Histology Of Urinary System 2 Flashcards
How do renal tubules modify Glomerular ultrafiltrate ?
- Reabsorption
- Secretion
- Reduces urine volume
- Creates a hyperosmotic fluid
Describe the structure of proximal straight henle
Also called thick descending portion of loop of Henle
- Found in the medullary ray of the cortex. Also found in outer medulla
- Shorter cells with poorly developed brush border and less complex basolateral and lateral interdigitations than the PCT’s
- Fewer and smaller mitochondria scattered throughout the cytoplasm
Where are thin segment of loop of henle located?
Longer in juxtamedullary nephrons and are found in the medulla
Describe the structure of thin segment of loop of henle
-Four distinct segment based on shape of cells, their contents of organelles, the depth of their tight junctions, and their water permeability
Epithelium varies from:
-thin simple squamous in both ascending and descending limbs in short nephrons
Squamous cells are modified in…
Certain parts of the loop of henle
Describe the vasa rectus and countercurrent exchange system of the nephron
Arteriole and venule rectae form loops parallel to the loop of Henlé (fenestrated capillaries)
Help maintain osmotic gradient in the interstitium
Hypertonic interstitium
- causes loss of water from the arterioles as they descend into medulla
- Movement of water into the venules as they ascend
Where is the distal straight tubule found?
Found in the medullary ray of the cortex. Also found in outer medulla
Describe distal straight tubule
Shorter cells with blunted brush border and less complex basolateral and lateral interdigitations
Smaller cells with less mitochondria scattered throughout the cytoplasm
What are the distal straight tubule of loop of henlé?
Also called thick ascending limb
- Cortical part found in the medullary rays
- Transports ions from the lumen of the tubule to the interstitium via mainly active transport
- Reabsorption of other ions: Ca2+ and Mg2+
Describe the distal convuluted tubule
Very short-starts at the macula densa and ends at connecting tubule
- Less numerous profile in sections as it is 1/3 the length of PCT
- Simple cuboidal epithelium
- Smaller cuboidal epithelium
- Less acidophilic cytoplasm
- Fewer and shorter microvilli however extensive basal folds
- Apically placed nucleus
What are the functions of the distal convuluted tubule?
- Reabsorption
- Na+ and secretion of K+
- bicarbonate and secretion of H+
- Secretion of ammonium
- Parathyroid regulated Ca2+ reabsorption
- Relatively impermeable to water
- Highest Na+/K+ ATPase activity
What are macula densa?
-Modified cells of the distal straight tubule
Located at the vascular pole -forms part of the juxtaglomerular apparatus which regulates blood pressure
- Narrower and taller cells
- Senses chambers in Na+ concentration within the lumen of the distal tubule and sends signals to the juxtaglomerular cells (Modified smooth muscle cells) located in the afferent arteriole
What features help identify DCT?
Ratio off PCT to DCT (6:1)
- Epithelial cells are smaller
- Smaller inter- nuclear distance (smaller profiles)
- Clearer lumen
- Relaatively basophilic cytoplasm (lesser mitochondria)
How does the kidney help regulate blood pressure?
Juxtaglomerular apparatus components
- Macula densa(osmoreceptors)
- Extra Glomerular mesangial cells (Lacis/ Polkissen cells)
- Juxtaglomerular cells(JG cells)
I. Modified smooth muscle cells of afferent arteriole
II. Produce renin—> cleaves angiotensinogen to angiotensin I
Where are angiotensin I converted to angiotensin II?
Angiotensin I converted to angiotensin II (pulmonary endothelial cells)
- potent vasoconstrictor
- stimulates aldosterone secretion from adrenal cortex
- aldosterone stimulates reabsorption of Na+ and secretion of K+ by connecting tubules and collecting ducts
What are connecting tubules?
- Connects DCT to cortical coll3cting duct
- Cortical nephrons- very short
- Mild cortical and JM nephrons, longer and arched
- Gradual transition of epithelium from DCT to collecting duct
- Contain cells from DCT and CD (principal cells)
- Secretes of K+ into lumen —>partly regulated by aldosterone
What is the cortical collecting duct?
- Found in the medullary ray of the cortex
- Connecting tubules lead into cortical collecting duct
- All nephrons within a renal lobule drain into one cortical collecting duct
- Lined by simple cuboidal epithelium with prominent cell boundaries
- The diameter of this duct progressively increases as it enters the medulla
What are medullary collecting ducts?
- Medulla: simple cuboidal transitions to simple columnar epithelium
- The lumen widens progressively from cortex to medulla
- Several merge to form papillary ducts (ducts of Bellini)
What are the functions of light/principal cells?
- Most abundant : pale staining
- true basal in folding:
Single primary ilium: short scattered microvilli
Abundant ADH regulated aqua porins (AQP-2) channels
What are dark or intercalated cells?
- fewer
- not present in the inner medulla
- Microvilli and microplicae at Apical cytoplasm
- Secretion of H+ or bicarbonate
Describe the physical structures of medullary collecting ducts
-Dark cells in outer medulla only
- Principal (light) cells increase in height
- lines the collecting duct of inner medulla
- Ducts of Bellini
- 200 to 300 um in diameter
- Empties at the area cribrosa at the apex of a renal papilla
What are the components of renal interstitium ?
The connective tissue of the kidney
- surrounds the nephrons and neurovasculature
Cell types:
- fibroblasts
- Mononuclear cells
Medullary interstitium:
-resemble myofibroblasts present along the descending vasa recta
What are the functions of excretory passages?
Transit and and storage of urine
Include: minor and major calices, renal pelvis, ureter, urinary bladder and urethra
Passages have the following features:
Mucosa
Muscularis
Adventitia
What are the 3 layers of the transitional epithelium?
Superficial: single layer of dome shaped (umbrella) cells
- The shape of the cell depends on the filling state
- Abundant tight junctions
- Impermeable to urine
Intermediate:
-Pear shaped cells —> abundant Desmosomes
Basal layer: stem cells
What are the special modifications of superficial cells of urothelium?
- Urethelial plaques: on the Apical surfaces (contains crystalline uroplakin which contributes to the permeability barrier)
- Apical scalloped surface covered by the uroplakin
Flattened elliptical vesicles (fusiform vesicles)
What is the ureter?
The conduit between the renal pelvis and the urinary bladder
What are the layers of the ureter?
-Urothelium + Lamina propria
- Muscularis—> 3 layers of smooth muscle
- Inner longitudinal
- Middle circular
- Outer longitudinal (only present in distal end)
Contraction of these muscle layers produces peristaltic waves
Adventitia
Describe the general organization of the urinary bladder
Mucosa-Epithelium+ fibroelastic CT
Muscularis
Muscularis of the bladder is thick and consists of smooth muscle arranged in an inner longitudinal, middle circular and outer longitudinal layer (oblique orientation of muscles)
-Adventitia/serosa
What is a urethra?
Conveys urine from the bladder to be evacuated outside
What are the segments of the male urethra?
- prostatic= transitional epithelium
- membranous= transitional epithelium
- Spongy: transitional epithelium fossa navicularis is lined by stratified squamous epithelium
Mucus-secreting glands if liter in the subepithelial connective
Describe the female urethra
Short—> high risk of urinary infections
Initial part—> transitional epithelium
Terminal part—> stratified squamous epithelium
