Histology of Small and Large Intestines Flashcards
The small intestine is divided into?
- duodenum (25-30 cm) : from Pylorus – duodenojejunal junction 2. jejunum (about first two-fifths of the rest) 3. Ileum (~ 3.5 m long) - The three segments have the same basic histological organization
What are the functions of the small intestine?
- Principal site for digestion 2. Absorption of products of digestion
Name the structural features which increase the luminal surface area?
- Pilcae circulares 2. intestinal villi 3. microvilli
What are pilcae circulares?
the numerous permanent crescentic filds of mucous membrane found in the small intestine especially in the lower part of the duodenum
Describe pilcae circulares?
- permanent structures, contain core of submucosa 2. absent from the first few centimetres of the duodenum and the distal part of the ileum 3. Numerous in distal part of duodenum and proximal part of jejunum 4. well developed in the jejunum
Describe intestinal villi?
- 1 mm long 2. Unique finger-like projections of mucosa 3. Extend from mucosa to the lumen
Intestinal villi is formed by?
- core of lamina propria 2. simple columnar epithelium
Epithelium of the villus is composed of?
- enterocytes
Describe enterocytes?
absorptive cells - 1. tall collumnal cells 2. basally located nuclei 3. microvilli forms striated border 4. tight junctions forms a barrier 5. secrete enzymes + water + electrolytes in secretory granules 6. have lateral plications 7. have elongated mitochondria
Describe goblet cells?
unicellulare mucin secreting glands
Describe the intestinal glands (crypts of Lieberkuhn)?
- simple tubular mucosal glands 2. openings located between the villi and extend through the lamina propria down to the muscularis mucossae 3. has simple columnal epithelium 4. secrete intestinal juice (2 liters/day) e.g. enteropeptidase (or enterokinase
Describe microvilli?
extensions of the apical surface membrane of enterocytes
What are the essential features of the small intestinal mucosa?
- the villi 2. intestinal glands 3. the lamina propria 4. GALT - gut associated lymphoid tissue 5. muscularis mucosa
Describe the epithelium of the intestinal glands?
- Goblet cells: -mucus-secreting 2. Enterocytes- absorptive cells 3. enteroendocrine cells – produce paracrine and endocrine hormones 4. Paneth cells are located at the bottom of the crypts -release a number of antibacterial substances 5. Intermediate cells – capable of dividing
Describe the Paneth cells?
- Found at the base of the gland 2. Regulate the normal bacteria flora in small intestine 3. Apical secretory granules contain antibacterial enzyme lysozyme 4.
Describe enteroendocrine cells?
- Concentrated in the lower portion of the gland 2. Widely distributed (diffuse neuroendocrine system)
Describe the 2 types of enteroendocrine cells?
- Open type – cellular apex presents microvilli and contacts lumen 2. Closed type – cellular apex covered by other epithelial cells
Describe the M (microfold cells)?
- specialised epithelial cells the overlie lymphoid follicles of peyer patches 2. Have numerous basal membrane inviginations (pits)- contain intraepithelial lymphocytes and macrophages 3. Can endocytose antigens and transport to macrophages 4. Basement membrane under M cells is discontinuous
The lamina propria is composed of?
- loose CT 2. blood and lymph vessels 3. nerve fibers 4. smooth muscle cells - lamina propria penetrates the core of the villi
Describe the lamina propria?
- Lamina propria penetrates the core of the villi 2. The lamina propria is, unusually cell rich 3. Lymphocytes invade the epithelium or form solitary lymphoid nodules (30-50 nodules) in the lamina propria - called Peyer’s patches
Describe the muscularis mucosa?
- has 2 layers 2. extends into the intestinal villi, where the smooth muscle cells form a longitudinal bundle in the centre of the villi
Describe the submucosa in the duodenum?
