Biological Sciences
Excretory System
The excretory system is responsible for removing waste and excess substances from the body, maintaining a balanced internal environment. Key organs include the kidneys, which filter blood and produce urine, and the bladder, which stores urine until it is excreted. Other components, such as the liver and lungs, also play roles in excretion by eliminating toxins and gases from the body.
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10 Key excerpts on "Excretory System"
eBook - PDF- Gerard J. Tortora, Bryan H. Derrickson(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
993 CHAPTER 26 As body cells carry out metabolic activities, they consume oxygen and nutrients and produce waste products such as carbon dioxide, urea, and uric acid. Wastes must be eliminated from the body because they can be toxic to cells if they accumulate. While the respiratory system rids the body of carbon dioxide, the urinary system disposes of most other wastes. The urinary system performs this function by removing wastes from the blood and excreting them into urine. Disposal of wastes through the release of urine is not the only purpose of the urinary system. The urinary system also helps regulate blood composition, pH, volume, and pressure; maintains blood osmolarity; and produces hormones. Q Did you ever wonder how diuretics work and why they are used? The Urinary System The Urinary System and Homeostasis The urinary system contributes to homeostasis by excreting wastes; altering blood composition, pH, volume, and pressure; maintaining blood osmolarity; and producing hormones. 994 CHAPTER 26 The Urinary System wastes and excrete them into a fluid called urine. Once formed, urine passes through the ureters and is stored in the urinary bladder until it is excreted from the body through the urethra. 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 sys- tems 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: 26.1 Overview of the Urinary System OBJECTIVE • Describe the major structures of the urinary system and the functions they perform.
- Gerard J. Tortora, Bryan H. Derrickson(Authors)
- 2017(Publication Date)
- Wiley(Publisher)
Besides the kidneys, several other tissues, organs, and processes contribute to the temporary confinement of wastes, the transport of waste materi- als for disposal, the recycling of materials, and the excretion of excess or toxic substances in the body. These waste management systems include the following: • Body buffers. Buffers in body fluids bind excess hydrogen ions (H + ), thereby preventing an increase in the acidity of body fluids. Buffers, like wastebaskets, have a limited capacity; eventually the H + , like the paper in a wastebasket, must be eliminated from the body by excretion. • Blood. The bloodstream provides pickup and delivery services for the transport of wastes, in much the same way that garbage trucks and sewer lines serve a community. • Liver. The liver is the primary site for metabolic recycling, as oc- curs, for example, in the conversion of amino acids into glucose or of glucose into fatty acids. The liver also converts toxic substances into less toxic ones, such as ammonia into urea. These functions of the liver are described in Chapters 24 and 25. • Lungs. With each exhalation, the lungs excrete CO 2 , and expel heat and a little water vapor. • Sweat (sudoriferous) glands. Especially during exercise, sweat glands in the skin help eliminate excess heat, water, and CO 2 , plus small quantities of salts and urea as well. • Gastrointestinal tract. Through defecation, the gastrointestinal tract excretes solid, undigested foods; wastes; some CO 2 ; water; salts; and heat. pelvic floor, the cerebral cortex can initiate micturition or delay its occurrence for a limited period. Urethra The urethra (ū-RE - -thra) is a small tube leading from the internal urethral orifice in the floor of the urinary bladder to the exterior of the body (Figure 26.22). In both males and females, the urethra is the terminal portion of the urinary system and the passageway for discharging urine from the body.
