The Urinary System

Topics: Kidney, Nephrology, Ureter Pages: 14 (3015 words) Published: September 25, 2010
The excretory (GUT) system includes the kidney, ureters, urinary bladder, urethra and the male and female genitalia [pic]The Kidney
• Two bean-shaped organs that lie in the retroperitoneal space on either side of the vertebral column at the level of T12 to L3 • Adrenal glands located on top of each kidney surrounded by capsule and fats • Right is lower than the left

• Each kidney is composed of:
- Renal parenchyma, Renal sinus and pelvis and Nephrons
Kidney: Major Functions
✓ C-ontrols electrolyte and fluid balance
✓ R-egulates homeostasis of blood and acid-base balance ✓ R-egulates RBC production
✓ E-liminates end products of metabolism,
✓ S-ecretes renin, parathyroid hormones and Vitamin D

The Kidney:
• Functional unit of the kidney that produces urine by filtration Blood Supply of the Kidney
• Renal artery- branch of the abdominal aorta

• Renal vein- drains into the inferior vena cava
The Ureters
• 2 long slender tubes 25-35cms long that extends from the renal pelvis to pelvic cavity where they enter the bladder and propels urine from the kidneys to the urinary bladder • Has smooth muscles and transitional epithelium and a uterovesical valve that prevents backflow of urine into ureters • Has innervations from the sympathetic and parasympathetic The Urinary Bladder

• Hollow pyramid shaped organ located in the pelvis behind the symphysis pubis • Composed of muscular, elastic tissue that makes it distensible • Serves as reservoir of urine (1 to 1.8L; moderately full bladder=500ml) • Lined with transitional epithelium

• Internal and external urethral sphincters control the flow of urine The Urethra
• Tube extending from the urinary bladder to the external urethral orifice 1. 3-5cms (1-2 inches) in females
2. 20 cms (8 inches) in males
• 3 Parts in Males
1. Prostatic urethra- most dilatable
2. Membranous urethra- least dilatable and shortest
3. Penile urethra- longest
Renal Physiology
Urine formation
1. Urinary blood flow
2. Glomerular filtration
3. Tubular reabsorption
4. Tubular secretion
Urine formation
Glomerular Filtration
• Ultrafiltration of blood by the glomerulus; beginning of urine formation • Requires hydrostatic pressure supplied by the heart and assisted by vascular resistance (glomerular hydrostatic pressure) and sufficient circulating volume • Pressure in Bowman’s capsule opposes hydrostatic pressure and filtration • If glomerular pressure insufficient to force substances out of the blood into the tubules filtrate formation stops • Glomerular Filtration Rate (GFR): amount of blood filtered by the glomeruli in a given time; normal is 125ml/min • Filtrate formed has essentially same composition as blood plasma without the proteins; blood cells and proteins are usually too large to pass the glomerular membrane Tubular Function

➢ The tubules and collecting ducts carry out the functions of reabsorption, secretion, and excretion ➢ Reabsorption of water and electrolytes is controlled by antidiuretic hormone (ADH), released by the pituitary, and aldosterone, secreted by the adrenal glands ➢ Proximal Convoluted Tubule

- reabsorption of certain constituents of the glomerular filtrate: 80% electrolytes and H2O, all glucose and amino acids, and bicarbonate; - secretes organic substances and wastes
➢ Loop of Henle
- reabsorption of water in the descending limb
- reabsorption of sodium and chloride in the ascending limb > descending limb - concentrates and then dilutes urine
➢ Distal Convoluted Tubule
- secretes potassium, hydrogen ions, and ammonia
- reabsorbs H2O (regulated by ADH and aldosterone) back into the tubule - reabsorbs bicarbonate
- regulates calcium and phosphate concentrations
➢ Collecting Ducts
- receives...
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