1. The Urinary System and Excretion Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lecture Outline

2. The Urinary System oExcretion – the removal of metabolic wastes from the body oKidneys are the primary organ of excretion oFour functions essential to homeostasis: Excretion of metabolic wastes Preservation of water-salt balance Maintenance of acid-base balance Secretion of hormones

3. 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Kidney Hilum Ureters Urethra Renal vein Renal artery Inferior vena cava Abdominal aorta Urinary bladder Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © CNRI/SPL/Photo Researchers, Inc.

4. The Urinary System Excretion of metabolic wastes  Urea  By-product of amino acid metabolism  Ammonia combines with carbon dioxide to produce urea  Less toxic than ammonia  Creatinine – result of the metabolic breakdown of creatine phosphate  Uric acid  Result from the breakdown of nucleotides  Insoluble  Gout occurs if excess uric acid collects in the joints

5. The Urinary System Preservation of water-salt balance  Blood volume is closely associated with the salt balance of the body  Salts have the ability to cause osmosis  The more salts there are in the blood, the greater the blood volume  Kidneys also maintain other ions in the blood  Potassium  Bicarbonate  Calcium  Maintenance of blood pressure  Kidneys influence cardiac output regulating blood volume  Kidneys influence peripheral resistance by producing renin ­Activates angiotensin ­Angiotensin constricts blood vessels

6. The Urinary System Maintenance of acid-base balance  Kidneys excrete hydrogen ions from the blood into the urine  Kidneys reabsorb bicarbonate ions and return them to the blood Secretion of hormones  Release renin when blood supply decreases  Erythropoietin  Released when the oxygen-carrying capacity of the blood is reduced  Stimulates red blood cell production  Kidneys help activate vitamin D  Precursor to calcitrol  Promotes calcium absorption

7. The Urinary System oOrgans of the Urinary System Kidneys  Paired organs  Located in the lumbar region  Retroperitoneal – covered by the parietal peritoneum  Held in place by the renal fascia  Covered by the renal capsule  Hilum  Renal artery enters  Renal vein and a ureter exit

9. The Urinary System Ureters  Extend from the kidneys to the bladder  Wall layers:  Mucosa (mucous membrane) – inner layer  Smooth muscle – middle layer  Fibrous connective tissue – outer layer Urinary Bladder  In the pelvic cavity  Stores urine  Three openings:  Two for the ureters  One for the urethra  Trigone – area at the base of the bladder outlined by the openings  Detrusor muscle  Middle layer of circular fibers  Two layers of longitudinal muscle  Mucosa of transitional epithelium  Sphincters  Internal sphincter around the opening to the urethra  External sphincter composed of skeletal muscle

10. The Urinary System Urethra  Extends from the urinary bladder to an external opening  In males  Averages 20 cm when penis is not erect  Encircled by the prostate gland  Carries urine during urination and sperm during ejaculation  In females  About 4 cm long  Prone to bacterial infection

11. The Urinary System oUrination (micturition) Stretch receptors in the bladder are stimulated when the bladder is full Nerve impulses from the spinal cord cause the bladder to contract and the sphincters to relax

12. Anatomy of the Kidney and Excretion oThree regions: Renal cortex Renal medulla Renal pelvis oAnatomy of a Nephron (renal tubules) Afferent arteriole Glomerulus Efferent arteriole Peritubular capillary network

13. Kidney Anatomy CortexMedulla PyramidsColumns

14. Kidney Anatomy PapillaSinusesMinor calyxes Major calyxes Renal pelvis Ureter

16. Anatomy of the Kidney and Excretion Parts of a Nephron  Renal corpuscle  Glomerular capsule (Bowman’s capsule)  Glomerulus  Renal tubule  Proximal convoluted tubule (PCT)  Loop of Henle  Distal convoluted tubule (DCT)  Collecting duct

17. Anatomy of the Kidney and Excretion oUrine Formation Glomerular Filtration  Whole blood enters the afferent arteriole and the glomerulus  Glomerular blood pressure causes blood to be filtered  Water  Nitrogenous wastes  Nutrients  Salts (ions)  Nonfiltered components leave the glomerulus by the efferent arteriole  Formed elements (blood cells and platelets)  Plasma proteins

19. Anatomy of the Kidney and Excretion Tubular Reabsorption  Involve both passive and active processes  Occurs in the PCT  Molecules and ions are reclaimed from the filtrate  Water  Nutrients (i.e. glucose and amino acids)  Required salts (ions)  Every substance has a maximum rate of transport

