lecture 4: digestive system Flashcards
name the 2 paths involved in the digestive system (common names)
path food takes
accessory organs
name the 6 essential activities of digestion
ingestion
propulsion
mechanical breakdown
digestion (chemical, enzymes needed)
absorption
defecation
name the 2 groups of organs of digestive system
alimentary canal organs
accessory glands
describe alimentary canal organs (digestive track)
food passes through
mouth –> pharynx –> esophagus –> stomach –> small intestine –> large intestine –> anus
describe accessory glands
secretes digestive juices into the canal to aid digestion
salivary glands, liver, gallbladder, pancreas
what type of epithelium is mouth pharynx and esophagus lines with
stratified squamous
why do we choke
food gets into airway - talking while eating or chewing too fast
name the important sections of oral cavity
soft palate - muscle and connective tissue
hard palate - bone
tongue - skeletal muscles
epiglottis - elastic cartilage
name steps of the mouth digestion
entry point of food (ingestion)
food is chewed (mechanical)
saliva is secreted by salivary glands (chemical, mechanical)
tongue
describe food being chewed
teeth of varying shapes cut, smash and grind food so its easy to swallow
increases surface area of food - so enzymes can work more efficiently
describe purpose of saliva
lubricates foods for swallowing (contains mucin)
neutralizes acid in mouth (since its basic)
antibacterial agents kill bacteria
contains salivary amylase
describe function of tongue
tastes food (papillae)
pushes food around while chewing
helps form bolus and push it into pharynx while swallowing
describe pharynx
connects mouth and nasal cavity to trachea and esophagus
epiglottis - covers airway when swallowing
oro + laryngo + naso pharynx = call it all the pharynx
what is swallowing and is it voluntary
propulsion
starts off as voluntary then becomes involuntary
what happens when bolus enters the pharynx
esophageal sphincter relaxes (opens)
larynx moves up and epiglottis moves down to cover glottis (opening to larynx)
how does bolus move through esophagus
PERISTALSISSSS
describe esophagus + digestive activities
conducts food from pharynx to stomach ~ 25cm long
propulsion via peristalsis
name the 2 sphincter of esophagus
esophageal - pharynx/esophagus
gastroesophageal - esophagus/stomach
what is a sphincter
circular ring of muscle that acts like a valve (opens and closes)
what is peristalsis
alternating contraction and relaxation of smooth muscle lining the digestive track
propels food towards anus (one direction)
is peristalsis voluntary?
NOPEee
involuntary
what happens during emesis (vomiting)
Involuntary
reverse peristalsis
name parts of walls of digestive track
mucosa
submucosa
muscularis externa
serosa (adventitia)
describe mucosa (walls of digestive track)
surface epithelium (simple columnar or stratified squamous)
lamina propria (areolar connective tissue)
thin layer of smooth muscle
describe submucosa (walls of digestive track)
areolar connective tissue containing glands, nerve endings, blood vessels and lymphatic vessels
describe muscularis externa (walls of digestive track)
circular smooth muscle (inner)
longitudinal smooth muscle layer (outer)
PERISTALSIs
describe serosa (walls of digestive track)
fibrous connective tissue
serous membrane (simple squamous)
what is strange about muscularis externa of stomach
extra internal layer called oblique layer - for churning
describe structure of stomach
located in upper abdominal cavity below diaphragm
muscularis externa = longitudinal layer, circular layer and oblique layer
name steps of the stomach digestion
stores food
churning (mechanical)
digestion (chemical)
empties chyme into duodenum (small intestine)
describe storing of food (stomach digestion)
rugae (accordion folds in mucosa) and very elastic wall allows stretching
accommodates up to 2L
describe churning (stomach digestion)
