Digestion and Nutrition

1. Digestion and Nutrition

2. Introduction • Digestion: mechanical and chemical breakdown of food into forms the cell membrane can absorb • Alimentary canals: extends from the mouth to the anus • Mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anal canal • Several accessory organs: release secretions into the canal • Salivary glands, liver, gallbladder, and pancreas

3. General Characteristics • 9-meter muscular tube • Structure of the Wall • Mucosa: mucous membrane • Inner most layer • Protects the underlying tissue • Carries out secretion and absorption • Epithelium, connective tissue, and smooth muscle • Tiny folds and projection in the lumen, passageway • Increase absorption through increased surface area • Glands: secrete mucus and digestive enzymes

5. Structure of the Wall • Submucosa • Loose connective tissue, glands, blood vessels, lymphatic vessels, and nerves organized into plexus • Vessels nourish surrounding tissue and carry away absorbed nutrients away • Muscular Layer • Moves the tube • Smooth muscle tissue and some nerves organized into a plexus • Serosa: serous layer • Visceral peritoneum: outer covering of the tube • Protect underlying tissue • Secrete serous fluid • Moistens and lubricates the tube’s outer surface

6. Layer of Digestive Tract

7. Tube Movement • Mixing Movement • smooth muscles in small segments of the tube contract rhythmically • Full stomach: movement mixes the food and digestive juices • Propelling Movement • Peristalsis: wave-like motion • Ring of contraction • Push food along the tube

8. Mouth • Receives food • Begins digestion • mechanically reducing the size of solid particles • mixing particles with saliva • Oral Cavity: chamber between palate and tongue • Vestibule: narrow space between the teeth, cheeks, and lips

9. Cheeks and Lips • Cheeks • outer layers of skin • pads of subcutaneous fat • muscles associated with expression and chewing • inner linings of moist stratifies squamous epithelium • Lips: highly mobile structures that surround the mouth opening • Skeletal muscles • Sensory receptors: temperature and texture • Red color: due to abundance of blood vessels near their surface

10. Tongue • Covered with mucous membranes • Frenulum: connects the midline of the tongue to floor of the mouth • Skeletal Muscle • Mix food particles with saliva • Move food toward the pharynx • Papillae: rough projections on surface • Provides friction to handle food • Contain taste buds • Root: posterior region • Connected to hyoid bone • Lingual tonsils: rounded masses of lymphatic tissue

11. Palate • Roof of oral cavity • Hard plate: anterior part • Soft plate: muscular arch, which extends downward to cone-shaped projection, the uvula • During swallowing, drawn upwards • Action closes the opening between the nasal cavity and pharynx • Palatine Tonsils: back of mouth, on either side • Tonsils of tonsillectomy • Pharyngeal Tonsils: adenoids • Posterior wall of pharynx

12. Tonsils and Adenoids

13. Teeth • Primary Teeth: 20 deciduous teeth • 6 months to 2 or 4 years • Secondary Teeth: 32 permanent teeth • 6 years to 17 or 25 years • Break pieces of food into smaller pieces • Increases surface area  digestive enzymes

14. Teeth • Crown: projects beyond the gum • Enamel: covers the crown • Ca salts; hardest substance in the body • Dentin: beneath the enamel; bone like • Root: anchored to the jaw

15. Teeth • Incisors: chisel-shaped • Bit off large pieces of food • Cuspids: cone-shaped • Grasp food and tear • Bicuspids and Molars • somewhat flattened surface • Grinding food particles

16. Salivary Gland • Secrete saliva • Moistens food particles, helps bind them, and begins the chemical digestion of carbohydrates • Solvent allowing food to be tasted • Helps cleanse the mouth and teeth

17. Salivary Secretions • Serous Cells: water fluid that contains amylase • Splits starch and glycogen molecules • Mucous Cells: thick liquid called mucus • Binds food particles • Lubricated during swallowing • Parasympathetic Nerves secrete watery saliva • see, smell, taste, or think about food • Food that looks, smells, or tastes unpleasant inhibits this

18. Major Salivary Glands • Parotid Glands: largest, anterior to each ear • Secrete a clear, watery fluid rich in amylase • Submandibular Gland: floor of the mouth on the inside surface of the jaw • Predominantly serous and some mucous • Sublingual Gland: floor of the mouth, inferior to the tongue • Smallest • Primarily mucous

19. Pharynx, Esophagus, Stomach, and Pancreas

20. Pharynx • Cavity posterior to the mouth from which the tubular esophagus leads to the stomach • Pharynx nor esophagus digests food

21. Pharynx • Structure of Pharynx: connects the nasal and oral cavities with larynx and esophagus • Nasopharynx: provides a passage way for air during breathing • Oropharynx: passageway for food moving downward from mouth and for air moving to and from the nasal cavity • Laryngopharynx: passageway to esophagus

22. Swallowing Mechanism • 1st stage: voluntary • food is chewed and mixed with saliva • Tongue rolls mixture into a mass, bolus and forces it into the pharynx • 2nd stage: food stimulates sensory receptors around the pharyngeal opening • Triggers swallowing reflex • Epiglottis: flap-like structure that closes the tops of the trachea • 3rd stage: peristalsis transports the food in the esophagus to the stomach

23. Epiglottis

24. Esophagus • Straight, collapsible tube about 25 cm long • Food passageway from the pharynx to the stomach • Mucous Glands: secretions moisten and lubricate the tube’s inner lining • Lower esophageal sphincter: close the entrance to the stomach • Prevents regurgitation of stomach contents

25. Stomach • J-shaped, pouch-like organ • inferior to the diaphragm • upper left portion of abdominal cavity • 1 L capacity • Functions: • Receives food from the esophagus • Mixes food with gastric juices • Initiates protein digestion • Carries limited absorption • Move food into small intestine

