1. Total body water (42L)
   1. Intracellular (30L)
   2. ECFV (12L)
      1. Interstitial
      2. Plasma
      3. Transcellular
   3. Affecting factors
      1. Osmolarity/Osmolality
      2. Starling's principle of fluid exchange
2. Imbalance of body fluid
   1. Dehydration
      1. ↓ Water intake
      2. ↑ Water loss
   2. Excessive fluid
      1. Congestive heart failure
      2. Huge ↑ in ECFV from sodium and water retention
3. Control of body fluid
   1. Organs involved
      1. Heart
      2. Brain
      3. Adrenal Gland
      4. Kidney
   2. Is the control of sodium and water balance
      1. based on -ve feedback
   3. osmoregulation
      1. Control of body water
      2. Based on control of the osmolality and of the ECFV
      3. Changes in body fluid osmolality - shift of water between IC and ECF
      4. ↑ Water intake → ↓ plasma osmolarity → ↓ ADH secretion → ↓ Urine ↑ osmolarity
      5. and Vice versa
      6. ADH increases water permeability in the collecting duct
   4. volume regulation
      1. Control of body sodium
         1. Sodium is the major electrolyte of the ECFV
      2. [Total body Na+] = Intake - eliminiation
      3. Change in sodium balance → change in ECFV →
         1. Blood Volume
         2. Interstitial volume
      4. Hormone system
         1. RASS
            1. Sodium retaining system
            2. The Renin-angiotensin-aldosterone system
            3. ↑ Sodium reabsorption
         2. ANP
            1. Sodium eliminating pathways
            2. Cardiac natriuretic peptides
            3. ↓ Sodium reabsorption
      5. ↑ Sodium intake → ↑ ECFV → ↓ RASS and ↑ ANP → ↑ Sodium excretion
4. Urine Formation
   1. 1. Glomerular Filtration
      1. Hydrostatic pressure forces fluids and solutes through the glomerular capillary membrane
      2. Small molecules pass readily- large ones (proteins and cells) cannot pass
      3. This leads to a plasma ultra filtrate in the Bowman’s capsule
      4. Glomerular filtration rate (GFR)
         1. Is the amount of filtrate kidneys produce each minute
         2. Is reduced in renal failure
         3. Plasma creatinine can be used as an index of GFR
   2. 2. Tubular Reabsorption
      1. Many substances are then reabsorbed from the tubular lumen into the peritubular capillaries
      2. Accompanied through:
         1. diffusion,
         2. osmosis, and
         3. carrier-mediated transport
      3. Maximum transport rate (Tm)
         1. determines renal threshold for reabsorption of substances in tubular fluid
         2. When amount in tubule is over Tm value, excess excreted in urine
      4. Water and glucose are reabsorbed
   3. 3. Tubular Secretion
      1. E.g. hydrogen ions, potassium, creatine, drugs, toxins etc.
   4. 4. Excretion of water and solutes in the urine
      1. Amount excreted = Amount filtered – reabsorbed + secreted
5. Renal nephron
   1. consists of special blood vessels and elaborate tubules
      1. Microscopic structures
      2. 1.25 million per kidney
      3. Where urine production begins
   2. Major structures
      1. Blood vessels
      2. The glomerulus
      3. Bowman capsule
      4. The renal tubule
6. Renal function
   1. Regulation of salt and water balance
   2. Control of blood pressure
   3. Regulation of electrolytes
   4. Removal of metabolic waste from the blood
   5. Removal of foreign chemicals in the blood
      1. e.g. drugs
   6. Erythropoietin
      1. Regulation of RBC production
7. The kidneys and the urinary tract
   1. Kidney
      1. Central function: urine production
   2. Ureter
      1. Transports urine towards the urinary bladder
   3. Urinary bladder
      1. Temporarily stores urine prior to elimination
   4. Urethra (The flower is singing!!!)
      1. Conducts urine to exterior