1. The Urinary System Excretion: The removal of metabolic wastes from the
body as a result of cellular
activities

2. Examples of Excretion:
Skin – Excretes sweat (a solution of water, salt, and some urea)
- Used to cool the body than secretion of wastes.
- Increase in wastes during times of renal failure (kidney)
Liver – Breaks down old red blood cells
- Yellow pigment in urine is also formed from the
breakdown of heme by the liver. It is then deposited in
the blood and later removed from the kidneys.
Lungs – Expiration removes carbon dioxide but it also results
in the loss of water.
Intestine – Certain salts, such as those of iron and calcium are
excreted directly into the cavity of the intestine by the
epithelial cells lining it and become part of feces.
Kidneys – Excrete urine, which contains a combination of the
end products of metabolism.

4. Urinary System Functions
Kidney: Produce urine
Ureters: Transport urine to the bladder
Bladder: Storage of urine
Urethra: Elimination of urine

6. Position of the kidney in the body:
The two kidneys lie in the lower, dorsal part of the abdomen.
They receive blood from the renal arteries to be cleaned.
The wastes, to be excreted, called urine collects in the pelvic
region of each kidney from where they are conducted by
peristalsis down to the urinary bladder.
When the urinary bladder becomes full, stretch receptor
trigger urination, and the fluid is excreted.

7. Microscopic Anatomy of the Kidney:
The kidney is composed of over 1 million nephrons (or renal corpuscles)
Bowman’s capsule and proximal convoluted tubule are located in the
cortex.
Loop of Henle in the medulla
Distal convoluted tubule in the cortex
Collecting ducts are located in the medulla and cortex
Renal Artery – Bring blood to the kidneys to be “cleaned” (high urea
content)
Renal Veins – Returns blood that is cleaned (Low urea content, no
glucose)
Each nephron has its own blood supply. Including 2 capillary regions:
1. At the Glomerulus
2. Surrounding the rest of the nephron

8. Nephron

9. URINE FORMATION
1. Pressure filtration
2. Selective reabsorption
3. Tubular excretion
4. Reabsorption of water
5. Excretion

10. Function of the Nephron
1. Pressure filtration:
Blood enters the Glomerulus which is surrounded by the Bowman’s
capsule. Here, occurs. Water, nutrients, and
wastes enter the Bowman’s Capsule. Large organic molecules do
not enter. The liquid that collects in the Bowman’s capsule
is blood plasma minus blood proteins.
Filtered Blood Components:
Water
Nitrogenous Wastes
Nutrients
Salt (ions)
Non-Filtered Blood Components:
Formed elements- (blood cells and platelets )
Proteins
Blood pressure is very important. If blood pressure is too low,
filtration will not occur. A hormone called rennin is released from
a specialized tissue in the Glomerulus that causes the
constriction of the Glomerulus thus the blood pressure is
increased to an adequate level.

11. Steps of Urine Formation

12. 2. Tubular Reabsorption:
occurs mainly at the proximal convoluted tubule. Required
nutrients glucose, amino acids, Vitamins, Minerals salt
molecules and some water are reabsorbed into the peritubular
capillary network. Requires ATP.

13. 3. Tubular Excretion:
Occurs at the distal convoluted tubule. Excess molecules in the blood,
such as H+ ions, Histamine, Penicillin, and ammonia are secreted into
the tubule from the blood, thereby helping to maintain homeostasis.
Helps maintain blood pH
5. Concentrated Urine from the collecting tubule collect and goes to
the Renal pelvis

14. 4. Reabsorption of Water:
The body can not afford to lose all this water. It must be
reabsorbed into the blood. The cells of the loop of Henle actively
pump Na+ out of the tubule and K+ into the nephron.
The result of this is that the negative ion (Cl-) and water follow
the sodium by osmosis (to even out electrical and concentration
gradients)
Water is reabsorbed along the entire length of the nephron.
There fore urine is concentrated. The blood in the capillaries are
hypertonic to the fluids in the fluid spaces. The loop of Henle
creates a high osmotic pressure in the medulla. The fluid going up
the distal side of the loop of Henle has a greater concentration of
wastes and little nutrient value.

15. 5. Excretion:
Concentrated Urine from the collecting tubule collect and goes
to the Renal pelvis

16. Antidiuretic hormone (ADH) - Negative feedback
ADH – controls reabsorption of water.
ADH increases the permeability of the distal convoluted
tubule and collecting duct so that more water can be
reabsorbed.
Therefore a decreased amount of urine results, but an
increase in urine concentration. Water and Urea=Urine.
Urea is a waste product in the metabolism of proteins.
With more water being reabsorbed, blood volume tends to be
increased.

17. If too little water is taken in orally, the hypothalamus releases
a hormone into the nerve tract to the posterior pituitary gland.
The posterior pituitary gland releases ADH and more water is
absorbed by the kidneys to maintain blood volume.
PH of blood is maintained by tubular excretion. If pH is too low,
Hydrogen ions are secreted into the nephron.
Alcohol has a negative effect on ADH. It sends a false
message to the hypothalamus that there is too much water
in the blood. ADH is not released in fact it is inhibited.
Therefore water is not reabsorbed and is lost in the urine.
That is why drinking alcohol, results in a lot of urination
and dehydrated.

18. Aldosterone - Negative feedback
Hormones which regulate the level of sodium and potassium
in the blood.
If sodium is too low, aldosterone causes more sodium to be
reabsorbed. If sodium concentration is high release of
aldosterone is inhibited.
Adrenal Cortex controls this hormone. The effect of this is the
same as that of ADH – more water is reabsorbed due to
osmosis in the loop of Henle