Renal/reproduction systems

• Urinary system organs


  • Kidneys
  • Ureters
  • Urinary bladder
  • Urethra
• Urinary bladder


  • Smooth, collapsible, muscular sac
  • Temporarily stores urine
  • Full: ~ 5 inches long and holds; 500 mL
  • Can hold 2X
  • Trigone
  • Three openings: Two from the ureters, One to the urethra
• Urinary bladder wall


  • Detrusor muscle - Three layers of smooth muscle
  • Mucosa: transitional epithelium
  • Walls are thick and folded in an empty bladder
• Urethral sphincters


  • Internal urethral sphincter: Involuntary, Bladder-urethra junction
  • External urethral sphincter: Voluntary muscle, surrounding urethra
• Kidneys


  • Right kidney is slightly lower than the left
  • Renal hilum- medial indentation,ureter,renal blood vessels,and nerves
  • Adrenal gland
• 1/4 cardiac output (1200ml) passes through the kidneys each minute
• Kidney structures


  • Renal cortex
  • Renal medulla: renal columns, renal pyramids, Papilla
  • Renal pelvis
• Nephrons


  • Structural and functional units of kidney
  • 1 million per kidney
  • Two main parts: renal corpuscle (glomerulus, glomerular capsule), renal tubule (proximal convoluted tubule, nephron loop, distal convoluted tubule)
• Types of nephrons


  • Cortical nephrons
  • Juxtamedullary nephrons
• Nephron-associated capillary beds


  • Glomerulus
  • Peritubular capillary bed
  • Vasa recta (only juxtamedullary nephrons)
• Glomerulus


  • Knot of capillaries
  • Within a glomerular (Bowman's) capsule
  • Fed and drained by arterioles: Afferent arteriole, Efferent arteriole
  • Pressure → fluid and small solutes into the glomerular capsule as Filtrate
  • Podocytes
  • 125ml/min (180 liter/day) Glomerular filtration rate (GFR)
• Tubular reabsorption


  1. From tubules into peritubular capillaries

  2. Reabsorb useful substances: Water, Glucose, Amino acids, Ions

  3. Most in proximal convoluted tubule

  4. Some is passive, most is active
• Tubular secretion


  1. Movement of materials from the peritubular capillaries into the renal tubules (opposite of reabsorption)

  2. Substances secreted: Potassium, Hydrogen ions, Choline, Creatinine, Penicillin

  3. Materials left in the renal tubule move toward the ureter
• Sites of filtration, reabsorption, and secretion in a kidney
• Excretion rate


  Amount of substance excreted = amount filtered + amount secreted – amount reabsorbed
• Urine

  • In 24 hours, about 1.0 to 1.8 liters produced
  • 95% water and 5% solutes
  • Clear
  • Cloudy may indicate urinary tract infection
  • Pale to deep yellow from urochrome
  • Pigment from hemoglobin breakdown (from bilirubin); more concentrated urine → deeper color
  • Abnormal color (pink, brown, smoky) from food ingestion, bile pigments, blood, drugs
• Urine odor

  • Slightly aromatic when fresh
  • Develops ammonia odor upon standing as bacteria metabolize solutes
• Urine pH


  • Slightly acidic (~pH 6, with range of 4.5 to 8.0)
  • Acidic diet (protein, whole wheat) → pH
  • Alkaline diet (vegetarian), prolonged vomiting, or urinary tract infections → pH
• Urine composition

  • Nitrogenous wastes: Urea, Uric acid, Creatinine
  • Electrolytes: Na+, K+, PO43-, SO43-, Ca2+, Mg2+, HCO3-
• Renal calculi (kidney stones)

  • Crystallized calcium, magnesium, or uric acid salts
  • Concentration of minerals=rock-->stone
  • Large stones block ureter-> pressure & pain
  • Treatment-shock wave lithotripsy-non-evasive
• Substances not normally found in urine

  • Glucose
  • Blood proteins
  • Amino acids
  • Red blood cells
  • Hemoglobin
  • White blood cells
  • Bile
• Urine flow

  1. Renal tubules->renal pelvis-> ureter->bladder

  2. Both sphincter muscles must open to allow voiding
• Water balance

  • Dilute urine (large volume) is produced if water intake is excessive
  • Concentrated (lower volume) is produced if large amounts of water are lost(sweat/dehydration)
  • Proper concentrations of various electrolytes must be present
• Osmolality

