CH 25 THE URINARY SYSTEM

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1 CH 25 THE URINARY SYSTEM The function of the urinary system is maintenance of homeostasis through the removal of waste products created from the metabolism of nutrients in body cells. These waste products include carbon dioxide and excess water and heat, as well as toxic metabolic by-products, such as nitrogenous wastes (ammonia and urea from the catabolism of proteins). This system is sometimes called the excretory system because waste removal is its primary function. Other body systems process/eliminate wastes, but that is not their primary job. ORGANS OF THE URINARY SYSTEM The urinary system consists of two kidneys, two ureters, one bladder, and one urethra. KIDNEYS Paired reddish, kidney bean-shaped organs found above the waist between the parietal peritoneum and the posterior wall of the abdomen (retroperitoneal). They are located between 12 th thoracic and 3 rd lumbar vertebrae. The right kidney is slightly lower than the left due to the large area occupied by the liver. Retroperitoneal Hilum (Hilus) Renal Sinus Renal Pelvis External Layers: The Kidney Capsule Renal Capsule Adipose Capsule Renal Fascia Internal layers: Parenchyma KIDNEY PARENCHYMA 1 RENAL CORTEX Extends from the renal capsule to the bases of the renal pyramids, and includes these features: 65

2 Glomerular Capsules Convoluted Tubules Renal Columns 2 RENAL MEDULLA Medullary Pyramids (8-18) Renal Papillae Formerly renal pyramids. A/k/a apices or renal apices. Renal Pelvis Major Calyces Minor Calyces URETERS The ureters are extensions of the pelvis of each kidney that enter the bladder at the superior lateral angle. They are retroperitoneal. Ureters have no valves; rather they respond to bladder pressure since they pass underneath the bladder. Pressure building up in the bladder prevents backflow during urination. Walls of the ureters have three layers of tissue: Mucosa Muscularis Fibrous Coat URINARY BLADDER A hollow muscular organ situated in the pelvic cavity posterior to the symphysis pubis. The bladder is anterior to the rectum in the male and to the vagina in the female. The bladder is a freely movable structure held in position by the folds of the peritoneum. Shape of the bladder depends on amount of urine contained within its structure at that particular moment. Trigone Four layers in the bladder walls: 66

3 Mucosa Submucosa Muscularis Formerly the detrusor layer. Serosa URETHRA The urethra is a small, thin-walled muscular tube extending from the urinary bladder to the body exterior. In the male, it serves a dual function providing for the passage of both urine as well as semen. In females it serves only a urinary function. The female urethra is posterior to the symphysis pubis, embedded in the vaginal wall. Urethral length in the female is approximately 3.8 cm (1-1/2 inches) and in the male it is about 20 cm (8 inches). The urethra is the terminal portion of the urinary system. Bladder Neck Internal Urethral Sphincter External Urethral Sphincter URINARY PHYSIOLOGY The functional unit of the kidney is the nephron. Each kidney contains approximately 500,000-1,000,000 nephrons and their blood vessels. Nephrons consist of: Glomerular Capsule Formerly Bowman s capsule. Glomerulus Glomerular Space Proximal Convoluted Tubule Descending Nephron Loop Ascending Nephron Loop Formerly descending loop of Henle. Formerly ascending loop of Henle. Distal Convoluted Tubule Collecting Duct 67

4 Afferent Arteriole Efferent Arteriole Peritubular Capillaries Renal Corpuscle TWO TYPES OF NEPHRONS Cortical Nephrons Peritubular Capillaries Juxtamedullary Nephrons Vasa Recta Capillaries BLOOD SUPPLY FOR THE NEPHRONS Arteries include: Renal Artery Segmental Arteries Interlobar Arteries Arcuate Arteries Cortical Radiate Arteries Interlobular Afferent Arteriole Efferent Arteriole Capillaries include: Glomerulus Peritubular Vasa Recta 68

5 Veins include: Cortical Radiate Veins Arcuate Veins Interlobar Veins Renal Vein NEPHRON MICROSTRUCTURE 1 CAPSULAR PORTION Glomerular Capsule Formerly Bowmans capsule. Capsular Space Parietel Layer Visceral Layer Podocytes Pedicels Filtration Slits Glomerulus Endothelial-Capsular Membrane Glomerular Endothelium Endothelial Basement Membrane Dialyzing Membrane Podocytes (Visceral Epithelium) 2 TUBULAR PORTION Proximal Convoluted Tubules Descending Nephron Loop Ascending Nephron Loop 69

6 Distal Convoluted Tubule Collecting Duct 3- JGA Juxtaglomerular Apparatus Macula Densa Granular Cells Formerly juxtaglomerular (JG) cells. Renin RENIN-ANGIOTENSIN PATHWAY Angiotensinogen + Renin = Angiotensin-I (AgI) Angiotensin-I + ACE = Angiotensin-II (AgII) Chemicals in BP Regulation include: Renin Angiotensinogen Angiotensin-I ACE Angiotensin-II ADH Aldosterone ANP (Atrial Natriuretic Peptide) PROCESS OF URINE FORMATION Glomerular Filtration Tubular Reabsorption Tubular Secretion 70

7 RENAL REGULATION Intrinsic (Local) Controls Negative Feedback Renin-Angiotensin Pathway Extrinsic Controls Sympathetic NS Baroreceptors in BV Aortic Sinuses Carotid Sinuses THE PRODUCT OF THE NEPHRON S FUNCTION IS URINE We produce approximately 1.5 liters of urine per day, and urine is 95% water. Urine has certain characteristics we measure to determine whether a person s urinary system is operating normally or not. These include: Color Urochrome Odor ph Specific Gravity Casts MICTURITION Micturition is urination. It occurs when approximately 200 ml of urine accumulates in the bladder, causing extension of the bladder walls. Micturition reflex centers are located in the sacral region of the spinal cord. When they receive impulses, parasympathetic fibers cause the detrusor muscles to contract and the sphincters to relax. As urine works its way into the urethra, afferent impulses are sent to the brain stem and cerebral cortex thereby creating the feeling of a need to void urine. 71

8 DISORDERS/DISEASES Anuria Abnormally low urinary output per day (less than 50ml/day). Cystitis Bladder inflammation. Diabetes insipidus Hydronephrosis An injury (or tumor) in the hypothalamus or posterior pituitary results in the underproduction of ADH and therefore the overproduction of urine. Kinked ureter causes urine to back up into kidney. It can lead to necrosis. Incontinence Inability to control micturition. Ptosis Pyelonephritis Renal calculi Urethritis Dropping of kidney due to loss of fatty tissue support. It is a big problem if/when ureter becomes kinked. Infection of renal pelvis and calyces. Can lead to infection of entire kidney. Kidney stones. Most are less than 5mm in diameter. Can have lithotripsy instead of invasive surgery for removal if not passed. Inflammation of the urethra. 72