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Digestive System Chapter 23.

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Presentation on theme: "Digestive System Chapter 23."— Presentation transcript:

1 Digestive System Chapter 23

2 Two major parts Alimentary canal
GI tract- long hollow canal from mouth to anal canal; continuous with outside of body Oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, anal canal Accessory organs Teeth, tongue, salivary glands, liver, pancreas

3 Functions of Digestive System
Mechanical and chemical breakdown of food absorption of nutrients elimination of waste products


5 Mechanical Breakdown of Food
Physical preparation of food for breakdown by enzymes Includes chewing, mixing of food with saliva, food churning in stomach, segmentation of food in small intestine

6 Chemical Breakdown of Food
Series of steps which breaks down large food molecules with enzymes secreted into the alimentary canal Begins in the mouth and is completed in the small intestine

7 Absorption of Nutrients
The passage of digested molecules of food, water, minerals, and vitamins from the lumen of the GI tract into the mucosal cells by active or passive transport into blood or lymph

8 Elimination of Waste Ridding the body of indigestible by products of digestion



11 Upper esophageal Tonic contractions are shown by sphincters; most are smooth muscle, some are skeletal. Lower esophageal Pyloric Oddi Ileocecal Internal anal Fig. 22-9, pg: 691 External anal

12 Histology of GI Tract 4 Basic Layers Mucosa Submucosa
Muscularis Externa Serosa

13 Quiz Picture

14 Mucosa Functions: Secretion of mucous, hormones, enzymes
Absorption of nutrients Protection against infection Simple columnar epithelium atop loose areolar connective tissue and lymphatic tissue with a base of smooth muscle that controls movement of this layer

15 Submucosa Dense CT layer with blood and lymph vessels, lymph follicles, nerve fibers

16 Muscularis Externa Layer responsible for segmentation and peristalsis
Inner circular and outer longitudinal layers of smooth muscle; thickened areas can form sphincters that act as valves

17 Serosa This is also the visceral peritoneum; formed of areolar CT and covered by simple squamous epithelium The esophagus doesn’t have a serosa because it is in the thorax; it has an adventitia (fibrous CT) that connects it to surrounding structures in chest




21 Homeostatic Imbalance
Peritonitis Inflammation of peritoneum Puncture wound of abdomen


23 Salivary Glands Parotid Glands- located anterior to ear
Sublingual Glands- located in floor of mouth Submandibular Glands- located under jaw Function: produce saliva- mostly water, salivary amylase, antimicrobials Saliva moistens food, starts starch breakdown, dissolves food chemicals for taste


25 Homeostatic Imbalance
Mumps Inflammation of parotid gland Passed by saliva In males can lead to testes infection

26 Homeostatic Imbalance
Halitosis Inhibited saliva production No saliva=no washing of mouth Cavities, anaerobic bacteria make hydrgen sulfide, methyl mercaptan and cadaverine which smell like rotten eggs, feces and corpes

27 Mouth, Pharynx, Esophagus
Mouth- place where mechanical breakdown of food begins with chewing Pharynx- has 2 skeletal muscle layers whose contractions propel food into esophagus Esophagus- long tube to stomach posterior to trachea; conduit for food; peristalsis (alternate waves of contraction/relaxation of muscle that propels food to stomach)


29 Swallowing uses contraction of tongue, upper pharynx constrictors, and laryngeal muscles.
Is voluntarily initiated, but medullary swallowing center coordinates muscles. Fig , pg: 692

30 Stomach Chemical breakdown of proteins begins here food becomes chyme
upper end to esophagus is cardiac portion; fundus is top middle is body and end is pylorus

31 Quiz Picture

32 Stomach Histology Epithelium- simple columnar
Gastric pits- primarily goblet cells Gastric glands- below gastric pits Neck Cells- produce acidic mucous Parietal Cells- secrete HCl and Intrinsic Factor Chief Cells- produce pepsinogen to digest protein Enteroendocrine Cells- release hormones; gastrin, histamine, endorphins, serotonin, cholecystekinin, somatostatin



35 Stomach Mucosal Barrier
Bicarbonate rich mucous on stomach wall Epithelial cells connected by tight junctions Gastric Gland cells impermeable to HCl Damaged epithelial cells replaced quickly; lining shed every 3-6 days

36 Functions of Stomach Protein digestion- only enzymatic type that occurs here Secretion of IF- essential for intestinal absorption of B12; B12 deficiency causes Pernicious Anemia

37 Control of Gastric Secretion
Neural Control- CN X (Vagus)- stimulation causes increase of all gland secretion Gut Brain local reflexes Hormonal Control- Gastrin- stimulates secretion of enzymes and HCl and hormones of small intestine

38 Homeostatic Imbalances
Gastroesophageal reflux disease (GERD) Heartburn Stomach acid travels back up esophagus Hiatal hernia Damage to esophagus if prolonged

39 Homeostatic Imbalances
Gastric Ulcers Erosion of stomach wall Breach mucosal barrier Stress, medicines, bacteria (helicobacter pylori



42 Small Intestine Three Sections 1. Duodenum 2. Jejunem 3. Ilium

43 Small Intestine 1. Duodenum- 10 inches; receives bile from the bile duct and pancreatic juice from the pancreatic duct; 2 ducts join together and secretion regulated by sphincter of Oddi

44 Small Intestine (con’t)
2. Jejunum- about 8 feet long 3. Ilium- about 12 feet long; joins the large intestine at the ileocecal valve

45 Peritoneum Serous membrane- double membrane
Mesentery is a sheet of 2 serous membranes fused back to back; holds part of the GI tract together; extends from body wall to digestive organs; provides route for blood/lymphatic vessels and nerves



