Digestive System Flashcards
What is the function of the digestive system
To break down food and drink into absorbable nutrients to be used for energy
How long does it take to digest something in average
24 hours
What are the 6 structures of the alimentary canal
The mouth, pharynx, esophagus, stomach, small intestine, and large intestine
What are accessory digestive organs
Organs that act in digestive processes (helps with absorption and makes things to be secreted into the alimentary canal) but food doesn’t pass through the structures
What organs are accessory digestive organs
The tongue, salivary glands, liver, gallbladder, and pancreas
What is ingestion
Putting food into the mouth
What is propulsion
Moving food through the canal (swallowing and peristalsis via smooth muscle)
What is peristalsis
Organized contraction and relaxation of smooth muscle layers to push food through the alimentary canal in one direction
What is mechanical digestion
Physical break down of food particles including chewing (with tongue), churning, and segmentation (in stomach)
What is segmentation
Contraction of smooth muscle to move chyme back and forth to mix it and break down
What is chemical digestion
Break down of food particles using enzymes
What is absorption
Particles (sugars, fatty acids, etc) transported from the canal/lumen into the blood and lymph capillaries
What is defecation
Indigestible products eliminated from body as feces
What is the only intracellular part of digestion
Absorption
What are the layers of the organs in the alimentary canal
The mucosa (lining the lumen), submocosa (support layer of CT), muscularis externa (smooth muscle layer), and serosa/visceral peritoneum (outer surface)
What layers of the alimentary canal have an epithelium
The mucosa and serosa layers
What are the 3 layers of the mucosa
The epithelium, lamina propria, and muscularis mucosa
What does the epithelium of the mucosa do
Produce mucus, absorb, and protect. Also continuous with many digestive (exocrine) glands where enzymes are being made
What are the characteristics of the lamina propria of the mucosa
Loose areolar CT, capillary rich (for absorption), made of mucosa associate lymphoid tissue (MALT) to protect against bacteria
What are the characteristics of the muscularis mucosa
A thin layer of smooth muscle for fine/localized movements
What are the 4 characteristics of the submucosa
Like loose areolar CT but thicker with more collagen fibers for support, highly vascularized (blood supply to mucosa for nutrient absorption), glands connecting to lumen, and submucosal nerve plexus (for control of muscle cells, glandular secretions, etc)
All for absorption and transport
What are the characteristics of the muscularis externa
2 layers of smooth muscle (circular inner layer to squeeze band longitudinal outer layer to shorten for peristalsis and segmentation) and the myenteric nerve plexus
What is the serosa
Serous membrane made of simple squamous epithelium with a thin loose areolar CT found in organs within the abdominal cavity
What’s another name for the serosa
Visceral peritoneum
What is the mesentery
2 layers of serous membrane coming together (neither lining the organ or the cavity)
What is the adventitia
Fibrous CT that forms outer layer of the esophagus (which doesn’t have a serosa) to help anchor
What do nerve plexuses do
Allow for a localized response within visceral organs, partially independent of central nervous system
What does the myenteric nerve plexus do
Controls peristalsis and segmentation within muscularis externa
What does the submucosal nerve plexus do
Controls secretions of glands and muscularis mucosa contractions within submucosa
What is the oral cavity/mouth involved in
Ingestion, mechanical digestion (chewing), and chemical digestion (saliva to break down carbs)
What epithelium lines the oral cavity and why
Stratified squamous because of the abrasion and temperature differences
What other tissue structure is the oral cavity made of
Thin submucosa layer anchored directly to underlying bone
What are the lips
Margin between skin and oral cavity made of keratinized like skin without any sudoriferous or sebaceous glands
How are human teeth characterized
Heterodont dentition (different shapes for different jobs), 20 deciduous/baby (6 months to 6 years), 32 permanent that slowly replace babies
