1. The Urinary System

2. The Urinary System Paired kidneys A ureter for each kidney
Urinary bladder
Urethra

3. Main Functions of Urinary System
Kidneys filter blood to keep it pure
Toxins
Metabolic wastes
Excess water
Dispose of nitrogenous wastes from blood
Urea
Uric acid
Creatinine
Regulate the balance of water and electrolytes, acids and bases

4. Kidneys are retroperitoneal organs (see next slide)
Superior lumbar region of posterior abdominal wall
Lateral surface is convex
Medial surface is concave
Hilus* is cleft: vessels, ureters and nerves enter and leave
Adrenal glands* lie superior to each kidney
(the yellow blob in pic) * *

7. Transverse sections show retroperitoneal position of kidneys
Note layers of adipose (fat), capsule, fascia
Transverse sections show retroperitoneal position of kidneys
Note also: liver, aorta muscles on CT

9. Kidney has two regions Cortex: outer Medulla: inner
Columns of cortex divide medulla into “pyramids”
Medulla: inner
Darker, cone-shaped medullary or renal pyramids
Parallel bundles of urine-collecting tubules

10. The human kidney has lobes
Pyramid and cortical tissue surrounding it
5-11 per kidney
Renal pelvis (=basin)
Expanded, funnel shaped, superior part of ureter
Branches to form two or three major calices (seen best on right pic below)
Each of these divides again, minor calices: collect urine from papillae of pyramids

11. The Arteries Aorta gives off right and left renal arteries
Renal arteries divides into 5 segmental arteries as enters hilus of kidney

12. Vasculature of the kidney
The glomerular capillary bed is unusual in having arterioles going both to it and away, from it, instead of a vein going away as most. (Afferent means going toward something and efferent means going away)

13. Understand at least this much:
Filtration
a. Fluid is squeezed out of the glomerular capillary bed
Resorption
b. Most nutrients, water and essential ions are returned to the blood of the peritubular capillaries
Secretion
c. Moves additional undesirable molecules into tubule from blood of peritubular capillaries

14. Nephron Functional Unit of the kidney
The structure that produces urine in the process of removing waste and filtering blood.
Bowman’s capsule is what holds the nephron inside the renal medulla
Glomerulus is a knot of capillaries
Show: Khan’s Academy (The kidney and Nephron)

15. For studying
Parts of the kidney: 1. Renal pyramid 2. Efferent vessel 3. Renal artery 4. Renal vein 5. Renal hilum 6. Renal pelvis 7. Ureter 8. Minor calyx 9. Renal capsule 10. Inferior renal capsule 11. Superior renal capsule 12. Afferent vessel 13. Nephron 14. Minor calyx 15. Major calyx 16. Renal papilla 17. Renal column

16. The Ureters
Slender tubes about 25 cm (10 “) long leaving each renal pelvis
One for each kidney carrying urine to the bladder

17. Ureters play an active role in transporting urine (it’s not just by gravity)
Three basic layers
Transitional epithelium of mucosa stretches when ureters fill
Muscularis
Inner longitudinal, outer circular layers
Inferior 3rd with extra longitudinal layer)
Stimulated to contract when urine in ureter: peristaltic waves to propel urine to bladder
Adventitia (external)

18. Urinary Bladder Collapsible muscular sac Stores and expels urine
Lies on pelvic floor posterior to pubic symphysis
Males: anterior to rectum
Females: just anterior to the vagina and uterus
See also brief atlas

22. If full: bladder is spherical and extends into abdominal cavity (holds about 500 ml or 1 pt)
If empty: bladder lies entirely within pelvis with shape like upside-down pyramid
Urine exits via the urethra
Trigone is inside area between ureters and urethra: prone to infection (see slide 25)

23. Bladder wall has three layers (same as ureters)
Mucosa with distensible transitional epithelium and lamnia propria (can stretch)
Thick muscularis called the detrusor muscle
3 layers of highly intermingled smooth muscle
Squeezes urine out
Fibrous adventitia

24. The Urethra Smooth muscle with inner mucosa
Changes from transitional through stages to stratified squamous near end
Drains urine out of the bladder and body
Male: about 20 cm (8”) long
Female: 3-4 cm (1.5”) long
Short length is why females have more urinary tract infections than males - ascending bacteria from stool contamination
urethra
Urethra____

25. Urethral sphincters Internal: involuntary sphincter of smooth muscle
External: skeletal muscle inhibits urination voluntarily until proper time (levator anni muscle also helps voluntary constriction)
Males: urethra has three regions (see right)
_________trigone
1. Prostatic urethra__________
2. Membranous urethra____
3. Spongy or penile urethra_____
female

26. With all the labels

27. Micturition center of brain: pons
AKA:
Voiding
Urinating
Emptying the bladder
Micturition center of brain: pons
(but heavily influenced by higher centers)
Parasympathetic Nervous system: to void
Sympathetic: inhibits micturition