- 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