Chapter 26 Urinary System
Functions Excretion & Elimination (micturition) of Wastes Urea, creatinine, uric acid Homeostasis:
Kidneys Held in position by: Sit on either side of vertebral column around 11-12th ribs Right is inferior b/c of liver adrenals on top
Blood Supply Receive 20-25% of total cardiac output ~1200mL each minute Afferent arteriole- Efferent arteriole-
Nephrons 4 2 5 Cortex 1 medulla 3
Types of Nephrons Cortical nephrons-85% Juxtamedullary nephrons-15%
1. Renal Corpuscle F(x): Bowman’s (glomerular) capsule- surrounding Simple squamous capsular epithelium & visceral epi Glomerulus (capillaries) Fenestrated (pores) Brought by Blood pressure
Glomerulus -around each glomerular capillary Visceral layer Podocytes/pedicles Filtration slits Fenestrated capillaries Mesangial cells Supporting cells that contract to control capillary diameter Affected by Glomerulus -around each glomerular capillary
Structures involved in Urine Formation Filtration: Water reabsorption: Solute reabsorption:
What is Urine? Homeostasis-regulates volume & composition of blood Urea- Creatine- Uric Acid-
Basic Processes of Urine Formation Glomerular filtration- BP forces water/solutes across capillaries Tubular Secretion- transport of solutes from peritubular capillaries into tubular fluid (backup to filtration, excretion of toxins) Tubular Reabsoprtion-removal of water/solutes from filtrate. Reclaims water, electrolytes & glucose (useful materials)
Glomerular Filtration Afferent > Efferent Opposing forces Opposing forces Glomerular Filtration Rate: Amt of filtrate produced by kidneys each minute Creatinine clearance test: estimate GFR in mL/min
Autoregulation of GFR Myogenic mechanism: *If this fails, then endocrine system kicks in
Hormonal Control EPO, Aldosterone, ADH- Renin-angiotensin system Drop in GFR = renin release by juxtaglomerular complex Renin converts angiotensinogen to angiotensin I Angiotensin converting enzyme (ACE) converts angiotensin I to angiotensin II in lungs Vasocontriction = increase in BP & blood volume, restores GFR ANP (atria) & BNP (ventricles): Blood volume increases = GFR increases (speed up fluid loss in urine) Dilation of afferent/constriction of efferent Increases GFR, Na+ secretion
2. Reabsorption & Secretion at PCT Reabsorption of organic nutrients/water Ion reabsorption Secretion Methods: Movement of Na+
3. Nephron Loop Countercurrent Multiplication Thin Descending Limb Thick Ascending Limb Water follows salt! Sodium/chloride pumped out of ascending limb Increases osmotic concentration around descending limb Results in flow of water out of descending limb
4. Distal Convoluted Tubule 5. Collecting Ducts Allows further reabsorption of water DCT CD
Controlling pH of Body Fluids pH drops = pH rises =
Water Reabsorption Obligatory Facultative Controlled ADH release =
Vasa Recta
Urine Urinalysis: analysis of urine sample Density compared to distilled water Urobilin-produced from urobilinogens made by bacteria in colon
Ureter F(x): 3 layers: Inner mucosa (transitional epi & lamina propria) Smooth muscle contracts about every 30 sec to move urine Outer CT layer
Urinary Bladder Hollow, muscular Stabalized by Detrusor muscle: Inner/outer longitudinal layer Middle circular layer Sphincters: Internal- External-
Urethra Mucous membrane (stratified squam. & lamina propria) Concentric layers of smooth muscle External urethral orifice (external opening) Male carries both urine & semen
Micturition Distention of urinary bladder Bladder fills = Afferent fibers > Efferent fibers > Voluntary relaxation of external urethral sphincter & involuntary relaxation of internal urethral sphincter
Aging Incontinence:
Diseases of the Urinary System Glomerulonephritis: Kidney Stones: Renal Failure: