UNIT I - DIGESTION Chapter 21

Transcription

1 UNIT I - DIGESTION Chapter 21

2 OBJECTIVES Core: I can describe the structure and function of the digestive tract. I can outline the chemical digestion of the 3 main macromolecules. I can explain the absorption process and refer to relevant structures (villi). I can explain how the liver supports the digestive system. Advanced: I can explain homeostasis of blood sugar regulation.

3 INTRODUCTION Getting Their Fill of Krill Whales are one of the largest animals in the world, it takes an enormous amount of food to support a 72-ton humpback whale These marine mammals eat small fishes and crustaceans called krill Humpback whales strain their food from seawater using large plates called baleen, which they have on each side of their upper jaw act like a sieve In a typical day, the whale s digestive system will process as much as 2 tons of fish and krill

4 OBTAINING AND PROCESSING FOODS Animals ingest their food in a variety of ways Animal diets are highly varied, and include - Herbivores, plant-eaters (cattle, gorillas, snails, sea urchins) - Carnivores, meat-eaters (lions, hawks, spiders, snakes) - Omnivores, eating both plants and other animals (crows, cockroaches, raccoons, humans!)

5 ANIMAL FEEDING MECHANISMS Suspension feeders: extract food particles suspended in the surrounding water (whales, clams, oysters, sponges!) Substrate feeders: live on their food source and eat their way through it (caterpillars and worms) Fluid feeders: obtain food by sucking nutrient-rich fluids from a living host, either plant or animals (Aphids, mosquitoes (female only) males live off plant nectar!) Hummingbirds benefit for their host Bulk feeders: meaning they ingest relatively large pieces of food.

6 21.2 FOOD PROCESSING OCCURS IN FOUR STAGES 1. Ingestion 2. Digestions 3. Absorption 4. Elimination

7 FOUR STAGES Ingestion: The act of eating Digestion: is the breaking down of food into molecules small enough for the body to absorb Typically occurs in two stages: mechanical digestion and chemical digestion Hydrolysis for chemical digestion, where water and enzymes are used to catalyze the reaction Proteins, fats, and carbohydrates are too big to pass through the cell membrane therefore it must be broken down. See chart polymers are broken down into monomers!

8 FOUR STAGES Absorption: the cells lining the digestive tract take up (absorb) the products of digestion like amino acids and simple sugars. These nutrients enter into the blood to the body cells where they can be joined to make macromolecules of the cells or broken down further for energy. Elimination: undigested material passes out of the digestive tract

9 21.3 DIGESTION OCCURS IN SPECIALIZED COMPARTMENTS Food vacuoles are digested in compartments which house hydrolytic enzymes Animals have a variety of ways to digest their foods; Sponges digest their food entirely in food vacuoles Cnidarians and flatworms have gastrovascular cavities with a single opening Most animals have a alimentary canal, a digestive tube with two openings

10 ALIMENTARY CANAL Food enters the mouth, pharynx, esophagus, crop, stomach(s), gizzards, intestine, and anus

11 HUMAN DIGESTIVE SYSTEM The human digestive system consists of an alimentary canal and accessory glands The rhythmic muscle contractions of peristalsis which squeeze food toward the stomach along the alimentary canal The pyloric sphincter: regulates the passage of food from the stomach to the small intestine

12 DIGESTION OCCURS IN THE ORAL CAVITY The teeth break up food, saliva moistens, and salivary enzymes begin the hydrolysis of starch The tongue pushes the bolus of food into the pharynx

13 THE PHARYNX 21.6 The food and breathing passages both open into the pharynx The swallowing reflex Moves food from the pharynx into the esophagus, while keeping it out of the trachea

14 CONNECTION The Heimlich maneuver can save lives The Heimlich maneuver: can dislodge food from the pharynx or trachea during choking

15 PERISTALSIS The esophagus squeezes food along to the stomach by peristalsis Peristalsis in the esophagus moves food into the stomach by using muscles contractions from smooth muscle to create a wave and push the bolus to the stomach

16 GASTRIC JUICES The stomach stores food and breaks it down with acid and enzymes Pepsin in the gastric juice begins the hydrolysis of protein Gastic juice is made up of mucus and enzymes and strong acid mixes with food to produce acid chyme

17 GASTRIC JUICES The gastric glands have three types of cells that secrete different components of the gastric juice 1. Mucous cells (dark pink) secrete mucous, which lubricates and protects the stomach lining 2. Parietal cells (yellow) secrete hydrochloric acid (HCl) 3. Chief cells (tan) secrete pepsinogen, an inactive form of the enzyme pepsin.

