Urinary system Flashcards
main function of the urinary system
production, storage and voiding of urine
what is urine?
aqueous solution of excess anions and cations and breakdown products of metabolic processes (esp. toxic ones)
location of the kidneys
solid bean shaped
high on posterior abdominal wall, beneath peritoneum
concave aspects face midline (aorta and IVC)
what is the concave area of the kidney called?
hilum
entry of renal arterial supply and venous drainage
pelvicalyceal system and ureters
hollow muscular tubes
specialised epithelium resistant to damage
smooth muscle - peristalsis
zones of the kidney
outer cortex
inner medulla
cortex of kidney
forms an outer shell
forms columns lying between individual medullary units (columns of Bertin)
what are columns of Bertin?
columns lying between individual medullary units by the cortex in the kidney
medulla of kidney
series of conical structures (medullary pyramids)
base of each cone is continuous w/ inner limit of cortex
pointed peak protrudes into urine collecting system
what is the papilla?
pointed peak of medullary pyramids in the kidney
how many pyramids are there in the kidney?
10-18
how does the kidney produce urine?
selective removal of substances from blood plasma
composition of urine is appropriate to internal environment and requirements
always has required amount of waste products and ions for homeostasis
what substances are controllingly reabsorbed by the kidney?
water, ions, salts, sugars, carbs, small molecular weight proteins
feature of kidney failure
inability to produce conc./dilute urine
inadequate excretion of nitrogenous waste products/potassium
how do the kidneys and lungs differ from other organs?
parenchymal components of organ are servants of the blood supply, as kidney filters/cleanses the blood
what percentage of CO do the kidneys receive? what is a consequence of this?
25
most kidney diseases result from abnormal blood vascular component
what hormones does the kidney produce?
erythropoietin and renin
kidney arterial supply
single renal artery - substantial, direct branch of abdominal aorta
runs towards hilum, divides into minor posterior branch and substantial anterior branch
divide into interlobular arteries running between medullary pyramids, one to each developmental lobe
branching of interlobular arteries
at midpoint of thickness of parenchyma - corticomedullary junction
several lateral arcuate arteries running laterally
capillary systems in renal microcirculation
glomerular tuft - blood from afferent arteriole, site of filtration of waste products from plasma
second one arises from efferent arteriole, varies in structure and function according to location
efferent arteriole after the glomerulus structure and function
divides into complex capillary system
interstitial spaces between cortical tubules
takes up substances resorbed from glomerular filtrate by tubular epithelial cells
what are juxtamedullary glomeruli?
glomeruli deep in the cortex
close to corticomedullary junction
capillary system originating from efferent arterioles leaving juxtamedullary glomeruli
divide into long, thin-walled vessels (vasa recta)
run into medulla alongside medullary components
ionic and fluid exchanges
where may vasa recta arise from?
efferent arterioles leaving juxtamedullary glomeruli
directly from arcuate artery
differences in roles between the capillary systems in the kidney
glomerular tuft doesn’t transfer oxygen to tissues, or take up CO2
gas exchange in second
O2 supplied to cortical and medullary parts of parenchyma (highest demand)
what areas of the kidney have the highest demand for oxygen, and why?
cortical and medullary parts
high metabolic activity
venous drainage of kidney compared to arterial supply
mirrors it
no equivalent of glomerular capillary tuft
what forms the origin of the interlobular veins?
subscapular arteriolar and capillary plexuses drain into subscapular venular and venous plexus of stellate veins, forming origin of interlobular veins
what happens as the interlobular veins approach the corticomedullary junction?
receive venous tributaries from peritubular capillary network
what happens as the interlobular veins approach the juxtamedullary zone?
receive venous tributaries from medulla (equivalent of arterial vasa recta)
where do arcuate veins run with?
run laterally w/ equivalent artery at corticomedullary junction
drain into large interlobular veins between adjacent medullary pyramids, then into major vein tributaries at hilum
where does the major renal vein open into?
