Mechanism of urine forming.ppt
- 3. The Nephron Is the Functional Unit of the Kidney • Each kidney in the human contains about 1 million nephrons, each capable of forming urine. The kidney cannot regenerate new nephrons. Therefore, with renal injury, disease, or normal aging, there is a gradual decrease in nephron number.
- 4. Function of Kidney • Regulation of extracellular fluid volume. The kidneys work to ensure an adequate quantity of plasma to keep blood flowing to vital organs. • Regulation of osmolarity. • Regulation of ion concentrations. • Regulation of pH. • Excretion of wastes and toxins. • Production of hormones.
- 5. Nephron Is the Functional Unit of the Kidney
- 6. Nephron Is the Functional Unit of the Kidney • Nephron is the basic functional unit of kidneys that consists of a glomerulus and its associated tubules through which the glomerular filtrate passes before it emerges as urine”
- 7. Nephron Is the Functional Unit of the Kidney
- 8. Nephron Is the Functional Unit of the Kidney
- 9. • Each nephron contains (1) a tuft of glomerular capillaries called the glomerulus, through which large amounts of fluid are filtered from the blood, and (2) a long tubule in which the filtered fluid is converted into urine on its way to the pelvis of the kidney.
- 11. Types of Nephron • Types of Nephron • There are two types of nephron: • Cortical nephron • These are the nephrons present within the cortex. These are short and comprise about 80% of the total nephrons. • Juxtamedullary nephron • These have long loops of Henle and extend into the medulla. These are about 20%.
- 12. • The renal corpuscle is the site of the filtration of blood plasma. The renal corpuscle consists of the glomerulus, and the glomerular capsule or Bowman's capsule. • The glomerulus is the network of filtering capillaries tuft, located at the vascular pole of the renal corpuscle in Bowman's capsule. Each glomerulus receives its blood supply from an afferent arteriole of the renal circulation. The glomerular blood pressure provides the driving force for water and solutes to be filtered out of the blood plasma, and into the interior of Bowman's capsule. • The Bowman's capsule, also called the glomerular capsule, surrounds the glomerulus. It is composed of a visceral inner layer formed by specialized cells called podocytes, and a parietal outer layer composed of simple squamous epithelium. Fluids from blood in the glomerulus are ultrafiltered through several layers, resulting in what is known as the filtrate. • The filtrate next moves to the renal tubule, where it is further processed to form urine. The different stages of this fluid are collectively known as the tubular fluid.
- 13. Renal tubule • The renal tubule is the portion of the nephron containing the tubular fluid filtered through the glomerulus. After passing through the renal tubule, the filtrate continues to the collecting duct system. • The components of the renal tubule are: • Proximal convoluted tubule (lies in cortex and lined by simple cuboidal epithelium with brush borders which help to increase the area of absorption greatly.) • Loop of Henle (hair-pin like, i.e. U-shaped, and lies in medulla) – Descending limb of loop of Henle – Ascending limb of loop of Henle • The ascending limb of loop of Henle is divided into 2 segments: Lower end of ascending limb is very thin and is lined by simple squamous epithelium. The distal portion of ascending limb is thick and is lined by simple cuboidal epithelium. • Thin ascending limb of loop of Henle • Thick ascending limb of loop of Henle (enters cortex and becomes - distal convoluted tubule.) • Distal convoluted tubule • Connecting tubule
- 14. • Urine formation begins with filtration from the glomerular capillaries into Bowman's capsule of a large amount of fluid that is virtually free of protein. • Most substances in the plasma, except for proteins, are freely filtered so that their concentrations in the glomerular filtrate in Bowman's capsule are almost the same as in the plasma. Glomerular capillary membrane
- 16. Glomerular Capillary Membrane • The glomerular capillary membrane is similar to that of other capillaries, except that it has three (instead of the usual two) major layers: • (1) the endothelium of the capillary, • (2) a basement membrane, and • (3) a layer of epithelial cells (podocytes) surrounding the outer surface of the capillary basement membrane. • Together, these layers make up the filtration barrier that, despite the three layers, filters several hundred times as much water and solutes as the usual capillary membrane.
- 17. The juxtaglomerular apparatus is a specialized structure formed by the distal convoluted tubule and the glomerular afferent arteriole. It is located near the vascular pole of the glomerulus and its main function is to regulate blood pressure and the filtration rate of the glomerulus.
- 18. • The macula densa plays an important role in controlling nephron function. Beyond the macula densa, fluid enters the distal tubule that, like the proximal tubule, lies in the renal cortex.
- 19. • Glomerular filtration is the process by which the kidneys filter the blood, removing excess wastes and fluids. • Glomerular filtration rate (GFR) is the volume of fluid filtered from the all nephrons of both kidney per minute. The GFR is typically recorded in units of volume per time, e.g., milliliters per minute (mL/min). • The normal range of Kidney Glomerular Filtration Rate is 100 to 130 mL/min/1.73m2 in men and 90 to 120mL/min/1.73m2 in women below the age of 40. GFR decreases progressively after the age of 40 years.
