objective 6 pt 2 Flashcards
food passes from mouth into oropharynx and then into laryngopharynx
allows passage of food, fluids, and air
stratified squamous epithelium lining contains mucus-producing glands
pharynx
what do external muscle layers consists of two skeletal muscle layers?
inner layer runs longitudinally
outer encircles wall of pharynx
flat muscular tube that runs from laryngopharynx to stomach
pierces diaphragm at esophageal hiatus to enter abdomen
joins stomach at cardinal orifice which is surrounded by the cardiac sphincter
esophahgus
keeps orifice closed when food is not being swallowed
mucus cells on both sides of sphincter help protect esophagus from acid reflux
cardiac sphincter
what are the two phases of deglutition?
buccal phase
pharyngeal-esophageal phase
voluntary contraction of tongue compacts food and makes a bolus that initiates swallowing
buccal phase
involuntary phase that primarily involves vagus nerve
controlled by swallowing center in medulla and pons
pharyngeal-esophageal phase
a temporary storage tank and performs physical and chemical breakdown of food into a slurry called chyme
located in upper left quadrant, nearly hidden by liver and diaphragm
stomach
what are the major regions of the stomach?
cardiac sphincter
fundus
body
pyloric part
greater curvature
lesser curvature
at end of esophagus before stomach; prevents acid reflux
cardiac sphincter
dome-shaped region beneath diaphragm
fundus
mid-portion; continuous with pyloric part
body
pylorus is continuous with duodenum through pyloric valve
pyloric part
convex lateral surface of stomach
greater curvature
concave medial surface of stomach
lesser curvature
extend from curvatures and ether stomach to other digestive organs
mesenteries
runs from lesser curvature to liver
lesser omentum
drapes from bottom of greater curvature over intestine, spleen, and transverse colon
greater omentum
fibers from thoracic region are relayed through the celiac plexus
sympathetic
fibers are supplied by vagus nerve
parasympathetic
has circular and longitudinal smoother muscle layers but also has extra layer of smooth muscle
muscularis externa
allows stomach to pummel food, which increases physical breakdown
inner oblique layer
consists mostly of mucuous cells
dotted with gastric pits, which lead into gastric glands that produce gastric juices
mucosa layer
folds in mucosa
ruage
what are the types of secreting cells in gastric glands?
mucous neck cells
parietal cells
chief cells
enteroendocrine cells
secrete thin, acidic mucus of unknown function
mucous neck cells
makes stomach contents acidic; breaks down protein, activates pepsin, breaks down plant cell walls, and kills many bacteria
hydrochloric acid
required for absorption of vitamin B12 in small intestine
intrinsic factor
what are the secretions of chief cells?
pepsinogen
lipases
activated by HCL to convert to pepsin
pepsinogen
fat digesting enzyme
digests ~15% of lipids
lipases
secrete variety of hormones including gastrin; chemical messenger
enteroendocrine cells
what are the processes carried out by stomach?
- Carries out breakdown of food
- Serves as holding area for food
- Delivers chyme to small intestine
- Denatures proteins by HCl
- Pepsin carries out breakdown of proteins
- Lipid-soluble alcohol and aspirin are absorbed into
blood - The only stomach function essential to life is secretion
of intrinsic factor for vitamin B12 absorption
what is the gastric mucosa regulated by neural mechanisms?
vagus nerve stimulation increases secretion
sympathetic stimulation decreased secretion
what is the gastric mucosa regulated by hormonal mechanisms?
- Gastrin stimulates secretion of enzymes and HCl
secretion - Gastrin antagonists are secreted by small intestine
what are the 3 phases of gastric secretions?
cephalic phase
gastric phase
intestinal phase
conditioned reflex triggered by aroma, taste, sight, thought. occurs before food enters stomach (minutes)
cephalic phase
lasts 3-4 hours and provides two-thirds of gastric juice released
gastric phase
stomach distension activates stretch, receptors, initiating both long and short reflexes
chemical stimuli, such as partially digested proteins, caffeine, and low acidity, activate secretion of gastrin
Release of gastrin initiates HCl release from parietal
cells and activates enzyme secretion
A Buffering action occurs as proteins (which tie up H+)
causes pH to rise, which activates more gastrin
secretion
stimulation of gastric phase
Low pH (below 2) inhibits gastrin secretion
Occurs between meals
Occurs during digestion as negative feedback
mechanism
The more protein, the more HCl acid is secreted,
causing decline in pH, which inhibits gastrin
secretion
Activation of fight or flight response
inhibition of gastric phase
begins with a brief stimulatory component but is primarily inhibition
intestinal phase
Partially digested food enters small intestine,
causing a brief release of intestinal (enteric)
gastrin
Encourages gastric glands of stomach to
continue secretory activities
Stimulatory effect is brief and overridden by
inhibitory stimuli as intestine fills
stimulation of intestinal phase
what are the 4 main factors in duodenum cause inhibition of gastric secretions?
