tbl 2 Stomach (Basic Science) Flashcards
Regions of the stomach
Orad Region: Opens to receive contents from the esophagus. It is thin walled.
- _______, _____ and part of body (corpus)
Caudad Region: This is where food is mixed and propelled into the small intestine. It is thick walled to handle the stronger contractions to help with peristalsis and trituration.
- part of body, _____, pylorus
cardia, fundus;
antrum
Sphincter:
1) ________ sphincter / lower esophageal sphincter (proximal end),
2) Pyloric sphincter (distal end).
Cardiac
Functions of stomach
- Reservoir that is able to relax to accommodate large volumes of food with only small increases in pressure.
- Grinds food to optimum-sized particles.
- Mixes the food bolus with gastric juice and converts the bolus into ______.
- Controls its own emptying, retaining the solid portion of the meal until most of the liquid has emptied.
- ______ the food, retaining large particles, permitting more time for its breakdown.
- Regulates the rate at which chyme is delivered to the intestine.
- Secretes ____________, which kills bacteria that enters with food.
- Secretes _______, which begins the digestion of proteins.
- The acid lowers the pH of the gastric lumen and allows the optimal activation of pepsin. The lower pH of the gastric lumen also releases _______ from insoluble ferric salts in food.
- Secretes intrinsic factor required for vitamin B12 absorption.
chyme; Sieves
hydrochloric acid; pepsin; ferric
What are the layers of the stomach (hint: Elvis Lives Making Sweet Soulful Original Country Music Love Songs.)
- Epithelium
- Lamina Propria
- Muscularis Mucosae
- Submucosa
- Submucosa plexus (Meissner’s plexus)
- Oblique muscle
- Circular Muscle
- Myenteric plexus
- Longituinal Muscle
- Serosa
Glands: The gastric mucosa contains several gastric glands, several of which open into a _______ on the surface of the gastric mucosa. In the pyloric and cardiac regions of the stomach, the gastric glands only secrete mucous. In the fundus and the body of the stomach, the gastric glands contain a variety of cells with different functions (see figure B). These secretions mix with mucus in the neck of the glands
and are then emptied into the stomach lumen.
1. Parietal cells (______ cells) – secrete HCl and Intrinsic factor (needed for vitamin B12 absorption)
2. Chief cells (_________ cells) – secrete pepsinogens, which are activated to the enzyme pepsin to digest proteins to peptides
3. G cells – secrete the hormone _____ (antrum)
4. D cells – secrete the hormone _____ (antrum)
5. Enterochromaffin-like cells (ECL cells) – secrete ______. They lie near parietal cells in gastric glands.
6. ______: secrete mucous
gastric pit;
Oxyntic; Zymogen
gastrin; somatostatin; histamine; Neck cells
Motor functions of fed stomach are
- Receptive relaxation of the _____ region
- Contraction of the stomach which includes peristalsis, _______and________.
- Gastric emptying moves contents into _______
orad; trituration; retropulsion; duodenum
Receptive relaxation of the orad region of the stomach
- Receptive Relaxation (Accommodation Reflex): Distension of lower esophagus by food relaxes the LES, and simultaneously relaxes the orad stomach.
- No action potentials and NO phasic contractions occur.
- The orad stomach in its relaxed state can accommodate 1.5L of food. - ___________: Both afferent and efferent limbs of the reflex are carried by the Vagus nerve. Vagotomy (cutting the Vagus nerve) abolishes receptive relaxation.
- Tonic contraction: Orad stomach generally under tonic contraction regulated by _______ changes in resting membrane potential. Tonic contractions maintain a constant level of contraction or tone without regular periods of relaxation. Action potentials are not recorded from proximal smooth muscle in the stomach. There are no ___________, unlike in the caudad stomach.
Vago-Vagal reflex; slow; phasic contractions
Contractions of the stomach
1. Peristaltic contractions: Peristalsis is a reflex response that is initiated when the gut wall is stretched by the contents of the lumen, and it occurs in all parts of the GI tract from the esophagus to the rectum. The stretch initiates a _______ contraction behind the stimulus and an area of relaxation in front of it. The waves of contraction move from orad to caudad direction. Waves begin in _________ and move distally along caudad stomach.
- In the receiving segment, the longitudinal
muscles ahead of the intraluminal contents _______ and the circular muscles _______ causing the lumen to expand and receive the intraluminal contents.
- Circular smooth muscles in the propulsive segment behind the intraluminal contents contract and
the longitudinal muscles relax, pushing the bolus forward. It is independent of the extrinsic innervation.
- _________ is the process for reducing the particle size of food by grinding. To enter the duodenum, solids must be reduced to particles of 1 mm3 or less. Muscle contractions break the food into smaller pieces and mix it with gastric secretions to begin the digestive process. The strength of contractions increases as the food bolus approaches the pylorus.
- Retropulsion: As the peristaltic wave approaches the pylorus, the pyloric sphincter closes, thus allowing only a small amount of ____________ to squirt through the sphincter into the duodenum. The more solid chyme is propelled back into the stomach for further mixing and further reduction of particle size to <1 mm3. Finally, when all the chyme is of the right size, it is propelled through the pyloric sphincter into the duodenum
circular; middle of stomach; contract; relax
Trituration;
liquefied chyme
Phasic contractions in the caudad stomach: These periodic contractions followed by relaxations are found in the caudad stomach and are involved in mixing and propulsion.
Neurohormonal control of contractions
- Parasympathetic stimulation (Vagus nerve), gastrin (hormone released by G cells in the _____) and motilin (a peptide released by M cells in the intestine and by ________________) increase action potentials and force of contractions.
