Chapter 11 Excretion - Lecture Notes

Chapter 11: Excretion Students should be able to: (a) Define excretion and explain the importance of removing nitrogenous and other compounds from the body (b) Outline the function of kidney tubules with reference to ultra-filtration and selective reabsorption in the production of urine (c) Outline the role of anti-diuretic hormone (ADH) in the regulation of osmotic concentration (d) Outline the mechanism of dialysis in the case of kidney failure

11.1 Metabolism, Waste Product and Excretion 11.1.1

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Definitions Metabolism = Catabolism + Anabolism

Complex molecules are broken down into smaller, simpler ones eg. Cellular respiration •

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Simple molecules are built up into more complex, larger ones eg. Photosynthesis

Excretion = Removal of metabolic waste products and toxic materials from the body of an organism.

Main waste products CO2 o

Produced during cellular respiration

o Dissolves in water  carbonic acid  affect pH  affect •

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enzyme activity o Excreted from the lungs Excess water o Produced by respiring cells o Can dilute body fluids  water flows into body cells from surrounding o Excreted mainly from kidneys Urea o Produced when excess amino acids in diet are deaminated in the liver o Can affect enzyme activity o Is the most harmful of the metabolic wastes o Excreted mainly from the kidneys Excess heat

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Produced by respiring cells o Can raise body temperature  affect enzyme activity o Excreted mainly from skin, kidneys and lungs o

11.2 Excretion of Carbon Dioxide 11.2.1

Process

CO2 from respiring cells diffuse into red blood cells

Carbonic acid is formed  changes to hydrogencarbonates

HCO3- moves into plasma  lungs

High CO2

In LUNGS • HCO3-  CO2 • CO2 diffuses out of capillaries into alveolar cavity during expiration (breathing in)

11.3 The Mammalian Urinary System 11.3.1

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Kidneys Functions: Removal of Urea and excess water from the blood Consists of: Kidneys, Ureters, Bladder, Urethra

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Selective reabsorption o Useful substances are reabsorbed along the nephron  maintain pH and composition of blood plasma

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Regulate salt & water balance in body fluid o Whenever amount of liquid taken in increases  kidneys remove more water

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o Less amount of liquid taken  kidneys remove less water (see selective reabsorption)

11.3.2

Structure of kidneys

Functions Organ that produces urea and remove it together with excess water from the blood

Functions Functions Opening which allows urine to pass through

Tube that transfer urine from kidneys to the bladder

Functions Elastic, muscular bag which stores urine Functions Muscles that relaxes to allow urine to flow into the urethra

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11.3.3

Structure of a Nephron

Ultrafiltration  water, mineral salts, glucose, amino acids and nitrogenous waste products

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Normal contents of urine: • Water (96g) • Mineral salts (1.8g) • Urea (2.0 g) • Other nitrogenous waste (0.2g)

Filtrate contains • Excess water • Mineral salts Urea & nitrogenous waste product

Selective Reabsorption  Water reabsorbed by osmosis  Glucose, amino acids absorbed back into the renal capillaries by active transport

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11.4 Dialysis Machine

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Allow urea & waste product to diffuse out (small) Does not allow body cells to diffuse out (big)

Contains essential salts for the body

Tubing is long and coiled  increase S.A: Vol ratio  speed up rate of exchange of substances btw blood & dialysis fluid

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