The Urinary System

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

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

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) * *

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

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

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

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

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)

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

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)

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

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

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)

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

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)

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

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____

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

With all the labels

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