histology of the urinary tract Flashcards
functional unit of the kidney + what it consists of
uriniferous tubule consisting of the nephron and collecting tubules
renal corpuscle structure
bowman’s capsule and glomerulus
two poles- vascular pole containing the afferent and efferent arteriole and the urinary pole where the proximal tubule leaves
what is the glomerulus?
knot of blood vessels
afferent glomerular arterioles supply it and efferent drain
structure of glomerulus capillaries
fenestrated, with large pores- 60-90 nm diameter- lacking diaphragms
structure of Bowman’s capsule
parietal layer, outside of capsule, formed of simple squamous epithelium
visceral layer envelops the capillaries, containing highly specialised epithelial cells called podocytes
bowman’s space, where fluid enters from the glomerulus
three layers of the filtration apparatus
fenestrated capillary, basal lamina and podocytes
function of fenestrated capillary
barrier to large macromolecules such as red blood cells
three layers of basal lamina + important molecules in each
lamina rara interna
lamina densa- collagen
lamina rara externa- heparin sulphate
function of basal lamina
collagen- separates molecules due to size
heparin- separates molecules due to charge
larger and more negatively charged molecules (proteins) are impeded
only small molecules and positive ions can pass through
structure of podocytes
envelop the capillaries with slit pores
interdigitate to cover basal lamina
primary processes- long cytoplasmic extensions
secondary processes- pedicels which completely envelop most of the capillaries
pedicels form narrow clefts that are covered by a thin diaphragm
how are pedicels attached?
attached to the basement membrane to laminin by integrins and attached to alpha actinin
pedicel functions
nephrin molecules from adjacent pedicels interact to form negatively charged slit pores
nephrin prevents the passage through endothelial fenestrations
what occurs in the renal corpuscle?
filtration
where does reabsorption take place?
tubular part of the nephron
three parts of the tubular system
proximal tubule, loop of Henle and distal tubule
two parts of proximal tubule
pars convoluta- tortuous region
pars recta- straight, descending portion that forms the first part of the descending loop of Henle
type of epithelium
leaky cuboidal
structure of the epithelium
brush border formed of abundant microvilli
canaliculi, invaginations of the plasma membrane
eosinophilic granular cytoplasm
long mitochondria
abundant lysosomes
type of epithelium in loop of Henle
simple squamous epithelium
number of tight junctions an composition of cells depends upon the function of that portion of the loop
three regions of the distal tubule
pars recta, macula densa and pars convoluta
distal tubule epithelium structure
cuboidal apart from macula densa where cells are tall and thin
shorter cuboidal cells and no brush border compared to PCT
elaborate basal membrane invaginations for ion transport
important blood vessel in the nephron
vasa recta
what is the vasa recta?
straight vessels that branch from the glomerular artery and surround the loop of Henle
vasa recta function
generate a hypertonic interstitium by counter current exchange
vasa recta structure
descending- continuous endothelial cells
ascending- fenestrated endothelial cells
explain vasculature of the kidney
interlobular arteries pass from the pelvis between the lobes
form the arcuate arteries at the cortico-medullary junction
afferent arterioles arise from the interlobular arteries in the cortex
glomerulus in the cortex
efferent arterioles drain the glomerulus to form the peritubular capillary network in the medulla that then form vasa recta
collecting duct structure
begin in medullary rays of cortex
principal cells with single cilium
intercalated cells with microvilli
several collecting ducts fuse at the ducts of bellini
which terminate at the area cribosa
juxtaglomerular apparatus definition
structure in the kidney that regulates the function of each nephron
JGA function
cells that synthesise, store and secrete the enzyme renin
regulate blood pressure and blood flow
regulate glomerular filtration rate
JGA structure
formed of the macula densa, extraglomerular mesangial cells and juxtaglomerular cells of the afferent glomerular arteriole
mesangial cell definition
specialised smooth muscle
two types of mesangial cells + location and function
extraglomerular- at vascular pole that relay information from macula densa
intraglomerular- situated within renal corpuscle, have pericytes that have a phagocytic role and respond to vasoactive hormone and contract to narrow capillaries
macula densa definition
region of the distal convoluted tubule
area in contact with the glomerulus at the vascular part
tall columnar cells
macula densa function
cells sensitive to the ion content and water volume of the fluid in the distal convoluted tubule
detect sodium, potassium and chloride concentrations
signal by releasing prostaglandins when they detect a fall
prostaglandin function
activate extraglomerular mesangial cells
ureter definition
muscular tube that delivers urine from collecting tubules to the urinary bladder
ureter structure
lined by mucosa
muscularis muscular coat- 2/3 layers
fibrous connective tissue- fibroelastic lamina propria
transitional epithelium lining
3-5 layers thick
bladder structure
transitional epithelium
thickened plaque regions within plasma membrane contain glycoproteins which protect cells
interplaque regions - where folding occurs
reserve membrane stored in vesicles for when bladder is stretched
plaque function
act as an osmotic barrier- impermeable to water and salt
urethra structure
longer in males than females
extrenal and internal sphincters
contain glands of litre and intrepithelial glands that secrete mucus, aiding the passage of urine
urethra epithelium
starts off as transitional as it exits the bladder
then becomes pseudostratified/stratified columnar
detrusor muscle location
smooth muscle found in the wall of the bladder
structure of detrusor muscle
fibres arise from the posterior surface of the body of the pubis in both sexes
fibers pass in a longitudinal manner up the inferior surface of the bladder, over its apex, descend along the fundus
become attached to prostate in the male and front of vagina in the female
three layers of muscle arranged longitudinal- circular- longitudinal
arranged obliquely and intersect one another
parasympathetic innervation of bladder + function
branches of pelvic splanchnic nerves to empty bladder
sympathetic innervation of bladder + function
branches of inferior hypogastric plexus
relax muscle, allow bladder to fill
