Stomach

Kiran Goushika

Index Index

EmbryologyAnatomyHistologyPhysiologyDiseases

Stomach is a j shaped enlargement of GI tract directly inferior to the diaphragm in the abdomen. The stomach connects the esophagus to the duodenum, the first part of small intestine. It is where digestion of protein begins. The stomach has three tasks. It stores swallowed food. It mixes the food with stomach acids. Then it sends the mixture on to the small intestine.

EMBRYOLOGYEMBRYOLOGY

DEVELOPMENT DURINGTHE FETAL PERIOD

DEVELOPMENT DURINGTHE FETAL PERIOD

The stomach begins to form as fusiform(spindle-shaped) dilation in the foregut during the 4th week.The developing stomach is attached to the body walls by dorsal and ventral mesenteries.The dorsal wall of stomach grow faster than the ventral wall. The differentiation start from the greater and lesser curvatures of stomach.

During 7th week , the stomach rotates 90 degrees cloackwise about a longitudinal axis this produce a space behind called lesser sac (omental bursa).During the 8th week the stomach and duodenum rotate about ventrodorsal (A-P) axis , pulling the end of stomach upward and attain a C-shaped. Postnatal position of stomach and deudenum is attained

ANATOMY ANATOMY

ANATOMYANATOMY

In adult life, stomach located T10 and L3 vertebral segmentCan be divided into anatomic regions based on external landmarks–4 regions

i. Cardiaii. Fundusiii. Corpus (body)iv. Pyloric part

4 PARTS4 PARTS

Cardia- region just distal to the GE junctionFundus- portion above and to the left of the GE junctionCorpus- region between fundus and antrum

Margin not distinctly external, has arbitrary borders

Pyloric part- which is divided into the pyloric antrum and pyloric canal and is the distal end of the stomach

POSITION POSITION

Stomach is positioned between the abdominal esophagus and the small intestine, it is in the epigastric, umbilical, and left hypochondrium regions of the abdomen.

OTHER FEATURESOTHER FEATURES

Openings: - Gastroestophageal: to esophagus -Pyloric: to duodenum Sphincters: -The cardiac sphincter(lower esophagus sphincter) closes off the top end of the stomach. - The pyloric sphincter closes of the bottom.

Anterio- superior: in contact with Left hemi-diaphragm, left lobe and anterior segment of right lobe of the liver and the anterior parietal surface of the abdominal wallPosterio-inferior: Left diaphragm, Left kidney, Left adrenal gland, and neck, tail and body of pancreasThe greater curvature is near the transverse colon and transverse colon mesenteryThe concavity of the spleen contacts the left lateral portion of the stomach

Surface:• Anterio-superior surface• Posterio-inferior surface

Curvature:

The greater curvature, which is a point of attachment for the gastrosplenic ligament and the greater omentumThe lesser curvature, which is a point of attachment for the lesser omentum.

· Layers of peritoneum attached to the stomach:

· Lesser omentum: attaches the liver to the lesser curvature.

· Greater omentum: attaches the greater curvature to the posterior body wall

VASCULATUREVASCULATURE

Arterial blood supply:– 3 Branches

• Left Gastric Artery– Supplies the cardia of the stomach and distal esophagus

• Splenic Artery– Gives rise to 2 branches which help supply the greater

curvature of the stomach » Left Gastroepiploic» Short Gastric Arteries

• Common Hepatic or Proper Hepatic Artery– 2 major branches

» Right Gastric- supples a portion of the lesser curvature

» Gastroduodenal artery-Gives rise to Right Gastroepiploic artery -helps supply greater curvature in

conjunction with Left Gastroepiploic Artery

Venous DrainageParallels arterial supplyRt &Lt gastric veins drain to the portalRt gastroepiploic drains to the SMV Lt gastroepiploic drains to the splenic

Lymphatic Drainage:

• Lymph from the proximal portion of the stomach drains along the lesser curvature first drains into superior gastric lymph nodes surrounding the Left Gastric Artery.

• Distal portion of lesser curvature drains through the suprapyloric nodes.

