Renal: Juxta-glomerular Apparatus & Renal Blood Flow

Question 1

definition of Juxta-glomular Apparatus

Answer 1

A specialised group of Vascular & Tubular cells that are in contact between afferent & efferent arterioles, & Distal Convoluted tubule of the same nephron, near the glomeruli

Question 2

Function of Juxta-glomerular apperatus

Answer 2

It senses changes in Arterial Blood pressure, so that it can:
1. Autoregulate renal Blood flow and glomerular flow rate (GFR) during those changes
2. Change in Arterial Blood pressure (of the body ) itself by RAAS

Question 3

Constituents of Juxta-glomerular Apperatus

Answer 3

• Macula densa
• Juxtaglomerular cells

Question 4

Describe Macula densa and its function

Answer 4

• Modified tubular cells
• Located in early Distal Conv. tubule
• Comes in contact with both Afferent & efferent Arteriole

Function: Chemorecepor; by monitoring fluid composition (NaCl)

Question 5

Describe Juxtaglomerular Cells & their function

Answer 5

• Epithelioid granular Cells
• Located in the Media of Afferent Arteriole (lesser in efferent)

Function: Baroreceptor; it’s stimulated by
1. decrease renal Perfusion pressure
2. Hypovolemia
stimulation causes secretion of Renin

Question 6

Average Rate of Renal Blood flow

Answer 6

1.2-1.3 Liter/ minute

21% of Cardiac Outpurt

Question 7

Enumerate the 2 capillary beds associated with the nephron & where they arise from

Answer 7

• Glomerular Capillary bed: arise from Afferent Arteriole
• Peritubular Capillary: Arise from efferent Arteriole

Question 8

Type of Capillary pressure in Glomerular Capillary bed

Answer 8

Highest Capillary pressure in the body=60 mmHg), for Rapid filtartion

Question 9

Type of Capillary pressure in Peritubular Capillary & its function

Answer 9

Low pressure= 13 mmHg, allow Fluid reabsorption from ISF to blood through the capillary

Question 10

Explain why Glomerular Capillary bed has the highest capillary pressure

Answer 10

• Renal Artery is a direct branch of Abdominal aorta
• Afferent Aterioles are short & straight
• Efferent has higher resistance than afferent, causing high pressure build up in the intermediate (glomular) capillary

Question 11

Describe the renal Blood flow distribution in the kidney

Answer 11

• Renal Cortex: 98% of RBF
• Renal Medulla: 2% of Renal Blood flow (sluggish flow)—-> formation of concetrated urine

Question 12

Importance of Autoregulation of Renal Blood flow

Answer 12

Keep Renal Blood flow & Glomerular flitration rate constant despite Marked changes in ABP between 90mmHg-220mmHg

Question 13

What is the 1st line of defense against rapid changes in Arterial Blood pressure in RBF autoregulation

Answer 13

Myogenic Autoregulation:
1. ABP increases above 200mmHg
2. Stretch of Afferent Arteriole
3. Opening of Ca+ channels
4. Contractile response—> Vasoconstriction

& Vice Versa

Question 14

Describe How Tubulo-glomerular balance takes place at marked increase of ABP (Feedback mechanism)

Answer 14

1. ABP increases, Renal Blood flow Increases
2. Solutes (Na+ & Cl-) increase in Macula Densa of DCT
3. Macula densa causes increase in Active reabsorption of the solutes
4. Increase in breakdown of ATP into Adensoine
5. Adenosine cause VasoConstriction of Afferent Arteriole
6. Decrease resistance, hydrostatic pressure & RBF (to Normal)

Question 15

Describe How Tubulo-glomerular balance takes place at marked Decrease of ABP (Feedback mechanism)

Answer 15

1. ABP decreases, Renal Blood flow decreases
2. Flow rate of Loop of henle decreases
3. Causes increase in Reabsorption at Ascedning loop (of NaCl)
4. Macula densa Detects Decrease In Solutes (NaCl)
5. Macula densa Causes Juxtaglomerular Cells to Release Renin
6. Renin Causes VC of effernet Arteriole (by RAAS) & VD of Afferent Arteriole

Causing Increase in Resistance, Hydrostatic pressure & Renal Blood flow (to normal)

Question 16

Describe Nervous Regulation of Renal Blood flow

Answer 16

Sympathetic Innervation= Causes Vasoconstriction of Afferent Arteriole and decrease RBF, such as in:
* Exercise (increase Blood flow to other organs & muscles)
* Hypovolemic shock (decrease blood flowing to Kidney to maintain vitality of other important organs)