L23 1502-2024 Intro Renal Physiology PDF

1502 Introduction to Renal Physiology Fall 2024 Lecture 23 Tuesday, Oct 15 - 9am Dr. Layla Al-Nakkash...

1502 Introduction to Renal Physiology Fall 2024 Lecture 23 Tuesday, Oct 15 - 9am Dr. Layla Al-Nakkash [email protected] 1 © L. Al-Nakkash 2020  Learning Objectives 1. Define the general function of the kidneys. 2. Review the functional anatomy of the kidney. 3. Describe the components making up the nephron. 4. Describe the filtration apparatus of the kidney. 5. Identify the route of blood flow in the kidney. 6. Understand the components of renal function. 7. Define balance, steady state, positive and negative balance. © L. Al-Nakkash 2024 2  Function of the Kidneys What are the primary function of the kidneys? – Excretory Organs: remove substances either in excess or those that are harmful from the body. – Regulatory Organs: maintain constant volume & composition of body fluids. How? Vary the excretion of solutes and water – Endocrine Organs: synthesize and secrete hormones. hormones? Erythropoietin (for RBC production) 1,25-dihydroxycholecalciferol (vit D activation) Also Renin (actually an enzyme- RAAS) 3 © L. Al-Nakkash 2024 1.Define the general function of the kidneys.  Gross Structure of the Kidneys Bilateral retroperitoneal organs. 3 main regions: outer cortex, inner medulla, papilla 4 © L. Al-Nakkash 2024 2. Review the functional anatomy of the kidney.  Gross Structure of the Kidneys Outer cortex: under the kidney capsule. Inner medulla: central region, divided into: – the outer (which has an outer and inner stripe) – the inner medulla. Papilla: innermost part of the inner medulla and empties into the calyces (extensions of the ureter) 3 main regions: outer cortex, inner medulla, papilla 5 © L. Al-Nakkash 2024 2. Review the functional anatomy of the kidney.  Gross Structure of the Kidneys Cortex- contains renal corpuscles (glomerular capillaries surrounded by Bowmans capsules). The corpuscles connect to the nephrons (the functional tubular units). The outer stripe of the outer medulla contains the thick ascending loops of Henle & collecting ducts. The inner stripe contains the pars recta, thick and thin ascending loops of Henle & collecting ducts. 6 © L. Al-Nakkash 2024 2. Review the functional anatomy of the kidney.  Gross Structure of the Kidneys Urine is emptied into the calyces, and renal pelvis, then into the ureter, which leads to the bladder. The bladder stores the urine until it is excreted. What is this process called? micturition 7 © L. Al-Nakkash 2024 2. Review the functional anatomy of the kidney.  Structure of the Nephron Nephrons –the kidney’s functional units Each nephron has a glomerulus and a tubule. > 1 million nephrons/kidney Glomerulus: a glomerulus capillary network, emerging from the afferent arteriole. The capillaries are surrounded by Bowman’s capsule (or space) - continuous with the initial part of the nephron. Function? Blood is ultrafiltered here, from the capillaries into the Bowman’ s space. The initial step in urine formation. The tubular nephron region is lined with specialized epithelial cells. Function? Reabsorption and secretion. Segments of the nephron: Bowman’s space, proximal convoluted tubule, proximal straight tubule, loop of Henle (comprising, thin descending limb , thin ascending limb and thick ascending limb), distal convoluted tubule and the collecting ducts. 8 © L. Al-Nakkash 2024 3. Describe the components making up the nephron.  Structure of the Nephron 9 © L. Al-Nakkash 2024 3. Describe the components making up the nephron.  Structure of the Nephron Nephrons - the kidney’s functional units Renal Corpuscle: Glomerulus (capillary network, filters urine) Bowman’s capsule Proximal tubule: Drains the Bowman’s capsule Brush border villi facilitates solute and water reabsorption Loop of Henle: Descending & ascending loops Maintains osmotic gradients, allowing for concentration of tubular fluid/urine 10 © L. Al-Nakkash 2024 3. Describe the components making up the nephron.  Structure of the Nephron Nephrons are the kidney’s functional units Juxtaglomerular apparatus: The thick ascending limb passes between the afferent and efferent arteriole. Distal Convoluted tubule: Electrolyte reabsorption Aldosterone acts here Collecting Duct: Water reabsorption Via aquaporins Controlled by which hormone? ADH/vasopressin 11 © L. Al-Nakkash 2024 3. Describe the components making up the nephron.  