Biological Sciences
Kidney
The kidney is a vital organ responsible for filtering waste products and excess substances from the blood to produce urine. It also helps regulate blood pressure, electrolyte balance, and red blood cell production. Each kidney contains millions of nephrons, which are the functional units responsible for these filtration and regulatory processes.
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11 Key excerpts on "Kidney"
eBook - PDF- Craig Freudenrich, Gerard J. Tortora(Authors)
- 2011(Publication Date)
- Wiley(Publisher)
The intricate anatomy and physiology of the Kidneys keep your body fluid composition in bal- ance, eliminating wastes and adjusting to various physiological conditions. Let’s take a closer look at the Kidneys and the other components of this remarkable system. The Urinary System and Fluid, Electrolyte, and Acid–Base Balance 436 437 CHAPTER OUTLINE The Urinary System Plays a Vital Role in Maintaining Homeostasis 438 • The Kidneys Do the Major Work of the Urinary System • The Kidney Is a Complex Filter • Urine Formation InvolvesThree Processes and Helps Maintain the Blood's Volume and Compostion • Glomerular Filtration Moves a Large Amount of Fluid into the Glomerular Capsule • Reabsorption and Secretion Occur Along the Length of the RenalTubule • The Nephron Loop Contributes to Water Conservation in the Body The Urinary Bladder Stores Urine and Expels It from the Body 450 • The Urinary Bladder Is aTemporary Storage Area • Urethral Structure Varies Between the Sexes • Urination Is a Spinal Reflex The Kidneys Regulate the Composition of Body Fluids 453 • Fluid Balance Depends Primarily on Electrolyte Balance • Water Regulation Involves a Balance of Intake and Loss • Water Levels Also Depend on Changes in NaCl Levels • How Do Kidney Stones Form? The Kidneys Help Maintain the Acid–Base Balance of Body Fluids 458 • Buffers Help to Maintain pH Levels Within a Narrow Range • The Lungs and Kidneys Can Help Compensate for Changes in pH • Large Changes in pH May Result in Acidosis or Alkalosis ■ What a Health Provider Sees: Renal Failure and Dialysis ✓ ✓ CHAPTER PLANNER ❑ Study the picture and read the opening story. ❑ Scan the Learning Objectives in each section: p. 438 ❑ p. 450 ❑ p. 453 ❑ p. 458 ❑ ❑ Read the text and study all visuals. Answer any questions. Analyze key features ❑ InSight, pp. 440–441 ❑ ❑ Process Diagram, p. 445 ❑ p. 448 ❑ p. 452 ❑ ❑ What a Health Provider Sees, p. 462 ❑ ❑ Stop: Answer the Concept Checks before you go on: p.
- 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)
26.1 Overview of Kidney functions LEARNING OBJECTIVE 26.1 List the functions of the Kidneys. The Kidneys do the major work of the urinary system (figure 26.1). The other parts of the system are mainly passageways and storage areas. Functions of the Kidneys include the following. • Regulation of blood ionic composition. The Kidneys help regulate the blood levels of several ions, most importantly sodium ions (Na + ), potassium ions (K + ), calcium ions (Ca 2+ ), chloride ions (Cl − ), and phosphate ions (HPO 4 2− ). • Regulation of blood pH. The Kidneys excrete a variable amount of hydrogen ions (H + ) into the urine and conserve bicarbonate ions (HCO 3 − ), which are an important buffer of H + in the blood. Both of these activities help regulate blood pH. • Regulation of blood volume. The Kidneys adjust blood volume by conserving or eliminating water in the urine. An increase in blood volume increases blood pressure; a decrease in blood volume decreases blood pressure. • Regulation of blood pressure. The Kidneys also help regulate blood pressure by secreting the enzyme renin, which activates the renin–angiotensin–aldosterone pathway (see figure 18.16). Increased renin causes an increase in blood pressure. • Maintenance of blood osmolarity. By separately regulating loss of water and loss of solutes in the urine, the Kidneys maintain a relatively constant blood osmolarity close to 300 milliosmoles per litre (mOsm/litre). * • Production of hormones. The Kidneys produce two hormones. Calcitriol, the active form of vitamin D, helps regulate calcium homeostasis (see figure 18.14), and erythropoietin stimulates the production of red blood cells (see figure 19.5). • Regulation of blood glucose level. Like the liver, the Kidneys can use the amino acid glutamine in gluconeogenesis, the synthesis of new glucose molecules. They can then release glucose into the blood to help maintain a normal blood glucose level.
