Ch. 25: The Urinary System
Describe the kidney's role in maintaining BP including the functions of the macula densa and juxtaglomerular cells
- Macula densa cells contain chemoreceptors that monitor NaCl concentration in filtrate; decr. BP causes decr. NaCl lvls & low blood vol causing decr GFR & decr NaCl filtrate lvls; incr lvls by vasodilation of afferent arterioles (myogenic mechanism) & stim of renin secretion(tubuloglomerular feedback mechanism); - juxtaglomerular cells responsible for production, storage, & release of renin that regulates BP - renin converts angiotensinogen(liver) into angiotensin I; ACE(lungs) converts angiotensin I into angiontensin II causing vasoconstriction of efferent arteriole & raises BP
What are the mechanisms of recovery in tubular reabsorption?
- active transport: uses ATP to move substance across a membrane from low to high concentration; must have specific receptor for transport; ex: Na+ out of cell & K+ in by Na+/K+pump moved in opposite directions from low to high concentration - simple diffusion: moves substance from higher to lower concentration down concentration gradient; no ATP needed; - facilitated diffusion: moves substance down concentration gradient; requires specific membrane receptors or channel proteins for movement; ex: movement of glucose & Na+ - symport mechanism: move 2 or more substances in same direction at same time using concentration gradients maintained by ATP pumps - antiport mechanism: move 2 or more substances in opposite directions across cell membrane using concentration gradients maintained by ATP pumps - secondary active transport: active transport powers transport of another substance; ex: glucose reabsorption in kidneys; Na+/K+ ATPases on basal membrane of tubular cell pump Na+ out of cell, maintaining electrochem gradient for Na+ to move into cell; Na+/glucose symport moves glucose into cell against concentration gradient as Na+ moves dwn electrochem gradient made by Na+/K+ ATPases; glucose molecule diffuses out by facilitated diffusion
What are the basic functions of the urinary system
1. cleansing blood and ridding body of wastes 2. regulation of pH 3. regulation of blood pressure 4. regulating concentration of solutes in the blood/RBC cell concentration(EPO production) 5. performing final synthesis step of vitamin D production, converting calcidiol to calcitriol
List the 4 regions of the male urethra
1. preprostatic: (short & in bladder wall), 2. prostatic: (passes thru prostate; receives sperm during intercourse; has bulbourethral glands that secrete mucus to buffer pH during sexual stimulation) 3. membranous: (passes thru perineum muscle) 4. spongy: (exits @ tip after passing thru corpus spongiosum)
Discuss the ureters
2 retroperitoneal tubes that carry urine one way from kidney to bladder by peristalsis; lateral in pelvis & pierce bladder obliquely creatine one way valve (physiological sphincter) preventing reflux back into ureter; inner mucosa lined w/transitional epithelium & goblet cells; longitudinal & circular muscle layer to move urine by peristalsis & w/o gravity; adventitia anchors to post abdominal wall
Describe the renal pyramids
6-8 cone-shaped tissues in medulla of kidney containing collecting ducts and loops of Henle of juxtamedullary nephrons
Describe reabsorption and secretion in the DCT
80% filtered water is recovered by time urine reaches DCT; Reabsorption(into blood) of: - H2O: 10-15% (osmosis) - Na+: 5% (symporters) - Cl-: 5% (syporters) - Ca2+: variable (stimulated by PTH) recovers Ca++ from filtrate & has PTH receptors; when bound to PTH, Ca++ channel insertion on apical membrane enhancing recovery; as Na+ pumped out of cell, gradient attracts Ca++ into cell; calcitriol induces production of Ca++ binding proteins that transport Ca++ into DCT cells & aid in exocytosis; any Ca++ not absorbed lost in urine
Describe juxtamedullary nephrons
Account for 15% of nephrons; Glomeruli are in cortex; loop of Henle penetrates deep into medulla
Discuss blood flow into and out of the kidney
Aorta → renal artery → segmental artery → interlobar artery(pass thru renal columns to reach cortex) → arcuate artery → cortical radiate artery → [Nephron assoc. vessels: afferent arteriole → Glomerulus(capillaries) → efferent arteriole → peritubular capillaries or vasa recta] → cortical radiate vein → arcuate vein → interlobar vein → renal vein → IVC
Describe the renal columns
CT extensions radiating down from cortex thru medulla separating pyramids & papillae; divides kidney into 6-8 lobes; supportive framework for vessels entering & exiting cortex
Define polyuria
Excessive urination. May be caused by excessive hydration, diabetes mellitus, diabetes insipidus, or kidney disease.
