1. Excretory System (sometimes called Urinary System)
Function and Parts

2. Body Water Balance Drinking & eating provides water
Kidney conserves water so output = intake

3. Why is excretion necessary?
In order for cells to stay alive, they must continually intake water and other molecules.
The cells would continue to get bigger and bigger if they only took in molecules
They must also export molecules
These molecules may be important signaling molecules such as hormones, or they may be molecules of glucose on their way to other cells, or they may be waste products of cellular metabolism that cells need to dispose.

4. Waste Products
Carbon dioxide – a waste product of cellular respiration is dumped into the blood stream and eventually removed by the lungs
Ammonia (NH3) is removed through water
This waste comes from the cell’s breakdown of old proteins
In these high physiological concentrations, it is poisonous to the cells and must be removed

5. Removal of Ammonia
Once excreted into the blood stream by cells, it is carried to the liver where it is converted from ammonia into urea which is much less toxic
It is then carried from the liver to the kidneys where it is removed

6. The Job of the Kidneys
They are responsible for cleaning the blood by removing metabolic wastes, excess solutes, and excess water and excreting them as urine
Besides removing urea, it also removes excess salts or glucose, the remnants of drugs (rationale for urine tests), and excess water.

7. Regulation of Water Levels
If the blood becomes too dilute or too concentrated with solutes, then it can interfere with normal cellular activity.
The kidneys are able to regulate water concentration in the blood by removing excess water if the blood is too dilute, or conserving water in the blood if it is not dilute enough

8. Regulation of Water Levels
If the blood becomes too dilute or too concentrated with solutes, then it can interfere with normal cellular activity.
The kidneys are able to regulate water concentration in the blood by removing excess water if the blood is too dilute, or conserving water in the blood if it is not dilute enough

9. Kidney Functions
Filter 200 liters of blood daily, allowing toxins, metabolic wastes, and excess ions to leave the body in urine
Regulate volume and chemical makeup of the blood
Maintain the proper balance between water, electrolyte salts, and acids and bases

10. Other kidney functions
Gluconeogenesis during prolonged fasting
Production of rennin to help regulate blood pressure and erythropoietin to stimulate RBC production
Activation of vitamin D

11. The Hard-working Kidneys
The two kidneys in the body receive between 180 – 220 liters of blood per day – about the volume of a car!
Because the body has only about 5.6 liters of blood, your blood runs through the kidneys to be cleaned about once every four minutes.

13. Kidney Location and External Anatomy

14. The Kidney

15. The Kidney

16. The Kidney

17. The nephron The nephron is the functional unit of the kidney
Each region is composed of cells suited to perform specific transport functions
Distal convoluted
tubule
Proximal
convoluted
tubule
Collecting duct
Ascending thin limb of loop of Henlé
Ascending thick limb of loop of Henlé

18. The Kidney

19. Structure of the Bowman’s (glomerular) capsule
Parietal layer of
glomerular capsule
Afferent arteriole
Juxtaglomerular
cell
Capsule
space
Efferent arteriole
Proximal
convoluted
tubule
Endothelium
of glomerulus
Podocyte
Pedicel

20. Formation of Urine
The kidneys filter the body’s entire plasma volume 60 times each day
The filtrate:
Contains all plasma components except protein
Loses water, nutrients, and essential ions to become urine
The urine contains metabolic wastes and unneeded substances

21. Formation of Urine
If there is too much water in the blood, then it is removed and put in urine.
If there is not enough water in the blood, the kidneys will not remove any.
If there is too much urea or other solutes in the blood, the kidneys will remove these excess solutes.
By regulating solute numbers and water volume, the kidneys normally maintain homeostasis in blood solute concentration.

22. Mechanisms of Urine Formation
Urine formation and adjustment of blood composition involves three major processes
Glomerular filtration
Tubular reabsorption
Secretion

23. Nephron Recycling: Overview

24. Water Reabsorption in Descending Loop of Henle
Countercurrent multiplier exchange
Medullary osmotic gradient
H2OECFvasa recta vessels

25. Factors that affect kidney function
Antidiuretic hormone (ADH) – prevents excess water loss from kidneys
Alcohol – inhibits secretion of ADH = more urine volume, leading to dehydration
Aldosterone – prevents excess loss of sodium and water from kidneys
Caffeine – increases rate of salt and water loss from kidneys
Increased blood pressure – increase rate of water loss from kidneys.

26. Normal kidneys Kidneys beyond help!
Chronic kidney disease
Normal kidneys Kidneys beyond help!
L RAS
End-stage kidneys

27. The Urinary System Part B25
The Urinary System
Part B

28. Tubular Reabsorption All organic nutrients are reabsorbed
Water and ion reabsorption is hormonally controlled
Reabsorption may be an active (requiring ATP) or passive process

29. Sodium Reabsorption: Primary Active Transport
Sodium reabsorption is almost always by active transport
Na+ enters the tubule cells at the luminal membrane
Is actively transported out of the tubules by a Na+-K+ ATPase pump

30. Sodium Reabsorption: Primary Active Transport
From there it moves to peritubular capillaries due to:
Low hydrostatic pressure
High osmotic pressure of the blood
Na+ reabsorption provides the energy and the means for reabsorbing most other solutes

31. Routes of Water and Solute Reabsorption
Figure 25.11

32. Osmotic Gradient in the Renal Medulla

33. Loop of Henle: Countercurrent Multiplier
The descending loop of Henle:
Is relatively impermeable to solutes
Is permeable to water
The ascending loop of Henle:
Is permeable to solutes
Is impermeable to water
Collecting ducts in the deep medullary regions are permeable to urea

34. Loop of Henle: Countercurrent Exchanger
The vasa recta is a countercurrent exchanger that:
Maintains the osmotic gradient
Delivers blood to the cells in the area

35. Loop of Henle: Countercurrent Mechanism
Figure 25.14

36. Formation of Dilute and Concentrated Urine
Figure 25.15a, b

37. Diuretics Chemicals that enhance the urinary output include:
Any substance not reabsorbed
Substances that exceed the ability of the renal tubules to reabsorb it
Substances that inhibit Na+ reabsorption

38. Diuretics Osmotic diuretics include:
High glucose levels – carries water out with the glucose
Alcohol – inhibits the release of ADH
Caffeine and most diuretic drugs – inhibit sodium ion reabsorption
Lasix and Diuril – inhibit Na+-associated symporters

39. Renal Clearance
The volume of plasma that is cleared of a particular substance in a given time
Renal clearance tests are used to:
Determine the GFR
Detect glomerular damage
Follow the progress of diagnosed renal disease

40. Renal Clearance RC = UV/P RC = renal clearance rate
U = concentration (mg/ml) of the substance in urine
V = flow rate of urine formation (ml/min)
P = concentration of the same substance in plasma

41. Chemical Composition of Urine
Urine is 95% water and 5% solutes
Nitrogenous wastes include urea, uric acid, and creatinine
Other normal solutes include:
Sodium, potassium, phosphate, and sulfate ions
Calcium, magnesium, and bicarbonate ions
Abnormally high concentrations of any urinary constituents may indicate pathology

42. Micturition (Voiding or Urination)
The act of emptying the bladder
Distension of bladder walls initiates spinal reflexes that:
Stimulate contraction of the external urethral sphincter
Inhibit the detrusor muscle and internal sphincter (temporarily)
Voiding reflexes:
Stimulate the detrusor muscle to contract
Inhibit the internal and external sphincters

43. Kidney dissection