Lower GI Flashcards
What is the main function of the small intestine?
Absorption of nutrients
What are modifications in the small intestine that increase its surface area?
- Plicae circularis - permanent circular folds of mucosa and submucosa, numerous in duodenum and jejunum
- Intestinal Villi - processes of mucosa formed by epithelium and lamina propria
- Microvilli - located on apical surface of surface epithelium
What layers are in the small intestine typically?
Mucosa
Submucosa - duodenal glands in duodenum
Muscularis externa
Adentitia - parts of duodenum
Serosa - most
What is a typical submucosa like in the small intestine?
Lacks glands, except for duodenum
What is a typical muscularis externa like in the small intestine?
Typical of GI tube
What is a typical serosa like in the small intestine?
Most lined with serosa except for portions of duodenum
What is a typical mucosa in the small intestine?
Epithelium - simple columnar cells with well developed microvilli and striated border. Goblet cells present that secrete mucus for lubrication. T cells (intraepithelial lymphocytes)
Lamina propria - loose CT that extends into villi. Contains lacteals (lymphatic capillaries), intestinal glands, and unremarkable muscularis mucosae
What are the intestinal glands?
Crypts of Lieberkuhn
Lined by simple columnar epithelium on a basal lamina
Open into lumen of small intestine at base of and between villi
Simple tubular glands
Contain many cell types:
- paneth cells - part of immune response, secrete bactericidal agents and maintain intestinal flora
- goblet cells
- stem cells near base
- enteroendocrine (DNES) cells - secrete hormones
What makes the duodenum different from other parts of small intestine?
Presence of duodenal or Brunner’s glands in submucosa
Secrete bicarbonate mucus that neutralizes acidic chyme from stomach
What makes the jejunum different from other parts of the small intestine?
Lacks distinct distinguishing features
Plicae circulares well developed
Narrow villi
What makes the ileum different from other parts of the small intestine?
Transition from jejunum to ileum is gradual
Contains Peyer’s patches formed by lymphatic nodules
Patches contain M cells that function in antigen transport and immune response
What is the function of the large intestine?
Absorption of water and electrolytes
Elimination of waste
What layers are present in the large intestine?
Mucosa
Muscularis externa
Serosa
Adventitia
What are the characteristics of the mucosa of the large intestine?
Lacking villi
Surface cells with short, irregular microvilli
Intestinal glands numerous and longer
Goblet cells more numerous to lubricate fecal mass
What are the characteristics of the muscularis externa in the large intestine?
Inner layer is complete
Outer layer of smooth muscle reduced - 3 teniae coli
What are the characteristics of the serosa and adventitia of the large intestine?
Serosa lines most of the large intestine (intraperitoneal)
Part of rectum is retroperitoneal so it is lined with adventitia
What is unique to the structure of the vermiform appendix?
Mucosa is typical of colon bt with fewer and short glands
Abundant lymphoid nodules in lamina propria and submucosa - suggest it plays a role in immune system
2 uniform layers of muscularis externa present but lacks teniae coli
What is appendicitis and what can it be caused by?
Inflammation of vermiform appendix
Blockage of appendix leads to buildup of mucus, increase pressure, and rupture
Infection of mucosa causes inflammation and ulceration
What is unique about the structure of the rectum?
Transverse rectal folds - folds of inner circular layer of muscularis externa
Longitudinal folds - folds of submucosa and mucosa that allow for distension
2 complete layers of of muscularis externa but no tenia coli
Adventitia and serosa - intraperitoneal lined with serosa and retroperitoneal lined with adventitia
What is the function of the rectum?
Storage and voiding of waste
What is the function of the anal canal?
Voiding of waste
What is the structure of the anal canal?
Transition to stratified squamous epithelium, transition in innervation and in muscle type
Anal columns - columns of Morgagni, folds of submucosa and mucosa, superior border marks the rectoanal junction
Anal valves - compress sinuses
Anal sinuses - located behind valves, contain anal glands that secrete mucous for movement of feces
Pectinate line
Intersphincteric line - between internal and external sphincters
What is the epithelium below and above the anal columns?
Simply columnar above
Simple cuboidal below
What is the pectinate line? How does the epithelium change?
Formed by inferior border of anal columns and anal valves
Anal columns to pectinate line is simple cuboidal and muscularis mucosae terminates at pectinate line
Below pectinate line is stratified squamous epithelium
What is the intersphincteric line? How does the epithelium change?
Divides internal from external anal sphincters
Internal anal sphincter - thickening of inner circular layer of muscularis externa
External anal sphincter - skeletal muscle
Pectinate line to intersphincteric line is nonkeratinized stratified squamous epithelium
Inferior to intersphincteric line is keratinized stratified squamous epithelium
What is intestinal sprue?
Disorders of small intestine related to disruption of mucosa
Presents as malabsorption like weight loss, diarrhea, steatorrhea, anemia, and vitamin deficiencies
What is celiac disease?
Inflammatory response triggered by gluten
Biopsy of small intestine necessary to confirm diagnosis
4 features: villus atrophy, disordered epithelial with atrophied microvilli, inflammation of lamina propria, and intestinal gland hyperplasia
What is Hirschsprung’s Disease?
Congenital megacolon
Absence of enteric nerves in portion of bowel due to failure in migration of neural crest cells
Results in absence of peristalsis in affection portion of the gut
Feces backs up into functional bowel increasing diameter
