Digestive system Flashcards
Digestive system function
Process food molecules and move them into the blood
What is the flow of the digestive tract?
Gastrointestinal (GI) tract –> alimentary canal –> digestive tract –> gut
Organs of the digestive system
Mouth, pharynx, esophagus, stomach, small intestine, large intestine
Accessory organs of the digestive system
Salivary glands, liver, gallbladder, pancreas
What do accessory organs help with?
Assisting with digestion but do not carry food at any time
Membrane
2 layers (epithelium lines space; CT nourishes epithelium)
Mucosa (mucous membrane)
Lines lumen of GI tract, has simple columnar for absorption/secretion
What is the CT layer in the mucosa?
Lamina propria
Serosa (serous membrane)
Lines peritoneal cavity, mesothelium is simple squamous for sliding around
What is the deep lining CT layer of the serous cavity?
Visceral peritoneum
What is the outer lining CT layer of the serous cavity?
Parietal peritoneum
Mesentery
Double layer of peritoneum connecting parietal and visceral peritoneum
What does the mesentery do?
Supports GI tract, carries vessels and nerves, stores fat
Mesentery order
Lumen, mucosa etc., visceral peritoneum, peritoneal cavity, parietal peritoneum, mesentery
During development, some organs in the abdominopelvic cavity become buried in the body wall, what is this?
Secondarily retroperitoneal (ex: pancreas)
Does the organ still have peritoneum after becoming buried?
Yes on one side and adventitia on other side
What are organs called that keep their mesentery?
Intraperitoneal (ex: stomach)
Mucosa
Closest to lumen
Epithelial layer of mucosa
Most simple columnar
Endocrine cells
Release product into blood (inside body)
Exocrine cells
Release product into lumen (“outside” body) (ex: mucus)
What are other epithelial cells used for in the mucosa?
Absorption
What is the rate of cell turn over of epethelium in the mucosa?
RAPID
Muscularis mucosae
A layer of smooth muscle unique to the digestive system
How does the muscularis mucosae dislodge sharp objects?
Twitching
Submucosa
Connective tissue (tough but flexible)
Submucosal nerve plexus
Network of nerves = part of enteric nervous system (in submucosa)
What else does the submucosa contain other than the submucosal nerve plexus?
Blood/lymph vessels, exocrine glands
Muscularis externa
Smooth muscle layer
Myenteric nerve plexus
Part of enteric nervous system
What is an example of a longitudinal muscle?
Peristalsis = pushes food along GI tract
Serosa
Serous membrane (visceral serosa or visceral peritoneum)
How does the serosa produce fluid?
Produces serous fluid by filtration (mostly)
What is the epithelium in the serosa?
Mesothelium
What are the steps of food processing?
Ingestion, mechanical breakdown, secretion, chemical digestion, absorption, propulsion, defecation
Ingestion
Food taken into mouth
Mechanical breakdown and mixing
Breaking down food into smaller parts = more surface area exposed to chemical action
Secretion
Ex: secretes enzymes and mucus
Chemical digestion
Breaking down large nutrient molecules (proteins) into smaller ones (amino acids)
Absorption
Small molecules actively taken up by epithelium = moves into blood or lymph
Propulsion
Move food along tract by swallowing and peristalsis (happens throughout process)
Defecation
Eliminate indigestible material from anus
Proximal describes the ______ of the GI tract
Beginning (following the tube)
Distal describes the ______ of the GI tract
End (following the tube)
Mouth (oral cavity)
Chewing forms bolus of food (has nonkeratinized stratified squamous)
Salivary glands
Secrete saliva into mouth (includes enzymes to initiate carbohydrate digestion in mouth)
Pharynx
Skeletal muscles propel food through pharynx = voluntary (has nonkeratinized stratified squamous)
Esophagus
Delivers food from pharynx to stomach (lined by nonkeratinized stratified squamous)
Where is the esophagus located?
Mediastinum (area between lungs and behind heart)
Where does heart burn stem from?
The esophagus
What kind of muscles does the esophagus have?
Smooth AND skeletal muscle (all involuntary) = peristalsis
Where is the cardiac sphincter?
Cardiac sphincter at exit into stomach (circular muscle layer of muscularis externa is thick)
What does the structure of the esophagus help with?
Preventing reflux from stomach
What does a hiatal hernia cause?