  • Number of solute particles in 1 kg of H2O
  • Reflects ability to cause osmosis
  • Kidneys maintain osmolality of plasma at 300 mosm
• Countercurrent mechanism


  1. Fluid flows in opposite directions in two adjacent segments of same tube

  2. Countercurrent multiplier – interaction of filtrate flow in descending/ascending nephron loop

  3. Counter current exchanger – Blood flow in ascending/descending limbs of vasa recta
• Countercurrent multiplier in nephron loop

  • Osmotic gradient established
  • Descending Limb: Permeable to water, No transport of Na+, Cl-, or K+
  • Ascending Limb: Impermeable to water, Transport of Na+, Cl-, and K+
• Roles of kidneys in maintaining blood composition

  • Excretion of wastes
  • Maintaining water balance of the blood
  • Maintaining electrolyte balance of the blood
  • Ensuring proper blood pH
• Water reabsorption


  1. Driven by movement of Na+ and other solutes

  2. Osmotic gradient for water

  3. Aquaporins: Always present in PCT, Inserted in collecting ducts only if Antidiuretic hormone (ADH) present
• Antidiuretic hormone (ADH)


  • Diuresis → process urine production
  • Diuretic → promotes urine production
  • Antidiuretic → inhibits urine formation
  • Reabsorption of water
  • Released from posterior pituitary gland from neurosecretory cells originating in hypothalamus
  • Primary stimulus for release is osmolality (osmoreceptors) of plasma
• Blood pressure and glomerular filtration rate (GFR)

  • BP predicted to GFR
  • GFR relatively constant with increases in BP due to intrinsic regulation until BP reaches 180 mm Hg
  • Decreases in blood pressure to less than 80 mm Hg: GFR → water filtered → water excretion
  • Increases in blood pressure to more than 180 mm Hg: GFR → water filtered → water excretion
• Sodium reabsorption in distal convoluted tubule (DCT) and collecting duct


  • Reabsorption hormonally regulated
  • Antidiuretic hormone (ADH) – Water
  • Aldosterone – Na+ (therefore water)
  • Atrial natriuretic peptide (ANP) – Na+
• Aldosterone

  • Steroid hormone
  • Secreted from adrenal cortex
  • Na+ reabsorption
  • Water
  • Na+ reabsorption → osmolarity → BP
  • Aldosterone stimulated by Angiotensin II
• Renin-angiotensin-aldosterone mechanism


  1. BP → Renin release from kidneys → Cleaves angiotensinogen → Angiotensin

  2. Angiotensin + Angiotensin converting enzyme (ACE) → Angiotensin II

  3. Angiotensin II→ Vasoconstriction → increase mean arterial pressure

  4. Angiotensin II→ Aldosterone → Na + and H20 reabsoprtion → MAP
• Atrial natriuretic peptide (ANP)


  • A peptide hormone
  • Released from atrium in response to stretch of wall
  • Increases sodium excretion
  • Antagonist of aldosterone
• Solute reabsorption, osmotic gradient, and water reabsorption

  • Solute reabsorption → osmotic gradient → water reabsorption
  • Aldosterone → sodium (and water) transport
  • Angiotensin II → Vasoconstriction, aldosterone, ADH secretion, and thirst
  • Atrial Natriuretic Peptide (ANP) → aldosterone and ADH secretion
• Acid-base homeostasis


  • Three lines of defense: Buffering of H ions (almost instant), Respiratory compensation (minutes), Renal compensation (hours to days)
  • Three major chemical buffer systems: Bicarbonate, Phosphate, Protein
• Blood buffers


  • Bind to H+ when pH drops
  • Release H+ when pH rises
  • Example: Hemoglobin (Bohr effect)
• Respiratory compensation


  1. Regulates pH by varying ventilation

  2. ventilation → CO2 → H+/ pH

  3. ventilation → CO2 → H+/ pH
• Renal compensation


  1. Increases H+ secretion

  2. Increases HCO3- reabsorption and synthesis

  3. No direct effect on CO2
• Metabolic acidosis


  • Decrease pH through something other than carbon dioxide (usually low free bicarbonate)
  • Causes: High protein diet, High fat diet, Heavy exercise, Severe diarrhea (loss of bicarbonate), Renal dysfunction