1. The Urinary System

2. The Problem – Nitrogenous Waste
As proteins and nucleic acids are catabolized, nitrogenous wastes, including ammonia, are produced in all animals.
NH3 (ammonia) is water-soluble, a strong base, and can change the pH of blood.
It must be eliminated!
From Beatrice the Biologist’s blog

3. How is Waste Eliminated?

4. Organs Kidneys – produce urine Ureters – transports urine to bladder
Urinary bladder – stores urine
Urethra – transports urine to exterior

5. Functions Primary Functions: Secondary Functions:
Eliminate metabolic wastes
Regulate blood volume
Regulate blood chemistry
Secondary Functions:
Metabolism of Vitamin D
Production of renin
Production of erythropoietin

6. Kidney Structure - External
Location: superior lumbar
Adrenal glands
Renal artery
Renal vein
Renal hilus
Renal capsule
Adipose capsule

7. Kidney Structure – Internal
Renal Cortex – superficial portion; urine formation
Renal Columns – extensions of cortex
Renal Medulla – deep to cortex
Medullary pyramids – stripes are due to collecting ducts

8. Kidney Structure - Internal
Renal Pelvis – funnel shaped tube; continuous with ureter
Calyces – cup-shaped extensions of the pelvis that enclose the tips of the pyramids

9. Formed in the renal cortex
Travels thru the collecting ducts in the renal medulla
Drips out of collecting ducts into the minor calcyes
Flows thru the major calyces
Flows thru the renal pelvis
Flows thru the ureter
Flows thru and is stored in the urinary bladder
Flows thru the urethra

10. Internal Kidneys – The Nephron
Glomerulus – blood pressure forces smaller molecules into
Bowman’s Capsule
Proximal convoluted tubule
Loop of Henle – concentrates urine
Descending loop
Ascending loop
Distal convoluted tubule
Collecting duct – transports urine to calyces
Capillaries – recapture needed molecules

11. Bowman’s Capsule & Glomerulus
High blood pressure in glomerulus causes nonselective, passive filtration
Any product smaller than proteins are forced out of blood & into capsule:
Water
Glucose
Salts
Nitrogenous wastes
Check out the size difference

12. Proximal Convoluted Tubule (PCT)
Reabsorption – Mainly active transport is used to reabsorb some nutrients : salt, water, glucose, amino acids
Secretion – Mainly active transport moves some unwanted materials into PCT: some poisons, hydrogen ions
Has lots of mitochondria & microvilli. Why?

13. Loop of Henle Concentrates urine Descending loop – permeable to water
Ascending loop – impermeable to water
Concentration gradient

14. Distal Convoluted Tubule (DCT) & Collecting Duct
DCT performs same role as PCT
Collecting duct receives urine from several DCT’s
Reabsorbs water, some urea (passive transport)
Reabsorbs salt (active transport)
Empties to calyx

16. Ureters & Bladder Urine flows through ureters due to:
Gravity
Smooth muscle
Bladder stores urine
Allows urine release to be discontinuous even though formation of urine is continuous.

17. Urethra & Control of Bladder
Female urethra is ~3-4cm long
Male urethra is ~20cm long
Internal urethral sphincter – smooth muscle, involuntary
External urethral sphincter – skeletal muscle, voluntary
Disorder: urinary tract infection (UTI)
More common in women than men

18. Micturition “Voiding,” or emptying the bladder
Voluntary control of an involuntary reflex
Steps
Bladder collects urine until reach ~200ml.
Stretch receptors activate, triggering bladder contraction reflexes
Urine is forced past the internal urethral sphincter into the upper part of the urethra, causing urge to void
If postponed, the reflex will occur again after another ml. are collected.

19. Urine Clear Pale to Deep yellow Slightly aromatic
Can be affected by food
Slightly more dense than water
Specific gravity – comparison of weight to that of water
pH is slightly acidic (~6)

20. Abnormal Urine Components

21. Homeostasis of Water & Electrolytes
ADH (antidiuretic hormone)
Prevents excessive water loss in kidney
Regulated by hypothalamus & secreted by posterior pituitary
Functions by making collecting duct more permeable to water

22. Homeostasis of Water & Electrolytes
Aldosterone
Normally, about 80% of sodium ions are reabsorbed in the PCT. When aldosterone is present, nearly all the rest is absorbed in the DCT & collecting duct.
Increases water reabsorption, because water follows salt.
Produced by adrenal cortex in response to renin-angiotensin mechanism triggered by low blood volume or pressure

23. Diuretics
Interfere with normal reabsorption, causing increased urination
Many drugs
Alcohol

24. Urinary Disorders – Kidney Stones