Unit VI- GI tract II

Question 1

Small intestine segments

Answer 1

• duodenum (25 cm)
• jejunum (2.5 m)
• ileum (3.5 m)

Question 2

Major functions of small intestine

Answer 2

• move chyme
• absorb nutrients
• immunodefense

Question 3

Lumenal surface area

Answer 3

• plicae circularis- permanent transverse circular folds of mucosa and submucosa that increase SA 2-3X
• villi are finger like( more distal, jejunum and ileum) or leaf-like (duodenum) projections of the surface 0.5- 1.5 mm tall area that increase SA 10X
• microvilli are projections of apical plasma membranes that increase SA 20X

Question 4

Crypts of Lieberkuhn

Answer 4

• also called intestinal glands

- simple tubular glands that extend from the surface epithelium down to the muscularis mucosae

Question 5

6 major cell types

Answer 5

• absorptive cell (enterocyte)
• goblet cell
• enteroendocrine cell
• paneth cell
• stem cell
• M (microfoldo) cell

Question 6

Absorptive Cells

Answer 6

• tall columnar cells with a striated border
• each microvillus is 1 micron tall and 0.1 micron in diameter
• disaccharides and peptidases are secreted by the absorptive cells and bind to microvilli where they produce monosaccharides and aa for absorption
• lipids are absorbed and reesterified to triglycerides, converted into chylomicrons, and released from later surfaces into the lamina propria where they are absorbed by the central lacteals

Question 7

Goblet Cells

Answer 7

• unicellular hglands that produce glycoproteins of the mucin type that lubricate and protect sm intestine
• few in duodenum
• many in ileum
• even more in large intestine

Question 8

Enteroendocrine Cells

Answer 8

• unicellular glands that synthesize hormones vasoactive peptides
• in small intestine most occur in the basal portion of the crypts of Lieberkuhn

Question 9

Gastrointestinal peptide hormones produced by enteroendocrine cells

Answer 9

• Somatostatin and VIP- start in fundus and go all the way to colon
• GIP and motilin just duodenum and jejunum
• gastrin starts in the antrum and tapers off till it gets to the start of ileum
• CCK and secretin start at duodenum and taper off till start of colon

Question 10

Paneth Cells

Answer 10

• exocrine cells found in small groups at base of crypts of Lieberkuhn
• apical granules contain lysozyme, phospholipase A2, and hydrophobic peptides called defensins with antibacterial activity
• Crohn’s disease may be a specific disorder of Paneth cells

Question 11

Stem cells

Answer 11

• located near the base of the crypts
• move upwards repopulating the crypts and villi in 3 to 6 days
• replaced every 30 days

Question 12

M(microfold) cells

Answer 12

• located in the ileum only
• specialized epithelial cells that cover Peyer’s patches
• basement membrane beneath M cells is discontinuous
• sunflower

Question 13

GALT

Answer 13

• 25% of mucosa in the gut is GALT
• Peyer’s patches re in groups of 20-40 covered by M cells. Antigens from lumen are taken up by the M cells and delivered to lymphocytes and other cells in Peyer’s patches
• SC (secretory component) is a 75 kD glycoprotein synthesized by the absorptive cells and inserted into the basal plasma membrane. Dimers of IgA bind to SC enter by endocytosis and exit the apical plasma membrane with SC bound forming secretory IgA that binds antigens, toxins, and microorganisms- host defense

Question 14

Regional Differences in the Sm Intstine

Answer 14

• duodenum has Brunner’s glands (secrete Alkaline mucous that helps protect against stomach acid and provide correct pH for pancreatic enzyme function) in the submocosa and squat villi; most of the duodenum has an adventitia because it is retroperitoneal
• jejunum has the most highly developed plicae circularis. The villi are longer and more finger like than in the duodenum and there are more goblet cells. It has serosa.
• ileum has the longest villi and the highest number of goblet cells. Peyers patches are unique to the ileum

Question 15

Large Intestine Gross Subdiviions

Answer 15

• colon
• cecum
• appendix
• rectum
• anal canal

Question 16

Chief functions of large intestine

Answer 16

• absorption of water, salts, minerals, and vitamins
• mucus secretion
• storage and elimination of fecal material

Question 17

Colon and cecum

Answer 17

• the plicae semilunares are temporary folds in the mucosa and submucosa
• there are no villi, only crypts lined with a simple columnar epithelium with a striated border. Goblet cells are especially large and numerous
• muscularis externa is unique. The outer longitudinal smooth muscle is subdivided into three bands of tenia coli. There is a thin layer of longitudinal smooth muscle between the bands. The bands puker the colon into haustra
• the transverse and sigmoid colon have a serosa. The ascending and descending colon and cecum have an adventitia

Question 18

Vermiform Appendix

Answer 18

• the epithelium resembles the colon, bit there are fewer and shorter crypts
• the lamina propria has many lymphoid cells and lymph nodules that often interrupt the muscularis mucosae. The submucosa is freq edematous
• the muscularis externa has two complete thin layers and no taenia
• there is a serosa

Question 19

Upper rectum

Answer 19

-resembles the colon but has less lymphoid tissue and no taenia coli

Question 20

Anal canal

Answer 20

• 2.5-4 cm long and the simple columnar epithelium of the rectum changes to stratified cuboidal and then stratified squamous nonkeratinized epithelium
• the crypts and muscularis mucosae disappear
• the epithelium changes to stratified squamous kertized epithelim in the ano-cutaneous area
• apocrine sweat glands called circumanal glands can be found in this area
• the inner layer of circular smooth muscle thickens to form the internal anal sphincter (involuntary)
• the outer longitudinal layer of the muscularis externa is replaced by skeletal muscle that forms the external anal sphincter (voluntary)