Lecture 12 Flashcards
What is the majority of the small intestine suspended by?
Mesentery
What are the circular folds in the small intestine called?
Plicae circularis
What is the evaginating part of the small intestine wall called?
Villus
What is the invaginating part of the small intestine wall called?
Intestinal gland or Crypt of Lieberkuhn
What is the function of the smooth muscle found in the core of the villus?
Smoth muscle contraction produces rhythmic beating of villi that is enhanced during digestion. Ensures maximal exposure of luminal contents with epithelial cells. Milks lacteal contents along.
What can happen to the blood supply to the small intestine in the elderly?
Decreased blood circulation leads to decreased absorption, which can lead to malabsorption and malnutrition
On which surface of epithelial cells are microvilli found?
Apical
What is the function of microvilli?
Increased SA for absorption and digestion
How does contraction of the smooth muscle in the lamina propria lead to mixing at the epithelial cells in the small intestine?
Actin filaments are inbedded in the microvilli and are connected to cytoskeleton filaments in the cell. When the smooth muscle contracts, this moves the basement membrane, which moves the epithelial cell above it. This is transferred to the cytoskeleton, which is transferred to the actin filaments, leading to localised mixing of the contents.
What is the glycocalyx? What is it made up of?
Slippery film made up of many glycoproteins and acidic mucopolysaccharides
What is the function of the glycocalyx?
Selective gatekeeper: attracts desirable and blocks unwanted molecules.
What are the functions of the goblet cells?
Help lubricate the surface
May contribute to glycocalyx layer
Do goblet cells have microvilli on their apical surfaces?
NO
Where are enteroendocrine cells found in the small intestine?
Deeper in crypts of Lieberkuhn but spread out.
Where are undifferentiated cells found in the small intestine?
In the gland region. Migrate upwards and downwards to replace cells.
Where are Paneth cells found in the small intestine?
Cul de sac region
What is the function of Paneth cells?
Important for antiviral and antibacterial functions
What are the 3 substances that Paneth cells produce?
TNF-alpha: Produces inflammation in response to bacteria and parasites
Lysozyme: Bactericidal, destroys bacterial membranes
Defensins: Increases ion channels in cell membranes of invading organisms, increasing permeability
Where are the enteroendocrine cell hormones released?
Liberated through basal lamina into capillaries of lamina propria
How long is the duodenum?
25 cm
What are the distinguishing features of the duodenum?
C-shaped
Brunner’s glands in submucosa
How long is the jejunum?
2.5 m
What is the distinguishing feature of the jejunum?
Increased plicae and therefore increased villi
How long is the ileum?
3.5 m
What are the distinguishing features of the ileum?
- Massive, macroscopically visible lymphatic aggregates called Peyer’s patches.
- Plicae not as pronounced
Describe Peyer’s patches
Centre of B cells surrounded by M cells that are antigen-sensing.
How long is the large intestine?
1.5 m
What are the functions of the large intestine?
Major absorptive role
Minor digestive role
What is the function of the ileocaecal valve?
Regulates passage of materials into caecum
What are the functions of the caecum?
Collects and stores the arriving materials and begins the process of compaction
Describe the appendix
Slender, hollow, vermiform, dominated by lymphoid nodules.
Describe the mucosal epithelium of the large intestine
- Smooth. No plicae or villi
- Mucosal glands are numerous
What is another name for the mucosal glands found in the colon?
Crypts of Lieberkuhn
What are the two predominant cell types found in the mucosal glands? What are their functions?
• Columnar absorptive cells (similar to the enterocytes of the small intestine):
- absorb water & electrolytes
- absorb vitamins produced by bacteria (B & K)
• Goblet cells: secrete mucus for lubrication.
What other cells are found in the Crypts of Lieberkuhn of the large intestine?
- Enteroendocrine cells occur, but are not visible in routine sections with the light microscope
- Undifferentiated cells found at base of glands
Describe the lamina propria of the colon
- Contains a dense layer of collagen immediately beneath the surface epithelium
- Also numerous lymphatic nodules (GALT / MALT - gut or mucosa associated lymphatic tissue) extending down into the submucosa.
Why is the rate of metastasis from some colon cancers relatively slow?
No lymphatic vessels drain the lamina propria until the level of the muscularis mucosae is reached
Describe the muscularis externa of the colon
Circular and longitudinal layers present. Outer longitudinal layer forms three distinctbands running along the colon (teniae coli)
What is the function of the teniae coli?
- Allow segments of the colon to contract independently
* Contraction pulls the intestinal tube into sac-like pockets (haustra coli)
What is the outermost layer of the large intestine?
Adventitia occurs on the posterior surface of the large intestine; elsewhere serosa.
What is the purpose of the rectum/anus?
Temporary storage of faecal matter
What triggers the urge to defecate?
Movement of material in the rectum
What is the final portion of the large intestine called? What does the mucosa of this region contain?
Anal canal: mucosa contains longitudinal folds called anal columns
What do the transverse folds of the anal canal mark?
Boundary between columnar epithelium and stratified squamous
Distinguish between the muscle types of the anal sphincters
Internal sphincter: smooth muscle
External sphincter: skeletal muscle
What is at the end of the anal canal?
Anus
Where are the stem/germinative cells located in the oes?
Basal part of the epithelium
What is the replacement rate of cells in the oes?
Days - quite frequent due to shearing forces
Where are the stem/germinative cells located in the stomach?
Near the neck of gastric galnds
What is the replacement rate of cells in the stomach?
Surface/superficial: days
Deeper: months
Parietal and chief cells cost a lot to replace as they are specialised and are found deep within glands, so are protected from acid
Where are the stem/germinative cells located in the small intestine?
Lower 1/2 of glands (Crypts of Lieberkuhn)
What is the replacement rate of cells in the small intestine?
Surface: days
Deeper: months
Where are the stem/germinative cells located in the large intestine?
Lower 1/3 of glands (Crypts of Lieberkuhn)
What is the replacement rate of cells in the large intestine?
Days
What is the function of columnar absorptive cells?
Absorb the small molecules resulting from digestion
What is another name for columnar absorptive cell?
Enterocytes
What is the membrane of columnar absorptive cells studded with?
Digestive enzymes such as glycosidase, which is involved with carbohydrate digestion
What are the cells found in the mucosa of the SI?
Columnar absorptive Goblet Enteroendocrine Undifferentiated Paneth