- Distension of duodenum due to entry of chyme
- Presence of acidic chyme
- Presence of fatty chyme
- Presence of hypertonic chyme
what are the 2 ways inhibition is achieved?
enterogastric reflex
enterogastrones
how does the duodenum inhibits acid secretion in stomach?
enteric nervous system
sympathetic nervous system and vagus nerve
how does the duodenal cells release important hormones that inhibit gastric secretion?
secretin
cholecystokinin
gastric inhibitory peptide
of smooth muscle in the fundus and body in anticipation of and food moving through esophagus. coordinated by vagus nerve
receptive relaxation
stomach can stretch without increasing tension or contracting expulsivity
gastric accomodation
peristalsis begins near gastroesophageal sphincter to pylorus
pyloric part acts as filter that allows only liquids and small particles pass through pyloric valve. approx 3ml released at a time
gastric contractile activity
- Duodenum can prevent overfilling by controlling how
much chyme enters - Duodenal receptors respond to stretch and chemical
signals - Enterogastic reflex and enterogastrones (hormones)
inhibit gastric secretion and duodenal filling - Stomach empties in ~4 hours, but increase in fatty chyme
entering duodenum can increase time to 6 hours or more - Carbohydrate-rich chyme moves quickly through
duodenum
regulation of gastric emptying
digestive function is production of bile
liver
fat emulsifier
bile
chief function is storage of bile
gallbladder
supplies most of enzymes needed to digest chyme, as well as bicarbonate to neutralize stomach acid
pancreas
what are the 4 lobes of the liver
right (larger), left (smaller), caudate, quadrate
a mesentery that separates right and left lobes
suspends liver from diaphragm and anterior abdominal wall
falciform ligament
remnant of fetal umbilical vein along free edge of falciform ligament
round ligament
anchors liver to stomach
lesser omentum
supplies oxygen
hepatic artery
brings nutrient filled blood from intestines
hepatic portal vein
what are the bile ducts
common hepatic duct
cystic duct
common bile duct
leaves liver
common hepatic duct
drains the gallbladder
cystic duct
formed by union of common hepatic duct and cystic ducts
common bile duct
hexagonal structural and functional units
composed of hepatocytes that filter and process nutrient-rich blood
liver lobules
leaky capillaries located between hepatic cells
liver sinusoids
in liver sinusoids remove debris and old RBCs
stellate macrophages
what are the liver functions?
Produce ~900 ml bile per day
Process blood-borne nutrients
* Store fat-soluble vitamins (A,D, E & K)
* Perform detoxification of waste and drugs
* Metabolism of fats, proteins and CHO
yellow-green, alkaline solution, containing bile salts, bile pigments, cholesterol, triglycerides, phospholipids and electrolytes
bile
cholesterol derivatives that function in fat emulsification and absorption
bile salts
bile pigment, a waste product of heme formed during breakdown of erythrocytes
bilirubin
a thin-walled muscular sac beneath right lobe of liver
functions to store and concentrate bile
contains many honeycomb folds that allow it to expand as it fills
gallbladder
flows into bile duct that empties into duodenum of SI
cystic duct
produces enzymes that break down all categories of food
soft, tadpole shaped, mostly retroperitoneal; deep to greater curvature of stomach; between spleen and small intestine
pancreas
what are the exocrine functions of the pancreas?
produce pancreatic juice
clusters of secretory cells to produce enzyme rich component of pancreatic juices
acini
secrete pancreatic juices to duodenum via main pancreatic duct; smaller duct cells produce water that make up the bulk of pancreatic juice and bicarbonate which makes it alkaline
ducts
what are the endocrine functions of the pancreas?
secretion of insulin and glucagon by pancreatic islet cells
what is the composition of pancreatic juice?
1200–1500 ml/day is produced containing:
* Watery, alkaline solution (pH 8) to neutralize acidic
chyme coming from stomach
* Electrolytes, primarily bicarbonate - > HCO3-
* Digestive enzymes:
Proteases
amylase
lipases
nucleases
secreated in inactive form to prevent self-digestion of pancreas, activated in the duodenum
proteases
breaks down carbohydrates (straches)
amylase
breaks down lipids (fats)
lipases
breaks down nucleatic acids
nucleases
what hormones control the regulation of pile and pancreatic secretions?
cholecystokinin
secretin
stimulates gallbladder to release bile
cholecystokinin
produced in response to acid
secretin
