Digestive System Flashcards
Why is food vital to life?
- provides energy
- provides building blocks for growth and maintenance
Why do we need a digestive system?
food comes to us as complex molecules and are too large to be absorbed into the blood
What are the complex molecules that make up the food that we eat? What do we do with them?
Carbohydrates => monosaccharides
Proteins => amino acids
Fats => Fatty Acids, glycerols, glycerides
What is the process of bringing food into the body by consuming via the mouth?
ingestion
What is peristalsis?
Movement of food
-Long tube food moves through (digestive tract)
-Movement of food through tube b/c of peristalsis
- Smooth muscle contraction (wave like pattern) moves
the food
What is the process of breaking down food into macromolecules called? What are they types?
Digestion
- Physically breaking down molecules (mechanical)
Smaller chunks it’s broken into = greater surface area
for chemical digestion via enzymes
- Chemical digestion: breaks it down into small
absorbable molecules
What is absorption? Where does absorption occur?
Absorbing molecules of food once they’ve been broken down through digestion
Absorption occurs via:
- Bloodstream
- Lymphatics (lipids absorbed here first)
What occurs after absorption?
Compaction and defecation
- Compaction: Water absorption
- Defecation: whatever is left
Cannot break it down into absorbable molecules and all water had been absorbed
What is the gastrointestinal tract? What is it’s organization?
AKA the alimentary canal
- Long tube that begins at mouth and ends at anus
mouth pharynx esophagus stomach small intestine large intestine
What are accessory organs of the digestive system? What are they?
everything that isn’t part of GI tract but assists in digestion
Mechanical digestion
- Teeth
- Tongue
Chemical Digestion
- Salivary Glands
- Liver
- Gallbladder
- Pancreas
What are the tissue layers of the gastrointestinal tract?
Mucosa, Submucosa, Muscularis Externa, Serosa or Adventitia
What is the tissue layer of the gastrointestinal tract, Mucosa?
Epithelium: actually in contact w/ food
- All absorption occurs here
Lamina Propria: thin layer of connective tissue
Muscularis Mucosae: thin layer of smooth muscle creates lots of folds = increased surface area
What is the tissue layer of the gastrointestinal tract, Submucosa?
loose connective tissue
What is the tissue layer of the gastrointestinal tract, Muscularis Externa?
lots of smooth muscle
- inner circular layer:
- outer longitudinal layer
What is the tissue layer of the gastrointestinal tract, Serosa or Adventitia?
connective tissue to anchor the GI tract
- Adventitia: organs that are tightly anchored in place
- Serosa: thinner connective tissue for some organs in
abdominal cavity that are not anchored as tightly (most
organs in abdominopelvic area)
What is the enteric nervous system?
local network of nerves within GI tract
- submucosal plexus: network of nerves within the
submucosa - myenteric plexus: network of nerves within the two
layers of smooth muscle in the muscularis externa
What is the peritoneum?
A continuous membrane which lines the abdominal cavity and covers the abdominal organs
What are the parietal and visceral layers of the peritoneum?
Parietal (outer) vs. visceral(inner) : layers of peritoneum
- Parietal covers the (external) abdominopelvic wall
- Visceral covers the surface of the organs
What is the peritoneal cavity?
Potential space between parietal and visceral layers of the peritoneum
- Filled w/ fluid to reduce friction
What is the Dorsal mesentery?
visceral peritoneum (part of continuation of serosa)
- Usually just called the mesentary
- Anchors small intestine
What is the Ventral mesentary?
visceral peritoneum (contains the serosa) but most anterior portion
- lesser omentum: anchors superior border of stomach to
liver
- greater omentum: anchors inferior border of stomach to
large intestine
What is the Mesocolon?
membrane that anchors the large intestine
What are the boundaries of the oral cavity?
Anterior boundary: behind teeth
Posterior boundary: oropharynx
Superior boundary: palates
What is the difference between the hard palate and the soft palate?
