Human Anatomy and Physiology

Renal function

Functions Regulation of water and electrolytes Maintain plasma volume Acid-base balance Eliminate metabolic wastes Hormone secretion

Kidney anatomy

Anatomy Functional unit is the nephron Components

Glomerulus Proximal tubule Loop of Henle Distal tubule Common Collecting duct

Nephron anatomy

•Nephron types• Juxtamedullary• Cortical

•Peritubular capillaries• Vasa recta

Renal processes Filtration

Water and solutes Protein (Not filtered)

Blood cells (No filtered)

Filtration based onsize and charge

Glomerular Filtration

Size barrier

Size barrier

Glomerular Filtration

Renal processes Reabsorption

99% of water & solutes Passive - water Active - sodium Proximal tubule (65%)

Reabsorption at cell level

Sodium moves passively across the apical membrane and actively into the plasma

Renal processes

Secretion Water and solutes (1%)

Secretion at cell level

Potassium is transported actively into the cell and passively into the tubular lumen

Urine formation

• Volume of fluid into kidneys per day 1,640 L• Volume filtered into the glomeruli per day 180 L• Volume of fluid excreted/day ~ 1.5L• Hence 180 - 178.5 L = amount reabsorbed (~99%)

Blood supply GFR will depend on blood supply Blood pressure drop in the glomeruli

Glomerular filtration

Total amount of filtrate formed per minute Influenced by:

Filtration surface area Filtration membrane permeability Net filtration pressure

Glomerular filtration Measured by a marker Characteristics

Freely filtered by the glomerulus Not reabsorbed or secreted Must not alter GFR

Glomerular filtration Inulin Renal clearance GFR x P(In) = U(In) x V

Regulation of GFR 3 mechanisms

Renal autoregulation Neural control Renin-angiotension system

(JG apparatus)

JG apparatus

Regulation of GFR

Countercurrent multiplication

65%

5%

14%

15%

Urea

Urine concentration

Vasopressin: antidiuretic hormone (ADH) Posterior pituitary,

increases the number of aquaporin water channels in the CD

Vasa recta Osmotic gradient

not washed out Blood supply

sluggish Medulla blood

flow is 2% of that to the kidneys

Urine concentration

The urine to plasma osmolality ratio [U]/[P] Plasma osmolality from 285 - 295 mOsm Example: [urine] = 1,200 mOsm,

ratio = 4.0

Urine dilution

Urine dilution

Atrial natriuretic peptide (ANP) Atrium of the heart, decreases Na+ and water reabsorption

ADH/ANP

ADH/ANP

Diuretics

Action of Diuretics- Alcohol: inhibits ADH- Caffeine: promotes renal vasodilation, increasing GFR- Drugs: any that inhibit sodium reabsorption

Micturition

Mechanism of action Contraction of detrusor muscle Relaxation of sphincters