48 Modifications for Absorption
Plicae Circularis- deep permanent folds of mucosa/submucosa Villi- fingerlike projections of mucosa; act like the loops of terry cloth to increase absorptive surface area; contains the lacteals of the lymph system for fat absorption Microvilli- fingerlike projections of plasma membrane of each individual cell of the simple columnar epithelium containing brush border enzymes

49 Quiz Picture

50 Quiz Picture

51 Sm Int

52 2) villi fingerlike projections on mucosa Surface cells for absorption
Contains capillary bed and lacteal (lymph capillary) Made of cells

53 3) microvilli tiny plasma membrane projections of absorptive cells of mucosa Fuzzy appearance called brush border Brush border enzymes located here On a single cell

54 Histology of Small Intestine
Epithelium- simple columnar with goblet cells; enteroendocrine cells that secrete intestinal Gastrin, Secretin, Cholecystikinin (CCK), GIP, VIP Intestinal Pits located above intestinal glands that are called Crypts of Leiberkuhn- secrete intestinal juice, lysozyme Brunner’s Glands- duodenum only; alkaline mucous


56 Liver Digestive function- produce bile for transport to small intestine Other functions include storage of Vit. A, D, E, and K and production of proteins including albumin, clotting factors and production of cholesterol

57 Gross anatomy of Liver About 3 pounds
Divided into right and left lobes Bile produced in the liver leaves through the common hepatic duct which joins the Cystic Duct of the gall bladder to form the Common Bile Duct Under R costal margin from 5th to 10th rib


59 Histology of Liver Functional Unit- Liver Lobule consisting of hepatocytes (liver cells) and vessels; hexagonal with each corner being a portal triad (artery, vein, bile duct); center is the central vein Sinusoids- leaky capillaries between liver cells; also Kupffer cells (macrophages Bile Canaliculi- canals between liver cells that take bile to bile ducts



62 Homeostatic Imbalances
Cirrhosis Chronic inflammation of the liver Obstructed blood flow through liver, portal hypertension Chronic alcoholism or hepatitis

63 Bile Bile Salts- cholesterol derivatives; emulsify fats Phospholipids
Electrolytes Bile Pigments



66 Gall Bladder Green muscular sac; about 4 inches long; stores bile until needed during digestion Major Stimulus for release- Cholecystekinin (CCK)


68 Pancreas Retroperitoneal organ under stomach
Endocrine and exocrine functions Digestive function is exocrine in nature; secretes pancreatic juice containing water, bicarbonate ions and enzymes Neural and hormonal control Secretin- release bicarb; CCK- release enzymes – pancreatic juice - on list


70 Large Intestine About 4-5 feet long
Function: absorb water from undigested food products and deliver waste to be eliminated

71 Gross Anatomy Teniae Coli- Longitudinal muscle of muscularis is tightened up to form a line through the outside of the LI Haustra- pocket-like sacs formed due to tone of teniae Epiploic Appendages- fat filled pouches of visceral peritoneum on surface

72 Quiz Picture

73 Subdivisions of Large Intestine
Cecum Appendix Colon Rectum Anal Canal

74 Microscopic Anatomy Simple columnar Epithelium up to anal canal which is stratified squamous epithelium Deep crypts containing an enormous number of goblet cells; no digestive enzymes


76 Homeostatic Imbalances
Appendicitis Infection of appendix Blocked by feces, swells and cut of venous flow so appendix dies adolescence

77 Homeostatic Imbalances
Diarrhea/Constipation Watery stools/Hard stools Food rushed through large intestine Irritation of colon Bad diet

78 Chemical Digestion/Absorption

79 Chemical Digestion/Absorption
Carbohydrates broken down into sugars Starts with salivary amylase in mouth and progresses to pancreatic amylase in small intestine and brush border enzymes in the microvilli


81 Chemical Digestion/Absorption
Proteins starts in stomach when pepsinogen is converted to pepsin by HCl environment of stomach Brush border enzymes and pancreatic enzymes (Trypsin/Chymotrypsin) digest proteins all the way to amino acids


83 Chemical Digestion/Absorption
Nucleic Acids broken down by pancreatic nucleases and by brush border enzymes in the small intestine


85 Chemical Digestion/Absorption
Lipids Small intestine is the only place that this occurs needs to be emulsified by bile into fat droplets some lipases secreted by pancreas as emulsifications get smaller they become micelles


87 Chemical Digestion/Absorption
Vitamins- A, D, E, and K are fat soluble and follow the absorption of fat; water soluble vitamins are absorbed by diffusion; B12 can only be absorbed if attached to IF; absorbed by endocytosis Electrolytes- absorbed by active and passive transport along entire small intestine

88 Chemical Digestion/Absorption
Water- directly coupled to solute intake; water chases particles and is absorbed by osmosis along the intestines Carbohydrates- facilitated diffusion and secondary active transport Proteins- coupled to the active transport of sodium ion Lipids- micelles by simple diffusion (into Lymph)

89 Nutrition Process by which an organism obtains substances to promote growth, maintenance and repair

90 Major Nutrients Carbohydrates Lipids Proteins

91 Vitamins Most used as coenzymes to accomplish some particular task

92 Minerals Seven required in large amounts: calcium, phosphorus, potassium, sulfur, sodium, chlorine, magnesium Trace amounts of several others: F, Co, Cr, Cu, I, Fe, Mn, Se, Zn Function: added to other molecules for strength and better function eg. Fe in hemoglobin

93 Adipose Tissue Metabolism
Stored fat in adipose tissue Most calories per gram compared to CHO and proteins Body will metabolize fat if glucose is not available

94 Energy Balance Energy Intake = Energy Output
If we consume more calories than we need to perform essential functions we store the excess as adipose If we consume fewer calories than we need to perform essential functions we lose adipose fat stores and can starve

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