Renal System and Fluid Balance Flashcards
what processes occur as filtrate is converted to urine?
- elimination of metabolic wastes, hormones, drugs
- regulation of ion levels
- regulation of acid base balance
- regulation of bp
what is the function of the fibrous capsule of the kidney?
- directly adhered to external surface of kidney
- maintains kidneys shape, protects it from trauma, and prevents pathogen penetration
what is perinephric fat?
adipose CT external to fibrous capsule that cushions and supports kidney
what is the renal fascia?
- dense irregular CT external to perinephric fat
- anchors kidney to surrounding structures
what is paranephric fat?
adipose CT that is outermost layer surrounding kidney and cushions and protects it
what are renal pyramids?
- portion of medulla divided by renal columns
- wide base at external edge of medulla
- apex is called renal papilla
what is the function of the renal sinus
medially located urine drainage area
what are the components of a nephron?
renal corpuscle and renal tubule
what is the renal corpuscle?
- enlarged bulbous region of nephron within renal cortex
- composed of glomerulus and glomerular capsule
what is the glomerulus?
tangle of capillary loops and glomerular capillaries
what is the glomerular capsule?
- internal permeable visceral layer
- external impermeable parietal layer
- capsular space between two layers
what are the three sections of the renal tubule?
- proximal convoluted tubule
- nephron loop
- distal convoluted tubule
what are the two types of nephrons?
cortical and juxtamedullary
what classifies a cortical nephron?
- oriented near peripheral cortex
- short nephron loop barely penetrates medulla
- 85% of nephrons
what classifies a juxtamedullary nephron
- renal corpuscles adjacent to corticomedullary junction
- long nephron loop extend deep into medulla
- help establish salt concentration gradient in interstitial space
how do nephrons drain?
- nephrons drain into a collecting tubule
- multiple collecting tubules empty into large collecting ducts
- numerous collecting ducts empty into papillary duct within renal papilla
what is the juxtaglomerular apparatus?
helps regulate blood filtrate formation, systemic blood pressure
What are the components of the juxtaglomerular appartus?
- granular cells
- modified smooth muscle cells of afferent arteriole that synthesize renin - macula densa
- modified epithelial cells in wall of DCT
- detect changes in NaCl concentration of fluid and signal granular cells to secrete renin - extraglomerular mesangial cells
- just outside glomerulus in gap between each arteriole
how is filtrate formed?
- blood flows through glomerulus
- water and solutes are filtered from blood plasma
- moves across wall of glomerular capillaries into capsular space
what is the new name for filtrate after it enters the PCT?
tubular fluid
- once it empties into larger collecting ducts it is called urine
How does urine flow out of the kindey?
- enters papillary duct within renal papilla
- flows within renal sinus to minor calyx to major calyx to renal pelvis
- renal pelvis connects to ureter which connects to urinary bladder
What is the first step of urine formation?
glomerular filtration
- separates some water and solutes from blood plasma
- filtrate enters capsular space of renal corpuscle
what is the second stage of urine formation?
tubular reabsorption
- movement of components within tubular fluid
- move by diffusion, osmosis, or active transport
- return to blood within peritubular capillaries and vasa recta
- all vital solutes and most water reabsorbed
what is the third stage of urine formation?
tubular secretion
- movement of solutes usually by active transport
- move out of blood within peritubular and vasa recta capillaries into tubular fluid to be excreted
what are some characteristics of the filtration membrane?
- porous, thin, negatively charged structure
- formed by glomerulus and visceral layer of glomerular capsule
what are the layers of the filtration membrane? (from in to out)
- endothelium of glomerulus
- fenestrations allow plasma and dissolved substances to pass but restricts large structures - basement membrane of glomerulus
- glycoprotein and proteoglycan molecules
- restricts passage of large plasma proteins - visceral layer of glomerular capsule
- composed of podocytes which restrict passage of most small proteins
how much filtrate is produced daily?
180 L
what are the three categories of substances in blood?
- freely filtered: small substances
- pass easily through membrane - not filtered: large proteins
- cannot pass through - limited filtration: medium size proteins
- usually blocked due to size or negative charge
how is blood pressure in the glomerulus different from bp in other systemic capillaries?
