Histology and Anatomy of the Digestive System - Owlcation - Education
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Histology and Anatomy of the Digestive System

Deniz Burunlu currently lives in London. He has a BSc Hons in Biomedical Sciences and currently studying Medicine.

Lip (Labia)

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The lip consists of a core of striated muscle called the orbicularis oris muscle, embedded in fibro-elastic connective tissue. The outer surface is covered with skin, stratified squamous keratinised epithelium, containing many hair follicles, sebaceous glands, and sweat glands. The red margin of the lip is a transitional zone between the outer skin and inner mucous membrane. The epithelium here is thinner than the rest of the lip and the redness of the lip margin is caused by blood in the large capillary loops in the underlying connective tissue.

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Tongue

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The right and left halves of the tongue are separated by the lingual septum. The mucous membrane of the upper surface of the tongue is divided into the oral (2/3) and the pharyngeal (1/3) parts by a V-shaped sulcus called the sulcus terminalis.

There are 4 types of papillae found on the dorsal surface of the tongue:

  • Filiform Papillae are the most numerous and the smallest. They are conical elongated projections of connective tissue covered with keratinised stratified epithelium without taste buds.
  • Fungiform Papillae are mushroom-shaped projections located on the dorsal surface of the tongue mostly on the apex. Each has a very vascular connective tissue core. The taste buds are present in the covering stratified squamous non-keratinised epithelium.
  • Vallate Papillae are located on the dorsal surface in a row immediately in front of the sulcus terminalis. It is surrounded by a moat-like invagination lined with non-keratinised squamous epithelium that contains taste bunds. Ducks of lingual salivary glands empty their serous secretion flushing material from the moat to enable the taste buds to respond rapidly to changing stimuli.
  • Foliate Papillae consists of parallel low ridges separated by deep mucosal clefts
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The tongue has two types of muscles: Intrinsic and Extrinsic.

The Intrinsic muscles have no external attachments and they alter the shape of the tongue:

  • Superior longitudinal muscle
  • Inferior longitudinal muscle
  • Vertical muscle
  • Transverse muscle

The Extrinsic muscles extend from the tongue to the mandible, styloid process, and soft palate. These muscles alter the position of the tongue:

  • Genioglossus muscle
  • Hyoglossus muscle
  • Styloglossus muscle
  • Palatoglossal muscle

Blood supply is via the lingual artery and the lingual vein. Nerve supply to the intrinsic and extrinsic muscles is via efferent motor nerve fibres from the hypoglossal nerve, except for the palatoglossus muscle, which receives innervation from the vagus nerve.

Oesophagus

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A muscular tube about 25 cm long that extends from the pharynx to the stomach. The oesophagus begins in the neck at the 6th cervical vertebra level and ends at the gastric cardiac orifice. It is situated in three topographic regions: cervical. thoracic, and abdominal.

The walls of the oesophagus consist of three layers:

  • Tunica Mucosa (mucous membrane)
    • Non-keratinised stratified squamous epithelium
    • Lamina propria
    • Muscularis mucosa (longitudinal smooth muscle)
    • Submucosa (tubulo-acinar mucous glands)
  • Tunica Muscularis (muscular coat)
    • Upper 1/3 is striated muscle (continuation of the muscle of the oropharynx)
    • Middle 1/3 is interwoven striated and smooth muscle
    • Distal 1/3 is smooth muscle (like the rest of the digestive system)
  • Tunica Adventitia
    • Outer layer by which the oesophagus is fixed to adjoining structures throughout its length in the thoracic cavity.

Stomach

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The stomach is an intraperitoneal organ located in the epigastric region. The stomach is divided into three regions: cardia, pylorus, fundus.

The fundus is a dome-shaped area that projects upwards. Glands of the fundus and body are simple tubular glands that posses four type of cells: peptic cells, parietal cells, mucous neck cells, and enteroendocrine cells.

The pylorus connects the stomach to the duodenum. It is considered to have two parts: Pyloric antrum (opening to the body of the stomach) and the Pyloric canal (opening to the duodenum). The pyloric glands are located in the pyloric antrum and they are branched, coiled, and tubular glands with a relatively wide lumen.

The stomach wall has three layers:

  • Tunica Mucosa
    • Mucous secreting simple columnar epithelium
    • Lamina propria
    • Muscularis mucosae (inner circular and outer longitudinal muscle)
    • Submucosa
  • Tunica Muscularis (important for mixing chyme)
    • Outer longitudinal
    • Middle circular
    • Inner oblique
  • Tunica Serosa
    • Continues with the peritoneum of the abdominal cavity via the omentum.
The Fundus

The Fundus

The Pylorus

The Pylorus

Small Intestine

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The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal fold. Functionally, the small intestines are the principal site for digestion and absorption of products of digestion. The small intestine can be divided into three parts: duodenum, jejunum, and ileum.

Vili are present with lamina propria core, and brush border on the outermost surface with goblet cells. The arterial supply to the ileum is from the superior mesenteric artery.

The duodenum is a c-shaped tube that curves are the head of the pancreas. It is divided into four parts: superior, descending, inferior, and ascending parts. The first 2.5cm of the duodenum resembles the stomach and it is covered on its posterior and anterior surface with peritoneum. In the duodenum, the submucosa contains compound acinotubular glands called Brunner’s glands. Blood supply is via the superior and inferior pancreaticoduodenal artery, while nerve supply is via the mesenteric plexuses.

Duodenum

Duodenum

Ileum

Ileum

Large Intestine

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The large intestine has three main parts:

  • Cecum (with appendix)
  • Colon (ascending, descending, transverse, and sigmoid colon)
  • Rectum and anal canal
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Large Intestine Wall:

  • Tunica Mucosa
    • Simple columnar epithelium (mucous cells, microfold cells, enteroendocrine cells, brush cells, goblet cells)
    • Lamina propria
    • Muscularis mucosa (longitudinal and circular layers)
    • Submucosa
  • Tunica Muscularis (smooth muscle layer)
    • Outer longitudinal
    • Inner circular
  • Tunica Serosa
    • Forms the outer most layer, consists of simple squamous epithelial tissue that secretes watery serous fluid to lubricate the surface of the large intestine, protecting it from friction between abdominal organs and the surrounding muscles and bones.
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Appendix

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The appendix is attached to the posteromedial wall of the cecum, just inferior to the end of the ileum. The appendix is narrow, hollow, blind-ended tube connected to the cecum. It has a large formation of lymphoid tissue.

The walls of the appendix are similar to the large intestine:

  • Tunica Mucosa
    • Simple columnar epithelium
    • Lamina propria
    • Muscularis mucosa
    • Submucosa
  • Tunica Muscularis (smooth muscle)
    • Outer longitudinal
    • Inner circular
  • Tunica Serosa
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© 2018 Deniz Burunlu