1. Urinary System
Nestor T. Hilvano, M.D., M.P.H.

2. Learning Objectives List the functions of the kidneys.
Identify the external and internal features of the kidney.
Trace the flow of blood through the kidney.
Describe the nephron and state the function of each segment.
Describe the glomerular filtration membrane and explain the factors that influence glomerular filtration rate.
Name the major nitrogenous waste and identify their sources.
Describe how the tubules reabsorb solutes.
Describe how the tubules secrete solutes from the blood into the tubular fluid.
Explain how the ADH and aldosterone regulate the volume and concentration of urine.
Describe the composition and properties of urine.
Describe the functional anatomy of the ureters, urinary bladder, and urethra.
Discuss micturation reflex and the regulation of urination.

3. Urinary System Major Functions Excretion (removal)
Elimination (discharge)
Homeostatic regulation
- blood volume and solute concentration, acid base balance
What are the organs of urinary system?
What is micturation?

4. Anatomy of Kidney Position Shape CT coverings level of T12 to L3
lateral surface - convex; medial - concave
CT coverings
Renal fascia: outer layer of dense fibrous tissue, binds to abdominal wall
Perinephric fat capsule: cushions kidney
Renal (fibrous) capsule: encloses kidney

5. Anatomy of Kidney
____ – outer part, reddish brown and granular
____ - inner part, consist of triangular structures called ____.
____ - consists of pyramid, overlying cortex, and renal columns; site of urine production
a. renal lobe c. renal cortex
b. renal medulla d. renal pyramid

6. Nephron and Collecting System
Nephron – functional/structural unit of kidneys (urine formation); consists of:
Renal corpuscle- made up of Bowman’s capsule and glomerulus; function = filtration
PCT- reabsorb organic nutrients, water, and electrolytes
Loop of Henle- descending loop= reabsorb water; ascending loop=reabsorb salts
DCT- last segment; function= secrete waste products, reabsorb water
Collecting system: Collecting (ducts) tubules, papillary duct, minor calyx, major calyx, renal pelvis, ureter, urinary bladder, urethra

7. Nephrons Cortical nephrons (85%) Juxtamedullary nephrons (15%)
short nephron loops
efferent arterioles branch off peritubular capillaries
Juxtamedullary nephrons (15%)
long nephron loops
efferent arterioles give rise to vasa recta

8. Renal corpuscle Bowman capsule Glomerulus
Filtration is passive (metabolic waste, excess ions, and small solutes)
Filtration membrane consists of fenestrated endothelium, lamina densa, and filtration slits
Why plasma proteins are not filtered under normal condition?

9. Renal Tubule Proximal convoluted tubule
Reabsorption of organic nutrients, ions, and water from filtrate
Nephron loop; descending and ascending limbs
thick segment = active transport of salts out of the tubule
thin segment = water permeable (out)
Distal convoluted tubule
active secretion of ions, drugs, acids, and toxins into tubular fluid for excretion
selective reabsorption of sodium, calcium, water

10. Juxtaglomerular Complex
JG cell= secrete renin
Macula densa = monitor salinity
Mesangial cell= release erythropoitin
Damage to JG complex – interfere w/ hormonal control of BP

11. Glomerular Filtration Rate (GFR)
Basic process of urine formation: filtration, reabsorption, and secretion (excretion)
Filtrate formed per minute
GFR = NFP x Kf = 125 ml/min or 180 L/day
filtration coefficient (Kf) depends on permeability and surface area of filtration barrier
99% of filtrate reabsorbed, 1 to 2 L of urine per day excreted

12. Effects of GFR Abnormalities
GFR, urine output rises  dehydration, electrolyte depletion
GFR  wastes reabsorbed (azotemia possible)
GFR controlled by adjusting glomerular blood pressure
Autoregulation (local response): GFR – paracrine secretion - constriction of afferent arteriole - GFR
Autonomic regulation (sympathetic control)
Hormonal regulation (kidneys): renin and angiotensin

