Chapter 16 – digestive system

Major components: mouth, esophagus, stomach, intestines, liver, gallbladder, and pancreas

Major functions: mechanical and chemical breakdown of food, absorption of nutrients and elimination of wastes

Histology of the digestive system

Four tissue layers (tunics):1. Mucosa – innermost tunic – mucus epithelium, lamina propria, muscularis mucosa2. Submucosa – thick layer of loose connective tissue3. Muscularis – inner layer of circular smooth muscle and outer layer of longitudial smooth muscle4. Serosa or adventitia – connective tissue layer

Structures:

Oral cavity: mouth – bounded by lips and cheeks and contains teeth and tongue

Muscles – (lips) – orbicularis oris, buccinator, tongue, frenulum - (function – mastication)

teeth

32 teeth in normal adult mouthLocated in mandible and maxillaIncisors, canines, premolars, molarsSee diagram page 452Permanent vs. deciduous teethStructure: crown, neck, root, pulp cavity, pulp, dentin, enamel, cementum, alveoli, gingiva, periodontal ligaments, periodontal membrane

Palate and tonsils

Palate – 2 parts:

1. Hard palate

2. Soft palate

Uvula

Tonsils – lateral, posterior walls of the oral cavity

Salivary glands

See diagram on pg. 453

Three pairs –

1. parotid

2.Submandibular

3.sublingual

pharynx

Nasopharynx

Oropharynx

laryngopharynx

esophagus

Muscular tube – extends from pharynx to stomach

About 10 inches (25 cm)

Passes through diaphragm

Upper and lower esophageal sphincters

Lined with mucous glands

Stomach

Cardiac opening

Cardiac region

Fundus

Body

Greater curvature

Lesser curvature

Pyloric opening (sphincter)

Pyloric region

Stomach, continued

Gastric pits

Gastric glands

Mucous cells

Endocrine cells

Pepsinogen/pepsin

rugae

Small intestine

About 6 meters long (almost 20 ft)

3 sections: duodenum, jejunum, ileum

Duodenum – about 12 inches, bile duct and pancreatic duct empty into it

Duodenum has : circular folds, villi and microvilli to increase surface area

Small intestine, cont’d

Jejunum and ileum are similar in structure to duodenum, but diameter and numbers of villi, microvilli and circular folds decreases as you progress the length of the small intestine

Ileocecal junction, sphincter and valve are found at the junction between the ileum and the large intestine

liver

Weighs about 3 pounds

Right upper quadrant of abdomen

2 blood sources

Ducts transport bile to gall bladder

pancreas

Pancreatic islets

Insulin production

Large intestine

Cecum

Colon

Rectum

Anal canal

Colon

1.5 m long

Ascending

Transverse

Descending

Sigmoid

Crypts

peritoneum

Serous membranes

Visceral peritoneum

Parietal peritoneum

Mesenteries

Lesser/greater omentum

Retroperitoneal organs

Physiology of digestive system

Oral cavity, pharynx and esophagus

Saliva – salivary amylase

Mucin

Mastication

Deglutition

Voluntary phase

Bolus

Swallowing, contd

Pharyngeal phase

Epitglottis

Esophageal phase

Peristaltic waves

Stomach

Secretions – chyme

Mucus

Hydrochloric acid

Pepsiogen

Pepsin

Intrinsic factor

gastrin

Regulation of stomach secretions

Cephalic phase

Gastric phase

Intestinal phase

Secretin

Movement in the stomach

Mixing waves

Peristaltic waves

Small intestine

Peptidases

Disaccharidases

Movement – segmental contractions, peristaltic contractions

absorption

liver

Digestive, excretory,stores and processes nutrients, synthesizes molecules, detoxifies

Bile/bile salts

pancreas

Trypsin

Pancreatic amylase

Lipases

Nucleases

insulin

Large intestine

Feces

Defecation

Mass movements

Digestion, absorption, transport

Carbohydrates – mono, di and poly saccharides

Lipids – triacylglycerol, saturated and unsaturated fats

Proteins – pepsin, trypsin, peptidases and amino acids

Water and minerals

9 L of water enters digestive tract per day

1.5 of those in food and drink

7.5 L from digestive secretions