1. The Urinary System

2. System Overview Consists of: –Kidneys –Ureters –Urinary bladder –Urethra

3. System Functions Removes certain salts and nitrogenous wastes from blood Helps maintain normal concentrations of water and electrolytes within body fluids Regulates the pH and volume of body fluids Helps control red blood cell (RBC) production and blood pressure

4. Kidneys - Function Remove substances from the blood Form urine Help regulate some metabolic processes by secreting hormones: –Erythropoietin –Renin

5. Kidneys - Location Either side of the vertebral column In a depression on the posterior wall of the abdominal cavity Between 12 th thoracic and 3 rd lumbar vertebrae Left kidney is usually higher Behind the parietal peritoneum Held in place by CT and adipose

6. Kidney Structure Hilium Renal pelvis –Calyces Renal papillae Renal medulla Renal cortex –Nephrons

7. Kidney Blood Supply Renal arteries –From abdominal aorta –Branches in kidney to form afferent arterioles Renal veins –Join the inferior vena cava

10. Nephron Structure Renal corpuscle –Glomerulus –Glomerular (Bowman’s) capsule Renal tubules –Nephron loops (loop of Henle) –Dump filtrate into collecting ducts  calyces Efferent arteriole Peritubular capillaries

13. Urine Formation Urine is a product of nephron activity. It is formed by 3 processes: 1.Glomerular filtration 2.Tubular reabsorption 3.Tubular secretion

14. Glomerular Filtration Produces filtrate (mostly water) Pressure for filtration comes from blood pressure Filtrate is similar to blood plasma

15. Tubular Reabsorption Substances are transported out of the tubular fluid and into the peritubular capillaries Allows reabsorption of glucose, amino acids, creatine, lactic, citric, uric, and ascorbic acids, phosphates, sulfates, Ca++, K+, Na+, and water Urea Uric acid Gout

16. Tubular Secretion Substances move from the plasma in the peritubular capillary into the fluid of the renal tubule Mostly hydrogen and potassium ions

18. Urine Composition Reflects the amounts of water and solutes that the kidneys must eliminate or retain to maintain homeostasis Contains urea, uric acid, electrolytes, traces of amino acids Average urine volume 0.6- 2.5 L/day Volume depends on fluid intake, temperature, relative humidity, emotional state, respiratory rate, body temperature Abnormal components: –Glucose, proteins, hemoglobin, ketones, and blood cells

19. Urine Elimination Nephron  collecting ducts  calyces  renal pelvis  ureter  urinary bladder  urethra  outside of the body

20. Ureters About 25 cm long Extend from renal pelvis to the underside of the urinary bladder Muscular walls propel urine by peristalsis Flaplike fold acts as valve into the bladder

21. Urinary Bladder Hollow, distensible, muscular organ Stores urine Forces urine into the urethra Behind the symphysis pubis Trigone Detrusor muscle –Internal urethral sphincter

25. Micturition Aka urination Reflex triggered by stretching of the bladder: 1.Detrusor muscle contracts. 2.Abdominal wall and pelvic floor muscles contract. 3.Voluntary relaxation of external urethral sphincter Reflex center located in the spinal cord. Reflex accompanied by sense of urgency. Bladder holds 600 ml,but urge begins at 150-300 ml.

26. Urethra Tube that conveys urine from the bladder to the outside of the body Contains urethral glands that secrete mucus into the urethral canal Incontinence