Digestive System Flashcards
The digestive system consists the ff.
oral cavity
pharynx
alimentary tract (canal)
anal canal
It lies within the mucosa or submucosa of their organ of origin.
intrinsic glands
It communicates with their organ of origin through ducts.
extrinsic glands
extrinsic digestive glands
major salivary glands including the parotid, sublingual, and submandibular (submaxillary) glands; the pancreas; and the liver.
Organs of the digestive tract typically have 4 concentric coats. Proceeding outward from the lumen these are:
(1) the mucosa (mucous membrane)
(2) the submucosa
(3) the muscularis (muscularis externa)
(4) the adventitia or serosa.
The mucosa has three components: .
(a) the epithelium and its underlying basement membrane,
(b) a thin underlying layer of loose, cellular connective tissue, the lamina propria, and
(c) a relatively thin layer of smooth muscle called the muscularis mucosae. The latter may consist of both circular and longitudinally arranged layers
The submucosa
is composed of a layer of dense, irregularly arranged connective tissue that contains nervous tissue (the submucosal plexus of Meissner) as well as blood vessels
nervous tissue of the submucosa
submucosal plexus of Meissner
muscularis externa consists of at least 2 layers of smooth muscle, what are these? Connective tissue separating the muscle layers contains nerves (myenteric plexus of Auerbach) and blood vessels.
inner circular and outer longitudinal layer
outermost layer which consists of a thin layer of loose connective tissue. Where the digestive system is covered by peritoneum the adventitial layer is called the serosa.
adventitia
Where the digestive system is covered by ______ the adventitial layer is called the _________.
peritoneum
serosa
It is a long tube that mechanically and enzymatically digests food into small molecules, then absorbs small molecules and electrolytes, and processes and excretes material that cannot be absorbed.
gastrointestinal tract
Different segments of the gastrointestinal tract perform different functions:
• Stomach
• Small intestine
• Large intestine (colon)
mechanical disruption of food and some enzymatic digestion
Stomach
enzymatic digestion and solubilization into small molecules and absorption of small molecules
Small intestine
processing of unabsorbed material into waste
Large intestine (colon
These organs contribute enzymes and other material to the gastrointestinal tract that help with digestion and solubilization of food.
liver and pancreas
The inner most layer of the wall of the GI tract is the _______. It consists of a layer of epithelium which is in direct contact with the contents in the lumen of the GI tract. The _________ sits on a basement membrane. Beneath the basement membrane is a thin layer of connective tissue called the _______. It contains blood vessels and lymphatics and in certain sections of the GI tract, large aggregates of immune cells localize to the lamina propria.
mucosa
epithelium
lamina propria
A thin layer of smooth muscle called the __________ sits beneath the mucosa.
muscularis mucosa
The layer beneath the muscularis mucosa is called the _________. It is a thick layer of connective tissue that contains arteries, veins, lymphatics and in some segments of the GI tract, nervous tissue.
submucosa
It surrounds the submucosa and is composed of two muscle layers: what are these muscles? an ________ in which the smooth muscle cells are arranged circumferentially around the GI tract and an ________ in which the smooth muscle cells are arranged longitudinally along the GI tract.
muscularis externa
inner layer
outer layer
The outer most layer of the GI tract is the _________.
adventitia
Adventitia which consists of the ff.
connective tissue containing blood vessels, nerves, and fat
The greatest structural and functional variations occur in the ___________, specifically the _________.
mucosal layers
epithelium
four distinct types of mucosa in the gastrointestinal tract:
• Protective mucosa
• Secretory
• Absorptive mucosa
• Absorptive mucosa
It is characterized by a stratified squamous epithelium and is found in the oral cavity, pharynx, esophagus, and anal canal.
Protective mucosa
It contains cells that are responsible for the secretion of digestive enzymes and acid and is found exclusively in the stomach.
