1. Dr. Aya M. Serry Renal Physiology 2017
Pathophysiology
Dr. Aya M. Serry
Renal Physiology
2017

2. Lecture objectives Introduction to the Renal (Urinary) system
Functions of the Kidneys
Functions of the Nephron
Juxtaglomerular apparatus and Renin

3. The Urinary system

4. The Urinary system- Kidneys
The Kidney is the main excretory organ in
the body, eliminating the body’s
metabolic waste products by filtering the
blood
Substances that are un-needed or present
in excess are filtered out of the blood and
formed into urine
The kidney also selectively reabsorbs
substances that are needed to maintain
the normal composition of the blood

5. Major Functions of the Kidneys
1. MAINTAINING OF HOMEOSTASIS
maintain the blood volume and the normal composition of body fluid compartments
excrete waste products ( urea, creatinine, uric acid, ammonia, which are toxic for the body
regulate the blood concentration of ions ( Na+, K +, Ca++,phosphate)
maintain the pH by secreting the H +
maintain the osmolarity and water volume (adjust the water reabsorption)
regulate arterial blood pressure

6. Major Functions of the Kidneys
2. ENDOCRINE ROLE
Synthesis of Erythropoietin (controls RBCs synthesis)
Role in metabolism of vitamin D and Calcium
- active vitamin D needed to reabsorb Ca²+ in small intestine
- to activate vitamin D: an additional hydroxyl group is added
    => 1,25 dihydroxycolecalciferol
-  Vitamine D pathway:
1. 7-dehydrocholesterol under the action of UV rays becomes colecalcipherol or vit. D3 ( in skin)
2. Vit. D3 in liver becomes 25-OH D3 and then in kidneys 1,25 (OH)2 D3 or calcitriol → increase Ca absorption in the intestine

7. Major Functions of the Kidneys
2. ENDOCRINE ROLE
RENIN- ANGIOTENSIN- ALDOSTERON SYSTEM (RAAS)
juxtaglomerular cells synthesize the enzyme RENIN, that catalyses the transformation of angiotensinogen (from liver) into angiotensin I.
Angiotensin I is transformed into Angiotensin II ( reaction catalyses by angiotensin converting enzyme – in the lungs)
Angiotensin II  causes vasoconstriction
Angiotensin II stimulates ALDOSTERONE secretion (in adrenal gland)
Renin is released in case of: renal ischemia (decrease of blood supply to the kidney), decreased blood volume, hypotension (low blood pressure (BP), cardiac failure

8. Major Functions of the Kidneys
2. ENDOCRINE ROLE
Release of prostaglandins Pg E₂, Pg F2 alpha & Pg I (Prostacyclin)
- Pg E₂ in hypertensive people :
- decrease the blood pressure HOW!!
- It increases :  A)  Renal blood flow and diuresis (volume of
excreted urine/day)
B)  Natriuresis (amount of Na excreted via
urine/day)
- Pg F2 alpha => vasoconstriction

9. The Nephron The Nephron is the functional unit of the kidney
Each kidney is made up of about 1 million nephrons
Each nephrons has two major components:
A glomerulous
A system of tubules

10. The Nephron Structure of Nephron Glomerulus ( A mass of capillaries)
Proximal convoluted tubule
Loop of Henle
descending limb
ascending limb
Distal convoluted tubule
Collecting duct

11. The Nephron Secretion Reabsorption Excretion Filtration
Functions of the Nephron
Secretion
Reabsorption
Excretion
Filtration

12. Functions of the Nephron

13. Renal Blood Supply

14. Renal Blood Supply
By the renal artery (directly from the abdominal aorta)
-> interlobar arteries -> arcuate arteries -> interlobular arteries -> afferent arterioles (enter the glomerolus) -> capillary tuft -> efferent arterioles-> peritubular capillaries -> interlobular veins -> arcuate veins -> interlobar veins -> renal vein -> inferior vena cava (heart)

15. Renal Blood Supply

16. Renal Blood Supply

17. Juxta-glomerular Apparatus
Renal Blood Supply
Juxta-glomerular Apparatus
The juxta-glomerular apparatus is a specialized structure formed by the distal convoluted tubule and the glomerular afferent arteriole
 its main function is to regulate blood pressure and the Glomerular Filtration Rate
It’s made up of juxtaglomerular cells and the macula densa
 The macula densa is a collection of specialized epithelial cells in the distal convoluted tubule that detect sodium concentration of the fluid in the tubule

18. Juxtaglomerular Apparatus
Renal Blood Supply
Juxtaglomerular Apparatus
Cells of the juxtaglomerular apparatus act as baroreceptors sensing changes in BP (cells are stimulated by stretching of the afferent arteriole; if not distended - release of RENIN)
Low BP => Renin secretion => Angiotensin II => increase reabsorption of Na and water => increase BP

19. Juxtaglomerular Apparatus
Renal Blood Supply
Juxtaglomerular Apparatus

20. Juxtaglomerular Apparatus
Renal Blood Supply
Juxtaglomerular Apparatus