- Contains coiled tubular glands called Brunner’s glands – secret alkaline substance 2. Lamina propria and submucosa of small intestine contain Peyer patches – component of GALT 3. Peyer patches are located on the antimesenteric side
Describe Brunners glands?
- Their secretion is mucous and slightly alkaline due to bicarbonate ions (pH 7-8) 2. The secretion of Brunner’s glands protects the duodenal mucosa
What is the large intestine made of?
- cecum including the appendix 2. colon 3. rectum 4. anal canal
The colon is subdivided into?
- ascending colon 2. transverse 3. descending colon 4. sigmoid colon
What are the gross distinctive features of the large intestine?
- Longitudinal layer of muscularis externa exhibits three thickened bands called Tinea coli 2. External surface of the caecum has succulations (Haustra) 3. Serosa has small fatty projections call (omental appendices)
What are the functions of the large intestine?
- reabsorption of water and inorganic salts 2. secretion of mucus, which acts as a lubricant 3. Elimination of undigested food and wastes
Describe the mucosa of the large intestine?
- The surface of the mucosa is relatively smooth 2. no plicae circulares or intestinal villi 3. Crypts of Lieberkühn are present and usually longer and straighter than those of the small intestine 4. Luminal surface has orderly patterned gland openings
Describe the epithelium of the mucosa of the LI?
- Glands consists of simple columnal epithelium 2. Goblet cells account for more of the epithelial cells than in the small intestine 3. Contains same types of cells except paneth cells ( absent)
Describe the lamina propria?
little lamina propria is squeezed between the glands.
What are the structural features of the lamina propria?
1.The collagen table 2. Well developed GALT 3. Well developed pericryptal fobroblast sheath 4. Absence of lymphatic vessels
Describe the muscularis mucosa?
forms 2 layers
Describe the submucosa?
- contains lymphatic vessels 2. contains considerable amount of fat
Describe the muscularis externa?
- Appears different from the small intestine 2. The inner circular muscle layer forms the usual sheath 3. The outer longitudinal muscle layer forms three flattened strands, the taenia coli 4. Only a thin layer of longitudinal muscle surrounds the inner circular muscle layer between the taenia coli
What is the vermiform appendix?
small blind-ending diverticulum from the cecum
What are the important features of the vermiform appendix?
- large accumulations of lymphoid tissue in the lamina propria and submucosa 2. no intestinal villi 3. infrequent crypts 4. fatty tissue in the submucosa 5. the muscularis externa is thinner 6. no taenia coli
What is a cause of appendicitis that has to do with lymphocytes?
An extreme proliferation of lymphocytes (lymphoid hyperplasia) as a consequence of bacterial or viral stimulation may lead to the obstruction of the lumen of the appendix
Describe the rectum?
- Dilated distal portion of the alimentary canal 2. Upper part has transverse rectal folds 3. Mucosa –like in colon
Describe the anal canal?
- Most distal portion of the alimentary canal (4 cm long ) 2. Extends from upper part of pelvic diaphragm to anus 3. Upper part has longitudinal folds- anal columns 4. Depressions between columns – anal sinuses
What are the zonea of the anal canal?
- colorectal zone 2. anal transition zone 3. squamous zone
Describe the colorectal zone?
- in the upper 1/3 2. Contains simple columnal epithelium
Describe the anal transition zone?
- in the middle 1/3 2. Represent transition between simple columnal (rectal) to stratified squamous epitheliun (perianal skin)
Describe the squamous zone?
- lower 1/3 2. stratified squamous
What are the glands of the anal canal?
- anal glands 2. circumanal glands
Describe the anal glands?
- extend into submucosa + muscularis mucosa 2. secrete mucus
Describe the circumanal glands? (apocrine glands)
- Found in skin surrounding anal orifice 2. Sex attractant
Describe the submucosa of the anal canal?
ramified with supeior rectal arteries – enlargement of these veins constitute internal hemorroids
Describe the muscularis externa of the anal canal?
circular thickens - internal sphincter muscle