Hard palate: bone (maxillary and palatine bones)
Soft Palate: palatoglossal + palatopharyngeal arches
- Muscle covered in epithelium
What are the palatoglossal arches?
Part of the oral cavity
- anterior arches on each side of uvula
What are the palatopharyngeal arches?
Part of the oral cavity
- posterior to palatoglossal arches (end of oral cavity)
What anchors the tongue and keeps you from swallowing it?
frenulum
What is the vestibule?
part of oral cavity
- behind lips but in front of teeth
What is the fauces?
Part of the oral cavity
- opening leading to oropharynx
What are the intrinsic muscles of the tongue? What movements is it used for?
Muscles that compose the tongue
- Tongue roller; bowing up
What are the extrinsic muscles of the tongue? What movements is it used for?
Attach tongue to the bone or other tissue but not part of tongue itself
- Moving tongue side to side, in and out.
When food is chewed and swallowed, what is the mixture called?
Bolus
What nerve innervates the tongue?
Hypoglossal nerve (XII)
Are the tongue/teeth part of the GI tract or are they accessory organs?
accessory organs
What are salivary glands?
accessory organs that secrete saliva
What are the types of salivary glands?
Intrinsic glands
Extrinsic glands
What are the characteristics of intrinsic glands?
1000’s of salivary glands that are part of mouth itself
- Lingual (tongue), labial (lips), buccal glands (mouth)
- low level continuous secretion: keeps oral cavity moist
What are the characteristics of the extrinsic glands?
Paired salivary glands that contain ducts leading to mouth
- parotid glands: located upper posterior jaw
- submandibular glands: located inside of mandible
- sublingual glands: located below tongue
What is saliva composed of?
- 5% water
1. 5% solutes
What is the pH of saliva?
pH 6.8 - 7.0
What are the solutes present in saliva?
salivary amylase lingual lipase mucus lysozyme immunoglobulin A electrolytes (Na+, K+, Cl-, HCO3-, HPO4--)
What is salivary amylase?
solute in saliva
enzyme that digests starch (begins chemical breakdown)
- Works best at ~neutral pH (6.8-7) otherwise the
- conformation will change = doesn’t bind starch as well
What is lingual lipase?
solute in saliva
breaks down lipids
- pH optimum at 4-5
- Doesn’t work as well b/c pH in mouth too high
What is mucus?
solute in saliva
coats bolus of food to make it slide better
What is lysozyme?
solute in saliva
non-specific antimicrobial (breaks down peptidoglycan in bacteria)
What is immunoglobulin A?
solute present in saliva
mucosal antibody
- Protected against digestion by enzymes
What are the electrolytes in saliva?
Na+, K+, Cl-, HCO3-, HPO4-
How is salivation controlled?
parasympathetic innervation via cranial nerves VII and IX
What types of stimuli initiate salivation?
Psychic: seeing/hearing = thinking about food = secretion of saliva (think pavlov’s dog)
Chemical: tastebuds activated by food in mouth = increased salivation
Tactile: tactile receptors activated by food in mouth = increased salivation
What kinds of digestion occurs in the mouth?
Mechanical and Chemical
What is the mechanical digestion that occurs in the mouth?
Physical breakdown of food through mastication (chewing)
What kind of chemical digestion occurs in the mouth?
no protein digestion; little fat digestion (lingual lipase below optimum pH)
Amylase at optimum pH so starch digestion occurs
- Breaks starch (polymer of glucose) down to maltose
(simple glucose-glucose molecule)
- Most maltose digestion finishes off in small intestine
because of longer length of time it spends there vs
mouth
What factors affect chemical digestion?
pH, Temperature, time affect amount of chemical digestion that occurs
What is accomplished through mastication and chemical digestion in the mouth?
Teeth have shredded and ground food, making it easier to swallow and with more surface area for chemical digestion
Starch digestion has begun
Mucus has bound food particles together into a soft, slippery, easily swallowed mass called a bolus.
