1. The Kidney and formation of urine

2. Objectives State the main functions of the kidney
Label a diagram to illustrate the location of the kidneys, ureters and bladder within the body
Label a diagram of the kidney (to illustrate the renal cortex, renal medulla, renal pyramid, renal pelvis, major and minor calyces, renal artery and vein and the ureter)
Label a diagram of a nephron (to illustrate the afferent and efferent arteriole, glomerulus, glomerular capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct)

3. Objectives
List and briefly explain the three stages in the process of urine formation
State the main role of ADH and aldosterone in the formation of urine
List the main constituents of normal urine
State the average urine output daily
Briefly discuss the importance of the kidney in relation to homeostasis

4. Main function of the Kidney
The main function of the urinary system is: Elimination of water-soluble substances
Each day the kidneys filter >150L of fluid from the blood plasma
Most of this fluid (containing vital constituents such as electrolytes, nutrients and water) is recovered by the kidneys and returned to the blood
This leaves only 1 - 2L of fluid (containing water soluble waste) to be excreted as urine

5. There are 2 kidneys,
situated at the back of the abdomen

6. The kidneys and homeostasis
The kidneys are regulatory organs that function to maintain a normal body state under variations in the environment (homeostasis) Which of the graphs best represents homeostasis?

8. The Nephron
Functional unit of the kidney is the nephron (about one million nephrons in each kidney)

10. Formation of Urine
Three Phases:- 1. Glomerular Filtration 2. Selective Reabsorption 3. Secretion

11. Glomerular Filtration
What you think will happen to water and other small (water soluble) molecules such as glucose, water, salts, urea?
Answer: They will be forced into glomerular capsule

12. Glomerular Filtration
What will happen to large molecules (such as blood cells and plasma proteins)?
Answer: They will remain in the capillary

13. Glomerular Filtration
good blood flow
high capillary pressures
Capillary wall
Capsule wall
Fluid in here = FILTRATE
Tubule
Peritubular capillary

14. Reabsorption
An extensive network of capillaries around the renal tubules provides a large surface area for contact

15. Reabsorption
How essential substances are recovered by the body (and not lost in the urine) = Reabsorption This will be achieved by re-absorption (or not) of constituents from the filtrate in the tubules to the blood in the peri-tubular capillaries Purpose of re-absorption is to reabsorb filtrate constituents needed by the body to maintain fluid and electrolyte balance and blood alkalinity

16. Formation of Urine: Re-absorption
Peritubular capillary
Tubule
The function of re-absorption is to:
Retain substances that are needed by the body
E.g. glucose, amino acids, water, salts

17. Reabsorption
What of the substances in the Filtrate would the body want to recover:
Completely?
Partially?
Not at all?

18. Reabsorption Complete reabsorption
Some constituents of the GF are completely reabsorbed (actively) unless present in excessive quantities
This is because they are needed by the body e.g. glucose 100% absorbed

19. Reabsorption Partial Reabsorption
The re-absorption of some substances varies according to the need e.g. Water and salts
Anti Diuretic Hormone (ADH) regulates the amount of water reabsorbed by the kidney

20. Reabsorption Increased blood concentration 
Detected by hypothalamus 
Secretion of ADH 
ADH released by the pituitary 
More water reabsorbed 
Decreased urine output and
Decreased blood concentration

21. Reabsorption Partial Reabsorption
The hormone aldosterone increases re-absorption of sodium by the kidney (water follows)
This will lead to a decreased urine output

22. Reabsorption No reabsorption
Waste products are absorbed only to a slight extent (e.g. UREA) or not at all (e.g. CREATININE)
Urea is the chief nitrogenous waste of mammals.
Creatinine is a break-down product of creatine phosphate in muscle, and is usually produced at a fairly constant rate by the body.

23. The urea cycle Breakdown of amino acids (deamination)  Ammonia
Ammonia is extremely toxic!
The liver contains enzymes
which quickly converts the
ammonia into urea.
(less toxic than ammonia)
Urea is removed efficiently by the KIDNEYS

24. Recap – Filtration and Reabsorption

25. Secretion
How excess waste (and / or toxic substances) is removed from the blood and added to the urine = Secretion
Addition of substances from the blood stream to the filtrate e.g. some drugs and H+ ions
Functions of secretion is to eliminate waste and maintain blood pH

26. Formation of Urine: Secretion
Peritubular capillary
Toxins, Drugs, Waste, H+
Tubule
The function of secretion is to:
* Remove substances that are toxic
* Maintain acid-base balance
Secretion is the opposite of re-absorption
Filtrate Urine  Bladder

27. Filtration, Reabsorption, Secretion

29. Normal amounts and constituents of urine
H2O L/day - average ?? mls/day – minimum 30 – 40 mls/hr - minimum Urea Creatinine Uric acid Na+, K+, Mg++

30. Formation of Urine: Filtration
Blood cells
Glomerular blood
Plasma proteins
Small molecules
Capillary wall
Capsule wall
Fluid in here = FLTRATE
Tubule
Peritubular capillary

31. Formation of Urine: Re-absorption
Peritubular capillary
Tubule
The function of re-absorption is to:
Retain substances that are needed by the body
E.g. glucose, amino acids, water, salts

32. Formation of Urine: Secretion
Peritubular capillary
Toxins, Drugs, Waste, H+
Tubule
The function of secretion is to:
* Remove substances that are toxic
* Maintain acid-base balance
Secretion is the opposite of re-absorption
Filtrate Urine  Bladder

33. Elimination of Urine: Micturition
Kidneys
Ureters
Bladder
Urethra

34. Case Study 1
Callum is 12 months old and has been having very loose stools for a couple of days.
What effect is this likely to have on his fluid balance?
What mechanisms should enable homeostasis to be maintained?
What advice would you give his mother?

35. Case Study 2
Stephen is 21 years old and has been drinking excessive amounts of alcohol!
How does alcohol effect his fluid balance?
What advice would you give him to maintain homeostasis and health?
What problems might you encounter in giving such advice?
What strategies are in place to reduce the amount of alcohol consumed by young people?

36. Case Study 3
Sarah has been taking Clozapine to control the symptoms of her schizophrenia.
Her CPN visits her and she confides in him that her housemates are stealing her possessions during the night and have also been trying to poison her.
She has started locking her door and is refusing to eat anything unless it is sealed and she has bought it herself from the local shop.
The CPN suspects that Sarah has been taking cannabis (she has a history of drug abuse).
How might the mental health team establish if Sarah is experiencing drug induced psychosis?
What other possible explanations are there for this situation?

37. Case Study 4
Caroline is 29 and expecting twins. She is 30 weeks into her pregnancy.
She visits the clinic for a routine assessment.
The nurse does a urine tests and finds that there is protein present in Caroline’s sample.
Should there be protein in Caroline’s urine?
If not, why not?
Does this indicate a problem with Caroline’s kidneys?
Where else might the protein have come from?

38. Case Study 5
Mrs Evans (who is 65 years of age) has Non Insulin Dependent Diabetes Mellitus (NIDDM).
She regularly tests her blood glucose levels.
This morning, after breakfast, it was 9mmol/L.
Would you expect her urine to contain glucose? (explain your answer)
After lunch it was 12mmol/L.
Now would you expect her urine to contain glucose? (explain your answer).
What are the implications in terms of urine testing for people with diabetes?