20. Anatomy of the Kidney and Excretion Tubular Secretion  Substances are removed from the blood  Hydrogen ions  Potassium ions  Creatinine  drugs  Active process  Occurs in the DCT

21. Regulatory Functions of the Kidneys oFluid and Electrolyte Balance Total water intake should equal total water loss How water enters the body  Liquids  Foods  By-product of metabolism How water exits the body  Urine  Sweat  Exhaled air  Feces

23. Regulatory Functions of the Kidneys Reabsorption of Water  Reabsorption of salt leads to the reabsorption of water  Most reabsorbed in the PCT  Excretion of hypertonic urine is dependent on the reabsorption of water from:  The loop of Henle  The collecting duct  Antidiuretic Hormone (ADH)  Causes water to be reabsorbed at the collecting duct  Decreases the amount of urine

25. Regulatory Functions of the Kidneys Reabsorption of Electrolytes  The electrolytes  Sodium  Potassium  Bicarbonate ion  Other ions ­Calcium ­Phosphate ions  The kidneys  Greater than 99% of filtered sodium is reabsorbed back into the blood  67% is reabsorbed at the PCT  25% is reabsorbed at the ascending limb of the loop of Henle  The rest is reabsorbed from the DCT and the collecting duct

26. Regulatory Functions of the Kidneys  Aldosterone  Promotes the excretion of potassium  Promotes the reabsorption of sodium and water  Kidneys release renin when blood pressure is too low to promote glomerular filtration  Renin converts angiotensinogen to angiotensin I  Angiotensin I is converted to angiotensin II  Angiotensin II stimulates the release of aldosterone  Atrial natriuretic hormone (ANH)  Secreted by the atria of the heart when blood volume is high  Inhibits the secretion of renin and aldosterone  Promotes the excretion of sodium and water

28. Regulatory Functions of the Kidneys Diuretics  Chemicals that increase the flow of urine  Examples:  Alcohol  Caffeine  Diuretic drugs

29. Regulatory Functions of the Kidneys oAcid-Base Balance Acid-Base Buffer Systems  Buffer – a chemical that can take up excess hydrogen or hydroxide ions  An important buffer in the blood is a combination of carbonic acid and bicarbonate ions Respiratory Regulation of Acid-Base Balance  Increasing the breathing rate rids the body of hydrogen ions  Breathing readjusts the proportion of carbonic acid and bicarbonate ions in the blood

30. Regulatory Functions of the Kidneys Renal Regulation of Acid-Base Balance  Can rid the body of a wide range of acidic and basic substances  Slower acting than other two systems  Have a more powerful effect on pH  Reabsorb bicarbonate ions and excrete hydrogen ions as needed to maintain a normal pH  Ammonia and phosphate ions are buffers for hydrogen ions in the urine

32. Problems with Kidney Function oWater accounts for about 95% of urine volume oRemaining 5% consists of electrolytes and various solutes oUrine usually does not contain proteins and blood cells oUrinalysis is an examination of the physical, chemical, and microscopic properties of the urine oComposition of urine changes if disease has altered body metabolism or if kidney function is abnormal

33. Problems with Kidney Function

34. oInfections Urethritis Cystitis Pyelonephritis oGlomerular damage May allow large substances to be filtered  Albumin, white blood cells, and possibly red blood cells  Detected by a urinalysis Extensive damage can cause uremia

35. Problems with Kidney Function Hemodialysis  Utilizes either an artificial kidney machine or continuous ambulatory peritoneal dialysis  Dialysate – dialysis solution  Used to extract waste products, toxic chemicals, and drugs from patient’s blood  Used to add needed substances to the patient’s blood  Three- to six-hour treatment twice a week

37. Problems with Kidney Function Replacing a Kidney  A functioning kidney from a donor is received by a patient with renal failure  Possibility of organ rejection  One-year survival rate is 97% if the kidney is from a relative and 90% if it is from a nonrelative  Patient must take anti-rejection medication for the rest of his or her life

38. Effects of Aging oTotal renal function may decrease to only 50% oKidneys decrease in size and have fewer nephrons oKidney stones are more common oInfections are more common oEnlargement of the prostate in males oIncontinence

39. Homeostasis oExcretion Sweat glands Liver Lungs Kidneys are the primary organ of excretion oKidneys are the primary organs of homeostasis Water-salt balance Acid-base balance oThe kidneys assist the endocrine and cardiovascular systems by producing erythropoietin oRegulation of blood calcium levels assist the skeletal, nervous, and muscular systems