Kidney , nephron and juxtaglomerual histology pre

Kidney , nephron and juxtaglomerual histology pre

1. Histology of kidneys Presented by: Roaa Salah Mostafa ebrahim

2. Objectives 1 3 2 4 General structure of kidney Juxtaglomerular appartus Histological structure of kidney: nephron, PCT and DCT Collecting system

3. General structure of kidney Shape: it has a bean shape with a concavity on the medial border called hilum where arteries, nerves, lymphatics and veins are located. It is a compound, tubular, excretory and endocrine gland. It filters a large amount of waste products from the blood by small tubules unit called uri-nephrous tubules . It is composed of : 1-Cortex 2- Medulla 3- Major and minor calyces 4-Renal pelvis

4. Histological section of the kidney A-Cortex: It is the dark outer layer. It has a granular appearance due to presence of the renal corpuscles and the convoluted renal tubules. B-Medulla: It is the pale inner layer. It has a striated appearance due to the longitudinally arranged straight renal tubules, collecting ducts& the surrounding vessels. The renal medulla • It is composed of 8-12 renal pyramids: Their bases: form the cortico-medullary junction. Their apices (the renal papillae): protrude into the minor calyces. • The tip of the papilla is perforated by the openings of the larger collecting ducts and so, it is called the area cribrosa

5. Urinephrous tubule It is formed of: Nepfron : consists of: 1- Renal corpuscle 2- Proximal convoluted tubule 3-loop of henle 4-Distal convoluted tubule Collecting duct

6. Nephron: functional unit of the kidney: Renal corpuscle: it is a rounded structure lying in the renal cortex. • It has two poles: 1- Vascular pole: where the afferent arteriole enters and an efferent arteriole leaves the glomerulus. 2- Urinary pole: where the proximal convoluted tubule begins. Components of the renal corpuscle 1-The Bowman’s capsule 2- Glomerulus 3- Mesengium

7. Bowmans capsule: A- Parietal layer: Simple squamous epithelium. At the urinary pole, the epithelium changes to simple cuboidal epithelium lining the proximal convoluted tubule. B- Visceral layer: Covers the glomerular capillaries. Formed of the podocytes (modified epithelial cells). Function: share in formation of renal filtration barrier C- Bowman’s space(urinary space): It is the space between the two layers of the Bowman’s capsule. It receives the fluid filtered from the glomerular capillaries.

8. Glomerulus: It is the vascular pole of the renal corpuscle, tuft of fenestrated capillary invaginated into the bowman's capsule. Function: Share in the formation of renal filtration barrier. Filtration barrier of the kidney : composed of 1-The fenestrated endothelium of glomerular capillaries: It forms an initial physical barrier to the passage of blood elements. 2-The glomerular basement membrane: It is the common fused basal lamina of the glomerular capillary endothelial cells and the podocytes. 3-The filtration slit diaphragms: it restricts filtration of the small protein

9. Mesengium Branched cells between the capillaries Functions: 1-Support the glomerular capillary walls where podocytes are lacking. 2-Continuous turnover of glomerular basement membrane by phagocytosis of the filtration residues (its renewal is done by the podocytes and the glomerular endothelial cells)

10. Proximal convoluted tubule: It is the longest segment of the nephron, begins at the urinary pole of the renal corpuscle in the cortex and end in the loop of henle . Structure: Simple cuboidal or low columnar cells with round large nuclei, apical acidophilic brush borders(microvilli) They rest on distincit basement membrane, have basal acidophilic striations(mitochondria and basal infoldings) and have indistinct lateral membrane. Functions: Reabsorption of glucose, proteins, amino acids Reabsorption of sodium, potassium and chloride ions. Reabsorption of 65% of water.

11. Loop of Henle: It is U shaped tubule extends from PCT in the cortex and dips into medulla and returns back to the cortex to end with DCT. Structure: It has four segments: 1- The thick descending limb: it is a straight continuation of the PCT in the medulla, with a lining epithelium similar to it. 2&3- The thin descending and the thin ascending limbs: take a U-shaped course in the medulla, lined by simple squamous epithelium with few organelles. 4- The thick ascending limb: it is the straight part of the DCT with its same lining epithelium. Function: 1- the descending limb reabsorps small amount of NaCl 2- the ascending limb reabsorps water to produce hypertonic urine .

12. Distal convoluted tubule: It is shorter and less convoluted than PCT, begins at the thick part of ascending loop of Henle and ends in the collecting tubule in the cortex. Structure: 1-Shape: they are lined by short cuboidal cells with spherical nuclei 2-The lumen: wide with no brush border. 3-Cytoplasm: pale acidophilic 4-Lateral cell boundaries: more distinct and prominent basal striations Functions: 1- reabsorps water and sodium 2- secretion of potassium and hydrogen 3- Macula densa cells act as receptors to control Na ion level

13. Juxtaglomerular apparatus: • Site: at the vascular pole of the glomerulus where the afferent and efferent arterioles come in close contact with the initial part of distal convoluted tubule. • Function : controls the systemic blood pressure, the rate of glomerular filtration & the rate of urine formation • Components : 1-Vascular component: Juxtaglomerular cells. 2-Tubular component: macula densa cells. 3-Supporting component: Extraglmoerular mesengial cells

14. • Definition: modified smooth muscle fibers in the tunica media of the afferent arteriole. • Function: 1- Secretion renin. 2- Secretion of erythropoietin • Structure: LM: large cell with granular basophilic cytoplasm. EM: protein secreting cells with secretory granules. Juxtaglomerular cells

15. Macula densa cells • Definition: modified cells of the distal tubule that come in close contact with the afferent arteriole at the vascular pole of the glomerulus. • Function : Osmoreceptors, sensitive to Na concentration to detect any decrease in BP. • Structure: 1- Shape: closely packed columnar cells with crowded and superimposed nuclei. 2- Cytoplasm: few mitochondria with no basal infoldings. 3- Apically: numerous microvilli and a central cilium that acts as a sensor for sodium ion concentration in tubular fluid.

16. Extraglomerular mesangial cells = Lacis cells • Definition: group of cells occupying the angle between the afferent and efferent arterioles. • Function : Support and coordination (intercellular signaling). • Structure : 1- Conical mass of small cells. 2- Extend cytoplasmic processes in a lace like network that contact the JGC, macula densa and the intraglomerular mesangial cells by gap junctions.

17. Collecting system: The cortical collecting ducts receive the filtrate from the connecting tubule and continue down into the medulla as medullary collecting ducts. Many medullary collecting ducts join to form a larger duct called the papillary ducts of Bellini which open in the area cribrosa at the apex of the renal papilla Structure: 1-Lumen: wide. 2-Cells: cuboidal (in cortical collecting ducts) then columnar (in medullary collecting ducts & papillary duct of Bellini) with distinct cell boundaries. 3-Cytoplasm: less acidophilic

18. Function: 1-Reabsorption of water (ADH) & salts (aldosterone). 2-Secretion of hydrogen or bicarbonate. 2-Intercalated cells(dark cells): Number: Few. Site: Mainly in the smaller collecting ducts Structure: Dark cytoplasm with numerous mitochondria. Function: Regulation of acid-base balance in the tubular fluid • Two types of lining cells: 1-Principal cells (light cells): Number: The majority. Site: Present in all parts of collecting ducts Structure: pale with few mitochondria. Function: Facultative reabsorption of water (ADH) Collecting system:

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