CA Biology Standards #9a,f,g 1

Kidneys

A Case Study in Homeostasis

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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.

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Urinary System Contributes to

homeostasis Keeps proper

levels of water, salts, etc.

Eliminates wastes

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Kidneys Key players in urinary system: the kidneys

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A Closer Peek Inside…

Unveiling the homeostatic magic:

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3 Steps to the Trick:

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1. Filtration: Separate Waste

Two main types of waste in the body: CO2 (Carbon dioxide)- produced by cells

Disposed of by lungs NH3 (Ammonia)- converted by liver into urea

NH2CONH2 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

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Filtration, cont’d: Glomerulus

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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

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Reabsorption, cont’d

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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

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Secretion, cont’d

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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 [H2O] outside duct . . .

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Discussion: ADH

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Reinforce

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