What are the 4 types of permanent teeth
Incisors, canines, premolars, and molars (last set of molars are the wisdom teeth)
What do incisors do and how many are there
4 pairs with 1 root and flat surface good for cutting and shearing food
What do canines do and how many are there
2 pairs with one root good for holding and tearing
What do premolars do and how many are there
4 pairs with 1-2 roots, at least 2 cusps, and a broad rounded surface good for grinding
What do molars do and how many are there
6 pairs with 2-3 roots and 4-5 cusps good for grinding surfaces
What are the regions of a tooth
Crown (above gumline), neck (within gums), and root (inside bone)
What are the layers of a tooth
Pulp, dentin, enamel, cementum, and periodontal ligaments
What is the pulp of a tooth
In the very center, loose areolar CT (with nerves and blood vessels), providing nutrients and sensation, and odontoblasts at the edge to create dentin
What is the dentin of a tooth
Thick layer that doesn’t remodel and mainly determines color, made of collagen (from odontoblasts) and minerals, harder than bone, no blood vessels or cells
What is the enamel of a tooth
Primarily clear, 99% calcium, added by ameloblasts during development, without cells or blood vessels
What is the cementum of the tooth
Only in the root to anchor the tooth to bone, calcified CT similar to bone, with cementoblasts continually replacing
What are periodontal ligaments
Dense CT attaching cementum to bony socket
What type of joint are periodontal ligaments
Gomphosis
What are cavities
Plaques made of sugar and bacteria erode enamel and dentin through acids that demineralize the tooth surface
What is a root canal
When pulp is infected, it’s drilled out to hill the tooth, the cavity is sterilized and filled, and the tooth is capped off for strength
Why is a root canal good
It allows the tooth to stay in place to prevent shifting
What are the characteristics of the tongue
Mainly skeletal muscle, covered in keratinized stratified squamous epithelium, moves food and mixed with saliva to form bolus, covered in filiform papilla and fungiform and circumvallate papilla
What do filiform papilla do
Rough surface made of projections of keratin to help grab and move food
What do fungiform and circumvallate papilla do
Contains taste buds
What is the lingual frenulum
Fold of mucosa layer (epithelium and CT) connecting the tongue to the floor of the mouth
What is a tongue tie
Lingual frenulum too far forward
What layer of the alimentary canal lines the lumen of a digestive organ
The mucosa
What are the layers of the esophagus
Mucosa is stratified squamous epithelium, areolar CT submucosa, muscularis externa (skeletal muscle in upper regions), and fibrous CT adventitia to anchor the esophagus in place
What are the characteristics of the salivary glands
Exocrine glands with distinct ducts, produces saliva, contains serous cells (secrete digestive enzymes) and mucous cells (secreted lubricating mucus)
What are the 4 functions of saliva
Solvent to cleanse teeth, dissolves food to aid in taste, contains digestive enzymes to break down carbs, and had mucus to help swallow
What are the 3 salivary glands and ducts
Parotid, submandibular, and sublingual
What are the characteristics of the parotid gland and duct
Largest, has serous cells (watery enzyme rich secretion), drains near 2nd upper molar
What are the characteristics of the submandibular gland and duct
50/50 serous to mucus cells, ducts open lateral to lingual frenulum just below tongue
What are the characteristics of sublingual gland and duct
Mucus cells (thicker mucus secretion), several ducts emptying below tongue
What is the pharynx
Connects oral cavity to the esophagus and nasal cavity (not involved in digestion)
What are the sections of the pharynx that are part of the digestive system
Oropharynx and laryngopharynx made of stratified squamous epithelium to protect from abrasion
What is the esophagus
Connects the pharynx to the stomach with mucous glands in submocosa and mucosa to secrete mucus to lubricator
Where is stratified squamous epithelium continuous from
Oral cavity to the stomach
What is the muscularis externa of the esophagus
Upper 1/3 skeletal, middle 1/3 mix of smooth and skeletal, lower 1/3 smooth muscle
What are the 4/5 characteristics/functions of the stomach