IVC
what is the nephron?
functional unit of the kidney parenchyma serving the blood supply
components of the nephron
glomerulus
cortical and medullary tubular systems
function of nephron components
glomerulus - initial blood filtration
tubular systems - conc. and chemical content of blood is controlled
what are the components of the medullary ray?
midpoint between adjacent interlobular arteries
vertically running arrangement of tubules and ducts
centre: main collecting duct which collects largely conc. urine from nephrons on either side
straight collecting tubules carrying urine from end of distal tubule to main cortical collecting duct
how do the duct systems of the medullary ray run?
vertically downward into medulla
what is the renal lobule?
subunit of the cortex
centrally placed medullary ray and nephrons on either side
each interlobular artery runs upward in cortex between adjacent lobules
afferent vs efferent arterioles
afferent is branch of interlobular artery, enters the glomerulus at vascular hilum
efferent arteriole emerges from glomerulus, divides into peritubular capillary network
where do arcuate veins and arteries run?
corticomedullary junction
example of injection showing renal microvasculature
carmine-gelatin injection
what is the first functional component of the nephron encountered by the microcirculation? what does it do?
glomerulus
initial filtration of blood arriving by afferent arterioles
division of afferent arteriole
enters glomerulus
divides into 5 main branches
each branch subdivides into its own capillary network
what is the short main branch (and its capillaries) of the afferent arteriole supported by?
own strip/stalk of mesangium
what is the consequence of the branching of the glomerular capillary network?
divides into 5 independent segments
implicit lobulation rarely apparent by light microscopy in health - evident in primary glomerular disease
when may lobulation of glomerular tuft be seen?
light microscopy in some primary glomerular disease
esp. when mesangial component is enlarged
independence of each segment seen by disease affecting only one segment
what is an example of a renal disease only affecting one segment of the glomerulus?
segmental glomerulonephritis
glomerulus structure
globular capillary network intruding into hollow sphere of epithelial cells (Bowmann’s capsule)
what is Bowmann’s capsule?
sphere of epithelial cells
bulbous, distended closed end of long hollow tubular system
epithelial cells of Bowmann’s capsule
flat and simple
become more cuboidal and acquire some organelles of proximal convoluted tubule epithelial cells near opening of tubular system
epithelial cells of glomerular capillary
lined internally by endothelial cells
ones lining capillary tuft are larger and have specialised and unusual structure
podocytes
urinary space
epithelium-lined space between coated glomerular capillary network and parietal shell of Bowman’s capsule
continuous w/ lumen of long tubular system of nephron
passage of blood
blood enters glomerular capillary network from afferent arteriole
ultrafiltration
filtrate passes into urinary space, passes down the tubular system
partly filtered blood leaves glomerulus via efferent arteriole and provides oxygenation
basement membrane in glomerular capillary network
unusually thick
glomerular filtration barrier
barrier between circulating blood and urinary space
components of glomerular filtration barrier
capillary endothelial inner layer
thick BM
podocyte (outer epithelial) layer
high polyanionic charge on some components
thickness of glomerular BM
310-350 nm
thicker in males
what contributes to the glomerular BM?
inner endothelial and outer epithelial cells contribute to its production
layers of glomerular BM
central electron-dense lamina densa
electron-lucent lamina rara interna on endothelial side
electron-lucent lamina rara externa on epithelial podocyte/urinary space side
development of layers of BM
clearly seen in rodents and children
less apparent in adults
lamina densa layer of glomerular BM
type IV collagen
fibril network acts as physical barrier to large molecules
polyanionic sites in glomerular BM
lamina rara layers and surfaces of some podocyte secondary foot processes contain negative sites composed of GAG
BM: heparan sulfate
foot process: sialic acid-rich substance, podocalyxin
GAG in BM and podocyte foot processes
heparan sulfate
sialic acid-rich substance (podocalyxin)
demonstrating polyanionic sites in glomerular BM
ultrastructurally
using cationic substance e.g. ruthenium or polyethylenimine
form regular lattice, spacing of 60nm
what may polyanionic sites act as?
charge barrier
prevent passage of cationic molecules
structure of glomerular capillary endothelial cells
small circular fenestrations 70 nm diameter
attenuated
where are the nuclei of the fenestrations located?
near the mesangium
what is the podocyte layer composed of?
specialised epithelium continuous at hilum w/ epithelium at Bowman’s capsule
why is the podocyte named so?
main body of the cell hovers above the external surface of glomerular capillary and sends down cytoplasmic extensions (foot processes)
foot processes of podocytes
cytoplasmic extensions that contact the BM
what is between adjacent foot processes?
consistent gap
30-60nm
filtration slit
what is the filtration slit membrane? what does it contain?
bridges gap between adjacent foot processes
cell adhesion molecule: nephrin
what is nephrin?
cell adhesion molecule
connects actin filaments within adjacent foot processes
what are the components of mesangium?
mesangial cells and extracellular mesangial matrix
mesangial cells structure
round/oval nucleus, larger than endothelial nucleus
dense rim of chromatin in nuclear membrane
small chromatin clumps throughout nucleoplasm
how do mesangial cell processes run?
