Unit 3: Digestion II

jejunum structure

- numerous plicae circulares - *numerous villi* - no glands in submucosa - no Payer's patches

large intestine function

- reabsorption of electrolytes & water - elimination of waste

Paneth cells

- secrete antibacterial lysozyme - play a role in regulation of normal bacterial flora of the small intestine - not found in large intestine

muscularis externa of appendix

- thick inner circular layer - outer longitudinal layer - no teniae coli

lamina propria of large intestine?

- thick layer of collagen - GALT present (M cells) - *no lacteal*

muscularis externa of large intestine

- thin, inner circular layer - outer longitudinal layer (has 3 bands of teniae coli)

goblet cells

- unicellular mucin- secreting glands - numerous in ileum

central lacteal

found in lymphatic capillaries

unicellular mucin secreting glands

goblet cells

GI portion: Peyer's patches

ileum

GI portion: reduced # & size of plicae circulares

ileum

lymphatic nodules of appendix

in mucosa & submucosa

microvilli with glycocalyx

increase surface area

what does the absorptive function of the jejunum depend on?

integrity of villi

GI portion: no Payer's patches

jejunum

GI portion: no glands in submuocsa

jejunum

GI portion: numerous villi

jejunum

GALt location

lamina propria

where are plicae circulares found?

mucosa & submucosa

submucosa of large intestine

no plicae circulares

epithelium of small intestine

simple columnar

rectum epithelium

simple columnar

appendix structure

- no villi - epithelium - lymphatic nodules

large intestine cells

- numerous goblet cells - apical columnar enterocytes - enteroendocrine cells

brush/striated border with glycocalyx, contain enzymes

*absorptive cells* with microvilli

ulcerative collitis: symptoms

*watery diarrhea & bleeding*

Peyer's patch: epithelium

- *Absorptive cells* - *M cells*

duodenum structure

- *Brunner's gland* in *submucosa* - distal part contains numerous plicae circulares

illeum structure

- *Peyer's patches* - middle: reduced # and size of plicae circulares

M cells

- Peyer's patch - cover enlarged lymphatic nodules - play role in transport of antigens from lumen to lamina propria

appendix cells

- absorptive cells - M cells - few goblet cells

commensals

- assists in digestion - synthesize vitamins B, E, K - prevent colonization of bacterial pathogens by competing with them

what part of the large intestine has simple columnar?

- colon - rectum

GI portion: numerous plicae circulares

- distal duodenum - jejunum

where are plicae circulares located?

- distal duodenum - jejunum - proximal ileum - terminal ileum

glycoproteins of the glycocalyx

- extending from tips of microvilli into lumen - inclue terminal digestive enzymes like dipeptidases & disaccharidases

villi

- folds of mucosa only - increase surface area

plicae circulares

- folds of submucosa - increase surface area

ulcerative collitis

- formation of granulation tissue associated with *proliferation of blood and lymphatic vessels in the lamina propria*- active inflammation

Celiac disease

- immune-mediated inflammation - leads to flattening of jejunal surface w/ extensive loss of vili - due to allergies to gluten

Crypts of Lieberkuhn

- intestinal glands in mucosa - increase surface area

Taeniae coli

- large intestine

what enzyme does the pancreas release to help with absorption?

- lipase - pancreatic amylase

accessory digestive organs

- liver - pancreas

Peyer's patches

- lymphatic nodules - epithelium: *absorptive cells & M cells*

ulcerative collitis: mechanism

1. *mucosa is lost over extensive area* 2. *destruction of absorptive epithelium* 3. *impairs water resorption* from colonic contents → *watery diarrhea & bleeding*

cells of the large intestine

1. absorptive cells 2. Goblet cells 3. enteroendocrine cels 4. stem cells

parts of small intestine

1. duodenum (0.25m) 2. jejunum (2.5m) 3. ileum (3.5m)

large intestine pathway

1. ileocecal junction 2. cecum 3. veriform appendix 4. ascending colon 5. transverese colon 6. descending colon 7. sigmoid colon 8. rectum 9. anus