The esophagus can’t close which leads to gastroesophageal reflux disease
Stomach
Store and churn food into chyme (for mechanical breakdown) where then the chemical digestion of proteins begins
Secreting acid (HCI)
Steralizies and prevents infection; separates molecules (EXOCRINE)
Secreting digestive enzyme
Breaks down proteins (EXOCRINE)
Secreting mucus and bicarbonate
EXOCRINE
Secreting gastrin hormone (messenger via blood)
Stimulates acid secretion (ENDOCRINE)
Absorption
Some water and ions, NO NUTRIENTS (molecules broken down for energy)
Pyloric sphincter
Thickened CIRCULAR muscle at the distal end of stomach = evens out flow of chyme to small intestine
Rugae
Folds of mucosa and submucosa = allows distention
What is muscularis externa third muscle layer?
Oblique (deepest layer)
Mucosa in stomach
Simple columnar, surface epithelium secretes bicarbonate
What is an example of bicarbonate that is secreted in the stomach?
Alkaline = neutralizes acid and mucus
Are there goblet cells in the stomach?
NO!
Gastric glands (mucous neck cells)
Secrete bicarbonate and mucus
Parietal cells (blue)
HCI (acid)
Chief cells (purple)
Pepsinogen (inactive enzyme) begins process of breaking down protein
Enteroendocrine cells (green)
Gastrin (hormone) secrete hormones and travel thru blood supply
Stem cells
Between pit/gland boundary
GI tract function (1)
Chemical digestion (primary site of digestion)
GI tract function (2)
Absorption (primary site of nutrient absorption)
GI tract function (3)
Secretion
GI tract function (4)
Mixing by segmentation (produces segments of contraction at a time)
Duodenum
Shortest part of small intestine that receives secretion from pancreas and bladder
Duodenal glands
(in submucosa) Secrete bicarbonate which neutralizes stomach acid and mucus
Jejunum
Most absorption occurs here
Ileum
Has peyer’s patches and is in lamina propria and submucosa
Peyer’s patches
Aggregated lymphoid nodules
Small intestine epithelium
Simple columnar
Plicae circulares (circular folds)
Folds of mucosa and submucosa that slow down the passage of chyme and increase surface area
Plicae circulares are permanent unlike what?
Rugae
What is the increased surface area in circular folds good for?
Increased surface area to absorption surface = more proteins embedded
Villi
Projections of mucosa
What does villi do?
Increase surface area for absorption
Where are the nutrients absorbed into villi going to?
From gut lumen to blood or lymph
What are the sugars and amino acids absorbed by in the villI?
Blood capillaries
What are the lipids absorbed by in the villi?
Lacteals (specialized lymph vessels)
Microvilli
Tiny bumps on individual cells
Absorptive cells
Folding of plasma membrane of enterocytes
What is microvilli’s functional benefit?
Adding surface area for speed of absorption
Goblet cells
Lubricant for passage of mucus (secretion)
Where are the intestinal crypts (glands)?
Hidden in mucosa, between villi
What are intestinal crypts good for?
Secreting intestinal juice and maintaining liquid state of chyme
Large intestine function (1)
Absorb water, ions, some vitamins. NO NUTRIENTS!
Large intestine function (2)
Passageway for materials that cannot be absorbed = feces
Where is the cecum?
Separated from small intestine by ileocecal valve
Cecum
Prevents backflow into small intestine
Vermiform appendix
Has lymphoid tissue
Appendicitis
Inflamed appendix
Peritonitis
Inflammation of the peritoneum (ruptured appendix)
Ascending colon
Travels across transverse and down descending
Transverse colon
Travels across
Descending colon
Traveling down
Sigmoid colon
Right before the rectum
Rectum
Muscular organ specialized for defecation
Anal canal
Opening controlled by internal anal sphincter (smooth muscle) and external anal sphincter (skeletal muscle)
Teniae coli
Three thickened bands of longitudinal muscle layer
Haustra
Ball shapes in large intestines to break up feces = due to contraction of teniae coli
Epithelium type in wall of large intestine
Mostly simple columnar
Colonocytes
Absorptive cells
What do goblet cells do in the wall of the large intestine?
Secrete mucus
What epithelium is in the distal part of the anal canal?
Nonkeratinized stratified squamous
MALT
Mucosa associated lymphoid tissue
Intestinal crypts protect what in the large intestine?
Lining (secretes mucus/stem cells)
