grade 8

1. Chapter 15 - The Digestive System
Irregular tube; open at both ends, called
“Alimentary canal” or “Gastrointestinal (GI) Tract”

29 feet long (adults) - 9 meters

Food & other substances that enter tube are not really
inside body

Passageway of food: broken down (digested) and
absorbed thru walls < entering body - cells
Both - Mechanical & Chemical Digestion

2. Break Down of Food
Teeth- first physical breakdown
Stomach-churning of food (physical)
Mouth- first chemical breakdown (salvia)
Digestive enzymes throughout GI tract
Digestion - Process where large food particles
reduced to absorbable molecules
Absorption - Process of small molecules passing thru
digestive system walls into body

3. Key Organs of the GI Tract
Know Main & Accessory organs, Table 16-2; page
476
Small Intestine : Duodenum, Jejunum, & Ileum
Large Intestines (elimination > feces):
Cecum, Colon: Ascending, Transverse, Descending,
Sigmoid

4. Wall of Digestive Tract -

Mouth to anus

Four layers of tissue; surrounding the hollow
space within the tube “lumen”

May vary in structure in different organs

Mucosa or mucous membrane - tough in
esophagus, delicate, for absorption or
secretion in rest of tract

Submucosa - connective tissue, blood
vessels & nerves

5. 
Muscularis - 2 layers, responsible for
wavelike, rhythmic contractions
(peristalsis), moves contents, assists in
mixing & mechanical breakdown

Serosa - outermost covering, composed
of visceral peritoneum

Mesentery - double folded peritoneal
tissue, anchors loops of digestive tract to
posterior wall of abdominal cavity

6. Mouth -

Oral cavity - hollow chamber (roof, a floor, & walls)

Entrance of food; digestion begins immediately

Mucous membranes > mucus, protects against
digestive juices & lubricates food passage

This mucous protects & lubricates

Hard palate - bony structure, front portion

Soft palate - posterior, chiefly muscles

Uvula - cone-shaped process hanging down from
soft palate. W/ help of soft pal., prevents food or
liquid from entering nasal cavity

7. Floor of the mouth -
Tongue - skeletal muscular structure, covered w/
mucous membrane

Anchored to bones in skull > hyoid bone
Frenulum- thin membrane; attaches tongue to floor
of mouth

Tongue-tied: too short
Papillae: small elevations on surface

Vallate type - largest, inverted V-shaped row of about
10-12 mushroomlike elevations - tastebuds

8. Teeth -
Four major types -

Incisors - (sharp/cutting)

Canines - cuspids (pierce/tear)

Premolars - bicuspids & Molars - tricuspids
(grinding/crush)
Mastication > chewing of food
Forms a bolus > ready for swallowing
By age 2 - full set 20 teeth (cut 1st - 2 yrs.)
By age 17 to 24 - 32 permanent teeth (cut 1st - 6
yrs.)

9. Typical Tooth -
Three main parts -

Crown - visible, covered w/ enamel (hardest tissue
in body)

Neck - narrow portion surrounds by gum tissue
(gingiva)

Root - fitted into socket in upper or lower jaw,
lined by fibrous, periodontal membrane

Inside Structure - Enamel on outside, Dentin, Pulp
cavity (blood vessels & nerves) moving inward

10. Salivary Glands -
3 Pairs - ducts drain saliva into oral cavity,
secretes about 1 liter/day

Parotid - in front of each ear (mumps -
tender)

Submandibular - ducts by fernullum

Sublingual - ducts into floor of mouth
Saliva contents - salivary amylase (begins
CHO digestion), mucus (moistens food)

11. Pharynx -

Behind nasal cavity & mouth

Tubelike structure made of muscles, lined w/
mucous membrane

Part of respiratory & digestive systems
Esophagus -

Passage for food to stomach

Tube-like structure, 10 inches long

Mucous lined

GERD - often caused by hiatal hernia

12. Stomach -

Upper part of abdominal cavity, under
diaphragm

Pouch for food, hollow, expands (can push up
on diaphragm > discomfort)

Lower esophageal sphincter (LES) or cardiac
sphincter - rings of muscle tissue at end of
esophagus - keeps food from reentering the
esophagus when the stomach contracts

13. 
Chyme - semi-solid mixture, produced
by contraction of stomach muscles that
mixes food w/ gastric juices
Stomach contractions -
Created by 3 layers of muscles, run
lengthwise, around, obliquely
Makes stomach one of strongest organs >
peristalsis
Breaks food into tiny particles

14. 
Mucous membranes line stomach -
contains gastric glands > secrete gastric
juice & hydrochloric acid

When empty, wrinkled folds - rugae
Three divisions of stomach -

Fundus, body, pylorus
Pyloric sphincter - holds food in stomach,
empties contents slowly into small
intestine

15. 
Ulcer - carterlike wound or sore in membrane of
stomach
• 1 in 10 persons suffer in USA
• Helicobacter pylori bacterium (H. pylori)
Small Intestines -

Portion of digestion tract that extends from the pylorus to
the ileocecal valve

12- 20 feet in length, coiled, convoluted, and occupies
most of the abdominal cavity

Intestinal glands - secrete digestive juices

Smooth muscle wall - contracts > peristalsis

16. 
Plicea - circular folds covered w/ villi,
increases surface area > absorption

In or on the villi -

Blood capillaries - absorb CHO & protein end
products (glucose & amino acids)

Lacteal - lymphatic vessel - absorb lipids

Microvilli - brushlike border, > surface more

Chemical digestion - most occurs in 1st
subdivision of duodenum

Minor & major duodenal papillae - ducts where
pancreatic enzymes & bile enter small intestine

17. Liver -

Large organ, fills R upper abdominal cavity

Exocrine gland - secretes bile into ducts

Hepatic - means liver

Bile - essential for breaking up or emulsification of
fats

CCK (cholecystokinin) - hormone secretion
triggered by lipids in chyme > makes gallbladder
contract & release bile

Drains from common bile duct into duodenum
Gallbladder - concentrates & stores bile

18. Pancreas -
C-shaped, exocrine gland that lies behind the
stomach & duodenum
Pancreatic juice - most important digestive juice -
contains enzymes for all 3 food groups
Sodium bicarbonate (alkaline substance) -
neutralizes hydrochloric acid
Enters small intestine thru same duct as bile
Islets of Langerhans - hormones produced
Pancreatitis - inflammation (blockage, CF)

19. Large Intestine -
Begins with the ending of the ileum at the ileocecal
valve - called the cecum
Approximately 5 feet in length, much larger in
diameter than small intestine
Contents - not called chyme
Function - reabsorb water & salts
Material acted on by bacteria > more nutrients from
cellulose & other fibers

Synthesis Vit. K needed for blood clotting,

Production of some B-complex vit.

20. Not as well suited for absorption as small intestine -
no villi
Normal passage of material thru large intestine - 3 to
5 days
Subdivisions - flow in GI Tract one-way
Cecum - pouchlike area
Ascending colon - right side of body

Bends at hepatic or right colic flexure
Transverse colon - extends across front

Bends at splenic or left colic flexure
Descending colon - left side abdomen

21. Sigmond colon - S-shaped segment,
terminates in rectum
Anal canal - terminal end of rectum, ends at
external opening - anus
Inner anal sphincter - involuntary, smooth
muscle, keeps anus closed except during
defecation
Outer anal sphincter - striated, voluntary
muscle

22. Appendix -

Vermiform appendix - “worm-shaped”, tubular structure,
blind tube

No important digestive fnc. - digest cellulose

Appendicitis - inflammation
Peritoneum -

Large, moist, slippery sheet of serous membrane

Peritoneal space - small space between parietal & visceral
layers - surfaces slide freely

Retroperitoneal - organs outside peritoneum

Extensions of peritoneum-mesentary, greater omentum -
both assist in anchoring abd. contents

23. Digestion -Chemical & mechanical breakdown
CHO - amylase in mouth, slight effect
amylase from pancreas - into small intestine

Absorption of simple sugars (glucose)
Proteins - stomach (HCL/pepsinogen> pepsin)

Finished in small intestine by pancreatic (trypsin)
& peptidases in intestinal juice

Amino acids - basic protein units

24. Fats - in small intestine

Bile emulsification of fats > pancreatic
lipase > fatty acids & glycerol
Key digestive juices & enzymes
* page 410 Table 15-2
Absorption - taking food, breaking it
down in form for utilization of body
Just as important as digestion