Large intestine - rectum - microscopic structure Flashcards
(15 cards)
What are the four layers of the large intestine and rectum?
The large intestine and rectum are made up of four layers:
Mucosa – the innermost layer
Submucosa – connective tissue layer with blood vessels
Muscularis externa – smooth muscle layer
Serosa/Adventitia – outermost layer, depending on the region
What type of epithelium lines the mucosa of the large intestine and rectum?
The mucosa is lined by simple columnar epithelium that is specialized for absorption and secretion, with abundant goblet cells that secrete mucus.
What are goblet cells, and where are they found?
Goblet cells are specialized columnar epithelial cells that secrete mucus. They are found throughout the mucosal lining of the large intestine and rectum to lubricate the passage of faeces.
What is the function of the crypts of Lieberkühn in the large intestine and rectum?
The crypts of Lieberkühn are tubular glands in the mucosa that contain enterocytes (absorptive cells), goblet cells (mucus-producing cells), and enteroendocrine cells (hormone-secreting cells), contributing to water absorption, mucus secretion, and digestive regulation.
What are enterocytes, and what is their role in the large intestine and rectum?
Enterocytes are absorptive cells in the mucosal layer of the large intestine and rectum. They are responsible for absorbing water, electrolytes, and small nutrients from the faecal material.
What is the role of Paneth cells in the large intestine?
Paneth cells are found in the crypts of Lieberkühn and secrete antimicrobial peptides such as defensins, which help to maintain the integrity of the gut and protect against infection. They are more common in the small intestine but are present in small numbers in the large intestine.
What is the difference in muscle structure between the rectum and large intestine?
The rectum has a continuous smooth muscle layer in the muscularis externa, whereas the large intestine has teniae coli, which are three longitudinal muscle bands that create haustra and contribute to segmenting and moving contents.
What are the layers of the muscularis externa in the large intestine and rectum?
The muscularis externa consists of:
Inner circular muscle layer
Outer longitudinal muscle layer (in the large intestine, this is gathered into teniae coli, except in the rectum where it is continuous)
What are enterendocrine cells, and what is their role?
Enterendocrine cells in the crypts of Lieberkühn secrete hormones like gastrin, secretin, and somatostatin, which help regulate motility, secretion, and other digestive functions in the large intestine and rectum.
What is the function of the submucosa in the large intestine and rectum?
The submucosa contains blood vessels, lymphatics, and nerve fibers. It provides nutrient and oxygen supply to the mucosal cells and helps with the defense mechanism through lymphatic vessels.
What is the role of the muscularis mucosa in the large intestine and rectum?
The muscularis mucosa is a thin layer of smooth muscle in the mucosa that helps to move the mucosal lining and aids in the contraction of the crypts to push contents toward the surface.
How does the epithelium change as you move from the rectum to the anal canal?
The epithelium in the rectum is simple columnar epithelium with abundant goblet cells, while in the anal canal, the epithelium transitions to stratified squamous epithelium to provide protection against abrasion during defecation.
What is the structure of the anal canal?
The anal canal is a short, cylindrical passage about 2–4 cm long that contains two sphincters:
Internal anal sphincter (involuntary, smooth muscle)
External anal sphincter (voluntary, skeletal muscle)
What is the role of the pectinate line in the anal canal?
The pectinate line marks the junction between endodermal (rectum) and ectodermal (anal canal) origins. It separates areas with different nerve supplies, blood supplies, and lymphatic drainage.
What are vascular sinusoids in the rectum, and what is their function?
Vascular sinusoids are large, thin-walled blood vessels in the submucosa that help in the absorption of water and nutrients in the rectum. They also assist in fluid balance in the colon and rectum.
