Digestive System: Esophagus Anatomy

Digestive System Overview

• The alimentary canal is a long tube comprised of segments with varying diameters.
• Key components include the Esophagus, Stomach, Intestinum, and Anal canal.
• These organs are generally hollow and located in the abdominal cavity.
• The esophagus runs through the neck and thorax to reach the abdomen.
• The rectum is situated in the pelvic cavity.

Esophagus

• Also known as oesophagus.
• Connects the pharynx to the stomach.
• Part of the alimentary canal.
• Features deep longitudinal folds in the tunica mucosa.
• Additionally, contains gll. esophageae (oesophageus).
• 'ca' indicates over entire length.
• 'su' indicates in cranial half.
• 'Ru, eq, fe' indicates only at the pharyngo-esophageal junction
• The tunica muscularis contains circular and longitudinal muscle layers (stratum circulare, stratum longitudinale).
• The outermost layer includes Tunica adventitia in the cervical portion.
• As well as Tunica serosa in the thoracic (pleura) / abdominal (peritoneum) portions.
• Composed of three parts:
• Cervical part (Pars cervicalis) is from the pharynx to the 1st rib.
• Thoracic part (Pars thoracica) is from the 1st rib to the diaphragm.
• Abdominal part (Pars abdominalis) is from the diaphragm to the stomach.

Esophagus in Different Animals

• Cattle: The esophagus measures 90-95 cm, distributed as follows: cervical part (42-44 cm), thoracic part (48-49 cm), and abdominal part (2 cm). It narrows at the thoracic inlet and cranial to the diaphragm's esophageal hiatus, expanding caudally to join the rumen's atrium at a right angle. Esophageal glands are only present at the pharyngoesophageal junction.
• Pig: The esophagus is short and wide with a thin muscular layer. Its diameter remains consistent from beginning to end. Esophageal glands are found solely in the cervical part.
• Horse: The esophagus is about 1.5 m long with a muscular layer that is 4-5 mm thick proximally, gradually thickening to 1.2-1.5 cm near the cardia. It joins the stomach at an acute angle, featuring a very strong sphincter (m. sphincter cardiae). Esophageal glands are only at the pharyngoesophageal junction.
• Carnivores: The pharyngoesophageal limen marks the division between the laryngopharynx and the esophagus.

Stomach

• Described as the dilated section of the alimentary canal.
• It is an expanded part of the gastrointestinal tract situated between the esophagus and the duodenum.
• Location: abdominal cavity, caudal to the liver, and against the left abdominal wall.
• The stomach wall consists of three primary layers: Tunica mucosa with gastric glands, Tunica muscularis, and Peritoneum.
• Types of stomachs can be divided based on compartmentation:
• Simple (monogastric) stomachs have one chamber [Car, su, eq].
• Complex (polygastric) stomachs have multiple chambers [Ru].
• Divided based on lining composition:
• Glandular stomachs have exclusively glandular mucosa with a simple columnar epithelium [Car].
• Composite stomachs include a glandular part (pars glandularis) and a non-glandular part (pars nonglandularis) that is lined by a stratified squamous epithelium [Ru, su, eq].
• Parts of the stomach:
• The cardiac part or cardia (pars cardiaca or cardia) is the area around the cardiac opening.
• The fundus (fundus ventriculi) is the left extremity of the cardiac part.
• Cardiac notch (incisura cardiaca) lies between the esophagus and the fundus.
• The body (corpus ventriculi) is located between the fundus and the pylorus.
• The pyloric part (pars pylorica) is in the narrowed section opposite the cardia.
• The pyloric opening (Ostium pyloricum) connects the stomach to the duodenum.
• The Pyloric part, also known as Pars pylorica, can be broken down into the following:
• The pyloric antrum (antrum pyloricum) is the initial wider part of the pyloric section
• The pyloric canal (canalis pyloricus) is the second, short, narrow segment leading to the duodenum.
• The pylorus is the distal constriction of the stomach that contains the pyloric sphincter (m. sphincter pylori).
• The ostium pyloricum is the opening between the stomach & the duodenum.
• The stomach has two surfaces:
• The parietal surface (facies parietalis) lies against the diaphragm and liver.
• The visceral surface (facies visceralis) is located against the abdominal organs.
• The stomach has two borders:
• The dorsal concave border: Lesser curvature (Curvatura ventriculi minor)
• Provides attachment for the lesser omentum
• Angular notch (Incisura angularis) found between the corpus and pyloric part
• Ventral convex border: Greater curvature (Curvatura ventriculi major).
• Much longer and facilitates attachments for greater omentum