oblique layer of smooth muscle pummels food and mixes with gastric juices –> produces chyme
describe digestion (stomach digestion)
hydrolysis of protein begins
enzyme pepsin
describe the emptying of chyme into duodenum (small intestine (stomach digestion)
pyloric sphincter separates stomach and duodenum (propulsion)
allows 3mL to enter small intestine at a time ~ 2-6 hrs to empty (slow digestion)
where is gastric juice found
stomach
secreted by gastric pit epithelium
what does stomach epithelium produce
alkaline mucus to protect the stomach lining
how often is stomach epithelium replaced
every 3 days
describe gastric juice
acidity kills bacteria, denatures proteins, breaks down cell walls
activates pepsin
name the 3 types of cells in gastric pits
parietal
chief
enteroendocrine
why is pepsin secreted in an inactive form (pepsinogen)
not to breakdown proteins in chief cells (pepsin is not specific, so it can attack all proteins)
pepsinogen is secreted from chief cells into stomach then HCl mixes with it and produced pepsin (activated enzyme)
describe parietal cells
secretes HCl
describe chief cells
secretes pepsinogen
in the presence of HCl pepsinogen is activated to pepsin
describe enteroendocrine cells
secrete hormones
name 4 hormones secreted by enteroendocrine cells
serotonin
histamine
somatostatin
gastrin
describe hormone serotonin (digestive track)
stimulates muscle contractions
excitatory
describe hormone histamine (digestive track)
stimulates release of HCl (sometimes why stomach hurts during allergic reaction)
excitatory
describe hormone somatostatin (digestive track)
inhibitory
describe gastrin (digestive track)
stimulatory, excitatory
ex: HCl secretion
name 3 parts of small intestine and functions
duodenum - digestion
jejunum - absorption
ileum - absorption
describe small intestine
3 parts
longest section ~ 6 meters long
length = maximizes surface area for absorption
what happens in duodenum
acidic chyme mixes with secretions from other organs
name and briefly describe 3 organs (secretions) that chyme mixes with in duodenum
pancreas - enzymes and alkaline solution
liver and gallbladder - bile
intestinal epithelium- brushborder enzymes
what is the purpose of the many structures of the small intestine
maximize surface area (250m^2) for absorption
name the 3 structural modifications of small intestine
circular folds
villi
microvilli
describe circular folds of small intestine
folding of mucosa and submucosa - like little hills
describe villi of small intestine
finger like projections of mucosa (on tops of hills)
blood capillaries for absorption
lymphatic vessels
describe microvilli of small intestine
projections of plasma membrane and epithelial cells
looks like brush
does ALL absorption occur in small intestine?
NOOO
some in stomach for things like alcohol, aspirin, drugs, water, vitamins (faster absorption)
what is segmentation
occurs in small intestine
squeezing at top and bottom
helps mix and breakdown food
what digestive activities occur in small intestine
propulsion (whole digestive system)
mechanical breakdown (segmentation and bile)
digestion (chemical)
absorption
which digestive activities do not occur in small intestine
ingestion and defecation
what does liver do
produces bile
metabolism
detoxification
what does pancreas do
produced hydrolytic enzymes (for carbs, fats, proteins and nucleic acids)
produced alkaline solution, rich in bicarbonate - neutralizes acidic chyme
what are bile salts
amphipathic and act as detergent or emulsifier to break up fat into small pieces (more access for lipases)
what does gallbladder do
stores excess bile
what two things are secreted into duodenum and from where
bile - liver/gallbladder
alkaline solution - pancreas
what does bile do
makes fat soluble in water (breaks down)
attaches to fat and gives it a hydrophilic side
helps enzymes work
is bile mechanically or chemically digesting fats?
