Genitourinary System

Functions of the Kidney

• Excretion –

• Removal from the body of the waste products of metabolic pathways

• Osmoregulation –

• Is the control of the water balance of the blood, tissue, or cytoplasm of a living organism.

Kidney Structure

Nephron – the functional unit of the kidney

Ultrafiltration in the glomerulus

Ultrafiltration specifics

• Production of filtrate from blood

• 20% of blood plasma passes through walls of glomerulus; higher than any other cap. bed.

• Why?

• 1. bp is very high due to diameter differences of the efferent and afferent arterioles

• 2. glomerular capillaries are fenestrated

• Pores large : all substances can pass through

• But basement membrane acts as a filter

• The Urinary System• Plasma, Filtrate, and Urine ComparisonsTable. Average

Composition of Blood Plasma, Glomerular Filtrate, and Urine 

•   Blood Plasma Glomerular Filtrate Urine• Substance  (total amount) (amount per day) (amount per day)• Water 3 L 180 L 1-2 L

• Urea 4.8 g 53 g 25.0 g• Chloride 10.7 g 639 g 6.3 g• Sodium 9.7 g 580 g 4.6 g• Potassium 0.5 g 30 g 2.0 g• Creatinine 0.03 g 1.6 g 1.6 g • Uric acid 0.15 g 8.5 g 0.8 g• Protein 200.0 g 2.0 g 0.1 g• Bicarbonate 4.6 g 275.0 g 0.0 g • Glucose 3.0 g 180.0 g 0.0 g

Selective Reabsorption in the PCT

• Filtrate at this point contains waste and substances the body needs

• PCT consists of a single layer of cuboidal epithelial cells with microvilli = increased SA

PCT cont’d• IMPs all cell over surfaces for AT

• Mitochondria in large numbers producing ATP to drive AT

What’s Re-absorbed?

• 100% of glucose

• 80% of mineral ions (including Na)

• AT of solutes makes cell hypertonic

which cause water to follow.

• 80% of water is re-absorbed; 20% of water remains in the renal tubule and heads towards the LOH

Role of the LOH• Descending and acsending limbs differ in

permeability.

• Major role?• To create an area of high solute conc. in the

medulla (hypertonic interstitial fluid)

Osmoregulation in the CD• Water conc. in blood too low =

• ADH release from pituitary gland in brain =

• Increase in aquaporin production in CD cells

• CD passes through zone of high solute conc created earlier by the LOH

• Hypertonic urine is produced

• If water conc in blood is too high (hypotonic blood) =

• ADH is not secreted =

• Aquaporins are broken down =

• CD becomes less permeable to water

• Dilute, hypotonic urine is produced