eBook - PDF- Bryan H. Derrickson(Author)
- 2019(Publication Date)
- Wiley(Publisher)
686 CHAPTER 19 The Urinary System The Urinary System and Homeostasis • The urinary system contributes to homeostasis by excreting wastes; altering blood composition, pH, volume, and pressure; maintaining blood osmolarity; and producing hormones. LOOKING BACK TO MOVE AHEAD… • Tight junctions are proteins that fuse together the outer surfaces of adjacent plasma membranes to seal off passageways between adjacent cells (Section 3.8). • Secondary active transport is a type of active transport in which a substance moves against its concentration or electrochemical gradient using the energy stored in an ionic electrochemical gradient (Section 5.5). • Creatine phosphate is an energy-rich molecule in muscle fibers that transfers its phosphate group to ADP to form ATP (Section 11.4). • Movement of fluid across blood capillary walls depends on the balance of four pressures (Starling forces): capillary hydrostatic pressure and interstitial fluid colloid osmotic pressure promote filtration, whereas plasma colloid osmotic pressure and interstitial fluid hydrostatic pressure promote reabsorption (Section 15.2). Introduction As body cells carry out metabolic activities, they consume oxygen and nutrients and produce waste products such as carbon dioxide, urea, and uric acid. Wastes must be eliminated from the body because they can be toxic to cells if they accumulate. While the respiratory system rids 19.2 Organization of the Kidneys 687 the body of carbon dioxide, the urinary system disposes of most other wastes. The urinary system consists of two kidneys, two ureters, one urinary bladder, and one urethra. 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.
eBook - ePub- Zoe Davies(Author)
- 2017(Publication Date)
- Wiley-Blackwell(Publisher)
Chapter 14 The Urinary SystemThe urinary system is primarily involved in the extraction and removal of waste products from the blood. It filters the blood. In particular it is responsible for the removal of nitrogenous waste, and together with the digestive system it removes most of the waste products produced in the body, except gaseous carbon dioxide which is removed via the lungs. While removing these waste products, the urinary system is closely involved with the water balance, acid–base balance and salt balance. These processes are highly complicated and involve the influence of hormones. The products of excretion of the horse are shown in Figure 14.1 .Excretory products of the horse.Figure 14.1The urinary system is composed of two kidneys, two ureters, one bladder and the urethra (Figures 14.2 and 14.3 ). Each day approximately 1000–2000 litres of fluid are delivered to the kidneys of the horse. Since only approximately 5–15 litres of urine are excreted daily, the kidneys must remove most of the substances present in them. If the kidneys did not reabsorb fluid entering them, horses would lose their entire water and salt content in less than half a day.Position of the urinary organs.Figure 14.2Dorsal view of the urinary system.Figure 14.3Kidneys
The kidneys are a pair of reddish-brown organs and in the horse lie on either side of the body, approximately midway between the withers and the croup underneath the spine. The left kidney lies farther back towards the last rib, whereas the right kidney lies under the last three ribs. In this position they are well protected from external injury. The kidneys are situated outside the abdominal cavity but are bound to the upper wall of the abdomen by a layer of peritoneum which prevents the kidneys moving about as the horse moves. There are often large collections of fatty tissue around the kidneys which also helps to protect them.
eBook - PDF- Cecie Starr, Beverly McMillan(Authors)
- 2015(Publication Date)
- Cengage Learning EMEA(Publisher)
Studying the urinary system will tap your knowledge of pH and buffer systems (2.7) and of osmosis and transport mechanisms (3.10, 3.11). You will also use what you have learned about blood circulation (7.1) and the movement of substances into and out of blood capillaries (7.7). KEY CONCEPTS LINKS TO EARLIER CONCEPTS Ed Kashi/VII/Documentary/Corbis Maintaining the Extracellular Fluid The body must eliminate chemi-cal wastes from extracellular fluid, including the blood, and manage the levels of water and solutes in it. The urinary system performs this task. Section 12.1 Light or dark? Clear or cloudy? A lot or a little? Like blood, urine can tell a lot about a person’s health. Acidic urine can signal metabolic problems, while alkaline urine may be a sign of a bacterial infection. Too much protein in urine might mean the kidneys are not functioning properly. Specialized urine tests can detect chemicals produced by certain cancers. Do-it-yourself urine tests are popular for monitoring hormones that indicate a woman’s fertile period or early signs she may be pregnant. Urine can also tell the tale if you use any of a variety of illegal drugs. That urine can be such a trusty indicator of health, the presence of hormones, and drug use is a tribute to the urinary system. As you will discover in this chapter, the kidneys are the urinary system’s all-important blood filters. Top: © Ferenc Cegledi/Shutterstock.com; Middle: both © Cengage Learning; Bottom: Arthur Glauberman/Photo Researchers/Getty Images THE URINARY SYSTEM 12 The Urinary System The urinary system consists of the kidneys, ureters, bladder, and ure-thra. In the kidneys, structures called nephrons filter substances from the blood, eliminating unneeded ones in urine. Section 12.2 How the Kidneys Form Urine The kidneys form urine in steps called filtration, reabsorption, and secretion. Hormones and a thirst mechanism adjust the chemical makeup of urine.
