Looks like no one added any tags here yet for you.
What are the major structures included within the GI tract?
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
What are the major structures outside of the GI tract?
Salivary glands
Pancreas
Biliary system (liver, gallbladder, and bile ducts)
How long is the GI system from the mouth to the anus?
7 meters
What are the 5 main functions of the GI system?
Motility
Secretion
Digestion
Absorption
Elimination
What is another name for the oral cavity?
Mouth
What is the significant of the oral cavity?
Point of entry for nutrients
Site of initial breakdown of nutrients into a usable form
Food is broken down and moistened by saliva
What are the main functions of saliva?
Moistens food and allows the tongue to convert a mouthful of food into a bolus that can be swallowed easily
Allows for taste perception
Contains salivary amylase/ptyalin (a digestive enzyme) that initiates carbohydrate digestion by breaking down polysaccharides (AKA starch) into dextrin and maltose
What are the three types of salivary glands?
Parotid
Submandibular
Sublingual
What is another name for the pharynx?
Throat
What are the three parts of the pharynx?
Nasopharynx
Oropharynx
Laryngopharynx
What structure separates the nasopharynx from the oropharynx?
soft palate
What are the functions of the pharynx?
Serves as the entry way for the respiratory and GI systems
Transports food to the esophagus
Protects airway from aspiration of food particles via epiglottis
Swallowing via peristaltic waves
What is the length of the pharynx?
12 cm
What is the length of the esophagus?
25 cm
What is the function of the esophagus?
Initiates the progress of food through the gut after ingestion
What is food facilitated by in the esophagus?
Mucus secreted by cells in the epithelial lining
What kind of epithelium is present in the esophagus?
Stratified squamous epithelium
What propels nutrients to the stomach?
Strong muscular contractions and gravity (when the body is in an upright position)
Where is the lower esophageal sphincter (LES) located?
At the lower end of the esophagus, about 2 to 5 cm above its juncture with the stomach
Why does the LES remain tonically constricted, in contrast to the middle and upper portions of the esophagus?
To prevent the highly acidic gastric contents from moving in a retrograde motion (refluxing) back into the esophagus
What can happen if the LES is not working properly?
It can lead to reflux (GERD) or heartburn/dyspepsia
What is the function of the stomach?
An elastic food reservoir for food, mixing, and initial digestion of proteins (pepsin)
What is the normal capacity of the stomach?
1000 to 1500 mL
What areas of the stomach absorb nutrients?
Cardia
Fundus
Body
Antrum
Pylorus: pyloric sphincter?
What area of the stomach does not have rugae?
the antrum
What is the function of the pyloric sphincter?
It is a muscular sphincter between the stomach and duodenum that serves to control gastric emptying and limits the reflux of bile from the small intestine
What are the 4 specialized cells in the stomach?
Chief cells
Parietal cells
Mucous cells
Gastrin cells
What is the function of chief cells?
Produce pepsinogen (the inactive form of the enzyme pepsin)
What is the function of parietal cells?
Produce hydrochloric acid and intrinsic factor
What is the function of mucous cells?
Produce a layer of alkaline mucus to shield the stomach wall and neutralize the acidity in the immediate area of the lining
What is the function of gastrin cells?
Have surface microvilli that monitor intragastrical pH
How long is the small intestine?
~5 to 6 meters long (the longest portion of the GI tract)
What is the function of the small intestine?
Digestion and absorption
What 2 enzymes are secreted in the small intestine?
Secretin and cholecystokinin
What are the 3 sections of the small intestine in order?
Duodenum
Jejunum
Ileum
What is the largest section of the small intestine?
Ileum
What is the smallest section of the small intestine?
Duodenum
In the duodenum, what is the relation to the pancreas?
The pancreas delivers digestive enzymes and bicarbonate to the duodenum
In the duodenum, what is the relation to the gallbladder?
The gallbladder delivers bile salts to the duodenum
What is the function of the ileocecal sphincter?
Normally closes so that contents of the large intestine cannot reflux back into the small intestine
Opens in response to peristaltic contractions moving intestinal contents towards the large intestine
What is plicae circulares?
Circular folds of a mucous membrane on the entire inner wall of the small intestine
Permanent ridges that do not lose their elasticity when the intestine is distended.
What is intestinal villi?
Fingerlike projections in the lining of the small intestine
What is the function of intestinal villi?
Serve to increase the surface of the intestine for digestion and absorption of nutrients
What are microvilli?
Microscopic projections on each of the intestinal villi
What do microvilli contain?
They are covered by a fuzzy coat called a brush border, which contains many digestive enzymes
What are the Crypts of Lieberkuhn?
AKA intestinal glands
Found between the intestinal villi
Secretes fluid into the lumen of the intestine, which is quickly reabsorbed by the villi
How much fluid do the Crypts of Lieberkuhn secrete a day?
About 2 L of fluid daily
What reabsorbs the fluid that the Crypts of Lieberkuhn secrete?
The villi of the small intestine
What do goblet cells and Brunner cells secrete?
