Renal Blood Flow & Its Control PDF

Renal blood flow & Its control  Functions of kidney:  Keeping the internal environment constant through: 1. Homeostatic a) Total body water, and electrolyte balance. function: b) PH regulation. a) Renin-angiotensin system....

Renal blood flow & Its control  Functions of kidney:  Keeping the internal environment constant through: 1. Homeostatic a) Total body water, and electrolyte balance. function: b) PH regulation. a) Renin-angiotensin system. b) Regulate plasma volume through Controlling Na+ & water 2. Regulation excretion. MCQ of ABP: c) Production of vasoactive substances as PGs (prostaglandins) and Kinins (bradykinin).  Kidney can excrete: 3. Excretory a) Waste products such as (urea, uric acid & creatinine). function: Chronic renal failure cause uremia. b) Many drugs and toxins. a) Secretion of renin enzyme. b) Secretion of Erythropoietin , so renal failure leads to anemia. 4. Endocrinal MCQ function: c) Activation of Vitamin D3 (1,25 di-hydroxy-choli-calciferol) which is important in Ca homeostasis. MCQ d) PGs & kinins: important regulators of local renal blood flow. 5. Metabolic a) Degradation of hormones as insulin & glucagon. function: b) Gluconeogenesis during prolonged fasting and acidosis. DR. M. M. Page| 1  Types of nephrons: Cortical superficial nephrons Juxta medullary nephron  85 % of total number of  15 % of the total number of Percentage nephrons. nephrons.  Glomeruli lie in outer 2/3 of  Glomeruli lie in inner 1/3 of Site cortex. the cortex.  Short.  Long  Lies only in outer medulla.  Dips into inner medulla Loop of  Makes bend at junction ( )  Makes bend in deep inner Henle: outer & inner medulla. medulla  No thin ascending cortex.  They have thin ascending limb  Give peritubular capillaries  Give peritubular capillaries in Efferent (PTC) in cortex without vasa the cortex with vasa recta in arterioles: recta. medulla.  Glomeruli are of small in size.  Glomeruli are of large in size. Glomeruli &  Tubules have low capacity to  Tubules have greater capacity tubules: reabsorb salt &H2O. to reabsorb salt & H2O.  Minor role in urine  Major role in urine concentration (water concentration (water Significance: reabsorption capacity) reabsorption capacity)  Minor role in counter current  Major role in counter current multiplier system. MCQ multiplier system. DR. M. M. Page| 2  Blood supply:  Diameter of efferent arteriole is smaller than afferent arteriole → favor high hydrostatic pressure in glomerular capillary → favor high filtration of plasma through glomerular capillaries.  Nerve supply:  The kidney is supplied mainly by sympathetic fibers. MCQ  There are two types of adrenergic receptors: α1 adrenergic receptors β1 adrenergic receptors  Renal blood vessels: VC Present  Juxta-glomerular apparatus  Renal tubules: increase Na in: cells : to release renin. MCQ reabsorption. DR. M. M. Page| 3  Juxta glomerular apparatus (JGA)  Definition: Combination of vascular, tubular and interstitial cells.  Consists of: 3 types of cells Extra glomerular Juxta glomerular Macula densa cells mesangial (Granular) cells (Lacis) cells  May act as functional  Modified smooth Nature:  Densely crowded tubular syncytium linking muscle with epitheloid epithelial cells. macula densa with appearance. granular cells.  Transitional zone between  In between afferent &  At media of afferent Site: intermediate & distal efferent arterioles. arteriole function. portion of renal tubules.  Monitor (sense)  They form renin which composition of urine (NaCl is involved in Function: concentration).  Has phagocytic regulation of ABP activity. and Na balance.  control GFR and renin  They are supplied by secretion. sympathetic (β1). DR. M. M. Page| 4  Mechanism of rennin release:  Decreased ABP leads to Renal ischemia which Stimulates renin secretion which convert angiotensinogen into angiotensin I. MCQ  Then, angiotensin I is converted into angiotensin II by Angiotensin converting enzyme (ACE).  Angiotensin 2 Has the following functions: written Q  Stimulate ADH secretion: increase water reabsorption from 2 Hypothalamus: kidney.  stimulate thirst center: to increase water intake 2 Heart & blood  ↑ Force of contraction. vessels:  V.C of blood vessels.  