Histo! Flashcards
What is the kidney’s function? what is a renal lobe?
regulate volume & composition of body fluids
produce ultrafiltrate of blood plasma
ultrafiltrate modified in uriniferous tubule (tubular parenchyma of kidney)
end product is urine which is moved through ureters by peristalsis and stored in bladder (vesical). The bladder is empted through urethra.
Kidneys –> ureter –> urinary bladder –> urethra
Renal Lobe = one medullary pyramid and its overlying cortex
What is the general structure of the kidney? Stroma? parenchyma? renal pelvis? renal sinus?
Stroma: very limited thin capsule of collagen fibers surrounding the kidney that consists of reticular fibers that subtend the basement membrane
Parenchyma: functional area of the kidney, this is the largest part
- composed of epithelial cells arranged into uriniferous tubules,, which drain into the renal pelvis
Renal Pelvis: expansion of the proximal ureter, which lies within the renal sinus, and becomes the ureter
Renal Sinus (hilum): central cavity which opens medially and provides passage for the renal pelvis, nerves, vessels and lymphatics that pass into the kidney
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What are uriniferous tubules?
Any tubule in the kidney that collects/ conducts urine
Arranged in **medullary pyramids: **
- conical structures with base facing the capsule and the apex (renal papilla) oriented toward renal sinus
- inserts into minor calyces
- 6-17 per human kidney
Minor Calyces: where the renal papilla drain into the renal sinus
Major Calyces: 3-4 minor calyces collected together.
Cortex vs. Medulla
Cortex:
- lies b/w bases of pyramids and capsule, and between adjacent pyramids
- outer portion
Renal Lobe:
- composed of one medullary pyramid and its overlying cortex
Medulla:
- more central
Medullary Rays:
- Where the medulla pushes up and extends into the cortex
Nephron
Functional unit of the kidney: divided into renal corpuscle (w/Bowman’s capsule) and the secretory tubule (uriniferous tubule)
The nephron feeds into the collecting duct
Bowman’s Capsule: components? purpose?
The Bowman’s capsule (or glomerular capsule) is a cup-like sac at the beginning of the tubular component of a nephron in the mammalian kidney that performs the first step in the filtration of blood to form urine. A glomerulus is enclosed in the sac. Fluids from blood in the glomerulus are collected in the Bowman’s capsule (i.e., glomerular filtrate) and further processed along the nephron to form urine. This process is known as ultrafiltration.
- double walled **epithelial structure: **
- parietal epithelium: squamous outer wall
- visceral epithelium: reflected tubular epithelium made of podocytes: capillary **bed lies under the visceral epithelium **
- “Bowman’s Space” = urinary space: space between parietal and visceral epithelium that receives glomerular filtrate
Glomerulus? Two poles of Bowman’s Capsule?
Glomerulus = tuft of capillaries found within the Bowman’s capsule
Vascular Pole = entrance/exit for vessels into Bowman’s capsule. Affarent arteriole enters. Efferent arteriole exits.
Urinary Pole = Area where ultrafiltrate exists corpuscle
- cuboidal epithelium
Cells of the Renal Corpuscle? What is the renal corpuscle filtration barrier composed of?
a renal corpuscle is the initial blood-filtering component of a nephron. It consists of two structures: a glomerulus and a Bowman’s capsule.
- Squamous Cells of parietal epithelium
- endothelial cells of capillaries: have large fenestrae
- mesangial cells: modified smooth muscle cells lying between capillaries. They regulate blood flow
- podocytes: squamous cells of visceral epithelium which have foot processes that wrap around glomerular capillaries, and form filtration slits.
The renal corpuscle filtration barrier is composed of: the fenestrated endothelium of glomerular capillaries, the fused basal lamina of endothelial cells and podocytes, and the filtration slits of the podocytes. This barrier permits passage of water, ions, and small molecules from the bloodstream into Bowman’s space
What makes up the glomerular filtration barrier?
trilaminar appearance, that forms the primary barrier to filtration. Rich in heparin-sulfate and chondroitin-sulfate and some hyaluronic acid and dermatin sulfate
Innermost layer: fenstrated endothelial cells of the capillaries
_Middle layer: _
- lamina rara interna (LRI): Charge Barrier
- lamina densa (LD): Size Barrier
- lamina rara externa (LRE): Charge barrier
Outer layer: Podocytes: epithelial cells
- trabeculated with foot processes (pedicels) that form to make filtration slits which are closed by diaphragms
What are the biochemical elements resulting in the filtration barrier? What is the size restriction?
LRE/LRI: form the charge barrier
- made of laminin and heparan sulfate
- heparin sulfate makes a strongly anionic filtration barrier, thus plasma proteins (anionic) are repelled, but cations pass more readily through the barrier
LD: forms the size barrier
- made of Collage Type IV
Most filtered molecules are restricted at the LRI
- <5,2000 MW pass freely
- molecules > 69,000 MW can’t pass (i.e. albumin and other plasma like proteins)
How do you determine proximal convoluted tubule vs. distal convoluted tubule?
Proximal:
- darker pink staining, with more fuzz in lumen. Due to acidophillic (mitochondria) and larger microvilli
Distal:
- usually smaller
- cells appear more dense, and less microvilli present
- lighter pink staining due to less mitochondria present
What is the proximal convoluted tubule?
