Histology Flashcards
3 functions of kidney and urinary tract?
maintain water and electrolyte homeostasis, body fluid osmolality and acid-base balance
excrete toxic metabolic waste products (urea and creatinine)
acts as an endocrine gland producing renin and erythropoietin
what is erythropoietin
related to RBC production and maintainance
what are the papillae?
apices of medullary pyramids which point towards the hilum, ending on the minor calyces
at what point does urine drip off from the kidney/
papillae
what are the renal columns?
acts as conduit for renal blood supply
give structure
blood supply to the kidneys?
arteries enter and travel up through renal columns to supply the renal capsule
the medulla receives its supply from the capsule
basic functional unit of the kidney?
nephron
what are nephrons composed of and how long are they?
renal corpuscle and renal tubules
each is around 45-65mm long
nephrons empty into what?
collecting system
what does the renal corpuscle do?
production and collection of glomerular filtrate
structure of the renal corpuscle?
formed of a tuft of capillaries called the glomerulus and the cup of simple squamous epithelium at the blind end of the nephron which the capillaries invaginate into called bowmans capsule
how does the renal corpuscle develop?
tuft of capillarie envaginate into bowmans capsule (cup of squamous epithelium)
coating the capillaries in the epithelium
what 2 cell layers separate the blood from the glomerular filtrate?
capillary endothelium and a specialised epithelium which lies on top of the glomerular capillaries (made of podocytes)
the endothelium is fenestrated with pores and the podocytes have interdigiting cell processes forming filtration slits
how much glomerular filtrate is produced per minute? how does this compare to urine production?
100-125ml/min
only 1ml/min of urine
afferent vs efferent arteriole?
afferent is larger as some volume is lost from capillaries at bowmans capsule
vascular vs urinary pole of glomerulus?
the beginning of the proximal renal tubule is opposite where the afferent and efferent arterioles enter and leave bowmans capsule
= vascular end and urinary pole
what is the mesangium?
stalk like core of the renal corpuscle made of mesangial cells and their extracellular matrix
what are podocytes?
cells which cover most of the capillary surface within the glomerulus
structure of podocytes?
branch in large branches, then small brnaches, then small foot branches called pedicles which intertwine to form filtration slits for glomerular filtration
filtrate from the capillaries must cross what 3 layers?
fenestrated endothelium of the capillary wall
thick basement membrane shared by endothelium and podocyte)
filtration slits between pedicles
what does the proximal convoluted tubule do?
reabsorption of water, proteins, amino acids, carbohydrates and glucose
what is resorbed in the proximal tubule?
70% of sodium (active transport) and water follows (diffusion)
almost all glucose and amino acids (by co-transport)
why are tight junctions important in proximal tubule cells?
to prevent the nutrients which have been resorbed being released into the space between cells
what lines proximal convoluted tubules?
cuboidal epithelium
what lines the loop of henle?
cuboidal epithelium
changes to simple squamous as it dives into the medulla as it has to be thinner
becomes cuboidal again as it ascends out of the medulla
what does the loop of henle do?
creates hyperosmotic environment in the medulla
proximal vs distal tubule?
proximal = thicker and more fuzzy/wooly, many many microvilli distal = more smooth, less microvilli
what are the components of the loop of henle?
thick descending limb
thin descending limb which makes a hairpin turn and journeys back
thin ascending limb
thick ascending limb
describe blood supply tot he medulla
loops of thin walled vessels that dip down into the medulla from above and then climb back up to the cortex
= collectively called the vasa recta
why is the vasa recta needed?
as a normal blood supply through the medulla would carry all the salts etc from the hyperosmotic environment created by the loop of henle around the body, destroying the osmotic gradient in the body
what does the distal convoluted tubule do?
acid-base and water balance (absorption of water, Na and bicarbonate, excretion of K and H ions)
what regulates reabsorption of Na in the distal convoluted tubule?
aldosterone
what are medullary rays?
parallel bundles of collecting ducts, straight portions of the proximal tubules and distal tubules
running perpendicular to the surface of the kidney
visible to the naked eye as stripes in the cortex that point towards the medulla
what happens in the collecting ducts?
ADH from the posterior pituitary increases the permeability of the collecting duct to water
therefore permeability of the duct is high during passage through the medulla and because of the high salt content in the surrounding tissue, water passes out of the lumen and a concentrated urine results
what structures open into the minor calyxes at the renal papillae?
collecting ducts
all parts of the urinary tract are lined with what?
transitional epithelium (or urothelium)
- stratified (3-6 layers)
- very impermeable
- contains umbrella cells at luminal surface
- special thickened, flexible membrane facing lumen
how does transitional epithelium change?
as the bladder fills the transitional epithelium thins and stretches out
what sits below the transitional epithelium?
lamina propria of connective tissue 2-3 layers of smooth muscle - inner longitudinal - outer circular - another longitudinal layer (only in the bladder)
describe female urethra
3-5cm
initial lined with transitional epithelium with transitions to stratified squamous near its termination
describe male prostatic urethra
3-4cm
extends from bladder and through prostate gland
lined by transitional epithelium
describe membranous urethra in males
1cm
from prostate to bulb of penis
transitional changes to stratified columnar
penile urethra?
15cm
lined by stratified columnar epithelium which becomes stratified squamous near the tip of the penis