haphazardly through extracellular mesangial matrix
what does the mesangial cell cytoplasm contain?
myosin-like filaments
angiotensin-II receptors
mesangial matrix structure
encloses mesangial cells, permeated by their cytoplasmic processes
variable electron density
in continuity w/ glomerular BM where capillary and BM meet
acellular
what is the mesangial matrix produced by?
mesangial cell
functions of the mesangium
support of glomerular capillary loop system
control of blood flow through glomerular loop by myosin-angiotensin mechanism
phagocytosis
maintenance of glomerular BM
which parts of the tubules are close to the glomeruli?
convoluted parts of proximal and distal tubules
which parts of the tubules are in parts devoid of glomeruli?
straight parts of tubular system and cortical parts of collecting duct system
what is the first part of the tubular system?
proximal tubule - continuation of Bowman’s capsule
path of proximal tubule
initially has convoluted course, remains close to Bowman’s capsule
straightens and descends toward medulla
merges w/ thin limb of loop of Henle
runs down in cortex, then in medulla, toward papillary tip (descending thin limb)
loops back on itself and forms distal straight tubule
path of distal tubule
comes from ascending thin limb from proximal tubule, as a thick straight tubule
close to the glomeruli, becomes convoluted
empties into collecting tubule
empties into collecting duct within medullar ray
path of collecting ducts
descend into medulla
converge to form large diameter ducts in papillae (papillary ducts/ducts of Bellini)
where do capillary ducts open into?
calyces at tips of papillae
what is the area cribosa? what is it produced by?
sieve-like surface appearance of the capillary tip
concentration at the openings
main variation in length in the tubular system
thin ascending and descending loops of Henle
proximal convoluted tubule is longer than the distal convoluted tubule
what is the function of the proximal tubule?
reabsorption of components of the glomerular filtrate
structure of proximal tubule cells
cuboidal/columnar
centrally placed nucleus
well-developed luminal brush border
microvilli, closely packed
what is the structure of the luminal brush border in proximal tubule cells?
microvilli, closely packed, 1mm
pinocytotic vesicles close to lysosomes
BM of each tubule cell
extensive basal interdigitation and some lateral interdigitation
lateral border is irregular and difficult to define
what is the purpose of the microvilli and mitochondria in proximal convoluted tubule cells?
immense SA for absorption
mitochondria are numerous and prominent in the convoluted section
energy for active transport of substances against gradients
substances going into proximal convoluted tubule cells
Na+, H20, Cl-, amino acids, glucose, proteins, polypeptides, carbs
transport of Na+ into proximal convoluted distal tubule cell
ATPases bring Na+ into cell
other ions, H+/K+ may leave the cell
membrane pumps in basolateral membrane push Na+ into intercellular space - creates high osmotic force
what does passage of Na+ ions into the intercellular space cause?
high osmotic force
what is the paracellular route?
the high osmotic force caused by Na+ pulls H20 and Cl- into intercellular space
what happens to H20 and Cl- once in the cell?
pass through BM into interstitium
hydrostatic pressure forces them into adjacent peritubular capillaries
transport of protein, polypeptides and some carbohydrates
reabsorbed into cell by endocytosis
broken down by lysosomal enzymes into amino acids and small molecular sugars
pass into intercellular space, then the interstitium and capillaries
transport of glucose and amino acids into proximal convoluted distal tubule cells
specific transport systems at the microvillar surface
arrangement of mitochondria in lower half of each proximal tubule cell
elongated mitochondria are closely associated w/ basal interdigitations from adjacent cells
arranged in parallel w/ interdigitating basal cytoplasmic membranes
variations in specialisations in cells
membrane and cytoplasmic specialisations most developed in convoluted part
microvilli become smaller and less numerous as thin loop of Henle is approached
basal and lateral interdigitation less marked
mitochondria and lysosomes fewer
cells more cuboidal
why is the thin-walled part of the loop of Henle considered a distinct functional and structural entity?
thick descending and ascending components are ultrastructurally identifiable with the proximal and distal convoluted tubules
transitions between thick and thin tubules are abrupt - thick ascending and descending parts merge gradually with proximal and distal tubules
length of thin limbs of loop of Henle
those associated w/ juxtamedullary glomeruli are long, extend deep into medulla towards papillary tip
those associated w/ midcortical or subscapular glomeruli extend halfway into medulla
epithelium lining thin limbs of loop of Henle
flat lining
little cytoplasmic specialisation
like a dilated capillary
function of the thin limb of loop of Henle
creates osmotic gradient of hypertonicity
where does the gradient of hypertonicity in the thin limb extend?