eBook - PDF- Joseph D. Bronzino, Donald R. Peterson(Authors)
- 2014(Publication Date)
- CRC Press(Publisher)
2 -1 2.1 Introduction The Kidney regulates body fluid composition and distribution To accomplish this, it separates wastes from the blood, controls the total volume of body fluid (water), manages blood pressure, plays a role in the regulation of body fluid pH and solute concentration, and secretes or modifies certain hormones that relate to its other physiologic roles (Guyton and Hall 2006) With the exception of its role as an endocrine organ, most of these functions are accomplished via selective and actively adjusted filtration of the blood The adjustment of blood composition in the Kidney involves three processes: (1) filtration —the selective filtration of small solutes from blood plasma, along with water, to form an ultrafiltrate, (2) reabsorption —the recovery of water and valuable solutes from the ultrafiltrate, which are too small to be retained by the filter, and (3) secretion —the addition of waste products to the ultrafiltrate by secretion from specialized cells All these processes take place along the nephron , which is the basic functional unit of the Kidney An individual nephron is in some ways analogous to a single-channel microfluidic 2 Kidney Structure and Physiology 21 Introduction 2 -1 22 Kidney Anatomy 2 -2 23 Vasculature of the Kidney 2 -4 24 Architecture of the Nephron 2 -4 25 Structure of the Glomerulus and the Glomerular Filtration Barrier 2 -5 26 Mechanical Properties of the Glomerulus 2 -7 27 Glomerular Filtration 2 -8 28 Factors Governing Glomerular Filtration 2 -9 Hydraulic Permeability of the Glomerular Barrier • Surface Area of the Glomerular Barrier • Ultrafiltration Coefficient • Intraluminal Hydrostatic Pressure of the Glomerular Capillary 29 Permselectivity of the Glomerular Barrier 2 -11 210 Tubulo-Interstitial Structure and Organization 2 -12 211 Solute Recovery from the Ultrafiltrate 2 -14 Mechanisms of Solute Transport •
eBook - PDF- Gerard J. Tortora, Bryan H. Derrickson(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
26.2 Anatomy of the Kidneys 995 • Excretion of wastes. By forming urine, the Kidneys help excrete wastes from the body. Some wastes excreted in urine result from metabolic reactions. These include urea and ammonia from the deamination of amino acids; creatinine from the breakdown of creatine phosphate; uric acid from the catabolism of nucleic acids; and urobilin from the breakdown of hemoglobin. Urea, ammonia, creatinine, uric acid, and urobilin are collectively known as nitrogenous wastes because they are waste products that contain nitrogen. Other wastes excreted in the urine are for- eign substances that have entered the body, such as drugs and environmental toxins. • Regulation of blood ionic composition. The Kidneys help regu- late the blood levels of several ions, most importantly sodium ions (Na + ), potassium ions (K + ), calcium ions (Ca 2+ ), chloride ions (Cl − ), and phosphate ions (HPO 4 2− ). The Kidneys accomplish this task by adjusting the amounts of these ions that are excreted into the urine. • Regulation of blood pH. The Kidneys excrete a variable amount of hydrogen ions (H + ) into the urine and conserve bicarbonate ions (HCO 3 − ), which are an important buffer of H + in the blood. Both of these activities help regulate blood pH. • Regulation of blood volume. The Kidneys adjust blood volume by conserving or eliminating water in the urine. An increase in blood volume increases blood pressure; a decrease in blood volume de- creases blood pressure. • Regulation of blood pressure. The Kidneys also help regulate blood pressure by secreting the enzyme renin, which activates the renin– angiotensin–aldosterone pathway (see Figure 18.15). Increased renin causes an increase in blood pressure. • Maintenance of blood osmolarity. By separately regulating loss of water and loss of solutes in the urine, the Kidneys maintain a rela- tively constant blood osmolarity close to 300 milliosmoles per liter (mOsm/liter).* • Production of hormones.
