Microanatomy

Question 1

what are the normal functions of the GI system

Answer 1

1. absorption of nutrients from ingested food

2. protection against ingested pathogens

Question 2

what are the 4 phases of nutrient abospriton

Answer 2

fragmentation
digestion
absorption
elimination

Question 3

describe fragmentation

Answer 3

• this starts in the oral cavity
• it is aided by saliva
• continues in the stomach and small intestine

Question 4

describe digestion

Answer 4

• starts int he mount
• continues in the stomach and small intestine
• aided by salivary, gastric and pancreatic secretions, enzymes associated with the brush border of enterocytes and bile salts

Question 5

describe absorption

Answer 5

• occurs in the jejunum and ileum and is facilitated by the large surface area of these regions and microvilli on enterocytes
• capillaries and lacteals transport absorbed nutrients away from the mucosa

Question 6

describe elimination

Answer 6

• by defacation of solid faeces occurs after absorption of water in the large intestine

Question 7

what is the basic structure of the alimentary tract

Answer 7

• basically is an muscular tube with the same basic structure though the length

Question 8

what are the 4 basic layers in the alimentary tract

Answer 8

1. mucosa
2. submucosa
3. muscularis propria
4. adventtia or serosa

Question 9

what is the mucosa compromised of

Answer 9

• epithelium
• lamina propria
• muscularis mucosa
  it varies between regions and changes abruptly at several places for example at the oesophageal gastric junction

Question 10

describe the submucosa

Answer 10

• loose connective tissue that carries blood and lymphatic vessels and nerves
• ganglion cells found in clusters here form the submucosal (meissner’s) plexus of the enteric nervous system and supply parasympathetic innervation to control the muscularis mucosa, glandular secretion and local blood flow

Question 11

describe the muscualris propria (externa)

Answer 11

• compromised of an inner circular layer and an outer longitudinal smooth muscle layer
• intrinsicu muscle contractions are responsible for peristalsis
• ganglion cells of the myeternic (Auerbach’s) plexus are found between the muscle layers and modulate muscle activity

Question 12

describe the adventitia or serosa

Answer 12

• • when the alimentary tract is located int he peritoneal cavity it is covered by a mesothelium which is supported by a thin loose connective tissue (serosaa)
• in other areas an outer connective tissue layer called the adventitia connects it to underlying tissues, major vessels and nerves travel in this layer

Question 13

where are vili only found

Answer 13

• only found in the small intestines only

Question 14

what does the lamina propria do

Answer 14

• supports the epithelium

Question 15

describe the lamina propria

Answer 15

• very cellular
• has fibroblasts that make the supportive fibrocollagenous extracellular matrix
• has defence cells such as lymphocytes and plasma cells
• it is part of MALT (mucosa associated lymphoid tissue)
• smooth muscle comes up into the villus from the underlying muscularis mucosa, this smooth muscle moves the villus and increases its contact with the watery digesting food in order to aid further digestion and absorption

Question 16

where does nutrient abospriton occur

Answer 16

small intestine

Question 17

what happens to the absorbed nutrients

Answer 17

• ## they are carried away in capillaries and lymphatic vessels called lacteals, these carry materials away

Question 18

what does the smooth muscle do in the lamina propria

Answer 18

• smooth muscle comes up into the villus from the underlying muscularis mucosa, this smooth muscle moves the villus and increases its contact with the watery digesting food (watery digestive food is called chyme) in order to aid further digestion and absorption

Question 19

what does the oesophagus do

Answer 19

• it conveys food from the oropharynx to the stomach

Question 20

describe the structure of the oesophagus

Answer 20

• it is lined by stratified squamous epithelium in order to resist abrasion
• has slightly more collagen in its lamina propria and a thicker muscularis mucosa
• glands are found along the length of the oesophagus to secrete mucus to help keep it lubricated

Question 21

describe the muscles of the oesophagus

Answer 21

• imitation of swallowing is voluntary
• involves the skeletal muscle of the oropharynx
• upper 1/3 of the oesophageal muscularis externally is also comprised of skeletal muscle
• the lower 1/3 of the muscularis external is comprised of only smooth muscle
• in the middle part the oesophagus, skeletal muscle mixes with the smooth muscle

Question 22

what happens when the oesophagus is relaxed

Answer 22

• deeply folded

- can accomodualte a bolus of food passing down it

Question 23

what does the outermost loose connective tissue do to the oesophagus

Answer 23

• supports and protects it by anchoring to other structures in the mediastinum

Question 24

what colour is the normal oesophageal mucosa

Answer 24

white due to the thick stratified squamous epithelium

Question 25

describe the mucosa of the stomach

Answer 25

- the mucosa of the stomach is glandular - has tubular glands that extend downwards from the surface - in both the cardia and pylorus they secrete protective mucus - fundus and body glands secrete acid and pepsin in addition to the mucus