What is the renal tubule?
Part of the nephron where reabsorption takes place; it leaves the Bowman's capsule as the PCT, drops into a loop of Henle, then winds into the DCT before emptying into the collecting duct.
Discuss reabsorption and secretion in the Loop of Henle
Reabsorption(into blood) of: - H2O: 15% (osmosis in descending limb) - Na+: 20-30% (symporters in ascending limb) - K+: 20-30% (symporters in ascending limb) - Cl-: 35% (symporters in ascending limb) - HCO3-: 10-20% (facilitated diffusion) - Ca++&Mg++: variable (diffusion) Secretion(into urine) of: - Urea: variable (recycling from collecting duct) *at end of Loop, tubular fluid is hypotonic (100-150mOsm/L)
Describe reabsorption & secretion in the PCT
Reabsorption(into blood) of: - H2O: 65% (osmosis) - Na+: 65% (sodium pumps, symporters, antiporters) - K+: 65% (diffusion) - Glucose: 100% (symporters & facilitated diffusion) - AAs: 100% (symporters & facilitated diffusion) - Cl-: 50% (diffusion) - HCO3-: 80-90% (facilitated diffusion) - Urea: 50% (diffusion) - Ca++&Mg++: variable (diffusion) Secretion(into urine) of: - H+: variable (antiporters) - NH4+: variable, incr. in acidosis (antiporters) - Urea: variable (diffusion) - Creatinine: small amount *at end of PCT, tubular fluid is still isotonic to blood (300mOsm/L) - 1st point at which forming urine is modified
What is hydrostatic pressure?
The pressure that the fluid exerts on the walls of its container.
Describe cortical nephrons
account for 85% of the nephrons in the kidneys. Except for small parts of their nephron loops that dip into the outer medulla, they are located entirely in the cortex.
What is the glomerulus?
afferent arterioles form tuft of capillaries(capillary bed) surrounded by Bowman's capsule; filters the blood based on size; fenestrated endothelium allowing solute-rich, but protein free fluid (filtrate) to pass from blood into glomerular capsule
Describe the efferent arteriole
after passing thru the renal corpuscle, capillaries form a second arteriole and connects the glomerulus to the peritubular capillaries and vasa recta forming a capillary network around the distal end of the nephron before returning to the venous system
Explain how glucose and sodium are symported
almost all glucose, AAs, & vitamins recovered in PCT; if circulating glucose lvls exceed glucose transport capacity in PCT glucose appears in urine(glycosuria), an indication of diabetes; both glucose & Na+ bind to same symport proteins; Na+ moves down chem & concentration gradient into cell & takes glucose w/it; Na+ actively pumped out of cell; glucose leaves by facilitated diffusion; energy to move glucose comes from Na+/K+ ATPase that pumps Na+ out of cell
Define hematuria
blood in the urine
Describe kidney autoregulation
blood pressure fluctuates; kidney autoregulates glomerular filtration rate despite fluctuations w/2 internal mechanisms that operate w/o outside influence: myogenic mechanism & tubuloglomerular feedback mechanism
Discuss the vasa recta
branches of the efferent arterioles that parallel the course of loops of Henle and are continuous with peritubular capillaries; w/glomerulus, form a portal system
Describe the renal papillae
bundles of collecting ducts transporting urine from nephrons to kidney calyces for excretion; renal pyramids + renal columns = kidney lobes
Describe the macula densa
cells found in initial part of DCT when it comes in direct contact w/the afferent & efferent arterioles forming JGA; cuboidal epithelial cells; monitors the fluid composition flowing thru DCT & senses Na+ concentration releasing paracrine signals(ATP & adenosine); have single nonmotile cilium that responds to rate of fluid movement in tubule; regulate renin release from juxtaglomerular cells of afferent arteriole
What is an aquaporin?
