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dr fawzy lecture 13
- 1. Renal Physiology Fawzi A. Babiker Department of Physiology E-mail: [email protected] Reference: Human Physiology, by: Stuart Ira Fox; 11th Edition.
- 2. Physiology of thekidneys Contents: Structure and function of the kidney. Glomerular filtration (GF). GF regulation and reabsorption of salt and Water. Renal plasma clearance. Renal control of electrolyte and acid-base balance. Step by step flow up of urine formation. Short clinical ideas.
- 3. Functions of thekidney Regulation of the blood plasma volume (Blood pressure). Removal of metabolic wastes products from the blood (urea). Electrolytes balance (Na+, Ca+2, K+, Mg+, SO4-2, HCO3- and other ions) Removal of toxic chemicals from the blood (drugs). Acid-base balance (pH). Hormone secretion.
- 4. Hormone secretion In additionto its excretory function the kidney acts as an endocrine gland as it secretes three hormones. 1- Erythropoieten which controls erythrocytes (blood cells) production. 2- Renin, which controls the formation of angiotensin which influences blood pressure and sodium balance. 3- 1.25-dihydroxyvitamin D3 which influences calcium balance.
- 5. Structure of theurinary system Adrenal gland Urinary vein Urinary artery Abdominal Inferior vena aorta cava
- 6.
- 7. Structure of theKidney
- 8. The nephron Nephron isthe functional unit of the kidney. Types of nephrones: Cortical nephrons: Small nephrons with short tubules. Juxtamedullary nephrons: Big nephrons with long tubules. Both types of nephrons originate in the cortex.
- 9. Structure of aNephron
- 10. The glomerulus Glomerular capillaries
- 11. Glomerular Filtration Capillaries ofthe glomerulus are fenestrated (have pores). Blood pressure (hydrostatic pressure is the main driving force for filtration). The amount of plasma that goes to the kidneys each minute ~ 600 ml/min (RPF= renal plasma flow). Glomerular Filtration Rate (GFR) is the volume of filtrate/min ~ 125 ml/min, (15- 20% of RPF).
- 12. Regulation of theglomerular filtration rate (GFR) GFR is the volume of filtrate produced by the two kidneys per minute. 115 ml per min in females. 125 ml per min in males. About 180 liters per day. What happens if all this has to be excreted? What happens in reality?
- 13. Regulation of theglomerular filtration Factors that regulate filtration: PGC: hydrostatic pressure in the glomerular capillary. πGC: oncotic pressure in the glomerular capillary. PBS: hydrostatic pressure in Bowman's space. πBS: oncotic pressure in Bowman's space. PUF: net ultrafiltration pressure. The negative signs for PBS and πGC indicate that these forces oppose formation of the glomerular filtrate.
- 14. Regulation of theglomerular filtration rate Glomerular filtration and renal blood flow is regulated by renal nerves. The kidney is innervated by sympathetic nerve fibers (only constriction). Sympathetic nerves secretes Noradrenalin (NE) which cause vasoconstriction. Constricted afferent arterioles = GFR Dilatation of afferent arterioles = GFR Reduction 1- Sympathetics Vasoconstriction in GFR 2- Local effects: Autoregulation; effect of local chemicals Pressure x radius4 Blood flow α Viscosity x length
- 15. Regulation of theglomerular filtration rate cont… 1- Effect of the sympathetic nerves Effect of the sympathetic nerve
- 16. Regulation of theglomerular filtration rate cont.. 2- Intrinsic (Autoregulation) Systemic Afferent Renal blood pressure pressure flow Net result is a constant renal blood flow Systemic Afferent Renal blood pressure pressure flow When blood pressure increases afferent arterioles constricts to prevent the increase of renal blood flow and GFR. When blood pressure decreases the afferent arterioles dilates to prevent the decrease of renal blood flow and GFR. Thus, this means that auto regulation happens in the afferent arterioles to keep renal blood flow and GFR constant.
- 17. Regulation of theglomerular filtration rate (GFR) Fight/Flight High Blood Pressure Autoregulation Keep GFR constant
- 18. The formation ofthe glomerular ultrafiltrate Due to the blood pressure some fluids enters the glomerular capsule (ultrafiltrate). Although the capillary pores are large enough to pass proteins but that never happens because of the negative charges of the proteins and that of the Glycoproteins in the basement membrane.