eBook - PDF- Cecie Starr, Beverly McMillan(Authors)
- 2015(Publication Date)
- Cengage Learning EMEA(Publisher)
Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 226 CHAPTER 12 glomerulus Cluster of blood capillaries in a neph-ron, where substances move from the blood into the nephron. Kidneys Organs that adjust fluid balance and filter wastes from blood. The Kidneys also perform other physiological functions. nephrons Blood-filtering units in the Kidneys. ureter Tube that carries urine from Kidneys to the bladder. urethra Tube that carries urine to the outside of the body. urinary bladder Hollow organ that stores urine. The Urinary System: Built for Filtering and Waste Disposal intestine to absorb calcium in food. In addition, Kidneys make the enzyme renin, which helps regulate blood pres-sure, as you will read later in this chapter. The main func-tion of Kidneys, however, is to remove metabolic wastes from the blood and adjust fluid balance in the body. In addition to the two Kidneys, the urinary system includes “plumbing” that transports or stores urine. Once urine has formed in a Kidney, it flows into a tubelike ureter , then on into the urinary bladder , where it is stored until you urinate. Urine leaves the bladder through the urethra , a tube that opens at the body surface. Nephrons are the Kidney filters Each Kidney lobe contains blood vessels and more than a million slender tubes called nephrons . Nephrons are the structures that filter water and solutes from blood. A nephron is shaped a bit like the piping under a sink (Figure 12.4A). Its wall is a single layer of epithelial cells, but the cells and junctions between them vary in different parts of the tube.
eBook - PDF- Gerard J. Tortora, Bryan H. Derrickson(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
Nephrology (nef-ROL-ō-jē; nephr- = Kidney; -ology = study of) is the scientific study of the anatomy, physiology, and pathology of the Kidneys. The branch of medicine that deals with the male and female urinary systems and the male reproductive system is called urology (ū-ROL-ō-jē; uro- = urine). A physician who specializes in this branch of medicine is called a urologist (ū-ROL-ō-jist). Functions of the Kidneys The Kidneys do the major work of the urinary system. The other parts of the system are mainly passageways and storage areas. Functions of the Kidneys include the following: • Excretion of wastes. By forming urine, the Kidneys help excrete wastes from the body. Some wastes excreted in urine result from metabolic reactions. These include urea and ammonia from the deamination of amino acids; cre- atinine from the breakdown of creatine phosphate; uric acid from the catabolism of nucleic acids; and urobilin from the breakdown of hemoglobin. Urea, ammonia, cre- atinine, uric acid, and urobilin are collectively known as nitrogenous wastes because they are waste products that contain nitrogen. Other wastes excreted in the urine are foreign substances that have entered the body, such as drugs and environmental toxins. Q Which organs constitute the urinary system? FIGURE 26.1 Organs of the urinary system in a female. Urine formed by the Kidneys passes first into the ureters, then to the urinary bladder for storage, and finally through the urethra for elimination from the body. Functions of the Urinary System 1. Kidneys regulate blood volume and composition; help regulate blood pressure, pH, and glucose levels; produce two hormones (calcitriol and erythropoietin); and excrete wastes in urine. 2. Ureters transport urine from Kidneys to urinary bladder. 3. Urinary bladder stores urine and expels it into urethra.
