Excretion Notes

excretion: the removal of cellular waste products from an organism

[Wastes Produced by Metabolism]

Respiration: carbon dioxide + water

Dehydration Synthesis: water

Certain metabolic processes: mineral salts

Protein metabolism: nitrogenous wastes (urea)

** Nitrogenous wastes are produced from excess amino acids..

deamination: process of removing the amine group from an amino acid and converting it to another form

** Deamination occurs in the liver in humans.

Excretory wastes may be either toxic or nontoxic. When toxic wastes are produced they are normally released, as in animals, or sealed off and stored, as in plants. Nontoxic waste materials may either be retained, released, or recycled in other metabolic activities.

Major Human Excretory Organs

(a.) Lungs

-- excrete carbon dioxide and water

-- presence of carbon dioxide may be demonstrated by blowing into a solution of limewater (turns milky) or a solution of bromothymol blue (turns yellow)

(b.) Liver -- deaminates amino acids and converts ammonia to urea because ammonia is very poisonous to the tissues

(c.) Skin -- has two main layers -- possesses sweat glands

2 Chief Sweat Gland Functions:

1. Aid in temperature regulation of the body.

2. Excretes urinelike wastes. (water, salt, and some urea)

** Perspiration is only incidentally excretory, its primary function is that of temperature regulation. Evaporation of the sweat (98% water and 2% salts and urea) occurs when heat is absorbed from skin cells. This absorption of heat lowers body temperature.

** Temperature regulation is an example of homeostasis.

(d.) Large Intestine: expels feces and excess salts

(e.) Kidneys

-- chief urinary system organ

-- bean shaped, reddish-brown organs, in the pit of the back

Kidney Cross-Sectional Picture

2 Major Functions:

1. They excrete most of the urea.

2. They control the concentration of most of the constituents of the body fluids. (the kidney filters out wastes and resorbs needed materials like water)

(Other Key Excretory Structures)

ureter: carries urine from the pelvis to the urinary bladder (one from each kidney)

urinary bladder: short term storage area for the urine

urethra: conducts urine from the bladder to the outside of the body

The Human Urinary Tract