Plica circularis | anatomy | misjon.info
The plicae circulares and villi & microvilli. of digestion and absorption of ingested food occurs in the small intestine (approximately 80% of all. If the search does not return a results, a link to a Google search is presented. of two muscle layers, the inner circular layer and outer longitudinal layer. . Microvilli make up a brush border on the surface of the columnar cells of the of the small intestine that maximize its surface area: plicae circularis, villi, and microvilli. Also called a plica circulare, a circular fold is a deep ridge in the mucosa and submucosa. There are about 20 to 40 villi per square millimeter, increasing the surface There are an estimated million microvilli per square millimeter of small .. The resulting difference in pain threshold is due to the fact that the upper.
In many regions the mucus is partially preserved and stains with hematoxylin. At the base of the crypts, undifferentiated cells and endocrine cells are present; however, Paneth cells are not usually present.
The appearance of the lamina propria is essentially the same as in the small intestine: Leukocytes are abundant and the isolated lymphoid nodules present in this tissue extend into the submucosal layer survey the left lower area of slide The muscularis mucosae is a bit more prominent compared to the small intestine, and consists of distinct inner circular and outer longitudinal layers. The submucosa of this specimen is particularly well fixed such that you may better appreciate the mixture of irregular connective and adipose tissue, numerous blood vessels, and several excellent examples of ganglion cells and nerves of the submucosal plexus.
This section happened to be cut such that a piece of one of these longitudinal bands may be seen. The mucosa resembles that of the colon, but Here you will observe a narrow zone of transition from the simple columnar epithelium of the intestine to the keratinized stratified squamous epithelium of skin. Within the transition zone, you may find stratified columnar or sometimes cuboidal epithelium followed by nonkeratinized stratified squamous epithelium.
While looking, move the image from the colon toward the direction of the recto-anal junction.
Small and Large Intestine | histology
The muscularis mucosa is a thin layer of smooth muscle that supports the mucosa and provides it with the ability to move and fold. The submucosa is a thick connective tissue layer that contains arteries, veins, lymphatics, and nerves.
The muscularis externa surrounds the submucosa and is composed of two muscle layers, the inner circular layer and outer longitudinal layer.
These two layers move perpendicularly to one another and form the basis of peristalsis. The adventitia consists of connective tissue containing blood vessels, nerves, and fat. In the portions of the tract within the peritoneal cavity, it is lined by the mesothelium.Layers of the Small Intestine
Recall from the Laboratory on Epithelia that the mesothelium is a specially named layer of simple squamous epithelial cells. In these tissues, the adventitia is referred to as serosa. These four layers can be identified in most gastrointestinal segments, although different segments demonstrate important structural variations that can provide clues to their functions. The greatest structural variations occur in the mucosal layers. There are four distinct types of mucosal variations: Protective mucosa is characterized by a stratified squamous epithelium.
It is found in the oral cavity, pharynx, esophagus, and anal canal. Secretory mucosa contains cells that are responsible for the secretion of digestive enzymes. It is found exclusively in the stomach. Absorptive mucosa contains two key structures, crypts and villi, and is responsible primarily for absorbing digested nutrients. It is found along the entirety of the small intestine. It is found in the large intestine.
There are four junctions in the GI tract that are characterized by abrupt changes in the mucosal lining: Gastrointestinal Motility In Physiology, you will study the movement of food through the GI tract in detail.
For now, it is important to understand a few basic principles and to relate them to the histological structure of the digestive system. In the first portion of the GI tract, from the oral cavity to the upper esophagus, food moves by voluntary muscular action.
In the following portion, from the lower esophagus through the large intestine, food moves by peristalsis. Material moves through the rest of the tract by mass movements, which transport tract contents over long distances. The motility of the GI tract is accomplished via a diffuse neuroendocrine system that involves the autonomic nervous system and hormones.
The enteric nervous system is composed of several groups of nerve cells: The interstitial cells of Cajal serve as the pacemaker cells of the GI tract and are modulated by the parasympathetic nervous system.
The submucosal plexus, or Meissner's plexus, is located in the submucosal layer and controls the mucosal glands and the muscularis mucosa. The myenteric plexus, or Auerbach's plexus, is located between the two layers of the muscularis externa and is responsible for peristaltic movements.
With this understanding of the basic structural features of the GI tract, we will now take a more focused look at different portions of the tract. Be sure you understand the function of each portion of the tract before you study the structure in detail in the Laboratory Slides. Oral Cavity and Esophagus Food enters the digestive tract in the oral cavity, where it is masticated into particles on which digestive enzymes can act more efficiently.
In the mouth, food particles are mixed with saliva, which lubricates them and initiates their digestion. The salivary glands will be discussed in detail in the next laboratory.
The tongue is a muscular organ covered by oral mucosa that manipulates the food and contains the sensory organs for taste. The taste buds will be discussed in detail in the Laboratory on Sensory Systems.
Intraepithelial lymphocytes mostly T-cells. Duodenum Look at this picture of a section through the human duodenum. Identify villi, crypts, muscularis mucosae, mucosa, muscularis externa and Brunner's glands.
The first part of the small intestine is the duodenum, and its structure is similar to that seen elsewhere in the small intestine, with some differences. The villi are broader, Peyers Patches are less common, and it has one unique feature: Brunner's glands, which are found in the sub-mucosa.
Surface area of the digestive tract - revisited.
The duodenum is often mistaken for the small intestine, so take a moment to compare this section to that of the small intestine in the picture above. Make sure you can distinguish correctly between the two, and identify Brunner's glands correctly. Both Brunner's glands, and the goblet cells in the duodenum secrete mucus. The mucus secreted by Brunner's glands is alkaline, and helps to neutralise the acid chyme produced by the stomach, to produce chyme with a pH suitable for the digestive enzymes of the small intestine.
The chyme is mixed with pancreatic enzymes, and molecules are absorbed by the enterocytes. Proteins are denatured and chopped up by pepsin from gastric glands, and then further broken down by trypsin, chymotrypsin, elastase and carboxypeptidases in the lumen of the small intestine. Further enzymes in the plasma membrane of the enterocytes complete breakdown into amino acids, and each amino acid is actively transported into the enterocyte.
Carbohydrates are hydrolysed by amylases, and membrane bound enzymes convert sugars to monosaccharides which are absorbed by facilitated diffusion. Lipids are converted into an coarse emulsion in the stomach, and into a fine emulsion in the duodenum by pancreatic lipases.