Hormones of the kidney, micturition

Learning objectives:
1. atrial naturietic hormone
2. overview of fluid/solute balance, role of kidney
3. diuretics
4. micturition
Atrial Natriuretic Peptide
1. synthesised and released from cardiac atrial cells
2. released in response to atrial stretch (increased ECV)
3. Atrial = heart. Natriuretic = put sodium into urine
4. ANP released in response to:
  1. low Na+ resabsorption
  2. inhibition of aldosterone production
  3. reduction of renin release
  4. vasodilation of afferent arteriole = increased GFR
  5. Results in INCREASED SODIUM EXCRETION into urine, REDUCTION OF ECV
    1. (water moves from blood into urine as Na+ is excreted into it- so reduced blood ECV as water leaves)
Overview of sodium regulation
1. Na+ vital for regulation of ECF volume
2. occurs via changes in ECV - renin - angiotensin system and aldosterone
3. ANGIOTENSIN 2 - increases Na+/H+ exchange in proximal tubule - increases Na reabsorption and collecting duct
4. ALDOSTERONE - promotes Na+ reabsorption in distal tubule and collecting duct
5. ANP - reduces Na+ reabsorption in collecting duct - also acts on distal tubule. Also increases GFR
Sodium regulation hormones
1. Angiotensin 2 - enhancement of Na+ + H+ exchange in the proximal tubule. Reduction of GFR
2. ANP - increases GFR
3. Aldosterone - increased Na+ reabsorption in distal tubule and collecting duct
4. ANP - decreased Na+ reabsorption in distal tubule and collecting duct
Potassium regulation
1. Low dietary K+ = K+ secreted into capillaries
  1. 67% secreted -proximal tubule
    1. 20% secreted - ascending loh
      1. Distal tubule and collecting duct - variable secretion/reabsorption according to dietary intake
2. ALDOSTERONE - promotes K+ secretion in collecting duct - hormonal effect
3. normal /high levels of K+ intake = 5-30% K+ secreted into urine - collecting duct
Calcium reabsorption
1. 67% reabsorbed - proximal tubule. 20% reabsorbed = acending limb. 8% reabsorption - distal tubule
  1. Distal tubule = secondary active transport of Ca2+ using Ca2+ATPase antiport with Sk+
    1. Ca2+ moved from apical membrane of collecting duct into capillaries
2. Ca2+ATPase uses active form of Vitamin D = 2,25 dihydroxycholecalciferol)
Dieuretics
1. Proximal tubule = osmotic direutics = manitol, glucose = CARBONIC ANHYDRASE inhibitors
  1. Distal tubule - THIAZIDE diuretics - block Na+ transporter in distal tubule
  2. Collecting duct = K+ sparing diuretics - aldosterone antagonist, lower reabsorption of Na+ and secretion of K+ from principal cells = SPIRONOLACTONE
    1. Na+ channel blockers - lower Na+ entry across apical membrane e.g. AMILORIDE
2. Loop diuretics = inhibit Na+ reuptake in ascending limb - decreases solute of medulla - lower osmolarity of urine e.g. FUROSEMIDE
  Annotations:
  - thick ascending limb = TAL Furosemide - water diuretic pill
Renal physiology - main functions
1. Regulation of water and salt balance
  1. excrete or conserve H2O, Na+ and K+
2. Removal of metabolic waste products
  1. urea/uric acid, excess solutes
3. Removal of foreign substances
  1. drugs or metabolites
4. Regulation of pH
  1. i.e. HCO3- and H+
Other important renal functions
1. Hormone production
  1. RENIN - regulates angiotensin 2
  2. ERYTHROPROTEIN - stimulation of erythrocyte production
  3. CALCITROL (vitamin D) - calcium regulation
2. Production of glucose from substances other than CHO's = glucneogenesis
Erythroprotein, EPO
1. Hormone produced in the kidney
2. stimulates red blood cell production in bone marrow
3. Also involved in:
  1. wound healing
  2. neuronal protection e.g. after stoke
  3. angiogenesis
4. (used by endurance cyclists)
Micturition
1. Excreting urine
2. urine composition leaving bladder remains same leaving renal pelvis EXCEPT HORSE
  1. Transported along ureters -> bladder -> peristalic contractions of SMOOTH muscle
3. Tonic S activity = bladder relaxed, internal sphincter closed
  1. Tonic SOMATIC activity = external sphincter closed
4. Bladder full = increased pressure = increased activity in sensory neurone
  1. reflex emptying = increased parasympathetic -> bladder contractions -> decreased somatic activity to external sphincter
5. Parasympathetic and Somatic = S2-S4
  1. PS =smooth muscle wall of bladder
    1. somatic = outer urethral sphincter -> higher brain centres
6. Sympathetic = L1-L2
  1. S= inner urethral sphincter
KEY POINTS
1. 1. ADH (vasopressin) - regulation of ECF osmolarity
2. 2. ANP - up regulation of sodium excretion
3. 4. Overview of mechanisms for regulating body fluid
4. 3. Renin - angiotensin - regualtion of fluid volume
5. 5. Role of sodium in regulating body fluid volume
6. 6. Main characteristics of classes of diuretics
7. 7. Mechanisms of the control of micturition

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Hormones of the kidney, micturition

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	Created by Florence Papworth over 7 years ago