Renal Physiology PDF

Renal Physiology  Learning Objectives By the end of this unit you will be able to:- 1. State functions of the kidney. 2. Describe the mechanism of urine formation. 3. Define glomerular filtration rate. 4. Discuss the role of the kidney water balance and acid-base regulation.  Uri...

Renal Physiology  Learning Objectives By the end of this unit you will be able to:- 1. State functions of the kidney. 2. Describe the mechanism of urine formation. 3. Define glomerular filtration rate. 4. Discuss the role of the kidney water balance and acid-base regulation.  Urinary System The urinary system consists of:- 1. Two kidneys. 2. Two ureters. 3. Urinary bladder. 4. Urethra.  Functions of the Urinary System 1. Excretory function (drugs , toxins, urea, creatinine, uric acid and excess water, Na⁺, K⁺, H⁺ or HCO3₋). 2. Homeostasis:- – acid –base regulation – Water balance 3. Endocrine functions: ❖ Renin & angiotensin (essential for arterial blood pressure regulation). ❖ Synthesis of erythropoietin. ❖ Activation of Vit D3.  Kidney Functions Renin-angiotensin Erythropoietin Active Vitamin D3 Urine The functional unit of the kidney  TYPES OF NEPHRONS Cortical nephron Juxta-medullary nephron 85%of the nephrons 15 % of the nephrons glomerulus in the outer 2/3 cortex. glomerulus in inner contain juxtaglomerular cortex (near the apparatus medulla) function is homeostasis no apparatus and sodium regulation its function is concentration of urine  Urine Formation The kidneys excrete excess water, excess ions, chemicals and drugs. The kidneys excrete the biggest amount of solutes in the least volume of urine. The least amount of urine to do this function is 400ml/day. Urine is formed by the following steps:- 1. Filtration of plasma by glomerular capillaries. The filtered fluid has the same composition of plasma except for plasma proteins. To excrete any substance from the body , it should be first filtered. 2. Renal tubular reabsorption and secretion These two processes modify composition of glomerular filtrate. Renal tubules reabsorb essential elements.e.g. water, Na⁺, K⁺, Ca⁺, Po₄⁻³, glucose and amino acids. Renal tubules secrete waste products.e.g. urea, H⁺, chemicals and drugs. GFR= NFPX Kf  Glomerular Filtration Rate (GFR) It is the volume of fluid filtered by all glomerular capillaries /minute. In a young healthy man it equals 125ml/min.i.e. 180 L / day. With advanced age, GFR declines Forces involved in glomerular filtration:- 1. Capillary hydrostatic pressure( filtering force). 2. Osmotic pressure of plasma (reabsorbing force). 3. Bowman’s capsule hydrostatic pressure (reabsorbing force). The filtering force exceeds the reabsorbing forces leading to filtration of plasma. Regulation Of Hydrogen Ion Concentration Hydrogen ion concentration is expressed as pH (i.e. pH is the –ve log of hydrogen ion concentration).  Threats To pH The major threats to pH of the body fluids are acids formed in metabolic processes. These acids are divided into three categories:- 1. Volatile acids (CO₂). CO₂ is produced by metabolic processes , then it dissolves in body water to form H₂CO₃. 2. Fixed acids(H₂SO₄, H₃PO₄). These acids are produced from metabolism of sulfur and phosphorus containing -amino acid. 3. Organic acids ( lactic acid, acetoacetic acid ) These acids are normally metabolized to CO₂. In some metabolic disorders (.e.g. diabetic ketoacidosis & circulatory shock) these acids accumulate and exert H+ load.  capillary H+ H+ H+ H+ H+ Blood H+ H2CO3 H2CO3 H+ H+ H+ H2CO3 H+ H2CO3 H+ H+ H+ H+ H+ H+ Interstitial fluid H+ H+ H+ CO2 CO2 CO2 CO2 Lactic Lactic Lactic H2SO4 acid H3PO4 acid H3PO4 H2SO4 H3PO4 H2SO4 acid Threats to pH Tissue cells  PH Control Systems 1. Chemical buffer system. A buffer is a chemical substance that can maintain the pH of its medium by releasing hydrogen when the surrounding pH increases and accepting hydrogen then the surrounding pH decrease. 2. Respiratory system. Its function is to wash out CO2. 3. Renal system. It is the most efficient buffer system in the body.  Renal Regulation Of pH The kidney regulate pH by regulating plasma {HCO3⁻}. This involves three tasks:- 1. Secretion of Hydrogen. 2. Reabsorption of filtered HCO3⁻, thus preserving this important blood buffer from being lost in urine. 3. Synthesize new HCO₃⁻ to replace the HCO₃⁻ lost in buffering of the various strong acids formed in the body every day. Both reabsorption and generation of HCO3- are coupled to H+ secretion. Thank You