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Urinary System
Anatomy and Physiology of the Urinary System
73
Anatomy
Undergraduate 4
03/07/2012

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Term
Parts of the Urinary System
Definition
kidneys, ureters, urinary bladder, urethra
Term
Functions of the Urinary System
Definition
filter the blood, regulation of blood volume, synthesis of vitamin D, gluconeogenesis
Term
Kidney location
Definition
behind peritoneum on posterior abdominal wall, protected by lumbar vertebrae and rib cage, right kidney lower than left b/c of liver
Term
Kidney Functions
Definition
removal of toxins and excess ions from blood, regulation of blood volume, chemical composition, pH, renin (BP) and erythropoitin (RBCs) endocrine functions, activation of vitamin D
Term
External anatomy of kidneys
Definition
Renal fascia (CT, anchors kidneys) --> perirenal fat (cushioning) --> renal capsule (fibrous CT)
Hilum (arteries and nerves enter) --> Renal Sinus (cavity)
Term
Internal anatomy of kidneys
Definition
cortex --> medulla --> renal pyramids --> renal papilla (apex) --> minor calyces --> major calyces --> renal pelvis --> ureter
Term
Nephron
Definition
structural unit of kidney, includes renal corpuscle and renal tubule
Term
Juxtamedullary vs Cortical Nephrons
Definition
J - loops of henle extend much further into the medulla
Term
Renal Corpuscle
Definition
Bowman's Capsule - parietal and visceral layers
Glomerulus - network of capillaries
Term
Afferent arteriole
Definition
where blood enters the glomerulus
Term
efferent arteriole
Definition
where blood exits the glomerulus
Term
Visceral layer of Bowman's capsule
Definition
contains podocytes that wrap around the capillaries
Term
fenestrae
Definition
window like openings in the endothelium of glomerulus
Term
filtration slits
Definition
gaps between the processes of podocytes
Term
filtration membrane
Definition
includes capillary endothelium, gel like basement membrane, and podocytes. Where the first stage of urine formation occurs by passing into the lumen
Term
Juxtoaglomerular apparatus
Definition
sight of renin production
Term
Juxtaglomerular cells
Definition
ring of smooth muscle around the vessels at the bowman's capsule that sense pressure
Term
macula densa
Definition
specialized tubule cells of the distal tubule
Term
Nephron Anatomy
Definition
Renal Corpuscle - glomerulus, bowman's capsule
Proximal tubule
Loop of Henle - descending and ascending limb
Distal tubule
Collecting Ducts
Term
Renal Arteries
Definition
Abdominal aorta --> renal arteries --> segmental arteries --> interlobar --> arcuate --> interlobular --> afferent arterioles
Term
Peritubular capillaries
Definition
form plexus around tubules
Term
Vasa Recta
Definition
part of peritubular capillaries that extend into the medulla with the loop of henle
Term
Renal Veins
Definition
Interlobular --> arcuate --> interlobar --> renal
Term
Filtrate
Definition
blood plasma, water, small molecules, ions pass into the Bowman's capsule because of pressure
Term
Urine
Definition
1% of total filtrate, 1-1.8L, contains wastes and unneeded substances
Term
filtering blood
Definition
entire plasma volume filtered 60x day
Term
Mechanisms of Urine Formation
Definition
1. Glomerular filtration - movement of filtrate across filtration membrane into Bowman's capsule
2. Tubular reabsorption - returns glucose, amino acids, 99% water, and other components to blood
3. Tubular secretion - selective addition to urine
Term
Glomerular Capillary Pressure
Definition
BP inside capillary, highest type of pressure
Term
Blood Colloid Osmotic Pressure
Definition
osmotic pressure caused by proteins in blood, favors fluid movement into capillary
Term
Capsule Hydrostatic Pressure
Definition
pressure of filtrate already in the lumen
Term
High GCP
Definition
causes low resistance to blood flow in afferent arterioles and glomerular capillaries, high resistance to BF in efferent arterioles
Term
Autoregulation of glomerular filtration rate
Definition
increased BP leads to increased BF past cells of macula densa signals the juxtaglomerular apparatus causing the afferent arteriole to constrict
Term
Sympathetic regulation of GFR
Definition
NE --> constriction of afferent arterioles --> decreased renal BF --> decreased filtrate formation (why you dont have to pee when exercising)
Term
tubular reabsorption
Definition
occurs as filtrate flows through the lumens of proximal tubule, loop of henle, distal tubule, and collecting ducts
Through diffusion, facilitated diffusion, active transport, symport, and osmosis
Term
Reabsorption in PCT
Definition
must pass through apical and basal membrane, active transport of Na into the cell, water moves by osmosis
Number of carrier molecules limits rate, affected by glucose
volume reduced by 65% by the end of PCT
Term
Reabsorption in descending loop of Henle
Definition
highly permeable to water, moderately permeable to urea and Na
Reduces volume by 15%
Term
Reabsorption in ascending loops of henle
Definition
permeable to solutes which diffuse out, not permeable to water, Na transported into interstitial space, K and Cl symported, ions pass my facilitated diffusion
Term
Reabsorption in DCT and collecting duct
Definition
NA actively transported out, water moves by osmosis
Term
Urea
Definition
enters filtrate, only 40-60% reabsorbed, high in urine
Term
Toxic substances in urine
Definition
urate, creatine, sulfates, phosphates, nitrates
Term
ammonia
Definition
produced by epithelial cells of nephron from deamination of amino acids. Eliminated in urine
Term
H+
Definition
secreted into filtrate at proximal tubules
Term
K+
Definition
secreted into filtrate at distal tubules
Term
Urine production in PCT
Definition
Na+ and other substances removed
Water follows passively reducing filtrate volume
Term
Urine production in descending loop of Henle
Definition
Water exits passively, solute enters
Filtrate volume reduced 15%
Term
Urine production in ascending loop on Henle
Definition
Na+, Cl-, K+ transported out of filtrate
Water remains
Term
Urine production in DCT and collecting ducts
Definition
Na actively transported out to interstitial fluid
Water reabsorption regulated by ADH
If absent, water not reabsorbed and dilute urine produced
If ADH present, water moves out, concentrated urine produced
Term
Insufficient hydration
Definition
Kidneys produce small volume of concentrated urine
Term
When a lot of water is consumed
Definition
kidneys produce large volume of dilute urine
Total amounts of electrolytes lost not increased
Term
Urine Concentration
Definition
Maintenance of high concentration of solutes in medulla
Control of permeability of distal nephron to water
Countercurrent functions of loops of Henle
Term
ADH mechanism
Definition
Increased ECF osmolality stimulates OsmoRs in supraoptic nucleus ADH from posterior pituitary
Decreased stretch stimulation of baroRs in atria, large veins, carotid sinus, aortic arch  sensory afferents to SON  ADH from post pit
ADH triggers reabsorption of H2O in the distal tubules and collecting ducts by insertion of aquaporins into tubule cell membrane
99% of H2O in filtrate is reabsorbed.
Term
Renin/Angiotensin/Aldosterone Mechanism
Definition
Decreased stretch of afferent arteriole (dt decreased BP)
chemoreceptors in Macula Densa senses decreased [Na]filtrate
Renin secr’n from juxtaglomerular apparatus
Renin converts angiotensinogen to angiotensin I ---> angiotensin II  BP + aldosterone secrt’n.
Aldosterone  thirst sensation, salt appetite, and ADH secretion
Aldosterone increases transport proteins for Na+ in nephron tubules  Na+ and water reabsorption  concentrates urine