- Sympathetic stimulation, secretin (hormone released by S cells in the small intestine) and ___________________(peptide released by K cells in the small intestine) decrease action potentials and force of contractions.
antrum; peptidergic nerve endings; Gastric Inhibitory Polypeptide
Gastric emptying: Stomach effects
- Duration: ≈ 2-4 hours.
- Size: Solids <1 mm3 enter duodenum.
- Liquids (<20 min) empty faster than solids (<120 min).
- Isotonic solutions empty faster than hypo-/hypertonic solutions.
- _________ meals empty faster than protein-rich meals, which empty faster than ________ meals.
- High caloric meals empty slowly to keep rate of delivery of caloric input to the small intestine within a narrow range.
- Increased intragastric volume speeds up gastric emptying by triggering _________ in the stomach.
- _______ speeds up gastric emptying by increasing force of contraction.
- Pyloric sphincter relaxation is mediated by the Vagus nerve; vagotomy decreases relaxation of the sphincter and slows gastric emptying of solids.
- _____________: This is a narrowing (stenosis) of the outlet of the stomach so that food cannot pass easily from it into the duodenum.
Carbohydrate; fatty;
mechanoreceptors;
Gastrin;
Pyloric stenosis
Gastroparesis : Defective gastric emptying without ________________of the stomach or the duodenum can occur as a primary event, due to inherited or acquired disorders of the gastric pacemaker, or it can be secondary to disorders of autonomic nerves (particularly diabetic neuropathy) or the gastroduodenal musculature (e.g. systemic sclerosis & amyloidosis). _________ treat gastroparesis.
mechanical obstruction; Prokinetic agents
Fat in the duodenum: Fat digestion triggers the production of CCK, PYY, VIP, GIP that reduce gastric motility and thereby decrease gastric emptying. Since fats are particularly effective in inhibiting gastric emptying, some people eat cheese with crackers, or snack on bread with olive oil before a cocktail party. The fat keeps the alcohol in the stomach where its absorption is slower than in the small intestine; the intoxicant enters the blood stream slowly.
- PYY, a 36-amino acid protein released by _________ in the intestinal mucosa, slows gastric motility.
- Cholecystokinin (CCK), a hormone released by ______ in the intestinal mucosa and by colonic nerve endings in response to products of digestion, increases _____________ (preventing reflux of duodenal contents into the stomach) and slows gastric emptying.
- Gastric Inhibitory Polypeptide released by K cells of the ______________ inhibits gastric secretion and motility.
- _______________________ released by peptidergic fibers of the vagus nerve decreases gastric motility.
L cells;
I cells; pyloric sphincter tone; duodenum and jejunum;
Vasoactive intestinal peptide (VIP)
Acidity of the duodenum slows gastric emptying
• __________ released from S cells in the small intestine in response to acid entry into the duodenum causes contraction of the pyloric sphincter and reduces gastric emptying.
• H+ receptors in the _______________ detect low pH (pH 3-4) due to acid entry and relay this information to gastric smooth muscle via interneurons in the ____________________. Upon stimulation of the local enterogastric reflex, the release of ______ is suppressed. This reduction delays gastric emptying because Gastrin normally increases phasic contractions in the stomach, and decreased gastrin means fewer action potentials and weaker contractions.
• Why the delay? By slowing down gastric emptying, the gastric contents are delivered slowly to the duodenum, permitting time for neutralization of H+ by ______________, as is necessary for optimal function of pancreatic enzymes.
Secretin; duodenal mucosa; myenteric (Auerbach) plexus; gastrin; pancreatic HCO3-
During _____________ (between meals), clearance of residual food is achieved by Migrating Motor Complexes (MMCs) that spread from the stomach or duodenum to the ileum. MMCs immediately stop with ingestion of food, but not if food is given parenterally. MMCs are not seen in the digestive period. MMCs occur in three phases, each cycle lasting 90 min.
• Phase I lasts about ____ there are no contractions or spike potentials on the underlying Basic Electric Rhythm (BER).
• Phase II lasts around 6 min and is associated with ____________ on the BER and irregular contractions.
• Phase III lasts around 3 min and is associated with regular spikes on the BER and regular contractions. It is associated with a rise in plasma motilin. Motilin, a 22 amino acid protein released by ________ in the intestinal mucosa, acts on motilin receptors on smooth muscle and on enteric nerves and increases MMCs.
inter-digestive periods; 80min; irregular spikes; M cells
Secretions during MMCs: During ____________________, there is an increase in the secretion of _________, bile and pancreatic juices that clear the stomach and small intestine of luminal contents in preparation for the next meal. MMCs are possibly responsible for __________________.
__________ terminate the MMC. Vagal inputs also regulate the MMC.
phase II and phase III; “hunger contractions”
Gastrin and CCK
Basal electric rhythm
• The BER are ____________ (also called pace-setter potentials) due to oscillating depolarizations and repolarizations.
• _________ or Pacemaker cells are star-shaped mesenchymal cells that lie near the myenteric plexus (between the circular and longitudinal muscle layers) and make electrical synapses with smooth muscle. They determine the frequency of BER.
gastric slow waves; Interstitial cells of Cajal
HCl
- Cell: Parietal cell
- site: Body
- Function: initiates _____ digestion, frees _______ from food, frees vitamin B12 from food, kills bacteria
protein; ferric
Intrinsic factor
- cell: parietal cell
- site: body
- function: required for absorption of B12 in _______
ileum
Pepsinogen
- cell: chief cell, ___ cell
- sites: body, _____
- Precursor of pepsin that initiates protein digestion
mucus;
antrum
Gastrin
- cell: G cell
- site: ____
- induces histamine and HCl secretion
- increases gastric motility
- _____ to gastric mucosa
antrum; trophic
Somatostatin
- cell: ____
- site: ____
- inhibits gastric secretion from G cell
D cell; antrum
Histamine
- cell: ______
- site: body
ECL cell