Secretory mucosa
It is responsible primarily for absorbing digested nutrients and is found along the entirety of the small intestine.
Absorptive mucosa
It primarily involved in water absorption and electrolyte balance is found in the large intestine.
Absorptive mucosa
Unlike the lung where the epithelium undergoes gradual transitions from _________ to __________.
pseudo-stratified to columnar to cuboidal to squamous
esophagus to stomach has a sharp change in epithelia from _________ to ___________
stratified squamous to simple columnar
Four junctions in the GI tract that are characterized by abrupt changes in the mucosal lining:
• Gastro-esophageal junction
• Gastro-duodenal junction
• Ileo-cecal junction
• Recto-anal junction
• Gastro-esophageal junction
at the transition from esophagus to stomach
Gastro-duodenal junction
at the transition from stomach to small intestine
• Ileo-cecal junction
at the transition from small intestine to large intestine
Recto-anal junction
at the transition from rectum to anus
The first three junctions have a sphincter of smooth muscle that controls the passage of material across the junction.
Gastro-esophageal junction
Gastro-duodenal junction
Ileo-cecal junction
controls the passage of material across the junction
sphincter
two basic structures to increase its surface area
Glands and outward folding into the lumen of the GI tract
It is where the epithelia invaginates toward and occasionally into the sub-mucosal layer. .
glands
Glands are found in the ff organs.
stomach, small intestine and colon
The second structure involves outward folding into the lumen of the gastrointestinal tract of the mucosal and even sub-mucosal layer. These structures are found in the _________.
small intestine
Segments of the Gastrointestinal Tract
Esophagus
Stomach
Gastric glands
Cells of gastric glands
Parietal cells
It is a muscular tube that transports food from the pharynx to the stomach.
esophagus
Esophagus is lined by a ___________ and has a prominent muscularis mucosa and thick muscularis externa
stratified squamous epithelium
The esophagus ends in what junction?
gastro-esophageal junction
It is notable because the epithelium transitions from stratified squamous in the esophagus to simple columnar epithelium in the stomach
gastro-esophageal junction
The ________ is a distinct layer of smooth muscle that separates the esophagus from the stomach.
lower esophageal sphincter
It allows coordinated movement of food from the esophagus into the stomach while preventing reflux of acidic gastric fluids into the esophagus.
sphincter
mechanically and chemically digests food
stomach
The mixture of food, enzymes and acid generate a fluid mass called ______.
chyme
The stomach is functionally divided into four functional regions: what are these?
cardia, fundus, body and antrum.
It controls passage of chyme from the stomach into the duodenum which is the initial segment of the small intestine.
pyloric sphincter
Cardia
Mucus and bicarbonate
Body
Mucus
Bicarbonate
HCl
Pepsin
Antrum
Mucus
Bicarbonate
Pepsin
stomach mucosa is found in prominent folds called ____
rugae
It allows for distension of the stomach after a large meal.
Rugae
The functional unit of the stomach
gastric gland
It contains secretory cells that release enzymes or acid into the lumen of the stomach and endocrine cells that mediate communication between the sections of the stomach to regulate the activity of the secretory cells in the epithelium.
Gastric glands
It also releases hormones that regulate the activities of cells in other organs.
endocrine cells
begins at the gastric pit which opens to the lumen of the stomach
gastric gland
deepest portion of the gland called the ________
base
Both of which protects the stomach epithelium from the damaging effects of acid.
mucus and bicarbonate ions
It coats the surface of stomach epithelium and traps bicarbonate which neutralizes acid in the stomach before it can damage the epithelium.
Mucus
It secrete hydrochloric acid and intrinsic factor, which is important for the absorption of vitamin B12 in the ileum.
Parietal cells
Parietal cells secrete what?
hydrochloric acid and intrinsic factor
Hydrochloric acid and intrinsic factor is important for the absorption of ________ in the ileum.
vitamin B12
It creates a low pH environment in the lumen of the stomach which serves two main functions.