mechanically
facilitates chemical breakdown BUT it isn’t chemical breakdown - just takes fats that are stuck together and beaks them up
what does bile contain
bile salts and pigments - byproducts of destruction of red blood cells in liver
dark green or yellowish brown
pigments are eliminated with feces
what is the hepatic portal vein
carries nutrient rich blood from capillaries of villi (all blood from intestines passes by liver before going to heart)
why does blood have to pass by the liver before going to the heart
stores vitamins and minerals
detoxifies
converts glucose into glycogen
regulates amino acid levels
converts ammonia to urea
describe large intestine
connected to small intestine at a T junction (includes cecum and illeocecum)
ileocecal valve (sphincter) controls movement from small to large intestine
shaped like a U 1.5 m long
what does large intestine do
reabsorbs water to form solid feces
slow peristalsis (propulsion) 7L secreted and almost all reabsorbed
what do bacteria in the colon produce
gases and some vitamins (vit k, B vits, folic acid)
where are feces stored (explain process)
rectum until eliminated via anus
internal sphincter - involuntary
external sphincter - voluntary
what is feces
undigested food stuff (ex cellulose)
bacteria
what causes diarrhea or constipation
diarrhea - moves fast through large intestine, not enough water reabsorbed
constipation - moves slow through large intestine, too much water reabsorbed
has to do with muscle contractions - frequency affects how long it is in small intestine
where does digestion of carbs start and where does it go ? explain areas
mouth
continues in small intestine (duodenum)
name the enzymes involved in digestion of carbs
salivary amylase
pancreatic amylases
brush border enzymes
describe pancreatic amylase (digestion of carbs)
hydrolyzed to oligosaccharides and disaccharides
describe brush border enzymes (digestion of carbs)
hydrolyses to monomers
disaccharides
finalizes digestion of carbs
describe digestion of proteins (where)
starts in stomach
continues into small intestine - duodenum
name enzymes used to digest proteins
pepsin (stomach)
pancreatic enzymes
brush border enzymes
describe pancreatic enzymes (digestion of proteins)
polypeptides to small polypeptides
trypsin
chymotrypsin
carboxypeptidase
secreted in inactive forms
describe brushborder enzymes (digestion of proteins)
small polypeptides to amino acids and some dipeptides/tripeptides
dipeptidase
aminopeptidase
carboxypeptidase
where does digestion of fats start
small intestine
name enzymes that help digestion of fat
pancreatic lipases
bile
describe pancreatic lipases (digestion of fats)
breaks down fat into glycerol, fatty acids and monoglycerides
describe bile (digestion of fat)
emulsifies fat
increases surface area exposed to lipases
where does digestion of nucleic acids start
small intestine (duodenum)
name enzymes that help digest nucleic aids
pancreatic nucleases
brush border enzymes
describe pancreatic nucleases and brush border enzymes (digestion of nucleic acids)
breaks down polynucleotide into sugars, bases and phosphates
describe absorption of carbs and proteins
from intestinal lumen –> crosses intestinal epithelium
–> crosses interstitial fluid –> crosses epithelium of capillaries
how are carbs and proteins (nutrients) separated from blood
2 layers of cells
describe absorption of fats (name steps)
from intestinal lumen –> crosses intestinal epithelium –> crosses interstitial fluid –> crosses epithelium of lacteals
what are lacteals
lymphatic capillary
describe crossing intestinal epithelium (absorption of fats)
inside epithelial cell they (re)form triglycerides –> chylomicrons
describe crossing epithelium of lacteals (absorption of fats)
lacteals converge into larger vessels of lymphatic system
eventually drain into large veins
what are chylomicrons
triglycerides packaged with phospholipids (balls on outside - hydrophilic head), cholesterol and proteins
make fat soluble in water - environment of circulatory system
name the hormones that regulate digestion
gastrin
secretin
cholecystokinin (cck)
describe gastrin (regulates digestion, from where and what)
from stomach wall
released in response to food
stimulates secretion of gastric juices
low stomach pH inhibits release of gastrin
describe secretin (regulates digestion, from where and what)
from duodenum wall
releases in response to acidic chyme
stimulates release of bicarbonate from pancreas
describe cck (regulates digestion, from where and what)
from duodenum wall
released in response to presence of amino acids/fatty acids
stimulates release of bile from gallbladder and release of pancreatic enzymes
why does it take longer to digest a fatty meal
fatty chyme in duodenum –> stimulates release of secretin and cck in high levels
THIS inhibits peristalsis of stomach and the secretion of gastric juices
what is the mesentery
mesocolon = mesentery
fold of tissue that attaches organs in abdominal cavity to body wall
blood vessels, nerves, and lymphatic vessels branch through mesentery to supply organs