channel protein that facilitates the passage of water across lipid rich hydrophobic cell membrane; allows for large recovery of water from filtrate back into blood
What is a renal corpuscle?
consists of glomerulus and Bowman's capsule; all located in cortex
Describe the collecting duct
continuous w/but not part of nephron; collects filtrate from nephron; empties at papilla; about 30 that merge deep in medullar; lined w/simple squamous & ADH receptors; ADH stimulation causes aquaporin protein insertion in membrane allowing water to pass from duct lumen thru cells into interstitial space for vasa recta recovery; only water can pass; no ADH = no aquaporin channels & excretion of water in dilute urine form
Discuss the pudendal nerve
controls voluntary function of external urethral sphincter
What does it mean if glucose is found in urine?
could be a sign of diabetes mellitus
Describe the calyces
cup-like structures receiving urine from the collecting ducts where it passes on to the renal pelvis and ureter
What is the Bowman's capsule?
cup-shaped sack lined by simple squamous epithelium(parietal surface) & specialized cells called podocytes(visceral surface) that participate in filtration process; receives filtrate which then passes on to the PCTs
Define oliguria
decreased urine production; may be caused by dehydration, blood loss, diarrhea, cardiogenic shock, kidney disease
Describe the countercurrent multiplier
depends on 3 properties of loop to estab. osmotic gradient: 1. countercurrent flow thru ascending & descending limbs 2. descending permeable to water & not NaCl 3. ascending impermeable to water & pumps out NaCl filtrate enters isomotic; water moves out in descending limb, down osmotic gradient concentrating filtrate; filtrate reaches highest concentration @ bend of loop(1200); NaCl pumped out of filtrate in ascending, increasing IF osmolality; filtrate @ most dilute leaving loop(100mOsmol) & hypoosmotic to IF; properties estab. positive feedback cycle that uses flow of fluid to multiply power of salt pumps; more NaCl leave in ascending, more water diffuses out of descending & saltier the filtrate in descending becomes; ascending limb uses salty filtrate in descending to raise osmolality of medullary IF further estab positive feedback cycle producing increased osmolality in descending limb & IF; b/c of countercurrent flow nephron loop able to multiply small changes in solute concentration into gradient change along vertical length of loop(in&out) closer to 900mOsmol; most NaCl reabsorption active in ascending via Na+,K+,2Cl cotransport in thick ascending limb; some passive in thin
Describe the loop of Henle
descending and ascending portions b/t the PCT & DCT that run parallel to ea. otr.; aka nephron loop; both ascending & descending portions: initial short thin portion(simple squamous) & long thick portion(simple cuboidal)
Describe the distal convoluted tubule (DCT)
distal to loop of Henle; receives hypoosmotic filtrate from loop of Henle emptying it into collecting duct; shorter than PCT w/cells not as active; fewer microvilli
Describe the renal hilum
entry & exit for renal artery, vein, ureters, lymphatics and ureters; medial facing;
Discuss the filtration membrane
fenestrae in glomerular capillaries match spaces between pedicels w/only their basement membranes separating them and comprises the filtration membrane; permits very rapid movement of filtrate from capillary to capsule; has mesangial cells that can contract to help regulate filtration rate of glomerulus
Describe the 3 kidney coverings
fibrous capsule covering of dense irreg. CT for shape & protection; renal fat pad covers capsule & is shock absorbing layer of adipose encompassed by renal fascia; fascia & peritoneum anchor to post abdominal wall in retroperitoneal position; adrenal glands cover superior aspect
What are the 3 principle functions and 2 secondary functions of nephrons?