- 21. Renal clearance • Renal clearance describes the volume of plasma completely cleared of a substance by the kidneys per unit time. A higher renal clearance suggests the substance may be cleared almost completely in one pass through the kidneys while a low value describes a substance that may not be eliminated by the kidneys at all.
- 22. Significance of Renal clearance • Renal clearance uses to determine renal function. The practical aspect of the clearance principle is that by applying it to select compounds, one can estimate glomerular filtration rate and renal plasma flow. • To measure GFR. • It is useful for renal handling of different substances.
- 23. • Creatinine clearance (CrCl) is the volume of blood plasma cleared of creatinine per unit time. It is a rapid and cost-effective method for the measurement of renal function. Both CrCl and GFR can be measured using the comparative values of creatinine in blood and urine • Normal creatinine clearance is 88–128 mL/min for healthy women and 97–137 mL/min for healthy men.
- 24. Renal threshold • the renal threshold is the concentration of a substance dissolved in the blood above which the kidneys begin to remove it into the urine. When the renal threshold of a substance is exceeded, reabsorption of the substance by the proximal convoluted tubule is incomplete. • When the blood glucose level exceeds about 160–180 mg/dL (8.9-10 mmol/L), the proximal tubule becomes overwhelmed and begins to excrete glucose in the urine. This point is called the renal threshold for glucose
- 25. PHYSIOLOGIC CONTROL OF GLOMERULAR FILTRATION AND RENAL BLOOD FLOW • The determinants of GFR that are most variable and subject to physiologic control include the glomerular hydrostatic pressure and the glomerular capillary colloid osmotic pressure. • These variables, in turn, are influenced by the sympathetic nervous system, hormones and autacoids (vasoactive substances that are released in the kidneys and act locally), and other feedback controls that are intrinsic to the kidneys.
- 27. Function of nephrone Video
- 28. URINE FORMATION • The rates at which different substances are excreted in the urine represent the sum of three renal processes, (1) glomerular filtration, (2) reabsorption of substances from the renal tubules into the blood, and (3) secretion of substances from the blood into the renal tubules. • Expressed mathematically, • Urinary excretion rate = Filtration rate • - Reabsorption rate + Secretion rate
- 29. Mechanism of glucose reabsorption
- 30. Mechanism of glucose reabsorption
- 31. Mechanism of glucose reabsorption
- 32. Mechanism of glucose reabsorption • the glucose in the proximal tubule is co-transported with sodium ions into the proximal convoluted tubule walls via the SGLT2 and SGLT1 cotransporters. Some (typically smaller) amino acids are also transported in this way. Once in the tubule wall, the glucose and amino acids diffuse directly into the blood capillaries along a concentration gradient. This blood is flowing, so the gradient is maintained. Lastly, sodium/potassium ion active transport pumps remove sodium from the tubule wall and the sodium is put back into the blood. This maintains a sodium concentration gradient in the proximal tubule lining, so the first step continues to happen.
- 33. Mechanism of bicarbonate reabsorption
- 34. Why Are Large Amounts of Solutes Filtered and Then Reabsorbed by the Kidneys? • One advantage of a high GFR is that it allows the kidneys to rapidly remove waste products from the body that depend primarily on glomerular filtration for their excretion. Most waste products are poorly reabsorbed by the tubules and, therefore, depend on a high GFR for effective removal from the body. • A second advantage of a high GFR is that it allows all the body fluids to be filtered and processed by the kidney many times each day. Because the entire plasma volume is only about 3 liters, whereas the GFR is about 180 L/day, the entire plasma can be filtered and processed about 60 times each day. This high GFR allows the kidneys to precisely and rapidly control the volume and composition of the body fluids.
- 35. Podocytes • The final part of the glomerular membrane is a layer of epithelial cells (podocytes) that encircle the outer surface of the capillaries. • The foot processes are separated by gaps called slit pores through which the glomemlar filtrate moves. The epithelial cells, which also have negative charges, provide additional restriction to filtration of plasma proteins.
- 36. Filtration, Reabsorption, and Secretion of Different Substances • In general, tubular, reabsorption is quantitatively more important than tubular secretion in the formation of urine, but secretion plays an important role in determining the amounts of potassium and hydrogen ions and a few other substances that are excreted in the urine. • Most substances that must be cleared from the blood, especially the end products of metabolism such as urea, creatinine, uric acid, and urates, are poorly reabsorbed and are, therefore, excreted in large amounts in the urine. • Certain foreign substances and drugs are also poorly reabsorbed but, in addition, are secreted from the blood into the tubules, so that their excretion rates are high.
- 38. Filtration, Reabsorption, and Secretion of Different Substances • Nutritional substances, such as amino acids and glucose, are completely reabsorbed from the tubules and do not appear in the urine even though large amounts are filtered by the glomerular capillaries. Each of the processes - glomerular filtration, tubular reabsorption, and tubular secretion - is regulated according to the needs of the body.
- 42. Countercurrent mecanism and concentration of urine
- 45. haemodialysis