13. DCT and Collecting Duct
involved in salt/water balance; acid/base balance
Function = fluid reabsorption is variable, regulated by hormonal action
Aldosterone effects
 BP  renin release  angiotensin II formation (in the capillaries of lungs)
angiotensin II stimulates adrenal cortex
adrenal cortex secretes aldosterone
promotes Na+ reabsorption  promotes water reabsorption   urine volume  maintains BP

14. DCT and Collecting Duct
Effect of ADH
dehydration stimulates hypothalamus
hypothalamus stimulates posterior pituitary to release ADH
 water reabsorption
 urine volume
ADH hyposecretion results to diabetes insipidus

15. DCT and Collecting Duct
Atrial natriuretic peptide (ANP)
atria secrete ANP in response to  BP
has four actions:
dilates afferent arteriole, constricts efferent arteriole -  GFR
inhibits renin/angiotensin/aldosterone pathway
inhibits secretion and action of ADH
inhibits NaCl reabsorption
Promotes Na+ and water excretion,  urine volume,  blood volume and BP

16. Control of Water Loss Producing hypotonic urine
NaCl reabsorbed by cortical CD
water remains in urine
Producing hypertonic urine
dehydration   ADH   CD’s water permeability
more water is reabsorbed
urine is more concentrated

17. Countercurrent Multiplier: Nephron loop
Recaptures NaCl and returns it to renal medulla
Descending limb
reabsorbs water
concentrates tubular fluid
Ascending limb
reabsorbs Na+, K+, and Cl-
tubular fluid becomes hypotonic

18. Countercurrent Exchange System
Formed by vasa recta
provide blood supply to medulla
Descending capillaries
water diffuses out of blood
NaCl diffuses into blood
Ascending capillaries
water diffuses into blood
NaCl diffuses out of blood

19. Composition of Urine
Appearance – clear yellow; yellow color due to urobilin pigment (generated in kidneys from urobilinogens)
Odor – varies; bacteria degrade urea to ammonia
Specific gravity - ranges from
Osmolarity - ranges from 855 to 1,335 mOsm/L
pH - range: , usually 6.0
Chemical composition: 93% to 97% water, 5% solutes by volume (urea, NaCl, KCl, creatinine, uric acid)
Urine volume – 1 to 2 L/day
Polyuria > 2L/day; Oliguria < 500 mL/day;
Anuria - 0 to 100 mL/day
Hematuria- presence of blood in the urine

20. Diuretics Effects Uses Mechanisms of action ____ urine output
____ blood volume
Uses
hypertension and congestive heart failure
Mechanisms of action
____ GFR
____ tubular reabsorption
Increase
Decrease

21. Ureter and Urinary Bladder
Ureter (about 25 cm long)
3 layers
mucosa
muscularis
Adventitia
___ Where is the common site of obstruction of urine
flow?
Urinary bladder- located in pelvic cavity, posterior to pubic symphysis
- Histologic features of bladder = thick muscular layer
(detrusor muscle); capacity (500 ml. moderately full; ml. maximum)
___ What is urinary trigone?

22. Male Urethra Male Urethra Female Urethra 18 cm long
Internal urethral sphincter
External urethral sphincter
3 regions: _______, _______, _______
Female Urethra
3 to 4 cm long

23. Micturition 200 ml urine in bladder, stretch receptors send signal to
sacral spinal cord (S2-S4)
Signals ascend to cortex
Signals descend to
stimulate parasympathetic neurons
Result = urge to urinate
Contraction of detrusor muscle
relaxation of internal urethral sphincter
External urethral sphincter – voluntary control
How incontinence may develop in elderly?

24. Homework (Self-review)
Define the following: kidney, ureters, urinary bladder, urethra, glomerular filtration, tubular reabsorption, tubular secretion, nephron, renal lobe, nephrolithiasis, micturation, incontinence, polyuria, and anuria.
Name the structure involves in the following: filtration of solutes and water, reabsorption of salt and secretion of K+, countercurrent multiplier, countercurrent exchange system, temporary storage of urine, urine formation, release renin.
Discuss the effect/s of renin- angiostensin- aldosterone on GFR, tubular reabsorption, and urine output.
Identify the structures in renal cortex and medulla.
Identify parts of nephron and collecting system.
Describe the normal properties of urine.