BSC2086-The Digestive System

What are the 5 stages of digestion?

-ingestion

-digestion

-absorption

-compaction

-defecation

What is mechanical digestion?

the physical breakdown of food into smaller particles

What is chemical digestion?

a series of reactions that breaks down macromolecules into monomers; carried out by the digestive enzymes produced by salivary glands, the stomach, pancreas, and small intestine

What is the monomer of polysaccharides?

monosaccharides

What is the monomer of protein?

amino acids

What is/are the monomer(s) of fats?

fatty acids and monoglycerides

What is the monomer of nucleic acids?

nucleotides

What are the organs of the digestive tract?

mouth, pharynx, esophagus, stomach, small intestine, large intestine

What are the accessory organs of the digestive tract?

teeth, tongue, salivary glands, liver, gallbladder, and pancreas

What are the layers of the basic structure of the digestive tract wall?

-mucosa

-submucosa

-muscularis externa

-serosa

Where is the mucosa located in the digestive tract?

lining the lumen

What are the layers of mucosa (the mucous membrane)?

-inner epithelium

-lamina propria

-muscularis mucosa

inner epithelium

simple columnar layer in most of the digestive tract, but stratified squamous from mouth through esophagus, and in the lower anal canal

lamina propria

loose connective tissue layer

muscularis mucosa

thin layer of smooth muscle; tenses mucosa creating grooves and ridges that enhance surface area and contact with food

submucosa

thicker layer of loose connective tissue that contains blood vessels, lymphatic vessels, and mucous-secreting glands that secrete lubricating mucous into the lumen

What are the two layers of muscularis externa?

-inner circular layer

-outer longitudinal layer

muscularis externa

responsible for the motility that propels food and residue through the tract

serosa

layer composed of areolar tissue topped by simple squamous mesothelium

where does the serosa begin?

in the lower 3 to 4 cm of the esophagus

where does the serosa end?

just before the rectum

adventitia

a fibrous connective tissue layer that blends into the adjacent connective tissue of adjacent organs

where is adventitia located?

in the pharynx, most of the esophagus, and the rectum

mesenteries

connective tissue sheets that loosely suspend the stomach and intestines from the abdominal wall

parietal peritoneum

serous membrane that lines the wall of the abdominal cavity

lesser omentum

a ventral messentery that extends from the lesser curvature of the stomach to the liver

greater omentum

hangs from the greater curvature of the stomach; forms a pouch, covers the small intestines like an apron; serous membranes formed around the spleen and transverse colon

mesocolon

the mesentery that anchors the colon to the posterior abdominal wall

intraperitoneal

where an organ is enclosed by mesentery on both sides; applies to the stomach, liver, and some parts of the small and large intestines

retroperitoneal

when an organ lies against the posterior body wall and is covered by peritoneum on its anterior side only; applies to the duodenum, pancreas, ascending and descending colons, and rectum

enteric nervous system

a nervous network in the esophagus, stomach, and intestines that regulates digestive tract motility, secretion, and blood flow

can the enteric nervous system work independently of the central nervous system?

yes, it can, but the CNS still exerts a significant influence over its actions

what are the two networks of neurons in the enteric nervous system?

-submucosal plexus

-myenteric plexus

what is another name for the submucosal plexus?

the Meissner plexus

what is another name for the myenteric plexus?

the Auerback plexus

submucosal plexus

in submucosa; controls glandular secretion of the mucosa and controls movements of muscularis mucosae

myenteric plexus

parasympathetic ganglia and nerve fibers between the two layers of the muscularis externa; controls peristalsis and other contractions of muscularis externa

How are motility and secretion of the digestive tract controlled?

by neural, hormonal, and paracrine mechanisms

What are the regulation mechanisms of the digestive tract?

-motility and secretion

-hormones

-paracrine secretions

Name some examples of hormones in the digestive tract?

gastrin and secretin

Name some examples of paracrine secretions in the digestive tract?

histamine and prostaglandins

What are the functions of the mouth?