What is the technical term for swallowing?
DEGLUTITION
What are the phases of DEGLUTITION?
Buccal phase (voluntary)
Reflexive Pharyngoesophogeal Phase (non-voluntary)
What is the Buccal phase (voluntary) of deglutition? What cranial nerves carry this out?
Tongue bowing and pushing the bolus of food toward the rear of the mouth
Cranial nerves 5 and 7 innervate muscles that carry this out
What is the Reflexive Pharyngoesophogeal Phase (non-voluntary)?
As food gets pushed back towards Oropharnyx it causes soft palate to be pushed up and closes off nasal cavity
Larynx moves up and closes glottis off with epiglottis
Pharynx smooth muscle closes off from superior to inferior and pushed bolus of food down to the beginning of esophagus (why called pharyngoesophageal phase)
Sphincter at entry to esophagus dilates when food gets there
- Causes smooth muscle in esophagus to contract (wavelike peristalsis) pushing bolus of food down
Go over the gross anatomy of the esophagus.
Starts just below pharynx
Passes through diaphragm
- Esophageal hiatus (the hole that esophagus passes
through)
-Descending aorta passes through this hole as well
Aorta and esophagus develops first in fetus and
diaphragm develops around it
What is the esophageal hiatus?
opening in the diaphragm through which the esophagus and the vagus nerve pass
What are the features of the mucosa of the esophagus?
Mucosa is non-keratinized stratified squamous epithelium.
- Protects from abrasive foods (chips = jagged edges)
- Ends at end of esophagus
What is the muscularis?
Two layers of smooth muscle in the esophagus
- One layer runs longitudinally
- One layer runs circularly
- More important = wavelike peristalsis
What closes the esophagus off from the pharynx and the stomach?
Upper Sphincter
Lower Sphincter (gastroesophageal sphincter) - When food reaches this point it causes reflexive dilation of the sphincter
Where in the body is the stomach located?
left hypochondriac region
What are the divisions of the stomach?
Cardia
- region surrounding the gastroesophageal sphincter
Fundus
- mean deep in latin
Corpus
- body of stomach (between fundus/cardia and pylorus
Pylorus
- end region before pyloric sphincter
What is the pyloric sphincter?
sphincter that controls movement of food from stomach to small intestine
What are the curvatures of the stomach?
Lesser Curvature: attached to the lesser omentum
Greater Curvature: connected to greater omentum
What are the rugae of the stomach?
folds of stomach wall (when stomach is empty)
- Gives increased surface area
- Allows for expansion of stomach
What kind of cells make up the mucosa of the stomach?
Simple columnar epithelium
- Secretion and absorption
- Creates folds as well
- Form gastric pits
What are the types of gastric glands make up the mucosa of the stomach?
Mucous cells Parietal cells Chief Cells Enteroendocrine Cells (G cells) Regenerative Stem Cells
What are the features of the mucous cells?
Gastric Gland of the stomach mucosa
secretes mucous that coats surface of stomach and gastric pits
- Creates barrier from low pH
What are the parietal cells?
Gastric Gland of the stomach mucosa
Secretes:
- hydrochloric acid (HCl) : causes low pH
- intrinsic factor (helps w/ absorption of absorption of B12
in small intestine)
- ghrelin (appetite-regulating hormone)
What are the chief cells?
Gastric gland of stomach mucosa that secrete enzymes
Pepsinogen (Precursor)
- Once it gets to lumen of stomach it will be activated by
- presence of HCl (pepsin) (pH 1-3)
Gastric lipase
- Not very active b/c optimum pH = 4-5 (pH too low)
What are enteroendocrine cells?
Gastric gland of stomach mucosa
Releases gastrin hormone which regulates stomach activity
What are regenerative stem cells?
Gastric gland of stomach mucosa
Constantly dividing (rapid mitosis) Turnover quick of cells in epithelium of stomach
What is chyme?
the pulpy acidic fluid that passes from the stomach to the small intestine, consisting of gastric juices and partly digested food.
