Stomach

Embryology

Derived from primitive foregut
Fusiform dilation noted at end of 4th wk
Faster dorsal growth creates greater curvature
Stomach rotates 90 degrees clockwise on longitudinal axis
Endoderm lined primitive gut -cuboidal or columnar epithelium

Foveolar cells produce mucous and line primitive gastric crypts
Foveolar epithelium eventually covers the surface of the stomach and upper 2/3 gastric pits
Eventually encircled by splanchnic mesoderm

Mesoderm differetiates into smooth muscle layers

Anatomy

J-shaped expanded portion of the alimentary canal distal to the esophagus
Position and location varies widely depending on body habitus
slightly larger than the large intestine when empty,

can expand to hold 2-3L (adult)

newborn stomachs hold ~30mL

Parts of the stomach

Cardial orifice - the opening or entrance to the stomach continguous with the distal esophagus, The area within the stomach surrounding this orifice is called the cardia
Fundus - the dome or top part of the stomach most notable when expanded. seperated from the esophagus by the cardial notch (which also approximates the lower border of the fundus) the fundus usually reaches the level of the 5th intercostal space
Body - the major and central portion of the stomach. lies between the fundus and the pyloric antrum

smooth and reddish brown in color
covered by continuous mucous layer
longitudinal ridges called gastric folds or rugae (roo-jee) most marked toward pyloric part and greater curvature.
Gastric Canal - is a canal that forms between longitudinal folds of the mucosa when swallowing.

caused by firm attachment of mucosa to muscular layer (no oblique layer in this section).
Liquids, saliva, and masticated food pass to the pyloric antrum along this canal when stomach is mostly empty
Can be seen radiographically and endoscopically
Dissappears when stomach distends

Pyloric part:

Pyloric antrum the wide part of the funnel shaped exit of the stomach
Pyloric canal the narrow part of the funnel
Pylorus - the distal sphincter, the gatekeeper to the pyloric orifice through which food must pass to enter the duodenum

Lesser curvature:

shorter concave border of the stomach
angular incisure - notch or indentation in the lesser curvature found approx 2/3 distance of lesser curvature. It marks the division between the Body and the pyloric part
the lesser omentum (gastrohepatic ligament) attaches to the lesser curvature

Greater curvature

the lower longer convex border of the stomach

the greater omentum (gastrocolic ligament) attaches to the greater curvature

Vasculature (a picture is worth a thousand words!)

Arterial blood supply derives from the Celiac Trunk

Lesser curvature supplied by the L and R gastric arteries
Greater Curvature - L and R gastro-omental (gastroepiploic)
Fundus - short gastric a and posterior gastric a(branches off splenic artery)
distal stomach /pylorus - Gastroduodenal a

Venous drainage follows the arterial supply however:

The inferior mesenteric vein enters the splenic vein which joins with the Superior mesenteric vein to form the portal vein superiorly
R gastro-omental joins the pancreaticoduodenal v which enters the superior mesenteric vein below its convergence with the splenic vein
The prepyloric vein lies over the pylorus and is frequently used as a surgical landmark

prepyloris vein enters the R gastric v, the right gastric vein enters the portal v

Lymphatic drainage essentially follows arteries

Gastric lymph nodes - drain superior 2/3 of stomach
Pancreatico-splenic lymph nodes - fundus and superior part of body
Pyloric lymph nodes - inferior 1/3 (Right half)
Gastric and gastro-omental lymph nodes receive drainage from the superior surfaces
Celiac Lymph nodes - common final pathway for lymph leaving all these nodes

Innervation

Parasympathetic

Anterior and posterior vagal trunks entering the abdomen through the esophageal hiatus - innervate smooth muscle of the stomach and gastric glands

Anterior from L Vagus (CN X) - runs along lesser curvature and gives off the hepatic and duodenal branches and eventually the anterior gastric branches
Posterior from R Vagus (CN X) - enters along posterior surface of esophagus. Branches innervate the anterior and posterior stomach. it gives off the Celiac Branch

Sympathetic

T6 - T9
Celiac plexus through greater splanchnic nerve
action is vasoconstrictive and antiperistaltic

PAIN

Pain from an organ is typically poorly localized and radiates to the level of the dermatome - referred pain

Right Shoulder and Right Upper back - liver, gall bladder, and duodenum due to irritation of the diaphragm
Center of back (between shoulder blades) and from xyphoid process curving down along left costal margin - Stomach

pain only located in circle under xyphoid may be - duodenal or head of pancreas

Right costal margin wrapping around back (descending) - Liver
Right costal margin wrapping around back (ascending) - gall bladder
suprapubic central - cecum and ascending colon
Left side pain over ribs - Spleen

Physiology

Stomach layers

Mucosa

Epithelium - simple columnar epithelial cells (surface mucous cells)

extends down into the lamina propria - forms columns of secretory cells called gastric glands which open into channels called gastric pits
secretory cells create gastric juice which amounts to about 2-3L / day

Lamina propria - areolar connective tissue
Muscularis mucosae - smooth muscle

Submucosa -areolar connective tissue
Muscularis - three layers of muscle (outer longitudinal muscle, middle circular, and inner oblique muscle layer - mostly in the body)
Serosa - simple squamous epithelium -mesothelium and areolar connective tissue

part of the visceral peritoneum

extends upward as the lesser omentum
extends downward as the greater omentum draping over the intestines

Several minutes after food enters the stomach, peristaltic movements (mixing waves) occur every 15-25 seconds which creates a liquid called chyme

peristalsis not seen in fundus which has a storage function (reservoir)
each mixing wave pushes chyme against the pylorus which normally remains almost fully closed. As each waves passes about 3mL of chyme is pushed out into the duodenum (gastric emptying)

Exocrine Cell

Cell type	Location	Function
Mucous (neck) Cells	all 4 parts	Secrete mucous layer -protect stomach
Parietal Cells (Oxyntic)	Primarily Body (Corpus)	Secrete intrinsic factor and HCl (gastric acid)
Chief Cells (Zymogen)	Primarily Body (Corpus)	Pepsinogen I & II, Gastric Lipase

Endocrine Cells - secrete hormones

Cell Type	Location	Hormone
G Cell	Mainly pyloric antrum	Gastrin
Enterochromaffin-like (ECL) cells	Primarily Body (Corpus)	Histamine
Enterochromaffin cells	all 4 parts	Serotonin and Melatonin
Gastric D cells	all 4 parts	Somatostatin

Chyme mixing with gastric acid

inactivated salivary amylase
activates lingual lipase - breaks down triglycerides into fatty acids and diglycerides

Production of HCl in the parietal cell

H2O and CO2 combine via the enzyme carbonic anhydrase to form H2CO3 (carbonic acid) which dissociates to form H+ and HCO3- (bicarb)

bicarb builds up in the cytosol and is exchanged for Cl- (via Cl-/HCO3- antiporters in the basolateral membrane) and enters the blood stream

Alkaline tide - Large amounts of bicarb entering the bloodstream following a meal can slightly elevate blood pH and raise urine pH

Signaled by several mechnisms (receptors for all 3 are found in plasma membrane of parietal cells) including:

Acetylcholine ACh released by parasympathetic neurons
gastrin released by G cells
Histamine

H+ released into the lumen via the H+/K+ ATPase Proton pump

Histology

Gastric Pits (foveolae) / Gastric Glands

organization of gastric gland

Lumen at the top -surface mucous cells
Isthmus - mostly mucous cells, some parietal cells. it is basically the elongated entrance to the pit
Neck - stretch of cells between the isthmus (sometimes isthmus and neck used interchangably) and the body/Fundus
Base or Fundus at the bottom of the gland

Cell types

Mucous cells - start in base of pit and migrate upwards as they mature.

they are replaced every 3-5 days

Parietal (oxyntic) cells - stain Red with H&E, Migrate downward as they mature (most numerous in upper and middle parts of the neck)

large cells, sometimes binucleate, triangular shape with base on basal lamina. Intracellular canaliculus - communicates with the lumen

Chief Cells - stain Blue with H&E, lots of rER (produces proteins) mostly at the base/fundus

Gastric pit variation by stomach location

Cardia -shallow, mostly mucous cells
Fundus/Body - deep branched pit, mucous at apex, parietal cells past neck/body/fundus of pit. Chief cells and neuroendocrine cells at the base
Pyloric Antrum

deep pits, mucous, parietal, neuroendocrine (G cells and D cells)

References:

Kliegman, Robert. Nelson Textbook of Pediatrics. Edition 21. Philadelphia, PA: Elsevier, 2020.
Tortora, Gerard J. Principles of Anatomy and Physiology. 15th ed. Hoboken, NJ: J. Wiley, 2009. Print.
Moore, Keith L.,, Arthur F. Dalley, II, and Keith L Moore. Clinically Oriented Anatomy. Fifth edition. Baltimore: Wolters Kluwer Health, 2009. Print.
Kleinman RE, Goulet O, Mieli-Vergani G, et al, eds. Pediatric Gastrointestinal Disease: Pathophysiology, Diagnosis, and Management. 5th ed. Hamilton, Ontario: BC Decker; 2008.
The NASPGHAN fellows concise review of pediatric gastroenterology, hepatology, and nutrition. 1st edition (2011)
Wyllie, Robert & Hyams, J.S.. (2011). Pediatric Gastrointestinal and Liver Disease. 10.1016/C2009-0-53242-4. (Accessed online Feb 2020)
Coran, Arnold G, and N S. Adzick. Pediatric Surgery. Philadelphia, PA: Elsevier Mosby, 2012. Internet resource.