1. By: Erica Oates & Maschal Mohiuddin

2. What is the digestive system?  The digestive system:  ingests and breaks down food  absorbs nutrients  eliminates undigested material

4. 21.1 Animals ingest their food in a variety of ways  Three dietary categories:  Herbivores:  Definition: an animal that eats only plants or algae (mainly autotrophic organisms)  Examples: cattle, gorillas, sea urchins, snails  Carnivores:  Definition: an animal that mainly eats other animals  Examples: lions, hawks, spiders, whales  Omnivores:  Definition: an animal that ingests both plants and animals  Examples: humans, crows, cockroaches, raccoons

5. How do animals obtain and ingest their food?  Suspension feeders  Extract food particles suspended in the surrounding air  Examples: clams, oysters, humpback whales  Substrate feeders  Live in or on their food source and eat their way through it  Example: caterpillars  Fluid feeders  Obtain their food by sucking nutrient-rich fluids from a living host that is either a plant or an animal  Examples: aphids, bloodsuckers  Bulk feeders  Ingest large pieces of food, may use utensils such as tentacles, claws, teeth, pincers to tear off pieces of meat  Example: grey herring

6. Quick Question:  Blue whales, the largest animals ever to live, feed on krill. Name their diet category and type of feeding.

7. 21.2 Overview: Food processing occurs in four stages  Ingestion  The act of eating  Digestion  The breaking down of food into molecules small enough for the body to absorb  Mechanical  Chemical

9.  Absorption  The cells lining the digestive tract take up the products of digestion (small molecules)  Nutrients travel in the blood to body cells where they are joined together to make macromolecules of the cells or broken down further to provide energy  Elimination  Undigested material passes out of the digestive tract

10. INGESTIONDIGESTIONABSORPTIONELIMINATION Food Mechanical digestion Pieces of food Chemical digestion (enzymatic hydrolysis) Small molecules Nutrient molecules enter body cells Undigested material

11. Quick Question:  What are the two main digestive processes?

12. 21.3 Digestion occurs in specialized compartments  Food vacuoles  Simplest digestive compartments  Food is engulfed by phagocytosis and the newly formed food vacuole fuses with the lysosome, containing hydrolytic enzymes  Example: sponges  Most animals have a more complex internal compartment for digesting food  Digestion occurs outside of cells so larger food can be devoured than what would fit in a vacuole

13.  Gastrovascular cavity:  Definition: a digestive compartment with a single opening (mouth)  Process:  Gland cells lining the gastrovascular cavity secrete digestive enzymes  Digestive enzymes break down the soft tissues of the prey  Other cells engulf small food particles  Food particles are broken down into food vacuoles

14. Gastrovascular cavity Mouth Food Tentacles Epidermis Gastrodermis Mesoglea Gland cells Flagella Nutritive muscular cells Food vacuoles Mesoglea

15.  Alimentary canal:  Definition: a digestive tract with two openings, a mouth and an anus  Since food moves in one direction, specialized regions of the tube can carry out digestion and absorption of nutrients in sequence

16. Process  Food entering the mouth usually passes into a pharynx, or throat.  Depending on the species, the esophagus may channel food to a crop, gizzard, or stomach.  Crop: a pouch-like organ in which food is softened and stored  Stomachs and gizzards may also store food temporarily, but they are more muscular and they churn and grind the food.

17.  Intestine:  Chemical digestion and nutrient absorption occur here  Anus:  Undigested materials are expelled through here

18. Gizzard Intestine Anus Crop Esophagus Pharynx Mouth Earthworm Typhlosole Lumen of intestine

19. Foregut Midgut Hindgut Rectum Anus Esophagus Mouth Crop Gastric ceca Grasshopper

20. Anus Esophagus Mouth Crop Bird Stomach Gizzard Intestine

21. Quick Question:  What is an advantage of an alimentary canal, compared to a gastrovascular cavity?

22. 21.4 The human digestive system consists of an alimentary canal and accessory glands  Process:  Food enters the mouth, is chewed in the oral cavity, and pushed by the tongue into the pharynx  Once food is swallowed, muscles propel it through the alimentary canal by:  Peristalsis - alternating waves of contraction and relaxation of the smooth muscles lining the canal  Enables us to process and digest food even while lying down

23.  Sphincters  Definition: muscular, ringlike valves that regulate the passage of food into and out of the stomach  The sphincter controlling the passage out of the stomach works like a drawstring to close it off.  Accessory Glands  Salivary glands  Pancreas  Gall bladder  Liver

24. Esophagus Stomach Liver Salivary glands Gall- bladder Pancreas Rectum Anus Large intestines Small intestines Mouth A schematic diagram of the human digestive system

25. Quick Question:  By what process does food move from the pharynx to the stomach of an astronaut in the weightless environment of a space station?

