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Key Terms Chapter 25: The Urinary System

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    62677
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    anatomical sphincter
    smooth or skeletal muscle surrounding the lumen of a vessel or hollow organ that can restrict flow when contracted
    angiotensin I
    protein produced by the enzymatic action of renin on angiotensinogen; inactive precursor of angiotensin II
    angiotensin II
    protein produced by the enzymatic action of ACE on inactive angiotensin I; actively causes vasoconstriction and stimulates aldosterone release by the adrenal cortex
    angiotensin-converting enzyme (ACE)
    enzyme produced by the lungs that catalyzes the reaction of inactive angiotensin I into active angiotensin II
    angiotensinogen
    inactive protein in the circulation produced by the liver; precursor of angiotensin I; must be modified by the enzymes renin and ACE to be activated
    anuria
    absence of urine produced; production of 50 mL or less per day
    aquaporin
    protein-forming water channels through the lipid bilayer of the cell; allows water to cross; activation in the collecting ducts is under the control of ADH
    Bowman’s capsule
    cup-shaped sack lined by a simple squamous epithelium (parietal surface) and specialized cells called podocytes (visceral surface) that participate in the filtration process; receives the filtrate which then passes on to the PCTs
    brush border
    formed by microvilli on the surface of certain cuboidal cells; in the kidney it is found in the PCT; increases surface area for absorption in the kidney
    calyces
    cup-like structures receiving urine from the collecting ducts where it passes on to the renal pelvis and ureter
    cortical nephrons
    nephrons with loops of Henle that do not extend into the renal medulla
    countercurrent multiplier system
    involves the descending and ascending loops of Henle directing forming urine in opposing directions to create a concentration gradient when combined with variable permeability and sodium pumping
    detrusor muscle
    smooth muscle in the bladder wall; fibers run in all directions to reduce the size of the organ when emptying it of urine
    distal convoluted tubules
    portions of the nephron distal to the loop of Henle that receive hyposmotic filtrate from the loop of Henle and empty into collecting ducts
    diuretic
    compound that increases urine output, leading to decreased water conservation
    efferent arteriole
    arteriole carrying blood from the glomerulus to the capillary beds around the convoluted tubules and loop of Henle; portion of the portal system
    endothelins
    group of vasoconstrictive, 21-amino acid peptides; produced by endothelial cells of the renal blood vessels, mesangial cells, and cells of the DCT
    external urinary sphincter
    skeletal muscle; must be relaxed consciously to void urine
    fenestrations
    small windows through a cell, allowing rapid filtration based on size; formed in such a way as to allow substances to cross through a cell without mixing with cell contents
    filtration slits
    formed by pedicels of podocytes; substances filter between the pedicels based on size
    forming urine
    filtrate undergoing modifications through secretion and reabsorption before true urine is produced
    glomerular filtration rate (GFR)
    rate of renal filtration
    glomerulus
    tuft of capillaries surrounded by Bowman’s capsule; filters the blood based on size
    glycosuria
    presence of glucose in the urine; caused by high blood glucose levels that exceed the ability of the kidneys to reabsorb the glucose; usually the result of untreated or poorly controlled diabetes mellitus
    incontinence
    loss of ability to control micturition
    intercalated cell
    specialized cell of the collecting ducts that secrete or absorb acid or bicarbonate; important in acid–base balance
    internal urinary sphincter
    smooth muscle at the juncture of the bladder and urethra; relaxes as the bladder fills to allow urine into the urethra
    inulin
    plant polysaccharide injected to determine GFR; is neither secreted nor absorbed by the kidney, so its appearance in the urine is directly proportional to its filtration rate
    juxtaglomerular apparatus (JGA)
    located at the juncture of the DCT and the afferent and efferent arterioles of the glomerulus; plays a role in the regulation of renal blood flow and GFR
    juxtaglomerular cell
    modified smooth muscle cells of the afferent arteriole; secretes renin in response to a drop in blood pressure
    juxtamedullary nephrons
    nephrons adjacent to the border of the cortex and medulla with loops of Henle that extend into the renal medulla
    leaky tight junctions
    tight junctions in which the sealing strands of proteins between the membranes of adjacent cells are fewer in number and incomplete; allows limited intercellular movement of solvent and solutes
    leukocyte esterase
    enzyme produced by leukocytes that can be detected in the urine and that serves as an indirect indicator of urinary tract infection
    loop of Henle
    descending and ascending portions between the proximal and distal convoluted tubules; those of cortical nephrons do not extend into the medulla, whereas those of juxtamedullary nephrons do extend into the medulla