filtration, reabsorption, & secretion; renin production, RBC production(via hormone EPO), calcium absorption(conversion of calcidiol into calcitriol, active form of vitamin D)
What is a nephron?
functional unit of the kidney; creates cell & protein free filtrate from blood by balancing plasma, osmolarity, & excreting toxins; ea. consists of renal corpuscle & tubule
Describe the renal pelvis
funnel-shaped tube that connects to the ureter as it leaves the hilus; formed from major & minor calyces; smooth muscle funnels urine via peristalsis into ureter
Define glycosuria
glucose in the urine
Discuss the bladder
highly distensible, collects urine from both ureters, & partially retroperitoneal(dome); interior is transitional epithelium; volume= 0-600ml; strength diminishes w/age
What does it mean if protein are found in urine?
if excessive protein is detected it usually means that the glomerulus is damaged and is allowing protein into the filtrate
Describe the renal medulla
inner layer of kidney contains tubules and the collecting duct Renal pyramids, columns of bertin (cortical tissue) Darker
Describe the tubuloglomerular feedback mechanism
involves JGA & paracrine signaling mechanism utilizing ATP, adenosine, & NO; mechanism stimulates either relaxation or contraction of afferent arteriole muscle cells; DCT connects w/afferent & efferent arterioles & macula densa that respond to changes in fluid flow rate & Na+ concentration; increase GFR = less time for NaCl reabsorption in PCT leading to increased osmolarity in filtrate; increase fluid movement deflects single nonmotile cilia on macula densa cells; increase osmolarity of urine & increase flow rate w/in DCT activates macula densa to release ATP & adenosine that stimulate myogenic juxtaglomerular cells of afferent arterioles to constrict, slow blood flow & decrease GFR; ↓GFR, less Na+ in urine w/most reabsorbed before reaching macula densa = ↓ATP & adenosine, afferent arteriole dilates & ↑GFR; NO relaxes afferent arteriole while ATP & adenosine stimulates contraction thus finetuning effects of adenosine & ATP on GFR
Discuss the detrusor muscle
irregular crisscrossing bands of smooth muscle in the bladder wall; fibers run in all directions to reduce size of organ when emptying it of urine; contracts w/signif. force in young & diminishes w/age
What happens if the osmolarity of the filtrate is too high (hyperosmotic)?
juxtaglomerular cells contract, GFR decreases & less plasma filtered, less urine formation, greater fluid retention; ultimately decreases blood osmolarity physiologic norm (osmolarity up, filtration & urine formation decrease & water is retained)
What happens if the osmolarity of the filtrate is too low?
juxtaglomerular cells relax, GFR increases, more loss of water to urine causing blood osmolarity to rise (osmolarity down, filtration & urine formation increase and water is lost by way of urine)
Basicly describe the countercurrent multiplier system
juxtamedullary nephrons create osmotic gradient w/in renal medulla allowing kidney to produce urine of varying concentration; osmotic gradient: osmolality(solute concentration) of medullary IF; progress increases 300-1200 top to bottom; long nephron loops create gradient & act as countercurrent multipliers; vasa recta preserves gradient acting as current exchanger; collecting ducts of all nephrons us gradient to adjust urine osmolality
What does it mean if ketones are found in urine?
ketones are byproducts of fat metabolism and suggests the body is using fat as an energy source instead of glucose. W/Diabetes type I or II, cells can't take up glucose w/o insulin so it remains in bloodstream and cells are forced to use fat as energy source instead; may also appear if there's a severe protein or carb deficiency
Define ketonuria
ketones in the urine & evidence of body using fat as energy source, diabetes, or protein/carb deficiency
Describe the juxtaglomerular apparatus (JGA)
lies outside Bowman's capsule and glomerulus; @ juncture where afferent & efferent arterioles enter & leave Bowman's capsule, initial part of DCT comes into direct contact w/the arterioles; allows 2 types of specialized cells to monitor the composition of fluid in DCT and adjust the glomerular filtration rate
Define anuria
little to no urine; may be caused by kidney failure or obstruction
Describe adrenal gland location
located on the superior aspect of the kidney
What does it mean if leukocytes are found in urine?