26. 21.5 Digestion begins in the oral cavity  While you anticipate your food, your salivary glands start delivering saliva through ducts to the oral cavity, even before you take a bite.  This is a response to the sight or smell of food.  The presence of food in your oral cavity continues to stimulate salivation.

27. Salivary Glands Tongue TEETH Incisors Canine Premolar Molars Wisdom Teeth

28.  Saliva:  Contains several substances important in food processing:  Glycoprotein - protects the soft lining of the mouth and lubricates food for easier swallowing  Buffers – neutralize food acids, helping prevent tooth decay  Antibacterial agents – kill many of the bacteria that enter the mouth with food  Digestive enzyme amylase

29.  Mechanical and chemical digestion:  Begin in the oral cavity  Chewing makes it easier to swallow and exposes more food surface to digestive enzymes  Four kinds of teeth:  Starting at the front:  Two bladelike incisors – help with biting your food  Canine teeth – help rip apart your food  Two premolars and three molars – grind and crush your food  Tongue  a muscular organ covered with taste buds  manipulates food and helps shape it into a ball, called a bolus

30. Quick Question:  Chewing functions in what kind of digestion? What does the amylase in saliva do?

31. 21.6 After swallowing, peristalsis moves food through the esophagus to the stomach  Our breathing and swallowing are usually carefully coordinated  When you start to swallow the tongue pushes the bolus of food into the pharynx, triggering the swallowing reflex  The esophageal sphincter relaxes and allows the bolus to enter the esophagus  At the same time, the larynx moves upward and tips the epiglottis (a flap of cartilage and fibrous connective tissue) down over the opening of the larynx  In this position, the epiglottis prevents food from passing into the trachea

32. Epiglottis up Bolus of food Esophageal sphincter contracted Esophagus To stomach To lungs Trachea Tongue Pharynx Glottis Larynx Esophageal sphincter relaxed Epiglottis down Glottis up and closed Epiglottis up Esophageal sphincter contracted Relaxed muscles Glottis down and open Relaxed muscles Contracted muscles Stomach Epiglottis up Bolus of food Esophageal sphincter contracted Esophagus To stomach To lungs Trachea Tongue Pharynx Glottis Larynx Esophageal sphincter relaxed Epiglottis down Glottis up and closed Epiglottis up Esophageal sphincter contracted Relaxed muscles Glottis down and open Relaxed muscles Contracted muscles Stomach

33.  The esophagus is a muscular tube that conveys food boluses from the larynx to the stomach.  The structure of the esophagus fits its function:  A tough yet elastic connective tissues allow it to stretch to accommodate a bolus  Layers of circular and longitudinal smooth muscles for peristalsis  A stratified epithelial lining that replenishes cells abraded off during swallowing

34. Quick Question:  What prevents food from going down the wrong tube?

35. 21.7 The Heimlich maneuver can save lives  Procedure invented by Dr. Henry Heimlich in the 1970s  Allows people with little medical training to step in and aid a choking victim  Necessary when our swallowing mechanism goes awry, like when someone eats too quickly or fails to chew food thoroughly  Choking happens when air is not allowed to enter the trachea or pharynx because they are blocked

36. Quick Question:  If food is stuck in the pharynx, what effect could it have on nearby structures?

37. 21.8 The stomach stores food and breaks it down with acid and enzymes  Some chemical digestion occurs in the stomach  The stomach secretes gastric juice which is made up of mucus, enzymes and strong acid  The interior surface of the stomach wall is highly folded and dotted with pits leading into tubular gastric glands  Gastric glands have three types of cells that secrete different components of the gastric juice  Mucous cells- secrete mucus which lubricates and protects the cells lining the stomach  Parietal cells- secrete hydrogen ions and chloride ions which combine in the cavity of the stomach to form hydrochloric acid  Chief cells- secrete pepsinogen, an inactive form of the enzyme pepsin

