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Terms in this set (121)
What is the digestive system?
- breaks down food into forms that can be absorbed and used by cells
- absorbs water, vitamins, minerals
- eliminates wastes
Gastrointestinal Tract (GI Tract)
tube through which food passes while being digested
What is another name for the GI tract?
Where does the GI tract extend to?
begins in mouth and ends with the anus
- food doesn't pass through
- aids digestion
Functions of Digestive System
ingestion, secretion, motility, digestion, absorption, defecation
taking in food
water, acid, buffers (usually alkaline), enzymes
churning and moving through GI tract
physical and chemical breakdown of food
digested products pass from GI tract into blood and lymph
elimination of feces from GI tract
What are the 4 layers of the GI tract?
inner lining of digestive tract
What does the mucosa consist of?
epithelium, lamina propria, muscularis mucosa
simple columnar and nonkeratinized stratified squamous
helps increase surface area for digestion and absorption
- areolar CT
- binds mucosa to muscularis
- blood and lymphatic vessels to absorb food
- submucosal plexus
What is the submucosal plexus?
network of neurons
What is the muscularis layer made up of?
skeletal and smooth muscle
- voluntary swallowing
- voluntary control of defecation
- involuntary contractions
- myenteric plexus
- serous membrane
- superficial layer of organs suspended in abdominal cavity
- visceral peritoneum
Enteric Nervous System (ENS)
consisted of myenteric plexuses and a submucosal plexus
- between circular and longitudinal muscle of muscularis
- motor neurons control motility
- within mucosa
- motor neurons control secretions of mucosal epithelium
interconnect with neurons of myenteric and submucosal plexuses
ENS Sensory Neurons
- supply mucosal epithelium
- detect stimuli in GI tract of lumen
What are the 2 types of sensory neurons of the ENS?
chemoreceptors and mechanoreceptors
Autonomic Nervous System (ANS)
- parasympathetic innervation
- form neural connections with ENS
- sympathetic innervation
GI Reflex Pathways
- regulate GI secretion and motility
- respond appropriately to stimuli detected in lumen of GI tract
- involve ENS, ANS, CNS
the largest serous membrane
lines the abdominal cavity
covers abdominal organs
- organs on posterior abdominal wall
- outside of peritoneal cavity
What are retroperitoneal organs?
What are the 5 peritoneal folds?
greater omentum, falciform ligament, lesser omentum, mesentery, mesocolon
- fatty apron
- from stomach & duodenum to anterior small intestine
attaches liver to anterior abdominal wall and diaphragm
- connects stomach to liver
- pathway for blood entering liver
- binds jejunum and ileum to posterior abdominal wall
- blood & lymphatic vessels, and lymph nodes between double layers
- 2 folds
- carries blood & lymphatic vessels to intestines
- secret saliva
- small glands
- keeps mucous membranes of mouth and pharynx moist
- cleanses mouth and teeth
- increases when food enters mouth
labial, buccal, palatal, lingual
What are the 3 major salivary glands?
- inferior anterior to the ears
- parotid ducts
- floor of mouth
- submandibular ducts
- beneath tongue
- lesser sublingual ducts
chemical digestion of complex carbohydrates
dissolves for taste and digestive rxns
- serous secretion
- salivary amylase
- fluid with salivary amylase
- plus mucus
- thicker mucus fluid
- small amount of salivary amylase
- secretion stops during dehydration
How is salivation stimulated?
feel, taste, smell, sight, sound, thought of food
- skeletal muscle covered with mucous membrane
- upper and lateral surfaces have papillae
project into the mouth and are adapted for mechanical digestion
physical breakdown of food
salivary amylase converts polysaccharides to disaccharides
throat; passageway for food to the esophagus and air to the larynx
connects pharynx to stomach
Upper Esophageal Sphincter (UES)
regulates movement of food from pharynx to esophagus
Lower Esophageal Sphincter (LES)
regulates the movement of food from the esophagus into the stomach
What is the LES also known as?
process of swallowing
steps in swallowing (deglutition)
1. voluntary stage
2. pharyngeal stage
3. esophageal stage
bolus passed to oropharynx
involuntary passage through pharynx into esophagus
involuntary passage of the bolus through the esophagus and into the stomach
Where does peristalsis begin?