may indicate an UTI; Leukocyte esterase released by leukocytes and if detected in urine can be taken as direct evidence of UTI
Describe juxtaglomerular cells
modified smooth muscle cell lining afferent arteriole that contracts or relaxes in response to ATP or adenosine released by macula densa; contraction & relaxtion regulate blood flow to glomerulus; also releases renin
Discuss the formation of urine in the nephron and briefly discuss the processes of filtration, reabsorption, and secretion
nephron is functional unit of kidney responsible for urine formation; 1. filtration: occurs in glomerulus; blood enters kidney as filtrate via afferent arteriole; filtrate carried to glomerulus; hydrostatic pressure force that drives blood into system to filter urine & determined by ttl fluid vol. & BP; osmotic pressure(# of particles in blood) & if high blood pulls water to dilute particles producing osmotic pressure; 2. reabsorption: responsible for reabsorbing water, ions, & molecules in glomerulus for re-entrance into circulation; kidneys filter waste, but need to keep valuable substances that help body function; w/in nephron, filtrate passes into PCTs, thru loop of Henle & collecting ducts, then to ureters for excretion; During process, PCT reabsorbs salts, vitamins, glucose, and amino acids; Certain hormones in body like ADH signal the kidneys to hold on to more water& certain particles like RBCs too lg to reabsorb and pass out through the efferent tubule; process and flow of particles can occur by diffusion, active transport, or cotransport; peritubular capillaries carry filtrate away 3. secretion: responsible for transferring H+, drugs, urea, & creatinine to collecting duct for removal; filtrate passes from peritubular capillaries thru loop of Henle into the DCT; it's excreted thru ureters as urine; secretion removes harmful substances from blood such as K+, H+, ammonium ions, urea, certain hormones, & drugs/medications; filtrate & fluid pass thru lumen of tube or capillary; - pathway of urine: begins as blood; flows into nephrons via afferent arterioles to glomerulus where processes filtrate & passes it to Bowman's capsule for further processing; after fluid is filtered it passes PCT, loop of Henle, & then DCT for reabsorption of vital substances & water; from tubules, filtrate passes to collecting duct to renal calyces to pass to ureters as urine; urine flows from ureter to bladder & then passes out of body thru urethra
What does it mean if nitrates are found in urine?
occur normally in urine; gram negative bacteria metabolize nitrate into nitrite(NO2-), and its presence in urine is indirect evidence of infection
Discuss the reabsorption and secretion in the ascending loop
only considers thick portion that's completely impermeable to water w/no aquaporin proteins; Na+ & Cl- actively reabsorbed by cotransport w/2 effects: 1. NaCl removal while keeping water = hypoosmotic filtrate by time it reaches DCT; 2. pumping NaCl into interstitial space contributes to hyperosmotic environment in kidney medulla; Na+/K+ATPase pumps in basal membrane create gradient & reabsorption of Cl- by Na+/Cl symporters in apical membrane; @same time Na+ pumped out of basal membrane(paracellular route) into IF by leaky tight junctions(found b/t cells of ascending loop & allow certain solutes to move according to concentration gradient); K+ enters via symporters & returns to lumen dwn concentration gradient thru channels in apical membrane; K+ returns to lumen leaving 1Na+ & 2Cl in interstitium of ascending loop creating negative environment & attracting cations (Na+, K+, Ca++, & Mg++) from lumen to interstitial space & vasa recta
Describe the renal cortex
outer region of the kidney; lighter in color than rest of kidney
Discuss retroperitoneal
outside of peritoneal cavity
Discuss filtration slits
pedicels (finger-like arms) interdigitate leaving small gaps forming a sieve; as blood passes thru capsule, 10-20% plasma filtered, captured by Bowman's capsule, & funneled to PCT;
Define urinalysis
physical, chemical and microscopic analysis of urine. Color, appearance, specific gravity, red blood cells, white blood cell count.
