1. Human Form & Function
The urinary system

2. Urinary system
The major structural components of the urinary system are:
Kidneys
Urinary bladder
Ureters
Urethra

3. Urinary system Function
To rid the body of wastes, especially nitrogenous wastes such as urea.
To regulate the balance of fluid, salt & pH.
The blood is filtered as it passes through the kidneys.
Waste substances are removed by the processes of filtration and tubular secretion.
Useful substances are returned to the body by the process of selective re-absorption.

4. The kidneys The functional unit of the kidney is the nephron
A nephron consists of a Bowman’s capsule, a renal tubule and the associated blood supply.
It filters waste products out of the blood
Each kidney contains about 1.2 million nephrons
2/23/2019
3HBS

5. The kidney Proximal convoluting tubule Glomerulus Capsule Cortex
Distal convoluting tubule
Medulla
Renal artery
Collecting duct
Renal vein
Loop of Henle
Renal pelvis
Capillaries
Ureter
KIDNEY
A NEPHRON

6. The kidneys Renal medulla – loops of Henle Renal artery Renal vein
Renal cortex – Bowman’s capsules
Ureter –
to the bladder
2/23/2019
3HBS

7. The nephron Common collecting duct Bowman’s capsule Renal corpuscle
Distal convolute tubule
Proximal convolute tubule
Loop of Henle

8. The renal corpuscle Filtration takes place in the renal corpuscle.
The renal corpuscle consists of the Bowman’s capsule and a mass of blood capillaries – the glomerulus.

9. The renal corpuscle Afferent arteriole Efferent arteriole
Bowman’s capsule
Glomerulus
Proximal convolute tubule

10. Filtration
Filtering the blood is a passive process and occurs under high pressure.
The filtrate includes:
Water
Urea
Glucose
Amino acids
Vitamins
Salts (sodium & chlorine)

11. Microscopic section through a kidney
Glomerulus
Tubule

12. Photograph of a glomerulus taken with a scanning electron microscope
Capillaries of the glomerulus
Wellcome Images – David Gregory & Debbie Marshall

13. Re-absorption water salts water glucose amino acids urine vitamins
Not all substances in the filtrate are waste products
The nephron re-absorbes needed nutrients
These include:
water
glucose,
amino acids
vitamins
salts
salts
water
glucose
amino acids
vitamins
urine
- water
- urea
- salts

14. Section through a renal tubule taken with a scanning electron microscope
Wellcome Images – David Gregory & Debbie Marshall

15. The proximal tubule
Microvilli line the proximal convolute tubule and create a brush border
This greatly increases the surface area for re-absorption.
Microvilli
L Slomianka ANHB - UWA

16. Re-absorption Structure Substance Active/passive
Proximal convolute tubule
Water (60-70%)
Passive (osmosis)
Salts (60-70%)
Glucose (100%)
Amino acids (100%)
Vitamins (100%)
Active transport
Loop of Henle
Water (25%)
Na+/Cl- (25%)
Distal convolute tubule
Water (5%)
Na+/Cl- (5%)
Collecting duct

17. Tubular secretion
Wastes are transfered from the blood into the tubules for excretion
This is an active process H+
NH4+ (ammonium)
Creatinine
Toxins
Drugs
Neurotransmitters

18. Tubular secretion Process Structure Substance Mode Tubular secretion
Proximal collection tubule (PCT)
Distal collection tubule
(DCT) H+
NH4+ (ammonium)
Creatinine
Toxins
Drugs
Neurotransmitters
Active transport
Creatinine is a chemical waste molecule that is generated from muscle metabolism.

19. Filtration – a summary
Blood enters the glomerulus (Bowman’s capsule) under high pressure.
Water and other small molecules are forced out of the blood vessels
This filtrate is collected and passes through several tubules
Some water and useful substances are reabsorbed
The rest passes through to the ureters and is stored in the bladder for excretion
2/23/2019
3HBS

20. Filtration Re-absorption + Tubular secretion Excretion
Filtration – a summary
Filtration Re-absorption + Tubular secretion Excretion
Renal cortex
Renal medulla

21. Deamination
Definition: The stripping of nitrogen from amino acid & nitrogen bases (RNA)
Deamination occurs in the liver
Nitrogen occurs in the amino (NH2) part of an amino acid.
Nitrogen is toxic to the human body and must be removed.
The amino group
Alanine

22. Deamination – chemical reaction
Amino acid → ammonia + organic compounds (used for respiration)
Ammonia (very toxic) + CO2 → urea (H2NCONH2)

23. Nitrogen wastes Nitrogen compound Source Amount Relative toxicity Urea
Amino Acids
21 g/day
Moderate
Creatinine
Muscle metabolism
1.8 g/day
High
Uric acid
RNA
480mg/day
Weak

24. Urine
Urine is a clear, transparent fluid. It normally has an amber colour.
It is collected in the bladder and eliminated through the urethra.
The average amount of urine voided in 24 hours is about 1,200 cm3.

25. Composition of urine
The composition of urine varies but typically contains:
95% water
5% other
solutes (organic molecules)
urea
creatinine
uric acid
ions
sodium & chloride ions
other metabolic wastes.

26. Elimination vs. excretion
Elimination is the removal of undigested food and waste from the body.
Excretion is the removal of metabolic waste produced by cells from the body

27. Kidney Failure
Most kidney diseases affect the glomeruli which reduces their ability to filter the blood (proteins and RBCs will be present in urine)
Some lifestyle measures to reduce the risk of kidney damage include:
Maintain a healthy weight
Don’t smoke
Drink plenty of water
Alcohol only in moderation
Kidney failure is when kidneys lose their ability to
excrete waste and control the level of fluid in the
body.
23/02/2019
Stage 2 HBS: Excretory System

28. Dialysis
Dialysis is a method of removing wastes from the blood when kidney failure occurs. There are two types of dialysis
peritoneal dialysis
haemodialysis
23/02/2019
Stage 2 HBS: Excretory System

29. Peritoneal dialysis
Peritoneal dialysis occurs inside the body using the peritoneum (a membrane that lines the inside of the abdominal cavity and covers organs such as stomach, liver and intestines)
A fluid containing glucose and other substances at concentrations similar blood (and no wastes) is pumped via catheter into the abdominal cavity.
Because of the concentration gradient wastes diffuse from the blood into the fluid in the abdominal cavity, useful products stay in the blood as there is not concentration gradient.

30. Peritoneal dialysis Peritoneal dialysis is usually done each day
23/02/2019
Stage 2 HBS: Excretory System

31. Haemodialysis
Haemodialysis involves passing blood through an artificial kidney or dialysis machine
The blood is passed through many tubes made of differentially permeable membrane and immersed in a bath of fluid.
The concentration of substances in the fluid bath are similar to those in the blood (fluid has no waste)
Due to concentration gradient wastes are passed from the blood into the fluid, useful substances remain in blood (no concentration gradient)
23/02/2019
Stage 2 HBS: Excretory System

32. Haemodialysis Haemodialysis is done for 4 to 5 hours per week.
23/02/2019
Stage 2 HBS: Excretory System