Layers of the Stomach Wall

• The tunica muscularis consists of:
• An outer longitudinal layer (stratum longitudinale) containing fibre longitudinales, fibre oblique externae, and fibre oblique internae.
• An Inner Circular layer (stratum circulare) that forms the m. sphincter cardiae and m. sphincter pylori.
• The stomach is loosely connected to neighboring organs via ligaments.
• The greater omentum links the stomach to the diaphragm through the gastrophrenic ligament and to the spleen via the gastrolienal ligament.
• Moreover, the lesser omentum connects the stomach to the liver through the hepatogastric ligament.

The Stomach in Canines

• In dogs (ca) the somach is a simple glandular type
• Size, shape, and position depend on the fullness.
• Capacity: 0.5 - 6L.
• Empty: weight of 65-270g; elongated U-shape with wrinkled mucosa(plicae gastricae)
• It resides in the intrathoracic part of the abdominal cavity: pars cardiaca is opposite the ninth intercostal space, while the fundus and corpus are on the left side. It's in median plane, in contact with the diaphragm and liver. The pars pylorica is ventral to the right, against the liver.
• In dogs, when moderately full, expands cranially to IX-XII rib and caudally to 1st-2nd lumbar vertebrae (VL I-II). The ventral part of the body including parts of the pyloric atrium, make contact with the abdominal floor.

The Stomach in Felines

• In cats (fe) the stomach is Simple Glandular with a C shape
• The angular notch (incisura angularis) is deep and has with a capacity of ≈ 250 ml.

The Stomach in Equines

• The horse (eq) stomach is of the Simple Composite type.
• Small relative to the animal, with a 6-15 L capacity.
• Located in the left cranial abdominal region.
• Sharply bent and elongated bag shape.
• Sharp cardial notch (incisura cardica), placing the cardia and pylorus close together.
• Distinct fundus projecting as a blind sac (saccus cecus [caecus] ventriculi).
• The Non-glandular part extends from cardia and includes the blind sac:
  • The gastric mucosa is thick
  • Pale with a raised ridge (margo plicatus) between non-glandular and glandular parts.
• In contrast, the glandular part has a color of mucose from reddish brown to yellowish pink.
• It Includes cardiac opening/region and the fundus/fundic region, margo plicatus etc

The Stomach in Porcines

• In pigs (su), the stomach is of SIMPLE-COMPOSITE type.
• It is located in the left abdominal cavity.
• The parietal surface rests against the gastric impression of the liver and the dorsal part of the diaphragm.
• The cardia is at the level of the 11th-12th thoracic vertebra.
• Its capacity ranges from 1 to 6 L.
• The fundus features a flattened conical pouch known as the ventricular diverticulum (diverticulum ventriculi) directed right and caudally.
• Has a deep Incisura angularis (antrum pyloricum)
• Also has Protuberantia in pylorus - torus pyloricus
• Caused by circular muscle, fat, & mucose

The Stomach in Ruminants

• In ruminants, the stomach is COMPLEX COMPOSITE
• Consists of:
• Pars nonglandularis: Forestomach (proventriculus) of 3 compartments
• Rumen (100-145 L)
• Reticulum (~12 L )
• Omasum (7-18 L)
• Pars glandular (true stomach): Abomasum (~20 L)

Communication Between Chambers in Ruminants

• The rumen connects with the reticulum via the ruminoreticular opening (ostium ruminoreticulare)
• The reticulum connects to the omasum via the reticuloomasal opening (ostium reticuloomasicum)
• The omasum connects to the abomasum via the omasoabomasal opening (ostium omasoabomasicum).

Rumen First Compartment

• It is huge with a volume of 100-145L and has pars nonglandularis
• Is laterally compressed sac on left side of the animal running from the diaphragm to the animals pelvic bone.
• Each surface has the following characteristics:
  • The parietal surface (facies parietalis), faces mainly the left of animal
  • Related to the diaphragm, as well as the left abdominal wall and the abdominal floor
  • The visceral surface (facies visceralis) faces to the right.
• In relation to the intestines, liver, omasum, and abomasum
• The rumen has two ends:
  • A cranial end (extremitas cranialis) and a caudal end (extremitas caudalis).
• The Rumen exterior includes sulcus cranialis, sulcus caudalis, and sulcus longitudinalis
• Specific visible structures include:
  • Sulcus coronarius dorsalis
  • Sulcus coronarius ventralis
  • Saccus caecus caudodorsalis
  • Saccus caecus caudoventralis
  • Curvatura dorsalis + ventralis.

