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. Urinary Bladder Accumulates, stores urine
Stretchable epithelium, w/ smooth muscle (detrusor)
Internal urinary sphincter
Involuntary, circular muscle
Keeps ureter closed
Can hold up to 1 liter of urine
Stretch receptors signal need to void (micturate) when 20% of bladder capacity reached

8. Urethra Single, muscular tube
Controlled by external urethral sphincter
Voluntary
Longer in males
More prone to infection in females

9. Voiding Urination = micturition
Innervated by reflex arc; voluntary control gained as one ages
Incontinence – loss of voluntary control
Anuria – lack of urine production
Urinary retention – failure to expel urine
Oliguria – decreased urine production
Polyuria – excessive urine production

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

12. Microscopic Structure of the Kidney

13. Microscopic Structure of the Kidney

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

15. 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

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

17. Formation of Urine

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

19. 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

20. 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

21. 180 L of urine a day?
No…
Luckily, most of the fluid that leaves blood during filtration returns to the blood during reabsorption…

22. 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)

23. Mechanism? Several… Active transport Passive Transport
Active transport of sodium ions from tubule into interstitial fluid
Passive Transport
Creates high concentration of sodium, which diffuses into bloodstream
Sodium (Na+) in blood attracts negative ions (Cl-, (PO4)3-), which diffuse into blood

24. Another Mechanism? Osmosis! (Flow of water from High to Low)
Attracted to blood due to ion flow

25. Another, another Mechanism?
Facilitated Diffusion
Amino acids
Glucose
Cotransported/symported with sodium
Almost all glucose reabsorbed (340 mg/min)
Exceptions exist!
Diabetes mellitus – too much sugar in bloodstream, exceeds ability of kidney tubule cells to reabsorb (not enough Na+ to cotransport)
glycosuria (glucose in blood)
Water is lost along with glucose transport… most people with diabetes mellitus urinate excessively!

26. Loop of Henle Descending loop:
Reabsorbs water (20%), large ions and molecules
Ascending loop:
Active transport of Na, Cl ions

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

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

29. Regulation of Urine Formation

30. Regulation Regulated by hormones
Antidiuretic hormone (ADH) – increases water reabsorption from collecting duct into bloodstream
Angiotensin II – constricts efferent, systemic arterioles – alters filtration rate, increases pressures
Aldosterone – Produced by adrenal cortex; retains sodium, excretes potassium – raises blood pressure by incr. water absorption in DCT, Collecting duct
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

31. 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)