38. How pepsinogen, hydrochloric acid and pepsin interact:  Pepsinogen and hydrochloric acid are secreted into the cavity of the stomach  The hydrochloric acid converts pepsinogen to pepsin  Pepsin then activates more pepsinogen starting a chain reaction  Pepsin begins the chemical digestion of proteins

39. Esophagus Cardiac orifice Pyloric sphincter Small intestine Folds of epithelial tissue Stomach Epithelium Pepsin (active enzyme) Pepsinogen HCl Pepsinogen and HCl are secreted into the lumen of the stomach. HCl converts pepsinogen to pepsin. Pepsin then activates more pepsinogen, starting a chain reaction. Pepsin begins the chemical digestion of proteins. Parietal cellChief cell Chief cells Mucus cells Parietal cells Interior surface of stomach Gastric gland 5 µm

40. What prevents gastric juice from digesting away the stomach lining?  Secreting pepsin in the inactive form of pepsinogen helps protect the cells of the gastric glands  Mucus helps protect the stomach lining from both pepsin and acid

41. Other protections for the stomach:  Our gastric glands do not secrete acidic gastric juice constantly; their activity is regulated by a combination of nerve signals and hormones  Once you have food in your stomach, substances in the food stimulate cells in the stomach wall to release the hormone gastrin into the circulatory system  Gastrin circulates in the blood stream, returning to the stomach wall  When it arrives there, it stimulates additional secretion of gastric juice

42.  Negative-feedback mechanism:  Inhibits the secretion of gastric juice when the stomach contents become too acidic  The acid inhibits the release of gastrin  As a result of mixing and enzyme action, nutrient-rich acidic broth known as chyme develops  The sphincter between the stomach and the small intestine helps regulate the passage of chyme from the stomach into the small intenstine

43. Quick Question:  If you add pepsinogen to a test tube containing protein dissolved in distilled water, not much protein will be digested. What inorganic chemical could you add to the tube to accelerate protein digestion? What effect will it have?

44. 21.9 Digestive ailments include acid reflux and gastric ulcers  A stomach full of digestive juice laced with strong acid:  Breaks apart the cells in our food  Kills bacteria  Begins the digestion of proteins  These chemicals can be harmful:  Acid reflux –  back flow of chyme into the lower end of the esophagus,  causes the feeling called heartburn  GERD  Gastroesophageal reflux disease  Harms the lining of the esophagus  Treated with:  Lifestyle changes  Medications  Surgery – strengthens the lower esophageal sphincter

45. Can all this acid also cause problems in the stomach?  A gel-like coat of mucus usually protects the stomach wall from the corrosive effect of digestive juice  Gastric ulcers, or open sores, can develop in the stomach wall  Respond to a combination of antibiotics and bismuth  Helicobacter pylori – a spiral shaped bacterium, which is the primary culprit of gastric ulcers  Defense by white blood cells causes gastritis

46. Quick Question:  In contrast to most microbes, the species that causes ulcers thrives in an environment with a very low ________.

47. 21.10 The small intestine is the major organ of chemical digestion and nutrient absorption  The chemical digestion of large molecules occurs in the small intestine.  The nutrients that result from this digestion are absorbed into the blood from the small intestine.  A length of more than 6 meters

48. Sources of digestive enzymes and bile:  Two large organs, the pancreas and the liver, contribute to digestion in the small intestine  Pancreas  Produces pancreatic juice, a mixture of digestive enzymes and an alkaline solution rich in bicarbonate  The bicarbonate acts as a buffer to neutralize the acidity of chyme as it enters the small intestine  Liver  Produces bile, which contains bile salts that emulsify fats, making them more susceptible to attack by digestive enzymes  Gallbladder  Stores bile until it is needed in the small intestine

49.  Intestinal wall itself produces digestive enzymes, some of which are secreted into the lumen (cavity) of the small intestine while others are bound to the surface of epithelial cells  Duodenum  First 25 cm of the small intestine  Where chyme squirted from the stomach mixes with :  Bile from the gallbladder  Pancreatic juice from the pancreas  Digestive enzymes from gland cells in the intestinal wall

50. Stomach Pancreas Liver Gall- bladder Duodenum of small intestine Intestinal juice Bile Acid chyme Pancreatic juice

51. Digestion in the small intestine:  All four types of large molecules are digested in the small intestine  Carbohydrates  Digestion that began in the oral cavity is completed in the small intestine  Pancreatic amylase hydrolyzes starch into maltose  Maltase then splits maltose into glucose

