1. Unit O – Urinary System

2. Definition:
Excretion- The removal of metabolic wastes from the body (the useless and potentially dangerous by-products of cellular reactions)

3. Roles of Organs in Excretion
Skin – Excretes perspiration (a solution of water,
salt, and some urea)
- Used to cool the body rather than secretion of wastes.
- Increase in wastes during times of renal
failure (kidney)

4. 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.

5. Lungs – Expiration removes carbon
dioxide but it also results in
the loss of water.

6. 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.

7. Kidneys
- Remove wastes from the blood, then return “clean blood” to the circulatory system.
- Excrete urine, which contains a combination of the end products of metabolism.

8. Entrance and exit of water
Enters: Drink water
2.   Absorbed from food eaten
Exits:
Exhalation
2.     Urination
3.     Perspiration
4.     Tears (small amounts)
5.     Expectorating (phlegm)
6.     Defecation

9. Urinary System Functions
Kidney – Produce urine
Ureters – Transport urine to
the bladder
Bladder – Storage of urine
Urethra - Elimination of urine

10. Kidney Structure

11. When a kidney is sliced longitudinally (sagittal section), it shows 3 regions.
1.     Outer granulated region called the cortex
2.     Striated or lined layer called the medulla
3.     Inner cavity called the pelvis where urine
collects

13. The kidneys are
in the lower,
dorsal part of
the abdomen.
They receive
blood from the
renal arteries
to be cleaned.

14. The wastes to be excreted, called urine, collect 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 receptors trigger urination, and the fluid is excreted

16. Microscopically, the kidney is composed of over 1 million nephrons (or renal tubules)
Bowman’s capsule (which contains the glomerulus) and proximal convoluted tubule are located in the cortex.
 Distal convoluted tubule is in the cortex
Loop of Henle is
in the medulla
 Collecting ducts
are located in
the medulla and
cortex

18. Renal Artery – Bring blood to the kidneys to be “cleaned”
- high urea content
Renal Veins – Returns blood that is cleaned
- Low urea content

19. Each nephron has its own blood supply.
Including 2 capillary regions:
1. At the Glomerulus
2.  Surrounding the rest of
the nephron

21. URINE FORMATION
A.    pressure (glomerular) filtration
B.    selective tubular reabsorption
C.    reabsorption of water
D.    tubular secretion
E.    excretion

22. Function of the Nephron
A. Pressure Filtration. Blood enters the Glomerulus which is surrounded by the Bowman’s capsule.
Here, pressure filtration occurs. Water, nutrients, and wastes enter the Bowman’s Capsule.

23. Large organic molecules do not enter Bowman’s capsule (stay in blood)
Large organic molecules do not enter Bowman’s capsule (stay in blood). The liquid that collects in the Bowman’s capsule is blood plasma minus blood proteins.

24. Water - Formed elements (blood cells and platelets)
Filtered Blood Components Non-Filtered Blood Components
(taken out of blood and move into (stays in blood, does not enter Bowman’s Bowman’s capsule) capsule)
Water - Formed elements (blood cells and platelets)
Nutrients
Nitrogenous wastes - plasma proteins
Salt (ions)
(see animation)

25. Blood pressure is very important
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.

26. B. Selective 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 (blood) Requires ATP

27. Reabsorption of Water. The body cannot afford to lose all this water
Reabsorption of Water.The body cannot 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 to make the medulla hypertonic.

28. The hormone aldosterone (secreted from the adrenal cortex above the kidney) promotes the reabsorption of Na+

29. The result of this is that the negative ion Cl- and water follows the sodium by osmosis (to even out electrical and concentration gradients)

30. Water is reabsorbed along the length of the nephron
Water is reabsorbed along the length of the nephron. Therefore urine is concentrated.
(see video)

31. The loop of Henle creates a high osmotic pressure in the medulla
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.

32. D. Tubular Secretion occurs at the distal convoluted tubule
D. Tubular Secretion 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

33. Excretion. The collecting duct is another site of water reabsorption, leaving concentrated urine. The urine from the collecting tubule collects and goes to the renal pelvis to be excreted via the ureter, bladder and urethra.
(see video)

34. Antidiuretic hormone (ADH) Good example of Negative feedback loop
ADH – controls reabsorption of water.
ADH increases the permeability of the
distal convoluted tubule and collecting
duct so that more water can be reabsorbed.

35. Therefore a decreased amount of urine results, but an increase in urine concentration. Water and Urea=Urine. Less water, more urea concentration.
Urea is a waste product in the metabolism of proteins. With more water being reabsorbed, blood volume tends to be increased.

36. If too little water is taken in orally the hypothalamus releases a hormone into the nerve tract to the posterior pituitary gland.  

37. 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.

38. 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.

39. Therefore water is not reabsorbed and is lost in the urine
Therefore water is not reabsorbed and is lost in the urine. That is why when you drink alcohol, you urinate a lot and become dehydrated.

40. Aldosterone
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.

41. Adrenal Cortex controls this hormone
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