What is the mechanical digestion that occurs in the stomach?
Regular gentle peristaltic waves
Mixing waves that produce chyme (bolus of food becoming fluid)
What is the chemical digestion that occurs in the stomach?
Pepsinogen + HCl => Pepsin (pH 1-3)
- Pepsin is the enzyme that breaks down proteins into peptides
Gastric Lipase
- pH 5-6 so not really used in stomach
Rennin (infant stomach only)
- curdles milk, milk will spend more time in the stomach=BETTER DIGESTION
How are the actions of the stomach regulated?
Three Phases of Control:
Cephalic phase: chewing food, thinking about meal, activates stomach via parasympathetic innervation
Gastric phase: stretch receptors of the stomach
Intestinal phase: CHYME (fluctuates with gastric phase)
Go over the specifics of the cephalic phase?
1st phase of gastric regulation
Thought, taste, smell of food => Parasymp NS output via vagus nerve => stimulate enteric NS = increased gastric secretion + increased gastric motility
Go over the specifics of the gastric phase?
2nd phase of gastric regulation
Food enters stomach => increased stretch of stomach + increased pH => input to brainstem => stimulate enteric NS + Parasymp NS output via Vagus + increased gastrin secretion = increased gastric secretion + increased gastric motility
Go over the specifics of the intestinal phase.
pH of chyme after being in stomach and entering small intestine = low pH
Chemoreceptors will activate enteric nervous system of small intestine
When chyme arrives at small intestine the stomach is inhibited
- Small intestine will release cholecystokin (CCK) which
inhibits stomach
Brainstem
- increased symp NS output + decreased parasymp NS
output = decreased stomach activity
Stomach activity decreased = less juices secreted, less contraction of smooth muscle = less chyme to small intestine = more time for small intestine to digest
Go over the specifics of the intestinal phase.
pH of chyme after being in stomach and entering small intestine = low pH
Chemoreceptors will activate enteric nervous system of small intestine
When chyme arrives at small intestine the stomach is inhibited
- Small intestine will release cholecystokin (CCK) which
inhibits stomach
Brainstem
- increased symp NS output + decreased parasymp NS
output = decreased stomach activity
Stomach activity decreased = less juices secreted, less contraction of smooth muscle = less chyme to small intestine = more time for small intestine to digest
What is accomplished by digestion at the STOMACH?
starch => maltose by salivary amylase (action stops in stomach)
- Amylase and carb digestion stops at stomach pH too
low
proteins => (mostly) partially digested proteins (action of pepsin)
lipids => (less) partially digested fats(action of lingual and gastric lipase)
creation of chyme from food, drink, saliva, and gastric juice
What kind of absorption occurs at the stomach?
no significant absorption by stomach mucosa
What is absorbed is:
- water
- electrolytes
- aspirin and some lipid-soluble drugs
What are the accessory organs to Digestive system?
Pancreas, Liver, Gall Bladder
What is the pancreas?
CONE SHAPED, POSTERIOR TO STOMACH, BEHIND THE PARIETAL Perotineum
MAJORITY OF THE TISSUE IS EXOCRINE GLANDS (DUCTS: MAIN PANCREATIC DUCT/ACCESSORY PANCREATIC DUCT) TO (EPITHELIUM),
HORMONES PRODUCED BY ISLETS OF LANGERHANS CELLS (ENDOCRINE into blood)…AT THE END OF THE MAIN PANCREATIC DUCT IS AN HEPATOPANCREATIC AMPULA(TWO DUCTS COMING TOGETHER), HERE IS A SPHINCTOR CALLED “SPHINCTER OF ODDI”
WHere is the liver located?
superior/anterior to the stomach/tucked underneath the diaphragm
Where is bile produced?
Produced in liver and piles up in the liver
Where is bile produced?
