M10S4: Intestines

Question 1

Intestines introduction

Answer 1

-digested material travels from stomach into intestines where further digested and eventually excreted from body
2 components:
1. Small intestines
2. Large intestines

Question 2

Small intestines: gross anatomy

Answer 2

-approximately 6 meters in length
-3 portions
-attached to the posterior abdominal wall

Duodenum (25 cm) - C shaped and encloses head of pancreas
Jejunum (2.5 m) - most lies in left upper quadrant of abdomen
Ileum (3.5 m) - most lies in right lower quadrant of abdomen

Question 3

Small intestine: histology

Answer 3

-unique

Inside to out

1. Mucosa
   -many important features
   Villi-> finger like projections that extend into lumen of small intestine
   Epithelium -> found on the villli and is simple columnar with many absorptive cells whose apical surface has microvilli, aka brush border. British border increases surface area for absorption of nutrients. Between these absorptive cells are goblet cells, which secrete mucus to help lubricate the passage of food. Also enteroendocrine cells here that secrete hormones involved in regulation of satiety, blood sugar level, and growth of epithelial cells
   Lamina propria -> forms the core of each villus and contains blood capillaries and lymphatic capillaries. Collections of lymphatic tissue located in lamina propria, known as Peyer’s patches, that primarily abundant in ileum
   Intestinal glands -> aka crypts of lieberkuhn. These glands/crypts are deep folds of mucosa between vili and secrete intestinal juices
   Plicae circulares -> mucosa and Submucosa form these which are permanent traverse folds that help increase surface area for absorption and causes material to spiral through small intestine
2. Submucosa
   -Submucosa of duodenum notable as it has duodenal (brunner’s) gland that secrete alkaline mucus
   -purpose of this mucous is to help protect small intestine from stomach acid that any prevent in partially digested food after leaving stomach
   -glands are not found in Submucosa of jejunum and ileum
3. Muscularis externa (longitudinal layer and circular layer)
   -small intestine has two smooth muscle layers which organized into circular and longitudinal layers
   -nerve plexus located between these two layers of muscle
4. Serosa
   -as in stomach wall, the outer layer of small intestine is serosa

*refer to goodnote images

Question 4

Large intestine: gross anatomy

Answer 4

-terminal portion of digestive tract
-3 sections (cecum, colon and rectum) that extend from small intestine to anal canal
-like a garbage compactor in that compacts waste for removal

1. Cecum
   -first portion of large ingestion
   -extension off of it called vermiform appendix
2. Colon
   -second portion
   -4 sections
3. Ascending colon -> extends from cecum up the right side of abdomen to join the traverse colon just below the liver
4. Traverse colon -> extends from below liver, crossing abdomen to join descending colon just below the spleen
5. Descending colon -> extends down the left side of abdomen from splenic end of traverse colon to sigmoid colon
6. Sigmoid colon -> S-shaped terminal portion of colon that leads to rectum
7. Rectum
   -extends from sigmoid colon to anal canal
   -last portion of large intestine
   -temporarily stores fecal matter before defecation

Anal canal

*refer to goodnotes

Question 5

Large intestine: histology

Answer 5

1. Mucosa
   -somewhat similar to small intestine but doesn’t contain plicae circulares or villi
   Features:
   Epithelium -> simple columnar and contains increasing amount of goblet cells as move towards anus (note in anal canal a change from simple columnar to stratified squamous epithelium takes place)
   Intestinal glands -> present like in small intestine but in additional, accumulations of lymphatic tissue are present in lamina propria (and submucosa)
2. Submucosa
   -contains blood vessels, lymphatics, glands, and nerve plexuses
3. Muscularis externa
   -different from that of small intestine
   -depending on location have unique arrangements
   Cecum and colon -> outer longitudinal layer forms three longitudinal bands (teniae Coli) that contract and bunch up the wall of large intestine, forming sac-like structures called haustra
   Rectum -> the three teniae Coli merge to form continuous longitudinal muscular layer
   Anal canal -> within, the circular muscle layer thickens into the internal anal sphincter, which involved in waste excretion
4. Adventitious/Serosa
   -can be covered in either

*refer to goodnotes

Question 6

Chrons disease

Answer 6

Inflammation of the lining of digestive tract and most often in lower aspects of small intestine or areas of large intestine
-causes abdominal pain, diarrhea, fatigue and malnutrition
*refer to goodnotes

Question 7

Anal canal

Answer 7

-last portion of digestive tract that leads to external world
-several gross anatomical features including:
Anal column -> longitudinal ridges in canal
Internal and external anal sphincters -> maintain continence and relax to enable evacuation during defecation
*refer goodnotes