Unit 3 - Chapter 38 structure and function of renal / urologic system

Question 1

Kidney main function

Answer 1

• maintain fluid, electrolyte, acid-base, and blood pressure balance
• excrete wastes
• secrete hormone renin (when low bp => liver (angiotensinogen) => both react to form angiotensin I => ACE (from lungs) convert angiotensin I to II => angiotensin II [acts on blood vessels stimulating vasoconstriction] stimulates adrenal gland to release aldosterone => aldosterone acts on kidneys to stimulate reabsorption of salt and H2O) and erythropoietin (Lack of O2 (hypoxia) is a stimulus for the synthesis of erythropoietin (Epo), primarily in the kidneys // red blood cell production
• activate vitamin D (It is a fat-soluble vitamin that has long been known to help the body absorb and retain calcium and phosphorus; both are critical for building bone) // vitamin D3 (1,25-OH2D3) => calcium absorption in gut

Question 1

Kidney main function

Answer 1

• maintain fluid, electrolyte, acid-base, and blood pressure balance
• excrete wastes
• secrete hormone renin (when low bp => liver (angiotensinogen) => both react to form angiotensin I => ACE (from lungs) convert angiotensin I to II => angiotensin II [acts on blood vessels stimulating vasoconstriction] stimulates adrenal gland to release aldosterone => aldosterone acts on kidneys to stimulate reabsorption of salt and H2O) and erythropoietin (Lack of O2 (hypoxia) is a stimulus for the synthesis of erythropoietin (Epo), primarily in the kidneys // red blood cell production
• activate vitamin D (It is a fat-soluble vitamin that has long been known to help the body absorb and retain calcium and phosphorus; both are critical for building bone)

Question 2

Kidney structures

Answer 2

• capsule [outside] w/ outer cortex region (1) that has glomeruli of nephron and inner medulla (2 - triangle regions surrounded by cortex) w/ tubules and collecting ducts that drain into the calyces.
• calyces join to form the renal pelvis (near exist of kidney with vein, artery, and ureter) and are continuous with the upper end of the ureter [small cup-shaped spaces that collect fluid before it moves into the bladder. This is also where extra fluid and waste become urine]

Question 3

Nephron

Answer 3

urine-forming unit of kidney with glomerulus (enters a cluster of tiny blood vessels—the glomerulus. The thin walls of the glomerulus allow smaller molecules, wastes, and fluid—mostly water—to pass into the tubule.) + proximal convoluted tubule + loops of henle + distal convulated tubule + collecting duct

1) Blood enters a glomerulus at high pressure. Much of the fluid part of blood is filtered through small pores in the glomerulus, leaving behind blood cells and most large molecules, such as proteins. The clear, filtered fluid enters Bowman space and passes into the tubule leading from Bowman capsule. Nearly all this fluid (and the electrolytes contained in it) is reabsorbed by the kidney. Only about 1.5 to 2% of the fluid is excreted as urine.

2) proximal convoluted tubule =>
* Na+, K+, Mg++, Ca++, Cl-, HCO3- (bicarbonate), water, glucose, amino acids, protein, vitamins, lactate, urea, uric acid [antioxidiant - small amoun] (active transport -** tubular reasborption**)
* Tubular secretion - Urea (amino acid catabolism, neuron damange), uric acid (gout // catabolism of purines [DNA/RNA]), creatinine (msucle breakdown; high levels of creatinine in blood and low levels in urine indicate kidney disease or another condition that affects kidney function. These include: Autoimmune diseases. Bacterial infection of the kidneys), H+ (acid-base regulation), NH4+ (ammonia // death of neruons, mental retardation) from capillaries => interstital => tubules
* Obligatory water reabsorption (PCT and loop of henle] – since Na+ is reabsorbed, water follows it via osmosis to balance changing osmotic gradient [no work]