-ingestion

-gustation

-mastication

-chemical digestion

-swallowing

-speech

-respiration

what kind of cells line the oral cavity?

stratified squamous epithelium

where are the cells lining the oral cavity keratinized?

in areas subject to food abrasian; gums and hard palate

where are the cells lining the oral cavity nonkeratinized?

in other areas of the oral cavity like the floor of the mouth, soft palate, and insides of cheeks and lips

What cells cover the surface of the tongue?

nonkeratinized stratified squamous epithelium

lingual papillae

bumps and projections of the tongue; site of most taste buds

body of the tongue

the anterior two-thirds of the tongue which occupies the oral cavity

root of the tongue

posterior one-third which occupies the oropharynx

what is the main purpose of the palate?

separated the oral cavity from the nasal cavity (makes it possible to breathe while chewing food)

hard palate

anterior portion composed of palatine rugae; helps the tongue hold and manipulate food

soft palate

posterior portion composed of skeletal muscle and glandular tissue; contains the uvula

uvula

the bit that hangs down at the back of the throat; helps retain food in the mouth until one is ready to swallow

what are the functions of the teeth?

-mastication

-makes food easier to swallow

-exposes more SA for action of digestive enzymes

-first step in mechnical digestion

What is the difference between dentin, cementum, and enamel?

cementum and dentin can regenerate, but enamel cannot

gingiva

gums

crown

portion of the tooth above the gum

root

portion embedded in the gum

dentin

hard, yellowing tissue that makes up most of the tooth

enamel

covers the crown and neck

cementum

covers the root

cusps

facilitate grinding and tearing of food

root canal

where the blood vessels, nerves, and lymphatic vessels are located

apical foramen

poor at the basal end of each root canal

what are the functions of saliva?

-moistens and cleanses the mouth

-begins starch and fat digestion

-inhibits bacterial growth

-dissolves molecules so they can stimulate the taste buds

-moistens food and binds it together into bolus to aid in swallowing

what is the composition of saliva?

97%-99.5% water and various solutes

what are the solutes contained in saliva?

-salivary amylase

-lingual lipase

-mucus

-lysozyme

-immunoglobulin A

-electrolytes

what is the pH of saliva?

6.8-7.0

salivary amylase

enzyme that begins starch digestion

lingual lipase

enzyme that digests fat after food is swallowed; activated by the stomach

what is the function of mucus in saliva?

binds and lubricates food bolus and aids in swallowing

lysozyme

enzyme that kills bacteria

immunoglobulin A

an antibody that inhibits bacterial growth

which electrolytes are contained in saliva?

sodium, potassium, chloride, phosphate, bicarbonate

intrinsic salivary glands

small glands dispersed amid other oral tissues; lingual, labial, and buccal glands

extrinsic salivary glands

3 pairs of glans located outside the oral cavity and connected by ducts

what are the 3 pairs of extrinsic salivary glands?

-parotid

-submandibular

-sublingual

know locations of the 3 pairs of extrinsic salivary glands

see notes

list the mechanisms of salivation

see notes pg. 6

which two tracts of the body intersect in the pharynx?

the respiratory and digestive tracts

pharynx

connects the oral cavity to esophagus and allows entrance of air from nasal cavity to larynx

what are the 3 parts of the pharynx?

-nasopharynx

-oropharynx

-laryngopharynx

esophagus

extends from pharynx to stomach

esophageal hiatus

where the esophagus passes through the diaphragm

upper esophageal sphincter

remains contracted when not swallowing to exclude air from the esophagus

lower esophageal sphincter

prevents stomach contents from regurgitating into the esophagus; protects the esophagus from erosive effects of stomach acid

what is deglutition?

swallowing

how many muscles does swallowing require?

22 muscles

what coordinates swallowing?

the swallowing center located in the medulla oblongata

what are the 2 phases of swallowing?

-buccal phase

-pharyngoesophageal phase

understand the buccal phase and pharyngoesophageal phase of swallowing

see notes pg. 7

which nerves communicate with the swallowing center in the medulla oblongata?

trigeminal, facial, glossopharyngeal, and hypoglossal nerves

understand the role of peristalsis in swallowing

see notes pg. 7

stomach

mechanically breaks up and liquiefies food and begins the chemical digestion of protein and fat

chyme

soupy mixture of semidigested food in the stomach

what are the 4 regions of the stomach?

-cardiac region

-fundic region

-body

-pyloric region

what is the largest region of the stomach?

the body or corpus

The stomach receives parasympathetic fibers from which nerves?

the vagus nerves

The stomach receives sympathetic fibers from what structure?

the celiac ganglia

how does the wall structure of the stomach differ from other digestive organ structures?

the muscularis externa has 3 layers in the stomach instead of 2