M5 U1 Digestive System Flashcards
The primary function of the digestive system
bring essential nutrients into the internal
environment
the process of altering the chemical and
physical composition of food
Digestion
The process of digestion depends on
-endocrine and exocrine secretions
-controlled movement of ingested food
The process of complex foods taken in
INGESTION
Complex nutrients are broken down into simpler nutrients
From the breakdown of large chunks of food into smaller bits, and move it along the gastrointestinal tract
DIGESTION
Movement by the muscular components of the digestive tube
MOTILITY
- Release of digestive enzymes to breakdown large molecules into small molecules in the gastrointestinal tract
SECRETION
Movement of nutrients through the mucosa into the internal environment
ABSORPTION
The material not absorbed must then be excreted to make room for more material
ELIMINATION
gastrointestinal tract is also known as
alimentary tract (alimentary canal)
tube open at both ends formed by the main
organs of the digestive system
GASTROINTESTINAL TRACT
provides the body with a continual supply of water, electrolytes, vitamins, and nutrients.
GASTROINTESTINAL TRACT
parts of the mouth
Lips
Cheeks
Tongue
Teeth
Uvula
Gums
Hard and soft palate
Salivary glands
Food material is ingested into the oral (buccal)
cavity and is reduced by
chewing/mastication
anterior teeth (incisors) provide
strong cutting action
posterior teeth (molars) provide
grinding
serve to mix food with saliva in preparation of swallowing
chewing movements/ mastication
rate of digestion is dependent on the
total surface area exposed to the digestive secretions
located inferior and anterior to the ears, between the skin and the masseter muscle
Parotid gland
found in the floor of the mouth; they are medial and partly inferior to the body of the mandible.
Submandibular gland
Beneath the tongue and superior to the submandibular glands.
Sublingual gland
THREE MAJOR SALIVARY GLANDS
Parotid gland
Submandibular gland
Sublingual gland
Secreted by the salivary glands
Salivary amylase
Initiates the breakdown of starch
Salivary amylase
secreted by lingual glands in the tongue
Lingual lipase
becomes activated in the acidic environment of the stomach and thus starts to work after food is swallowed
Lingual lipase
It breaks down dietary triglycerides (fats and oils) into fatty acids and diglycerides
Lingual lipase
serves as an air passageway that propels mucus
Nasopharynx
Nasopharynx is lined with
pseudostratified ciliated columnar epithelium
serves as a passageway for both air and swallowed food
Oropharynx
Oropharynx is lined with
nonkeratinized stratified squamous epithelium
opens into the esophagus (food tube) posteriorly, and the larynx (voice box) anteriorly
Laryngopharynx
Laryngopharynx is lined with
nonkeratinized stratified squamous
epithelium
The process of swallowing
DEGLUTITION
three stages of deglutition
Oral stage
Pharyngeal stage
Esophageal stage
esophagus to stomach
Esophageal stage
oropharynx to esophagus
Pharyngeal stage
mouth to oropharynx
Oral stage
From here on, swallowing becomes entirely – or almost entirely – automatic and ordinarily cannot be stopped
ORAL STAGE
functions primarily to conduct food
rapidly from the pharynx to the stomach
esophagus
lubricates the bolus and reduces friction.
Mucus secreted by esophageal glands
The movement of food bolus down the esophagus is accomplished through
peristalsis
A long tube that extends from the oropharynx into the stomach.
ESOPHAGUS
prevents food and secretions from leaking into the windpipe. Also prevents air from entering during respiration.
Upper esophageal sphincter
help prevent significant reflux of stomach contents into the esophagus
Lower esophageal sphincter (cardiac sphincter)
A progression of coordinated contractions and
relaxations of the circular and longitudinal layers of the muscularis
Occurs in the esophagus, stomach, small and large intestine.
PERISTALSIS
The backward flow of stomach acid up through the LES and into the lower esophagus.
ACID REFLUX
chronic, more severe form of acid reflux.
Gastroesophageal reflux disease
Hydrochloric acid (HCl) from the stomach contents can irritate the esophageal wall, resulting in a burning sensation that is called
heartburn
Storage of large quantities of food until the food can be processed in the stomach, duodenum, and lower intestinal tract
STOMACH
Mixing of this food with gastric secretions until it forms a semifluid mixture called
chyme
adult stomach can typically hold
1 - 1.5 liters
four regions of stomach
- Cardia
- Fundus
- Body
- Pyloric part
When the stomach is empty, the mucosa lies in large folds called
rugae (wrinkles)
the muscle sphincter connecting the stomach to the duodenum
Pyloric sphincter
Forward and backward movement of
gastric contents, mixing food with gastric juices to form chyme.