Internal Surface of Rumen Includes

• Corresponding grooves with Pila
• Pila cranialis, caudalis, longitudinalis dextra, longitudinalis sinistra accessoria dextra/sinistra as well as coronaria dorsalis / ventralis.
• The Plica ruminoreticularis – ruminoreticular fold.

Rumen Papillae

• The rumen walls consist of a stratified squamous epithelium
• Lacks digestive glands.
• Lining forms projections which are up to 1 cm long: known as ruminal papillae (papillae ruminis).

Reticulum Second Compartment

• Is pars nonglandularis and the most cranial compartment in animal and sits between diaphragm and rumen.
• Sits on ventral adbominal wall at level of 6th-9th intercostal space, containing a volume of 12L.
• Has two surfaces, the diaphragmatic and visceral.
• Convex diaphragmatic surface is in contact with diaphragm and the visceral surface lays against rumen.
• The right reticulum is related to the left liver lobe, the omasum, and abomasum.
• Sometimes connected to ventral spleen on left
• Has ventral greater curvature and lesser curvature connecting to omasum on right/caudal side.
• Interior walls form what are called reticulum cells, they are cells subdivded by creasts.

Omasum Third Compartment

• Is pars nonglandularis
• The compartment sits on the right abdominal side in intrathoracic area, ventral to spaces (VII-X) - Has volume of 7-18 L
• Exterior walls face/connect as follows:
  • Parietal walls: Liver
  • Visceral walls: Rumen
• The Curvatura faces dorsocaudally to the right.
• Interior is Omasal laminae has highest connection to dorsal, lowest to parietal.
• Missing in fundus but covered with papillae of 5nm length.
• The highest has 90-130 segments
• The number for the highest segment is normally 12-16

Abomasum Fourth Compartment

• The abomasum is a pars glandularis, a true stomach were feed enzymes act
• Composed of a glandular mucosa
• The ostium is towards omasoabomasicum side.
• On right costal arch, in lower part in front, oppisote the 7th-11th ribs
• It is pear -shaped
• Spiral holds of mucosa+ permanent spiral, a form which consists of spirales
• It is five CM in height,
• Which can include 12-16 for bo, 13-15 for ov, 16-17 for cap

Gastric Groove

• Well developed, it is marked by a a ridge:
• Runs through all the parts of the fore-stomach.
• From the cardiac part and toward the abomasum side
• includes the reticular, omasal and Abomasal groove
• A high mucosal is made containing lips edges

Stomach Peculiarities of Small Ruminants

• Rumen has 12-25L and Saccus caecus caudoventralis (long) is longer vs caudodorsalis
• Reticulum : 1-2L, ellipsoidal
• omasum 0.3-0.9L
• abomasum 1.8-3.5L

Poultry Anatomy

• Has an ESOPHAGUS (Esophagus, Oesophagus) and STOMACH (Gaster)
• In poultry, the esophagus (Esophagus;Oesophagus) has two parts:
• Pars cervicalis is located on the right side of the neck.
• Thin walled, has longitudinal folds and is distensible.
• The crop or ingluvies is located at the thoracic inlet
• Ingesta is temporarily stored/moistening.
• Pars thoracica is then located at level of the VI vertebral rib and dilates, opening to the proventriculus.
• The avian stomach called Gaster consists of 2 parts:
• The proventriculus (proventriculus gastris - pars glandularis) is the anterior glandular part.
  • Is spine-shaped and thin-walled.
  • It is 4cm +- in length
• The Gizzard: (ventriculus gastris – pars muscularis) is the posterior muscular part-
  • Constitutes largest avian organ
• Thick, lens shapped.
• Used for mechinal grinding of food along with hard grit

Explore the alimentary canal with a focus on the esophagus, its structure, and its components such as tunica mucosa and tunica muscularis. Learn about the different layers and their locations within the digestive system. Understand the esophagus' role in connecting the pharynx to the stomach.