Large amounts of mucus
What is the large intestine?
A muscular tube 1.5 m long and 6.5 cm in diameters that forms a frame around the small intestine
What is the function of the large intestine?
What is the appendix?
The colon is considered what part of the large intestine?
From the cecum to the rectum
Does the colon contain villi? Digestive enzymes?
No to both
What does the large intestine absorb?
Water and electrolytes
What cells in the large intestine produce mucus?
Goblet cells lining the glandular crypts in the surface epithelium of the colon
What is peristalsis? Is it a propulsive or mixing movement? Is it in one or two directions? What muscles are involved? Where does it occur?
The basic propulsive movement of the GI tract
Moves in one direction → downward
Involves longitudinal and circular muscles
Occurs in the whole GI tract
What is segmentation? Is it a propulsive or mixing movement? Is it in one or two directions? What muscles are involved? Where does it occur?
Mixing movement
Both directions
Involves circular muscle
Occurs in stomach, small intestine, and large intestine
Does the PNS or the SNS increase motility/secretions?
PNS increases motility/secretions
CNS decreases motility/secretions
What is also known as the “second brain”?
GI motility is regulated by...
the enteric nervous system, the ANS, and hormonal mediators
The myenteric branch of the enteric nervous system contains what plexus?
The Auerbach plexus
Where is the myenteric branch located?
Between the longitudinal and circular muscular layers
What does the myenteric branch control? How?
GI movements
Stimulation of the myenteric plexus → activity of GI tract increases →
Tonic contracts of the intestinal wall increase
Rhythmic contracts increase in intensity and rate
Velocity of conduction of excitatory waves along the intestinal wall increases
The submucosal branch of the enteric nervous system contains what plexus?
The Meissner plexus
Where is the submucosal branch located?
In the submucosa
What does the submucosal branch control?
Secretion and sensory functions
What is gastrin secreted by and when?
The stomach mucosa (G cells) when food enters the stomach
What is the function of gastrin? What does it cause?
Increases stomach motility
Stimulates the exocrine (secretory) cells of the gastric glands to produce their specific products (HCl)
Causes increased constriction of the LES
What cells does gastrin primarily provoke? What do these provoked cells release?
Enterochromaffin-like cells (ELC)
Provokes ELCs to release histamine → induces parietal cells to release acid
What is cholecystokinin secreted by?
Jejunum mucosa (I cells)
When is cholecystokinin secreted?
When fat enters jejunum
What does cholecystokinin stimulate/what is its function?
Stimulates pancreatic secretion
Helps regulate gastric emptying and bowel motility
Induces satiety
Increase contractility of gallbladder
What is secretin secreted by?
The mucosa of the duodenum
When is secretin secreted?
In response to the entry of acidic gastric juice from the stomach
What does secretin stimulate/what is its function?
Stimulates pancreatic fluid and bicarbonate secretion → neutralizes acidity of intestinal contents
Does secretin increase or decrease motility?
Mild inhibitory effect on motility in most of the GI tract (decreases motility)
Where is gastric inhibitory peptide (GIP) released from?
The upper portion of small intestine
What is the release of gastric inhibitory peptide (GIP) in response to?
Fat in chyme and carbohydrates
Does gastric inhibitory peptide (GIP) increase or decrease stomach motility?
Decreases stomach motility
What is ghrelin secreted by?
The stomach
What are the function(s) of ghrelin?
Increases appetite
Stimulates growth hormone secretion
Produces weight gain
Regulates mealtime hunger and meal intitiation
Salivary amylase is also known as what?
Ptyalin
What are the 3 major functions of the salivary glands?
Moistening actions allows tongue to convert food into a bolus to allow easy swallowing by moistening
Moistening action changes dry food into a solute form to allow for taste perception by tongue
Digestive enzyme (salivary amylase) initiates carbohydrate digestion by breaking down polysaccharides (starch) into dextrin and maltose
What 2 cells types fall under the category of gastric glands?
Chief cells and parietal cells
What do chief cells secrete?
Pepsinogen
What do parietal cells secrete?
Hydrochloric acid (HCl) → converts pepsinogen to pepsin
Intrinsic factor (IF) → increase vitamin B12 absorption
Parietal cell secretion is stimulated by what 3 hormones?
Acetylcholine
Gastrin
Histamine
What is the function of peptidase?
Digests proteins
What is the function of lipase?
Digests lipids
What is the function of lactase?
Digests sugars
In the pancreas, what is the function of amylase?
Digests sugars
In the pancreas, what is the function of trypsin?
Digests proteins
In the pancreas, what is the function of chymotrypsin?
Digests proteins
In the pancreas, what is the function of lipase?
Digests lipids
In the pancreas, what is the function of bicarbonate?
Neutralizes stomach acid
In the gallbladder, what is the function of bile?
Digests lipids
What is digestion?
The process of converting large molecules to simpler forms
What two processes make up digestion?
Mechanical and enzymatic (chemical)
Why is digestion necessary?
It is a necessary prelude to absorption → only simple molecules can cross the intestinal epithelia