from the corticomedullary junction to the top of papilla
what is the gradient of hypertonicity in the thin limb affected by?
variable passage of sodium and chloride ions between the lumen and the interstitium
what does this gradient of hypertonicity do?
allows conc. of the urine in collecting duct system
what is the explanation for the gradient mechanism?
countercurrent multiplier hypothesis
what is the macula densa?
distal tubule runs close to hilum at the junction between the straight and convoluted parts
what is the countercurrent multiplier hypothesis?
descending thin limb of loop of Henle is freely permeable to water, Na+ and Cl- ions
ascending thin limb is impermeable to water, actively pumps Cl- ions out of lumen into interstitium, which Na+ ions follow to maintain neutrality. retains water
produced hypotonic tissue/fluid
cells lining the distal tubule
cuboidal epithelial cells basal and lateral interdigitations microvilli less formed and scanty (to proximal tubule) numerous, close to interdigitations no invaginations or vesicles
control of acid-base balance in the distal tubule and what this function depends on
Na+ ions reabsorbed from dilute urine in lumen, K+ ions excreted
bicarbonate ions reabsorbed, H+ excreted -> acidic urine
dependent on aldosterone (secreted by adrenal cortex)
function of ADH
antidiuretic hormone
secreted by posterior pituitary
acts on last part of distal convoluted tubule
absorption of water -> conc. urine
collecting ducts - absorption of water from lumen into hypertonic intersitium, into vasa recta
dependent on countercurrent exchange system
what does the tubular and duct system depend upon for its oxygen supply?
glomerular capillary network and arteries supplying glomeruli
hypoxia of tubular epithelial cells
reduced blood flow
enzyme systems and pumping mechanisms stop functioning
biochemical abnormalities
features of renal failure
acidosis (high conc. of H+ ions)
hyperkalemia (high conc. of K+ ions)
retention of nitrogenous waste material
connecting segment
where convoluted distal tubule opens into collecting system
epithelial lining contains both cell types randomly
what are the collecting tubules lined by?
clear cells
intercalated dark cells
clear cells
cuboidal/flat in proximal segment light, poorly staining cytoplasm few organelles basal membrane infoldings, become less apparent microvilli short and sparse
intercalated dark cells
many mitochondria
well developed microvilli
vesicles at base of microvilli
no basal infoldings
epithelium and BM of collecting ducts
initially identical to tubules
pass down medullary rays and into medulla
decreased intercalated dark cells
clear cells taller and more prominent
regular straight sided columnar clear cells
progressively thicker BM as it nears papillary tip
countercurrent exchange system
dilute urine in collecting tubule is progressively conc. by osmotic transfer of water from lumen into the hypertonic medullary interstitial tissue
reabsorbed into vasa recta
high vs low ADH levels
high: water lost from collecting duct lumen into interstitium
low: water remains within lumen, lost in form of dilute urine
vasa recta and the conc. of urine
on the descending (arterial) side, the walls are permeable to water and salts
water passes into interstitium, and salts into lumen
on the ascending (venous) side, vice versa
variation of the interstitial space in the kidney
cortex: small, small blood vessels and lymphatics
medulla: significant in bulk and function
tip of papilla: increases in size and importance
what is the medullary interstitium composed of?
loose electron-lucent acellular material
protein and GAGs
scattered collagen fibres, lipid droplets and basal lamina material
interstitial cells
what is the most common interstitial cell in humans?
irregular in outline
narrow, stellate cytoplasmic processes extending in all directions into matrix
what does the cytoplasm of interstitial cells contain?
mitochondria, lysosomes, lipid droplets, small RER
function of juxtaglomerular apparatus
maintaining BP and volume by producing renin
adaptation of vascular and tubular tissues allowing blood flow to affect renin output
what are the components of the juxtaglomerular apparatus?
renin-producing cells
lacis cells
macula densa
where are renin-producing cells located?
walls of afferent and efferent arterioles at vascular hilum of glomerulus
what are the features of renin-producing cells?
highly specialised myoepithelial cells, with some contractile filaments
what do renin-producing cells contain?
type 1 and 2 granules
what do type 1 granules contain?
irregular in shape
rhomboidal crystalline bodies (protogranules) - precursors of other granules
what are protogranules? where are they founde?
rhomboidal crystalline bodies, precursors of other granules
type 1 granules in renin-producing cells
what are type 2 granules?