eBook - PDF- Gerard J. Tortora, Mark Nielsen(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
Both of these activities help reg- ulate blood pH. • Regulation of blood volume. The Kidneys adjust blood volume by conserving or eliminating water in the urine. An increase in blood volume increases blood pressure; a decrease in blood volume decreases blood pressure. • Enzymatic regulation of blood pressure. The Kidneys also help regulate blood pressure by secreting the enzyme renin, which indirectly causes an increase in blood pressure. • Maintenance of blood osmolarity. By separately regulat- ing loss of water and loss of solutes in the urine, the kid- neys maintain a relatively constant blood osmolarity. The osmolarity of a solution is a measure of the total number of dissolved particles per liter of solution. • Production of hormones. The Kidneys produce two hor- mones. Calcitriol, the active form of vitamin D, helps regu- late calcium homeostasis, and erythropoietin stimulates the production of red blood cells. • Regulation of blood glucose level. Like the liver, the kid- neys can use the amino acid glutamine in gluconeogene- sis, the synthesis of new glucose molecules. They can then release glucose into the blood to help maintain a normal blood glucose level. • Excretion of wastes and foreign substances. By forming urine, the Kidneys help excrete wastes—substances that have no useful function in the body. Some wastes excreted in urine result from metabolic reactions in the body. These include ammonia and urea from the deamination of amino acids; bilirubin from the catabolism of hemoglobin; creati- nine from the breakdown of creatine phosphate in muscle fibers; and uric acid from the catabolism of nucleic acids. Other wastes excreted in urine are foreign substances from the diet, such as drugs and environmental toxins.
eBook - PDF- Bryan H. Derrickson(Author)
- 2019(Publication Date)
- Wiley(Publisher)
The Kidneys filter blood of wastes and excrete them into a fluid called urine. From the Kidneys, urine passes through the ureters to the urinary bladder, where it is stored until it is excreted from the body through the urethra. Disposal of wastes through the release of urine is not the only purpose of the urinary system. As you are about to discover, this system carries out a number of other important functions as well. 19.1 Overview of Kidney Functions Objective • Describe the functions of the Kidneys. The Kidneys do the major work of the urinary system. The other parts of this system are mainly passageways and storage areas. Functions of the Kidneys include the following: • Excretion of wastes. By forming urine, the Kidneys help ex- crete wastes from the body. Some wastes excreted in urine result from metabolic reactions. These include urea and am- monia from the deamination of amino acids; creatinine from the breakdown of creatine phosphate; uric acid from the ca- tabolism of nucleic acids; and urobilin from the breakdown of hemoglobin. Urea, ammonia, creatinine, uric acid, and urobilin are collectively known as nitrogenous wastes be- cause they are waste products that contain nitrogen. Other wastes excreted in the urine are foreign substances that have entered the body, such as drugs and environmental toxins. • Regulation of blood ionic composition. The Kidneys help regulate the blood levels of several ions, including sodium ions (Na + ), potassium ions (K + ), calcium ions (Ca 2+ ), chloride ions (Cl − ), and phosphate ions (HPO 4 2− ). The Kidneys accom- plish this task by adjusting the amounts of these ions that are excreted into the urine. • Regulation of blood pH. The Kidneys excrete a variable amount of hydrogen ions (H + ) into the urine and conserve bi- carbonate ions (HCO 3 − ), which are an important buffer of H + in the blood. Both of these activities help regulate blood pH. • Regulation of blood volume.