Hydrochloric acid
Two main functions of hydrochloric acid
The first is to activate digestive enzymes such as pepsin. A low pH environment is also inhospitable to bacteria and therefore limits proliferation of bacteria and the risk of infection
These are usually found in the isthmus region of the gastric gland. In H&E-stained samples, these cells have a characteristic “fried-egg” appearance, with a basophilic, centrally located nucleus and a rather eosinophilic cytoplasm.
Parietal cells
Parietal cells are found exclusively in the ______ section of the _______.
body
stomach
The apical surface of parietal cells forms a narrow channel called a ________.
canaliculus
It increase acid production before and during eating. Three molecules are primarily responsible for stimulating parietal cells to increase the secretion of HCl.
Parietal cells
It is released by the vagus nerve onto the surface of parietal cells.
Acetylcholine
It is produced by endocrine cells (ECL) in the body region of the stomach.
Histamine
It acts in a paracrine fashion.
Histamine
It is produced by G cells in the antral region of the stomach and the duodenum (initial segment of the small intestine).
Gastrin
protein kinases, all of which ultimately increase in acid production.
Protein Kinase A and Protein Kinase C
It also stimulate ECL cells to produce histamine.
acetylcholine and gastrin
Have both direct and indirect effects on acid production
acetylcholine and gastrin
What triggers release of acetylcholine, gastric and histamine?
Stimulation of acid production proceeds in three phases: cephalic, gastric and intestinal.
It is associated with the sight, smell, taste and even thought of food. Swallowing is also part of this phase.
Cephalic phase
Stimuli in the cephalic phase trigger ____________ via the vagus nerve and its release of acetylcholine
acid production
three phases
cephalic, gastric and intestinal
It stimulate acid production through physical and chemical mechanisms.
gastric phase
The entry of food into the stomach causes distention which triggers the vagus nerve to release _________.
acetylcholine
In addition, the presence of digested protein and amino acids in the antrum region of the stomach stimulates G cells to release _____.
gastrin
Digested protein and amino acids trigger G cells in the duodenum to release gastrin.
intestinal phase
It inhibits acid production in parietal cells.
somatostatin
These are found in the base of the gastric glands and produce pepsinogen, which is stored in large apical secretory granules.
Chief cells
These are found in the base of the gastric glands and produce pepsinogen, which is stored in large apical secretory granules.
Chief cells
Chief cells produce what?
Pepsinogen
After pepsinogen is secreted, it is converted by the acidic environment of the stomach to _______ which is an active ________.
pepsin
protease
It stimulate chief cells to release pepsinogen by activating pathways that increase cytosol IC calcium
acetylcholine and gastrin
The mucosa in the body section contains __________ that produce histamine.
enterochromaffin-like (ECL) cells
The antrum also contains ______ that release somatostatin which inhibits acid secretion by parietal cells.
D cells
It is a circumferential ring about 3 centimeters deep distal to the gastro-esophageal junction.
cardia
Its glands tend to be convoluted and are lined primarily by mucus-secreting cells that lubricate the incoming food and protect the lining of the stomach near the gastro-esophageal junction.
Cardia
Below the glands of the mucosal layer are the ______ and ________, which are responsible for support and folding, respectively.
lamina propria and muscularis mucosa
It is the main part of the stomach and is bounded by the greater and lesser curvatures.
body
Its glands are straight with limited branching and are lined by a smaller population of mucus-secreting cells than those of the cardia.
The ____ and _______ contain large numbers of parietal cells whereas the base contains chief cells and enterochromaffin-like (ECL) cells that release hormones. The muscularis mucosa and submucosa are also visible.
neck and isthmus
It is the distal third of the stomach. It possesses glands with deeper pits and large amounts of coiling and branching.
antrum
These glands contain many mucus-secreting cells, D-cells, and G-cells but lack parietal cells.
