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The Excretory System

Gets rid of wastes and other substances that the body doesn�t

need.

Definitions

Excretion - release of metabolic wastes and

excess water - eg. Urinate (aka #1)

Metabolic Wastes •  produced by chemical reactions like respiration,

hydrolysis, synthesis and neutralization. •  Water •  Carbon Dioxide •  Salts •  Urea

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Definitions Elimination - release of unabsorbed wastes from

the digestive tract - eg. Feces via defecation (aka #2)

Removal of Wastes - Examples

•  Liver - excretes bile •  Skin - sweat, excretes salt and urea •  Lung - excretes CO2 and H2O

•  KIDNEYS •  Excrete UREA,water, salts and various other

wastes as part of the urine

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Organs of Excretion

" Skin – Allows water, salt and urea to

diffuse from the blood (capillaries) into the sweat glands.

– Releases sweat from the sweat glands through the sweat ducts out to the skin pores.

Organs of Excretion " Liver

– Part of the digestive, circulatory and excretory systems.

– Removes excess amino acids from the body.

– Breaks down the amino acids through deamination to form the urea which is excreted in the urine.

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Organs of Excretion

" Lungs –  Excretes the waste product of respiration during exhalation.

–  Carbon Dioxide and Water Vapor.

Organs of Excretion " Kidneys

– Major excretory organs of the body which removes most of the body wastes.

– Purify blood by filtering out water, salts, digested food particles and urea in the form of urine.

– Urine passes out through the urinary tract.

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Urinary System

Excretion of Urine

" Kidney " Ureter – a tube that transports urine to the

urinary bladder. " Urinary Bladder – a sac of tissue that has

the ability to expand as it fills with urine. " Urethra – a tube at the bottom of the

bladder where urine passes out of the body.

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Kidney

Nephron

Nephron

- the functional unit of the kidney

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Human Biology

Urinary System - Formation of Urine

Nephron Structure

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Urine Formation

3 Steps:

1.  Glomerular Filtration

2.  Selective Reabsorption

3.  Tubular Secretion

•  Blood flows into nephron via afferent arteriole & then into glomerulus •  Site of Glomerular Filtration

Afferent arteriole

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•  The filtrate is pushed out into the Bowman’s capsule •  These are small particles (water, urea, ions (H+,

HCO3-, Na+), glucose, amino acids, vitamins… etc.

•  Larger molecules (RBC, WBC, proteins) carry thru the efferent arteriole

•  Leads to peritubular capillaries eventually to the renal vein

efferent arteriole

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•  Filtrate enters the proximal convoluted tubule (PCT) •  Site of Selective reabsorption

Reabsorption of:

-  most glucose

-  most A.A.

-  ~65% of Na+

-  ~65% water

-  small proteins

-  HCO3-

-  vitamins

- Other ions

Glucose, A.A., water

•  Concentrated filtrate moves into the loop of Henle •  Descending loop - 10-20% water reabsorbed •  Ascending loop - 20% Na+

Na+

H2O

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•  Concentrated filtrate moves into the distal convoluted tubule (DCT)… from efferent arteriole… •  Site of Tubular Secretion (some in the PCT too!)

H+ NH3

This is a mechanism for

removing unwanted

substances from the plasma via active transport

H+ NH3 NH4

Excess K+

Penicillin Etc…

•  Concentrated filtrate moves into the Collecting Duct •  and now the URINE passes into the:

renal pelvis → ureter → urinary bladder → urethra → out of body

H2O

Urine

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Composition: •  Dissolved salts (NaCl) •  Metabolic waste (ammonia, urea)

•  Note: ammonia is toxic so it is quickly converted to urea in the liver

•  Small molecules from the breakdown of hormones •  Sometimes there is protein, glucose, blood

•  These are NOT normal and usually signal something is nor functioning properly

Urine

n Crash Course – Excretory System