Upper GI tract anatomy

Question 1

What is the GI system

Answer 1

system of hollow organs and support organs which facilitate breakdown of food to simple chemical structures to fuel cellular metabolism

Question 2

Functions of GI tract

Answer 2

• motility: movement of food mostly by action of smooth muscle (i.e. peristalsis)
• secretion: from GI tract irself or accessory organs as result of stimuli (hormonal/food/neural)
• digestion: chemical breakdown of food by enzymatic digestion and mechanical breakdown of food (i.e. mastication)
• absorption: transfer of absorbable products of digestion into the blood or lymph to allow these simple chemical structures to facilitate cellular metabolism

Question 3

Responsibilities of mucosa

Answer 3

protection, secretion, absorption

Question 4

Responsibilities of submucosa

Answer 4

secretion and absorption (contains Meissner plexus in places)

Question 5

Responsibilities of muscularis externa

Answer 5

motility (i.e. peristalsis)

Question 6

Innervation of GI tract

Answer 6

• enteric nervous system (mesissner plexus (submucosal plexus), myenteric plexus (auerbach plexus))
• sympathetic nervous system (splanchnic nerves)
• parasympathetic nervous system (vagus nerve (CN X)

Question 7

Responsibilities of oral cavity

Answer 7

• ingestion
• mastication (chewing)
• digestion
• deglutition (swallowing)

Question 8

Function of the tongue

Answer 8

• moves food during mastication
• skeletal muscle fibres in 3 planes allow finer control over movements
• covered in specialised mucosa which includes salivary glands and taste buds
• taste buds detect 5 different tastes through ion channel activation (salty and sour) or GPCR activation (sweet, bitter, and umami)

Question 9

Function of the salivary glands

Answer 9

• serous fluid protection to lubricate mouth
• aids in initial digestion of carbohydrates and lipids
• provides antimicrobial / bacteria protection
• sublingual gland secretes mixed serous and mucous solution
• submandibular gland secretes mixed serous and mucous solution
• parotid gland secretes serous fluid

Question 10

Proteins contained in secretions

Answer 10

• lactoferrin (anti-microbial)
• lysozyme (anti-bacterial)
• IgA (anti-viral and anti-bacterial)

Question 11

Enzymes contained in secretions

Answer 11

• amylase (digests carbohydrates)
• lipase (digests lipids)

Question 12

Oral preparatory phase of swallowing

Answer 12

• voluntary
• pushes bolus towards pharynx
• one bolus touches pharyngeal wall, pharyngeal phase begins

Question 13

Pharyngeal phase of swallowing

Answer 13

• involuntary
• soft plate seals off nasopharynx
• pharyngeal constrictors push bolus downwards
• larynx elevates, closing epiglottis
• vocal cords adduct (protecting airway) and breathing temporarily ceases
• opening of upper oesophegeal sphincter

Question 14

Oesophageal phase of swallowing

Answer 14

• involuntary
• closure of upper oestophegeal sphincter
• peristatic wave carries bolus downwards into oesophegous

Question 15

How is the epithelium of the oesophagus divided

Answer 15

• mucosa
• submucosa
• muscularis externa

Question 16

Mucosa of the oesophagus epithelium

Answer 16

• stratified squamous epithelium, fibroelastic lamina propria, muscularis mucosa
• interspersed antigen presenting cells (Langerhans cells) help with immunity in GI tract
• cardiac glands in lamind propria help lubricate boluses of food (makes swallowing easier)

Question 17

Submucosa of the oesophagus epithelium

Answer 17

• houses the oesophageal glands proper which secrete directly into oesophageal lumen
• composed of mucous and serous cells

Question 18

Muscularis externa of oesophagus epithelium

Answer 18

• upper 1/3rd: skeletal muscle (unique to oesophegous, arranged perpendicularly)
• middle 1/3rd: skeletal smooth muscle
• lower 1/3rd: smooth muscle

Question 19

Peristalsis in the oesophagus

Answer 19

• sequential pinching motion -> moves from head to anus to facilitate digestion and absorption
• moves at rate of 50mm/minute down oesophegas
• reflux of bolus is prevented by sphincters