A&P ii Unit 4: Digestive System

Describe the six general functions of the digestive organs.

•ingestion of food and water

•mixing and moving the ingested food and water through the digestive tract

•adding secretions to food to digest larger food molecules into smaller, absorbable molecules

•absorbing nutrients and water into blood and lymph

•expelling waste products from the body

Name the organs of the gastrointestinal tract and the accessory organs that secrete digestive substances into the tract.

Gastrointestinal (GI) Tract – a continuous tube from mouth to anus

•oral cavity (mouth)

•pharynx

•esophagus

•stomach

•small Intestine

•large Intestine

Accessory Organs

•salivary glands, pancreas, and liver secrete digestive substances

•gallbladder stores liver secretion (bile)

•teeth and tongue – aid in chewing and swallowing

Describe the structure of the gastrointestinal tract wall, its layers, and the major functions of the layers.

mucosa — inner lining: mucous membrane, composed of epithelium (simple columnar epithelium, stratified squamous epithelium in esophagus) in contact with lumen, underlying connective tissue (lamina propria: areolar connective tissue with small blood and lymph vessels — absorption nutrient molecules), and thin layer of smooth muscle, Smooth muscle layer helps shake the lining to release secretions and mix materials)

submucosa — areolar and dense irregular connective tissue deep to the mucosa, contains larger blood vessels, lymphatic vessels, nerves, and glands, Mucosa-Associated Lymphoid Tissues located here and in the lamina propria.

muscularis — composed of two layers of smooth muscle: Inner circular layer & Outer longitudinal layer, also includes nerve branches, function = motility (movement). Circular layer contractions constrict the lumen of the digestive tube. Longitudinal layer contractions shorten the digestive tube.

adventitia or serosa — Outermost layer – adventitia in some areas, serosa in others. Adventitia – areolar connective tissue covering with collagen and elastic fibers. Serosa – same composition but covered with visceral peritoneum serous membrane, occurs only on structures that are within the peritoneal cavity.

lumen – space inside

Distinguish between the two types of motility in the gastrointestinal tract.

Motility types from contractions:

Mixing – back and forth movements that blends ingested material with secretions

Propulsion – movement of materials through the digestive tract by peristalsis

•contraction of the muscularis from one spot to the next to propel material forward.

Describe the six general functions of the digestive organs.

Ingestion – introduction of solids and liquids into the oral cavity

Motility – mixing and movement of materials through the digestive tract through muscle contractions

Secretion – production and release of substances that aid digestion and movement through the GI tract

Digestion – Breakdown of ingested food into smaller, absorbable molecules

•mechanical digestion – breaking of food into smaller pieces without changing chemical structure; chewing

•chemical digestion – conversion of more complex molecules into smaller one through actions of digestive enzymes

Absorption – Transport of absorbable molecules (from digested foods), electrolytes, vitamins, and water across the epithelial lining of the GI tract into blood or lymph

Elimination – Release of indigestible components through the anal canal

Briefly describe the roles of nervous system structures/divisions in regulating digestive activities.

Enteric Nervous System

•motor and sensory neurons within the wall of the GI tract

•innervates smooth muscle and glands of the GI wall

•controls muscular contractions for motility

Autonomic Nervous System

•parasympathetic and sympathetic nerves innervate the GI tract wall.

•parasympathetic nerves generally increase GI tract activity.

•sympathetic nerves generally decrease GI tract activity.

Reflexes from both systems control GI tract activity

Name the digestive hormones and the organs that secrete them.

Hormonal Control – several hormones regulate digestion processes:

•Gastrin – produced by the stomach

•Secretin – produced by the small intestine

•Cholecystokinin – produced by the small intestine

•Motilin – produced by the small intestine

Describe the serous membranes of the abdominopelvic cavity, including the greater omentum and mesentery proper.

Peritoneum = two–layered serous membrane of the abdominopelvic cavity:

Parietal peritoneum – outer layer

Visceral peritoneum – inner layer that contacts many organs in the cavity

•some lie generally posterior to the peritoneum and are called retroperitoneal

Peritoneal Cavity – space in between the two layers, filled with peritoneal fluid

Mesentery – double layer of peritoneum that supports, suspends, and stabilizes the intraperitoneal organs of the GI tract (blood vessels, lymph vessels, and nerves between the folds)

Greater Omentum – extends like an apron from stomach across most of the organs; accumulates fat

Mesentery Proper – often simply called the mesentery; suspends most of the small intestine and is rich in blood vessels

Name the upper gastrointestinal tract organs and describe their general functions.