Question 26

what is the glandular make up of the cardia

Answer 26

secretion - mainly mucus | cell type - mucus neck cells

Question 27

what is the glandular make up of the fundus

Answer 27

secretion - mucus - HCL pH 1 and intrinsic factor, pepsin - gut hormones cell type - mucous neck cells - parietal cells - chief cells - endocrine cells

Question 28

what is the glandular make up of the pylorus

Answer 28

secretion - mainly mucus - gut hormones including gastrin cell type - mucous neck cells - endocrine including G cells

Question 29

the gastric pit is the..

Answer 29

opening of the gland and it is lined by surface mucous cells - in the bases there are mainly pepsinogen secreting chief cells

Question 30

what is the oesophageal gastric junction

Answer 30

- this is the place where the oesophagus enters the stomach

Question 31

describe the structure of the small intestine

Answer 31

- same structure as the rest - in order to continue digestion and absorb nutrients from the digested food it posses several adaptations to increase its surface area - these include fingerlike villli and larger folds called place circulates v - the enterocytes also have microvilli that act to increase each cells digestive absorptive surface

Question 32

what are intestinal cells called

Answer 32

enterocytes

Question 33

how long is the small intestine

Answer 33

4-6m

Question 34

enterocytes make up....

Answer 34

the majority of the simple columnar epithelial cells

Question 35

what do the enterocytes do

Answer 35

1. they continuous digestion of food by having enzymes incorporated into their apical plasma membranes 2. absorb nutrients and water from digestive food

Question 36

what do goblet cells do

Answer 36

- lubricate the passage of good | - mucus protects the small intestines like it does in the stomach from auto digestion

Question 37

what does peridocia cid ship stain

Answer 37

- stains carbohydrates red - - labels the goblet cell mucin which is highly glycosylated and the enterocyte microvilli which have a glycocalyx, a coating of glycoproteins and polysaccharides that protects against auto digestion and binds to digestive enzymes to the enterocyte surface enabling the final stages of digestion of carbohydrates and proteins

Question 38

what are the major cells of the lining epithelium of the small intestine

Answer 38

the enterocyte and goblet cell

Question 39

What are the small intestine glands that extend deeper into the lamina propria from the bases of the vili

Answer 39

crypt of LieberKuhn

Question 40

where is the enterocyte located and what is its function

Answer 40

Located - lining villus - in crypt function - lining villus - digestion using brush border enzymes, absorption - in crypt - secretion of watery intestinal juice, mainly water and enteropeptidase that activates pancreatic trypsin

Question 41

where is the goblet cell located and what is its function

Answer 41

located - scattered along villus between enterocytes, increased numbers distally ``` function - mucus secretion for protection/lubrication ```

Question 42

where is the endocrine cell located and what is its function

Answer 42

located - crypt ``` function - regulation of gut function ```

Question 43

where is the stem cell located and what is its function

Answer 43

located - crypt ``` function - regeneration of the epithelium ```

Question 44

where is the paneth cell located and what is its function

Answer 44

located - crypt ``` function - antimicrobial agent's, defensives, lysozyme, these regulate the bacterial content of the intestine ```

Question 45

what do crypt cells include

Answer 45

- include stem cells that divide and form daughter cells that move up the villus and differentiate to replace the villus epithelium

Question 46

what is the lifespan of enterocytes and goblet cells

Answer 46

3-5 days

Question 47

what do enteroendocrine cells do

Answer 47

- release hormones including secretin and cholecystokinin and are found in crypts

Question 48

describe what happens in coeliac disease

Answer 48

- this is when the immune system reacts to gliadin, which is present in wheat - antibodies in the blood can confirm this - the immune reaction acts to destroy the mucosa of the small intestine which causes the loss of enterocytes and the entire vili - the stem cells in the crypts try to replace the damaged cells resulting in elongation of the glands - there are increased intrapeithelial lymphocytes - increase lymphocytes and plasma cells in the lamina propria

Question 49

describe the structure of the large intestine

Answer 49

- along most of the large intestine except the rectum and appendix, the longitudinal smooth muscle of the msucarulis external is collected in three bands called Tania coli - intestinal glands and crypts make up some of the mucosa - there are no vili - glands are longer than the small intestine - glands contain both enterocytes for absorption of mainly water and goblet cells to provide protective mucus