18 PEPSIN 1. Pepsinogen and HCl are secreted into the lumen (cavity) of the stomach 2. The HCl converts the pepsinogen to pepsin 3. Pepsin then activates more pepsinogen in a chain reaction as a positive feedback loop

19 REGULATION Secreting pepsin in the inactive form, pepsinogen, protects the cells of the gastric glands Mucus helps protect the stomach lining from both pepsin and acid Cells in our gastric gland do not secrete gastric juice constantly, their activity is regulated by a combination of nerve signals and hormones When you see, smell, or taste food, your brain signals your stomach to secrete gastric juice When food is in your stomach, gastrin hormones are released in your bloodstream to secrete gastric juices

20 REGULATION CONT D A negative-feedback mechanism inhibits the secretion of gastric juices when the stomach contents become too acidic. The acid inhibits the secretion of gastrin, thus gastric juices Your stomach churns every 20s producing the acid chime which is a nutrient broth of digested food GERD gastroesophageal reflux disease (chronic heartburn)

21 ACID CHYME Pyloric sphincter helps regulate the passage of acid chime in squirts into the small intestine This can take 2-6 hours to empty after a meal An acid chime rich in fats slows the squirting down to allow for slower digestion and more digestive enzymes to be released As you will see, there are other enzymes released from your gall bladder and pancreas to aid in digestion

22 ULCERS Bacterial infections in the stomach and duodenum are associated with ulcers from the bacteria Helicobacter pylori They are tolerant of the low ph of the stomach and eat away and burrow into stomach linings. Your white blood cells cause inflammation and your body can t keep up with the loss of cells and replace them before a hole develops This hole, or ulcer, can become very dangerous.

23 21.11 THE SMALL INTESTINE The small intestine is the major organ of chemical digestion and nutrient absorption The small intestine has a length over 6m and about 2.5cm diameter Nutrients enter into the bloodstream through the small intestine with the aid of two glandular organs The pancreas The liver

24 THE PANCREAS The pancreas produces a mixture of digestive enzymes and an alkaline solution rich in bicarbonate The alkaline solution neutralizes the very acid chyme from the stomach The major enzymes produced in the pancreas include; Pancreatic amylase (maltose and other dissacharides) Trypsin & Chymotrypsin Nucleases & nucleosidases Lipase These enzymes are secreted into the small intestine, specifically the duodenum (first 25 cm)

25 THE LIVER The liver performs a wide variety of functions, including the production of bile. Bile contains bile salts that emulsify fats Increase surface area, which allows digestive enzymes to attack fat droplets easier The gallbladder stores bile is until it is needed

26 ENZYMES AND DIGESTION Know the enzymes in the chart! Lactase digests milk sugar, children>adults

27 PROTEIN DIGESTION The small intestine completes the digestion of proteins that began in the stomach. The pancreas and the duodenum secrete hydrolytic enzymes that completely dismantle polypeptides into amino acids The enzyme trypsin and chymotrypsin break polypeptides into small polypeptides Aminopeptidases and carboxypeptidase split off one amino acid at a time Dipeptidases hydrolyzes fragments of two or three a.a long

28 THE SMALL INTESTINE STRUCTURE Structurally, the small intestine is well suited for its task of absorbing nutrients. Its surface area is huge ~300m 2 (size of a tennis court) It has a series of folds and projections that are circular in structure These finger-like projections are called villi Each of the epithelial cells lining a villus has many tiny surface projections called microvilli These extend into the lumen of the small intestine which contributes to the high surface area

29 THE SMALL INTESTINE CONT D Some nutrients are absorbed by simple diffusion; others are pumped against their concentration gradient into the epithelial cells The small lymph vessel (yellow) and network of capillaries (red, purple, and blue) penetrate the core of each villus. Fatty acids and glycerol are transported into the lymph vessel Other absorbed nutrients, like amino acids and sugars pass into the capillaries.

30 THE SMALL INTESTINE CONT D The capillaries that drain away nutrients from the villi converge into larger veins and eventually into a main vessel, the hepatic portal vein, that leads directly to the liver The liver converts many of these nutrients into substances the body needs, like glycogen. The liver also detoxifies any toxins ingested

31 THE LARGE INTESTINE The large intestine, also known as the colon, is 1.5m long and 5cm in diameter There is a small blind pouch called the cecum which is the start of the large intestine There is also a finger-like extension called the appendix which houses white blood cells

32 THE LARGE INTESTINE CONT D The main job of the large intestine is to absorb water About 7L of fluid enters the lumen and approx. 90% is absorbed back into the blood and tissue fluids. As the water is reabsorbed, the remains of the digested food become more solid and are called feces Feces is mainly indigestible plant fibers and prokaryotes that live in the colon. These bacteria, like E. coli are important as they help in digestion but produce important vitamins like biotin, folic acid, several B vitamins and vitamin K.

33 21.17 EIGHT ESSENTIAL AMINO ACIDS

34 21.18 Vitamins and minerals Are essential in the human diet Most of these vitamins function as coenzymes A healthy diet includes these 13 vitamins

35 ESSENTIAL MINERALS ARE REQUIRED FOR MANY BODY FUNCTIONS Minerals are inorganic nutrients that play a variety of roles