Digestive System part 2 Flashcards
increase in salivation caused by
- parasympathetic stimulation of the facial and glossopharyngeal nerves to stimulate salivary glands to increase production
- cerebral cortex mediated salivation caused by sight, smell, sounds, memories of food, and tongue stimulation
reduction in salivation caused by
sympathetic stimulation: dry mouth feeling stimulates desire for water (thirst)
mechanical digestion in the mouth
mastication breaks food into pieces and mixes it with saliva to form bolus
chemical digestion in the mouth
salivary amylase and lingual lipase at work here
salivary amylase
begins starch digestion of polysaccharides to disaccharides
- is deactivated by stomach acid once swallowed
lingual lipase
secreted by glands in the tongue but doesn’t do anything in the tongue
- is activated by stomach acids where it breaks down TG into FAs and glycerol
where does the bolus travel between the mouth and esophagus?
through the pharynx
- deglutition begins here and is facilitated by saliva and mucus
esophagus structure (layers)
mucosa: stratified squamous with mucous glands at terminal end
submucosa: mucous glands
muscularis: upper 1/3 is skeletal muscle, middle is mixed and lower 1/3 is smooth muscle, it forms sphincters on either end
adventitia: areolar CT that connects esophagus to other structures in mediastinum (only layer of GI sys w/o serosa)
upper esophageal sphincter
consists of skeletal muscle, thus is under conscious control
lower esophageal sphincter
consists of smooth muscle, movement of bolus signals opening to let contents into stomach
what is the esophagus?
a collapsible muscular tube that lies post. to trachea
- it enters mediastinum ant. to vertebrae
- pierces diaphragm at esophageal hiatus
- ends at superior portion of the stomach
function: secrete mucous and transport food from mouth/pharynx to stomach
3 stages of deglutition
- voluntary stage
- pharyngeal stage (involuntary)
- esophageal stage
voluntary stage of swallowing
tongue moves upward into soft palate and bolus is pushed into oropharynx
pharyngeal stage of swallowing
involuntary
- sensory nerves send signals to deglutition centre in brainstem (triggered by bolus entering esophagus)
- soft palate is lifted to close nasopharynx
- larynx lifts and epiglottis bends to cover glottis
esophageal stage of swallowing
- when bolus enters esophagus the upper sphincter relaxes when the larynx is lifted
- peristalsis moves bolus through esoph.
- travel time is 4-8 sec for solids and 1 sec for liquid to move through esoph.
- lower sphincter relaxes when food approaches, allowing bolus to enter stomach
peristalsis
circular fibers behind bolus contract, then longitudinal fibers in front of bolus shorten distance of travel
4 main regions of the stomach
fundus
cardia
body
pyloric region
fundus region of stomach
- most superior
- holding area for bolus up to one hour so salivary amylase is still active because bolus doesn’t contact gastric juices while it’s here
cardia
region of stomach closest to esophageal sphincter opening
body of stomach
largest region
- responsible for churning, mixing contents
pyloric region of the stomach
has 3 parts
pyloric antrum: triangle shaped region, entrance to pyloric part
pyloric canal: leads to SI
pylorus: gateway controlled by pyloric sphincter (muscularis layer) to SI
lesser curvature of the stomach
lesser omentum is an extension of serosa in regions of lesser curvature
greater curvature of the stomach
more lateral side of the stomach
greater omentum begins here and does folding
rugae of mucosa
found in the body of the stomach
- ridges that allow for expansion as the stomach fills
muscularis layer in the stomach
there are 3 layers rather than 2
- longitudinal, circular, oblique
- purpose is to liquify bolus and create even more peristaltic action to churn food
functions of the stomach
- mix food, saliva, gastric juices to from chyme
- serve as reservoir for food before SI
- secrete gastric juice (HCl, pepsin, intrinsic factor, gastric lipase)
- gastrin (hormone secreted by endocrine cells signals digestive processes)
gastric glands
columns of secretory cells at the base of projections in the lamina propria
gastric pits
narrow channels formed by gastric glands
what types of cells are found in the stomach
surface mucous cell mucous neck cell parietal cell chief cell G-cell
surface mucous cell
found in stomach