3) loop of henle
* ascending limb of loop of henle [impermeable to water] - ion active transport only for Na+, K+, and Cl- => interstital => vasa recta [artery] (network of capillaries) [establishes osmotic gradient that drives water out of descending limb] // as ions leaves then the osmolarity decreases
* descending limb of loop of henle - impermeable to ions; as filtrate descends more water gets reabsorbed on descending side [obligatory water reabsorption] (increasing osmolarity - measure of concentration of filtrate // 300 to 1200[highest]) => water osmose into the interstitial space => vasa recta (vein)
* countercurrent multiplication is this anti-parallel forces or opposite directions (amplifying reabsorption)

====
urea - natural degradation production product of amino acid catabolism (inside liver or peripheral tissues)
* amino acid (2 products) -
1) oxidative deamination => carbon skeleton => “enzymatic pathway” => energy
2) Other product is ammonia from deamination => kidneys/urea cycle [converts it] => urea (toxic in high amounts, must be removed]
3) Nephron uses urea (additional fx) as a solute to drive more water reabsorption in loop of henle
* Urea is moved into interstitial from collecting duct (later discussed) // similar to Na+ or K+, urea increases osmotic pressure in left interstitial space [same interstitial space where ascending loop of henle dump its ions to increase osmotic pressure too] equal urea cycling => drives further h2o reabsorption in descending loop
* this urea does enter back into asecnding loop of henle but ALOT of the urea is excreted from kidneys and fraction used to drive water reabsorption
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3) Distal convoluted tubule
* hormonally regulated (facultative reabsorption) - same with collecting duct
* tubular reabsorption (Na+, Ca++, cl-, HCO3-, h2o
* tubular secretion (H+ (excess acid in blood), K+, NH4+ (amino acid breakdown))
* Aldosterone (a steroid mineralocorticoid)
a. Na+ reabsorption and water follows (facultative; regulated) as well + K+ secreted (eliminiate in urine)
b. if alot of aldosterone then filtrate becomes more concentrated (w/ higher osmolarity 100-300)
* PTH or parathyroid
a. Ca++ reabsorbed (blood clotting, muscle contraction)

4) collecting ducts
* major site of water reabsorption
* facultative reabsorption
* there are K+/CL- symporter that allow leakage of these ions into extracelluar
* intercatalated cells that secrete H+ while reabsorbing HCO3- (type a; hydrogen-ATPase and H+/K+ - ATPase transporters) + once H+ is inside lumen of tubule reacts w/ phosphate (HPO42-) or ammonia (NH3) to make (NH4+/H2PO42-) to prevent ions from reentering system [acidosis]
* There are typbe intercalated cells that have H+/HCO3- channels; net effect is secretion of HCO3- and reabsorption of H+ important in alkalsosis!
* ADH (antidiuretic hormone)
1) low fluid volume then activates this to bring back up blood volume and concentrates urine
2) Aquaporins insert into membrane of collecting ducts (proteins that allow water to move)
* osmolarity 300-1200 as filtrate descends
* l/t minor calyx => major calyx => renal pelvis => ureter => bladder

Question 4

Bonus question - what is reabsorbed in capillaries?

Answer 4

• O2 and co2 (lipid soluble) => simple diffusion
• Na+ and glucose (not lipid soluble => via intracellular clefts, gaps in membrane)

Question 5

Glomerulus

Answer 5

• contains loops of capillaries inside bowman capsulte
• capillary walls (or capillaries suspended inside bowman’s space) has three layers from inner to outermost => endothelium, basement membrane, and epithelium
• Embedded wtih epithelium are these podocytes that interlock to provide filtration slits - an anion charge across filtration membrane restrict filtration of negatively charged molecules such as proteins
• mesangial cells (capillaries bud off this root base) - remove trapped residues and aggregated protein from the basement membrane thus keeping the filter free of debris // supported with matrix

Question 6

Juxtaglomerular cell

Answer 6

• secrete renin
• located around afferent arteriole (surrounding it)
• contigious (similar) to sodium-sensing macula densa cells of distal convoluted tubule

Question 7

bowman capsule

Answer 7

• between visceral (glomerus capillary) <=> capsular space <=> parietal layer (outside)

Question 8

proximal tubule structure

Answer 8

• lined with microvilli to increase surface area and enhance absorption

Question 9

loop of henle strcuture

Answer 9

• hairpin-shaped loops of henle selectively transport solutes and water
• hypertonic state of medulla (above is cortex)

Question 10

Distal tubule importance

Answer 10

adjusts acid-base balance by excreting acid into the urine and forming new bicarbonate ions.

