Urinary system Flashcards
Components of the urinary system
Components include: Kidneys, Ureters, Urinary Bladder, Urethra
Function of the urinary system
elimination of nitrogenous wastes produced by protein catabolism, maintenance of ionic and osmotic balance w/in body
Mechanism of operation for the kidney
(ultra)filtration of blood plasma followed by reabsorption of most water and small molecules (e.g., glucose) and secretion of certain ions (mostly divalents)
Results in different end-product concentration compared to plasma
Accessory function of the urinary system
erythropoietin release; this is a hormone which stimulates RBC production
Sequence of flow of the urinary system
Urine produced in kidneys, drains toward hilum (“dent” in kidney bean shape), entering renal pelvis where it leaves the kidneys.
Upon exiting kidney, urine enters ureters which carry it to the urinary bladder (muscular-walled sac serving as reservoir for urine storage).
Urethra drains urinary bladder to exterior.
Basic structural unit of the kidney
nephron (millions)
made of renal tubule or kidney tubule
Hilum
depression thru which urine exits and blood vessels enter (and exit) the kidney
Renal pelvis
expansion of the upper part of ureter within the hilum, divided into large and small cups (major and minor calyces)
Collecting ducts
empty into calyces, these are structures into which renal tubules drain (many nephrons empty into a single collecting duct)
Structure of the kidney
As a gross structure, the kidney is surrounded by a dense CT capsule which gives off trabeculae extending toward the interior that produce a lobular organization.
Divided into an outer cortex and an inner medulla. (contain diff portions of the nephron)
The medulla contains the loops of Henle (found only in mammals and some birds) and the collecting ducts.
Reptiles/amph/fish can only equilibrate fluids because loop of Henle concentrates.
Medullary rays extend into cortex
Renal corpuscle structure
blind end of nephron; consists of a thin capsule of simple squamous epithelial tissue (Bowman’s Capsule) surrounding a ball of capillaries (glomerulus).
Blood plasma filters from glomerular capillaries into Bowman’s capsule, thereby entering the renal tubule.
Filtration barrier of the nephron
capillary endothelium (fenestrated; exchange of dissolved molecules) + relatively thick (to support capillaries) glomerular basement membrane (functions in support of capillary network) +
Bowman’s Capsule epithelium (simple squamous cells = podocytes).
Podocytes look like leaves; interlock with adjacent podocytes
Filtration slits lie between podocytes, but are closed by a slit membrane (diaphragm = 5-6 nm thick; composed of basal lamina; porous but prevents passage of large molecules).
Block out plasma proteins, allow glucose (small molecules) to filter through
Mesangial cells
= lie in extracellular matrix between glomerular capillaries, serve a phagocytic function; also can expand or contract to locally modify filtration.
In between loops
Expand: less blood flow, contract: dilate, more flow.
Describe the proximal convoluted tubule location, histology. What does the PCT function in?
Takes a winding path thru the cortex; leads from Bowman’s capsule to descending loop of Henle.
To distinguish from distal convoluted tubule:
In c.s., tubules are more numerous since proximal tubule is longer
Consists of larger, more triangular cells in proximal tubules with spherical nucleus and indistinct lateral borders (simple cuboidal epithelium)
Microvilli are present on the lumenal surface (forms brush border)
Proximal tubule is active in reabsorption of water, NaCl, glucose, amino acids, vitamins, etc.
What is the loop of henle composed of?
Thick descending portion, actually is a continuation of proximal tubule simple cuboidal
Thin descending portion simple squamous
turn
Thin ascending portion simple squamous
Thick ascending portion, leads into distal convoluted tubule simple cuboidal
How does the epithelium of the loop of henle change?
Thick portion is lined by simple cuboidal, thin portion is lined by simple squamous.
What does the loop of Henle do?
Functions to concentrate urine by removing water(first) and NaCl (later)
How far do the loops of Henle descend into the medulla?
These loops extend variable distances into medulla, depending on position of renal corpuscle. (upper cortex, don’t extend very far into medulla, vise versa)
Describe distal convoluted tubules function and histology
Takes a winding path to empty into collecting duct
Lined by cuboidal cells with relatively distinct lateral borders; lack brush border
Functions in Na2+ reabsorption
Tend to stain pale
Medulla and medullary rays contain mostly this.
Collecting ducts
Histology and function of the collecting ducts.
Lie mainly within medulla and medullary rays extending into cortex
Lined by simple cuboidal/columnar cells with very distinct lateral borders
Main function is to reabsorb water
What is the countercurrent multiplier system?
Countercurrent Multiplier System
Each region has a special permeability for water, ions, and/or urea
Interstitial spaces (between everything) accumulate ions and urea to build up a concentration gradient that is more concentrated the deeper into the medulla it is.
Parallel to nephrons lies a capillary network (vasa recta or peritubular capillaries) which has freely permeable walls, these capillaries passively participate in maintenance of the concentration gradient in the interstitium by removal of reabsorbed water and NaCl
What is the juxtaglomerular apparatus composed of?
Composed of:
Modified smooth muscle cells of tunica media of afferent arteriole (Juxtaglomerular Cells)
Macula Densa
Mesangial cells that are closely associated with Juxtaglomerular cells = Lacis Cells - function is uncertain
Macula densa
= specialized region of nephron epithelial cells at the junction of the ascending loop of Henle with the distal convoluted tubule; forms row of cells adjacent to glomerulus.