Produced in liver by hepatocytes
- fed into Bile canliculi which lead to Bile ducts which join to the main hepatic duct
Doesn’t mix w/ blood
What is the falciform ligament?
The falciform ligament is a ligament that attaches the liver to the anterior (ventral) body wall
What is the falciform ligament?
The falciform ligament is a ligament that attaches the liver to the anterior (ventral) body wall
What are hepatic lobules?
liver is divided into 1000’s of lobules
- each lobule has a central vein that runs through it
- each lobule has a portal triad associated w/ it
What makes up the portal triad?
hepatic portal vein: comes from large/small intestine
- oxygen poor and last screen for nutrients
hepatic artery: brings oxygen to liver
Hepatic artery+vein empty into sinusoid which leads to central vein
bile duct: bile made by hepatocytes is emptied into bile duct which joins to main hepatic duct
What are sinusoids?
that serves as a location for mixing of the oxygen-rich blood from the hepatic artery and the nutrient-rich blood from the portal vein
What is the direction of blood flow in the liver?
hepatic portal vein branch + hepatic artery branch →
sinusoid → central vein →inferior vena cava
What is the direction of bile flow in the liver?
hepatocytes → bile canaliculi → bile duct
Is bile an enzyme?
No
What is bile?
a detergent used to emulsify fats
- breaks up large fat molecule into many oil droplets
- increase surface area for digestion by lipase
- helps w/ mechanical digestion
When is bile produced?
continuously at slow rate
How is Bile production controlled?
Parasympathetic control by vagus nerve
Endocrine control through secretin
What macromolecules are metabolized by the liver?
Carbohydrate metabolism
- glycogenesis
- glycogenolysis
- gluconeogenesis
Lipid metabolism
- lacteals in small intestine → lymphatic
system→blood→liver
- liver can turn lipid→glucose
Protein metabolism
- deamination (-NH2→NH3→Urea)
- urea formation
- plasma protein production
What are the functions of the liver besides bile production and macromolecule metabolism?
Detoxification (drugs, hormones, other chemicals)
Storage (glycogen, ferritin, vitamins, heavy metals)
Phagocytosis of RBCs
Activation of vitamin D
Where is the gall bladder located? What is it?
beneath the liver
where bile is stored and concentrated before it is released into the small intestine
- too concentrated = gall stones
What are the rugae of the gall bladder for?
Folds that allow for expansion
What is the biliary tract?
common hepatic duct + cystic duct → common bile duct + main pancreatic duct → ampulla of Vater (space in small intestine)
The sphincter of Oddi controls release into small intestine
How is bile secretion regulated?
Acid Chyme in duodenum → Enteroendocrine cells stimulated → cholecystokinin secretion→ Gall Bladder contraction + relaxation of the sphincter of oddi →release bile into duodenum
Where does most of the absorption during digestion occur?
90% in small intestine
- mostly in the ileum
What are the parts of the smalle intestine?
duodenum (10 in.)
retroperitoneal - behind peritoneum
jejunum (8 ft.)
suspended by mesentery
ileum (10 ft.)
suspended by mesentery
ileocecal (ileocolic) sphincter
What are the anatomical features of the small intestine?
Three folds to increase surface area
1) plicae circulares: 1 large fold that spirals down SI
- chyme rotates around spiral as it goes down
2) villi: fingerlike projection visible to naked eye
3) microvilli (brush border): microscopic projection on surface of villi
What are lacteals?
Lymphatic capillary inside the villi along w/ blood capillary
- lipids absorbed through the villi are transported to the lacteals which brings it into the lymph system
What are peyers patches?
lymphocytes behind the mucosa of the small intestine that screen for pathogens
What kind of mechanical digestion occurs in the small intestine?
Segmentation: sloshing back and forth
- no net movement forward
- smooth muscle contracts/relaxes (sausage link)
- moves chyme back/forth
Peristalsis: moves the chyme forward
Where is the pancreas located?
lying posterior to greater curvature of stomach
- connects directly to duodenum of small intestine
Go through the exocrine function of the pancreas.
