Excretory System

1. The Human Excretory
System

2. What is Metabolism?
 Metabolism is the biochemical
modification of chemical
compounds in living organisms
and within living cells.
 Metabolism includes the
biosynthesis of complex organic
molecules (anabolism) and their
breakdown (catabolism).
 Metabolism usually consists of
sequences of enzymatic steps,
also called metabolic pathways.
 The total metabolism are all
biochemical processes of an
organism.

3. What is Homeostasis?
 Homeostasis is the property of an open
system, especially in living organisms, to
regulate its internal environment to
maintain a stable, constant condition, by
means of multiple dynamic equilibrium
adjustments, controlled by interrelated
regulation mechanisms.

4. Excretion
 During normal metabolism,
many waste products are
produced that must be
eliminated by the body.
 During excretion toxic
chemicals and excess water,
salts, and carbon dioxide
are removed from the body.
 This is done to maintain
both osmotic and pH
balance.

5. Organs of Excretion
 The lungs excrete
excess carbon dioxide
and water vapor from
the body. Both wastes
leave the body during
exhalation.

6. Organs of Excretion
 The liver removes nitrogen wastes (NH3) from the blood
that result from the break down of amino acids.
 In the liver ammonia (NH3) is converted to a less toxic
substance called urea, then can be carried more safely in
the blood to the kidneys where it is finally removed as a
part of urine.
 Breaks down other toxins that are in the body.

7. Organs of Excretion
 Breaks down old red blood cells.
 When the liver is overworked
it becomes diseased.
 If the liver fails to function
properly a person will die.
 It is a resilient organ and can
regenerate itself to some extent.
 A person can still live with
only 30% of the liver functioning
properly. Lower than 30% of the
liver functioning will result in
death.

8. Organs of Excretion
 The kidneys excrete
nitrogenous wastes
(urea), salts, water,
and other substances
that make up urine.

9. Organs of Excretion
 Each kidney is about the size of
fist.
 Each kidney is made up of about a
million microscopic units called a
nephron.
 Nephrons are tiny cup shaped
capsules surrounded by capillaries.
 As blood flows through the
nephron the following occurs:
filtration, reabsorption, secretion,
and urine formation.

10. Organs of Excretion
 Filtration takes place in glomerulus. The pressure
from the arteries (heart) forces water, salt, amino
acids, glucose, and urea is forced out of the blood.
Blood cells and protein remain in the blood they are
too big to be filtered out.
 Reabsoprtion of some of the filtrate occurs in the
Bowman’s capsule. As the filtrate passes through the
nephron, 99% of water, glucose, amino acids and
salts are reabsorbed.
 Whatever is left (water, urea and some salts)
becomes urine.
 Urine that is produced leads to ducts that lead to
ureters that connect to the bladder. When the bladder
is full a person will urinate.
 When the kidney fails, the other kidney will enlarge to
compensate. When both fail, a person will need a
kidney transplant or will have to be put on dialysis.

11. Organs of Excretion
A Nephron

12. Organs of Excretion
Background Information
 Skin is the largest organ in the
body.
 It protects the body, and has a
role in keeping conditions with
in the body constant.
 There are two layers or skin. As
new skin cells are created they
push the older ones to the
surface.
 Layers beneath the surface
pigments that give skin its color.
 Glands in the skin release oils
that keep hair soft.

13. Organs of Excretion
Background Information
 There are structures in the
skin that maintain
homeostasis, Nerve endings
detect temperature and touch.
Hair and capillaries in the skin
regulate body temperature.
 Sweat glands release sweat to
regulate body temperature.
Also wastes are excreted
through sweat.

14. Organs of Excretion
 The skin excretes sweat,
which is a mixture of
water, salts, small amount
of nitrogen wastes (urea),
and other trace
substances.