Lecture 38

Question 1

Digestive system

Answer 1

Structure
Irregular tube
Open at both ends – ‘outside’ the body!
Alimentary canal or gastrointestinal (GI) tract
Organs (see Box in Textbook)

Functions
Digestion
Absorption
Metabolism

Question 2

Walls of the GI tract

Answer 2

Four layers of tissue
Structure varies among organs
From inside to outside, they are:

Mucosa
Submucosa
Muscularis
Serosa

Question 3

Mucosa layer

Answer 3

Production of mucus to coat lining of ‘tube’.
Secretion of digestive enzymes and hormones
Absorption of the end products of digestion
Protection against pathogens

Question 4

Submucosa layer

Answer 4

Connective tissue layer
Contains glands, blood vessels, lymphatic vessels, & parasympathetic nerves
Contains lots of elastic fibres, allowing the tube to stretch and recoil (especially the stomach)

Question 5

Muscularis layer

Answer 5

Mixes & churns food
Peristalsis
Consists of 2 or 3 layers (depending on location in GI tract):
1Inner circular (lots at sphincters)
2Outer longitudinal
3Oblique

Question 6

Serosa layer

Answer 6

Protective outermost layer

Composed of visceral and parietal peritoneum in abdominal cavity

Question 7

Mouth (oral/buccal cavity)

Answer 7

Where process of digestion begins!

Hollow ‘chamber’
Lined with mucosa
3 ‘parts’:
Roof
Floor
Walls

Question 8

Mouth roof

Answer 8

Hard palate (2 maxillary & 2 palatine bones)
Soft palate (arch-shaped muscle; separates mouth from nasopharynx)
Uvula – projection of soft palate
Uvula & soft palate prevent food & liquid from entering nasal cavities

Question 9

Floor of mouth

Answer 9

Tongue and its muscles
Tongue is skeletal muscle, and is anchored to floor of mouth by the frenulum
Consist of a tip, a body and a root
Small nipple-like projections on tongue, called papillae
Taste buds found in many papillae

Question 10

Ankyloglossia

Answer 10

Tongue tied

Frenulum is unusually short and thick
Can be mild (bands) to complete (entire tongue is attached to the floor of the mouth)
Affects feeding/eating, swallowing, oral hygiene/structure, speech
May recede on its own; surgery is an option

Question 11

Mouth walls

Answer 11

Lateral walls formed by the cheeks (buccinator muscle); contain mucous-secreting glands
Anterior wall formed by the lips
Skin on outside, mucous membrane on inside; junction highly sensitive
Line of contact between closed lips = oral fissure

Question 12

Salivary glands

Answer 12

Function:
Secrete approximately 1 litre of saliva (salivary amylase + mucus) each day!

Parotid glands (largest)
Submandibular glands (‘below mandible’)
Sublingual glands (‘below tongue

Question 13

Parotid glands

Answer 13

Largest

Bottom of ear at jaw angle
Ducts secrete into mouth cavity

Function:
Produce watery saliva containing enzymes

Question 14

Submandibular glands

Answer 14

Middle of mandible
Ducts secrete on either side of lingual frenulum

Function:
Contain enzyme- and mucous-producing substances

Question 15

Sublingual glands

Answer 15

Anterior to submandibular glands
Ducts secrete into floor of mouth

Function:
Produce a mucus type of saliva

Question 16

Sections of a typical tooth

Answer 16

Crown
Neck
Root

Question 17

Crown

Answer 17

Covered by enamel
Enamel = hardest tissue in body, perfect for withstanding the abrasion of chewing food
Pulp cavity in centre of tooth contains connective tissue, blood & lymphatic vessels & sensory nerves

Question 18

Neck of tooth

Answer 18

Joins crown to root

Surrounded by pink tissue = gingival tissue = ‘gums

Question 19

Roots

Answer 19

Fits in socket/jaw bone

Socket lined with periodontal membrane – anchors tooth to bone

Question 20

Deciduous teeth

Answer 20

Baby teeth 
20 teeth
6 months: average age for first eruption
8 incisors are cut first
Complete set at about 2 years of age
No premolars; 2 pairs of molars per jaw
Lost between 6 – 13 years of age

Question 21

Permanent teeth

Answer 21

Adult teeth

32 teeth
6 years: average age for first eruption
Complete set of 32 teeth between 17-24 years of age

Question 22

Pharynx

Answer 22

Tube-like structure made of muscle and lined with mucous membrane
Dual function: digestion & respiration - RECALL:
Air must pass through pharynx on its way to the lungs
Food must pass through pharynx on its way to the stomach
Three divisions - RECALL

Question 23

Esophagus

Answer 23

Muscular, mucus-lined tube (25cm long)
Connects the pharynx with the stomach; sphincters at both ends
Peristaltic action conducts food to the stomach
Mucous secretion facilitates passage of food
Collapses when not moving food

Question 24

Stomach

Answer 24

In upper abdominal cavity (under diaphragm & liver)
Temporary ‘storage’ sac for chewed food
Where chemical digestion of protein begins
About the size of a large sausage when empty - expands after large meal (1.0 to 1.5 litre capacity)

Question 25

Divisions of stomach

Answer 25

Cardia: collar-like region at junction with esophagus
Fundus: enlarged portion to the left and above the opening of the esophagus into the stomach
Body: central portion of the stomach
Pylorus: lower part of the stomach

Question 26

Cardiac sphincter

Answer 26

Lower esophageal sphincter (LES)

Ring of muscle at end of esophagus
Prevents stomach contents from refluxing back into esophagus

Question 27

Hiatal hernia

Answer 27

Due to weakening of ‘hiatus’ (opening in diaphragm for esophagus)
End of esophagus may bulge
Part/all of stomach can bulge upwards
Can lead to GERD

Question 28

Pyloric sphincter

Answer 28

Controls emptying of stomach into the duodenum (first part of small intestine)

Question 29

Stomach wall layers

Answer 29

Gastric mucosa*
Gastric submucosa
Gastric muscularis*
Gastric serosa

Question 30

Gastric mucosa

Answer 30

Epithelial lining has rugae marked by gastric pits. Gastric glands below the gastric pits secrete the majority of gastric juice:
Chief cells secrete the enzymes of gastric juice
Parietal cells secrete HCl instrinsic factor B12
Endocrine cells – secrete hormones (gastrin & ghrelin)

Question 31

Gastric muscularis

Answer 31

3 different directions/arrangements (oblique, ciruclar, and longitudinal) that allow the stomach to ‘churn’ (contract) in many directions

Question 32

Stomach functions

Answer 32

‘Holding tank’ for food until it is partially digested and moved further along the GI tract
Secretes gastric juice to aid in digestion of food
Breaks food into small particles and mixes them with gastric juice
Secretes intrinsic factor
Performs limited absorption
Produces gastrin and ghrelin
Helps protect the body from pathogenic bacteria swallowed with food