1. Organs of the Urinary System
Kidneys
Ureters
Urinary Bladder
Urethra

2. The Kidneys Perform most of the work of the urinary system
Continuously cleanse the blood and filter the fluids from the bloodstream
Helps dispose of wastes and excess ions
Produces the enzyme renin, which regulates blood pressure
Produces the hormone erythropoietin, which stimulates red blood cell production
Coverts Vitamin D to its active form

3. The other organs
Ureters – slender tubes that carry urine by peristalsis from the kidney to the bladder
Urinary Bladder – a smooth, collapsible muscular sac that stores urine temporarily
Urethra – thin walled tube that carries urine by peristalsis from the bladder out of the body. It has two sphincter muscles to help with bladder control.
Internal urethral sphincter – an involuntary muscle that keeps the urethra closed when urine is not being passed
External urethral sphincter – a voluntary muscle (skeletal) near the floor of the pelvic region

4. Micturition Also known as voiding
This is the act of emptying the bladder
Ordinary, the bladder will hold urine until about 200 mL is gathered. At this point, the bladder begins to stretch, activating stretch sensors.
This causes contractions which forces urine through the internal urethral sphincter. But we can choose whether or not to allow the urine past the external urethral sphincter. If we relax this muscle, urination occurs.

5. So, what is urine? Urine results from three processes Filtration
Tubular reabsortion
Tubular secretion

6. Filtration
Kidneys contain millions of tiny structures called nephrons, which contain two structures, the glomerulus and renal tubule.
The glomerulus, or knot of capillaries, acts as the filter
Filtration occurs when a force is applied to the fluids in the glomerulus. This force pushes the smaller molecules through the glomerulus, but bigger particles are too large to pass through and are retained.

7. Tubular Reabsorption
Some of the small ions that are removed are still needed, so the body must reclaim them.
This is completed by a portion of the renal tubule.
The tubule cells act as transporters that take up needed substances from the filtrate and taking them to the extracellular space, where they are reabsorbed by blood capillaries. Most of this occurs by active transport and therefore requires energy.
Needed molecules: glucose, some ions, and amino acids
Unneeded molecules: urea, uric acid, and creatinine

8. Tubular Secretion Essentially tubular reabsorption in reverse.
Certain larger molecules are moved into the tubule to be excreted
This could be certain drugs or certain molecules that help maintain the blood’s pH

9. Characteristics of Urine
Urine is the end result of cleaning the filtrate and returning the nutrients and most of the water to the blood stream.
It mainly contains nitrogenous wastes and unneeded substances.
Urine can be clear to deep yellow.
Yellow is caused mainly by the pigment urochrome, which results from the destruction of hemoglobin and other dissolved solutes
It is slightly acidic (pH of about 6) but can change with diet
Is more dense than distilled water

10. Blood Composition
The composition of the blood depends on three major factors
Diet
Cellular metabolism
Urine output
The kidneys help maintain the blood by
Excreting nitrogen containing wastes
Maintaining water levels
Maintaining electrolyte balances
Ensuring proper blood pH

11. Maintaining Water Levels
If massive amounts of water is taken in, the kidneys will allow a large amount of it to pass out of the body with the urine.
If water is scarce, the kidneys will reabsorb the water from urine and make the urine more concentrated.

12. Maintaining electrolyte balances
Water will follow salt, so it is important to maintain the correct balance of electrolytes (salts dissolved into water)
As a result, the kidneys respond to hormones to either reabsorb or release ions in the blood with the urine
Egg video

13. Ensuring proper blood pH
The body uses blood buffers to maintain a pH between 7.35 and 7.45.
The main buffer system in the body is the bicarbonate buffer system and made by mixing the weak carbonic acid and its salt sodium bicarbonate.
The salt can act as a base an help to neutralize acids, while the carbonic acid can help to neutralize bases.