Biological Sciences
Nephron
The nephron is the functional unit of the kidney responsible for filtering blood and producing urine. It consists of a renal corpuscle, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct. Each nephron plays a crucial role in regulating the body's fluid balance, electrolyte levels, and waste excretion.
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10 Key excerpts on "Nephron"
eBook - PDF- Gerard J. Tortora, Bryan H. Derrickson(Authors)
- 2018(Publication Date)
- Wiley(Publisher)
What is the functional unit of the kidney? Describe its structure. (b) Parts of a Nephron Glomerular capsule Renal corpuscle: Glomerulus Descending limb of the Nephron loop Nephron loop: Ascending limb of the Nephron loop Proximal convoluted tubule Distal convoluted tubule Figure 21.4 Continued Q A water molecule has just entered the proximal convoluted tubule of a Nephron. Which parts of the Nephron will it travel through (in order) to reach the renal pelvis in a drop of urine? Clinical Connection Kidney Transplant A kidney transplant is the transfer of a kidney from a living donor or a cadaver to a recipient whose kidney(s) no longer function. In the proce- dure, the donor kidney is placed in the pelvis of the recipient through an abdominal incision. The renal artery and vein of the transplanted kidney are attached to a nearby artery and vein in the pelvis, and the ureter is then attached to the urinary bladder. During a kidney transplant, the patient re- ceives only one donor kidney, since only one kidney is needed to maintain sufficient renal function. The diseased kidneys are usually left in place. As with all organ transplants, kidney transplant patients must be ever vigilant for signs of infection or organ rejection. The transplant patient will take immunosuppressive drugs for the rest of his or her life to avoid rejection of the “foreign” organ. Donor: Functioning kidneys Recipient: Functioning kidneys Transplanted kidney Kidney transplant 21.3 Functions of the Nephron 509 water and most solutes in blood plasma across the wall of glomerular capillaries. The fluid filtered by the glomerulus that enters the glomerular capsule is called glomerular filtrate. Filtration occurs in glomeruli just as it occurs in other capillaries (see Figure 16.3). Tubular reabsorption occurs as filtered fluid flows along the renal tubule and through the collecting duct.
No longer available |Learn more- R. Michael Akers, D. Michael Denbow(Authors)
- 2013(Publication Date)
- Wiley-Blackwell(Publisher)
The kidney and especially the elegant arrangement of the sections of the Nephron, associated blood supply, and, finally, creation of a continuously maintained osmotic gradient within the tissue of the renal medulla are critical to kidney function. The Nephron is a highly convoluted but nonetheless simple tube composed of a single layer of epithelial cells. The tube is essentially closed because of the tuft of capillaries and filtered fluid as it leaves the Bowman's capsule, but it is open at its distal end as it joins the collecting ducts that ultimately empty into the renal pelvis. We will explore these relationships by discussing in some detail the cellular structure of different epithelial cells located along the course of the Nephron. To understand the role of the kidney in long-term control of blood pressure, blood flow, and stimulation of erythrocyte production, we will describe the importance of a specialized cluster of modified distal convoluted cells called the macula densa and the juxtaglomerular cells of the wall of the afferent arteriole, which together make up the juxtaglomerular apparatus. In addition, we'll consider the significance of the network of peritubular capillaries that intertwine around the loop of Henle and the curved course of blood flow that mirrors the hairpin bend in the loop of Henle called the vasa recta. Fig. 16.7. Nephron diagram. This simplified diagram illustrates key aspects of a juxtaglomerular Nephron. While in reality the convoluted tubules are more extensive, relative orientation is maintained. Notice that the branches of the efferent arteriole that supplies the region surrounding the convoluted tubules give rise to the network vessels surrounding the loop of Henle (LH) and the vasa recta, which allows blood from the region of the convoluted tubules to flow around the loop of Henle but in the opposite direction of fluid flow within the tubule
eBook - PDF- Stefan Silbernagl, Agamemnon Despopoulos(Authors)
- 2011(Publication Date)
- Thieme(Publisher)
148 7 Kidneys, Salt, and Water Balance 7 Kidneys, Salt, and Water Balance Three fundamental mechanisms characterize kidney function: (1) large quantities of water and solutes are filtered from the blood. (2) This primary urine enters the tubule, where most of it is reabsorbed , i.e., it exits the tubule and passes back into the blood. (3) Certain sub-stances (e.g., toxins) are not only not reab-sorbed but actively secreted into the tubule lumen. The non-reabsorbed residual filtrate is excreted together with the secreted sub-stances in the final urine . Functions: The kidneys (1) adjust salt and water excretion to maintain a constant extra-cellular fluid volume and osmolality ; (2) they help to maintain acid-base homeostasis ; (3) they eliminate end-products of metabolism and foreign substances while (4) preserving useful compounds (e.g., glucose) by reabsorption; (5) they produce hormones (e.g., erythropoietin) and hormone activators (renin), and (6) have metabolic functions (protein and peptide cata-bolism, gluconeogenesis, etc.). Nephron Structure Each kidney contains about 10 6 Nephrons , each consisting of the malpighian body and the tubule. The malpighian body is located in the renal cortex ( A ) and consists of a tuft of capillaries ( glomerulus ) surrounded by a double-walled capsule ( Bowman’s capsule ). The primary urine accumulates in the capsular space between its two layers ( B ). Blood en-ters the glomerulus by an afferent arteriole ( vas afferens ) and exits via an efferent arteriole ( vas efferens ) from which the peritubular capil-lary network arises ( p. 150). The glomerular filter ( B ) separates the blood side from the Bowman’s capsular space. The glomerular filter comprises the par-tially fenestrated, partially perforated en-dothelium of the glomerular capillaries (50– 100 nm pore size) followed by the basal mem-brane as the second layer and the visceral membrane of Bowman’s capsule on the urine side.