Food turned to chyme within ~4 hours with mechanical and chemical digestion, made of simple columnar epithelium (mucous cells protect from acids), absorbs water and drugs that’re lipid soluble
What epithelium is continuous from the stomach to the intestines
Simple columnar
What are the features of the stomach
Rugae and sphincters (cardiac and pyloric)
What are rugae
Folds of mucosa that increase surface area and allow stomach to expand
What are sphincters
Thickened regions of muscularis externa (smooth muscle)
What does the cardiac sphincter do
Prevents food from moving back into the esophagus
What does the pyloric sphincter do
Controls the release of chyme into the duodenum
What’s special about he muscularis externa of the stomach
It has a 3rd innermost layer, the oblique
What are the elements in the stomach epithelium
Mucous cells, gastric pits, gastric glands
What cells are in the gastric gland
Mucous neck cells, parietal cells, chief cells, and enterendocrine cells
What are mucous cells
Mucus secreting cells that prevent the stomach from eating itself
What are gastric pits
Regions where epithelium pushes down into gastric gland (duct of the gland)
What are gastric glands
Exocrine glands connected to the lumen through the gastric pit
What do mucous neck cells do
Secrete mucus
What do parietal cells do
Produce and secrete HCl (destroys bacteria) and gastric intrinsic factor/GIF (helps with absorption) into lumen for pepsin
What do chief cells do
Produce and secrete pepsinogen that interacts with HCl
What do enterendocrine cells do
Releases hormones (e.g. gastrin to signal parietal and chief cells and control release of gastric juices)
What is pepsin
Breaks down proteins in food, mix of pepsinogen and HCl
How often are stomach cells replaced
3-7 days by undifferentiated stem cells found at the junction between gastric pits and gastric glands
What is a gastric fistula
Abnormal connection between the stomach and the skin that left and open hole to the stomach
What are the characteristics of the small intestine
Longest segment of canal (9-15 feet), simple columnar, most of absorption and chemical digestion, chyme moves from stomach to small intestine via peristalsis and mixed via segmentation
What are the segments of the small intestine
Duodenum, jejunum, and ileum
What are the characteristics of the duodenum (what does it get/where)
Shortest, gets chyme from stomach, digestive enzymes from pancreas and bile from liver and gallbladder
What are the characteristics of the jejunum
Majority of absorption here
What are the characteristics of the ileum
Longest, aids in absorption, connects to large intestine
What are the related organs of the duodenum
The gallbladder, pancreas, and hepatopancreatic sphincter
What does the gallbladder do
Stores and adds bile, breaks down fats, duct and sphincter controls release, empties directly into the duodenum
What does the pancreas do (3 things)
Adds digestive enzymes (pancreatic juices neutralize chyme), main duct and sphincter control release, emptied directly into the duodenum
What does the hepatopancreatic sphincter do
Final control valve
What’s the ~surface area of the small intestine
2000 square feet
What 4 features of the small intestine increase surface area
Length (~15 feet), plucae circulares (circular folds of mucosa and submucosa), villi (folds of mucosa), and microvilli (plasma membrane of apical cell surface)
What are the associated features of the villi
Lamina propria, capillaries, lacteals, and muscularis mucosa
What is the lamina propria in the villi
Highly vascularized, allows for increased absorption
What are lacteals
Larger than capillaries, transport fats too large for capillaries
What does the muscularis mucosa do in the villi
Moves villi within lumen to increase contact with nutrients to aid in absorption
What are the 4 specialized epithelial cells of the small intestine
Enterocytes/Absorptive cells, goblet cells, enterendocrine cells, and cells of intestinal gland
What are enterocytes and how do they move things
Majority of epithelial cells with microvilli, protein pumps move sugars and amino acids, endocytosis moves macromolecules
What are goblet cells
Secrete mucus onto lumen to protect epithelium
What do enterendocrine cells in the small intestine do
Secrete hormones to control the release of other substances (cholecystokinin/CCK and secretin)
What do cells of the intestinal gland do
