Digestive and Excretory Systems Section 3 Excretion Preview

Digestive and Excretory Systems Section 3: Excretion Preview • • Bellringer Key Ideas Metabolic Wastes Cleaning the Blood Urinary Excretion Kidney Failure Summary Section 3

Digestive and Excretory Systems Section 3 Bellringer The blood in your body must be cleaned regularly. Without looking in your book, try to figure out how your body cleans your blood. Then check your answer with the explanation in this section.

Digestive and Excretory Systems Section 3 Key Ideas • Why is excretion important? • What do the kidneys do? • How are metabolic wastes removed? • How does kidney damage affect the body?

Digestive and Excretory Systems Section 3 Metabolic Wastes • The process of eliminating metabolic wastes is called excretion. • Some metabolic reactions produce toxic, nitrogencontaining wastes, such as urea. Urea is found in urine and other body fluids. • By removing wastes and toxic chemicals, excretion enables the body to maintain its osmotic and p. H balance. • The skin, lungs, and kidneys are organs involved in excretion.

Digestive and Excretory Systems Section 3 Visual Concept: Waste Substances and Excretion Sites

Digestive and Excretory Systems Section 3 Metabolic Wastes, continued • The body needs an adequate amount of water to move nutrients and wastes efficiently. • Water also helps regulate body temperature by absorbing and distributing heat. • A healthy person needs 2. 4 L (2. 5 qt) of water every day to replace water lost through excretion. • Activity level, diet, and hot, humid weather can affect a body’s need for water.

Digestive and Excretory Systems Section 3 Visual Concept: Sources of Water Balance in Humans

Digestive and Excretory Systems Section 3 Cleaning the Blood • The kidneys filter wastes out of the blood and balance levels of molecules. • The kidneys are a pair of fist-sized, bean-shaped organs that are located in the lower back. • The functional unit of the kidney is called a nephron. Nephrons are tiny blood-filtering tubes surrounded by a tight ball of capillaries.

Digestive and Excretory Systems Section 3 Cleaning the Blood, continued • Three different processes occur as blood flows through a nephron: filtration, reabsorption, and secretion. • Filtration begins in a bed of capillaries called a glomerulus which is located inside a structure called Bowman’s capsule. • A filtered fluid called filtrate forms in the capsule and passes into the renal tubules.

Digestive and Excretory Systems Section 3 Cleaning the Blood, continued • Blood cells, proteins, and other large molecules do not collect in the filtrate because they are too large to cross the capillary membrane. • Glucose, ions, and some water in the filtrate are reabsorbed into the blood through the capillaries surrounding the renal tubules. • At the end of the renal tubules, additional substances, such as toxic materials, pass from the blood into the filtrate before the filtrate passes out of the nephron through collecting ducts.

Digestive and Excretory Systems Section 3 Visual Concept: Formation of Urine

Digestive and Excretory Systems Section 3 Urinary Excretion • Metabolic wastes are removed from the body through the formation and excretion of urine. • Urine is formed from the water, urea, and remaining salts that are left after the filtration, reabsorption, and secretion processes in the nephron. • The ureter is a tube made of smooth muscle that carries urine from the kidney to the urinary bladder. • The urinary bladder is a hollow, muscular sac that stores urine.

Digestive and Excretory Systems Section 3 Urinary Excretion, continued • Urine exits the body through the urethra. • A healthy adult eliminates from 1. 5 L (1. 6 qt) to 2. 3 L (2. 4 qt) of urine a day, depending on the volume of fluids consumed. • Nerve cells in the bladder indicate when the bladder is full. The bladder’s muscular walls contract, while the rings of muscle closing off the urethra relax.

Digestive and Excretory Systems Urinary Organs Section 3

Digestive and Excretory Systems Section 3 Kidney Failure • The most common causes of kidney failure are infection, diabetes, high blood pressure, and damage to the kidneys by the body’s own immune system. • Kidneys are often exposed to hazardous chemicals such as glues and aerosol sprays that have entered the body through the lungs, skin, or mouth. • Kidneys are vital to maintaining homeostasis, so damage to the kidneys may eventually become life threatening.

Digestive and Excretory Systems Section 3 Kidney Failure, continued • When kidneys fail, ions and toxic wastes such as urea accumulate in the blood plasma and increase to dangerous levels. • Kidney dialysis is a procedure that uses a machine to filter urea and excess ions from the blood. • A more permanent solution to kidney failure is a kidney transplant from a healthy donor.

Digestive and Excretory Systems Section 3 How a Kidney Machine Works

Digestive and Excretory Systems Section 3 Summary • By removing wastes and toxic chemicals, excretion enables the body to maintain its osmotic and p. H balance. • The kidneys are a pair of fist-sized, bean-shaped organs that are located in the lower back. • Metabolic wastes are removed from the body through the formation and excretion of urine. • Kidneys are vital to maintaining homeostasis, so damage to the kidneys may eventually become life threatening.