Salt & water retention by: MCQ a) Direct effect on proximal tubule 2 Kidneys: b) Indirect effect on distal tubule by stimulating aldosterone secretion from adrenal cortex. DR. M. M. Page| 5  Regulation of renin release A. Stimuli for renin release: a) Acute hypovolemia. 1. Mechanical b) Acute hypotension. Stimuli c) Renal artery stenosis. 2. Nervous  Sympathetic stimulation via β1 adrenergic receptor → stimulates Stimuli Juxta glomerular cells → increase renin release. MCQ 3. Chemical a) Hypokalemia Stimuli a) hyponatremia B. Inhibition of renin release: 1. Angiotensin II & angiotensin III 2. Atrial natriuretic peptide (ANP) 3. ADH 4. Hyperkalemia 5. Hypernatremia MCQ. DR. M. M. Page| 6  Renal blood flow (RBF)  = 1200 ml/min or  = 4 ml/min/1gm of renal tissues even the combined weight of both Value: kidneys is less than 0.5% of total body weight.  So renal fraction (fraction of COP that supply both kidneys) = RBF/COP = 22-25%. Written Q  High blood flow to the kidney greatly exceed its needs. Significance:  The purpose of high renal blood flow is to increase glomerular filtration to regulate plasma volume and remove waste product. A) 10% supply non-functioning structures of kidney: a) capsule b) pelvis c) perinephric fats B) 90% functioning structures: a) Cortex: 88% - 89% b) Medulla: 1- 2%, Low medullary blood flow is caused by: 1. Small number of vessels Distribution: 2. High length of Vasa recta 3. High viscosity of medullary blood flow DR. M. M. Page| 7  Regulation of renal blood flow 1. Intrinsic (auto-regulation)  Ability of the kidney to keep RBF & GFR relatively constant in spite Def: of change in ABP from 90 – 200 mmHg.  Controlled mainly by afferent arteriole resistance.  Autoregulation is not perfect because RBF & GFR changes < 10 % Range: with range of ABP from 90 to 200 mmHg. MCQ  Blunt or minimize large changes in RBF and GFR.  Occurs in Denervated kidneys or Isolated kidneys (i.e. it is not dependent on nerve supply or hormones). Significance a) Myogenic theory:  ABP RBF sudden stretch of the arterial wall Ca++ influx into smooth ms in wall of afferent arteriole contraction of smooth muscle of bl. vessel V.C of afferent arterioles RBF to normal. Mechanism b) Tubulo-glomerular –ve feedback mechanism = macula densa mechanism: written Q 1. ABP  RBF  GFR  NaCl delivery to macular densa  adenosine release from macula densa resulting in: a) VC of afferent arterioles RBF to normal. b)  renin release causing VD of efferent arteriole resulting in  GFR to normal. DR. M. M. Page| 8  2. ABP  RBF &  GFR  NaCl delivery to macula densa  PGs release from macula densa leading to: a) VD of afferent arteriole to  RBF to normal. b)  renin release formation of AII release which acts preferentially on efferent arteriole causing V.C which  GFR to normal. DR. M. M. Page| 9  2. Extrinsic regulation: a) Nervous regulation (sympathetic nervous system):  Causes VC of renal vessels to decreases RBF and GFR  urine volume in cases of exercise or hemorrhage. b) Hormones and paracrine regulation : a. Vasoconstrictors:  Low concentration: V.C of efferent arteriole only maintaining GFR. Angiotensin II:  High concentration: V.C of afferent & efferent arteriole  GFR  Secreted by endothelial cells of renal vessels.  Causes VC of afferent & efferent arterioles and  GFR & Endothelin: RBF.  Endothelin production is  in disease states e.g. renal disease associated with diabetes mellitus.  Causes VC of the afferent arteriole (in contrast to its vasodilator effect on most blood vessels), thereby  RBF Adenosine: and GFR.  It plays a role in Tubulo-glomerular feedback. DR. M. M. P a g e | 10  b. Vasodilators:  An endothelium-derived factor that causes VD of the afferent and efferent arterioles. Nitric oxide:  Counteracts the VC produced by angiotensin II and catecholamines.  Not act in healthy kidney. Prostacyclin &  But act during pathological conditions such as hemorrhage prostaglandin E2 : to dampen the VC effects of sympathetic nerves & angiotensin II to prevent renal ischemia.  Produced in the kidney , is a vasodilator that  GFR & Bradykinin: RBF.  Produced in the kidney , is a vasodilator that  GFR & Dopamine: RBF. NB:  Na & Cl are responsible for about 90% of ECF osmotic (water holding activity) DR. M. M. P a g e | 11