Digestive System Flashcards
Swallowing
Begins with voluntary muscle action but finishes with involuntary peristalsis.
Upper one-third of the esophagus, the muscularis is exclusively skeletal muscle
The middle portion of the esophagus has a combination of skeletal and smooth muscle fibers
The lower third the muscularis is exclusively smooth muscle
Esophagus layers
The four layers of the GI tract are present. The esophageal mucosa has nonkeratinized stratified squamous epithelium.
Innermost: Mucosa
Submucosa
Muscularis
Outermost: Serosa
Esophageal glands
Small mucus-secreting glands in the submucosa which lubricate and protect the mucosa.
Stomach functions
Functions:
To continue the digestion of carbohydrates initiated by the amylase of
saliva,
To add an acidic fluid to the ingested food and mixing its contents into a viscous mass called chyme by the churning activity of the muscularis
To begin digestion of triglycerides by a secreted lipase
To promote the initial digestion of proteins with the enzyme pepsin.
Stomach regions
The wall in all regions of the stomach is made up of all four major layers of the GI tract.
Cardia, pylorus, fundus, and body
Cardia
A narrow transitional zone, 1.5-3 cm wide, between the
esophagus and the stomach
Pylorus
The funnel-shaped region that opens into the small intestine. Both regions produce mucus and are similar histologically.
Fundus and body
The much larger fundus and body regions are identical in structure and are the sites of gastric glands releasing acidic gastric juice.
Rugae
The mucosa and submucosa of the stomach have large, longitudinally
directed folds called rugae, which flatten when the stomach fills with food.
Mucosal surface
A simple columnar
epithelium that invaginates deeply into the lamina propria. The invaginations form millions of gastric pits.
Gastric glands
The gastric pits of the mucosal surface lead to long, branched, tubular gastric glands. In
the fundus and body the gastric glands themselves fill most of the mucosa.
Secretory cells of the gastric glands
Mucous neck cells
Parietal (oxyntic) cells
Chief (zymogenic) cells
Enteroendocrine cells
Mucous neck cells
Secretes acidic fluid containing mucin
Parietal (oxyntic) cells
Produces hydrochloric acid (HCl).
Chief (zymogenic) cells
Has all the characteristics of active protein-secreting cells. They produce pepsins, which starts the breakdown of protein, and gastric lipase, which starts the breakdown of lipids.
Enteroendocrine cells
Scattered epithelial cells with endocrine or
paracrine functions. Some secrete serotonin and others produce the peptide gastrin.
Gastric and duodenal ulcers
Painful erosive lesions of the mucosa that may extend to deeper layers.
Can occur anywhere between the lower
esophagus and the jejunum.
Causes:
Bacterial infections with Helicobacter pylori.
Effects of nonsteroidal anti-inflammatory drugs
Overproduction of HCl or pepsin.
Lowered production or secretion of mucus or
bicarbonate.
Small Intestine
The site where the digestive processes are completed and where the nutrients are absorbed.
Same four layers as other parts of the GI tract
Mucosa (inner), submucosa, muscularis, serosa, outer mesentery
Small Intestine segments
Duodenum (first), jejunum, and ileum
Mucosa of small intestine
Densely covering the entire mucosa of the small intestine are short mucosal outgrowths called villi that project into the lumen.
Villi of small intestine
finger- or leaflike mucosal projections covered by a
simple columnar epithelium of absorptive cells called
enterocytes, with many interspersed goblet cells that produce mucus.
plicae circulares
The mucosa and
submucosa form circular
folds or plicae circulares,
which increase the
absorptive area.
Small Intestine Cell Types in Mucosa
Enterocytes
Goblet cells
Paneth cells
Enteroendocrine cells
Enterocytes
The absorptive cells, are tall columnar cells. The
apical end of each enterocyte displays a striated (or brush) border, which is a layer of densely packed microvilli through
which nutrients are taken into the cells.
Goblet cells
Secrete mucus to protect and lubricate the lining of
the intestine.
Paneth cells
For innate immunity. They release lysozyme and
other peptides that break down membranes of microorganisms.
Celiac disease (celiac sprue)
A disorder of the small
intestine mucosa that causes malabsorption and can lead to damage or destruction of the villi.
An immune reaction
against gluten or other proteins in wheat. The resulting inflammation affects the enterocytes, leading to reduced nutrient absorption.
Crohn disease
A chronic inflammatory bowel disease in
the ileum or colon; its cause is not understood. a
combination of immune, environmental, and genetic factors.
Large Intestine
Absorbs water and electrolytes and forms
indigestible material into feces, has the following regions: the short cecum,
with the ileocecal valve and the appendix; the ascending, transverse,
descending, and sigmoid colon; and the rectum, where feces is stored prior to evacuation.
Mucosa of the large intestine
The mucosa lacks villi and except in the rectum has no major folds.
Cell types:
Goblet cells
Enterocyte
Enteroendocrine cells
Colonocytes
Colonocytes
Have irregular microvilli and dilated intercellular spaces indicating active water absorption.
Lymphoid tissue of the large intestine
The richness in MALT (lymphatic nodules) is related to the large bacterial population of the large intestine.
Muscularis of the colon
The fibers of the outer layer gathered in three
separate longitudinal bands called teniae coli.
Colorectal cancer
An adenocarcinoma that
develops initially from benign adenomatous polyps in the mucosal epithelium.
Rectoanal junction
At the rectoanal junction the simple columnar
epithelium is replaced by stratified squamous
epithelium, typical of the epidermis.
Hemorrhoids
Swollen blood vessels in the mucosa or submucosa
of the anal canal
Results from a low-
fiber diet, constipation, prolonged sitting, or straining at defecation, conditions that produce increased pressure on these blood vessels.
Functions of salivary glands
(1) to moisten and lubricate ingested food and the oral mucosa
(2) to initiate the digestion of carbohydrates and lipids with amylase and
lipase, respectively.
(3) to secrete innate immune components such as lysozyme.
Three epithelial cell types of salivary glands
Serous cells
Mucous cells
Myoepithelial cells
Serous cells
Protein-secreting cells (enzymes and other proteins).
Mucous cells
Contain apical granules with mucins that provide lubricating properties in saliva.
Myoepithelial cells
have contractile processes around the secretory unit
or duct that move secretory products into and through the ducts.
Parasympathetic stimulation of salivary glands
Usually elicited through the smell or taste of
food, provokes a copious watery secretion with relatively little organic content.
Sympathetic stimulation of salivary glands
Inhibits such secretion and produces dry mouth
often associated with anxiety
Pancreas
A mixed exocrine-endocrine gland that produces both digestive
enzymes and hormones.
Pancreas exocrine
The digestive enzymes are produced by cells of serous acini in the larger exocrine portion. This somewhat resembles the parotid gland histologically.
Secretes alkaline pancreatic juice into duodenum where bicarbonate ions neutralize the acidic chyme from the stomach
Pancreas endocrine
Involves primarily smaller cells located in clusters called the pancreatic islets (islets of Langerhans)
