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

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

The Urinary system

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

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

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

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

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

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

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

The Nephron Secretion Reabsorption Excretion Filtration Functions of the Nephron Secretion Reabsorption Excretion Filtration http://www.youtube.com/watch?v=aQZaNXNroVY

Functions of the Nephron

Renal Blood Supply

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)

Renal Blood Supply

Renal Blood Supply

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

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

Juxtaglomerular Apparatus Renal Blood Supply Juxtaglomerular Apparatus

Juxtaglomerular Apparatus Renal Blood Supply Juxtaglomerular Apparatus