Chapter 20 - Urinary System PDF

Urinary System Chapter 20  Learning Objectives Lesson 20.1: Kidney Physiology and Organs of the Urinary Tract 1. Describe the location and structure of the kidneys and explain how they act as vital organs in maintaining homeostasis. 2. Identify the parts of a ne...

Urinary System Chapter 20  Learning Objectives Lesson 20.1: Kidney Physiology and Organs of the Urinary Tract 1. Describe the location and structure of the kidneys and explain how they act as vital organs in maintaining homeostasis. 2. Identify the parts of a nephron and describe the role each component plays in the balancing of blood and formation of urine. 3. Explain the importance of filtration, tubular reabsorption, and tubular secretion in renal physiology. 4. Discuss the mechanisms that control urine volume. 5. Describe the structure and function of the ureters, urinary bladder, and urethra.  Kidneys  Location of the kidneys  Kidneys lie under back muscles, behind parietal peritoneum, just above waistline  Right kidney is usually a little lower than left  Gross structure of the kidney  Renal cortex: Outer layer of kidney  Renal medulla: Inner portion of kidney Urinary System Overview (1 of 2) From Abrahams P, Hutchings RT, Marks SC: McMinn's color atlas of human anatomy, ed 5, St Louis, 2003, Mosby. Urinary System Overview (2 of 2) Internal Structure of the Kidney From Abrahams P, Marks S, Hutchings R: McMinn's color atlas of human anatomy, ed 6, Philadelphia, 2008, Mosby.  Gross Structure of the Kidney  Renal pyramids: Triangular divisions of medulla  Renal columns: Cortical tissue that dips down between renal pyramids  Renal papilla: Narrow, innermost end of pyramid  Renal pelvis: Expansion of upper end of ureter; lies inside kidney  Renal calyces: Divisions of renal pelvis  Microscopic Structure of the Kidney  Interior of kidney composed of more than 1 million microscopic nephron units  Unique shape of nephron well suited to function  Principle components are renal corpuscle and renal tubule  Renal Corpuscle (1 of 2)  Bowman capsule: Cup-shaped top of nephron  Glomerulus: Network of blood capillaries surrounded by Bowman capsule  Cortical nephrons: 85% of total; located mostly in renal cortex  Juxtamedullary nephrons: Have important role in concentrating urine; located near junction between cortex and medullary layers  Renal Corpuscle (2 of 2) Courtesy Andrew P. Evan, Indiana University School of Medicine.  Renal Tubule  Proximal convoluted tubule (PCT): First segment  Henle loop: Extension of proximal tubule; consists of descending limb, loop, and ascending limb  Distal convoluted tubule (DCT): Extension of ascending limb of Henle loop  Collecting duct (CD): Straight extension of distal tubule Location of Nephrons The Nephron Unit  Kidney Function  Excrete toxins and nitrogenous wastes  Regulate levels of many chemicals in blood  Maintain water balance  Help regulate blood pressure and volume  Regulate red blood cell production by secreting erythropoietin (EPO)  Formation of Urine (1 of 2)  Filtration  Goes on continuously in renal corpuscles  Glomerular blood pressure causes water and dissolved substances to filter out of glomeruli into the Bowman capsule  Normal glomerular filtration rate 125 mL per minute Formation of Urine (2 of 2)  Reabsorption (1 of 2)  Movement of substances out of renal tubules into blood in peritubular capillaries  Water, nutrients, and ions are reabsorbed  Water is reabsorbed by osmosis from proximal tubules  Sodium reabsorption occurs in the Henle loop using countercurrent flow  Reabsorption (2 of 2)  Countercurrent mechanisms keep the medulla hypertonic so that the kidney can reabsorb extra water  Amount of sodium reabsorbed depends on diet  More sodium intake = less sodium reabsorbed, more sodium excreted in urine  Chloride ions passively move into blood, owing to negative charge Reabsorption of Ions and Water  Reabsorption of Glucose (1 of 2)  Glucose is reabsorbed from the proximal tubules back into the blood for use as energy  If there is too much glucose, as in diabetes mellitus, blood concentration can reach a level called the renal threshold  Filtrate contains more glucose than can be reabsorbed  Glucose is left behind in the urine and is a sign of diabetes Reabsorption of Glucose (2 of 2)  Secretion  Movement of substances into urine in the distal and collecting ducts from blood in peritubular capillaries  Hydrogen ions, potassium ions, urea, uric acid, creatinine, and certain drugs are secreted by active transport  Ammonia is secreted by diffusion  Control of Urine Volume  ADH  Secreted by posterior pituitary; promotes water reabsorption by collecting ducts; reduces urine volume, a salt- and water- retaining hormone  Aldosterone  Secreted by adrenal gland, triggered by RAAS process; promotes sodium and water reabsorption in nephron; reduces urine volume  ANH  One of the peptide hormones (ANPs) secreted by atrial cells in heart; promotes loss of Renin-Angiotensin-Aldosterone System (RAAS)  Atypical Amounts of Urine  Anuria: Absence of urine  Oliguria: Scanty amounts of urine  Polyuria: Unusually large amount of urine  Ureters  Structure  Narrow long tubes with expanded upper end (renal pelvis) located inside kidney  Lined with mucous membrane and muscular layer  Function: Drain urine from renal pelvis to urinary bladder  Urinalysis  Examination of the physical, chemical, and microscopic characteristics of urine  May help determine the presence and nature of a pathological condition Ureter Cross Section From Telser A, Young J, Baldwin K: Elsevier’s integrated histology, Philadelphia, 2008, Mosby.  