MICROSCOPIC FEATURES OF NEPHRONS-UPDATED.pptx

student will learn the basics of kidney and histology of nephrons. it will help them learning and understanding the functions, different parts of nephrons.

1. MICROSCOPIC FEATURES OF NEPHRONS & COLLECTING DUCT Presenter name: Dr. Kashif Hussain Alvi Awan

2. KIDNEYS Kidney is a large bean shaped organ located retroperitoneally in the posteior abdominal wall. On the medial of the kidney is a depression ‘Hilum’ through which the renal artery enters and renal vein and ureter leave the organ. On naked eye inspection, the kidney shows outer reddish brown zone ‘CORTEX’ and inner lighter zone ’MEDULLA’. The Medullary substance of each kidney is arranged as 8 to 18 conical masses called Renal pyramids. Based on each pyramids lies adjacent to the cortex, whereas apex, known as papilla projects into a minor Calyx of the renal pelvis.

3. THE URINIFEROUS TUBULE The Uriniferous tubules forms the structural and functional unit of kidney. It consist of 2 parts i.e. Nephrons is the longest part of the uriniferous tubules. It is responsible for the production of urine. Collecting Tubules conveys the urine from the nephron to a collecting duct lying in a medullary ray.

4. NEPHRONS Each kidney contains approximately 1.5 millions nephrons. A nephron is along, epithelium-lined tube which begins blindly and ends by joining a collecting tubule. Each nephron begins as a double-walled, cup shaped dilatation known as Bowman’s capsule. A tuft of capillaries called glomerulus occupies the concavity of the capsule.

5. TYPES OF NEPHRONS Superficial cortical nephrons situated in the outer part of renal cortex. Mid cortical nephrons are situated in the mid region of the cortex and their Loop of Henle are of intermediate length. The Juxta-medullary nephrons have their renal corpuscles located in the deepest part of the renal cortex in close proximity to the base of the medullary pyramid.

6. RENAL CORPUSCLES The renal corpuscles are spherical bodies, ranging from 200 to 250 μ m in diameter. A renal corpuscles consist of a Bowman’s capsule and a glomerulus. The Bowman’s capsule is in the form of a double- walled cup i.e Parietal layer. Visceral layer. The parietal layer is made up of a simple squamous epithelium and its basal lamina which covers the outer surface of the squamous cell. The visceral layer covers the glomerulus. It is composed of specialized epithelial cells called podocytes .

7. PODOCYTES The podocytes are large, irregular star shaped cells which share a common basal lamina with the endothelial cells of the glomerular capillaries. The tentacles give rise to the numerous processes Pedicles. Podocytes play an important role in glomerular function. Together with endothelial cells of the glomerular capillary loop and the glomerular basement membrane they form a filtration barrier. Podocytes cooperate with mesangial cells to support the structure and function of the glomerulus

8. THE GLOMERULUS The glomerulus is a tuft of fenestrated capillaries connecting an afferent arterioles with an efferent arteriole. The two arterioles usually lie close together at the vascular pole of the renal corpuscles. MESANGIUM The space between the glomerular capillaries is occupied by a special type of connective tissue called mesangium . The mesangium function is to: Provide structural support for the capillary loops Act as a phagocyte. Can increase or decrease blood flow through their contractile property

9. PROXIMAL TUBULE The proximal tubule of the nephron consist of 2 parts: Proximal Convoluted Tubule Proximal Straight Tubule Proximal Convoluted Tubule is the longest and most tortuous part of the nephron. It is about 14mm long and has an outside diameter of about 60 μ m. It also occupy the major part of the cortex due to longest part of the nephron. PCT contains simple cuboidal epithelium. EM reveals that it contains numerous long mitochondria. The principle function of PCT is to actively absorb sodium from the Glomerular filtrate and to pump it into the intercellular space. Proximal Straight Tubule is lined by low cuboidal limb of Loop Of Henle. It forms the descending limb of Loop Of Henle.

10. LOOP OF HENLE The Loop Of Henle joins the Proximal straight Tubule to the distal straight tubule which constitute U shaped structure known as LOOP OF HENLE. FUNCTION OF LOH It is responsible for the concentration of the urine. The descending thin segment is permeable to water as it contain Aquaporin -1 water channel. The thick segment actively reabsorbs sodium, chloride and potassium ions from the filtrate and transfer them to the interstitial space between the tubules.

11. DISTAL CONVOLUTED TUBULES LM shows that the distal convoluted tubules are lined by Simple Cuboidal Epithelium . Principle function of the DCT is resorption of sodium from the glomerular filtrate under the influence of hormone ‘Aldosterone’.

12. COLLECTING TUBULES AND COLLECTING DUCT The collecting tubules have an average diameter of 40 μ m and are lined by simple cuboidal epithelium . A collecting tubules receives many DCT. The collecting tubules joins each other to form larger straight COLLECTING DUCTS. The collecting ducts are lined by a simple columnar epithelium . The epithelium lining the Collecting ducts contains two types of cells: Light cells Dark cells

13. LIGHT CELLS Light cells are pale staining cells containing oval, centrally-placed nuclei. Their luminal surface bears a few short microvilli. These cells possess a large number of Aquaporin-2 water channels which are permeable to water. MNNM DARK CELLS are further classified into: Alpha intercalated cells. Beta intercalated cells. Alpha cells secretes H+ Ions into collecting duct lumen. BETA cells resorbs H+ ions and secretes HCO3 into the lumen of the collecting duct.

14. The principle function of Collecting duct and collecting tubules and ducts is to conduct urine from the nephrons to the renal pelvis. However, under the influence of the ADH, These tubules resorb water from the glomerular filtrate.

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