Renal Urinary Flashcards
Kidney Functions
maintain the chemical consistency of blood
filter many liters of fluid from blood
send toxins, metabolic wastes, and excess water out of the body
main waste products: urea, uric acid, creatinine
Organs of the Urinary System
kidneys
ureters
urinary bladder
urethra
Kidneys (Location and External Anatomy)
located retroperitoneally
lateral to T12-L3 vertebrae
average kidney is 12 c, tall, 6 cm wide, 3 cm thick
hilum: on concave surface, vessels and nerves enter and exit
fibrous capsule surrounds the kidney: perirenal fat (external to renal capsule) and renal fascia (external to perirenal fat)
Kidneys (Frontal Section)
renal cortex
pyramids of renal medulla
renal pelvis: major and minor calyxes
Kidneys (Blood Vessels)
aorta renal arteries segmental arteries interlobar arteries arcuate arteries cortical radiate arteries afferent arterioles glomeruli capillaries efferent arterioles peritubularcapillaries (in cortical nephrons) and vasa recta capillaries (in juxtamedullary nephrons) cortical radiate veins arcuate veins interlobar veins renal veins inferior vena cava
Kidneys (Nerve Supply)
via the renal plexus
an offshoot of the celiac plexus
a network of autonomic fibers
Urine Production (Mechanisms)
filtration (glomerular): liquid filtrate of blood leaves kidney capillaries in glomerular capsule
resorption (tubular): most nutrients, water, and essential ions reclaimed through resportion from urine into peritubular capillaries
secretion (tubular): active process of removing undesirable molecules through secretion from peritubular capillaries into urine
Nephron
composed of a renal corpuscle and a renal tubule
Renal Corpuscle (1)
present only in kidney cortex
first part of nephron where filtration occurs
consists of a tuft of capillaries called a glomerulus which is surrounded by a cup-shaped, hollow glomerular capsule (Bowman’s capsule)
tuft of capillaries is supplied by an afferent arteriole and drained by a efferent arteriole
the endothelium of the flomerulus is fenestrated making the capillaries highly porous, allowing large quantities of fluid and small molecules to pass from the capillaries into the capsular space (interior of glomerular capsule)
Renal Corpuscle (2)
parietal layer of glomerular capsule is simple squamous epithelium
visceral layer covers glomerulus (glomerular capillaries) and consists of epithelial cells called podocytes which branch into foot processes
filtrate passes through clefts between foot processes called filtration slits
Renal Corpuscle (Filtration Membrane)
filter system between blood in the glomerulus and capsular space
consists of three layers:
1. fenestrated endothelium of the capillary
2. basement membrane formed by the fusion of the basal lamina of the endothelium and podocyte epithelium
3. filtration slits between foot processes of podocyte epithelium which are covered by a thin slit diaphragm
hold back most blood cells and proteins
allows passage of: water, ions, glucose, amino acids, urea
Renal Corpuscle (Filtration)
around 20% of fluid leaves the glomerulus and enters the capsular space and is processed into urine
80% remains within the blood of the capillary
filtrate proceeds from renal corpuscle into renal tube
Renal Tubule
proximal convoluted tubule
nephron loop (loop of Henle): descending and ascending limbs, thin and thick segments
distal convoluted tubule
collecting ducts: receive urine from several nephrons, play an important rold in conserving body fluids
Epithelial Cells of Nephrons
parietal layer of glomerular capsule: simple squamous
visceral layer of glomerular capsule: podocyte, basement membrane, fenestrated endothelium of glomerulus
proximal convoluted tubule in cortex: simple cuboidal cells with microvillli for efficient resorption
nephron loop thin segment in medulla: simple squamous
distal convoluted tubule in cortex: simple cuboidal specialized for selective secretion or resorption of ions
collecting ducts: simple cuboidal which thicken to become simple columnar in papillary ducts
Nephrons (Classes)
cortical nephones make up 85% of all nephrons
juxtamedullary nephrons make up 15% of all nephrons
Cortical Nephrons
located almost entirely within cortex
nephron loops dip only a short distance into the medulla
Juxtamedullary Nephrons
have renal corpuscles which lie near the cortex-medulla junction
nephron loops extend deeply into the medulla
thin segments in loops are much longer than those of cortical nephrons
contribute to kidney’s ability to concentrate urine
Nephrons (Blood Vessels)
nephrons associate closely with the following capillary beds:
glomeruli capillaries
peritubular capillaries of cortical nephrons
vasa recta of juxtamedullary nephrons
Glomeruli Capillaries
fed by afferent arterioles and drained by efferent arteriole
produce filtrate that moves through the renal tubule and becomes urine
glomeruli generate 1 liter of fluid filtrate every 8 minutes:
1 % of filtrate goes into urine
99% of filtrate is reabsorbed and returned to the blood in the peritubular and vasa recta capillary beds
(these ratios will change in relationship to degree of hydration of a person; solute concentration in urine is inversely related to amount of water taken by mouth)
Peritubular Capillaries in Renal Cortex
arise from the efferent arterioles of cortical nephrons
lie in the interstitial loose areolar connective tissue in the renal cortex
are adapted for absorption
tubular resportion: low-pressure, porous capillaries readily absorb solutes and water from renal tubule cells as these substances are resorbed from the filtrate
tubular secretion: all molecules secreted by nephrons into urine are from blood of peritubular capillaries
Vasa Recta in Renal Medulla
emerge from efferent arterioles of juxta medullary nephrons in deepest part of renal cortex
thin-walled looping vessels which descend into the medulla running alonside the nephron loops