eBook - PDF- Gerard J. Tortora, Mark Nielsen(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
The number of Nephrons is constant from birth. Any increase in kidney size is due solely to the growth of indi- vidual Nephrons. If Nephrons are injured or become diseased, new ones do not form. Signs of kidney dysfunction usually do not become apparent until function declines to less than 25 percent of normal because the remaining functional neph- rons adapt to handle a larger-than-normal load. Surgical removal of one kidney, for example, stimulates hypertrophy (enlargement) of the remaining kidney, which eventually is able to filter blood at 80 percent of the rate of two normal kidneys. Checkpoint 7. How do cortical Nephrons and juxtamedullary Nephrons differ structurally? 8. Describe the histology of the various portions of a Nephron and collecting duct. 9. Describe the structure of the juxtaglomerular apparatus. 25.4 Functions of Nephrons 907 25.4 Functions of Nephrons OBJECTIVES • Explain the role of the Nephrons and collecting ducts in glomerular filtration. • Outline the steps of tubular reabsorption and explain where it occurs. • Identify the events of tubular secretion and where they occur. • Describe the filtration membrane. To produce urine, Nephrons and collecting ducts perform three basic processes—glomerular filtration, tubular reabsorption, and tubular secretion (Figure 25.7): 1 Glomerular filtration. In the first step of urine production, water and most solutes in blood plasma move across the wall of capillaries in the glomeruli where they are filtered and move into the glomerular capsule and then into the renal tubule. 2 Tubular reabsorption. As filtered fluid flows through the renal tubules and the collecting ducts, renal tubule cells reabsorb about 99 percent of the filtered water and many useful solutes. The water and solutes return to the blood as it flows through the peritubular capillaries and vasa recta. Note that the term reabsorption refers to the return of filtered water and solutes to the bloodstream.
- Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Yvon Gonnella(Authors)
- 2021(Publication Date)
- Routledge(Publisher)
Nephritis (nĕf-rī′tĭs): Inflammation of the kidneysNephron (nĕf′rŏn): Functional unit of the kidneyNephropathy (nĕ-frŏp′ă-thē): Disease of the kidneyNephrotoxin (nĕf″rō-tŏk′sĭn): Substance that damages the kidneyOsmolarity (ŏs″mō-lăr′ĭ-tē): Concentration of osmotic particles in a solutionOsmoreceptor (ŏz″mō-rē-sĕp′tŏr): Receptor sensitive to changes in osmotic pressurePodocyte (pŏd′ō-sīt): Specialized epithelial cell in Bowman’s capsuleProteinuria (prō″tē-ĭn-ū′rē-ă): Protein in the urineTubuloglomerular(tū″bū-lō-glō-mĕr′ū-lăr): Referring to the tubule and the glomerulus of the NephronUreter (ū′rĕ-tĕr): Tube that transports urine from the kidney to the bladderUrethra (ū-rē′thră): Tube that transports urine from the bladder to the outside of the bodyVasa recta (vā′să rĕk′tă): Capillaries that lie parallel to the loops of HenleBibliographyCostanzo, L., Physiology, 3rd ed., W. B. Saunders Company, Philadelphia, PA, 2006.Fox, S. I., Human Physiology, 9th ed., McGraw-Hill, Boston, MA, 2006.Guyton, A. C., and Hall, J. E., Textbook of Medical Physiology, 11th ed., Elsevier/Saunders, Philadelphia, PA, 2006.Marieb, E. N., and Hoehn, K., Anatomy & Physiology, 3rd ed., Pearson Benjamin Cummings, San Francisco, CA, 2008.Jackson, E. K., Diuretics, in Goodman and Gilman’s The Pharmacological Basis of Therapeutics, 11th ed., Brunton, L. L., Lazo, J. S., and Parker, K. L., Eds., McGraw-Hill, New York, 2006, chap. 28.Koeppen, B. M., and Stanton, B. A., Renal Physiology, 4th ed., Mosby, St. Louis, MO, 2007.Porth, C. M., Pathophysiology, Concepts of Altered Health States
- Gerard J. Tortora, Bryan H. Derrickson, Brendan Burkett, Gregory Peoples, Danielle Dye, Julie Cooke, Tara Diversi, Mark McKean, Simon Summers, Flavia Di Pietro, Alex Engel, Michael Macartney, Hayley Green(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
