1. Digestive system – Alimentary canal
Chapter 14

2. 4 Functions Ingestion – taking in food
Digestion – mechanical and chemical breakdown
Absorption – movement of nutrients into blood
Defecation - removal of
indigestible residue

3. Alimentary canal Aka gastrointestinal (GI) tract
Continuous tube open at both ends
About 9m long in a cadaver; when living shorter due to muscle tone
Food is technically outside the body

4. Mouth (oral cavity) Mastication (chewing) occurs as saliva
mixes w/ food
Deglutition – swallowing
No absorption – exceptions: some
heart medications
Parts
Lips
Cheeks –walls
Hard palate – anterior roof
Soft palate – posterior roof
Uvula – projection of soft palate
Vestibule – btw lips/cheeks and teeth/gums
Oral cavity proper – area w/in teeth
Tongue
Attaches to 2 bones – hyoid, styloid process
Lingual frenulum – secures to floor
Palatine tonsils – posterior – sides
Lingual tonsils – on base of tongue

5. Pharynx Undergoes peristalsis Oropharynx – posterior to oral cavity
Laryngopharynx – joins esophogus

6. Esophagus Joins pharynx and stomach About 25cm long
4 tissue layers (tunics) –
esophagus to large intestine
Mucosa – inner
Lines lumen
Submucosa – contains blood
and lymphatic vessels, nerve endings
Muscularis externa – inner circular layer & outer longitudinal layer of smooth muscle
Serosa – outermost – visceral peritoneum
Connected to parietal peritoneum by mesentery

7. Stomach Digestion No absorption – exception aspirin and alcohol
4-6 hours
On left side of cavity
Regions
Cardiac region – around
cardioesophogeal
sphincter
Where food enters
Fundus – lateral to cardiac region
Body
Pyloric antrum – most activity here
Pylorus – terminal – around pyloric sphincter valve

8. Stomach cont. Length about 25cm Diameter varies
May hold about 4L of food
Forms rugae (folds) when empty
Greater curvature – convex lateral surface
Lesser curvature – concave medial surface
Joined to liver by lesser omentum (peritoneum)
Greater omentum – hangs down to insulate, cushion, and protect organs
Contains an extra muscle layer – an oblique layer
Allows churning and mixing

9. Stomach cont.
Lining has gastric pits w/ gastric glands that secrete gastric juices
Chief cells – protein enzymes – pepsinogens
Parietal cells – hydrochloric acid
Mucous neck cells – produce protective mucous
Enteroendocrine cells – gastrin
Chyme – processed food that enters intestine
Irritation in stomach may trigger emesis (vomiting)

10. Stomach cont.
Heartburn – cardioesophogeal sphincter doesn’t close tightly and stomach acid enters esophagus
Ulcers – insufficient mucus – hydrochloric acid and pepsin eat away mucosa

11. Small intestine Digestion and Absorption; 3-6 hrs
Average length 2.5-7m
Extends from the pyloric
sphincter to the ileocecal valve
3 divisions
Duodenum – “12 finger lengths long”
Bile duct and pancreatic duct join to form the hepatopancreatic ampulla and enter duodenum via the duodenal papilla
Allows pancreatic enzymes and bile to enter and complete digestion
Jejunum – “empty”
Ileum – “twisted intestine”

12. Small intestine cont. Pyloric sphincter – controls
movement of food into
intestine
Wall modifications
Microvilli – aka brush border
Tiny projections to increase surface area
Villi
Fingerlike projections
Contain capillaries and a
lacteal (modified lymphatic
capillary) – absorbed
nutrients move into
capillaries

13. Small intestine cont. Circular folds – aka plica circulares
Deep folds in mucosa and submucosa layers – increase surface area
Peyer’s patches – collections of lymphatic tissue – increase toward end of small intestine to keep bacteria out of blood

14. Large intestine 12-24 hours About 1.5m long
Extends from ileocecal valve to the anus
Bacteria breakdown few remaining nutrients
Produce vitamin K and some vitamin B with a byproduct of methane and hydrogen sulfide
Absorbs water from indigestible food
Gets rid of wastes
(feces) = defecation

15. Large intestine cont. Subdivisions Cecum – sac-like
Appendix – hangs from
cecum
Appendicitis – build up of
bacteria
Colon
Ascending colon – up right side of body – turns at right colic (hepatic) flexure
Transverse colon – moves across
body – turns at left colic (splenic) flexure
Descending colon – moves down left side

16. Large intestine cont. Sigmoid colon – enters pelvis Rectum
Anal canal – opens to exterior
at anus
Voluntary sphincter (external anal sphincter) – skeletal muscle
Involuntary sphincter – smooth muscle
Diarrhea – food is rushed through large intestine and there isn’t time for water to be absorbed – may result in dehydration
Constipation – food moves too slowly and too much water is absorbed

17. Accessory organs – salivary glands
Empty into mouth
Parotid glands – anterior to ears – mumps
Submandibular glands – floor of mouth
Sublingual glands – floor of mouth
All produce saliva – mixture
Mucus – moistens and
binds food into a bolus
Serous fluid – contains
salivary amylase – begins
starch digestion

18. Accessory organs - teeth
1st set – deciduous teeth – baby teeth;
milk teeth – 20
Should have full set by 2 years
Begin to lose btw 6-12 years old
2nd set – permanent teeth – 32
Should have all but third molars (wisdom teeth) by end of adolescence
Wisdom teeth emerge btw 17-25
Types – pairs listed for top ½ of mouth
Incisors (2 pr) – cutting
Canines (1pr)– tearing/piercing
Premolars (2 pr) and molars (3 pr) – grinding

19. Teeth cont. Parts Crown – exposed portion Above gingiva (gum)
Covered by enamel
Dentin – bulk of tooth – under enamel
Pulp cavity – contains blood vessels and
nerves
Neck – connects crown to root
Root – embedded in jawbone
Cementum – covers outer surface and attaches to periodontal membrane (holds tooth in place)
Root canal – where pulp cavity enters root

20. Accessory organs Pancreas – produces digestion enzymes
Also produces insulin and glucagen
Liver – largest gland in body – 4 lobes
Lies over stomach
Hangs from diaphragm and abdominal wall by falciform ligament
Produces bile – leaves via the common hepatic duct – breaks down fat
Composed of bile salts and phospholipids which aid digestion
Salts emulsify fats by breaking large globules into smaller ones

21. Accessory organ - gallbladder
Small, green sac on the inferior surface of the liver
Connected to liver via the cystic duct
Stores bile until needed
Gallstones – form when bile is stored too long or too much water is removed cholesterol crystallizes