- stimulates formation of active form of vitamin D (calcitriol)
this initial form of vitamin D is synthesized in the skin with the help of UV light
vitamin D3
this initial form of vitamin D is ingested in the diet
vitamin D2
the liver converts vitamin D2 and D3 to this (due to presence of 25-hydroxylase)
calcidiol
this is found within the proximal tubular cells of the nephron and acts on calcidiol to form calcitriol (the active form of vitamin D)
1⍺-hydroxylase
what affect does PTH have on the synthesis of 1⍺-hydroxylase (and therefore the formation of calcitriol)?
increases it
this is responsible for the day-to-day control of serum [iCa]
calcitriol
what effect does calcitriol have on the serum [Ca] and serum [phosphorus]
increases both
what is the major site of action for calcitriol
intestinal tract
what effect does calcitriol have on the intestinal tract?
increases calcium and phosphate absorption
what effect does calcitriol have on the kidney?
stimulates reabsorption of both calcium and phosphate w/in distal tubule
what effect does calcitriol have on the bones?
bone resorption (increases circulating Ca and phosphorous)
what effect does PTH have on the kidney?
stimulates Ca reabsorption by thick limb of LoH and inhibits phosphate reabsorption in proximal tubule
what effect does PTH have on bones
activates osteoclasts (bone breakdown so more Ca and Phosphorous into circulation)
name 4 factors that stimulates PTH release
- hypocalcemia
- hyperphosphatemia
- decr. PTH
- decr. calcitriol
name 4 factors that stimulates calcitriol release
- hypophosphatemia
- hypocalcemia
- incr. PTH
- decr. calcitriol
name 4 factors that inhibit PTH
- hypophosphatemia
- hypercalcemia
- incr. PTH
- incr. calcitriol
name 4 factors that inhibit calcitriol
- incr. calcitriol
- hypercalcemia
- hyperphosphatemia
- decr. PTH
name the effect hypercalcemia has on PTH, calcitriol, and calcitonin
decr. PTH, decr. calcitriol, incr. calcitonin
name the effect hypocalcemia has on PTH, calcitriol and calcitonin
incr. PTH, incr. calcitriol, decr. calcitonin
this is a hormone synthesized and released from the thyroid gland in response to increased calcium concentration
calcitonin
which hormone essentially has the opposite effects to PTH
calcitonin
this is a protein secreted mainly by osteocytes with the overall effect to decrease plasma concentration of ionized phosphorous
fibroblast growth factor 23 (FGF-23)
what is the equation for pH?
pH = -log[H+]
under this pH, the patient will be dead
< 6.8
above this pH, the patient will be dead
> 8
is considered normal pH
7.4
this is the main extracellular buffer
bicarbonate (HCO3-)
these are weak acids or bases which can either bind to or release H+ (H+ titration) to prevent large changes in pH
buffers
what is the equation for bicarbonate buffering with H+
HCO3- + H+ <-> H2CO3
when bicarbonate titrates H+, the extra CO2 produced stimulates this in order to eliminate it from the lungs
hyperventilation
what is the kidneys’ role in maintaining acid-base balance (metabolic component)
reabsorption of filtered bicarbonate and generation of new bicarbonate
what is the lungs’ role in maintaining acid-bace balance (respiratory component)
eliminate or retain CO2 based on H+ concentration
this acts as a urinary buffer to allow excretion of H+
ammonium (NH4)
Describe the process of renal ammoniagenesis in the proximal tubule and fate of the ammonium
- glutamine is taken up by the proximal tubular cells and converted to bicarbonate and ammonium
- ammonium is secreted into tubular lumen
- ammonium is reabsorbed into medullary interstitium at LoH
- ammonium is secreted again into the collecting duct
this is the enzyme which catalyzes H2O + CO2 <-> HCO3- + H+ reaction; it is present in large quantities in the proximal tubule brush border and cytosol of cells
carbonic anhydrase
what happens to H+ secreted from the proximal tubule into the tubular lumen?
recombine with filtered HCO3- (prevents loss of bicarbonate)
this is where 80%of bicarbonate is reabsorbed
proximal tubule
this part of the nephron secretes a quantity of H+ equal to that generated by the animal’s metabolism; secrete H+ combines with a urinary buffer to be excreted in the urine
collecting duct (distal nephron)
this type of cell in the collecting duct secretes H+
type A intercalated cells
this type of cell in the collecting duct secretes HCO3-
type B intercalated cells
urine leaving the collecting duct of carnivores has this pH
5.5-7.5
urine leaving the collecting duct of ruminants has this pH
6-9
