- Nitrogenous Wastes: are by products of
the breakdown of proteins. Amino acids must be deaminated if they
are not going to be used in protein synthesis. The
NH2 end group is removed
and a Hydrogen is added to form ammonia. Animals will dilute this
with water and excrete it into the environment. Land animals must
change it into the substance urea.
This change occurs in the liver. Birds, reptiles, and insects
change ammonia into uric acid. Uric
acid requires a tremendous amount of energy to
- The removal of nitrogenous waste from body
fluids is tied to osmoregulation,
the balance between salts and water.
- Freshwater Bony fish:
- Do not drink water.
- Osmotic uptake of water occurs through the
- salt is taken up by active transport through
- and they have
- Marine bony fish:
- Drink salt water,
- salt output is through the gills using active
- ammonia and osmotic water loss also occurs
through the gills.
- Their urine is isotonic.
- Drink no water,
- urea retained,
- water is lost from the body by osmosis through
- Marine birds:
- Salt water is excreted through nasal glands,
- they drink salt water,
- and rid their body of concentrated urine via
- Whales: drink water and have
- Function of the Excretory
- a). collects fluids from somewhere in the
- b). modifies the fluids by reabsorbing
substances the body needs.
- c). provides a way to expel the excretory
product from the body.
- These organs expend metabolic energy to carry
out these functions. The human kidney makes up .05% of the bodies
weight and uses 7.2% of the oxygen it consumes.
- The Human Kidney:
- Every vertebrate has a pair of kidneys.
- Their functional units are called
nephrons. The kidney contains more
than a million nephrons, which collect fluid from filtered blood.
- The renal
arteries and renal
veins carry blood to and from the kidney.
- The collected waste material leaves the kidney
via the ureter and is stored in the
urinary bladder; it is then expelled
from the body through the urethra.
- The kidney filters 1600 liters of blood per
day, producing 1 liter of urine.
- Function of the Nephrons: Let's follow
the process of urine formation in a nephron.
- The nephron's cup shaped Bowmans
Capsule surrounds a knot of blood capillaries
called the glomerulus. Much of the
bloods fluid filters into the glomerulus due to pressure from the
circulatory system. Left behind are large proteins and whole
cells, which are too large to fit through. This filtrate is then
passed through the nephron tubule,
which has 4 main parts (
proximal convoluted tubule, loop of Henle, distal
convoluted tubule, and the collecting duct).
- In the proximal convoluted
tubule, a considerable amount of resorbtion
occurs. Small proteins, glucose, and ions are returned to the
blood by active transport. Negatively charged ions follow
passively, followed by the osmosis of water. About 75% of the
filtrate is returned in this section of the nephron.
- The loop of
Henle, lie in the medulla of the kidney, the
other parts of the nephron lie outside of the medulla in the
cortex. Salt is actively transported out of the filtrate, and
since this area impermeable to water, water cannot follow the ions
- The distal convoluted
tubule, urine is then passed through here to
the collecting duct where it is concentrated due to its
permeability to water. It leaves the collecting duct into the
pelvis of the kidney, which leads to the ureter and the bladder
where it is stored.
- Regulation of Kidney
- Urine composition and the rate of urine
formation are largely regulated by hormones
angiotensin, and the enzyme
- Vasopressin (ADH) is produced by the
posterior pituitary gland and increases the bodies ability to
resorbtion of water. it increase the permeability of the
- Diabetes insipidus is caused due to a
lack of this hormone. It is characterized by thirst, and the
production of large amounts of dilute urine.
- Angiotensis and
Aldosterone are hormones that
regulate the amount of sodium that is resorbed from the filtrate
in the nephrons. Aldosterone is produced by the adrenal gland. it
promotes the resorbtion of sodium by the distal tube. Its action
is directed by the bloods salt content. The kidney secretes an
enzyme rennin, which changes a plasma protein angiotensinogen into
angiotensin, which helps to increase the production of aldosterone
and the blood pressure of the kidney.