52.  Proteins  Digestion originally begins in the stomach  Pancreas and duodenum secrete hydrolytic enzymes that completely dismantle the polypeptides into amino acids  Enzymes trypsin and chymotrypsin break the polypeptides into smaller p0lypeptides  Two other enzymes, aminopeptidase and carboxypeptidase, split off one amino acid at a time  Dipeptidase hydrolyzes the fragments, only two or three amino acids long

53.  Nucleic acids  Nucleases from the pancreas split DNA and RNA into their component nucleotides  Fats  Remain undigested until they reach the duodenum  Hydrolysis is different because fats are insoluble in water, which results in a special process:  Bile salts and bile cause fat globules to be physically broken up into smaller fat droplets, called emulsification  Lipase – a pancreatic enzyme that breaks fat molecules down into fatty acids and glycerol  Main function of the rest of the small intestine is the absorption of nutrients and water

54. Absorption in the small intestine:  Since the small intestine has a huge surface area, it is well- suited for absorbing nutrients  The surface area results from several kinds of folds and projections, which are found around the inner wall of the intestine, such as large circular folds with small, finger-like projections called villi  Each of the epithelial cells lining a villus has many tiny surface projections called microvilli  Microvilli extend into the lumen of the intestine and greatly increase the surface area across which nutrients are absorbed  Mechanisms of absorption:  Simple diffusion  Other nutrients are pumped against concentration gradients into the epithelial cells

55. Nutrient absorption Microvilli (brush border) Epithelial cells Lacteal Lymph vessel Villi Large circular folds Epithelial cells Blood capillaries Vein carrying blood to hepatic portal vessel Muscle layers Villi Intestinal wall

56. Quick Question:  Amylase is to ________ as _________ is to DNA.

57. 21.11 One of the liver’s many functions is processing nutrient-laden blood from the intestines  Location – between the intestines and the heart  Capillaries from the small and large intestines converge into veins that lead into the hepatic portal vein  This large vessel transports nutrients absorbed by the intestines directly to the liver

58.  Functions of the liver:  Removes excess glucose from the blood and converts it to glycogen, which is stored in liver cells  Regulates body metabolism  Converts many of the nutrients it receives into new substances  Modifies and detoxifies substances absorbed by the digestive tract before the blood carries these materials to the heart for distribution to the rest of the body  Produces bile, which aids in the digestion of fats and also processes nitrogen waste from the breakdown of proteins for disposal in urine

59. Quick Question:  What two functions of the liver relate to the hepatic portal vein?

60. 21.12 The large intestine reclaims water and compacts the feces  The large intestine, or colon, is about 1.5 meters long and 5 cm in diameter  Joins the small intestine at a T-shaped junction, where a sphincter controls the passage of unabsorbed food material out of the small intestine  Cecum - one arm of the T, a blind pouch which absorbs water and salts from undigested food  Appendix – a small, fingerlike extension of the cecum that contains a mass of white blood cells that make a minor contribution to immunity

62. Functions of the large intestine:  One major function is to absorb water from the alimentary canal  As water is absorbed, the remains of the digested food become more solid as they move along the colon by peristalsis  Feces - waste products that consist mainly of indigestible plant fibers and prokaryotes that normally live in the colon  Stored in the final portion of the colon, the rectum, until they can be eliminated  If the lining of the colon is irritated, the colon is less effective in reclaiming water and diarrhea may result  Constipation occurs when peristalsis moves the feces along to slowly and they become to compacted  Results from a diet that does not include enough plant fiber

63. Quick Question:  Explain why treatment with antibiotics for an extended period may cause a vitamin K deficiency.

64. 21.13 Evolutionary adaptations of vertebrate digestive systems often relate to diet  Large expandable stomachs are common adaptations in carnivores  The length of an animal’s digestive tract is often correlated with diet  Herbivores and omnivores have longer alimentary canals, relative to their body size, than carnivores  Herbivores also have cellulose-digesting microbes housed in special chambers  Ruminants such as cows process food with the aid of microbes in four stomach chambers

65. Small intestine Stomach Cecum Colon (large intestine) Carnivore Herbivore Small intestine

66. Quick Question:  What are two advantages of a longer alimentary canal in herbivores?