Lecture #24: Digestive System--Histology and Upper GI Tract

Question 1

What is the function of the mouth?

Answer 1

mechanical and chemical
breakdown, deglutition
(swallowing)

Question 2

What is the function of the Pharynx and esophagus?

Answer 2

swallowing and avoiding airway

Question 3

What is the function of the stomach?

Answer 3

mechanical and
chemical breakdown with some
absorption

Question 4

What is the function of the small intestine?

Answer 4

chemical and mechanical breakdown with

major absorption

Question 5

What is the function of the large intestine?

Answer 5

absorption of electrolytes and some vitamins

Question 6

What is the function of the rectum and anus?

Answer 6

Defecation

Question 7

Draw and label the parts of the GI Tract.

Answer 7

Mucosa
Submucosa
Muscularis
Serosa

Question 8

What is the GI tract regulated by?

Answer 8

The Enteric Nervous and the Extrinsic set of nerves that are part of the ANS.

Question 9

What is the Enteric Nervous System?

Answer 9

Consists of 100 million neurons that extend from the esphagus to the anus and falls into two plexus the myenteric plexus and submucosal plexus.

Question 10

What is the myenteric plexus?

Answer 10

located between the longitundal and circular smooth muscle layers of the muscularis

Motor neurons of the myenteric plexus supply the longitundinal and circular smooth muscle layers of the muscularis, this plexus mostly controls the GI tract movment, particularly the frequency and strength of the contraction of the muscularis.

Question 11

What is the submucosal plexus?

Answer 11

Found within the submucosa; motor neurons of the submucosal plexus supply the secretory cells of the muscosal epithelium, controlling the secretions of the organs of the GI tract.

Question 12

What do the interneurons do in the ENS?

Answer 12

They interconnect the neurons of the myenteric and the submuscosal plexus.

Question 13

What the sensory neurons do in the ENS?

Answer 13

Supply the mucosal epithelium and contain receptors that detect stiumuli in the lumen of the GI tract.

Contain two types of receptors: Chemoreceptors (chemical reaction of food present in the lumen) & Mechanoreceptors (strech receptors)

Question 14

What is the 1st layer of the GI tract?

Answer 14

1st Layer of the GI Tract: Mucosa

Question 15

What is in the 1st layer of the mucosa?

Answer 15

Epithelium
Lamina Propria
Muscularis mucosea

Question 16

What is the purpose of the epithelium?

Answer 16

– stratified squamous in mouth, esophagus and anus

– simple columnar in the rest of the GI tract
• secretes enzymes and absorbs nutrients
• specialized cells (goblet) secrete mucous onto cell surfaces
• enteroendocrine cells secrete hormones controlling organ function

Question 17

What is the purpose of the lamina propria?

Answer 17

– thin layer of loose connective tissue

– contains blood vessels and lymphatic tissue

Question 18

What is the purpose of the muscularis mucosae?

Answer 18

– thin layer of smooth muscle causes folds to form in mucosal layer
– drives local movements to increase absorption by exposing ingested material to absorptive surfaces

Question 19

What is the 2nd layer of the GI tract?

Answer 19

Submucosa

Question 20

What is composed of the submucosa?

Answer 20

Loose connective tissue 
Submuscosal plexus (Meissner's plexus)

Question 21

What is the purupose of the loose connective tissue?

Answer 21

– containing blood vessels, glands and lymphatic tissues

Question 22

What is the purpose of the submucosal plexus (Meissner’s plexus)?

Answer 22

– part of the enteric nervous system

– receives input from sympathetic (thoracic and lumbar
spinal cord) and parasympathetic neurons (vagus nerve
and sacral spinal cord)

– regulates blood vessel diameter, secretion from glands
and neurosecretory neurons, and local motility caused by
muscularis mucosae

Question 23

What is the 3rd layer of the GI tract?

Answer 23

Muscularis

Question 24

What parts of the body have muscularis?

Answer 24

Mouth, pharynx, and superior and middle parts of the esophagus contains skeletal muscle that produces voluntary swallowing.

Question 25

What does the muscularis control?

