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UNIT B: Human Body Systems Chapter 8: Human Organization Chapter 9: Digestive System: Section 9.2 Chapter 10: Circulatory System and Lymphatic System Chapter 11: Respiratory System Chapter 12: Nervous System Chapter 13: Urinary System Chapter 14: Reproductive System

Chapter 9: Digestive System UNIT B Chapter 9: Digestive System Chapter 9: Digestive System In this chapter, you will learn about the structure and function of the digestive system. What is our current understanding of the structure and function of the digestive system, including the stomach? Which substances produced by the stomach and other organs help with the chemical breakdown of foods? Chapter opener figure background: Canadian Alexis St. Martin became the unexpected live test subject for research that shed new light on how the digestive system works. St. Martin was working in the fur trade in 1822 on Mackinac Island in Lake Huron when an accident left him with gunshot wounds to his thorax and abdomen. Under the care of United States army surgeon Dr. William Beaumont, St. Martin survived his severe injuries. However, St. Martin’s stomach wound did not close over; instead, it healed permanently attached to surrounding muscle and skin, leaving a direct opening from his stomach to the outside world. This unusual situation led Beaumont to perform groundbreaking research on the stomach’s role in digestion. For almost 11 years, Beaumont made direct observations into the workings of St. Martin’s stomach. He placed a variety of foods attached to a string into his patient’s stomach and later removed them. He also drew samples of stomach fluids for investigation. His research led to a new understanding of the mechanical and chemical nature of the digestive action of the stomach. Alexis St. Martin was an unexpected live test subject for Dr. William Beaumont’s research on how the digestive system works. TO PREVIOUS SLIDE

9.2 Accessory Organs of Digestion UNIT B Chapter 9: Digestive System Section 9.2 9.2 Accessory Organs of Digestion The accessory digestive organs are the pancreas, liver, and gall bladder. Figure 9.8 Liver, gall bladder, and pancreas. a. The liver makes bile, which is stored in the gall bladder and sent (black arrow) to the small intestine by way of the common bile duct. The pancreas produces digestive enzymes that are sent (black arrows) to the small intestine by way of the pancreatic duct. TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.2 The Pancreas The pancreas is an organ that has both endocrine and exocrine functions. Exocrine function of the pancreas Pancreatic cells produce pancreatic juice (to neutralize stomach acid) and digestive enzymes Endocrine function of the pancreas Pancreas secretes insulin and glucagon, hormones that regulate blood glucose (sugar) levels pancreas: a digestive organ with both endocrine and exocrine functions TO PREVIOUS SLIDE

Structure and Function of the Pancreas UNIT B Chapter 9: Digestive System Section 9.2 Structure and Function of the Pancreas The pancreas contains pancreatic islets (islets of Langerhans), which are clusters of at least three types of endocrine cells: Alpha cells: produce glucagon Beta cells: produce insulin Delta cells: produce somatostatin pancreatic islets: clusters of at least three types of endocrine cells: alpha cells, beta cells, and delta cells TO PREVIOUS SLIDE

Structure and Function of the Pancreas UNIT B Chapter 9: Digestive System Section 9.2 Structure and Function of the Pancreas Insulin Hormone secreted when blood glucose level is high Stimulates the uptake of glucose by cells (liver, muscle, adipose tissue) to lower blood glucose Glucagon Hormone secreted when blood glucose level is low Stimulates the liver to break glycogen down into glucose to increase blood glucose Stimulates adipose tissue to break fat down to glycerol and fatty acids (to make glucose) insulin: the hormone released by the pancreas that lowers blood glucose levels by stimulating uptake of glucose by cells, especially muscle and liver cells glucagon: a hormone secreted by the pancreas, usually when the blood glucose level is low TO PREVIOUS SLIDE