26. Parts of the Stomach • Cardiac: small area near the esophageal opening • Fundic: balloons above the cardiac portion • Temporary storage area • Body: main part • Pyloric: narrows as it approaches the sm. Intestine • Pyloric sphincter: muscle valve controlling gastric emptying

27. Gastric Secretions • Mucous Membrane of stomach contains many gastric pits, ends of gastric glands • Mucous cells: large quantities of thin mucus • Chief cells: digestive enzymes • Parietal cells: HCl

28. Gastric Secretions • Digestive Enzymes • Pepsin: protein • Mucus and other alkaline secretions prevent pepsin from digesting the stomach itself • Intrinsic Factor: need for B12 absorption

29. Regulation of Gastric Secretions and Absorption • Gastric juices are continuously produced, but the rate varies • Parasympathetic impulses and the hormone gastrin enhance gastric secretion • Food moving into the sm. intestines inhibits secretions • Gastric absorption: only a few substances in small quantities • Water, certain salts, alcohol, and some lipid-soluble drugs

30. Mixing and Empting Actions • Chyme: mixture of food particles and gastric juices • Production aided by movement of stomach • Peristaltic waves push chyme toward pyloric sphincter • Stomach relax with accumulation of chyme, a little at a time, is pushed into the small intestines

31. Mixing and Empting Actions • Liquid pass quite rapidly • Solid remain until they are well mixed • Fatty foods remain 3-6 hours • Proteins: quicker • Carbohydrates: faster than protein and fats • As food enters the duodenum, accessory organs add their secretions • Pancreas, liver and gallbladder

33. Pancreas • Secretes pancreatic juice into the duodenum • Contains enzymes to digest carbohydrates, fats, nucleic acids, and proteins • Pancreatic amylase: carbohydrate digesting enzyme • Pancreatic lipase: fat digesting enzyme • Nucleases: nucleic acid digestion enzyme • Trypsin, chymotrypsin, and carboxypeptidase: protein digesting enzymes

34. Pancreas Regulation • Stimulation the release of pancreatic juices • Nervous and endocrine system • Food in duodenum • Pancreatic juices are high in bicarbonate ions • Neutralizes chyme • Intestinal contents to be alkaline

35. Liver, Small Intestines, and Large Intestines

36. Liver • Located in the upper right quadrant of the abdominal cavity • Fibrous capsule encloses the liver • Connective tissue divides the organ into a large right lobe and a smaller left lobe • Each lobe is separated into tiny hepatic lobules • Liver’s functional units • Bile canals carry bile from hepatic lobules to hepatic ducts

37. Liver Function • Metabolizes carbohydrates, lipids, and proteins • Stores some substances • Filters blood • Destroys toxins • Secretes bile • Important in digestion

38. Bile • Bile salts, bile pigments, cholesterol, and electrolytes • Only bile salts have digestive functions • Bile salts emulsify fats and aid in the absorption of fatty acids, cholesterol, and certain vitamins • Gallbladder stores bile between meals • Cholecystokinin from the small intestine stimulates bile’s release • Enters the duodenum

39. Small Intestine • Receives secretions from the pancreas and liver • Completes nutrient digestion • Absorbs the products of digestion • Transports the residues to the large intestine • Parts • Duodenum • Jejunum • Ileum

40. Small Intestine • The wall is lined with villi • Increase in surface area • Aid in mixing and absorption • Intestinal glands are located between the villi • Secretions of the small intestine • Mucus and digestive enzymes • Digestive enzymes split sugars, proteins, and fats • Gastric juice, chyme, and reflexes stimulated by distention of the small intestine wall stimulate secretion

41. Absorption • Microvilli: absorb monosaccharides, amino acids, fatty acids, and glycerol • Fat molecules with long chains enter the lacteals of the villi • Fatty acids with short chains enter blood capillaries in villi

42. Movement • Mixing and peristalsis • Ileocecal sphincter: controls movement between small and large intestines

43. Large Intestines • Parts • Cecum, colon, rectum, and anal canal • Colon is divided into ascending, transverse, descending, and sigmoid portions • Unique layer of longitudinal muscle fibers arranged in distinct bands

44. Large Intestines • Functions: • Little or no digestive function • Secretes mucus • Absorbs water and electrolytes • Forms and stores feces • Movement: similar to small intestine • Mass movement occurs two to three times a day • Feces: water, undigested material, electrolytes, mucus, and bacteria • Color is due to bile salts that have been altered by bacteria

45. Nutrition

46. Nutrition • Process of ingestion and utilization of necessary food substances, or nutrients • Carbohydrates: organic compounds that primarily supply cellular energy • Sources: starch, glycogen, disaccharides, and monosaccharides • Cellulose: polysaccharide that humans cannot breakdown

47. Carbohydrates • Utilized for: • Oxidation energy release from glucose • Excess glucose is stored as glycogen or converted to fat • Most carbohydrates supply energy • Some cells require a continuous supply • Requirements: humans can survive with a wide range of carbohydrate intake

48. Lipids • Supply energy and used to build cell structure • Sources: triglycerides from plants and animals • Animals: most cholesterol

49. Lipids • Lipid Utilization • Liver and adipose tissue control triglyceride metabolism • Linoleic acid: essential fatty acid • Corn, cotton seed, and soy oil • Lipid Requirements: amounts and types are unknown • Fat intake must be sufficient to carry fat soluble vitamins • A,D,E,K

50. Proteins • Serve as structural materials, function as enzymes, and provide energy • Sources: meats, dairy products, cereals, legumes • Requirements • Supply essential amino acids and nitrogen for the synthesis of nitrogen containing molecules