The rate of urinary excretion of any solute is equal to its rate of glomerular filtration, plus its rate of secretion, minus its rate of reabsorption. By filtering, reabsorbing, and secreting, Nephrons help maintain homeostasis of the blood’s volume and composition. The situation is somewhat analogous to a recycling centre: garbage trucks dump garbage into an input hopper, where the smaller garbage passes onto a conveyor belt (glomerular filtration of plasma). As the conveyor belt carries the garbage along, workers remove useful items, such as aluminium cans, plastics, and glass containers (reabsorption). Other workers place additional garbage left at the centre and larger items onto the conveyor belt (secretion). At the end of the belt, all remaining garbage falls into a truck for transport to the landfill (excretion of wastes in urine). ....................................................................................................................................................................................... CHECKPOINT 6. How do tubular reabsorption and tubular secretion differ? 1284 Principles of anatomy and physiology 26.4 Glomerular filtration LEARNING OBJECTIVE 26.4 Describe glomerular filtration. The fluid that enters the capsular space is called the glomerular filtrate. The fraction of blood plasma in the afferent arterioles of the kidneys that becomes glomerular filtrate is the filtration fraction. Although a filtration fraction of 0.16–0.20 (16–20%) is typical, the value varies considerably in both health and disease. On average, the daily volume of glomerular filtrate in adults is 150 litres in females and 180 litres in males. More than 99% of the glomerular filtrate returns to the bloodstream via tubular reabsorption, so only 1–2 litres (about 1–2 qt) is excreted as urine.
eBook - PDF- Gerard J. Tortora, Mark Nielsen(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
Glomerular filtration: In the glomerulus, blood plasma and dissolved substances (smaller than most proteins) get filtered into the glomerular capsule. 1 2 3 Glomerular filtrate in renal tubule means entry of new substances into the body, as occurs in the gastrointestinal tract. ➌ Tubular secretion. As fluid flows through the renal tubules and collecting ducts, the renal tubule and duct cells secrete other materials, such as wastes, drugs, and excess ions, into the fluid. Notice that tubular secretion removes a substance from the blood. Solutes and the fluid that drain into the minor and major caly- ces and renal pelvis constitute urine and are excreted. The rate of urinary excretion of any solute is equal to its rate of glomerular filtration, plus its rate of secretion, minus its rate of reabsorption (excretion = filtration + secretion − reabsorption). By filtering, reabsorbing, and secreting, Nephrons help maintain homeostasis of blood volume and blood composition. The situation is somewhat analogous to a recycling center: Garbage trucks dump garbage into an input hopper, where the smaller garbage passes onto a conveyor belt (filtration of plasma by the glomerulus). As the conveyor belt carries the garbage along, workers remove useful items, such as aluminum cans, plastics, and glass containers (reab- sorption). Other workers place additional garbage left at the center and larger items onto the conveyor belt (secretion). At the end of the belt, all remaining garbage falls into a truck for transport to the landfill (excretion of wastes in urine). Glomerular Filtration The fluid that enters the capsular space is called the glomerular filtrate because it is filtered by the glomerulus. On average, the daily volume of glomerular filtrate in adults is 150 liters in females and 180 liters in males, a volume that represents about 65 times the entire blood plasma volume.
