Urinary System

1. Urinary System

2. Functions of Urinary System • Filter Blood • Regulation of Blood Volume/Pressure [renin] • Regulation of the solute concentration of the Blood: Na+, Cl-, K+, Ca+2, HPO4-2 • pH regulation of extracellular fluid • Regulation of RBC synthesis [erythropoietin] • Vitamin D activation

3. Anatomy of the Urinary System

4. Kidneys • Primary organs of the urinary system • Located between the 12th thoracic and 3rd lumbar vertebrae. Right is usually lower due to liver. • Lie in shallow depressions against the posterior abdominal wall and behind the parietal peritoneum – retroperitoneal • Held in place by connective tissue [renal fascia] and surrounded by thick layer of adipose [perirenal fat]

5. Each kidney is approx. 3 cm thick, 6 cm wide and 12 cm long • Indentation on medial aspect = hilus – where renal vessels and ureter transverse • Pyramids • Papillae • Calyces – major/minor • Columns

7. Nephrons Blood enters the nephron from a network that begins with the renal artery. This artery branches into smaller and smaller vessels –and enters each nephron as an afferent arteriole. The afferent arteriole ends in a specialized capillary called the Glomerulus. Each kidney has a glomerulus contained in Bowman’s Capsule. Any cells that are too large to pass into the nephron are returned to the venous blood supply via the efferent arteriole. The efferent arteriole will divides to become the peritubular capillaries. • Each kidney contains over a million nephrons [functional structure]

9. Nephron

10. , • Proximal Convoluted Tubule [PCT] – H2O, Na+, Cl-, glucose, amino acids, Ca+, Mg+, K+, micronutrients [ Zn, Cu, Fe] • Descending Loop – H2O, Cl-, Na+ • Ascending Loop – Cl-, Na+ [ not permeable to H2O] • Distal Convoluted Tubule [DCT] – H20, Na+, Cl-, HCO3-

11. URINE FORMATION At least 500 mL (17 oz) of urine must be eliminated every day because this amount of fluid is needed to remove potential toxic materials from the body to maintain homeostasis. A normal adult eliminates from 1.5 L (1.6 qt) to 2.3 L (2.4 qt) of Urine a DAY, depending on the amount of water taken in and the amount of water lost through Respiration and Perspiration. Urine flows from the nephron to the collecting ducts, which extend to the tips of the pyramids, and empty into the calyces. All the urine will leave the kidney via the ureters.

12. Juxtaglomerular Apparatus • Monitors blood pressure and secretes renin, is formed from modified cells in the afferent arteriole and the ascending loop of the nephron • The cells of the arteriole are called juxtaglomerular cells and the cells of the loop are called macula densa. The macular densa cells monitor NaCl in the urine, and the juxtaglomerular cells produce renin

14. Renin-Angiotensin-Aldosterone • Renin: secreted by juxtaglomerular cells if blood pressure in afferent arteriole is low, or [Na+] of urine decreases as it passes the macula densa cells. • Renin: enters the gen’l circulation via peritubular capillaries and activates angiotensinogen to angiotensin I. Angiotensin I  angiotensin II via a converting enzyme found in the plasma.

15. Angiotensin II is a vasoconstrictor, acts on the hypothalamus causing the sensation of thirst, salt appetite and ADH secretion. It also causes the secretion of aldosterone from the adrenal cortex. • Aldosterone [ a steroid hormone] acts on the cells of the nephron [ esp. those of the ascending loop and DCT] to reabsorb more Na+.

16. ureters Each ureter is about 25 cm long and carries urine from the renal pelvis to the urinary bladder via peristaltic waves. . The wall of the ureter consists of three layers. The outermost is a fibrous coat, middle layer is muscular [ circular & longitudinal] and the innermost layer is called the mucosa, a transitional epithelium that is continuous with the lining of the renal pelvis and bladder, also secretes a protective mucus.

17. The Urinary Bladder is a ‘temporary storage’ reservoir for urine. When empty it resides in the pelvis, when full will rise above the symphysis pubis. A triangular region, called the trigone, is formed by three openings in the floor of the bladder. Two are from the ureters, and third from the urethra. There are flaps of mucosa covering the openings of the ureters and act as valves. A band of muscles encircles the opening to the urethra forming the internal urethral sphincter.

18. The innermost lining of the urinary bladder is a mucous membrane layer, continuous with the ureters. This layer covers the transitional epithelium. When empty, the mucosa forms folds called rugae. The second layer is called the submucosa. It contains elastic connective tissue fibers. The third layer is the muscularis: this collection of smooth muscle is known as the detrusor muscle. Contraction of this muscle expels urine from the bladder. The outermost layer is dense connective tissue.

20. Male Urethra 20 cm long [7-8 in] Transports both urine & semen Eternal urethral orifice opens at tip of penis Female Urethra 3-4 cm long [1.5 in] External urethral orifice opens just anterior to the vaginal opening Urethrathin walled tube – conveys urine from bladder to external environment. Similar structure to ureterSphincters: internal urethral [involuntary] & external urethral [ voluntary]

22. Kidney Stones Kidney stones affect more than a million Americans each year. Twelve to 24 million Americans will develop stones in their lifetime and the incidence rate has increased dramatically over the last 20 years with approximately 350,000 new stone cases reported each year. In the United States, 7 to 10 of every 1,000 hospital admissions are due to kidney stones.

23. Kidney stones are solid masses of mineral salt deposits that are normally filtered through the kidney and voided in urine. Urine naturally contains substances that dissolve the waste materials that form these solids or calculi. However, when the amounts of these salts are excessive, the urine may be unable to dissolve them all, leaving crystals that accumulate in the kidney and gradually increase in size. The stones can be as small as a grain of sand or as large as a golf ball. The size, shape, and location of the stone can cause many different symptoms.

24. Most renal calculi are so small they are passed through the urinary tract without any symptoms. Larger calculi can obstruct the renal ducts, or become lodged in the ureters. These larger obstructions cause sharp, severe pain in the sides and back as they move through the urinary tract. In medical parlance, this condition is called renal colic.

25. Well, I guess you don’t have kidney stones after all.

26. Urinalysis • Ancient Greeks & Roman physicians routinely studied urine when diagnosing patients • Today a urinalysis is done to check for microorganism content, as well as chemical and physical properties • Physical characteristics routinely checked: color, turbidity, pH & specific gravity

27. Urinalysis • Healthy urine is sterile • bacteria can enter sample from 1) incorrect sample collection or 2) infection • Infection can also be caused by fungus or protozoans • Electrolytes in urine have clinical implications – Ca2+, Cl-,K+, Na+