Urinary System 2

High GFR, Rapid flow of filtrate in renal tubules, Sensed by macula densa, Paracrine Secretion, Constriction of afferent arteriole, Reduced GFR

• Sympathetic nervous system and adrenal epinephrine constrict afferent arterioles during exercise and when blood pressure drops.
• Reduces GFR and urine output
• Redirects blood to heart, brain, skeletal muscles
• In extreme athlete, it can lead to hypoxia in the kidneys, and proteinuria and hematuria

• Renin secreted by juxtaglomerular cells when blood pressure drops (systemic or local), renal artery blockage occurs, or the sympathetic nervous system is activated
• Renin converts angiotensinogen to angiotensin 1
• Lungs and kidneys convert angiotensin I to angiotensin II (with angiotensin-converting enzyme)
• Angiotensin affects constriction

• Promotes vasoconstriction throughout the body
• Except: lowers blood pressure in peritubular capillaries to enhance reabsorption of NaCl and water
• Stimulates aldosterone and ADH secretion

• Proximal convoluted tubule reabsorbs about 65% of glomerular filtrate
• Reabsorbs almost all glucose, amino acids, electrolytes through special channels and ion pumps
• Water is reabsorbed through aquaporins
• As water leaves, it pulls urea and electrolytes with it
• 40-60% of urea reabsorbed, creatinine remains in filtrate
• Most reabsorbed water and solutes diffuse into peritubular capillaries

• A limited number of solutes can be reabsorbed in tubules
• Limited number of transport proteins
• Blood glucose over 220 mg/dl exceeds maximum transport, so glucose appears in urine

• Renal tube extracts chemicals from capillary blood and secretes them into tubular fluid
• Necessary because filtration doesn't remove everything from blood (and reabsorption adds some things back to blood)

• Urea, uric acid, bile acids, ammonia, catecholamines, prostaglandins, some creatinine
• Clears pollutants, morphine, penicillin, aspirin, other drugs

Secretion of H+ and bicarbonate regulates pH of body fluids

• Loop of Henle generates salt gradient that helps collecting duct concentrate urine and conserve water
• Thick segment reabsorbs about 25% of the sodium, potassium, and chloride that we in glomerular filtrate
• Impermeable to water
• Thin segment reabsorbs about 15% of water that was in glomerular filtrate

• Fluid arriving in distal convoluting tubule still contains 20% of water and 7% of salts from filtrate
• Amounts of water/salt reabsorbed regulated by hormones
• Aldosterone, ADH, parathyroid hormone, atrial natriuretic peptide

• Aldosterone secreted when blood Na+ concentration falls or blood pressure drops
• Stimulates reabsorption of NaCl and water
• Reduces urine volume

• ADH secretion during dehydration
• Stimualtes reabsorption of water
• Reduces urine volume

• Parathyroid hormone secreted when blood calcium levels are low
• Acts on thick segment and DCT to increase calcium reabsorption

• Secreted by atrial myocardium when blood pressure is high
• Dilates afferent arteriole and constricts efferent arteriole to increase GFR
• Inhibits renin, aldosterone, and ADH secretion
• Inhibits NaCl reabsorption

• PCT reabsorbs 65% of filtrate and returns it to peritubular capillaries
• Nephron loop reabsorbs 25% of filtrate
• DCT reabsorbs NaCl and water
• Tubule extract (secrete) drugs, wastes from peritubular capillaries into tubular fluid
• Collecting duct conserves water

• Collecting duct (CD) reabsorbs water and concentrates urine up to 4 times
• Medullary part of CD is more permeable to water than NaCl
• Medulla fluid is very salty, so water leaves

• Pumping ions out of the thick segment of the loop increases osmolarity of medulla
• Increased osmolarity of medulla causes lots of water conservation

• Need blood supply to medulla, but don't want blood to carry away salt
• Vasa recta exchanges salt and water to maintain osmolarity of medulla

• Urine has a low concentration of solutes
• Typically from water diuresis (drinking lots of water)

• Urine has high concentration of solutes
• Dehydration
• High blood osmolarity causes ADH release, more water is reabsorbed, urine more concentrated

• Provides a very good "snapshot" of the physiological state of the body
• Examination of physical and chemical properties of urine
• Appearance: clear to deep amber; yellow color due to breakdown of hemoglobin. Cloudiness, pus or blood suggests some kind of infection or trauma
• Odor: due to breakdown of urea. Abnormal odor can indicate diabetes mellitus, UTI, or other condition
• Specific gravity: reflects solute concentration
• Osmolarity: reflects hydration state of body
• pH: reflects pH regulation in tissues
• Chemical composition: 95% water, 5% solutes

Typically average adult produces 1-2 L/day

• Excess of 2 L/day
• Symptom of diabetes

• Less than 500 ml/day
• Can result from kidney disease, dehydration, prostate enlargement

• 0-100 ml/day
• Body can't get rid of waste

• Kidneys can't maintain homeostasis because of nephron destruction
• When >75% of nephrons are lost
• Hemodialysis: procedure for clearing wastes from blood

Any metabolic disorder resulting in chronic polyuria

• Type 1, type 2, and gestational
• High concentration of glucose in blood; opposes the reabsorption of water; glycosuria

ADH hyposecretion, so not enough water is reabsorbed in collecting duct; risk of dehydration

• Any chemical that increases urine volume
• Some increase GFR
• Caffein dilates afferent arteriole
• Some reduce tubular reabsorption of water
• Alcohol inhibits ADH secretion
• Commonly used to treat hypertension

• Muscular tubes about 25 cm long
• Enter on posterior surface of bladder
• Valve prevents urine from going back into ureter when bladder contracts

Connective tissue connecting ureter to surround tissue

Smooth muscle that contracts in peristaltic waves

Transitional epithelium that can contract and expand

Muscular sac on the floor of pelvic cavity, posterior to pubic symphysis

Three layers of smooth muscle

Wrinkles in the mucosa of a relaxed bladder

Triangle formed by urethra and ureters

• Cystitis: infection of urinary bladder
• Especially common in females due to short urethra
• Frequently triggered by sexual intercourse
• Can spread up ureter
• Pyelitis: infection of renal pelvis
• Pyelonephritis: infection that reaches nephrons

• Kidney stones
• Hard granule of calcium phosphate, calcium oxalate, uric acid, or struvite
• Form in renal pelvis
• Large stones can block renal pelvis or ureter, which causes pressure buildup in kidney and destroys nephrons
• Causes: hypercalcemia, dehydration, pH imbalances, frequent UTIs, enlarged prostate

• 3-4 cm long
• Bound to anterior wall of vagina
• External urethral orifice between vaginal orifice and clitoris
• Internal urethral sphincter: detrusor muscle thickening that is involuntarily controlled
• External urethral sphincter: where urethra passes through pelvis floor, under voluntary control

• Approximately 18 cm long
• Prostate urethra passes through prostate
• Membranous urethra passes through floor of pelvic cavity
• Spongy (penile) urethra passes through penis
• Same two sphincters as female

• As bladder fills, detrusor muscles relax, urethral sphincters closed
• Urination occurs when bladder contracts and both sphincters open
• Micturition: act of urinating
• Micturition Reflex: spinal reflex that partly controls urination