Structure of the Nephron Segments of the nephron: Bowman’s space, proximal convoluted tubule, proximal straight tubule, loop of Henle (comprising, thin descending limb , thin ascending limb and thick ascending limb), distal convoluted tubule and the collecting ducts. Each region is distinct. The epithelial cells for each region are different. Cells in the proximal convoluted tubule, have microvilli (a brush border), on the luminal side. Function? Increase surface area The proximal convoluted tubule’s major function is reabsorption. 12 © L. Al-Nakkash 2024 3. Describe the components making up the nephron.  Structure of the Nephron smaller Two types of glomeruli nephrons: Larger Superficial cortical glomeruli nephrons: have glomeruli in the outer cortex Loop of Henle? Short Descend into? Outer medulla Juxtamedullary nephrons: have glomeruli near the corticomedullary border. Loop of Henle? Long Descend into? Inner medulla & papilla 13 © L. Al-Nakkash 2024 3. Describe the components making up the nephron.  Juxtamedullary and Cortical nephrons Cortical nephrons: Short loops of Henle. Dipping only slightly into the medulla Juxtaglomerular nephrons: Long loops of Henle. Plunge deep into the medulla 14 © L. Al-Nakkash 2024 3. Describe the components making up the nephron.  The Glomerulus The glomerulus is a capillary system, from which an ultrafiltrate of plasma enters into the Bowman’s space. The glomerular capillary has a fenestrated epithelium and basement membrane. – This prevents filtration of blood cells and larger proteins into the glomerular ultrafiltrate. The glomerulus is surrounded by epithelial cells (podocytes), providing a filtration barrier. Glomerular filtration occurs due to size & charge: the basement membrane and podocytes are negatively changed, therefore most proteins, which are also negatively charged, can not be filtered. 15 © L. Al-Nakkash 2024 4. Describe the filtration apparatus of the kidney.  The Glomerulus 16 © L. Al-Nakkash 2024 4. Describe the filtration apparatus of the kidney.  The Juxtaglomerular Apparatus The area where the distal convoluted tubule (DCT) returns to the “parent” or same nephron glomerulus. Specialized macula densa cells are in contact with the DCT & afferent arteriole, forming the juxtaglomerular apparatus (JGA). Macula densa cells: – Sense blood flow and sodium delivery to the distal nephron. – Regulate renal plasma flow. Due to close proximity to afferent arteriole – Regulate glomerular filtration rate (GFR). – Regulate and release renin from the Juxtaglomerular cells. 17 © L. Al-Nakkash 2024 4. Describe the filtration apparatus of the kidney.  Renal Vasculature Blood enters the kidneys via the renal artery. The renal artery branches into smaller arteries. The smallest arteries subdivide into the first set of arterioles (the afferent arterioles). These deliver blood to the first capillary network, the glomerular capillaries (where ultrafiltration occurs). Blood leaves the glomerulus via a second set of arterioles (the efferent arterioles). These deliver blood to the second capillary network, the peritubular capillaries (surrounding the nephrons, where solutes and water are reabsorbed). Blood from the peritubular capillaries flows into the small veins, then renal vein. 18 © L. Al-Nakkash 2024 5. Identify the route of blood flow in the kidney.  Components of Renal Function Glomerular Filtration (GF) – Filtration of a protein-free plasma from the glomerulus into the Bowman’s capsule Tubular Reabsorption (TR) – Selective movement of filtered substances from the tubular lumen into the peritubular capillaries Tubular secretion (TS) – Selective movement of nonfiltered substances from the peritubular capillaries into the tubular lumen Urine excretion – Elimination of water and substances from the body © L. Al-Nakkash 2024 6. Understand the components of renal function. 19  Balance Concept The body’s ability to maintain homeostasis and balance internal composition of: Water-balance, electrolyte balance (sodium/potassium), acid-base balance – ______________________________________________________________ INPUTS OUTPUTS Beverages Sweat Food Fecal Metabolic Urinary (breakdown of Insensible foods) (water lost in breath) © L. Al-Nakkash 2024 7. Define balance, steady state, positive and negative balance. 20  Balance Concept WATER OUTPUT WATER INPUT Food & Beverages = 1900 ml Fecal = 150 ml Oxidative water = 400 ml Sweat = 250 ml Total Input = 2300 ml Insensible = 800 ml Total Output = 1200 ml Balance = Total In – Total Out 2300-1200 = 1100 ml/day unaccounted for , i.e. excreted in urine If URINE flow : = 1100 ml/day, the subject is in steady state. >1100 ml/day, the subject is in negative water balance. Lose water