Discuss principal cells
possess channels for recovery of loss of Na+ & K+; line collecting ducts; have ADH(reg. of water recovery) & aldosterone(reg. of Na+ recovery) receptors; Aldosterone stimulates principal cells to manufacture luminal Na+ & K+ channels & Na+/K+ ATPase pumps on basal membrane; high Aldosterone = more Na+ recovered from forming urine w/water following; pump recovers Na+ for body & K+ pumped into urine in opposite direction; low Aldosterone = Na+ remains in urine & more K+ recovered in circulation; symport channel move Na & Cl together & otr. channel secretes K+ into collecting duct in direct proportion to recover Na+
What is colloid osmotic pressure?
pressure exerted by colloids w/in glomerulus(in case of glomerulus)
Discuss the fenestrations in the glomerular capillaries
prevent filtration of blood cells, lg proteins, & globulins, but allow most otr constituents thru; another factor affecting ability of substances to cross barrier is charge b/c proteins assoc. with these pores are negatively charged repelling negative proteins & positively charged substances thru
Describe endocrine regulation: renin
produced by granular cells of afferent arterioles at the JGA; converts angiotensinogen(liver) into angiotensin I; release stimulated by prostaglandins & NO from JGA when ECF volume low
Describe endocrine regulation: ACE
produced in lungs & enzymatically converts inactive angiotensin I into active angiotensin II; important in raising blood pressure & ppl w/increased blood pressure prescribed ACE inhibitors to lower it
Discuss the male urethra
proximal: transitional & distal: stratified squamous; passes thru prostate gland before passing below pubic symphysis; 20cm; mucus glands found along length & protect from urine pH; 4 regions: 1. preprostatic: (short & in bladder wall), 2. prostatic: (passes thru prostate; receives sperm during intercourse; has bulbourethral glands that secrete mucus to buffer pH during sexual stimulation) 3. membranous: (passes thru perineum muscle) 4. spongy: (exits @ tip after passing thru corpus spongiosum)
Discuss the female urethra
proximal: transitional epithelium & distal: stratified squamous; embedded in ant. vaginal wall inf. to clitoris; short(4cm); less of a barrier to fecal matter & explanation for greater instance of UTIs; voluntary control of external urethral sphincter: pudendal nerve from sacral region(S2-S4 of sacral plexus)
Define pyuria
pus in the urine
Describe the proximal convoluted tubule (PCT)
receives filtrate from Bowman's capsule; most active part of nephron in reabsorption & secretion; microvilli in lumen create brush border to maximize surface area, absorption, secretion of solutes(Na+, Cl-, glucose, etc.), & most essential functions of nephron portion; actively transports ions across membrane & possesses increases # of mitochondria for enough ATP; simple cuboidal
Describe the myogenic mechanism
regulates blood flow w/in kidney & depends on smooth muscle cell stretch & contraction; -afferent arteriole: blood pressure increase, smooth muscle stretch & contract in arteriole wall to resist pressure resulting in little flow change; blood pressure decrease, smooth muscle cells relax & lower resistance allowing continued even flow of blood -constriction = restriction of blood flow to glomerulus & keeps GFR lvl ideal for kidney func. -dilation = increase glomerular hydrostatic pressure maintaining normal NFP & GFR
Describe endocrine regulation: Aldosterone