eBook - PDF- Kathleen A. Ireland(Author)
- 2018(Publication Date)
- Wiley(Publisher)
Define the functions of the urinary system. 2. Identify the organs of the urinary system. 3. Diagram the anatomy of the kidney and the nephron. The urinary system excretes fluid waste as it maintains fluid balance and blood volume. It also regulates blood composition, helps to main- tain blood pressure, monitors and maintains red blood cell levels, and assists in vitamin D synthesis. In addition, the urinary system is responsible for monitoring and adjusting the ionic composition of the blood, regulating the pH of the blood, maintaining blood glucose lev- els, and producing hormones that regulate calcium levels. It does all this with four organs: pairs of kidneys and ureters, the urinary bladder, and the urethra. (Figure 17.1). Listing all of these functions at once, it becomes obvious that the four organs of the urinary system are responsible for regulating the fluid environment of the body. As a whole, these are such vital functions that if the urinary system fails, the body will shut down within a few days. Urine is not the goal of the urinary system, but rather is formed as a by-product of the system’s functions. All waste materials removed from the blood by the urinary system leave the body in urine. The Kidneys Are Filtering Organs The kidneys filter blood and produce hormones. These two fist-sized, bean-shaped organs lie immediately beneath the back musculature, embedded in a protective layer of fat. The kidneys are retroperitoneal, meaning they lie posterior to the peritoneal membrane. Because of this relatively unprotected placement, the kidneys are susceptible to injury from an external blow. Consequently, football pads are designed to cover the kidney area, and boxers and ultimate fighters are not per- mitted to punch opponents in the back. Due to the placement of the liver, the right kidney is slightly lower than the left. The kidneys themselves are covered with a tough outer mem- brane, the renal capsule (Figure 17.2).
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 - PDF- Gerard J. Tortora, Mark Nielsen(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
894 CHAPTER 25 The Urinary System Introduction As body cells carry out their metabolic functions, they con- sume oxygen and nutrients and produce substances, such as carbon dioxide, that have no useful functions and need to be eliminated from the body. While the respiratory system rids the body of carbon dioxide, the urinary system disposes of most other unneeded substances. As you will learn in this chapter, however, the urinary system is not merely concerned with waste disposal; it carries out a number of other important func- tions as well. The kidneys allow you to conserve water by secreting hormones to reabsorb water that is normally lost to the urine. When you exercise, you remove toxins in your body through increased sweating and therefore lose more water than when you are at rest. Not only do you lose water, but important ions such as sodium and potassium (important to electrical trans- mission in your body) are also lost. This is why athletes often drink sports drinks that contain water as well as sodium, potas- sium, and glucose (for quick energy supply). Most people think that the first sign of dehydration is thirst and are unaware that muscle fatigue and soreness occur first and thirst later. In order to ensure that you are getting enough fluids you should really never let yourself get to the point of thirst. When you partici- pate in exercise or activities that increase your metabolism, it is even more important to drink fluids or suffer the consequences of lactic acid buildup and muscle fatigue to the point of muscle spasm. Q Did you ever wonder how diuretics work and why they are used? You can find out in Section 25.4, Clinical Connection: Diuretics. Shawn Miller and Mark Nielsen 25.1 Overview of the Urinary System 895 25.1 Overview of the Urinary System OBJECTIVE • Describe the major structures of the urinary system and the functions they perform.