important part of the kidney’s urine concentrating mechanism
desert vertebrates tend to have very well developed vasa recta to conserve their water
Antidiuretic Hormone (Vasopressin)
produced by hypothalamus and released by posterior part of pituitary gland
released when the body needs to conserve water
Vasopressin Effect on Distal Tubules and Collecting Ducts
the antidiuretic hormone (vasopressin) increases the permeability of distal tubules and collecting ducts allowing water from the filtrate to be resorbed into the surrounding blood capillaries which decreases urine volume
alcohol can significantly reduce the production of the ADH resulting in increased urination
Aldosterone Effect on Distal Tubules and Collecting Ducts
aldosterone is a hormone produced by the adrenal cortex that increases the resorption of sodium ions and water and the secretion of potassium in the distal convoluted tubules and the collecting ducts which results in increased blood pressure
Pharmacology of Some Diuretics and Caffeine
block the resorption of sodium from distal convoluted tubules which increases urine production and lowers blood pressure
Juxtaglomerular Apparatus
a structure that functions in regulating blood pressure
an area of specialized contact between terminal end of the ascending limb of nephron loop and afferent arteriole
within the apparatus, the structures of both tubule and the arteriole are modified
granular cells, macula densa, extraglomerular mesangial cells, mesangial cells between glomerular capillaries
Juxtaglomerular Apparatus (Granular Cells)
modified smooth muscle cells with secretory granules
contained in the walls of the afferent and efferent arterioles and appear to contain mechanoreceoptors
granular cells contain the hormone renin which is secreted in response to falling blood pressure in afferent arterioles which triggers the renin-angiotensin system which increases aldosterone levels
Juxtaglomerular Apparatus (Macula Densa)
at the end of nephron loop
adjacent to granular cells
tall, closely packed epithelial cells
act as chemoreceptors and monitor solute concentration in the filtrate
when solute concentrations fall below a certain level, the cells of the macula densa signal granular cells to secrete renin
Juxtaglomerular Apparatus (Extraglomerular Mesangial Cells)
interact with macula densa and granular cells to help regulate blood pressure
Juxtaglomerular Apparatus (Mesangial Cells Between Glomerular Capillaries)
located around base of the glomerulus
these cells have contractile properties which help regulate blood flow within the gomerulus
Urine Movement
capsular space of renal corpuscle proximal convoluted tubule nephron loop distal convoluted tubule collecting duct renal calyzes renal pelvis ureter
Ureters
carry urine from the kidneys to the urinary bladder
enters into posteriolateral corner of bladder and run medially in bladder wall before opening into bladder’s interior
Ureters (Histology)
mucosa: transitional epithelium on fibroelastic lamina propria
muscularis: inner longitudinal and outer circular layer of smooth muscle; in inferior (lower) 1/3rd of ureter there is a 3rd layer (external longitudinal layer)
adventitia: connective tissue
Urinary Bladder (Layers)
three layers:
- mucosa with transitional epithelium
- thick muscular layer - detrusor muscle: contraction of this muscle squeezes urine from the bladder during urination
- fibrous adventitia
Trigone
a triangular region in the posterior wall of the bladder which is defined by the openings of the two ureters and urethra
Urinary Bladder
a collapsible muscular sac that stores and expels urine
empty bladder - lies entirely within the pelvis
full bladder expands into the abdominal cavity and becomes spherical and the mucosa rugae flatten out
a full adult bladder can hold 500 ml of urine
Urinary Tract Epithelium
ureters: transitional epithelium
bladder: transitional epithelium
proximal urethra: transitional epithelium
mid-urethra (males): stratified and pseudostratified columnar
distal urethra: stratified squamous epithelium
Prostate Gland (Males)
lies directly inferior to the bladder
surrounds the urethra
Urethra
in females: 3-4 cm long
in males: 20 cm in length with three regions
1. prostatic urethra: passes through the prostate gland
2. membranous urethra: passes through the urogenital diaphragm
3. spongy (penile) urethra: passes through the length of the penis
Urethra (Sphincters)
internal urethral sphincter: involuntary smooth muscle keeps urethra closed when urine not being passed
external urethral sphincter: surrounds urethra within the sheet of muscle called the urogenital diaphragm; this skeletal muscle sphincter inhibits urination until person is ready to urinate; voluntarily relaxed which enables urination
Micturition
- bladder fills and stretch receptors in the bladder wall send message via visceral afferent impulses to spinal cord and then via ascending tract up to pontine micturition center
- micturition response initiated and sent down descending tracts to spinal cord
- parasympathetic efferent extend from spinal cord and stimulate contraction of the detrusor muscle and opening of internal urethral sphincter
- sympathetic efferents to the bladder are inhibited
- somatic motor efferents to the external urethral sphincter are inhibited which causes the voluntary muscle of this sphincter to relax to allow urine to exit the urethra
Disorders of the Urinary System
urinary tract infections: more common in females, burning sensation during mictruition
renal calculi: kidney stones
bladder cancer: 3% of cancers, more common in men
kidney cancer: arises from epithelial cells of urine tubules
Urinary System Throughout Life
kidney and bladder function declines with advancing age
nephrons decrease in size and number
tubules less efficient at secretion and reabsorption
filtration declines
recognition of desire to urinate is delayed
loss of muscle tone in the bladder
