CA Biology Standards #9a,f,g1 Kidneys A Case Study in Homeostasis

2 Homeostasis All living things maintain stable internal conditions External conditions are unstable, disorganized, changing Life is a fight against “entropy” All organ systems of the human body contribute to homeostasis How? By keeping blood and tissue constituents and values within a normal range. Why? Because abnormal ranges will lead to death.

3 Urinary System Contributes to homeostasis Keeps proper levels of water, salts, etc. Eliminates wastes

4 Kidneys Key players in urinary system: the kidneys

5 A Closer Peek Inside… Unveiling the homeostatic magic:

6 3 Steps to the Trick:

7 1. Filtration: Separate Waste Two main types of waste in the body: CO 2 (Carbon dioxide)- produced by cells Disposed of by lungs NH 3 (Ammonia)- converted by liver into urea NH 2 CONH 2 Disposed of by kidneys Filtration of urea from the bloodstream occurs in the glomerulus of the kidney WARNING: Contents under pressure! Water, urea, glucose, vitamins, salts forced out of glomerulus into Bowman’s capsule

8 Filtration, cont’d: Glomerulus

9 2. Reabsorption: Recycle Filtration is too efficient: the body needs to reclaim some of the filtrate Recovered filtrate leaves renal tubule, enters capillaries, and leaves through renal vein (and back to the body) 75% of water is returned by osmosis Glucose, sodium, potassium, calcium are returned by active transport

10 Reabsorption, cont’d

11 3. Secretion Other wastes, toxins from blood are secreted into the filtrate Fluid + wastes in tubule = urine Flows into collecting duct Urine is further concentrated in duct because of water leaving by osmosis 99ml/100ml water retained this way

12 Secretion, cont’d

13 Secretion, cont’d Q: Who’s to blame for this osmosis? A: The loop of Henle Cells in the wall of the loop actively transport Cl- from the filtrate to the fluid between loops and collecting duct High [Na+]/Low [H 2 O] outside duct...

14 Discussion: ADH

15 Reinforce Movie: “kidney-G” Movie: “reabsorb_secrete-S” Movie: “hormones_kidney-S” Review: “neuron_NaKpump-G” Review: “neuron_transmit-G”