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EXCRETORY SYSTEM

Excretory System

How does the excretoryHow does the excretory system maintain homeostasis?–It regulates heat water salt–It regulates heat, water, salt, acid-base concentrations and metabolite concentrations

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ORGANS OF EXCRETION

Skin and associatedSkin and associated glands: Removes heat and saltsLungs: Removes carbonLungs: Removes carbon dioxide

Kidneys (part of the y (pUrinary system): MAJOR excretory organs that excrete metabolic wastes, regulate water-salt balance and acid-water salt balance and acidbase balance.Liver: Removes metabolic wastes

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Urinary System

PARTS OF THE URINARY SYSTEM (pg. 374)

Kid filt bl d tKidneys: filter blood to produce urine.Ureters: carry urine from the kidneys to the urinarykidneys to the urinary bladder

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Urinary Bladder: storesUrinary Bladder: stores urine.Urethra: carries urine from the bladder to the outside ofthe bladder to the outside of the body.

IMPORTANT BLOOD VESSELS

Renal Artery: carriesRenal Artery: carries contaminated blood into the kidney.Renal Vein: carries purified pblood from the kidney and returns it back into circulation by way of the inferior vena cava.

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The Kidney

KIDNEY PARTS (pg. 375)

Cortex: the outer partCortex: the outer part

Medulla: the middle part

Pelvis: the inner cavity where urine collects

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MAJOR FUNCTIONSOF KIDNEYS

1. Filters blood of:Urea – formed in the liver from the

breakdown of ammoniaCreatinine – formed in the musclesU i A id f d lt f th Uric Acid – formed as a result of the

breakdown of nucleic acids (DNA and RNA)

2 Controls the balance of2. Controls the balance of water in our bodies3. Regulates pH of the blood4. Regulates the4. Regulates the concentration of dissolved ions in the blood

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5 Secretes a hormone that5. Secretes a hormone that causes a production of red blood cells6 Activates Vitamin D6. Activates Vitamin D production in the skin

NEPHRONS (pg. 375)

Tiny filtering units calledTiny filtering units called nephrons fill the cortex and medulla of the kidney.

Each kidney contains 1 to 1.25 million nephrons.

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•Each nephron is composed of 5 main parts: B ’Bowman’s capsule, proximal tubule,loop of Henle,loop of Henle,distal tubule & collecting duct

Nephron Function (4 stages)

1. Filtration:1. Filtration: Blood travels from the renal artery, to an arteriole and then into the glomerulus, a mass of

ill i d d b thcapillaries surrounded by the Bowman’s capsule.

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Blood pressure forces someBlood pressure forces some plasma of the blood, containing both waste and useful material, into the Bowman’s capsule. This material is called the nephric filtrate.

The filtrate contains suchThe filtrate contains such things as: water, urea, uric acid, salt, glucose, amino acids, ions and vitamins.acids, ions and vitamins.

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2. Re-absorption: From the Bowman’s capsule the filtrate is pushed into the proximal tubule. The process of re-absorption, of useful pmaterials within the filtrate, into the capillary network that surrounds the nephron than begins.

Reabsorption occurs byReabsorption occurs by osmosis, diffusion, and active transportReabsorbed materials include water, glucose, amino acids, ions and vitamins

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When the filtrate reaches theWhen the filtrate reaches the end of the distal tubule the solution is isotonic (the filtrate and the surrounding cells have the same concentration of water and solutes).

The filtrate then moves downThe filtrate then moves down the descending loop of Henle; as the loop descends further into the inner medulla, sodium concentrations in theconcentrations in the surrounding tissue increase which draws water out of the filtrate (by osmosis).

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At the bottom of the loopAt the bottom of the loop sodium ions in the filtrate are at high concentration and therefore diffuse out of thetherefore diffuse out of the tubule.

Positive sodium ions arePositive sodium ions are followed by negative chloride ionsWater cannot reenter the ascending loop because this loop is impermeable to water

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3. Secretion:Occurs in the distal tubuleInvolves active transport of substances from the capillaries i t th t b linto the tubuleSubstances include hydrogen ions, creatinine and drugs

4. Elimination:The fluid than enters the collecting duct as urine. It passes through the pelvis into the ureter. Most of the water ions and usefulMost of the water, ions and useful nutrients (glucose, amino acids) have been reabsorbed.

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Path of filtrate through nephron:

Bowman’s capsule proximalBowman s capsule proximal tubule loop of Henle distal tubule collecting duct

Control of Water Balance

When water levels are too low:1) The hypothalamus stimulates

the pituitary gland to secrete a hormone called anti-diuretic hormone (ADH). ADH travels through blood to kidneys.

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2) ADH increases the2) ADH increases the permeability of the tubules and collecting ducts

3) More water is reabsorbed into the blood so the urine is more concentrated

When water levels are too high:g1)Hypothalamus doesn’t stimulate

ADH secretion2)Little water is reabsorbed into the )

blood so the urine is more dilute.