Lecture 19: Kidney Anatomy & Function PDF

Lecture 19: Kidney Anatomy & Function Adapted From: Textbook Of Medical Physiology, 13th Ed. Arthur C. Guyton, John E. Hall Chapter 26 John P. Fisher © Copyright 2024, John P. Fisher, All Rights Reserved ...

Lecture 19: Kidney Anatomy & Function Adapted From: Textbook Of Medical Physiology, 13th Ed. Arthur C. Guyton, John E. Hall Chapter 26 John P. Fisher © Copyright 2024, John P. Fisher, All Rights Reserved  Kidneys Introduction The kidneys act to both rid the body of waste as well as to control the volume and composition of bodily fluids The kidneys perform their functions by filtering the plasma and removing substances from the filtrate, with the rate of removal depending upon the current needs of the body Cleared substances are excreted in the urine Needed substances are returned to the blood Specific functions of the kidney include Regulation of water and electrolyte balance Regulation of osmolality and electrolyte concentration Regulation of acid-base balance Excretion of waste products Regulation of arterial pressure Secretion of hormones Gluconeogenesis © Copyright 2024, John P. Fisher, All Rights Reserved  Kidneys Introduction Regulation of water and electrolyte balance Excretion of water and electrolytes must match their intake Increased salt intake causes an increase in salt excretion by the kidneys Salt intake (typically 10 mEq/day) can increase or decrease by 1 order of magnitude with little change in plasma sodium concentration or extracellular fluid volume Changes in chloride, potassium, calcium, hydrogen, magnesium, and phosphate ions can all be balanced by renal functions Guyton & Hall. Textbook of Excretion of waste products Medical Physiology, 11th Edition Excretion of waste products must match their production and intake Excreted metabolic products include urea, creatinine, uric acid, bilirubin, and metabolites from various hormones Excreted toxins include pesticides, drugs, and food additives © Copyright 2024, John P. Fisher, All Rights Reserved  Kidneys Introduction Regulation of arterial pressure Regulation occurs by excreting variable amounts of salt and water as well as through systems such as renin production Regulation of acid-base balance Regulation occurs by excreting acids and controlling buffering capabilities Regulation of erythrocyte production Kidneys secrete nearly all endogenous erythropoietin, which stimulates RBC production under both normal and hypoxic conditions Regulation of 1,25-dihydroxy vitamin D3 Kidneys produce the active form of vitamin D Glucose synthesis Kidneys synthesize glucose from amino acids and other precursors during long periods of fasting © Copyright 2024, John P. Fisher, All Rights Reserved  Kidney Anatomy Physiological Anatomy of the Kidneys The two kidneys lie on the posterior wall of the abdomen, outside the peritoneal cavity Each weighs about 150 gm and is about the size of a clenched fist Medial side contains an indented region known as the hilum, allowing passage of a number of structures Renal artery and vein Lymphatics Guyton & Hall. Textbook of Medical Physiology, 11th Edition Nerve supply Ureter, which carries urine out of the kidney to the bladder © Copyright 2024, John P. Fisher, All Rights Reserved  Kidney Anatomy Physiological Anatomy of the Kidneys A coronal section of the kidney shows two regions Outer cortex Inner medulla Medulla is divided into renal pyramids, whose bases originate at the border with the cortex and whose apex terminates in the papilla, which projects into the renal pelvis Urine from the tubules of each papilla is Guyton & Hall. Textbook of Medical Physiology, 11th Edition then collected into the minor and major calices Walls of the calics, pelvis, and ureter are contractile, allowing the movement of urine to the bladder © Copyright 2024, John P. Fisher, All Rights Reserved  Kidney Anatomy Physiological Anatomy of the Kidneys Blood flow to the kidneys is normally 21% of cardiac output (1200 ml/min) Blood enters the kidney through the renal artery, and then branches progressively to form interlobar arteries, arcuate arteries, interlobular arterioles, and afferent arterioles Afferent arterioles lead to the glomerular capillaries, which then coalesce to form efferent arterioles, and then the peritubular capillaries Glomerular capillaries are the site of fluid and solute filtration Efferent arterioles