eBook - PDF- Gerard J. Tortora, Mark Nielsen(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
811 1. The Kidneys regulate blood volume and composition; help regulate blood pressure, pH, and glucose levels; produce two hormones (calcitriol and erythropoietin); and excrete wastes in the urine. 2. The ureters transport urine from the Kidneys to the urinary bladder. 3. The urinary bladder stores urine and expels it into the urethra. 4. The urethra discharges urine from the body. FUNCTIONS OF THE URINARY SYSTEM Diaphragm Esophagus Left adrenal (suprarenal) gland Abdominal aorta Inferior vena cava Rectum Right Kidney Right renal artery Right ureter Left ureter Left Kidney Left renal vein Urinary bladder Urethra Left ovary Uterus (a) Anterior view of urinary system • Tubular Reabsorption 824 • Tubular Secretion 824 25.5 Urine Transportation, Storage, and Elimination 825 • Ureters 825 • Urinary Bladder 828 • Urethra 829 25.6 Development of the Urinary System 831 25.7 Aging and the Urinary System 832 Key Medical Terms Associated with the Urinary System 832 25.1 Overview of the Urinary System 811 25.2 Anatomy of the Kidneys 813 • External Anatomy of the Kidneys 813 • Internal Anatomy of the Kidneys 813 • Blood and Nerve Supply of the Kidneys 816 25.3 The Nephron 817 • Parts of a Nephron 817 • Histology of the Nephron and Collecting Duct 819 25.4 Functions of Nephrons 822 • Glomerular Filtration 823 25.1 OVERVIEW OF THE URINARY SYSTEM O B J E C T I V E • Describe the major structures of the urinary system and the functions they perform. The urinary system consists of two Kidneys, two ureters, one urinary bladder, and one urethra (Figure 25.1). The branch of medicine that deals with the male and female urinary systems and the male reproductive system is called urology (u ¯-ROL-o ˉ-je ˉ; uro-=urine). A physician who specializes in this branch of medi- cine is called a urologist (u ¯-ROL-o ˉ -jist). Like the respiratory and digestive systems, the urinary system forms an extensive area of contact with the cardiovascular system.
eBook - ePub- William J. Marshall, Márta Lapsley, Andrew Day, Kate Shipman(Authors)
- 2020(Publication Date)
- Elsevier(Publisher)
Chapter| 5 |The Kidneys
Introduction
The Kidneys have three major functions:They also contribute to glucose supply in the fasting state through gluconeogenesis. Each Kidney comprises approximately 1 million functional units, called ‘nephrons’.- • excretion of waste
- • maintenance of extracellular fluid (ECF) volume and composition, including acid–base balance
- • hormone synthesis.
The Kidneys have a rich blood supply and normally receive about 25% of the cardiac output. Most of this is distributed initially to the capillary tufts of the glomeruli, which act as high-pressure filters. Blood is separated from the lumen of the nephron by three layers: the capillary endothelial cells, the basement membrane and the epithelial cells of the nephron (Fig. 5.1 ). The endothelial and epithelial cells are in intimate contact with the basement membrane; the endothelial cells are fenestrated, and contact between the epithelial cells and the membrane is discontinuous so that the membrane is exposed to blood on one side and to the lumen of the nephron on the other side.The glomerular filtrate is an ultrafiltrate of plasma ; that is, it has a similar composition to plasma except that it is almost free of large proteins. This is because the endothelium provides a barrier to red and white blood cells, and the basement membrane, although permeable to water and low molecular mass substances, is largely impermeable to macromolecules. This impermeability is related to both molecular size and electrical charge. Proteins with molecular masses lower than that of albumin (68 kDa) are filterable, at least to some extent; negatively charged molecules are less easily filtered than those bearing a positive charge. Almost all the protein in the glomerular filtrate is reabsorbed and catabolized by proximal tubular cells, with the result that normal urinary protein excretion is <150 mg/24 h.Filtration is a passive process. The total filtration rate of the Kidneys is mainly determined by the difference between the blood pressure in the glomerular capillaries and the hydrostatic pressure in the lumen of the nephron, the nature of the glomerular basement membrane and the number of glomeruli. The difference in the osmotic pressures of the plasma and the ultrafiltrate provides a small force that opposes filtration. In adults, the normal glomerular filtration rate
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.
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