secretes slightly alkaline mucus to protect cells from stomach acid
- does the same thing as mucous neck cells
parietal cell
found in stomach
secretes HCl and intrinsic factor
mucous neck cell
found in stomach
secretes slightly alkaline mucus to protect cells from stomach acid
- does the same thing as surface mucous cell
chief cell
found in stomach
secretes pepsinogen and gastric lipase
G-cell
a type of enteroendocrine cell found in stomach
typically found in pyloric antrum region of stomach
- secretes the hormone gastrin into the blood supply which controls digestion inn other regions of the GI tract
mechanical digestion in the stomach
- fundus stores bolus up to 1 hr
- peristaltic waves start as soon as bolus enters and are coordinated with contractions that mix the bolus with gastric juices (occur every 15-25 seconds)
- body of stomach responsible for vigorous mixing via propulsion and retropulsion
propulsion
pushing fluids ands bolus towards pyloric region
retropulsion
large particles that haven’t been broken down yet get pushed back to the body of the stomach for further breakdown
gastric emptying
- pyloric sphincter slightly open to allow small amounts of chyme to enter the small intestine
- at any time there is 3ml passing through
chemical digestion in the stomach
enzymes involved: HCl, pepsin, pepsinogen, gastric lipase and lingual lipase
- further protection by mucus produced by surface mucous cells and mucous neck cells
absorption in the stomach
very minimal
- water, ions, alcohol, drugs (ex. aspirin)
HCl
denatures proteins
kills microbes
- activates pepsinogen
pepsinogen
the inactive form of pepsin, activated by HCl
it’s inactive to keep it from digesting the chief cells it’s released from
pepsin
digests proteins in low pH regions
- optimal pH of 2
gastric lipase in the stomach
has limited role in digestion of lipids in the stomach because its optimal pH is 5-6
lingual lipase in the stomach
becomes active in high acid env’t of stomach and helps break down TG
HCl production in the stomach
H+ comes from dissociated bicarbonate ions
- the HCO3- goes into the blood supply creating an alkaline tide, which changes the blood pH slightly
Cl- enters parietal cell by way of an antiporter from the chloride shift and Cl- is secreted into the stomach env’t
HCl is formed in the stomach and not in the cell so it doesn’t damage the cell it’s coming from
when and where do the pancreas and liver add their secretions?
they add their secretions at the beginning of the small intestine
pancreatic duct
tube that runs through the pancreas and collects pancreatic juice
- splits into accessory duct and hepatopancreatic duct
hepatopancreatic ampulla
where the common bile duct (liver) and other part of pancreatic duct join to add secretions to SI
- opening controlled by a sphincter
what types of cells are found in the pancreas?
acini cells islet cells (Islets of Langerhans)
acini cells
exocrine glands
99% of pancreatic cells
- produce and secrete pancreatic juice, digestive enzymes and secrete it into the pancreatic duct
- surround islet cells
islet cells
Islets of Langerhans 1% of pancreatic cells - endocrine cells that secrete hormones into blood capillaries ex. insulin is secreted by beta cells glucagon is secreted by alpha cells
pancreatic juice
composed of water, digestive enzymes and sodium bicarbonate
sodium bicarbonate
deactivates pepsin
makes pancreatic juice alkaline (pH 7-8)
serves as a buffer for acidic contents entering the SI
enzymes present in pancreatic juice
pancreatic amylase - starch pancreatic lipase - main breaks down TG proteases: trypsinogen -> trypsin - chymotrypsin - carboxypeptidase - elastase ribonuclease deoxyribonuclease
trypsinogen
protease present in pancreatic juice activated by enterokinase (a brush border enzyme of duodenum)
- forms trypsin, the active form that activates chymotrypsinogen, procarboxypeptidase, and proelastase
functions of the liver
bile production storage detoxification phagocytosis activates vitamin D metabolism of CHO, PRO, lipids
storage in the liver
CHO and lipids as energy
fat soluble vitamins: A, D, E, K, B12
minerals: copper, iron
detoxification in the liver
drugs, alcohol, hormones (thyroid and estrogen)
- things that aren’t found normally in the body and are broken down so they aren’t toxic
major duodenal papilla
ridge in SI where ducts empty (hepatopancreatic ampulla empties here)
lobes of the liver
2 lobes, the right is larger than the left