eBook - PDF- Gerard J. Tortora, Bryan H. Derrickson(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
1010 CHAPTER 26 The Urinary System passes through the proximal convoluted tubule, cells located more distally fine-tune the reabsorption processes to maintain homeo- static balances of water and selected ions. Most small proteins and peptides that pass through the filter also are reabsorbed, usually via pinocytosis. To appreciate the magnitude of tubular reabsorption, look at Table 26.3 and compare the amounts of substances that are filtered, reabsorbed, and secreted in urine. The third function of Nephrons and collecting ducts is tubular se- cretion, the transfer of materials from the blood and tubule cells into glomerular filtrate. Secreted substances include hydrogen ions (H + ), K + , ammonium ions (NH 4 + ), creatinine, and certain drugs such as penicillin. Tubular secretion has two important outcomes: (1) The secretion of H + helps control blood pH. (2) The secretion of other substances helps eliminate them from the body in urine. As a result of tubular secretion, certain substances pass from blood into urine and may be detected by a urinalysis (see Section 26.8). It is especially important to test athletes for the presence of performance-enhancing drugs such as anabolic steroids, plasma ex- panders, erythropoietin, hCG, hGH, and amphetamines. Urine tests can also be used to detect the presence of alcohol or illegal drugs such as marijuana, cocaine, and heroin. Reabsorption Routes A substance being reabsorbed from the fluid in the tubule lumen can take one of two routes before entering a peritubular capillary: It can move between adjacent tubule cells or through an individual tubule cell (Figure 26.11). Along the renal tubule, tight junctions surround and join neighboring cells to one another, much like the plastic rings that hold a six-pack of soda cans together.
eBook - PDF- Gerard J. Tortora, Bryan H. Derrickson(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
Once fluid passes through the proximal convoluted tubule, cells located more dis- tally fine-tune the reabsorption processes to maintain homeo- static balances of water and selected ions. Most small proteins and peptides that pass through the filter also are reabsorbed, usually via pinocytosis. To appreciate the magnitude of tubular reabsorption, look at Table 26.3 and compare the amounts of substances that are filtered, reabsorbed, and secreted in urine. The third function of Nephrons and collecting ducts is tubular secretion, the transfer of materials from the blood and tubule cells into glomerular filtrate. Secreted substances include hydrogen ions (H + ), K + , ammonium ions (NH 4 + ), creati- nine, and certain drugs such as penicillin. Tubular secretion has two important outcomes: (1) The secretion of H + helps control blood pH. (2) The secretion of other substances helps eliminate them from the body in urine. TABLE 26.2 Regulation of Glomerular Filtration Rate (GFR) Type of Regulation Major Stimulus Mechanism and Site of Action Effect on GFR Renal autoregulation Myogenic mechanism Increased stretching of smooth muscle fibers in afferent glomerular arteriole walls due to increased blood pressure. Stretched smooth muscle fibers contract, thereby narrowing lumen of afferent glomerular arterioles. Decrease. Tubuloglomerular feedback Rapid delivery of Na + and Cl − to the macula densa due to high systemic blood pressure. Decreased release of nitric oxide by juxtaglomerular apparatus causes constriction of afferent glomerular arterioles. Decrease. Neural regulation Increase in activity level of renal sympathetic nerves releases norepinephrine. Constriction of afferent glomerular arterioles through activation of α 1 receptors and increased release of renin. Decrease. Hormone regulation Angiotensin II Decreased blood volume or blood pressure stimulates production of angiotensin II. Constriction of afferent and efferent glomerular arterioles.
- Gerard J. Tortora, Bryan H. Derrickson(Authors)
- 2017(Publication Date)
- Wiley(Publisher)
This size permits all solutes in blood plasma to exit glomerular capillaries but prevents filtration of blood cells. Located among the glomerular capillaries and in the cleft between afferent and efferent arterioles are mesangial cells (mes-AN-jē-al; mes- = in the middle; -angi- = blood vessel) (see Figure 26.6a). These contractile cells help regulate glomerular filtration. 2 The basement membrane, a layer of acellular material between the endothelium and the podocytes, consists of minute collagen fibers and negatively charged glycoproteins. The pores within the basement membrane allow water and most small solutes to pass through. However, the negative charges of the glycoproteins repel plasma proteins, most of which are anionic; the repulsion hinders filtration of these proteins. 3 Extending from each podocyte are thousands of footlike processes termed pedicels (PED-i-sels = little feet) that wrap Q When cells of the renal tubules secrete the drug penicillin, is the drug being added to or removed from the bloodstream? Glomerular filtration occurs in the renal corpuscle. Tubular reabsorption and tubular secretion occur all along the renal tubule and collecting duct. FIGURE 26.7 Relationship of a Nephron’s structure to its three basic functions: glomerular filtration, tubular reabsorption, and tubular secretion. Excreted substances remain in the urine and subsequently leave the body. For any substance S, excretion rate of S = filtration rate of S − reabsorption rate of S + secretion rate of S. Renal corpuscle Renal tubule and collecting duct Peritubular capillaries 3 Urine (contains secreted substances) Blood (contains reabsorbed substances) 2 1 Afferent arteriole Efferent arteriole Glomerulus Glomerular capsule Tubular secretion: All along the renal tubule and collecting duct, substances such as wastes, drugs, and excess ions get secreted from the peritubular capillaries into the renal tubule. These substances ultimately make their way into the urine.
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