Urinary System Chapter 25. Urinary System Organs blood-in-the-urine/ 2 Kidneys forms urine 2 Ureters transport.
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Urinary System
Chapter 25
Urinary System Organs
http://findmeacure.com/2008/03/27/hematuria-blood-in-the-urine/
• 2 Kidneys forms urine
• 2 Ureters transport urine
• Urinary bladder stores urine
• Urethra transports urine
Functions
• Primary– Filters and excretes toxins, wastes, and ions– Regulates blood volume, pressure, & composition– Maintain balance in blood (H20, salt, acids &
bases)• Supporting– Gluconeogenesis w/ fasting– Renin and EPO production– Vitamin D activation
Kidney Anatomy (external)
http://www.arizonatransplant.com/images/kidney_large_1.JPG
• Paired retroperitoneal organs – Right lower b/c liver– Renal ptosis: kidney falls w/
emaciation kinks ureters• Hydronephrosis w/ resulting urine
backup
• Adrenal glands on top• Renal hilum for vessel entry
Kidney Anatomy (internal)
http://tejatechblog.blogspot.com/2010/06/internal-struture-of-kidney.html
• Renal capsule• Renal cortex• Renal medulla
– Renal (medullary) pyramids w/ papilla
– Renal columns• Renal pelvis
– Walls are smooth muscle peristalsis
– Major and minor calyces– Pyelitis when inflamed
• Pyelonephritis all inflamed
Blood and Nerve Supply
• ¼ total CO– 90% of supply enters cortex
• Renal plexus off of celiac plexus (SNS)
Nephron
http://kvhs.nbed.nb.ca/gallant/biology/nephron_structure.html
• Forms urine from filtrate• Renal corpuscle
– Glomerulus is a fenestrated capillaries– Glomerular (Bowman’s) capsule surrounds
• Outer sim. squ. & inner podocyte
• Renal tubules – PCT: sim. cub. w/ microvilli & mitochondria (cortex)
• Increase SA for absorbing H20 & solutes and secretion
– Loop of Henle: sim. cub. sim. squ. sim. cub/col• Cortical vs juxtamedullary nephrons
– DCT: see PCT, but no microvilli (cortex)• Collecting ducts: sim. cub. (medullary pyramids)
– Intercalated cells: abundant microvill and maintain acid/base balance– Principal cells: sparse microvilli and maintain H2O and Na+ balance
Nephron Blood Supply
• Glomerulus– Afferent artery in from cortical radiate– High BP (wider too) force solute & fluid out– Produces filtrate
• Peritubular capillaries– Efferent artery out– Porous & low pressure to reabsorb filtrate (99% to
venules)– Modified as vasa recta in juxtamedullary nephrons
Juxtaglomerular (JG) Apparatus
• Regulate BP and rate of filtrate formation
• Specialized cells– Juxtaglomerular (JG) cells in
afferent arteriole• Smooth muscle w/ renin secreting
granules • Mechanoreceptors for BP
– Macula densa in renal tubule• Columnar cells• Chemoreceptors for changing
[NaCl] in filtrate
http://pclab.cataegu.ac.kr/physiology/Kidney.htm
Filtration Membrane
• B/w blood and intercapsular space• Layers– Fenestrated epi. of glomerulus
• All, but blood cells pass
– Basement membrane (b/w epi and podocytes)• All, but smallest proteins• (-) electrical charge assists repulsion of (-) proteins
– Podocyte• Filtration slits b/w feet w/additional slits prevent
macromolecule escape
Kidney Physiology (overview)
• Steps– Cell and protein free blood into tubules/collecting
duct (1)– Vasa recta reclaims needs and excretes rest• All glucose, AA’s, salt, and 99% H2O (2)
– Selective addition of other molecules (3)• Terminology– Filtrate is everything in blood, but protein– Urine is metabolic waste & excess substances
Glomerular Filtration (1)
• More efficient than other capillaries– High permeability and SA of glomerulus– Glomerular BP higher – Higher net filtration pressure (NFP)
• H2O, glucose, AA’s, & nitrogenous waste diffuse– Similar composition of filtrate & blood
• Large proteins prevented– Maintain colloid pressure– Prevent all H2O loss from blood– Proteins in blood = imbalance
Net Filtration Pressure (1)
• Review chpt 19– Hydrostatic pressure, fluid force on wall
• Filters fluids from cells and proteins
– Colloid osmotic pressure• Nondiffusible molecules encourage osmosis
• Determines filtrate formation (glomerulus)– Glomerular hydrostatic pressure pushes H2O out into
intercapsular space– Colloid osmotic pressure of glomerular blood and
capsular hydrostatic pressure opposes– NFP = HPg – (OPg + HPc)
Glomerular Filtration Rate (GFR) (1)
• Volume of filtrate made/min (~ 120 -125 ml/min)
• Regulation– SA for filtration– Filtration membrane permeability– NFP
• Directly proportional to NFP
Intrinsic Regulation of GFR (1)
• Myogenic mechanism (JG cells monitor)– Up systemic BP vasoconstrict aff. art. down flow to
glomerulus• Decreased GFR protects glomerulus
– Down systemic BP reverses• Tubuloglomerular feedback mechanism (macula
densa monitor)– GFR up = insufficent reabsorption = high NaCl
vasoconstrict aff. art. = down flow to glomerulus• NFP and GFR down to allow time for filtration
– Low NaCl reverses– Adaptable except low BP (< 80 mm Hg) = stops
Extrinsic Regulation of GFR (1)
• SNS maintain systemic BP– NE w/ stress vasoconstrict aff. art. down filtrate formation– Stimulates macula densa and JG cells
• Renin – angiotensin mechanism restores blood volume and BP– Renin converts angiotensinogen to angiotensin I