larger, spherical, uniformly electron dense, ill-defined membrane
mature renin-secreting granules
what is the structure of lacis cells?
network of interwoven processes separated by acellular matrix of BM like material
where are lacis cells located?
triangular region bordered by macula densa at base and afferent and efferent arterioles at the sides
apex is formed by base of glomerular mesangium
what is the macula densa?
specialised zone of distal tubule where it’s in close contact w/ vascular hilum
specialised adaptation of its epithelium
epithelium of the macula densa
taller
tightly packed
nuclei closer to luminal surface
Golgi between nucleus and BM
what is the function of renin?
catalyses conversion of inactive angiotensin
what is angiotensin?
alpha2 globulin produced in the liver, converted by renin to decapeptide angiotensin I.
conversion of angiotensin I to II
by ACE in lung
stimulates secretion of aldosterone by zona glomerulosa of adrenal cortex
what is aldosterone and its action?
mineralcorticoid hormone
regulates Na+ and K+ levels by effect on pump mechanism
promotes resorption of ions in distal tubules
mechanisms for feedback control of renin synthesis and release
macula densa cells monitor Na+ conc. in distal tubule, affect renin release by granulated cells
juxtaglomerular cells monitor arteriolar stretching
secretion of erythropoietin
kidney, not sure where exactly
lymphatic systems in kidney
main ones run with interlobular, arcuate and interlobar vessels and emerge at hilum
minor runs in renal capsule and receives some tributaries from cortex
some communication between them in cortex
nerve supply to kidney
autonomic
adrenergic and cholinergic fibres
components of lower urinary tract
calyceal collecting system - large collecting ducts of Bellini discharge urine into this renal pelvis ureter bladder urethra
calyceal collecting system
part of lower urinary tract
large collecting ducts of Bellini in papillae discharge urine into here
renal pelvis
reservoir at hilum into which calyces pass urine
ureter
long muscular tube which conducts urine down into bladder
bladder
reservoir, holds urine until voiding
urethra
urine stored in bladder is voided to exterior through here
sphincters in lower urinary tract
close off parts of tract to act as reservoir
one at junction between bladder and urethra is under voluntary control
urothelium
multilayered epithelium in lower urinary tract
variation of urothelium
in calyces, only 2-3 layers thick
empty bladder, 5-6 layers
distention of urothelium
ability to stretch, shift and flatten
distended: stretched, flat cells, fewer layers
non-distended: compact, cuboidal basal layer, polygonal celled middle layers, surface layer of tall columnar cells (binucleate)
surface layer of urothelium
specialised
luminal aspect is convoluted
deep clefts run down to cytoplasm
fusiform vesicles lined by cell membrane identical to luminal surface
BM of urothelium
thin, indistinct
supported by dense subepithelial tissue of mainly collagen (lamina propria)
surface cells during distension
flattened
lose convex apical bulge
deep clefts and vesicles disappear
what is the urothelium supported by?
lamina propria and layers of smooth muscle
arrangement of smooth muscle in ureter
loose spiral muscle (longitudinal)
tight spiral muscle (circular - outer)
what prevents urine reflux during micturition?
functional valve
innervation of the bladder
ANS
sensory fibres from bladder transmit signals to sacral spinal cord i.e. its distension
parasymp. fibres ending in muscles and adventitia of bladder act as effector muscle for micturition
symp. fibres innervate blood vessels to bladder
female urethra - length, opening
short
5cm long
runs from bladder, opens to exterior in midline of genital vestibule between clitoris and superior border of vaginal introitus
what is the urethra lined by?
stratified squamous epithelium
lamina propria has vascular channels and small mucus-secreting glands
what is the urethral muscle wall?
continuation of the involuntary smooth muscle of the bladder
what is the external sphincter? where is it? what is it composed of?
striated muscle
voluntary control
midportion of urethra as it passes through striated muscles of pelvic floor
male urethra - length
20-25cm long
what are the segments of the male urethra?
prostatic, membranous, penile
prostatic urethra
begins at bladder neck
runs through prostate gland
periurethral glands open into it through short ducts
openings of ejaculatory ducts
membranous urethra
short segment 1cm long runs through pelvic floor muscles voluntary control external sphincter
penile urethra
runs through corpus spongiosum
opens to exterior at external meatus of glans penis
small mucous glands open into this
what is the male urethra lined by?
transitional epithelium -> non-specialised pseudostratified -> stratified squamous as it merges with that of glans penis