Antrum
The _________ is connected to the initial segment of small intestine by short section of stomach called the ________.
antrum
pylorus
It is responsible for the continued digestion of food and absorption of nutrients and is divided into three segments that have slightly different structures and functions. The first segment is called the ______ which is followed by ________ and then ______.
Small Intestine
duodenum
ileum
It digest and absorb nutrients, contain microvilli along their apical surfaces.
enterocytes
These are small projections of the cell membrane that are supported structurally by actin filaments.
microvilli
It increases the surface area of the apical cell membrane to generate greater capacity for digestion and absorption of nutrients.
Microvilli
finger-like projections of the epithelium and lamina propria called _______
villi
one region of the small intestine contains outward foldings of submucosa called ________ which creates a tree-like structure with each branch a villus.
Plicae circulares
All sections of small intestine contain there.
villi
Within the lamina propria is a central lymphatic vessel known as a _____, which is crucial for the absorption of lipids from the intestine
lacteal
It digest macromolecules and absorb nutrients.
Enterocytes
It secretes mucus which protects the epithelial layer.
Goblet Cells
The base of a villus that is closest to the submucosa is known as the _______
crypt of Lieberkuhn
It appear spotted and eosinophilic in H&E stained samples, support the host defense against microbes by releasing several different types of antimicrobial peptides that prevent the growth of enteric pathogens. In addition, it also nurture the stem cells of the epithelium.
Paneth cells
Segments of the Small Intestine
Duodenum
Jejunum
Ileum
It contains the same wall layers seen in the previous portions of the GI tract:
mucosa, submucosa, and muscularis externa. The mucosa and lamina propria form long villi. The epithelial cells of the mucosa contain enzymes that facilitated digestions of large macromolecules.
Duodenum
In addition, it receives digestive enzymes produced in the pancreas. It can be distinguished from the other segments of the small intestine by the presence of glands within its submucosa called Brunner’s glands. The cells in the glands secrete an alkaline mucus that neutralizes the pH of chyme from the stomach and protects the epithelium of the duodenum.
A region of tremendous nutrient absorption and to support this absorption creates the largest surface area of the three segments of the small intestine.
Jejunum
It has the shortest villi and is characterized by abundant Peyer’s patches in the submucosa.
ileum
These are diffuse lymphoid tissue that play an important immunological role in sampling the contents of the GI tract.
The small intestine ends with the ileo-cecal junction
Peyer’s patches
processes the indigestible material that comes from the small intestine. It absorbs sodium, chloride and water to concentrate waste material that is formed into feces.
Large Intestine or colon
It can either absorb or secrete potassium and absorbs vitamins.
large intestine
The large intestine feeds into the ________, which stores the feces and has a columnar epithelium with abundant goblet cells. Feces pass out of here, through the anus, and out of the body.
The ________ is characterized by a stratified squamous epithelium that undergoes a gradual transition to skin containing sebaceous and apocrine sweat glands.
features an important change in epithelial structure. The rectum is characterized by the same columnar epithelium that lines the majority of the gastrointestinal tract’s secretory and absorptive areas. The anus, on the other hand, has a stratified squamous epithelium that provides a greater deal of protection to the underlying tissue.
Recto-Anal Junction
pancreas comprises two functional units
Exocrine and endocrine pancreas
The largest is the ________ portion that secretes digestive enzymes and bicarbonate. The second is the _______ which secretes hormones that regulate plasma glucose levels (e.g. insulin, glucagon, etc.).
exocrine
endocrine pancreas
exocrine pancreas has two main cell types
Acinar cells and Duct cells
It synthesize and secrete digestive enzymes.
Acinar cells
Mainly secrete fluid rich in bicarbonate
duct cells
The acinar cells form a small cluster called an ______ with their apical surfaces facing a central lumen.
acinus
A group of acini form a _________. Ducts from different acini in a lobule merge to and empty into interlobular ducts
lobule
