Large intestine - rectum - histology Flashcards
(24 cards)
What type of epithelium lines the mucosa of the large intestine and rectum?
The mucosa is lined by simple columnar epithelium, which is specialized for absorption and secretion. This epithelium contains many goblet cells for mucus secretion.
What is the role of goblet cells in the large intestine and rectum?
Goblet cells are columnar epithelial cells that secrete mucus, which lubricates the intestinal contents and protects the epithelium from mechanical and chemical damage.
What is the function of enterocytes in the histology of the large intestine and rectum?
Enterocytes are absorptive cells in the epithelium. They are responsible for absorbing water and electrolytes from the contents of the large intestine and rectum.
What are crypts of Lieberkühn, and where are they located?
The crypts of Lieberkühn are tubular invaginations of the mucosa found throughout the large intestine and rectum. They contain various cell types such as enterocytes, goblet cells, and enteroendocrine cells.
What is the role of Paneth cells in the large intestine?
Paneth cells are found in the crypts of Lieberkühn, and they secrete antimicrobial peptides, such as defensins, which help protect the intestinal lining from bacterial invasion.
What is the histological structure of the muscularis externa in the large intestine and rectum?
The muscularis externa consists of two layers of smooth muscle:
Inner circular layer
Outer longitudinal layer (in the large intestine, this layer is arranged into teniae coli, but in the rectum, it is continuous).
How does the histology of the rectum differ from the rest of the large intestine?
The rectum lacks haustra and teniae coli, which are present in the rest of the large intestine. Instead, the rectum has a smooth muscle layer and a more continuous structure to help with the storage and movement of faeces.
What is the histological structure of the serosa/adventitia in the large intestine and rectum?
The serosa is a peritoneal covering found on the anterior and lateral sides of the upper rectum and large intestine.
The adventitia is a connective tissue layer that surrounds the lower part of the rectum and parts of the large intestine that are extraperitoneal.
What are the histological differences between the rectum and anal canal?
The rectum is lined with simple columnar epithelium with goblet cells.
The anal canal transitions to stratified squamous epithelium, providing increased protection against abrasion during defecation.
What is the role of enterendocrine cells in the large intestine and rectum?
Enterendocrine cells are found in the crypts of Lieberkühn. They secrete hormones such as gastrin, secretin, and somatostatin, which regulate digestive functions such as motility, secretion, and absorption.
How does cell turnover occur in the histology of the large intestine and rectum?
Cells in the crypts of Lieberkühn undergo constant turnover. New cells are produced at the base of the crypts, and as they mature, they migrate upward to replace older cells in the mucosal lining.
What is the role of the muscularis mucosa in the large intestine and rectum?
The muscularis mucosa is a thin layer of smooth muscle that helps to move the mucosal lining, assisting in the contraction of crypts to help move contents and facilitate absorption and secretion.
How is the histology of the anal canal adapted for its function?
The anal canal has stratified squamous epithelium for protection against abrasion. The muscularis externa includes both an internal anal sphincter (involuntary) and an external anal sphincter (voluntary), providing control over defecation.
What is the histological structure of goblet cells in the large intestine and rectum?
Goblet cells are columnar epithelial cells in the mucosal layer that secrete mucus. They are abundant in the large intestine and rectum, especially in areas where the intestinal contents need lubrication and protection. They appear as mucin-filled cells in histological sections.
How does the density of goblet cells vary in different parts of the large intestine?
The density of goblet cells increases as you move from the proximal colon to the distal colon and rectum, as more mucus is needed to facilitate the passage of the more solid faeces. The rectum contains a high concentration of goblet cells for additional lubrication.
How does the histology of the muscularis externa in the large intestine differ from the rectum?
The muscularis externa in the large intestine contains teniae coli, three longitudinal muscle bands, which create haustra.
In the rectum, the muscularis externa is continuous, with no teniae coli, allowing for smooth, coordinated peristalsis for faeces propulsion.
What is the distribution of enterendocrine cells in the large intestine and rectum?
Enterendocrine cells are present in the crypts of Lieberkühn and are responsible for secreting hormones like gastrin, serotonin, and somatostatin. These cells are found throughout the large intestine and rectum, though they are less numerous compared to goblet cells and enterocytes.
How do enterocytes in the rectum and large intestine differ from those in the small intestine?
Enterocytes in the large intestine and rectum are primarily involved in water absorption, as opposed to nutrient absorption in the small intestine. They are taller and less specialized than those in the small intestine, which have more complex structures like microvilli for nutrient absorption.
What is the function of Paneth cells in the crypts of Lieberkühn?
Paneth cells secrete antimicrobial peptides such as defensins. These peptides help maintain a healthy gut flora and protect the intestinal lining from bacterial infections. They are more common in the small intestine but are also present in smaller numbers in the large intestine.
What role do the crypts of Lieberkühn play in the large intestine and rectum?
The crypts of Lieberkühn are glandular structures that contain various cell types, including goblet cells, enterocytes, and Paneth cells. They are responsible for secreting mucus, absorbing water, and contributing to defense mechanisms of the intestine by secreting antimicrobial substances.
How does the epithelium change in the transition from rectum to anal canal?
The rectum is lined by simple columnar epithelium with goblet cells, while the anal canal transitions to stratified squamous epithelium, which provides increased protection against abrasion during defecation.
What is the histological difference between the upper and lower portions of the rectum?
The upper portion of the rectum is lined with simple columnar epithelium, while the lower part of the rectum (closer to the anal canal) begins transitioning into stratified squamous epithelium, reflecting the change in functional needs (from absorption to protection).
What are the histological features of the muscularis mucosa in the large intestine and rectum?
The muscularis mucosa is a thin layer of smooth muscle located beneath the mucosa. It helps move the mucosal layer, facilitating the movement of contents in the crypts and supporting the contraction of the mucosa during digestion and absorption processes.
What is the function of enterocytes in the rectum and large intestine?
Enterocytes are the primary absorptive cells in the mucosal lining. In the large intestine and rectum, their primary function is to absorb water and electrolytes, helping to form solid stool.