• Renin w/ down stretch, activation by macula densa, and Epi receptor stimulation
– Angiotensin I to angiotensin II • MAP up (vasoconstriction)• Increase Na+ reabsorbed by PCT• Adrenal cortex release aldosterone
Tubular Reabsorption (2)
• All glucose and AA’s• H2O and ions dependent on
hormones• Can be active or passive– Transcellular route though renal
tubule cells• Lumen and basement membrane
peritubular capillaries
– Paracellular route between renal tubule cells• Tight junctions hinder, but in PCT (Ca2+,
Mg2+, K+, & Na+)
Na+ Reabsorption(2)
• Primary cation in filtrate moved actively – 1° active transport:• Na+-K+ ATPase pumps Na+ into interstitial fluid • Low HP and high OP (undiffusible proteins) into
capillaries
– 2° active transport• From (-) electrochemical gradient primary set up
– Na+ low inside and K+ rapidly leak out– Na+ passively into cells (facilitated diffusion)
• Cotransport of glucose, AA’s, lactic acid ,and vitamins
More Reabsorption(2)
• Passive tubular transport from 1° and 2° active transport – Aquaporins
• Responsible for obligatory H2O reabsorption in PCT• Absent in collecting ducts w/o ADH
– Up [solute] in filtrate solutes diffuse out• Lipid soluble toxins and drugs also
– (-) electrochemical gradient anions diffuse out
• Transport maximum (Tm) reflects number of carriers present– Relative to need for molecule– At saturation excess molecules excreted
• Diabetes mellitus has increase [glucose] in urine
Renal Tubular Activity (2)
• PCT (previously) most active• Loop of Henle– Descending H2O in, but no ascend [aquaporins]– Solutes opposite– Role in dilute vs concentrated urine
• DCT– Depends on body needs
• ADH adds aquaporins = H2O reabsorption up• Aldosterone (renin-angiotensin) up Na+ reabsorption
– H2O follows = BP increase
• ANP encourages Na + loss– W/ high atrial pressure to drop blood volume and pressure
Diuretics (2)
• Chemicals enhancing urine output– Substances nor reabsorbed– Substances exceeding renal tubules ability to
reabsorb– Substances inhibiting Na+ reabsorption
• Alcohol inhibits ADH (H2O reabsorption) • Caffeine, drugs, and other Na+
reabsorption inhibitors• Stop obligatory H2O reabsorption
Tubular Secretion (3)
• Reabsorption in reverse– PCT mainly, but cortical collecting ducts too
• Functions– Eliminate drug bound proteins (not filtered)– Eliminate urea and uric acid (protein metabolism)– Eliminate excess K+ ions– Control blood pH• Up acidity = excess H+ in urine and HCO3
- reabsorbed
• Down acidity = HCO3- in urine and Cl- reabsorbed
Ureters
• Two tubes containing a tri-layered wall– Transitional epi. mucosa (kidney pelvis and bladder too)– Inner longitudinal & outer circular smooth muscle
• 3rd external longitudinal layer in lower 1/3
– Fibrous CT adventitia• Urine transport through peristalsis
– Stretch signal more than neural• Imbalances
– Renal calculi (kidney stones) from Ca2+, Mg2+, or uric acid salts precipitating• Bacterial infections, urine retention, high ion levels, and alkaline pH
predispose• Cranberry juice acidifies and H2O dilutes
Urinary Bladder
• Ureteral and urethral orifices form trigone– Common site of infections
• Similar tri-layer wall as ureters– Middle layer resemble lower 1/3 ureter = detrusor
muscle– Walls w/ rugae for distension
Urethra• Trans. pseudostrat. colum. strat. sqam.• Internal urethral sphincter @ junction w/ bladder
– Contraction opens• External urethral sphincter @ urogenital diphragm
– Levator ani assists• External urethral orifice• Males w/ 3 regions
– Prostatic, membranous, and spongy• Imbalances
– Dysuria (painful urination)• Indicators: up urgency, frequency, and/or presence of blood
– UTI’s from bacterial infections• Females predisposed b/c location, intercourse, wiping• Can cause urethritis, cystitis, pyelitis , inflammation of urethra, bladder, or
kidney
Urine Characteristics• Color and turbidity
– Yellow shades from urochrome, product of Hb breakdown– Higher concentration is darker yellow– Abnormal colors from foods, bile pigments, or blood– Cloudiness could indicate UTI
• Odor– Fresh is aromatic, but standing more ammonia b/c bacterial activity– Drugs, vegetables (asparagus & onions), & diseases can alter
• pH – Usually ~ 6– Down w/ acidic diet (high protein, whole wheat)– Up w/ vegetarian diet, prolonged vomiting, and infection
• Specific gravity, ratio of urine to dH2O– Higher than 1.0 b/c H2O + solutes– [solutes] determines, 1.001 – 1.035 is normal
Chemical Composition of Urine
• 95% water• 5% solutes– Nitrogenous wastes• Urea, uric acid, and creatinine (AA, nucleic acid, & CP
breakdown respectively)
– Na+, K+, Ca2+, Mg2+, HCO3- also
• Abnormal amounts, protein, or WBC presence indicates disease/imbalance
Micturition (Urination)
• Voiding of bladder• Distension of bladder walls initiates spinal reflex
– Contraction of external urethral sphincter– Inhibit detrusor muscle and internal sphincter (temporarily)
• Reflexive control till ~ 2 or 3 years of age (pons)• Incontinence when can’t control
– Laughing and coughing up abdominal pressure– Pregnancy stretches muscles
• Urinary retention when can’t go– Common after anesthesia or w/ prostate enlargement
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