Regents Biology

38.3 – Excretory System

Regents Biology

Objectives §  Explain how animals manage toxic nitrogenous waste §  Discuss the 3 types of nitrogenous waste §  Contrast the way in which aquatic animals eliminate

waste with that of terrestrial animals §  Identify the components of the human excretory system

and discuss their functions §  Explain how “form fits function” by citing specific

examples from the excretory system

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§  Animal cells move material across the cell membrane by diffusion

§  What sort of materials?

What do animal cells do to stay alive?

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Unicellular to Multicellular

§  All cells in direct contact with environment à can easily get nutrients in and waste out by diffusion

§  Internal cells not in direct contact with environment à can’t easily get nutrients in and waste out

§  need organ systems

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What liquid waste do we make? §  Digesting protein makes poison (ammonia)

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§  ammonia (freshwater)

§  urea (land) §  uric acid (egg

layer)

Nitrogen waste

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Nitrogen waste disposal in water §  lots of water around à waste can be poisonous §  Freshwater fish excrete ammonia through gills and as

dilute urine §  Saltwater fish excrete ammonia in concentrated urine

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Nitrogen waste disposal on land §  Land animals need to conserve water à evolved less poisonous waste product (urea)

§  excrete urea and (little) water as urine

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Nitrogen waste disposal in egg §  Egg-laying land animals (birds, reptiles, insects) have no

place to get rid of waste while in egg à needs waste that doesn’t dissolve in water inside egg (uric acid)

§  stays a powder, doesn’t dissolve in water §  Bird poop is really… pee!

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KIDNEY

BLADDER

URETER

§  located on either side of the spinal column near the lower back

§  ureter carries urine from each kidney to bladder

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Renal Cortex

Renal Medulla

URETER

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§  cortex (outer) and medulla (inner) § nephrons – filters § Nephrons are located in the renal cortex (except for their

loops of Henle which descend into the renal medulla).

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The Kidneys §  Blood enters the kidney

through renal artery. §  The kidney removes: -  urea -  excess water -  other waste products

§  The clean, filtered blood leaves the kidney through the renal vein and returns to circulation.

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§  Each nephron has its own blood supply (an arteriole, a venule, a network of capillaries)

§  Each nephron releases fluids to a collecting duct, which leads to the ureter.

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Filtration and Reabsorption §  The filtration of blood

mainly takes place in the glomerulus

§  Fluid from the blood flows into Bowman’s capsule.

§  Filtered from the blood: water, urea, glucose, salts, amino acids, and some vitamins

§  Plasma proteins, cells, and platelets remain in the blood

http://www.youtube.com/watch?

feature=player_embedded&v=qfWx8msgHqM

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§ material removed from the blood at Bowman's capsule (~ 99% of the water and most nutrients) is reabsorbed into the blood

§ Urine drains into the collecting duct

§  Loop of Henle – where water is conserved and volume of urine is minimized

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Osmoregulation § Urine is stored here

until it is released from the body through a tube called the urethra.

§  The activity of the kidneys is mostly controlled by the composition of the blood (osmoregulation).

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Kidney Disorders