1. Water in the Body

• Water contributes 55-60% to the body weight
• $\frac{2}{3}$ is intracellular, $\frac{1}{3}$ is extracellular
• Conc. of substances in Plasma and Interstitial Fluid are about the same, except for proteins
  • conc. of protein is higher in Plasma than Interstitial Fluid
• The exchange of substances in Plasma(blood) and cells is through the Interstitial Fluid
• Water is gained by :
  • Oxidation of organic material
  • Ingestion via liquids or food
• Water is lost through:
  • Skin, lungs, kidneys, GI system
  • Menstrual and bleeding

2. Kidney

• The human kidneys are two bean-shaped organs, located against the dorsal body wall on either side of the backbone

Function

• Homeostasis - the kidneys regulate water(BP), Inorganic Ions(Electrolytes) and Acid Balance(pH)
• Excretion - the removal of metabolic waste and foreign chemicals
  • Including Urea, Creatine and etc.
• Metabolism - Gluconeogenesis, Glycogenolysis and Calcitriol Synthesis(involved in $Ca^{2+}$ balance, Calcitriol )
• Endocrine Function and Enzyme Production
  • Erythropoietin - control of Erythrocyte production
  • Renin - control of formation and secretion of Angiotensin which controls BP and $Na^+$ balance

Structure

• Each kidney is supplied with blood from Renal Artery and is drained by Renal Vein
• Urine passes out of the kidney via the Ureter to the Bladder
• From a longitudinal section, the regions of the kidney is divided as:
  • A surrounding tough Capsule
  • Outer region - Cortex
  • Inner region - Medulla
  • Centre - Pelvis - leading to Ureter

3. Nephron

• Nephron is the functional unit of the kidney
• Mainly two types:
  • Juxtamedullary Nephrons
  • Cortical Nephrons
• Responsible for Urine Formation and involved in the following processes:
  • Ultrafiltration of blood
  • Selective Tubular Reabsorption of filtered materials
  • Tubular Secretion

Functional Compartments

• Renal Corpuscle
  • Filters plasma, creates Ultrafiltrates
• Proximal Convoluted Tubule, PCT
  • in both Nephron type
  • Bulk reabsorption of water and solutes, secretion of solutes
• Loop of Henle and Vasa Recta
  • of the Juxtamedullary Nephron
  • Generates osmotic gradient in renal medulla for water reabsorption
• Peritubular Capillaries
  • accompanying the rest of Juxtamedullary Nephron and Cortical Nephrons
  • Involved in reabsorption and secretion of substances
• Distal Convoluted Tubule, DCT
  • Fine tuning of reabsorption of water and urea under physiological control
• Collecting Duct
  • Collect urine and send to Pelvis

Renal Corpuscle

Glomerular Ultrafiltration

• Ultrafiltration of the blood takes place at the Glomerulus producing a fluid that enters the cavity of Bowman’s Capsule
  • Renal Corpuscle Filtrate
• The Afferent Arteriole branches to form a network of capillaries - Glomerulus
  • These reunite to form Efferent Arteriole
  • Diameter: Afferent > Efferent
    • Generates a pressure difference
• The pressure in Glomerulus is higher than that in Bowman’s Capsule
  • the pressure difference pushes fluid out of the blood
• Filtration through 3 layers:
  • Capillary Endothelium
    • One-cell thick, resting on Basal Lamina
  • Basal Lamina (Basement Membrane)
  • Layer of Podocytes
• From the blood vessels, plasma filtrate is passed through Fenestrae on Endothelium and the Basal Lamina, then through Filtration Slits in the Podocytes before it reaches the Bowman’s space

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• Only small molecules, present in the blood, can pass through layers of filter
• Substance that enters the lumen of the Bowman’s Capsule from the blood include:
• Blood cells and proteins remain in the capillaries

4. Basic Renal Processes

5. Regulation and Filtration