Question 11

Ureters

Answer 11

• extend from renal pelvis to posterior wall of bladder; urine flows through ureters by means of peristaltic contraction of ureteral muscles

Question 12

Bladder

Answer 12

• composed of detrusor (longitudinal and circular, outer – contract to push urine) and trigone muscles (inside triangle region - allow efflux, guard against reflux)

Innervated by branches of
* parasympathetic (contracts the bladder and relaxes the urethra)
* sympathetic (relaxes bladder, contracts proximal urethral sphincter)
* somatic (striated urethral sphincter) pathways - controls genitals and anus + pee via pudendal nerve utilizing Ach
* When urine accumulates to 250-300 cc, mechanoreceptors - respond to stretching of tissue stimulating micturition reflex (urination, requiring coordination of above pathways using higher center brains)

Question 13

Renal blood flow

Answer 13

• 1000-1200 cc/min
• 20-25% of cardiac ouput

Question 14

Glomerular filtration

Answer 14

• favored by capillary hydrostatic pressure AND opposed by oncotic pressure in capillary and hydrostatic pressure in bowman capsulre => net filtration pressure (NFP)
• GFR (rate) is 120 ml/min and 99% filtrate is reabsorbed

Question 15

Proximal convoluted tubule vs distal tubule

Answer 15

• proximal - reabsorbs about 60% to 70% of the filtered sodium and water and 90% of other electrolytes.
• proximal (cont.) - Because most molecules are reabsorbed by active transport, the carrier mechanism can become saturated at the Tm (transport maximum). Molecules not reabsorbed are excreted with the urine.
• distal - reabsorb sodium and water and secrete potassium and hydrogen for the regulation of fluid, electrolyte, and acid-base balance.
• (cont) - The concentration of the final urine is a function of the level of ADH that stimulates the distal tubules and collecting ducts to reabsorb water.
• countercurrent exchange system of the long loops of Henle and their accompanying capillaries establishes a concentration gradient within the renal medulla to facilitate the reabsorption of water from the collecting duct.

Question 16

GFR

Answer 16

• blood flow through glomerular capillaires => constant rate in spite of wide rage of systemic arterial pressures (autoregulation)
• autoregulation of renal blood flow + sympathetic neural regulation of vasconstriction this constant GFR

Question 17

Renin

Answer 17

• enzyme secreted from juxtaglomerular cells in the afferent arteriole
• it causes the generation of angiotensin I (angiotensinogen from liver), which is converted to angiotensin II by the action of ACE (lungs). Angiotensin II is a potent vasoconstrictor and also stimulates release of aldosterone from the adrenal cortex. Thus the renin-angiotensin-aldosterone system is a regulator of renal blood flow and blood pressure.

Question 18

Natruiretic peptides

Answer 18

• myocardium
• antagonize renin-angiotensin-aldosterone system
• promote Na+ and h2o secretion (dilates afferent arteriole [bringing fluid to glomerular capillaries] for diuresis and suppresses Na+ reabsorption in collecting duct and other segments) [exchange K+ for Na+)

Question 19

Aging and nephrons

Answer 19

• decrease in #/size of nephrons
• renal blood flow and glomerular filtration rate decline (90-120 ot 100-130 is good)

Question 20

Tubular transport and reabsorption w/ aging

Answer 20

decrease
* including response to acid-base changes + reabsroption of glucose delayed
* drugs remains longer in plasma => toxic reactions

Question 21

Neurogenic and myogenic changes

Answer 21

bladder may have sx of urgency and frequency or urine retention