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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