- Found in the cortex
- reabsorbs 70-80% of glomerular filtrate: including water, salt, amino acids, glucose, proteins
- Most of water is filtered here!!!
- made of cuboidal cells w/ dense microvillus (brush border)
- numerous basolateral interdigitations
- abundant mitochondria
Proximal straight tubule?
- found in cortex and medulla: runs in medullary ray from cortex(outer) to medulla(inner)
- reabsorbs glomerular filtrate
- similar to PCT:
- but cells are shorter
- microvilli less numerous/less developed
- few basal infoldings w/ mitochondria
- narrows abruptly into loop of Henle
Loop of Henle
Found in the medulla- establishes a hypertonic medullary interstitium
Countercurrent multiplier system: ascending limb pumps NaCl into interstitium (a mechanism that expends energy to create a concentration gradient)
Morphology:
- narrow lumen, with hairpin like bend
- made of **simple squamous epithelium **
What is the countercurrent multiplier system of the loop of Henle?
Countercurrent multiplier system: (a mechanism that expends energy to create a concentration gradient)
Descending limb: H2O and ions diffuse freely out of loop
- Na+/Cl-/K+ and urea also move freely into the loop
Ascending limb: impermeable to water
- Na+/Cl-?K+ acively transported back into medulla
countercurrent transport of ions
creates osmotic pressure
draws H2O into the medullary space
makes space hyperosmolar
makes filtrate hypertonic
moves toward isotonicity through loop
Distal Straight tubule
- continuous with ascending limb of loop of Henle
- impermeable to water
- transports ions from lumen to interstitium
- Morphology:
- cuboidal epithelium w/ basolateral interdigitations
- round smooth lumen
- apically-placed nuclei
- paler staining
Distal Convoluted Tubule
- Found only in the cortex
- “thick ascending limb”
- returns to renal corpuslce of origin
- 60% shorter than PCT
- under the influence of aldosterone:
- reabsorbs Na+
- secretes K+
- reabsorbs bicarbonate (and secretes H+)
- secretes ammonia
Function:
- reabsorbs salt under influence of aldosterone
Juxtaglomerular Apparatus
regulates body’s salt and water balance
monitors:
- salt levels - distal tubule
- blood pressure - affarent arteriole: renin is released when levels are low
it is found between the vascular pole of the renal corpuscle and the returning distal convoluted tubule of the same nephron.
comprised of three cell types:
- afferent arteriole (juxtamedular/ JG cells)
- macula densa ( of distal tubule)
- extraglomerular mesangial cells
What do JG cells do? macula densa? mesangial cells?
JG cells:
- modified smooth muscle of the afferent arteriole
- secrete the enzyme renin
Macula densa:
- closely packed cells in the DCT tubule wall adjacent to afferent arteriole
- monitor Na+ concentration in tubule and regulate filtration rate
- stimulate renin release from JG cells
- stimulates contraction of afferent arteriolar smooth muscle
Extraglomerular mesangial cells:
- fusiform/flat cells that provide support - their function is unclear
Collecting Ducts: what are three regions? what are two different types of cells present?
Cortical Portion:
- receives urine from several nephrons
- ducts run in center of medullary ray toward medulla
- cells are initially cuboidal, but become columnar
- lumen increases in width distally
Medullary Portion:
- site of final concentration of urine
- H2O is lost to increasingly hypertonic medullary intersitium
- ADH makes duct more permeable to H2O
Medullary portion (renal papilla region)
- ductal cells become **tall cuboidal to columnar **
- combine in medullar to form large papillary ducts
- papillary ducts open at area cribosa of papilla
Two basic cell types present:
- light cells (principle cells) - involved in releasing water from the tubule through aquaporin channels
- dark cells (intercalated cells) - two distinct cell types involved in controling acid/base balance of urine (a, secrete H+, B, secrete HCO3-)
Renal Interstitium: what are three cell types? functions of the cells?
- the renal interstitium surrounds collecting dugs
Made of three cell types:
- Principal Type I cells: produce powerful vasodilators - Prostaglandins (derivates of arachidonic a.)
- Type II interstitial cells: probably phagocytic
- Type III Interstitial cells: function unknown
Prostaglandins and leucotriences act to control Glomerular blood flow
Medullary Rays? Renal Columns?
Medullary Rays: areas of medulla that reach out into the cortex
- consist of loops of Henle, associated PST’s and DSTs, central collecting ducts
Renal columns: areas of cortex that extend into medulla
- renal copuscles
- PCT’s, DCTs
- loops of Henle
- associated PST’s and DST’s
- central collecting duct
Renal Lobule
lobules are found only in the cortex
surround collecting duct and medullary ray
include:
- medullary ray
- labyrinth surrounding ray
- renal corpuscles
- PCT and DCT
(not to be confused with renal lobe: which is renal pyramid and overlying cortex)
What is the renal vascular supply?
aorta –> renal artery –> segmental aa. –> interlobar aa. (between pyramids) –> arcuate aa. (arch over base of pyramid) –> interlobar aa. (from arcuate to capsule) –> affarent arterioles –> glomerulus
–> efferent arterioles –> vasa recta (in renal columns of medulla) or peritubular capillaries (in renal cortex)