• Proximal portion of the greater curvature is supplied by the lymphatic vessels that traverse the pancreaticosplenic nodes.

• Antral portion of the greater curvature drains into the subpyloric and omental nodal groups

INNERVATIONINNERVATION

The main innervations are Left and Right Vagus Nerves.

Parasympathetic innervation of Stomach- Vagus Nerve90% of fiber in vagal trunk is afferent (info transmitting from stomach to CNS)

Sympathetic innervation of Stomach- Splanchnic NerveDerived from spinal segement T5-T10

HistologyHistology

LAYERSLAYERS

• Serosa or visceral peritoneum

• Muscularies: 3 layers Outer

longitudinal Middle

circular Inner oblique

• Mucosa

CELLSCELLSo Parietal cells

Location- neck of gastric pitStimulated by Ach, Histamine and GastrinSecretes HCl + Intrinsic Factor

o Chief CellsLocation- base of gastric pitStimulus- VagalSecretes Pepsinogen (eventually leads to pepsin- digestive enzyme)

Antral Glandso Gastrin cells

Location- mucosa of distal stomachStimulus- amino acidsSecretion- Gastrin (stimulates HCl production by way of parietal cells)

o SomatostatinLocation- mucosa of distal stomach + DuodenumStimulus- HCl or low pH in duodenumActions- Inhibits gastric emptying, Pancreatic secretions, and gallbladder contraction

PHYSIOLOGYPHYSIOLOGY

OVERVIEWOVERVIEW

Gastric motilityGastric secretions

Gastric Motor ActivityGastric Motor Activity

Main function of gastric motility-Accommodate and store ingested

meal-Grind down solid particles(tituration)

-Empty all constituents of the meal in a carefully controlled and regulated

fashion into the duodenum.

Gastric AnatomyGastric Anatomy

3 Distinct regions 1. Proximal- cardiac, fundus,

proximal body2. Distal- distal body and antrum3. Pylorus

ElectrophysiologyElectrophysiology

Slow wave – omnipresent, highly regular and recurring electrical pattern in GI tract

Does not lead to contractions, but maximal frequency of contractile activity is directly related to slow wave frequency

Contractions are related to spike potentials

3 cycles/min in stomach

Slow waves thought to originate in “gastric pacemaker” site along the greater curvature in the proximal to middle body

Migrate in both circumferential and longitudinal directions

Electrical signals do not traverse the pylorus

ICC’s (interstitial cells of Cajal) in myenteric plexus generate slow wave activity are called pacemaker of stomach.

B.Muscel tension created by action potential peak.

B.Muscel tension created by action potential peak.A. Slow wave in different

part of stomach

Fundic smooth muscle cells are electrically silent – resting membrane potential is already above the mechanical threshold

Generates tone – AP not generated – neural and hormonal input modulates tone rather than generating peristaltic contractions

GI Motor ActivityGI Motor Activity

• Motor activity is highly organized into a distinct and cyclically recurring sequence of events known as MMC (migrating motor complex)

• 3 distinct phases of motor activity – I – quiescence – II – random and irregular contractions – III – burst of uninterrupted phasic

contractions • Patterns of MMC activity commence

and end simultaneously at all sites

Fasted StomachFasted Stomach

• Phase III – Basal tone in LES in increased and exhibits

superimposed phasic contractions – Tone increases in proximal stomach – One cycle/min high-amplitude waves develop

in body – Distal antrum 3-5 cycles/min – Antropyloroduodenal coordination increases

and high-amplitude contractions propagate through the antrum across the pylorus

• Extrinsic nerves (vagus) and hormonal factors (motilin) are involved – Phase III – may be induced by motilin released

from proximal duodenum – Phase II – mediated through vagus

Fed StomachFed Stomach• Initiation of swallow – fundus undergoes

vagally mediated receptive relaxation • As meal enters stomach tone and phasic

contractions in proximal stomach are inhibited – Accommodation – 2-3 fold increase in gastric

volume • Fundic tone – balance between cholingeric • ( excitatory) and nitrergic (inhibitory) input • Fasting – cholinergic dominates • Meal – accommodation response triggered

by distention-induced stimulation of mechanoreceptors

• Mediated by vasovagal reflex – fundic relaxation may be induced by activation of inhibitory input or the inhibition of excitatory vagal efferents to the fundus