retains Na+; released from adrenal cortex by stimulation of angiotensin II or increased plasma K+; promotes Na+ reabsorption in nephron & water retention; regulates K+ promoting excretion; as result, renin has immediate BP effect b/c of angiotensin II stimulating vasoconstriction & prolonged effect thru Na+ recovery due to Aldosterone; when Aldosterone causes increased Na+ recovery it also causes greater loss of K+; progesterone binds to Aldosterone receptor & weakly stimulates Na+ reabsorption & increases water recovery resulting in increased water retention(bloating) during menstrual cycles when progesterone lvls increase
Describe the kidney location
retroperitoneal; on sides of spine b/t parietal peritoneum & post. abdominal wall; protected by muscle, fat, & ribs(upper section protected by 11th & 12th ribs); right is lower due to liver displacement
Discuss the peritubular capillaries
second capillary bed of renal portal system; surround proximal and distal convoluted tubules; associated w/vasa recta
Discuss intercalated cells
secrete or absorb acid or bicarbonate; regulate blood pH by reabsorbing K+ & bicarbonate while secreting H+ lowering acidity of plasma & increasing acidity of urine
Define tubular reabsorption
selectively returns 99% of substances from filtrate to blood in renal tubules and collecting ducts; 180L/day pass thru nephrons; recovery occurs in PCT, loop of Henle, DCT, & collecting ducts; most reabsorption & secretion passive & based on concentration gradients, amnt of water reabsorbed or lost tightly regulated by ADH, aldosterone, & renin(indirectly); most H2O recovered in PCT, loop, & DCT; 10% reaches collecting ducts(under influence of ADH, collecting ducts can recover almost all H2O-dehydration, or none-overhydration)
Discuss reabsorption and secretion in the descending loop
simple squamous w/permanent aquaporin channels & unrestricted water movement out as osmolarity increases from 300-1200mOsmol; osmolarity increases = reabsorption of up to 15% of water entering nephron & some solutes (urea, Na+, & otr. ions); most solutes & 82% of water have been recovered as forming urine enters ascending loop
Discuss the external urethral sphincter
skeletal muscle; must be relaxed consciously to void urine; voluntary
Discuss the internal urethral sphincter
smooth muscle at juncture of bladder & urethra; relaxes as bladder fills to allow urine into urethra; involuntary
Discuss transitional epithelium
structurally suited for lg vol fluctuations of bladder; empty it resembles columnar but when stretched it transitions to squamous appearance
Describe the afferent arteriole
supplies ea. glomerulus; maintains high pressure in glomerulus needed for filtration that produces lg amnt of filtrate
Define osmolarity
the concentration of a solution expressed as the total number of solute particles per liter.
Discuss the renal portal system
the glomerulus(capillary bed) drains into a vessel that forms a second capillary bed(efferent arteriole connecting the peritubular capillaries and vasa recta); this is the only portal system that where an arteriole is found b/t the 1st and 2nd capillary beds
Define specific gravity
the ratio of the density of a substance to the density of a standard; measure of the density of urine compared with the density of water
What is net filtration pressure (NFP)?
the sum of osmotic & hydrostatic pressure = about 10mmHg; NFP = GBHP(glomerular blood hydrostatic pressure) - [CHP(capsular hydrostatic pressure) + BCOP(blood colloidal osmotic pressure)] or 55 - (15 + 30) = 10mmHg; low net pressure; minor changes in osmolarity of blood or capillary BP = major changes filtrate amnt; kidney copes w/changing blood pressures by autoregulation (smooth muscle in afferent arterioles) to keep blood & filtrate steady; as long as mean arterial pressure(systolic - diastolic x 1/3) is above 60mmHg, pressure is adequate to maintain glomerular filtration
What does it mean if blood is found in urine?