Pancreas creates pancreatic juice
Pancreatic juice fed into the main pancreatic duct
Main pancreatic duct joins the common bile duct at the hepatopancreatic ampulla (ampulla of vader)
- Accessory pancreatic duct bypasses hepatopancreatic
ampulla
Hepatopancreatic sphincter (of Oddi)
- controlling release of secretions (bile and pancreatic
secretions)
What is the endocrine function of the pancreas?
Insulin and glucagon: hormones produced by islets of Langerhans
What is the pancreatic juice produced by the pancreas?
Sodium bicarbonate (NaHCO3) buffer Pancreatic amylase Pancreatic lipase Cholesterol esterase Nucleases – DNAse and RNAse Protein-digesting enzymes
What are the protein digesting enzymes produced by the pancreas?
trypsinogen
chymotrypsinogen
procarboxypeptidase
All activated in small intestine by enterokinase
How are amino acids absorbed in the small intestine?
Hepatic Portal Blood → liver →inferior vena cava → general circulation
How are chylomicrons absorbed in the small intestine?
Lymph → lacteals → intestinal trunk → thoracic duct → general circulation
What are chylomicrons?
protein coated fats
What are the sections of the large intestine?
Ascending
Transverse
Descending
Sigmoid
What is the cecum?
transition between small/large intestine
empty pouch w/ appendix attached
What are haustra?
pocket like structures that make up the colon
What sphincters are in the colon?
internal sphincter (unconscious control) - smooth muscle
External sphincter (conscious control) - skeletal muscle
What comes after the sigmoid colon?
Rectum, anal canal and anus
What kind of epithelial cells are present in the colon?
Simple Columnar epithelium
What intestinal glands are present in the colon?
goblet cells for mucus
Are there any features to increase surface area in the large intestine?
No
No Plicae circulae
No villi
No microvilli
What muscle is present in the large intestine?
inner circular bands of smooth muscle
taenia coli: 3 outer longitudinal bands of smooth muscle
What kinds of mechanical digestion occur in the large intestine?
Peristalsis Haustral churning (every 30 min) Mass peristalsis (gastrocolic reflex) (1-3 times a day)
What is haustral churning?
haustra contract and move fwd to next haustra
- Fwd net moving of chyme unlike the segmentation in SI
What is mass peristalsis?
Powerful smooth muscle contraction that pushes feces fwd
Starts in the middle of the transverse colon (so feces by now not chyme)
Gastrocolic reflex: food arrives in stomach triggers parasympathetic output to LI to push feces toward rectum
What kinds of chemical digestion occur in the colon?
Bacterial fermentation → some simple molecules released
Helpful Bacteria secrete vitamin K and some B complex vitamins
What kind of absorption occurs in the large intestine?
little absorption and last little bit of water absorption
Simple molecules and vitamins
Most remaining water (~900 ml/day)
What does feces consist of?
Water Undigested food Bacteria Products of bacterial decomposition Sloughed epithelial cells
What is the defecation reflex?
Distension of the rectum activates stretch receptors which send signals to sacral spinal cord+sensory cerebral cortex
Sacral parasympathetic output causes:
- contraction of descending/sigmoid colon and rectum
- reflexive relaxation of internal sphincters
Voluntary relaxation of external anal sphincter
increased pressure = expulsion of feces
What are the digestive reflexes?
Gastric Reflex
Enterogastric Reflex
Gastroileal Reflex
Gastrocolic Reflex
What is the enterogastric reflex?
Caused by stretch in the duodenum wall
Suppresses stomach activity
What is the gastroileal reflex?
Caused by stretch of stomach
Moves chyme from the ileum of small intestine to large intestine by relaxing the ileocecal sphincter
What is the gastrocolic reflex?
Caused by food arriving in stomach
Triggers parasympathetic output to Large Intestine to push feces toward rectum
