JG apparatus.pptx

renal physiology

1. structure and functions of juxta glomerular apparatus and role of renin-angiotensin system

2. Juxtaglomerular apparatus The juxtaglomerular apparatus is the site of blood pressure regulation via the renin- angioensin -aldosterone system.  They are located at the vascular pole of Bowman’s capsule and are formed by the conjunction of cells of (1)Macula densa of the thick ascending limb of LOH (2) Juxtaglomerular cells (the modified muscle cells mainly of afferent arteriole) (3) Lacis cells (Extra glomerular mesangial cells)

3. Juxtaglomerular apparatus….. The macula densa is a portion of terminal distal straight tubule adjacent to the renal corpuscle.  These cells monitor the NaCl levels in the afferent arteriole and regulate the juxtaglomerular cells within that vessel.  The juxtaglomerular cells are specialized smooth muscle cells of the afferent arteriole which synthesize and secrete renin.  These cells also called as polkissen cells. Lacis cells are the extra glomerular mesangial cells. These cells secrete some quantity of renin & erythropoietin .

4. How does the Juxtaglomerular apparatus work The macula densa cells monitor NaCl levels in the fluid of the afferent arteriole.   Renin secretion of the juxtaglomerular cells is stimulated by paracrine activity from the macula densa .  Renin is a protease that cleaves plasma angiotensinogen into angiotensin I.  Angiotensin I is converted to angiotensin II in the lung (by an enzyme in the capillaries). 

5. How does the Juxtaglomerular apparatus work…….. Angiotensin II promotes vascular smooth muscle contraction and release of aldosterone from the suprarenal cortex.  Aldosterone stimulates absorption of NaCl and water in the distal convoluted tubule thus increasing blood volume resulting in an increase in blood pressure

6. Renin-Angiotensin-Aldosterone System Juxtaglomerular apparatus secretes renin . Renin acts on angiotensinogen (gamma globulin from the liver) giving angiotensin I Angiotensin converting enzyme (ACE) acts on angiotensin I giving angiotensin II

7. Renin-Angiotensin-Aldosterone System Renin : It is secreted by the juxtaglomerular cells in Kidney Changes in secretion is in response to changes in renal arterial pressure, sympathetic nervous system signals and some hormones Its substrate is angiotensinogen

8. Renin-Angiotensin-Aldosterone System Angiotensinogen It is a glycoprotein synthesized and secreted into the bloodstream by the liver Angiotensinogen Renin angiotensin I ACE Angiotensin III Angiotensin II

9. Renin-Angiotensin-Aldosterone System Angiotensin converting enzyme (ACE) is also known as kinanase II. It converts angiotensin I to II (vasoconstrictor) and inactivates bradykinin (vasodilator )’ The principal site of its action is vascular epithelium. It is inhibited by synthetically produced Captopril drug.

10. Renin-Angiotensin-Aldosterone System Angiotensin II Stimulates aldosterone production Stimulates ADH secretion from pituitary Highly potent vasoconstrictor Stimulates thirst Stimulates release of catecholamines by adrenal medulla Angiotensin III Stimulates aldosterone production without vasoconstriction

11. Role of Angiotensin II Hypertensive Angiotensin ll is a powerful vasoconstrictor . It constricts the blood vessels and raises the peripheral resistance, thereby acting to restore blood pressure. Angiotensin ll also increases the secretion of aldosterone leading to Na+ reabsorption.

12. Effects of Angiotensin II

13. Regulation of Aldosterone Angiotensin II and III stimulate aldosterone release Changes in volume ( long Negative feedback loop) Inhibition of renin secretion by angiotensin II (short negative feedback loop) Endothelin and vasopressin stimulate aldosterone secretion ANP is a potent inhibitor, dopamine also inhibits it.

14. Aldosterone Angiotensin II Angiotensin III Endothelin ADH Kidney Renin JGA Distal Tubules Blood Volume Na & H2O ANP Osmolarity

15. Q1. Function/s of kidney is/are: Glycogenolysis Secretion of erythropoietin Acid-base balance Both (b) and (c)

16. Q2. Average number of nephrons in both kidneys are: 1 million 2 million 4 million none

17. Q3. Glomerular capillary membrane is formed of: Endothelium of the capillary Basement membrane of the capillary Podocytes All of the above

18. Q4. True about juxtamedullary nephrons is: 70-80% Short loop of Henle Vasa recta All of the above

19. Q5. Albumin is not filtered because of: Large size /diameter Negative charge on basement membrane Both (a) and (b) None

20. Q6. Juxtaglomerular apparatus is formed of: Lacis cells Juxtaglomerular cells Macula densa All of the above

21. Q7. R enin is secreted by: Juxtaglomerular cells Interstitial cells around peritubular capillaries Macula densa Lacis cells

22. Thank you