Kidney Histology Flashcards
What are the capsules of the kidney?
there are three of them:
innermost is a CT capsule immediately on the surface
middle capsule is relatively thick layer of tat
outermost capsule is CT that binds the kidney to surrounding structures
WHat is the indentation on the medial side of the kidney that leads into the renal sinus?
the hilus
What enters at the hilus and what exits as the hilus?
the renal artery enters, the renal vein and ureter exit
plus nerves and lymphatics
Within the kidney parenchyma, what is the outer part and what is the inner part/
cortex is outer (darker staining)
medulla is inner (lighter staining)
What are the groupings of the medulla called?
medullary pyramids (6-18 per kidney)
WHat is contained in the cortex?
renal corpuscles and medullary rays
Bases of the medullary pyramids lie adjacent to the cortical tissue while the tips of the pyramids (renal papillae) point towards what?
minor calyces of the renal pelvis
What is the tip of the papilla called? Describe it.
Area cribrosa - it’s perforated by 10-25 small openings where the terminal segments of the uriniferous tubules open into the minor calyx
What areas extend between the medullary pyramids?
the renal columns
The renal sinus is basically just a potential space - what does it contain?
renal pelvis
major and minor calyces
arteries, veins, nerves, lymphatics
loose CT and fat
What is a medullary pyramid and the surrounding cortical tissue called?
a lobe
What does a lobule consist of?
straight tubules in medulla ray and the cortical substance immediately surrounding those tubules
What are the major components of a nephron?
- renal corpusle: with bowman’s capsule and glomerulus
- Tubular portion: proximal convoluted tubule, LOH (proxima; straight, thing seg, distal straight), and distal convoluted tubule
What does the distal convoluted tubule drain into?
the collecting tubules, which carry the urine to the renal pelvis
Bowman’s capsule has two distinct layers which are?
the parietal layer (simple squamous epithleium)
the visceral layer (composed of modified cells called podocytes)
WHat are the two distinct poles of the corpuscle?
urinary pole where the parietla epithelium is continuous with the cuboidal epithelium of the proximal convoluted tubule
vascular pole where the visceral epithelium reflects off the afferent and efferent arteriolsand becomes continuous with th eparietal epithelium
What lies between the visceral and parietal epitheliual layers of the capsule?
the lumen of the tubule, or Capsular (Bowman’s) space
What type of blood vessels make up the glomerulus?
it’s entirely arterial = an afferent arteriole and an efferent arteriole
Once within the capsule, the afferent arteriole quickly gives rise to what?
fenestrated capillaries that comprise the glomerular tift and form a complex anastomosing capilarry entwork
What do podocytes do?
they form the visceral epitheliual layer of bowman’s capsule
there are primary and secondary processes. the secondary processes (the feet) interdigitate with neighboring podocytes and then attach to the basal lamina of the capillary endothelium
What space is formed between the interdiitated podocyte food processes?
slit pores
What makes these fenestrated capillaries differnet from other fenestrated capillaries in the body?
these fenestrations lack the thin pore diaphragm
Since the endothelial pores only block large celllar components of blood and plasma, what else holds back molecules from the filtrate? How?
hte basal lamina. It has a large negative charge, so it repels things that ar enegatively charged and will block large molecules
Where are mesangial cells located?
occur where adjacent capillaries are soo close to each other that the podocytes cannot totally surround them - they’re probably very similar to pericytes
What do the mesangial cells do?
keep the glomerular filter free of debris
provide additional support at sites where basement membrane is lacking
help with basmenet membrane turnover
What part of the nephron makes up the bulk of the renal cortex?
the proximal convoluted tubule and proximal straight tubule
What type of epithelium comprises the tubules?
simple high cuboidal or two-columnar epithelium
How does the body increase surface area in the proximal tubules?
has a brush border composed of long regularly oriented and closely packed microvilli
What is the relationship between adjacent epithelial cells in the proximal tubules?
the lateral cell membranes are highly folded and interdigitate extensively with adjacent cells
Where are mitochondria located in high numbers in the epithleial cells of the proimal tubules?
they’re mostly found in the basal half of the cell - elongated and rod-like
This extensive infolding of the basal plasma membrane in the proixmal tubule gives what appearance to the luminal border?
they appear to have basal striations
What is the function of the proximal tubule/
1.65% of all water and NaCl is reabsorbed there
(Na is actively transported and chloride and water follow passively to maintain osmotic equilibrium)
2. glucose and amino acids reabsorbed
3. protein absorbed via pinocytosis at the luminal surface
What comes after the proximal convoluted tuule in the nephron?
the thing segment of the LOH
What does the epithelium change to in the thin segment?
changes from simple cuboidal to simple squamous and the brush border ceases (although a few short irregular microvilli may still be present)
What surrounds the thin segment?
capillaries - the vasa recta and efferent vessels of juxtamedullary glomeruli
What’s another term for the distal straight tubule?