• NO is primary inhibitor of fundic tone

• Other factors modulate fundic tone

-Relaxation

• Antral distention (gastrogastric reflex)

• Duodenal acidification

• Lipid and protein (duodenogastric reflex)

• Colonic distention (cologastric reflex)• Food ingested results in abolition of cyclical pattern

of MMC

• Replaced by random contractions called fed pattern

• May last 2.5-8 hours

Gastric EmptyingGastric Emptying

• Gastric emptying dependent on the propulsive force generated by tonic contractions of proximal stomach and

• resistance presented by antrum, pylorus, duodenum

• Fundamental property of stomach – ability to differentiate among different types of

• meals and the components of individual meals

infuse fluid fluid out

time

volume of stomach

tension in stomach wall

i. liquidsi. liquids

• Liquids rapidly disperse and begin to empty without lag period

• Non-nutrient liquids empty rapidly • Nutrient containing liquids are retained

longer and empty more slowly • Liquids • Emptying of liquids follows a simple,

exponential pattern • Rate influenced by volume, nutrient

content and osmolarity • Rate of emptying determined by gastric

volume and duodenal feedback mechanisms – Antroduodenal pressure gradient is primary

factor generating liquid emptying

ii. solidsii. solids

• 2 phases – initial lag phase followed by a linear emptying phase

• Solid component is first retained in proximal stomach

• As liquid empties, solid moves to antrum and is emptied

• Essential component of normal response is ability of antropyloric region to discriminate solid particles by size and restrict emptying of particles >1mm in diameter

• Antropyloric mill grinds down (titurates) larger particles to smaller ones

• During tituration, solid emptying does not occur • Duration of lag phase is directly related to size

and consistency of solid component of the meal – Typical solid-liquid meal - ~60min

• Tituration – coordinated high-amplitude waves originate in proximal antrum and are propagated to pylorus

• Pylorus opens and duodenal contractions are inhibited permitting trans-pyloric flow of liquids and suspended or liquefied solid particles

• When liquids and solids reach distal antrum, pylorus closes promoting retropulsion of particles too large to have been exited

• Pylorus regulates passage of material

• Relatively narrow and fixed lumen

• Maintenance of pyloric tone

• Generation of isolated pyloric pressure waves

iii. Fatty food & indigestible foodiii. Fatty food & indigestible food• Liquid at body temperature • Float on top of liquid layer but empty

more slowly • Products of fat digestion in

duodenum are potent inhibitors of gastric motor events and gastric emptying

Indigestible Solids • Not emptied in immediate post-

prandial period • Must await MMC activity • Swept out during phase III

GASTRIC ACID SECRETIONGASTRIC ACID SECRETION

Acid production by the parietal cells in the stomach depends on the generation of carbonic acidsubsequent movement of hydrogen ions into the gastric lumen results from primary active transport.

The acidity in the gastric lumen converts the protease precursor pepsinogen to pepsin; subsequent conversions occur quickly as a result of pepsin’s protease activity.

REGULATION OF GASRIC ACID SECRETION

REGULATION OF GASRIC ACID SECRETION

DISEASESDISEASES

COMMON DISEAESESCOMMON DISEAESES

• Peptic ulcerA lesion in the lining of the digestive tract, typically in the stomach or duodenum, caused by the digestive action of pepsin and stomach acid• GastritisInflammation of the lining of the stomach• GastroparesisCondition consisting of a paresis of the stomach, resulting in food remaining in the stomach for a longer period of time than normal. ...

Stomach cancerGastric cancer can develop in any part of the stomach and may spread throughout the stomach and to other organs; particularly the esophagus, lungs, lymph nodes, and the liver. stomach cancer causes about 800,000 deaths worldwide per year.Peptic ulcer diseaseAn ulcer of an area of the gastrointestinal tract that is usua

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