- higher than bp of other systemic capillaries
- required for filtration to occur
what is blood colloid osmotic pressure?
osmotic pressure exerted by dissolved solutes that opposes filtration and draws fluid back into glomerulus
what is capsular hydrostatic pressure?
pressure in glomerular capsule due to filtrate which impedes movement of additional fluid
what impact does increased net filtration pressure have?
- increases glomerular filtration rate
- increases solutes and water remaining in tubular fluid
- increases substances in urine
- decreases filtrate reabsorption
Which 2 mechanisms regulates constant bp and GFR in the kidney?
myogenic response and tubuloglomerular feedback mechanism
what is the myogenic response?
contraction or relaxation of smooth muscle of afferent arteriole in response to stretch
- compensates for high or low systemic bp
what is the tubuloglomerular feedback mechanism
- “backup” to myogenic response to increased bp
- if glomerular bp increased: amount of NaCl in tubular fluid also increases and results in further vasoconstriction of afferent arteriole
what are some limitations to maintaining GFR?
- renal autoregulation: mantains glomerular pressure when bp is 80-180mmHg
- decrease in bp below 80: decrease in glomerular bp and GFR
- increase in bp above 180: increase in glomerular bp and GFR which leads to increase urine production
how does the sympathetic nervous system decrease GFR?
- vasoconstriction of afferent and efferent arterioles
- granular cells of JG apparatus releases renin, which results in angiotensin II production and contraction of mesangial cells which decreases surface area of glomerulus
How does atrial natriuretic peptide increase GFR?
increases GFR through
- relaxation of afferent arteriole
- inhibits release of renin
- relaxation of mesangial cells increases filtration membrane area
what is paracellular transport?
movement of substances between epithelial cells
what is transcellular transport?
- movement of substances across epithelial cells
- must cross luminal membrane in contact with fluid
- must cross basolateral membrane on basement membrane
where does most reabsorption occur?
proximal convoluted tubule
- aided by microvilli which increase surface area
what is transport maximum?
maximum rate of substance that can be reabsorbed or secreted across tubule epithelium per a certain time
what is renal threshold?
max plasma concentration of a substance that can be transported in the blood without appearing in the urine
How does sodium reabsorption occur?
- 98% to 100% of Na+ reabsorbed from tubular fluid
- reabsorbed along the entire nephron tubule, mostly in PCT
- relatively high within tubule lumen and interstitial fluid
-Na+/K+ pumps embedded in basolateral membrane - reabsorption regulated by hormones near end of tubule
what role does aldosterone play in sodium reabsorption?
- steroid hormone produced by adrenal cortex
- stimulates protein synthesis of Na+ channels and Na+/K+ pumps
- increase in Na+ reabsorption
- water follows by osmosis
what role does atrial natriuretic peptide play in sodium reabsorption?
- inhibits reabsorption of Na+ in PCT and collecting tubules
- inhibits release of aldosterone
- more Na+ and water excreted in urine
- increases GFR
how does water reabsorption occur?
- reabsorbed by paracellular transport between cells and transcellular transport through aquaporins
- 65% reabsorbed in PCT
How much water is filtered daily?
180 L filtered dailty with all but 1.5 L reabsorbed
How much water is reabsorbed in the nephron loop
10% of filtered water
what hormones regulate water absorption?
aldosterone and ADH
what role does ADH play in water reabsorption?
- increases migration of vesicles containing aquaporins to membrane and adds channels to increase water reabsorption
- increases water reabsorption from filtrate to blood
- results in smaller volume of more concentrated urine
when would ADH levels be elevated
during dehydration
Is potassium secreted or reabsorbed?
- it is both reabsorbed and secreted
- 60% to 80% reabsorbed in tubular fluid
What influences the movement of potassium?
- sodium reabsorbed across luminal membrane, water follows
- increased concentration of remaining solutes in tubular fluid which creates gradient between tubular fluid and interstitial fluid
- K+ moves down gradient from tubular fluid by paracellular route
what role do intercalated cells and principal cells have in potassium secretion/reabsorption?
- intercalated cells reabsorb K+ continuously
- principal cells secrete K+ at varying rates based on aldosterone level
how is calcium and phosphate balance regulated?
- 60% in blood goes into filtrate
- 90% to 95% filtered as blood passes through glomerular capillaries
what role does parathyroid hormone play in calcium and phosphate balance?
