histology of GI tract

Question 1

Four main layers of the gut tube from lumen to outside

Answer 1

mucous membrane- mucosa

submucosa

muscularis externa

adventitia/serosa

Question 2

three layers of the mucosa + what is present in each

Answer 2

surface epithelium, lying on basal lamina

lamina propria - supporting tissue with abundant neurovasculature and cells of the immune system

muscularis mucosae- thin double layer of smooth muscle

Question 3

submucosa structure and components

Answer 3

formed of fibroelastic loose connective tissue with vessels and nerves of the submucosal plexus (Meissner’s), wandering lymphocytes and large quantities of fat

Question 4

muscularis externa structure

Answer 4

two thick layers of smooth muscle

inner layer is circular

outer layer formed of longitudinal fibres

between the muscle layers the myenteric nerve plexus (Auerbach’s) is located

Question 5

adventitia definition

Answer 5

thin outer layer of loose connective tissue that is continuous with the adjacent organ or tissue

Question 6

structure of adventitia if gut wall is free and mobile

Answer 6

covered in mesothelium and connective tissue forming the serosa which is joined to the mesentery

Question 7

serosa definition

Answer 7

smooth membrane consisting of a mesothelium and connective tissue layer containing neurovasculature

line and enclose several body cavities and secretre a lubricating fluid to reduce friction

Question 8

difference between adventitia and serosa

Answer 8

adventitia is a connective tissue layer which binds together structures rather than reducing friction between them

Question 9

mesentery definition

Answer 9

fold of peritoneum that attaches the small intestine, stomach, pancreas, spleen and other organs to the posterior abdominal wall

Question 10

two identifiable features of the oesophagus

Answer 10

non-keratinised stratified squamous epithelium

folded mucosa

Question 11

explain function of the adaptations

Answer 11

non-keratinised, as the epithelium must withstand a large amount of abrasion from food

Question 12

more structural features of oesophagus + functions

Answer 12

small amount of mucous glands in submucosa- secrete mucus that lubricates surface epithelium for passage of food

nerve plexuses- coordinate peristalsis of food bolus

Langerhans cells- antigen presentation, helps immune response

Question 13

which region is what type of muscle?

Answer 13

upper 1/3rd is skeletal

bottom 2/3rds is smooth

Question 14

function of stomach

Answer 14

mix and churn food into chyme

preliminary digestion via secretion of digestive enzymes

Question 15

structure present throughout the stomach + fuction

Answer 15

ruggae- longitudinal folds of mucosa and submucosa

allow the stomach to distend when food enters

Question 16

what epithelium lines the internal stomach?

Answer 16

simple columnar surface epithelium

Question 17

what does the surface epithelium form?

Answer 17

small invaginations called gastric pits (foveolae)

Question 18

what do the gastric pits connect to?

Answer 18

various glands of the stomach

Question 19

three histologically different regions of the stomach

Answer 19

fundus, cardia and pyloris

Question 20

three different stomach glands + locations and functions

Answer 20

principal gastric - present in the fundus and body, produce gastric acid

cardiac- cardiac region, produce mucus

pyloric - pyloris, produce mucus

Question 21

association between gastric gland and pit

Answer 21

gastric pit opens up into the gland

same type of cells

Question 22

different cells in the gastric gland and pit

Answer 22

surface lining cells

mucus neck cells

parietal cells

chief cells

DNES cells

stem cells

Question 23

organisation of cells

Answer 23

top of the pit is lined with surface lining cells

neck of pit lined with mucus neck cells

stem cells concentrated in neck

gland is formed of a mix of the other cells

Question 24

surfacing lining cell function

Answer 24

produces mucus, to lubricate the surface epithelium and protect cells from the acidic and enzymatic properties of gastric juices

Question 25

mucous neck cell function

Answer 25

secretes mucus, however less alkaline than that produced of surfacing lining cells

Question 26

parietal cell synonym

Answer 26

oxyntic cell

Question 27

oxyntic cell structure + function

Answer 27

large round or pyrimidal cells secrete intrinsic factor and HCL

Question 28

chief cell synonym

Answer 28

zygomatic cells

Question 29

zygomatic cell function

Answer 29

secrete pepsinogen and gastric lipase

Question 30

stem cell function + location benefit

Answer 30

replace damaged cells able to move up to replace pit cells or down to replace gland cells

Question 31

turnover of pit cells

Answer 31

5-7 days

Question 32

explain relative turnover of pit vs gland

Answer 32

pit exposed to HCL, so more damaged, higher turnover compared to gland

Question 33

what does DNES stand for?

Answer 33

diffuse neuroendocrine cells

Question 34

DNES function

Answer 34

secrete endocrine, paracrine and neurocrine hormones secrete gastrin

Question 35

difference in gastric pits in different histological regions

Answer 35

principal glands in fundus and body- have the greatest proportion of oxyntic and zygomatic cells cardiac glands- short, coiled and branched pyloric region- deeper gastric pit, with mainly mucous type cells

Question 36

three anatomical segments of the small intestine

Answer 36

duodenum, jejunum and ileum

Question 37

common histological features to all regions of the small intestine

Answer 37

inner lining forms transverse ridges called plicae circulares tall fingerlike projections- villi tubular glands, crypts of Lieberkuhn extend to or beyond the muscularis mucosae mucosal epithelium is simple columnar type covered in microvilli

Question 38

what does the microvilli form?

Answer 38

brush border

Question 39

microvilli function

Answer 39

increase SA, facilitating absorption and secretion

Question 40

two main cell types in small intestine

Answer 40

enterocytes- absorptive cells goblet cells- mucous secreting

Question 41

where are the crypts of Lieberkuhn located?

Answer 41

in the epithelial lining between villi

Question 42

crypts of Lieberkuhn structure

Answer 42

contain stem cells, enteroendocrine cells, Paneth cells and Peyer's patches (only in ileum)

Question 43

function of enteroendocrine cells

Answer 43

synthesise and secrete hormones

Question 44

function of Paneth cells

Answer 44

secrete defensive enzymes such as defensins and lysozymes

Question 45

differences in structure in small intestine

Answer 45

duodenum- contains submucosal Brunner glands that secrete alkaline mucoid secretion into crypts to neutralise stomach acid jejunum- tallest villi ileum- Peyer's patches in crypts

Question 46

what are peyer's patches?

Answer 46

contain mucosal- associated lymphoid tissue (MALT) which houses white blood cells and lymphocytes located in the submucosa

Question 47

villi structure

Answer 47

epithelialy covered finger like protrusions of the lamina propria contain core capillary loops blindly ending lymphatic channel, the lacteal

Question 48

lacteal structure

Answer 48

forms core of villi

Question 49

how are the epithelial cells replaced?

Answer 49

division, migration and differentiation of stem cells

Question 50

structure of colon

Answer 50

smooth surface bu appearance of infoldings due to contractions numerous crypts many goblet cells, outnumbered by absorptive enterocytes

Question 51

colon function

Answer 51

supply mucus to the bowel contents, facilitating passage extract water and electrolytes

Question 52

what is the outer muscularis externa transformed into?

Answer 52

three longitudinal strops of smooth muscle called the teniae colae

Question 53

function of teniae coloae

Answer 53

allow the different segments of the colon to contract independently promotes faecal compaction and general peristalsis

Question 54

are villi present in the large intestine?

Answer 54

no