1. The Urinary System

2. Functions of the urinary system
Homeostatic regulation of blood plasma
Regulating blood volume and pressure
Regulating plasma ion concentrations
Stabilizing blood pH
Conserving nutrients
Filter many liters of fluid from blood
Excretion - The removal of organic waste products from body fluids
Urea
Uric acid
Creatinine
Elimination - The discharge of waste products into the environment

3. Urinary System Kidneys – produce urine
Ureters –transport urine to bladder
Urinary bladder - stores urine
Urethra transports urine to exterior
Figure 26.1

4. Location and External Anatomy of Kidneys
Located retroperitoneally
Lateral to T12–L3 vertebrae
Average kidney
12 cm tall, 6 cm wide, 3 cm thick
Hilus
On concave surface
Vessels and nerves enter and exit
Renal capsule surrounds the kidney

5. Urinary System in Gross Dissection
Figure 26.3

6. Internal Gross Anatomy of the Kidneys
Frontal section through the kidney
Renal cortex
Renal pyramids
Renal pelvis
Major calicies
Minor calicies
Gross vasculature
Renal arteries
Branch into segmental arteries

7. Anatomy of the kidneys Superficial outer cortex and inner medulla
The medulla consists of 6-18 renal pyramids
The cortex is composed of roughly 1.25 million nephrons
Major and minor calyces along with the pelvis drain urine to the ureters

8. Nephron – The Functional Unit of Kidney
Nephron consists of:
Renal corpuscle
Renal tubule:
Proximal convoluted tubule (PCT)
Loop of Henle
Distal convoluted tubule (DCT)
Nephron empties tubular fluid into a system of collecting ducts and papillary ducts

9. Renal Corpuscle Consists of:
Glomerulus – tuft of fenestrated capillaries
Glomerular (Bowman’s) capsule
Parietal layer – simple squamous epithelium
Visceral layer – consists of podocytes
Blood travels from efferent arteriole to peritubular capillaries
Blood leaves the nephron via the efferent arteriole

10. Renal Corpuscle and the Filtration Membrane
Figure 23.6a

11. Glomerulus anatomy Podocytes cover lamina densa of capillaries
Project into the capsular space
Pedicels of podocytes separated by filtration slits

12. Two types of nephron Cortical nephrons Juxtamedullary nephrons
~85% of all nephrons
Located in the cortex
Juxtamedullary nephrons
Closer to renal medulla
Loops of Henle extend deep into renal pyramids

13. Nephron Proximal convoluted tubule (PCT) Loop of Henle
Actively reabsorbs nutrients, plasma proteins and ions from filtrate
Released into peritubular fluid
Loop of Henle
Descending limb
Ascending limb
Each limb has a thick and thin section

14. Nephron Distal convoluted tubule (DCT)
Actively secretes ions, toxins, drugs
Reabsorbs sodium ions from tubular fluid

15. Collecting Tubules (Collecting ducts)
Collecting tubules - Receive urine from distal convoluted tubules
Figure 23.8

16. Uriniferous Tubule
Figure 23.5a

17. Types Of Capillary Beds In Nephron
Glomerulus - Fed and drained by afferent and efferent arterioles
Peritubular capillaries
Arise from efferent arterioles
Low-pressure, porous capillaries
Absorb solutes
Vasa recta
Thin-walled looping vessels
Part of the kidney’s urine-concentrating mechanism

18. Mechanisms of Urine Production
Filtration - filtrate of blood leaves kidney capillaries
Reabsorption – most nutrients, water, and essential ions reclaimed
Secretion - active process of removing undesirable molecules

19. Microscopic Anatomy of the Kidney
Juxtaglomerular apparatus
Functions in the regulation of blood pressure
Juxtaglomerular cells – secrete renin
Macula densa
A portion of distal convoluted tubule
Tall, closely packed epithelial cells
Act as chemoreceptors

20. Summary of Nephron Function
Each segment of nephron and collecting system contribute
Glomerulus
PCT
Descending limb
Thick ascending limb
DCT and collecting ducts
Concentrated urine produced after considerable modification of filtrate

21. Urine Excretion Leaves Collecting System Enters renal pelvis
Rest of urinary system transports, stores and eliminates
Ureters
Bladder
Urethra

22. The Ureters Pair of muscular tubes
Extend from renal pelvis to the bladder
Peristaltic contractions force urine from the kidneys to the urinary bladder
Oblique entry into bladder prevents backflow of urine

23. Histology of Ureter Mucosa – transitional epithelium
Muscularis – two layers
Inner longitudinal layer
Outer circular layer
Adventitia – typical connective tissue

24. Urinary Bladder A collapsible muscular sac Stores and expels urine
Full bladder – spherical
Expands into the abdominal cavity
Empty bladder – lies entirely within the pelvis
Figure 23.13

25. Urinary Bladder Wall of bladder Mucosa - transitional epithelium
Muscular layer - detrusor muscle
Adventitia

26. The urethra
Extends from the urinary bladder to the exterior of the body
Passes through urogenital diaphragm (external urinary sphincter)
Differs in length and function in males and females
Internal urethral sphincter - involuntary smooth muscle
External urethral sphincter - voluntarily inhibits urination, relaxes when one urinates

27. Urinary Bladder and Urethra - Male
Males – 20 cm in length
Three named regions
Prostatic urethra - passes through the prostate gland
Membranous urethra - through the urogenital diaphragm
Spongy (penile) urethra passes through the length of the penis
Figure 23.16a

28. Urinary Bladder and Urethra - Female
In females - length of 3–4 cm
The smooth triangular region of the base is is called the trigone - many bladder infections persist in this region

29. Urethra Epithelium of urethra
Transitional epithelium at the proximal end (near the bladder)
Stratified and pseudostratified columnar – mid urethra (in males)
Stratified squamous epithelium at the distal end (near the urethral opening)

30. Micturition Bladder can hold 250 - 400ml
Greater volumes stretch bladder walls initiates micturation reflex:
Urination coordinated by micturition reflex
Initiated by stretch receptors in wall of bladder
Urination requires coupling micturition reflex with relaxation of external urethral sphincter

31. Blood Flow Through the Kidney