eBook - PDF- Mary Ann Clark, Jung Choi, Matthew Douglas(Authors)
- 2018(Publication Date)
- Openstax(Publisher)
41 | OSMOTIC REGULATION AND EXCRETION Figure 41.1 Just as humans recycle what we can and dump the remains into landfills, our bodies use and recycle what they can and excrete the remaining waste products. Our bodies’ complex systems have developed ways to treat waste and maintain a balanced internal environment. (credit: modification of work by Redwin Law) Chapter Outline 41.1: Osmoregulation and Osmotic Balance 41.2: The Kidneys and Osmoregulatory Organs 41.3: Excretion Systems 41.4: Nitrogenous Wastes 41.5: Hormonal Control of Osmoregulatory Functions Introduction The daily intake recommendation for human water consumption is eight to ten glasses of water. In order to achieve a healthy balance, the human body should excrete the eight to ten glasses of water every day. This occurs via the processes of urination, defecation, sweating and, to a small extent, respiration. The organs and tissues of the human body are soaked in fluids that are maintained at constant temperature, pH, and solute concentration, all crucial elements of homeostasis. The solutes in body fluids are mainly mineral salts and sugars, and osmotic regulation is the process by which the mineral salts and water are kept in balance. Osmotic homeostasis is maintained despite the influence of external factors like temperature, diet, and weather conditions. Chapter 41 | Osmotic Regulation and Excretion 1277 41.1 | Osmoregulation and Osmotic Balance By the end of this section, you will be able to do the following: • Define osmosis and explain its role within molecules • Explain why osmoregulation and osmotic balance are important body functions • Describe active transport mechanisms • Explain osmolarity and the way in which it is measured • Describe osmoregulators or osmoconformers and how these tools allow animals to adapt to different environments Osmosis is the diffusion of water across a membrane in response to osmotic pressure caused by an imbalance of molecules on either side of the membrane.
- 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)
Next, in chapter 27, we will see how the kidneys and lungs contribute to maintenance of homeostasis of body fluid volume, electrolyte levels in body fluids, and acid–base balance. CHAPTER 26 The urinary system 1317 THE URINARY SYSTEM FOCUS on HOMEOSTASIS CONTRIBUTIONS OF INTEGUMENTARY SYSTEM • Kidneys and skin both contribute to synthesis of calcitriol, the active form of vitamin D LYMPHATIC SYSTEM and IMMUNITY • By increasing or decreasing their reabsorption of water filtered from blood, kidneys help adjust volume of interstitial fluid and lymph; urine flushes microbes out of urethra RESPIRATORY SYSTEM • Kidneys and lungs cooperate in adjusting pH of body fluids URINARY SYSTEM • Kidneys help synthesise calcitriol, the active form of vitamin D, which is needed for absorption of dietary calcium REPRODUCTIVE SYSTEMS • In males, portion of urethra that extends through prostate and penis is passageway for semen as well as urine MUSCULAR SYSTEM ENDOCRINE SYSTEM • Kidneys participate in synthesis of calcitriol, the active form of vitamin D • Kidneys release erythropoietin, the hormone that stimulates production of red blood cells FOR ALL BODY SYSTEMS • Kidneys regulate volume, composition, and pH of body fluids by removing wastes and excess substances from blood and excreting them in urine • Ureters transport urine from kidneys to urinary bladder, which stores urine until it is eliminated through urethra CARDIOVASCULAR SYSTEM • By increasing or decreasing their reabsorption of water filtered from blood, kidneys help adjust blood volume and blood pressure • Renin released by juxtaglomerular cells in kidneys raises blood pressure • Some bilirubin from haemoglobin breakdown is converted to a yellow pigment (urobilin), which is excreted in urine SKELETAL SYSTEM • Kidneys help adjust levels of blood calcium and phosphates, needed for building extracellular bone matrix NERVOUS SYSTEM • Kidneys perform gluconeogenesis, which provides glucose for ATP production in neurons, especially during fasting or starvation • Kidneys help adjust level of blood calcium, needed for contraction of muscle 1318
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