Renal Lectures 1 BIOM 2012 2024 PDF

Renal Physiology I Dr Niwanthi Rajapakse [email protected] Textbook: Sherwood, 8th edition, Chapters 14, 15  BIOM2012 Renal Physiology Module Lecture 1: Basic role of the kidney, renal anatomy and physiology, filtration, secretion and reabsorption...

Renal Physiology I Dr Niwanthi Rajapakse [email protected] Textbook: Sherwood, 8th edition, Chapters 14, 15  BIOM2012 Renal Physiology Module Lecture 1: Basic role of the kidney, renal anatomy and physiology, filtration, secretion and reabsorption Lecture 2: Renal clearance, renal blood flow, glomerular filtration rate Lecture 3: Loop of Henle and countercurrent exchange, hormonal control of salt and water balance, role of vasopressin and aldosterone All content covered in my lectures is examinable. For all the lectures in the renal module, videos are provided to supplement the content covered in the lectures. The content in the videos is not examinable Lecture 1: Learning objectives At the end of Lecture 1 you should have a solid understanding of: Describe the structure and function of the kidney Structure of the nephron Glomerular filtration rate (GFR) Tubular reabsorption and secretion Hormones that affect tubular sodium and water reabsorption  Overview Two kidneys, on the posterior wall of the abdomen, outside peritoneal cavity Two ureters – about 25 cm, muscular, peristalsis Bladder for storage, distensible, up to 700 – 800 ml Emptying (micturition); voluntary contraction (learned), through urethra The paired kidneys form a filtrate of the blood that is modified by reabsorption and secretion; urine designated for excretion moves along the ureters to the bladder.  The urinary system Hepatic veins (cut) Esophagus (cut) Inferior vena cava Renal artery Adrenal gland Renal hilum Aorta Renal vein Kidney Iliac crest Ureter Rectum (cut) Uterus (part of female reproductive system) Urinary bladder Urethra © 2016 Pearson Education, Ltd.  Dissection of urinary system organs (male) Kidney Renal artery Renal hilum Renal vein Ureter Urinary bladder © 2016 Pearson Education, Ltd. Functions of the kidney – Regulation of water & electrolyte volume & osmolarity Sodium, chloride, potassium, calcium, phosphate, magnesium – Regulation of acid-base balance Hydrogen ions (pH) – Excretion of metabolic waste products and foreign chemicals Nitrogen – Removal of foreign chemicals from blood drugs, pesticides and food additives – Secretion of hormones: renin = controls the formation of angiotensin erythropoietin = stimulates red blood cell production 1,25-dihydroxy vitamin D3 STRUCTURE OF THE KIDNEY Pelvis Cortex Medulla Cortex Medulla Pelvis  STRUCTURE OF THE KIDNEY Distinct zones – the cortex, medulla and pelvis A normal kidney contains 800,000 to 1.5 million nephrons The outer layer of the kidney is termed the renal cortex. The inner part of the kidney is the renal medulla. Pelvis: the broadened top part of the ureter into which the kidney tubules drain Pyramid shaped structures contain kidney tubules STRUCTURE OF THE KIDNEY zones – the cortex, Distinct medulla and pelvis A normal kidney contains 800,000 to 1.5 million The outer layer of the kidney nephrons is the renal cortex; it is the site of glomerular filtration and the convoluted tubules. The inner part of the kidney is the renal medulla; this is the location of the longer loops of Henle, and the drainage of the collecting ducts into the renal pelvis and ureter. BLOOD VESSELS IN THE KIDNEY  Blood vessels of the kidney. Aorta Inferior vena cava Renal artery Renal vein Segmental artery Interlobar vein Interlobar artery Arcuate vein Arcuate artery Cortical radiate vein Peritubular Cortical radiate artery capillaries or vasa recta Glomerulus Afferent arteriole Efferent arteriole Glomerulus (capillaries) Nephron-associated blood vessels (see Figure 25.8) Path of blood flow through renal blood vessels © 2016 Pearson Education, Ltd.  BLOOD VESSELS IN THE KIDNEY – renal artery divides into smaller and smaller blood vessels ending in glomerular capillaries Glomerulus Interlobular artery = cortical radiate artery  Nephron The kidney is made of individual functional units called “nephrons” The nephron is made up of – a filtration component (renal corpuscle = the glomerulus and Bowmans capsule) and – a complex set of renal tubules, which are further divided into structural and functional regions Glomerulus  Nephron The kidney is made of individual functional units called “nephrons” Each nephron is made up of a very small filter, called a Each kidney has about 1 million nephrons glomerulus, which is attached to a tubule. (more info on glomerulus later) glomerulus Pyramid shaped structures contain kidney tubules More detailed version of the nephron The nephron is made up of – Vascular components (blood vessels) and – a complex set of renal tubules  Let’s first look at the vascular components of the nephron The nephron is made up of – Vascular components (blood vessels) and – a complex set of renal tubules which carries the fluid filtered by glomeruli termed the tubular filtrate (let’s discuss this later)  Vascular elements of the nephron and their function Renal artery Afferent arteriole Supplies blood to the glomerulus Glomerulus Ball of capillaries where filtration takes place Efferent arteriole Carries blood away from the glomerulus Peritubular capillaries Involved in exchange with tubular fluid in lumen (i.e reabsorption and secretion of substances) Renal vein NB: Shaded blue area indicates the vascular elements of the nephron Note that the renal artery which carries blood into the kidney divides into smaller and smaller blood