Oral Cavity and Salivary Glands – mechanical digestion and some chemical digestion begins

Pharynx – movement toward the esophagus

Esophagus – movement to the stomach

Stomach – ingested food mixes with gastric secretions; some mechanical digestion and chemical digestion

Duodenum of small intestine

Name the upper gastrointestinal tract organs and describe their general functions.

Oral Cavity = the mouth

Buccal Cavity – space between the teeth/gums and the lips/cheeks

Oral Cavity Proper – behind the teeth, between the palate and surface under the tongue

Palate – roof of the oral cavity proper, separates from the nasal cavity

•hard palate – bony (palatine processes of maxillae and palatine bones)

•soft palate – posterior portion, muscular (uvula – flap that closes off the nasopharynx when swallowing)

Tongue – primarily composed of skeletal muscle

Papillae – bumps on the surface with taste sensors

•note the salivary duct orifices on the diagram.

Salivary Glands – glands that produce saliva

Intrinsic Salivary Glands – unicellular, along oral cavity lining (produce lingual lipase – begins digestion of lipids)

Extrinsic Salivary Glands – multicellular, produce most of the saliva (ducts lead to the oral cavity)

Paired Glands (left and right): parotid salivary glands, sublingual salivary glands, submandibular salivary glands

12. Describe the functions of saliva and its components.

Most produced during meals, but small amounts continuously moisten the oral cavity

99.5% water plus mixture of solutes:

•electrolytes, mucin, lysozyme – protein enzyme that digests cell walls of bacteria, IgA antibodies, Salivary amylase – enzyme that begins the breakdown of starch (type of polysaccharide)

Bolus – ball of food mixed with saliva, prepared for swallowing

13. Name the mechanical and chemical digestion processes that occur in the oral cavity.

14. Describe the structures and functions of the pharynx and esophagus.

15. Describe Gastroesophageal Reflux Disease and its associated problems.

16. Describe the composition of chyme.

17. Describe the features of the gastric mucosa.

18. Explain the functions of the different gastric secretions.

19. Describe how hydrochloric acid in the stomach helps chemical digestion of proteins.

20. Describe the functions of the digestive enzymes secreted in the stomach.

21. Describe the functions of gastrin in stomach activity regulation.

22. Describe the effects of cholecystokinin and secretin on stomach activity.

23. Explain how peptic ulcers develop, and describe their associated problems.

24. Describe the general functions of the lower gastrointestinal tract organs and accessory organs.

25. Describe the features of the small intestine mucosa that increase surface area for absorption.

26. Describe the secretions of the intestinal glands.

27. Describe the accessory digestive organ ducts, the substances they carry, and the pathways from production of the substances to their location of release into the duodenum.

28. Describe the digestive functions of the hepatocytes in the liver.

29. Describe the components and function of bile in digestion.

30. Describe the functions of the gallbladder.

31. Describe the exocrine functions of the pancreas, including the components of pancreatic juice.

32. List the digestive enzymes produced by the pancreas.

33. Describe how the parasympathetic nervous system, cholecystokinin, and secretin regulate the accessory digestive organs.

34. Describe the structure and function of the large intestine, including the vermiform appendix.

35. Describe the beneficial roles of bacteria in the large intestine.

36. Explain the involuntary and voluntary processes of defecation.

37. List the six essential nutrients, and state the absorbable monomers of the four major types of biological macromolecules.

38. Define the different classes of carbohydrates based on their numbers of simple sugar monomers.

39. Recall the major functions of carbohydrates.

40. Describe the steps of carbohydrate digestion, including the enzymes used and where they are located or produced.

41. Describe the location and function of brush border enzymes in chemical digestion.

42. Explain where monosaccharide absorption occurs and where they go first after entering the bloodstream.

43. Define the terms associated with amino acids and chains of amino acids.

44. Explain how cells use amino acids after absorption, and state the functions of proteins.

45. Describe the steps of protein digestion, including the enzymes used and where they are located or produced.

46. Describe the basic structure and function of lipids.

47. Describe the steps of triglyceride digestion, including the enzymes used and where they are located or produced.

48. Explain how bile makes lipid digestion more efficient.

49. Describe how lipids are absorbed and transported in the lymphatic system and blood.

50. Recall the basic functions of the three types of lipoproteins in lipid transport; state which types are often called bad cholesterol and good cholesterol.

51. Recall the two types of nucleic acids and their functions.

52. Describe how nucleic acids in foods are digested and absorbed.

53. Explain how and where water is absorbed in the intestinal tract.

54. Recall how electrolytes are ingested and absorbed.

55. Define vitamin; compare and contrast absorption of fat-soluble vitamins with absorption of water-soluble vitamins.