Week 1: Renal Microanatomy Flashcards
Give overview of the nephron.
- Renal corpuscle=Bowman’s capsule and glomerulus. Bowman’s capsule is epithelial lined with parietal and visceral layers. Space within capsule i Urinary Space
- glomerulus=vascular structure which indents Bowman’s capsule, system of capillaries supplied be afferent arteriole and drained by efferent arteriole
- Proximal convoluted tubule: mostly in cortical tissue, straight terminal part can be in medulla
- Loop of Henle: thick and thin segments, mostly in medulla
- Macula densa: located at termination of loop of henle thick segment
- Distal convoluted tubule: only in cortex
- Collecting system of tubules: drains nephron
Give blood flow of the kidney.
- Renal artery–>dorsal and ventral branches–> interlobars (betw. pyramids) –>arcuate arteries–> cortico-radial arteries–> afferent glomerular arterioles–> glomerular capillaries–> efferent glomerular arterioles
- Most important resistance vessel is afferent arteriole
- the vein and artery of the cortico radial artery and vein and the arcuate artery and vein run close together and there is gas exchange that occurs. Makes the kidney one of the most hypoxic organs.
Describe the blood supplied by the efferent arterioles.
- In cortex, efferent arterioles become peritubular capillaries of cortex
- 10% of nephrons are juxtamedullary nephrons, their efferent arterioles form vasa recta, which are a redundant loop of thin walled vessels in medulla, enveloping those parts of nephron in the medulla
Describe light microscopic features of different parts of the nephron.
- Proximal Conv. Tubule: simple cuiboidal epithelium with brush border
- Loop of Henle
- Thin segment: simple squamous epithelium with smooth surface and thin walled
- Thick segment: low or medium cuboidal epithelium, basal striations - Distal Conv. Tubule: simple low-med cuboidal epithelium. No brush border. Basal striations.
- Collecting tubules
- principal/light cells predominate. Simple med. cuboidal to simple columnar cells. Single cilium/cell.
- intercalated cells (dark)-many microvilli and mitochondria
describe the 3 layers of the renal minimal border (layers of the glomeruli).
- Endothelial cells with open fenestrations
- Basal laminal (basement membrane): only continuous layer
- Foot processes of podocytes that are interdigitating. Slit diaphragm between the foot processes. (podocytes are on the visceral layer of Bowman’s capsule)
- Nephrin: protein specific to slit diaphragm. Aberrations in this protein linked to nephrotic syndromes.
Describe features of the proximal convoluted tubule at the EM level.
- longest part of nephron
- brush border of microvilli with numerous vesicles. Well developed endocytotic mechanisms
- Lateral edges of cells interdigitated. Tigh junctions.
- Basal surface infoldings, abundant Na/K ATPase activity
- Mitochondrial numerous in infoldings
- Peritubular capillaries are close to PCT
- Capillary hydrostatic pressure is low. Blood colloid pressure is high because proteins still in blood weren’t filtered at Glomeruli
Describe structure and function of Loop of Henle with EM level details.
- Thin segment: freely permeable to water and Na. Aquaporin I. no Active transport. Simple squamous.
- Thick segment: simple cuboidal epithelium with lots of mitochondria. Impermeable to water, actively pumps Na. No aquaporin. Strong tight junctions and basal infoldings.
- Counter current multiplication system: creates sodium gradient. Na pumped by thick segment into medullary interstitial, draws water from thin segment. Vasa recta has leaky epithelium, helps facilitate rapid exchange of diffusible substances.
Describe function and structure of distal tubule with EM level details.
- Structurally like thick segment of Loop of Henle
- function: actively pumps Na, not so impermeable to water
- more distal parts influenced by aldosterone and ADH
- thiazide sensitive Na transporters here
Describe function and structure of collecting tubule with EM level details.
- dominant cell: principal or light cell. Cuboidal to columnar. Single motile cilium at luminal surface. responsible for sodium reabsorption and adjustments in water reabsorption
- dark/intercalated cells: function in acid base balance
- Epithelial cells of CT have Aquaporin II
- Function of the CT system: conducts urine to calyces, modifies urine with regard to final Na and water retention
- primary cilia also have sensory role
- influenced by ADH and aldosterone
What are renal medullary interstitial cells?
-they interconnect tubular and vascular structures of the descending thin limb (DTL), thick ascending limb (TAL), collecting duct , and vasa recta (VR) capillaries. RMIC contain cytosolic granules
Describe the JG apparatus.
=JG cells+macula densa+mesangial cells
- Juxtaglomerular cells: modified SMC within media of afferent glomerular arterioles that secrete renin
- macula densa: dense plaque of epithelial cells located in terminal segment of thick segment of Loop of Henle, situated between afferent and efferent arterioles. Tightly packed, larger, columnar. Apically located nuclei. Basal lamina beneath MD is thin or absent.
- sense Cl- within lumen, if low, stimulates JG cells to release renin
- Mesangial cells: interstitial cells. Contractile, can be derived from monocytes or SMCs. Extra or intraglomerular
Function and contractility of mesangial cells
Intraglomerular mesangial cells provide structural support for and regulate blood flow of the glomerular capillaries by their contractile activity. The initiation of contraction of mesangial cells is similar to that of smooth muscle. Contraction of mesangial cells is coupled with contraction of the basement membrane of the endothelium of glomerular capillaries. This causes a decrease in surface area of the basement membrane and thus a decreased glomerular filtration rate.