Secrete intestinal juices to suspend nutrients (new cells replace epithelium every 3-6 days)
What does the presence of fats stimulate in the duodenum
Hormones travel through bloodstream and stimulate smooth muscle, CCK released, bile released, fats broken down
What does the presence of acids stimulate
Secretin travels through bloodstream, stimulates pancreatic cells, pancreatic juice released to neutralize acids and enzymes help with digestion of proteins, fats, and carbs
What are 3 characteristics of duodenal glands
In submucosa, ducts open into intestinal glands (crypts), secrete alkaline mucus to neutralize stomach acids in chyme
What are paneth cells
In intestinal glands of small and large intestine that secrete enzymes to selectively destroy bacteria
What is the Peyer’s Patch
MALT tissue with aggregated lymphoid nodules, monitors bacteria populations and prevents growth of pathogenic bacteria in the intestines
What part of the small intestinal mucosa is damaged due to celiac
Villi are flattened which decreases surface area
What are the characteristics of the large intestine
~3 feet in length, simple columnar epithelium, mainly water absorption, stores feces, peristalsis moves fecal matter
What are the 3 features of the large intestine
Epiploic appendages (fat tabs on outside), tenia coil (longitudinal strips of smooth muscle that create haustra when contracted), haustrum
What are the 7 regions of the large intestine
Cecum, ileocecal valve, vermiform appendix, colon, rectum, anal canal, and external anal sphincter
What is the cecum
Where the ileum enters into the large intestine
What is the ileocecal valve
Connects the ileum to the cecum
What is the veriform appendix
Worm like, opens into cecum, lined with MALT tissue
What are the areas of the colon
Ascending, transverse, descending, sigmoid
What type of epithelium is the anal canal
Stratified squamous (continuous with skin)
What is the external anal sphincter made of
Skeletal muscle
What are the features of the anal canal
External anal sphincter (skeletal muscle), internal anal sphincter (smooth muscle), hemorrhoidal veins (can swell and bulge under pressure)
What are the cells in the mucosa of the large intestine
Colonocytes/absorptive (mainly absorb water), goblet (mucus), intestinal glands (replace epithelial cells every 7 days)
What are the accessory digestive organs of the abdominal cavity
Liver, gallbladder, pancreas
What are the 2 functions of the liver
Produces bile and processes blood from stomach and intestines (stores vitamins, processed fats and proteins, stores glucose as glycogen)
How many lobes does the liver have
4: Right (largest), left, quadrate, and caudate
What are the other features of the liver
Hepatic proper artery, hepatic portal vein, and inferior vena cava
What’s the function of the hepatic proper artery
Provides oxygen rich blood to the liver
What’s the function of the hepatic portal vein
Transports nutrient rich blood with absorbed nutrients from stomach/intestines to the liver
What’s the function of the inferior vena cava
Removes blood from the liver after it’s been processed
How are cells of the liver organized
In lobules
What is a portal triad
Bile duct (bile out of lobule), portal venule (nutrient rich blood into lobule), and portal arteriole (oxygen rich blood into lobule)
What are the sinusoids
Channels where arterial and venous blood mix (transport blood from outside mobile to center)
What is the central vein
Drains blood from sinusoids out of liver
What are hepatocytes
Main liver cell, does all functions livers needed for, arranged into plates, borders sinusoids to add and take out stuff from blood, produces bile, regenerative
What are hepatic macrophages/kupffer cells
Move through sinusoids to destroy old blood cells and bacteria in the blood
What is a portal system
Blood flows through 2 capillary beds before returning to the heart
What is bile (4 things)
Cholesterol, bile acids, salts, and bilirubin (product of red blood cells being broken down)
What are gallstones
Cholesterol that precipitated out of bile when stored in gallbladder
What cells are in the pancreas
Acinar cells produce and secrete pancreatic enzymes (juices) that break down proteins and neutralize chyme
What is chron’s disease
Inflammation of alimentary canal, mainly ileum and colon that forms sores, controlled by diet