4 degrees of small intestine folding

1. plicae circulares 2. villi 3. Crypts of Lieberkuhn 4. microvilli with glycocalyx

large intestine epithelium

1. simple columnar 2. stratified squamous 3. keritinizing stratified squamous

Paneth cells location

Crypts of Lieberkuhn

T/F: Paneth cells found in large intestine

FALSE; Paneth cells only found in *small intestine*

T/F: Absorptive cells with microvilli have digestive enzymes

FALSE; absorptive cells do not have digestive enzymes

In the GI tract, the presence and appearance of glands can be very telling. Lets begin with the pharynx. The pharynx has no muscularis mucosa or submucosa and its glands can be found imbedded in layers of muscle beneath the epithelium. The esophagus is unique because it is one of two places in the gut where you will ever see submucosal glands. Stratified non-keratinizing squamous epithelium and glands in the submucosa (called esophageal glands proper) is characteristic of esophagus. In the stomach you can see various sized glands, all of which are located in the lamina propria, at the base of the gastric pits. These glands contain parietal, chief and enteroendocrine cells. The duodenum is the second place in the GI tract with submucosal glands (Brunner's glands). Unlike the esophagus, however, the duodenum has villi and intestinal glands in the lamina propria, like the rest of the small intestine (the submucosal glands of the duodenum are of secondary importance to the glands found in the lamina propria). The presence or absence of submucosal glands is a key difference between duodenum and the rest of the small intestine. In the remainder of the small intestine, glands (crypts) are located at the base of the intestinal villi in the lamina propria. These glands contain Paneth cells (which secrete lysozyme) and enteroendocrine cells. The colon, on the other hand, has no villi and has straight glands which are made up of abundant mucus secreting goblet cells.

How do the locations of glands in the GI tract help to identify what part of the GI tract you are looking at?

2. gastro-duodenal junction

Identify the region of the GI tract: 1. cardio-esophageal junction 2. gastro-duodenal junction 3. duodeno-jejunal junction 4. ileo-cecal junction 5. recto-anal junction

cover enlarged lymphatic nodules, e.g., Peyer's patch, transport antigens.

M cells (microfold cells)

pyramidal shaped with round nuclei located near their base. They contain brightly eosinophilic (almost orange) secretory granules in the apical cytoplasm

Paneth cells

secretion: antibacterial lysozyme. Paneth cells play a role in regulation of normal bacterial flora of the small intestine (absent in large intestine)

Paneth cells

3. submucosa

Rectal hemorrhoids are caused by dilation of blood vessels in the: 1. lamina propria 2. muscularis mucosae 3. submucosa 4. muscularis externa 5. adventitia

T/F: Goblet cells have a higher number in the lower colon

TRUE

T/F: mucosa of large intestine contains tubular glands of Lieberkuhn

TRUE

T/F: mucosa of large intestine lacks folds or villi

TRUE

T/F: M cells are found in large intestine

TRUE, also found in small intestines

2. smooth muscle cells of the muscularis mucosae

The cells indicated are: 1. fibroblasts of the lamina propria. 2. smooth muscle cells of the muscularis mucosae 3. fibroblasts of the submucosa. 4. neurons of the submucosal plexus. 5. smooth muscle cells of the muscularis externa.

6. Villus in the jejunum/ileum *note the absence of submucosal glands)

The structure indicated is a cross section of a: 1. Gastric pit. 2. Cardiac stomach gland. 3. Fundic stomach gland. 4. Pyloric stomach gland. 5. Duodenal submucosal (Brunner's) gland 6. Villus in the jejunum/ileum 7. Crypt of Lieberkühn in the jejunum/ileum. 8. Crypt of Lieberkühn in the colon.

ulcerative collitis: diagonsis

VEGF expression

enterocyte

absorptive cell with microvilli & glycocalyx

appendix epiplocia

aggregate of adipocytes surrounded by serosa

what part of the large intestine has stratified squamous?

anal canal

what part of the large intestine has keritinizing stratified squamous?

anal skin

how are the granules oriented in enteroendocrine cells?

basally-oriented

small intestine function

digestion & absorption

GI portion: Brunner's glands in submucosa

duodenum

Brunner's glands location

duodenum submucosa

secretion: gastrin, cholecystokinin (CCK), secretin, gastric inhibitory peptide (GIP), somatostatin, vasoactive intestinal polypeptide (VIP), motilin, enteroglucagon

enteroendocrine cells

regenerative cells

stem cells of small intestine

anal canal epithleium

stratified squamous