gallbladder layers
mucosa: simple columnar epithelium - rugae allow for distention
no submucosa
muscularis layer is a single layer of smooth muscle with fibers that run in all directions
serosa or visceral peritoneum
function of gallbladder
store and concentrate bile by removing water and ions (makes 10x more concentrated)
filling the gallbladder
when bile travels down common bile duct, it its sphincter is closed at the hepatopancreatic ampulla, the bile travels back into the gallbladder and fills it
bile
produced by hepatocytes
800-1000mL/day
- brownish-yellow or olive green colour depending on concentration level
pH 7.6 to 8.6 - helps make chyme less acidic
- excretory function: bilirubin and broken down drugs and alcohol
- digestive function: emulsifies fat for digestion
components of bile
- water
- cholesterol
- bile salts (Na and K salts) for emulsification of fat globules and lipid absorption
- bilirubin (bile pigment from heme broken down into iron and bilirubin from Hgb) forms stercobilin in intestine and gives feces brown colour
blood supply to the liver
- hepatic artery delivers oxygenated blood
- hepatic portal vein carries deoxygenated blood but has nutrients (also for detoxification)
- hepatic vein carries deoxygenated/detoxified blood back to the heart
how is the liver tissue organized in general
3 dimensional hexagonal arrangements of hepatocytes
hepatic laminae
sheets of hepatocytes
hepatic sinusoids
lined w endothelial cells (something like capillaries) located b/w hepatic laminae
- connect and mix blood from hepatic artery and hepatic portal vein which exits the central vein
central vein (liver)
joins together veins to lead blood to the inferior vena cava and to the heart
portal triad (liver)
composed of a bile duct, branch of the hepatic artery and branch of hepatic portal vein, loc towards the outside of hexagon shaped organized hepatocytes
bile canaliculi
small canals that run b/w each hepatocyte that lead to bile ducts
- bile travels toward the triad on the outside of the hexagon shaped arrangements
kupffer cells
aka stellate reticuloendothelial cell, found in the liver
- digests foreign material that has gotten as far as the liver
breaks down worn out red and white blood cells
bile flow
right and left hepatic duct common hepatic duct also from cystic duct (from gallbladder) common bile duct (joins w hepatopancreatic duct/ampulla) duodenum
blood flow in the liver
hepatic artery and hepatic portal vein drain to hepatic sinusoids to central vein to hepatic vein to inferior vena cava to the heart
carbohydrate metabolism in the liver
- maintenance of blood glucose levels
- glycogen storage/glucose release
- gluconeogenesis
- convert fructose and galactose into glucose
lipid metabolism in the liver
- TG storage/FA release
- synthesis of lipoprteins (HDL/LDL) and cholesterol
protein metabolism in the liver
deamination: detoxifiying AAs
- also produces plasma proteins, albumin and fibrinogen
gluconeogenesis
building glucose from metabolic byproducts
- uses some amino acids (ex. alanine), glycerol, lactate
deamination
detoxifying amino acids by removing NH2 (the amino group) from the AA to use what’s left for energy
- NH2 is converted to NH3 (ammonia which is toxic) which is converted into urea for excretion by the kidneys
small intestine
3 metres long (6.5 after death), 2.5 cm diameter, large surface area for absorption
3 parts: duodenum, jejenum, ileum
duodenum
25 cm long
C-shaped
retroperitoneal
jejenum
1 m long
lots of absorption here
ileum
2 m long
connects to large intestine at ileocecal sphincter (since opening to LI is cecum)
circular folds
fingerlike projections in submucosa that form a spiralling pattern, that chyme spins around and keeps contact w the walls
- highly vascularized layer in submucosa for absorption
villi
fingerlike projections in lamina propria layer of mucosa with different types of cells
- highly vascularized w blood capillaries and lacteals
lacteal
extension of lymphatic vessels in villi
microvilli
make fuzzy border that contain brush border enzymes which help breakdown food more
- gives fuzzy look to inside of SI and increases surface area for absorption
types of cells in mucosa layers of small intestine
absorptive cells
goblet cells
enteroendocrine cells
paneth cells
absorptive cells
found in small intestine, absorb nutrients and contain enzymes for digestion produced by intestines