    macula densa
    cells found in the part of the DCT forming the JGA; sense Na+ concentration in the forming urine
    medulla
    inner region of kidney containing the renal pyramids
    mesangial
    contractile cells found in the glomerulus; can contract or relax to regulate filtration rate
    micturition
    also called urination or voiding
    myogenic mechanism
    mechanism by which smooth muscle responds to stretch by contracting; an increase in blood pressure causes vasoconstriction and a decrease in blood pressure causes vasodilation so that blood flow downstream remains steady
    nephrons
    functional units of the kidney that carry out all filtration and modification to produce urine; consist of renal corpuscles, proximal and distal convoluted tubules, and descending and ascending loops of Henle; drain into collecting ducts
    net filtration pressure (NFP)
    pressure of fluid across the glomerulus; calculated by taking the hydrostatic pressure of the capillary and subtracting the colloid osmotic pressure of the blood and the hydrostatic pressure of Bowman’s capsule
    oliguria
    below normal urine production of 400–500 mL/day
    osteomalacia
    softening of bones due to a lack of mineralization with calcium and phosphate; most often due to lack of vitamin D; in children, osteomalacia is termed rickets; not to be confused with osteoporosis
    pedicels
    finger-like projections of podocytes surrounding glomerular capillaries; interdigitate to form a filtration membrane
    peritubular capillaries
    second capillary bed of the renal portal system; surround the proximal and distal convoluted tubules; associated with the vasa recta
    physiological sphincter
    sphincter consisting of circular smooth muscle indistinguishable from adjacent muscle but possessing differential innervations, permitting its function as a sphincter; structurally weak
    podocytes
    cells forming finger-like processes; form the visceral layer of Bowman’s capsule; pedicels of the podocytes interdigitate to form a filtration membrane
    polyuria
    urine production in excess of 2.5 L/day; may be caused by diabetes insipidus, diabetes mellitus, or excessive use of diuretics
    principal cell
    found in collecting ducts and possess channels for the recovery or loss of sodium and potassium; under the control of aldosterone; also have aquaporin channels under ADH control to regulate recovery of water
    proximal convoluted tubules (PCTs)
    tortuous tubules receiving filtrate from Bowman’s capsule; most active part of the nephron in reabsorption and secretion
    renal columns
    extensions of the renal cortex into the renal medulla; separates the renal pyramids; contains blood vessels and connective tissues
    renal corpuscle
    consists of the glomerulus and Bowman’s capsule
    renal cortex
    outer part of kidney containing all of the nephrons; some nephrons have loops of Henle extending into the medulla
    renal fat pad
    adipose tissue between the renal fascia and the renal capsule that provides protective cushioning to the kidney
    renal hilum
    recessed medial area of the kidney through which the renal artery, renal vein, ureters, lymphatics, and nerves pass
    renal papillae
    medullary area of the renal pyramids where collecting ducts empty urine into the minor calyces
    renal pyramids
    six to eight cone-shaped tissues in the medulla of the kidney containing collecting ducts and the loops of Henle of juxtamedullary nephrons
    renin
    enzyme produced by juxtaglomerular cells in response to decreased blood pressure or sympathetic nervous activity; catalyzes the conversion of angiotensinogen into angiotensin I
    retroperitoneal
    behind the peritoneum; in the case of the kidney and ureters, between the parietal peritoneum and the abdominal wall
    sacral micturition center
    group of neurons in the sacral region of the spinal cord that controls urination; acts reflexively unless its action is modified by higher brain centers to allow voluntary urination
    specific gravity
    weight of a liquid compared to pure water, which has a specific gravity of 1.0; any solute added to water will increase its specific gravity
    systemic edema
    increased fluid retention in the interstitial spaces and cells of the body; can be seen as swelling over large areas of the body, particularly the lower extremities
    trigone
    area at the base of the bladder marked by the two ureters in the posterior–lateral aspect and the urethral orifice in the anterior aspect oriented like points on a triangle
    tubuloglomerular feedback
    feedback mechanism involving the JGA; macula densa cells monitor Na+ concentration in the terminal portion of the ascending loop of Henle and act to cause vasoconstriction or vasodilation of afferent and efferent arterioles to alter GFR
    urethra
    transports urine from the bladder to the outside environment
    urinalysis
    analysis of urine to diagnose disease
    urochrome
    heme-derived pigment that imparts the typical yellow color of urine
    vasa recta
    branches of the efferent arterioles that parallel the course of the loops of Henle and are continuous with the peritubular capillaries; with the glomerulus, form a portal system
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