CHURNING
Peristaltic waves move gastric contents from the body of the stomach down into the antrum
propulsion
food particles are forced back
into the body of the stomach
retropulsion
Secreted by parietal cells
Needed for absorption of vitamin B12
Intrinsic factor
Secreted by parietal cells
H+ and Cl- are secreted separately
Kills microbes in food
Denatures proteins
Creates an acidic environment that converts
pepsinogen into pepsin
Hydrochloric acid
Secreted by chief cells
Converted into pepsin, the most important enzyme in gastric juice
Pepsin converts proteins into smaller peptides
Pepsinogen
Secreted by chief cells
Splits triglycerides into fatty acids and monoglycerides
Gastric lipase
-Hormone secreted by G cells
-Stimulates parietal cells to secrete HCl and chief cells to secrete pepsinogen
-Contracts lower esophageal sphincter, increases motility of stomach, and relaxes pyloric sphincter
Gastrin
occur when the stomach
has been empty for several hours or more.
Hunger contractions
person sometimes experiences mild pain in the pit of the stomach during hunger contractions
hunger pangs.
forcible expulsion of the contents of the upper GI tract (stomach and sometimes
duodenum) through the mouth.
VOMITING
characterized by overeating at
least twice a week followed by purging by
self-induced vomiting, strict dieting or fasting,
vigorous exercise, or use of laxatives or
diuretics
Bulimia nervosa
involved in both digestion and absorption.
SMALL INTESTINE
-shortest, C-shaped tube arising from the pyloric sphincter to the jejunum
- Where the pancreas, liver, and
gallbladder release their secretions
Duodenum
longest region that ends at the
ileocecal sphincter
Ileum
___contractions “chop” the chyme two to three times per minute, in this way promoting progressive mixing of the food with secretions of the small intestine.
segmentation
___contractions “chop” the chyme two to three times per minute, in this way promoting progressive mixing of the food with secretions of the small intestine.
segmentation
Secreted by the acinar cells of the pancreas
Contains various enzymes
PANCREATIC JUICE
- secreted as trypsinogen (inactive form)
- Converted by enterokinase in the intestinal tract.
- activates chymotrypsin, pancreatic lipase, nucleases, and amylase
Trypsin
starch-digesting enzyme
Pancreatic amylase
Triglyceride-digesting enzyme
Pancreatic lipase
Digest RNA and DNA into nucleotides
Ribonuclease and deoxyribonuclease
Secreted by the liver and stored and
concentrated by the gallbladder
BILE
Contains lecithin and bile salts that help break
down large drops of fat into smaller droplets,
making fat more digestible
BILE
- contain sodium bicarbonate which helps
neutralize chyme - contain waste products for excretion
BILE
-Produced by goblet cells in the intestinal
mucosa
-Buffers and lubricates material in the intestinal
lumen
-Increased pH of chyme also allows optimum
enzyme function
INTESTINAL JUICE
If bile contains either insufficient bile salts or
lecithin or excessive cholesterol, the cholesterol
may crystallize to form
gallstones
DIGESTION OF CARBOHYDRATES
Salivary amylase and pancreatic amylase
DIGESTION OF PROTEINS
Pepsin (stomach) and Trypsin (pancreatic juice)
DIGESTION OF LIPIDS
Lingual lipase, gastric lipase, and pancreatic lipase
DIGESTION OF NUCLEIC ACIDS
- Ribonuclease and deoxyribonuclease
Absorption of materials occurs via
diffusion
facilitated diffusion
osmosis
active transport
Any undigested or unabsorbed material
left in the small intestine passes on to
the
large intestine
enhance absorption by increasing surface area
and causing the chyme to spiral
The circular folds of the small intestine (plica)
vastly increases the surface area of the epithelium available for
absorption and digestion.
large number of villi
terminal portion of the GI tract.
large intestine
overall functions of the large intestine
completion of absorption
-production of certain vitamins
-formation of feces
-expulsion of feces from the body
intensifies peristalsis in the ileum
and forces any chyme into the cecum
gastroileal reflex
remain relaxed and become distended while they fill up.
When the distension reaches a certain
point, the walls contract and squeeze the
contents
Haustral churning
strong peristaltic wave that begins at about
the middle of the transverse colon and quickly
drives the contents of the colon into the
rectum.
Mass peristalsis
final stage of digestion occurs in the
colon
which gives feces their brown color
stercobilin (simpler pigment of bilirubin)
By the time chyme has remained in the large
intestine 3–10 hours, it has become solid or
semisolid because of water absorption and
is now called
feces
act of expelling feces is called
defecation
increase in the frequency, volume,
and fluid content of the feces caused by
increased motility of and decreased
absorption by the intestines.
Diarrhea
Frequent diarrhea can result in
dehydration and electrolyte imbalances
refers to infrequent or difficult defecation
caused by decreased motility of the
intestines
Constipation
Excessive motility may be caused by
-lactose intolerance
-stress
-microbes that irritate the gastrointestinal mucosa