J-shaped enlargement of the GI tract in the LES
What are the regions of the stomach?
cardia, fundus, body, pylorus
What is the pylorus region made up of?
pyloric antrum, pyloric canal, pylorus
What are the functions of the stomach?
1. mixes saliva, food, and gastric juice to form chyme
2. reservoir for food before release into small intestine
3. secretes gastric juice
4. secretes gastrin into the blood
breaks down proteins in the stomach
breaks down fats
Mechanical Digestion in Stomach
fundus stores food while it mixes with gastric juice
What are the steps of mechanical digestion?
- gastric emptying
peristaltic waves move from the fundus toward the pylorus
- pyloric sphincter is almost completely closed
- contents too large to pass and are forced back into the body
soupy mixture formed by repeating propulsion-retropulsion
chyme particles are small enough to pass through pyloric sphincter
- enzymes that digest carbohydrates, proteins, fats, and nucleic acids
- bicarbonate to buffers stomach acid
- empties contents into duodenum
What is pancreatic juice made up of?
- mostly H2O
- some salts
pancreatic exocrine cells
2 lobes divided by falciform ligament
major functional cells of the liver, secrete bile
ducts between hepatocytes that collect bile
capillaries that receive O2 rich blood
- stores bile secreted by liver
- a sphincter muscle controls the release of bile from common bile duct
secreted by liver
Where is the bile stored?
What do bile salts play a role in?
emulsification of lipids
pigment released by the liver in bile
What is in the small intestine?
duodenum, jejunum, ileum
True or False: Microvilli increases surface area.
provides a vehicle for absorption of substances from chyme as they come in contact with the villi
Brush Border Enzymes
break down food products
Where are the brush border enzymes located?
surfaces of microvilli on absorptive cells
2 Steps of Mechanical Digestion
Chemical digestion is the digestion of...
- nucleic acids
What are the functions of the colon?
- haustral churning (peristalsis)
- mass peristalsis drives contents of colon into rectum
- bacteria in colon convert proteins into amino acids, break down amino acids, and produce some vitamin B
- absorption of some water, ions, and vitamins
- formation of feces
- distension reaches a certain point
- walls of the haustra contract to squeeze contents onward
a strong peristaltic wave that begins in the transverse colon and quickly drives the contents of the colon into the rectum
How do the last stages of chemical digestion occur?
through bacterial action
- some vitamins
- inorganic salts
- sloughed off epithelial cells
- products of bacterial decomposition
- undigested portions of food
- rectal wall distends
- stretch receptors send sensory nerve impulses to the sacral spinal cord
- motor impulses travel back to the descending colon, sigmoid colon, rectum, and anus
- longitudinal rectal muscles contract and the internal anal sphincter opens
- if the external anal sphincter is voluntarily relaxed, defecation occurs and the feces are expelled
What are the 3 phases of digestion?
What does the cephalic phase prepare?
mouth and stomach for digestion
- smell, sight, thought of initial taste
- activates neural centers
- brain stem stimulates
What are the neural centers?
cerebral cortex, hypothalamus, brain stem
Gastric Phase of Digestion
neural and hormonal mechanisms promote gastric secretion and motility
Intestinal Phase of Digestion
occurs when the duodenum responds to chyme, gastric activity begins through hormones and reflexes
a hormone produced by cells of the intestinal wall. Target organ: the gallbladder. Response: release of bile and slowing of GI motility.
a hormone released into the bloodstream by the duodenum (especially in response to acidity) to stimulate secretion by the liver and pancreas.
THIS SET IS OFTEN IN FOLDERS WITH...
A & P: Chapter 20
A & P: Chapter 27
A & P: Chapter 19
A & P: Chapter 21
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