the thick segment of the ascending limb (LOH)
What does the epithelium change to in the distal straight tubule/
changes back from simple squamous to simple cuboidal
How does the lumen size compare between the proximal tubule and the distal straight tubule/
the lumen is larger in the distal straight tubule
How do the distal and proixmal tubules differ on histology?
the distal cell cytoplasm is less acidophilic
the lateral borders of cells are easier to identify
cells are also smaller, thus more nuclei are seen around the circumference of a tubule
also, the distal cells just have some microvilli - not a frank brush border
Which tubule has apical canaliculii, proximal or distal?
proximal
What does the distal straight tubule return to?
the renal corpuscle from which it originated
What does the distal straight tubule attach to at the renal corpuscle? WIth what?
attaches to the afferent arteriole at the vascular pole
Does so with its macula densa
What is the macula densa?
an eliptical disc of elongated cells in the wall of the ascending limb where it contacts the afferent arteriole - function unknown.
What does the distal straight tubule become after the macula densa?
the distal convoluted tubule
What special endocrine function does the distal convoluted tubule have?
ADH increases permeability of the cells to water here, which helps form a concentrated urine by promoting fluid reabsorption
What ar ethe two portiaons of the collecting tubule?
the arched portion (cortical locaiton and receive urine from distal convoluted) and the straight portion (in medullary rays and medulla)
As the straight portion of the collecting tubules descending, they unite with adjacent tubules and form what on their way to the renal papillae?
larger collecting ducts called the papillary ducts (or ducts of Bellini)
What type of epithelium is present in the collectinb tubules?
simple cuboidal to low columnar
What are the two types of epithelial cells in the collecting tubules?
light cells = collecting duct cells (CDs)
dark cells = intercalated cells (ICs)
Describe the light cells?
they have a single cilium with short, stubby microvilli
What do the dark cells probably do?
they probably play a role in acid-base balance by resorption and or secretion of bicarbonate and acid
Where are the dark cells located mostly?
more towards the cortx - they decrease in number as you descend into the medulla
What does the cytoplasm look like in cells of the collectin ducts?
clear or very light staining
What is the function of the collecting duct?
water resorption under the influence of ADH
Acid-base balance
What are the components of the juxtaglomerular apparatus?
juxtaglomerular cells, macula densa, extraglomerular mesangial cells
What are the juxta glomerular cells and where are they located?
they are specialized cells in the wall of (mostly) the afferent arteriole among the smooth muscle cells
The granules of the justaglomerular cells contain what?
renin
What is the function of the juxtaglomerular apparatus?
maintenance of normal blood pressure with release of renin in response to falling blood pressure
How do the juxtaglomerular cells know when to secrete renin?
there are a few possible mechanisms:
- respond to a decrease in stretch
- macula densa cell smonitor the Na concentration in the distal tubule and trigger renin secretion in response to low Na
What is the sequence of blood vessels in the kidney?
- renal artery
- interlobar artery
- arcuiate artery
- interlobular artery
e. afferent arteriole
f. glomerular capillaries
g. efferent arterioles
g. vasa recta OR cortical peritubular capillary netowk
h. arcuite veins
i. interlobar veins
j. renal vein
What are the two parts of the vasa recta?
the arteriolae rectae (the descending vessels) and the venae rectae (the ascending vessels)
How do the capillaries of the arteriolae rectae and venae rectae differ?
arteriolae - continuous endothelium
venae - fenestrated endothelium
Where does most of the innervation to the kidney come from?
sympathetic autonomic nervous system
What do sympathetic nerve activities do to the kidneys?
Differentially constricts either afferent or efferent arterioles:
constriction of afferent arterioles reduces the filtration rate and decreases urine production
constriction of efferent arterioles increases filtration rate and increases urine production
Loss of sympathetic innervation will lead to what in terms o urinary output?
increase urinary output
What evidence so we have that extrinsic nerve supply isn’t essential for renal function?
kidney transplants - nerves are cut, but kidneys sfunction normally
What kind of epithelium is located in the ureter?
transitional epithelium
What are the 4 layers of the ureter?
- mucosa
- submucosa - may not exist
- muscular coat
- adventitia
What are the layers of the musclar coat?
in the upper 2/3 of the ureter, there are two layers of smooth muscle with the inner arranged longitudinally and the outer one arranged circularly
In the lower 1/3 of the ureter, there is an additional third outer layer with longitudinal muscle fibers
Why are the muscle layers not as distinct as those of hte itnestine?
there is considerable CT from the lamina propria and adventitia that kingle in with the muscle fibers and obscure the layering
What is the adventitia made of?
fibroelastic CT
Transitional epithelium also makes up the mucosa of the urinary bladder. How are the surface cells modified on the luminal side?
the outer leaflet is thickened
How are adjacent surface cells attached in order to help make the barrier mor eeffective?
occluding junctions
WHat type of epithelium is present in female urethra?
transitional only near the bladder
after that, it’s stratified squamous the rest of the way
What are the three portions of the male urethra?
the prostatic portion
the membranous portion
the cavernous portion
