1. Urinary System
An overview

2. Functions of the Urinary System

3. Functions of the Urinary System
Produces, excretes urine
Essential for homeostasis
Keeps volume of bodily fluids constant
Keeps levels of essential chemicals constant
Electrolytes, water, acid/base balance
“Clears” (cleans) blood of waste products produced by cellular metabolism (e.g. nitrogenous wastes)
Uremia- toxic buildup of metabolic wastes
Blood pressure regulation

4. Characteristics of Urine
Normal Characteristics
Color:
Transparent yellow, amber, straw-colored
Compounds
Mineral ions (Na+, Cl-, K+)
Nitrogenous wastes (ammonia, creatinine, urea, uric acid)
Suspended solids (sediment, bacteria, blood cells, casts)
Urine pigments
Odor
Slight odor pH
Specific gravity

5. Structures of the urinary system (Macroscopic)

6. Major structures of the urinary system
Kidney
Retroperitoneal
Ureters
Urinary Bladder
Urethra

7. The Kidney Renal cortex – Outer “bark” Renal medulla – Inner
Renal pyramids
Triangular divisions
Renal columns
Divide pyramids
Renal papilla
Narrow, innermost point of a pyramid
Renal pelvis
Expanded end of upper end of ureter
Calyx
Division of renal pelvis

8. Microscopic Structure of the Kidney

9. Microscopic Structure of the Kidney

10. Functional Unit: Nephron
> 1 million in a kidney
Can be cortical or juxtamedullary
“Tiny funnel” with a very long stem
Highly convoluted (many bends)
2 principal components:
Renal corpuscle
Renal tubule

11. Renal corpuscle components
Bowman’s capsule
Cup/sac-like-shaped top of a nephron
Glomerulus
Ball of capillaries, lined with podocytes
Found in Bowman’s capsule
Afferent, efferent arterioles

12. Renal Tubule Composed of: Proximal convoluted tubule (PCT)
Loop of Henle (longer in Juxtamedullary)
Distal convoluted tubule (DCT)
Collecting tubule

13. Formation of Urine

14. Formation of Urine: Overview
Filtration
Secretion
Reabsorption
All occur within the functional unit of the kidney, the nephron

15. Filtration
Of water, dissolved substances out of blood into Bowman’s capsule
Occurs in “renal corpuscles”
Contains larger afferent, smaller efferent arterioles
Creates high pressure in glomerulus
Filters blood across fenestrated capillaries, lined w/ podocytes
Hold in proteins, cells
Lose water, ions = ultrafiltration

16. Glomerular Filtration Rate
120 ml/minute = 180 liters/day!
Must maintain a minimum blood pressure for kidneys to filter
Hemorrhage, etc., can cause kidney function (and urine output) to cease

17. 180 L of urine a day?
No…
Luckily, most of the fluid that leaves blood during filtration returns to the blood during reabsorption…

18. Reabsorption
Movement of substances out of renal tubules into the blood (into peritubular capillaries)
Water
Glucose
Other nutrients
Sodium, other ions
Begins in proximal convoluted tubule, continues in loop of Henle, distal convoluted tubule, and collecting tubule
Reabsorb ~178 L/day (97-98% of water)

19. Mechanism? Osmosis! (Flow of water from High to Low) Glucose:
Almost all glucose reabsorbed (340 mg/min)
Exceptions exist!
Diabetes mellitus – too much sugar in bloodstream, exceeds ability of kidney tubule cells to reabsorb
glycosuria (glucose in blood)
Water is lost along with glucose transport… most people with diabetes mellitus urinate excessively!

20. Ions (sodium, others) only partially reabsorbed
Most are actively transported back into blood from tubular urine
Amount varies from time to time… depends on salt intake
Allows body to maintain homeostasis (cells can be damaged by too much/too little salt)

21. Loop of Henle Descending loop:
Reabsorbs water, large ions and molecules
Ascending loop:
Final adjustment
Hormones regulate the amount of sodium, water reabsorption

22. Water reabsorption
90% passive thru osmosis in PCT, descending Loop of Henle, DCT
10% occurs in last parts of DCT, collecting ducts

23. Secretion
Substances move into urine in distal, collecting tubules from blood in capillaries around tubules
“Reabsorption in reverse”
H+, K+ ions, ammonia, drugs
(Bold = active transport; non-bold = diffusion)

24. Regulation Regulated by hormones
Antidiuretic hormone (ADH) – increases water reabsorption
Angiotensin II – constricts efferent, systemic arterioles – alters filtration rate, increases pressures
Aldosterone – Produced by adrenal cortex; retains sodium, excretes potassium – raises blood pressure
Affected by other substances
Diuretic (causes great outflow of urine)
Caffeine –decreases Na+ absorption, causing diuresis
Lasix – works on Loop of Henle, producing massive diuresis

25. Excretion Urine stored in bladder, leaves body through urethra A.k.a…
Urination
“Voiding”
Micturation
Urine stored in bladder, leaves body through urethra

26. Concentration
Glomerulus “squeezes” blood out into the Bowman’s capsule
Fenestrated inner lining
Podocytes, w/ small holes, trap small proteins
Filtrate runs across the capsule into the proximal convoluted tubule (PCT)
PCT lined with BV’s that reabsorb nutrients from it, excrete wastes into it.
PCT passes filtrate downward through loop of Henle, then back up
Juxtamedullary nephrons extend deep into the medulla, have much longer loops of Henle
Tubular Reabsorption –
Urine in tubules must be reabsorbed to prevent dehydration
Solutes are actively and passively reabsorbed (glucose, aa’s, sodium, chloride, potassium, phosphate, bicarbonate)