- enzymes produced from these cells get stuck in brush border on microvilli on top of these cells
- found on top of villus and are mixed throughout also
enteroendocrine cells of the small intestine
secrete hormones secretin and cholecystokinin
paneth cells
found in small intestine on villi secrete lysozyme (regulates microbial nature inside digestive tract) also capable of phagocytosis
intestinal juice
secreted by intestinal glands in mucosal layer by absorptive cells
1-2 L secreted/day
pH 7.6 which is more optimal for enzymes in this region
- consists of water, mucus, and bicarbonate ions
brush border enzymes
enzymes released from absorptive cells don’t get released into lumen, but get embedded into brush border of microvilli membranes instead
- last chance for breakdown into absorbable components
what enzymes are a part of the brush border enzymes
CARB ENZYMES: alpha dextrinase, maltase, sucrase, lactase
PROTEIN ENZYMES: aminopeptidase, dipeptidase
NUCLEOTIDE ENZYMES: nuleosidases, phosphatases
types of mechanical digestion in the SI
segmentation
migrating motility complex
segmentation
local mixing of chyme with intestinal juices and swishing back and forth
- triggered by distention of walls of small intestine. when volume of chyme decreases again, then segmentation stops
migrating motility complex
squeezing one end of small intestine from stomach to ileum with both types of muscles and peristaltic movement
- takes 1.5 to 2 hours and is thought to cause stomach rumbling sounds when hungry
how long does chyme stay in the small intestine?
3-5 hours in total
where does absorption occur?
90% small intestine
10& stomach and large intestine
what is the absorbable unit of carbs in the small intestine?
monosaccharides: glucose, fructose, galactose
what is the absorbable unit of lipids in the small intestine?
free fatty acids, glycerol and monoglycerides
what is the absorbable unit of proteins in the small intestine?
primarily single amino acids, dipeptides and tripeptides
glucose and galactose absorption in the small intestine
- pass through apical surface by secondary active transport using Na+ conc. gradient
- glucose and galactose compete for the same protein channel
- cross basolateral surface by way of facilitated diffusion
fructose absorption in the small intestine
passes through apical and basolateral surfaces via facilitated diffusion
amino acid absorption in the small intestine
- pass through apical surface via active transport or secondary active transport with Na+
- pass through basolateral surface via simple diffusion
dipeptide and tripeptide absorption in the small intestine
- pass through apical surface by way of secondary active transport with H+
- pass through basolateral surface via simple diffusion
small short chain FAs (10-12C) absorption in the small intestine
- simply diffuse through apical and basolateral surfaces
long chain fatty acids (>12C) and monoglycerides
- bile salts surround long chain FAs and form a micelle which picks up and drops off into other side of apical cell surface by simple diffusion
- TG are surrounded by chylomicrons (proteins that are too big to enter capillaries) so they enter the lymphatic system through a lacteal of a villus
- then travel through thoracic duct (central lymphatic vessel) to junction of left internal jugular and subclavian veins
emphysema
- when alveolar surface walls on inside start to breakdown and you end up with balloon lungs instead of bunches of grapes for lungs
- a types of COPD usually caused by external env’tal factors, characterized by difficulty breathing, shortness of breath
COPD
chronic obstructive pulmonary disorder
pulmonary function tests
FEV1: forced expiratory volume in 1 second
FVC: forced vital capacity
hallmark test for emphysema
FEV1 bc if it’s low relative to your vital capacity, it signals that you can’t exhale fast enough
- shows a decrease in the elastic recoil of the lungs due to loss of elastic fibers
- air becomes trapped in lungs and gets “stale” which gives feelings of shortness of breath
treatment options for emphysema
bronchodilators
inhaled steroids
oxygen therapy
bronchodilators as treatment for emphysema
drugs that help relieve coughing, shortness of breath and breathing problems by relaxing constricted airways
inhaled steroids as treatment for emphysema
corticosteroid drugs inhaled as aerosol spray to decrease inflammation and may help relieve shortness of breath