there should not be blood in urine unless in the case of menstrual contamination
Discuss the urethra
transports urine from bladder to outside of body & is only anatomical difference b/t males & females(all otr. urine transport structures are the same); post. & inf. to pubic symphysis; protects tissue from range of pH & osmolarity of urine; prevents infection; reproductive function(male); voiding regulation by ANS, internal urinary sphincter, and external urinary sphincter
Discuss the trigone
triangular-shaped area at base of bladder marked by 2 ureters in post. lateral aspect and urethral orifice in anterior aspect like triangle points
Discuss podocytes
uniquely shaped cells in visceral layer of glomerular capsule that cling to the capillaries and extend finger-like arms, pedicels, to cover the glomerular capillaries
Define micturition
urination
Describe the countercurrent exchanger: vasa recta
vasa recta preserves medullary gradient by: 1. preventing rapid Na+ removal from medullary interstitial space; 2. removing reabsorbed water; results in blood leaving & re-entering cortex w/nearly same solute concentration; blood moves slowly in capillaries allowing for nutrient & waste exchange; in vasa recta, flow must be slow enough to allow blood cells to lose & regain water w/o bursting or crenating; rapid flow would remove too much Na+ & urea killing osmolar gradient necessary for water & solute recovery; slow flow = countercurrent mechanism preservation; vasa recta descend, Na+ & urea freely able to enter & water freely able to leave; vasa recta ascend, Na+ & urea secreted into surrounding medulla while water reenters & is removed; volume of blood @ end greater than @ beginning
Describe endocrine regulation: angiotensin II
vasoconstrictor that plays immediate role in blood pressure regulation; systemic action causing vasoconstriction & constriction in both afferent & efferent arterioles of glomerulus; during blood loss or dehydration, reduction of GFR & renal blood flow limiting fluid loss & preserving blood volume; release stimulated by decrease in blood pressure; preservation of adequate blood pressure primary role
Describe bicarbonate recovery in the PCT
vital to the acid-base balance; catalyzed by carbonic anhydrase(found w/in kidney cells & bound to brush border on apical surface); in PCT lumen H+ combos w/HCO3- to form carbonic acid (H2CO3-) & catalyzed into CO2 & H2O; H2O moves osmotically across apical membrane thru aquaporins @ same time as H2CO3- produced by reverse reaction & cotransports w/Na+ across basal membrane to interstitial space around PCT; also @ same time Na+/H+ antiporter exretes H+ into lumen, recovers Na+; Hydrogen recycled so bicarbonate can be recovered; Na+ gradient created by Na+/K+ pump; recovery of solutes in PCT lumen to interstitial space creates osmotic gradient that promotes H2O recovery
Describe the micturition reflex
vol. reaches 150mL, urge to void sensed but can easily be overridden; result of stretch receptors in bladder wall sending nerve impulses to sacral micturition center resulting in spinal reflex, PSNS contraction of detrusor muscle, & relaxation of external urinary sphincter; nerves involved: hypogastric, pelvic, & pudendal; requires intact spinal cord & pudendal nerve(sacral micturition center)
What is glomerular filtration rate (GFR)?
volume of filtrate formed per minute by both kidneys; blood in glomerular capillaries and filtrate in Bowman's capsules has 2 main forces: hydrostatic pressure & colloid osmotic pressure - hydrostatic pressure: increased blood pressure in glomerulus = increased hydrostatic pressure & increases GFR by forcing more blood to be filtered; filtrate in Bowman's capsule increases, hydrostatic pressure increases causing GFR in Bowman's capsule to DECREASE(high hydrostatic pressure in glomerulus = incr. GFR & high hydrostatic pressure in Bowman's capsule = decr. GFR) - colloid osmotic pressure: pressure exerted by colloids in glomerulus(Albumin) that tries to hold water back; increased osmotic pressure in glomerulus opposes filtration; there should be no proteins in filtrate/Bowman's capsule unless kidney is diseased therefore osmotic pressure is higher in glomerulus & inconsequential in Bowman's; - protein presence in urine increases osmolarity, holds more water in filtrate, & increases urine volume; less protein(albumin) circulating = blood osmotic pressure falls, water isn't pulled into capillaries & hydrostatic pressure pushes it out into tissues producing systemic edema
Define urochrome
yellow pigment of urine
Describe the characteristics of urine
• Pale yellow-- dilute • Dark yellow-- concentrated, solutes • Normal composition: 95% water, Urea, Uric acid, Trace aa, Electrolytes - 1-2L daily; 500mL(min) urine vol. to rid body of wastes ○ pH 4-8, varies depending upon diet