- regulates excretion of calcium and phosphate
- inhibits phosphate reabsorption in PCT
- stimulates calcium reabsorption in DCT
- increases calcium blood levels
how are bicarbonate ions filtered?
- move freely across filtration membrane
- if not reabsorbed, blood becomes too acidic
- 80% to 90% reclaimed from tubular fluid
- remaining 10% to 20% taken up from thick segment of ascending limb
what happens if the blood becomes too acidic?
- synthesized HCO3- reabsorbed into blood
- H+ excreted within filtrate by type A intercalated cells
what happens if the blood becomes too alkaline?
- type B intercalated cells active
- secrete HCO3- and reabsorb H+
how is nitrogenous waste eliminated?
- 50% of urea excreted in the urine
- uric acid both reabsorbed and secreted
- creatinine only secreted
where does the secretion of most drugs and bioactive substances occur?
in PCT
How is the pressure gradient established in the nephron loop?
- positive feedback mechanism called countercurrent multiplier
- descending limb permeable to water, impermeable to salts
- ascending limb impermeable to water, salts pumped out
how does the countercurrent exchange system work?
- blood in vasa recta travels in opposite direction to tubular fluid of adjacent nephron loop
- water diffuses out of vasa recta by osmosis
- increases concentration of salt in vasa recta
- vasa recta next runs along descending limb of nephron
How is urea recycled?
- urea remoced from tubular fluid in collecting duct but diffuses back into tubular fluid in thin segment of ascending lumb
- remains within tubular fluid until it reaches collecting duct
How can GFR be measured?
- measured with inulin injection
- GFR = (concentration of inulin in urine x volume of urine produced per minute)/concentration of inulin in plasma
- normal is 125 mL/min
what is the composition of water?
95% water, 5% solutes
How does pH change in urine?
- normally between 4.5 and 8.0
- more acidic with larger amounts of protein or wheat in diet
- less acidic with diet high in fruits and vegetables
what is the specific gravity of urine?
- density of a substance compared to density of water
what are the tunics of the ureters?
- mucosa: transitional epithelium and lamina propria, impermeable to urine
- muscularis: inner longitudinal layer and outer circular layer of smooth muscle
- adventitia: external layer of collagen and elastic fibers within areolar CT
what is the trigone of the bladder?
- posteroinferior triangular area of bladder wall
- remains immobile as bladder fills and empties
what are the tunic of the bladder?
- muscosa: transitional epithelium with underlying lamina propria and mucosal folds for greater distension
- submucosa
- muscularis: 3 layers of smooth muscle
- adventitia: areolar CT
what are the two sphincters of the urethra?
- internal urethral sphincter: involuntary
- external urethral sphincter: voluntary
what is micturition?
expulsion of urine from the bladder
what two reflexes are associated with micturition?
storage reflex and micturition reflex
what is the storage reflex?
- continuous sympathetic stimulation which causes relaxation of detrusor to accommodate urine
- stimulates contraction of internal sphincter which retains urine in bladder
what is the micturition reflex?
- volume of urine in bladder 200 to 300 ml
- visceral sensory neurons signaled by baroreceptors
- micturition center alters nerve signals down spinal chord
- parasympathetic stimulation relaxes detrusor muscles and internal sphincter
where is conscious control of urination initiated?
initiated from cerebral cortex through pundendal nerve
what happens after the bladder is emptied?
- detrusor muscles relaxes
- micturition reflex inactivated
- storage reflex activated
what happens if urination is not activated at time of first reflex?
- micturition reflex activated again after another 200 to 300 mL
- urination occurs involuntarily between 500 ml and 600 ml
what factors is blood composition dependent on three factors
dier, cellular metabolism, and urine output
what roles do the kidneys play in maintaining blood composition?
- excretion of nitrogen containing wastes
- maintaining water balance of blood
- maintaining electrolyte balance of blood
- ensuring proper blood pH
what makes up the majority of body fluid?
intracellular fluid (about 2/3)
what are osmoreceptors?
cells in hypothalamus that react to small changes in solute blood composition by activating thirst center
what is diabetes insipidus?
- occurs when ADH is not released
- leads to huge outputs of dilute urine
what happens when blood pH rises?
bicarbonate ions are excreted and hydrogen ions are retained by kidney tubules
what happens when blood pH falls?
bicarbonate ions are reabsorbed and hydrogen ions are secreted
