Lecture #25: Digestive System--Stomach Flashcards
What muscle does the stomach have?
Smooth muscle
What does the smooth muscle do in the stomach?
Smooth muscle modulates luminal pressure and tension
Primarily under control of ANS-‘involuntary’
What does the smooth muscle look like?
Is present in sheets, bundles, or sheaths around tissues in the cardiovascular, respiratory, digestive, urinary, and reproductive system
When smooth muscles diffuse into nerve fibers, what transmitters are they inducing?
ACh and NE
Membran potential ~-50 to -60mV
What types of categories do smooth muscles have when they get excited?
- Single/unitary (visceral
2. Multi-unit
Where is the unitary smooth muscle cells found?
• Walls of the digestive tract, gallbladder, urinary bladder
What is the function of the unitary smooth muscle cells?
• Autorhythmic. Adjacent cells
connect via gap junctions →
transmission of APs from one
fiber to another.
• Cell membranes adhere to one
another → transmission of force
• Slow synchronized “graded”
contraction.
• Entire sheet of muscle contracts - “functional syncytium”
The structure of smooth muscle cells are composed of what?
• Sarcoplasmic reticulum is
poorly developed relative to
skeletal muscle.
• Thick filaments of SM have
actin-gripping heads along
their entire length.
• Thick and thin filaments are
arranged diagonally within
the cell contraction results
in twisting motion
What are some of the special features of smooth muscle?
• Capable of sustained contraction without fatigue and at very little energy cost.
• Maintains a low level of tension or tone even in the
absence of action potentials.
What response does smooth muscle give?
Stress-relaxation response
– Stretch causes initial increase in tension –> tension decreases within 1-2 minutes -> allows SM to change length but maintain ability to contract (important for storage organs)
What is the length-tension relationship?
• smooth muscles operate over a wider range of resting
lengths
• generally broader length-tension relationship in smooth
muscle compared to skeletal muscle
Name the major part of the stomach.
Cardia Fundus Body Pylorus Pyloric Sphincter
What happens when the stomach is being filled?
Triggers secretions and motility
Where does the stomach empty?
The stomach empties
slowly into the duodenum as small squirts of chyme
leave through the pyloric sphincter
What cell types are in the stomach?
Surface mucous cell Muscous neck cell Parietal cell Chief cell G cell
What does the surface and muscous neck cell secrete?
Surface mucous: secrets mucous, forms protective barriers that prevents digestion of stomach wall
Muscous neck cell are used for absorption, small quantity of water, ions, short-chain fatty acids, and some drugs enter bloodstream
What do parital cell secrete?
Secretes hydrochloric acid (kills microbes of food) and intrinsic factor (needed for absorption of vitamin B12)
What do chief cells secrete?
Secretes Pepsinogen (pepsin activated form-breaks down proteins into peptides) and gastic lipase (splits triglycerides into fatty acids and monoglycerides)
What do G cells secrete?
Secretes the hormone gastrin (stimulates HCl to be absorb by parietal cells and chief cells to secrete pepsinogen, relaxes pyloric sphincter)
What happens in the mechanical digestion of the stomach?
• Gentle mixing waves occur in the stomach to mix
the bolus of food with gastric juice (enzymes, acid,
water) and turn it into chyme (a thin liquid)
- More vigorous waves traveling from the body of stomach to the pyloric move the chyme along
- Intense waves near the pylorus lead to opening of the pyloric sphincter - squirting 1-2 teaspoons into the duodenum with each wave
What happens in the chemical digestion of the stomach?
• Protein digestion begins in the stomach
– HCl denatures (unfolds) protein molecules
– HCl activates pepsinogen into pepsin - an enzyme
that breaks peptide bonds between certain amino
acids
• Fat digestion continues
– gastric lipase splits the triglycerides in milk fat,
although this is most effective at pH 5-6 (infant
stomach)
- HCl kills microbes in food
- Mucous cells secrete mucus to protect the stomach walls from being digested
What nutrients does the stomach absorb?
- Water
- Electrolytes
- Some drugs (aspirin) & alcohol
• Fat content in the stomach
slows the passage of alcohol to
the intestine, where absorption
is more rapid
• Alcohol is absorbed more
slowly if taken with a meal
What are phases of digestion?
- Cephalic Phase
- Gastric Phase
- Intestinal Phase
What is the role of the cephalic phase?
• Prepare the mouth and
stomach for food
• Cerebral cortex - sight, smell, taste & thoughts of food stimulate the parasympathetic nervous system to stimulate --> Salivation (Facial and Glossopharyngeal) -->Gastric glands to secrete gastric juice (Vagus)
What is happening in the gastric phase?
• Neural influences over stomach activity
– stretch receptors & chemoreceptors (pH) signal
bolus entry
– vigorous peristalsis and gastric gland secretions
– chyme periodically released into the duodenum
• Endocrine influences over stomach activity
– distention and presence of food in stomach cause
G cells to secrete gastrin into the bloodstream;
gastrin increases gastric gland secretions and
motility, and causes pyloric sphincter relaxation
Once the gastrin is emptying, and as the bolus of food enters the stomach, what happens to the gastrin hormones?
distention of the stomach and presence of undigested contents increase the secretion of gastrin hormone & vagal nerve impulses
What happens when the gastrin hormone is secreted?
stimulates contraction of the lower esophageal sphincter and the stomach, as well as relaxation of the pyloric sphincter for emptying
What happens in the intestinal phase?
• Entry of chyme into duodenum slows gastric activity and increases intestinal
activity
• Neural influences: distension of the duodenum and chemical contents of the chyme activate sympathetic nerves, which
slow gastric activity (enterogastric reflex)
• Endocrine influences: distension of duodenum and contents of chyme trigger
hormonal release from enteroendocrine cells in the duodenum
– secretin hormone decreases stomach secretions
– cholecystokinin (CCK) decreases stomach emptying
What reflex regulates the amount of chyme released into the duodenum?
Enterogastric reflux
How is the enterogastric reflux initiated?
• initiated by distension of
duodenum & contents of the
chyme
they also cause cholecystokinin and secretin release from the duodenum and stimulate sympathetic impulses, both of which inhibit gastric emptying
So in short terms what does the cephalic phase do?
Anticipation
In short terms, what does the gastric phase do?
Breakdown
In short terms, what does the intestinal phase do?
Release