Urinary Bladder (1 of 2)  Structure  Elastic muscular organ, capable of great expansion  Lined with mucous membrane arranged in rugae, like stomach mucosa  Functions  Storage of urine before voiding  Voiding Urinary Bladder (2 of 2)  Urethra  Structure  Narrow tube from urinary bladder to exterior  Lined with mucous membrane  Opening of urethra to the exterior called urinary meatus  Functions  Passage of urine from bladder to exterior of the body  Passage of male reproductive fluid (semen) from the body  Learning Objectives Lesson 20.2: Micturition, Renal Physiology, and Disorders of the Urinary Tract 5. Describe the process of micturition and the control problems that frequently occur with this process. 6. Explain the purpose and importance of urinalysis. 7. List the major renal and urinary disorders and explain the mechanism of each disorder.  Micturition  Passage of urine from body (also called urination or voiding)  Regulatory sphincters  Internal urethral sphincter (involuntary)  External urethral sphincter (voluntary)  Bladder wall permits storage of urine with little increase in pressure  Emptying Reflex  Initiated by stretch reflex in bladder wall  Bladder wall contracts  Internal sphincter relaxes  External sphincter relaxes and urination occurs  Enuresis: Involuntary urination in young child  Retention and Suppression  Urinary retention: Urine produced but not voided  Urinary suppression: No urine produced but bladder is normal  Urinary Incontinence  Urine is voided involuntarily  Urge incontinence: Associated with smooth muscle overactivity in the bladder wall  Stress incontinence: Associated with weakened pelvic floor muscles  Overflow incontinence: Associated with urinary retention and overdistended bladder  Reflex incontinence occurs in absence of any sensory warning or awareness: Common after a stroke or spinal cord injury  Nocturnal enuresis: Nighttime bed wetting  Neurogenic bladder: Periodic but unpredictable voiding; related to paralysis or abnormal bladder function  Urinalysis  Definition: The physical, chemical, and microscopic examination of urine  Color, turbidity, odor, and specific gravity are used as diagnostic clues  Chemical analysis provides pH, urea concentration, or presence of abnormal chemicals, such as proteins or glucose  After being centrifuged, so heavier cells are separated, those cells can be examined for tell-tale “casts,” or small particles deposited in the renal tubules  Renal and Urinary Conditions  Obstructive conditions interfere with typical urine flow, possibly causing urine to back up and cause hydronephrosis or other kidney damage  Hydronephrosis: Enlargement of renal pelvis and calyces caused by blockage of urine flow  Renal calculi (kidney stones): Crystallized mineral chunks in renal pelvis or calyces; may block ureters, causing intense pain called renal colic  Tumors: Renal cell carcinoma (kidney cancer) and bladder cancer; often characterized by hematuria (blood in the urine)  Hydronephrosis From Kumar V, Abbas A, Fausto N: Robbins and Cotran pathologic basis of disease, ed 8, Philadelphia, 2010, Saunders.  Renal Calculi Courtesy of Dr. E. Mosher, Brigham and Women's Hospital, Boston, MA. In Kumar V, Abbas AK, Fausto N: Robbins and Cotran pathologic basis of disease, ed 8, Philadelphia, 2010, Elsevier. Imaging of Bladder Cancer Courtesy of B. Bracken, MD, Cincinnati, Ohio. In Weiss MA, Mills SE: Atlas of genitourinary tract disorders, Philadelphia, 1988, J.B. Lippincott/Gower Medical Publishing.  Urinary Tract Infections (UTIs)  Often caused by gram-negative bacteria  Urethritis: Inflammation of the urethra  Cystitis: Inflammation or infection of the urinary bladder  Pyelonephritis: Inflammation of renal pelvis and connective tissues of the kidney; may be acute (infectious) or chronic (autoimmune)  Glomerular Disorders (1 of 2)  Result from damage to the glomerular- capsular membrane of the renal corpuscles  Nephrotic syndrome accompanies many glomerular disorders Proteinuria: Protein in the urine Hypoalbuminemia: Low plasma protein (albumin) level; caused by loss of proteins to urine Edema: Tissue swelling caused by loss of water from plasma as a result of hypoalbuminemia  Glomerular Disorders (2 of 2)  Acute glomerulonephritis caused by delayed immune response to a streptococcal infection  Chronic glomerulonephritis is a slow inflammatory condition caused by immune mechanisms and often leads to renal failure  Kidney Failure  Kidney failure, or renal failure, occurs when the kidney fails to function  Acute renal failure: Abrupt reduction in kidney function that is usually reversible  Chronic renal failure: Slow, progressive loss of nephrons caused by a variety of underlying diseases Polycystic kidney disease (PKD): Numerous fluid- filled cysts destroy kidney tissue as they grow; hereditary Polycystic Kidney Disease From Kumar V, Abbas AK, Fausto N, Mitchell RN: Robbin's basic pathology, ed 7, Philadelphia, 2007, Saunders.  Progression of Kidney Failure  Stage 1: Early in this disorder, healthy nephrons often compensate for the loss of damaged nephrons  Stage 2: Often called renal insufficiency; loss of kidney function ultimately results in uremia (high BUN levels) and its life- threatening consequences  Stage 3: Called uremia or uremic syndrome; complete kidney failure results in death unless a new kidney is transplanted or an artificial kidney substitute is used Chronic Renal Failure Questions?