1. The Excretory System: Urine Formation
… eww

2. The Excretory System
Mammals must excrete many different wastes in order to remove toxic substance from the body
The wastes form as a result of the metabolic processes of the body and degeneration of cells (ie. urea, ammonia, CO2, lactic acid, etc.)
Much of the excretory system flows through the kidneys

3. Kidneys
Part of excretory system, controlled by nervous and endocrine system
Weighing ~0.5 kg each, kidneys may hold as much as 25% of the body’s total blood volume at any given time
Involved in the production of urine

4. Kidneys Stabilize internal environment by:
regulating water content (osmoregulation)
eliminating poisonous by-products of biological reactions
regulating ion concentration
Mechanisms of Regulation:
diffusion/osmosis
forced filtration
active transport

5. Nephron
Each kidney contains over 1 million slender tubules called nephrons
The functional units of the kidney

6. Nephron Structure Glomerulus: High-pressure capillary bed
The site of blood filtration
Bowman’s Capsule:
Funnel-like structure
‘Beginning’ of the nephron
Each nephron has its own independent blood supply (renal arterioles and veins)

7. Nephron Structure Components not entering capsule: Blood proteins
Blood Cells
Platelets

8. Nephron Structure Proximal Tubule:
Re-absorption of molecules important to the blood
Loop of Henle:
Concentration of urine (solutes to be excreted)

9. Nephron Structure Distal Tubule:
Final re-absorption and secretion of molecules
Collecting Duct
Collection of urine from multiple nephrons
Joins with the ureters; ultimately the bladder

10. Urine Formation Accomplished by 3 functions of the nephron:
Forced filtration of blood from the afferent arteriole into the glomerulus, and through Bowman’s capsule under high pressure
proteins, blood cells and platelets are too large to pass through & stay in the blood
sodium chloride, glucose, amino acids, ions enter the nephron

11. Urine Formation
Re-absorption of most fluids and solutes from the filtrate back into the blood
for every 120 mL of fluids filtered, only 1 mL becomes urine
many solutes are removed from the nephron into the capillary beds surrounding the convoluted tubules
passive transport moves Na+, Cl- and HCO3
active transport moves glucose and amino acids
an osmotic gradient is created by the solutes in the capillary bed, drawing water out of the nephron (in all tubules but the ascending Loop of Henle)

12. Urine Formation
Secretion moves wastes from blood into the distal tubule of the nephron
Urea, uric acid, ammonia, excess ions, minerals, drugs, etc. moved by active transport

13. How it all works:

14. How it all works:
YouTube Link:

15. Lab Exercise Comparing Solutes in the Plasma, Nephron & Urine
Activity: p.363