regulate pressure Guyton & Hall. Textbook of Medical Physiology, 11th Edition © Copyright 2024, John P. Fisher, All Rights Reserved  Kidney Anatomy Physiological Anatomy of the Kidneys Peritubular capillaries empty into the venous system which run in parallel to the arteriolar vessels Peritubular capillaries are the site of reabsorption Peritubular capillaries coalesce into the interlobular vein, arcuate vein, interlobar vein, and renal vein Thus, two capillary beds exist: glomerular capillaries and the peritubular capillaries High hydrostatic pressure in the glomerular capillaries allows rapid filtration Low hydrostatic pressure in the peritubular capillaries allows rapid reabsorption Guyton & Hall. Textbook of Medical Physiology, 11th Edition © Copyright 2024, John P. Fisher, All Rights Reserved  Kidney Anatomy Nephron, the Function Unit of the Kidney Each kidney contains about 1 million nephrons, which form urine In renal disease, there is a decline in the number of functional nephrons After age 40, total nephron function falls 10% every 10 years Each nephron has two major components Glomerulus through which large amounts of fluid are filtered from the blood Tubule in which the fluid is converted into urine on its way to Guyton & Hall. Textbook of Medical Physiology, 11th Edition the pelvis of the kidney © Copyright 2024, John P. Fisher, All Rights Reserved  Kidney Anatomy Nephron, the Function Unit of the Kidney The glomerulus is composed of a network of branching capillaries have a high hydrostatic pressure (60 mmHg) Glomerular capillaries are covered by epithelial cells Entire glomerulus is encased in Bowman’s capsule Fluid flows from the glomerular capillaries into Bowman’s capsule, into the proximal tubule, into the loop of Henle Loop of Henle consists of a Guyton & Hall. Textbook of Medical Physiology, 11th Edition descending and ascending limb © Copyright 2024, John P. Fisher, All Rights Reserved  Kidney Anatomy Nephron, the Function Unit of the Kidney Fluid flow continues past the Macula densa, into the distal tubule, connecting tubule, the cortical collecting tubule, and the cortical collecting duct Approximately 8 to 10 cortical collecting ducts join to form a larger duct, which runs downward to become the medullary collecting duct and ultimately the collecting duct Each kidney contains about 250 large collecting ducts, each of which collects from approximately 4000 nephrons Guyton & Hall. Textbook of Medical Physiology, 11th Edition © Copyright 2024, John P. Fisher, All Rights Reserved  Kidney Anatomy Nephron, the Function Unit of the Kidney Nephrons differ depending upon the location within the kidney Nephrons whose glomeruli are located in the outer cortex are called cortical nephrons and possess short loops of Henle Entire tubular system is surrounded by peritubular capillaries Nephrons whose glomeruli are located deep in the renal cortex are called juxtamedullary nephrons and possess long loops of Henle Tubular system is surrounded by vasa recta capillaries which lie side by side to the loop of Henle Guyton & Hall. Textbook of Medical Physiology, 11th Edition © Copyright 2024, John P. Fisher, All Rights Reserved  Kidney Function Urine Formation The rate of at which substances are excreted into the urine depends upon three factors Glomerular filtration Reabsorption of substances from the renal tubules into the blood Secretion of substances from the blood into the renal tubules Urinary excretion rate = filtration rate - reabsorption rate + secretion rate Guyton & Hall. Textbook of Medical Physiology, 11th Edition © Copyright 2024, John P. Fisher, All Rights Reserved  Kidney Function Urine Formation Urine formation begins with filtration from the glomerulary capillaries into Bowman’s capsule Here a large amount of fluid, which is protein-free, is collected Substances are freely filtered, so that their concentration are nearly the same in Bowman’s capsule as in the plasma - with the exception of proteins As fluid leaves Bowman’s capsule, water and specific solutes are reabsorbed back into the blood Also, other substances are also secreted from the blood into the filtrate Guyton & Hall. Textbook of Medical Physiology, 11th Edition © Copyright 2024, John P. Fisher, All Rights Reserved  Kidney Function Urine Formation Guyton & Hall. Textbook of Medical Physiology, 11th Edition © Copyright 2024, John P. Fisher, All Rights Reserved