1. May 14, 2018
Journal: What organs make up the digestive system?

2. Digestive Tract

3. Parts of the Digestive Tract
Oral Cavity  Pharynx  Esophagus  Stomach  Small Intestines  Large Intestines  Anus

4. Oral Cavity Tongue – muscular organ that moves food in the mouth
Teeth – used for mastication
Children have 20 deciduous teeth
Adults have 32 primary teeth
Salivary Glands – produce saliva that aids in chemical breakdown of food by producing amylase which breaks down starch
Largest is the Parotid gland located in the cheeks right in front of the ear

5. Pharynx Transmits food from the oral cavity into the esophagus
Epiglottis moves when swallowing to block the food from entering the larynx

6. Esophagus
Muscular tube lined with moist stratified squamous epithelium that connects the pharynx to the stomach
The openings of the esophagus contain sphincters that regulate how much food can move through the tube at a time
Top – Upper Esophageal Sphincter
Bottom – Lower Esophageal Sphincter

7. Swallowing
Phases:
Voluntary Phase – bolus in the mouth is pushed into the oropharynx by the tongue and hard palate
Pharyngeal Phase – reflex that pushes food through the pharynx and into the esophagus past the epiglottis
Esophageal Phase – food is moved from the pharynx to the stomach using peristalsis

8. Stomach Broken up into sections: Fundus – Superior part near the heart
Body – Largest part that curves
Pyloric Part – Inferior part that connects to the small intestines
Connection between stomach and small intestines is the pyloric sphincter

9. Tissues of the Stomach
Stomach itself is made up of three layers of smooth muscle that churn to help break down food
Inner layers of the stomach are arranged in large folds called rugae which can stretch out as the stomach becomes full

10. Epithelial Cells Lining the Stomach
Mucous Cells – produce mucus to coat and protect the stomach
Parietal Cells
Hydrochloric acid that converts pepsinogen to pepsin, kills pathogens, breaks down connective tissues in meat
Intrinsic factor which binds to B12 to make it digestible
Chief cells – produce pepsinogen used in protein digestion
Endocrine cells – produce gastrin to stimulate gastric glands to secrete gastric juices (HCl, pepsinogen, and mucus)

11. Phases of Gastric Secretion
Cephalic Phase – Smell or sight of food causes stomach to prepare for food by increasing gastric juice production
Gastric Phase – As food enters the stomach more gastric juice is produced and both chemical and mechanical digestion occur as chyme is formed
Intestinal Phase – Chyme moves into the first part of the small intestines, the duodenum, and gastric juice production decreases

12. Small Intestines
Primary site of digestion and where nutrients are absorbed into the blood stream
Sections:
Duodenum – first section about 25 cm long connected to stomach
Jejunum – middle section about 8 ft long
Ileum – last section about 7 feet long that connects to the large intestines through the ileocecal valve

13. Digestion in the Duodenum
Liver and gallbladder secrete bile into the duodenum which emulsifies fats
Pancreas secretes pancreatic juice into the duodenum which neutralizes the acidic chyme and breaks down most foods
Exocrine cells produce additional digestive enzymes and mucus that help break down food
Lactase, maltase, and sucrose break down disaccharides in starch
Peptidase breaks down peptides in proteins

14. Pancreatic Juice
Contains enzymes that are secreted into the small intestines to help break down food
Trypsin break down protein into amino acids
Lipases break down emulsified fats to glycerol and fatty acids
Amylase breaks down starch

15. Structure of the Small Intestines
Modifications to allow for increased surface area
Has circular folds
Each circular fold has villi, finger- like projections that extend out into the intestines
Each villi has an outer layer of columnar epithelial cells with microscopic extensions called microvilli

16. Absorption
Each villi contains a network of blood and lymph capillaries called a lacteal which aids in absorption
Amino acids from proteins
Sugars from carbohydrates
Glycerol and fatty acids from fats called chyle that get absorbed right into the lymphatic system

17. Large Intestine Connects from the small intestine to the anus
Functions:
Reabsorbing water
Absorbing vitamins
Compacting waste for elimination
Three Sections:
Cecum + Appendix
Colon
Rectum

18. Colon Where the majority of water and electrolyte reabsorption occur
Contains bacteria that help us break down indigestible materials and produce vitamins B and K
Further divided into four sections:
Ascending: up right side towards the liver
Transverse: across the abdomen
Descending: down the left side
Sigmoid: extends to the rectum

19. Rectum and Anus
Sigmoid colon connects to the rectum, which is where solid waste will condense until it is ready to be excreted out of the body through the anal sphincter