Kidney Physiology PDF

Renal Physiology Dr. Nermeen Bastawy Physiology Department Faculty of Medicine Cairo University  Renal Functions 1- Regulation of water and electrolyte balance. 2- Excretion of waste products 3- Acid base balance 4- Endocrine/ Paracrine: ✓ Secrete Renin → regulation of ABP ✓ E...

Renal Physiology Dr. Nermeen Bastawy Physiology Department Faculty of Medicine Cairo University  Renal Functions 1- Regulation of water and electrolyte balance. 2- Excretion of waste products 3- Acid base balance 4- Endocrine/ Paracrine: ✓ Secrete Renin → regulation of ABP ✓ Erythropoietin hormone → Erythropoiesis ✓ Activation of vit D → bone mineralization ✓ Prostaglandins (vasodilatation of renal vessels)  Nephron The structure and functional unit of the kidney 2 types: - cortical nephrons (85 %) - juxtamedullary nephrons (urine concentration) Efferent Afferent Juxtaglomerular Apparatus  Juxtaglomerular Apparatus A point of contact between the distal convoluted tubule and the afferent arteriole of the same nephron. It consists of: 1. Macula densa: -Chemoreceptors lie in the distal tubule that comes in contact with the afferent and efferent arterioles. They sense the changes in sodium delivery to the distal tubule. 2. Juxtaglomerular cells: -Granular cells (contain renin) lie in the media of the afferent and efferent arterioles as they enter the glomeruli. They secrete renin in response to decreased renal blood flow.  Glomerular Filtration 20% of the plasma Plasma – plasma proteins Glomerular filtration rate (GFR) is the volume of fluid filtered from glomerular capillaries into the Bowman's capsule per minute Normal GFR : > 60 ml/min, average 120 ml/min.  Starling Forces that control GFR Afferent HPGC OPGC HPBC Efferent Glomerular Hydrostatic Pressure HPGC 60 mmHg Net force pressure Glomerular Osmotic Pressure OPGC - 32 mmHg 10 mmHg - 18 mmHg Bowman capsule Hydrostatic Pressure HPBC  Starling Forces that control GFR  Glomerular Hydrostatic HPGC OPGC Pressure → GFR HPBC  Glomerular Osmotic Pressure →  GFR  Bowman capsule Hydrostatic Pressure →  GFR The endocrine function of the kidney involves: a.Secretion of ADH b.Absorption of vitamin B12 c.Secretion of somatomedin d.Activation of vitamin D Glomerular filtration rate represents ……. from the renal plasma: a.10 % b.20% c.30% d.40% The glomerular filtration rate may stopped if: a.Increase HP of the afferent arterioles b.Decrease OP of the glomeruli c.Stone in the right ureter d.Increase HP of BC to 28 mmHg  Na+ Handling by Renal Tubule All nephron segments contribute to the Na reabsorption (except thin descending limbs of loop of Henle). Na reabsorption is an energy-consuming process that is powered by a Na- and K- ATPase 60%–70% of total Na reabsorption takes place along the proximal convoluted tubule 25 % of the filtered Na is reabsorbed by the thick ascending portion of loop of Henle X  Na Hormonal Control in the kidney ↑ Reabsorption ↑ Excretion Aldosterone Prostaglandins Angiotensin II Endothelin Cortisol Atrial natriuretic peptide (ANP) Estrogen Glucose Reabsorption  Glucose Reabsorption ❑ All glucose is reabsorbed by the nephron ❑ 90 % is reabsorbed in the proximal tubules At brush border: 2ry active transport glucose & sodium are transported by SGLT (sodium-glucose transporter) At basolateral border: facilitated diffusion glucose is transported by GLUT2 (glucose transporter)  Glucosuria Def. presence of glucose in urine cause: glucose in glomerular filtration is > renal tubule absorption capacity 2 types: 1. Glucosuria with hyperglycemia: 2. Glucosuria without hyperglycemia: - exceed renal threshold (180 mg/dl) renal tubular dysfunction (renal glucosuria) - As in: diabetes mellitus, Cushing as in Fanconi syndrome disease, hyperthyroidism, drugs e.g. cortisol Water reabsorption X  Water reabsorption Passive process occurs through the whole nephron, except thick ascending loop of Henle. 2 types: 1- Obligatory water reabsorption (90 %) 2- Facultative water reabsorption (10 %) Obligatory Facultative Independent of ADH Controlled by ADH Proximal tubules Distal tubules Descending loop of Henle Cortical ducts ADH binds V2 Receptors → ↑ aquaporins → ↑H2O reabsorption → Concentrated urine