vessels until it gives rise to the afferent arteriole. Afferent arteriole brings blood into the glomerulus. Glomerulus is the filtration unit of the kidney Afferent arteriole gives rise to a ball of small blood vessels called capillaries. These are termed glomerular capillaries Glomerular capillaries then form the efferent arteriole which then becomes peritubular capillaries. Blood exists the glomerulus via the efferent arteriole Afferent arteriole supplies blood to the glomerulus (glomerulus = Ball of capillaries) NEPHRON Afferent arteriole Glomerulus Efferent arteriole tubule Peritubular capillary Copyright © The McGraw-Hill Companies, Inc. Permission required for reproductio or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glomerulus: cluster of capillaries which filter plasma  Let’s look at the tubular system of the nephron The nephron is made up of – Vascular components (blood vessels) and – a complex set of renal tubules STRUCTURE OF THE NEPHRON Tubular system Proximal (convoluted and straight) tubule – drains Bowmans capsule Loop of Henle – thin descending limb – thin ascending limb – thick ascending limb – Urinary concentration Distal tubule – macula densa Collecting duct – cortical and medullary  Function of different tubular segments Bowman’s capsule Surrounds the glomerulus; collects filtrate Proximal tubule Where the majority of reabsorption (unregulated) takes place Loop of Henle Important for producing urine of varying concentrations Distal tubule/collecting Controlled reabsorption (esp Na+ and H2O) duct and secretion (K+ and H+) Renal pelvis Collects urine and funnels to ureter/bladder  Juxtaglomerular apparatus Juxtaglomerular apparatus (indicated within the blue box in the diagram) 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 filtration rate of the glomerulus (More details in Lecture 3) Overview of Urine Formation in the Nephron - Summary Afferent arteriole Glomerulus Efferent arteriole Glomerular capsule Nephron Peritubular tubule capillary Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  The glomerulus The glomerulus is the filtration unit of the nephron The GLOMERULUS consists – of a tuft of interconnected capillaries (glomerular capillaries) – a fluid filled capsule (Bowmans capsule) Two capillary beds in series – glomerular capillaries – peritubular capillaries Excretion = Filtration - Reabsorption + Secretion Glomerular filtration – the movement of fluid and solutes from the glomerular capillaries into Bowman’s space. Tubular reabsorption – the movement of materials from the filtrate in the tubules into the peritubular capillaries. Filtration – Taking fluid back into the body! Tubular secretion Reabsorption – the movement of solutes from the peritubular capillaries into the tubules Secretion – Removing fluid from the body Urinary Excretion  Filtration, reabsorption & excretion >99% of plasma Efferent arteriole entering the kidney returned to systemic Peritubular capillary circulation Afferent arteriole 80% 99% of vol. excreted volume reabsorbed filters Bowman’s capsule Plasma volume entering afferent Glomerulus arteriole Reabsorption Quantitatively large – Plasma volume ~3L – GFR 125ml/min or 180L/day –  without tubular reabsorption → whole plasma volume & essential solutes excreted within 30min Selective – some substances almost completely reabsorbed – many ions highly reabsorbed – Waste products poorly reabsorbed Filtration, reabsorption & excretion  Where is sodium reabsorbed? Proximal tubules – 64% Distal tubule & Collecting Loop of Henle – 25% Duct – 7% -Descending - impermeable -Fine control - Ascending- Active transport -aldosterone Excreted – 1%  Where is water reabsorbed? Proximal Distal tubule tubules - 67% & Osmosis Collecting Duct – 9% Fine control ADH (Anti-diuretic hormone) Loop of Henle Descending- osmosis Ascending- impermeable Excreted – 320mg/min glucose in urine Guyton & Hall, Textbook of Medical Physiology, 2000  Tubular Secretion Tubular secretion is reabsorption in reverse which is the movement of solutes from the peritubular capillaries into the tubules Occurs almost completely in PCT (Proximal convoluted tubule) Selected substances are moved from peritubular capillaries through tubule cells out into filtrate – K+, H+, NH4+, creatinine, organic acids and bases – Substances synthesized in tubule cells also are secreted (example: HCO3–) © 2016 Pearson Education, Ltd.  Tubular Secretion Tubular secretion is important for: – Disposing of substances, such as drugs or metabolites, that are bound to plasma proteins – Eliminating undesirable substances that were passively reabsorbed (example: urea and uric acid) – Ridding body of excess K+ (aldosterone effect) – Controlling blood pH by altering amounts of H+ or HCO3– in urine © 2016 Pearson Education, Ltd.  For each substance in plasma, a particular combination of filtration, reabsorption & secretion can occur Substance A: Not filtered Substance B: Filtered but not Substance C: Filtered, (eg large proteins) reabsorbed or secreted completely reabsorbed & not (eg inulin) secreted. (eg glucose) Substance D: Filtered, some Substance E: Filtered, not Substance F: Filtered, not reabsorbed, not secreted reabsorbed, some secreted reabsorbed, completely (eg. many electrolytes) secreted (eg PAH) Lecture 1: Learning objectives Please make sure you have a solid understanding of: the structure and function of the kidney Structure of the nephron Glomerular filtration rate (GFR) Tubular reabsorption and secretion Hormones that affect tubular sodium and water reabsorption Revision Question Describe the structure and function of the kidney tubules