Answer 25

• Smooth muscle under involuntary control – inner circular fibers and outer longitudinal fibers – allows motility for mixing and propulsion

Question 26

What plexus is part of the muscularis?

Answer 26

• Myenteric plexus (Auerbach’s plexus) – part of the enteric nervous system with some functions shared with submucosal plexus – provides parasympathetic & sympathetic innervation of circular and longitudinal smooth muscle layers

Question 27

What is the 4th layer of the GI Tract?

Answer 27

Serose or Adventitia

Question 28

Where is serosa mostly found?

Answer 28

for stomach and intestines – A serous membrane also called the (visceral) peritoneum – Secretes serous fluid – Consists of areolar connective tissue covered with simple squamous epithelium

Question 29

Where is the common place that adventitia is found?

Answer 29

• Adventitia for esophagus – Consists of areolar connective tissue without the epithelium

Question 30

What is the peritoneum?

Answer 30

The largest serous membrane of the body; it consists of a layer of simple squamous eptithelium with an underlying supporting layer of areolar connective tissue.

Question 31

What is it called when there is a lining within the walls of the admiominal cavity?

Answer 31

Parietal Peritoneum

Question 32

What is it called when there is a cover over some of the organs in the cavity and is their serosa?

Answer 32

Visceral Peritoneum

Question 33

The slim space containing lubricating serous fluid that is between the parietal and visceral portions of the peritoneum is called what?

Answer 33

Peritoneal cavity

Question 34

What is mechanical digestion?

Answer 34

(mastication or chewing) • breaks food into pieces • mixes with saliva so that it forms a moist bolus

Question 35

What is Chemical Digestion?

Answer 35

• salivary amylase begins starch digestion in the mouth (pH 6.5-7.0) , but when the bolus hits the acidic gastric juices (pH 2.5) digestion stops • lingual lipase is secreted by glands in tongue and begins breakdown of triglycerides (lipids) into fatty acids and glycerol

Question 36

What are the major salivary glands?

Answer 36

Parotid, Submandibular, and sublingual glands

Question 37

Do they all have ducts that empty into the oral cavity?

Answer 37

Yes!

Question 38

What other functions does the salivary glands do?

Answer 38

Sight, smell, sounds, memory of food, and tongue stimulation increase salivation Fear and anxiety decrease salivation --> dry mouth

Question 39

What is the composition and functions of the saliva?

Answer 39

``` • Water, HCO3-, enzymes • Moistens food (swallow) • Dissolves food (taste) • HCO3 - buffers acidic foods • Protects mouth from infection with rinsing action • Lysozyme helps destroy bacteria ```

Question 40

What are the stages of swallowing?

Answer 40

Voluntary Stage | Involuntary Stage

Question 41

What is the Voluntary Stage?

Answer 41

Oral cavity to oropharynx

Question 42

What is the involuntary stage?

Answer 42

1. Pharyngeal stage: pharynx to esophagus | 2. Esophageal stage: esophagus to stomach

Question 43

In the oral stage, what is happening?

Answer 43

• Deglutition (swallowing) starts with the voluntary stage | – food bolus pushed by the tongue into the oropharynx

Question 44

In the involuntary stages, what is happening?

Answer 44

begin when sensory nerves in the pharynx that signal the deglutition center in brainstem – breathing stops – soft palate & uvula rise closing off nasopharynx – vocal cords adduct – larynx rises – epiglottis covers the larynx

Question 45

In the Esophageal stage, what is happening?

Answer 45

• Upper esophageal sphincter relaxes • Peristalsis pushes food down – circular fibers contract behind bolus – longitudinal fibers contract in front of bolus to shorten the distance of travel • Lower esophageal sphincter relaxes as food approaches

Question 46

What is the travel time for food to travel down the esphogeal stage?

Answer 46

4 to 8 sec. for solids | 1 sec for liquids

Question 47

What is Gastro-Esophageal Reflux Disease? (GERD)

Answer 47

• If lower sphincter fails to open – distension of esophagus feels like chest pain or heart attack • If lower esophageal sphincter fails to close – stomach acids enter esophagus & cause heartburn (GERD) – worsened by a weak sphincter – particularly bad when laying down after a large meal – smoking and alcohol make the sphincter relax worsening the situation