Urinary system

Announcements
- Urinary system
- Lab Practical Week after Spring Break
- Practical Review this Sunday 23rd at 3-5 pm

Functions of Urinary System
- Kidneys carry out four functions:
(a) Filter nitrogenous wastes, toxins, ions, etc. from blood to be excreted as urine.
(b) Regulate volume and chemical composition of blood (water, salts, acids, bases).
(c) Produce regulatory enzymes.
(d) Renin – regulates BP/ kidney function                                                           (e) Erthropoeitin – stimulates RBC production from marrow.
(f) Metabolism of Vitamin D to active form.

Urinary System

(a) Two Kidneys
- Perform all functions except actual excretion.

(b) Two Ureters
- Convey urine from Kidneys to Urinary Bladder

(c) Urinary Bladder
- Holds Urine until excretion

(d) Urethra
-  Conveys urine from bladder to outside of body

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Kidney general info
- Lie against posterior abdominal wall at level of T12-L3.
- Right kidney is lower than left kidney due to the shape of the liver.
- Lateral surface of kidney is convex while medial is concave : (a) Concave side has a cleft - Renal Hilus  (b) Inside hilus is Renal sinus - Where kidneys receive renal vessels and nerves.

Kidney External Anatomy
- Average size – 12cm x 6cm x 3 cm
- Weights 150 grams or 5 oz
- Surrounded by three membranes (deep to superficial) : (a) Renal capsule – fibrous barrier for kidneys (b) Adipose capsule – fatty tissue designed for protection / stability (c) Renal fascia – dense fibrous CTP anchors kidneys/ adrenals/ membrane 1 and 2 to surroundings.

Kidney Anatomy
- Renal arteries and veins
- Renal cortex
- Renal medulla
- Nephron
- Renal pyramids (6-10)
- Renal papilla
- Calyx (ces)
- Renal pelvis
- Ureter

Nephron
- Blood processing unit which serves to produce urine
- 1 million per kidney
- Consists of a glomerulus and tubules

Urinary system : Kidney and Nephron

Urine Formation III

Countercurrent Multiplication in the Nephron Loop:

(a) Descending limb
- Goes into medulla  - increasing salt gradient
- Water leaves
- Fluid concentrates

(b) Ascending limb
- Goes up toward cortex - decreasing salt gradient
- Na+ pumped out
- Fluid relatively diluted

Urine Formation IV
- Collecting duct
- Travels down into medulla
- Water leaves tubule and enters blood
- Urine becomes concentrated and enters renal papilla
- ADH controls water channel
- ADH – Antidiuretic hormone

Urine Formation : Micturition

(a) Ureters

- 25 cm long

- Enters on the floor of bladder

(b) Urinary Bladder

- Muscular sac on floor of pelvic cavity

- Muscle layer formed by detrusor muscle

- Average bladder volume is 500 ml

- Max capacity is 700-800 ml

(c) Urethra

- Conveys urine out of body

- Female urethra – 3 - 4 cm

- Opens into external urethral oriface

- Lies between vaginal oriface and clitoris

- Male urethra – 18 cm

- 3 regions:
(i) Prostatic urethra – 2.5 cm
(ii) Membranous urethra – 0.5 cm
(ii) Penile urethra – 15 cm

Kidney stones

- A hard granule of calcium, phosphate, uric acid and protein.

- Form in renal pelvis and get lodged in pelvis or ureter.

- Caused by urinary tract infections, dehydration, pH imbalances, or an enlarged prostate gland.

- Treated with stone dissolving drugs, surgical removal, or lithotripsy (ultrasonic vibrations).