Structure and Function of the Pancreas UNIT B Chapter 9: Digestive System Section 9.2 Structure and Function of the Pancreas Somatostatin A growth-hormone-inhibiting hormone Also produced by cells in the stomach and small intestine Inhibits the release of growth hormone Suppresses the release of insulin and glucagon Decreases the absorption of nutrients somatostatin: a growth-hormone inhibiting hormone produced by the pancreas and cells in the stomach and small intestine TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.2 Figure 9.9 Regulation of blood glucose level. Top: When the blood glucose level is high, the pancreas secretes insulin. Insulin promotes the storage of glucose as glycogen and the synthesis of proteins and fats (as opposed to their use as energy sources). Therefore, insulin lowers the blood glucose level to normal. Note: this is an example of negative feedback TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.2 Bottom: When the blood glucose level is low, the pancreas secretes glucagon. Glucagon acts opposite to insulin. Therefore, glucagon raises the blood glucose level to normal. TO PREVIOUS SLIDE

The Liver UNIT B The liver is the largest gland in the body. Chapter 9: Digestive System Section 9.2 The Liver The liver is the largest gland in the body. The liver has many functions, including: Detoxifying blood Making plasma proteins Maintaining blood glucose levels Producing bile, which contains bile salts that emulsify fat in the small intestine Producing urea, a nitrogenous waste product from the breakdown of amino acids liver: the largest gland in the body; produces urea and bile, detoxifies blood, stores glycogen, and produces the plasma proteins, among other functions bile: produced by the liver; contains bile salts that emulsify fat in the small intestine TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.2 TO PREVIOUS SLIDE

Structure and Function of the Liver UNIT B Chapter 9: Digestive System Section 9.2 Structure and Function of the Liver The liver contains about 100 000 lobules that serve as its structural and functional units. Three structures are located between the lobules: Bile duct: takes bile away from the liver Hepatic artery branch: brings oxygen-rich blood to the liver Hepatic portal vein: transports nutrients from the intestines TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.2 Figure 9.8 b. A hepatic lobule. The liver contains over 100 000 lobules, each lobule composed of many cells that perform the various functions of the liver. They remove and add materials to the blood and deposit bile in a duct. TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.2 Figure 9.10 Hepatic portal system. The hepatic portal vein takes the products of digestion from the digestive system to the liver, where they are processed before entering a hepatic vein. TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.2 The Gall Bladder The gall bladder is a muscular sac attached to the surface of the liver. Excess bile from the liver is stored in the gall bladder Bile leaves the gall bladder and proceeds to the duodenum via the common bile duct Bile emulsifies fat to prepare it for further breakdown by digestive enzymes gall bladder: an organ attached to the liver that serves to store and concentrate bile TO PREVIOUS SLIDE

Check Your Progress UNIT B Chapter 9: Digestive System Section 9.2 Check Your Progress Describe how pancreatic hormones regulate blood glucose levels. Explain why the liver is necessary for life, whereas the gall bladder can be removed with few consequences. ANSWERS 1. Insulin is secreted by the pancreas when blood glucose levels are high. When insulin binds to cell receptors, it causes glucose transport proteins to come to the cell membrane to enable glucose to leave the blood and enter cells. Insulin also causes glucose to form polymers of glycogen for storage in the liver and muscle. Glucagon is secreted by the pancreas when glucose levels are low. Glucagon stimulates the liver to break down glycogen to glucose and adipose tissue. Other metabolic changes ensure that the little glucose present is available to the brain for energy. Other metabolic pathways are activated so that protein and fat molecules are changed so that they can be used to make more glucose in the liver. The hormone somatostatin, also called growth hormone, suppresses the release of insulin and glucagon.   2. The liver performs functions essential for life including removing toxins from the blood, storing iron and vitamins, processing some wastes and synthesizing essential plasma proteins such as albumen and fibrinogen, and regulating blood cholesterol. The main function of the gall bladder is storing bile, which is made in the liver. Removal of the gall bladder is not life-threatening. TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.2 TO PREVIOUS SLIDE