stretch of afferent arteriole (i.e., increased BP, or [Na] filtrate  decreases Renin
Term
Atrial natriuretic hormone
Definition
Increased blood volume stimulates stretchRs in Rt atrium  release of ANH
Inhibits Na+ reabsorption
Inhibits ADH production
Increases volume of urine produced
Venous return is lowered, volume in right atrium decreases, BP decreased
Term
Diuretics
Definition
Chemicals that increases urinary output
Osmotic diuretics: substances not reabsorbed, (e.g., high glucose in diabetics)
ADH inhibitors such as alcohol
Substances that inhibit Na+ (and therefore H2O) reabsorption such as caffeine
Term
Glomerular Filtration Rate
Definition
Volume of plasma filtered per unit time
Estimated using plasma clearance: Volume of plasma cleared of a specific (test) substance each minute
Term
Renal Plasma Flow
Definition
volume of blood delivered to kidneys
Term
Tubular Load
Definition
Total amount of substances that passes through filtration membrane into nephrons each minute
Term
Tubular Maximum
Definition
Max rate at which a substance is reabsorbed

Each substance has its own
Term
diabetes mellitus
Definition
tubular load exceeds tubular maximum and glucose appears in urine. Urine volume increases because glucose in filtrate increases osmolality of filtrate reducing the effectiveness of water reabsorption
Term
Urine Movement
Definition
BP at afferent arteriole moves plasma thru glomerulus
Hydrostatic pressure forces urine from bowman’s capsule (10mmHg) through nephron (0mmHg)
Peristaltic contractions of sm muscles around ureters move urine through ureters to urinary bladder
Ureters enter bladder obliquely through trigone. Pressure in bladder compresses ureter and prevents backflow
Term
Trigone
Definition
interior of urinary bladder. Triangular area between the entry of the two ureters and the exit of the urethra. Area expands less than rest of bladder during filling
Term
Detrusor
Definition
muscle part of bladder wall is a thick layer of sm muscle
Term
Male Urethra
Definition
extends from the inferior part of the urinary bladder through the penis and carries semen and urine
Term
Female Urethra
Definition
shorter; opens into vestibule anterior to vaginal opening
Term
Internal Urinary Sphincter
Definition
Sm muscles. in males, keep semen from entering urinary bladder during ejaculation. No fxn’l equiv in females
Term
External Urinary Sphincter
Definition
skeletal muscle surrounds urethra as it extends through pelvic floor. Acts as a valve. Ctrls the flow of urine
Term
Micturition
Definition
Urination or voiding
Filling of bladder is continuous; elimination is controlled
When bladder is full, stretched
sensory afferents  sacral spinal cord
 info to pons and cerebrum urge to urinate
 reflexive contraction of sm muscles of bladder
 reflexive relx’n of skeletal muscles
 urinate
Cerebrum and pons can override temporarily
These higher control centers mature between ages 2 and 3
Term
Renal Calculi
Definition
Kidney stones
form in renal pelvis:
Crystallized calcium, magnesium, or uric acid salts
Large stones can block ureter; cause pressure and pain in kidneys
May be due to chronic bacterial infection, urine retention, Ca2+ in blood, pH of urine
Treated by surgery or shockwave therapy
Prevention by adding acidic foods and drinks to diet (cranberry juice)
Term
Glycosuria
Definition
excessive intake of sugary foods, diabetes mellitus
Term
Ketonuria
Definition
ketone bodies, as in starvation and untreated DM
Term
Hemoglobinuria
Definition
transfusion reaction, hemolytic anemia
Term
Protienuria/Albuminuria
Definition
high-protein diet, renal disease
Term
Diabetes insipidus
Definition
Absence of ADH stimulation
Central or nephrogenic
Symptoms:
Polyuria: excessive production of urine
( 15L /day)
Extreme thirst
Treatment:
Low Na+ diet
Synthetic vasopressin
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