oesophagus and stomach

Question 1

anatomy of oesophagus

Answer 1

oesophageal sphincter and epiglottis direct food and air to the right place
epiglottis covers the opening of the trachea during swallowing
upper oesophageal sphincter relaxes - allowing it to fit in the oesophagus
oesophagus is a conduit tube
close proximity with the lungs and major bv

Question 2

oesophageal sphincter

Answer 2

constrictor pharyngeal medius - commonality with circular muscle layer of GI tract
constrictir pharynges inferior - commonality with longitudinal muscle layer

Question 3

physiology of the oesophagus

Answer 3

25cm long
wall made of skeletal and sm
upper oesophagus = skeletal muscle only
lower = sm
middle third = mixture of 2 as the proportion of skeletal muscle tapers along its length
under -ve pressure, stomach under +ve pressure
lining - non-keratinised straitifed sqaumous cells - all the way to the lower oesophageal sphincter where cells are arranged as simple columnar epithelium to9 resist strong stomach acid
the epithelial change occurs within the spincter along a jagged line called Z line

Question 4

lower oesophageal sphincter

Answer 4

split into:
internal component - built into circular smooth muscle of oesophageal wall
external component - formed by right crus of diaphragm

Question 5

swallowing

Answer 5

stage 0 - oral phase - chewing and saliva help prepare bolus for swallowing - both sphincters are constricted
stage 1 - pharyngeal phase [- bolus moves to back of pharynx, the pharengeal musculature helps to guide it towards the oesophagus. Both oesophageal sphincters open.
stage 2 - upper oesophageal phase - upper sphincter closes, superior rings of circular muscle contract as inferior rings dilate, Sequential contractions of longitudinal muscle help guide the food down the gullet.
stage 3 - lower oesophageal phase - food passes through the lower sphincter that too closes, the peristaltic wave continues to push food into the stomach

Question 6

anatomical levels of the oesophagus

Answer 6

start from C5
close to trachea, aorta, recurrent laryngeal nerves
travel through diaphragm, only short region in abdo before reacing stomach

Question 7

function

Answer 7

conduit for food

secretions from pharynx to stomach

Question 8

epithelia organisation

Answer 8

non-keratinising
wear and tear lining
stratified squamous
lubrication - mucous secreting glands

Question 9

muscle organisation - skeletal/smooth

Answer 9

sphincters - upper and lower oesophageal
tonically active - closed at rest
swallowing centre - recognise swallowing - more powerful effect on upper, cause to open
upper - skeletal muscle
lower - smooth/skeletal

Question 10

layers of muscle

Answer 10

longitudinal near bottom of slide

circular near top

Question 11

peristalsis in oesophagus

Answer 11

local effect
nerve stimulate contraction above bolus, relaxation below
if food not moved - 2nd peristaltic signal from brain

Question 12

function of the gastrooesophageal sphincter

Answer 12

allow movement of food and fluids into the stomach, but ensure acidic contents of the stomach are separate from the vulnerable oesophageal tissue

Question 13

z line - gastrooesophageal sphincter

Answer 13

visible threshold between epithelia and the oesophagus - stratified squamous and stomach - simple columnar

Question 14

stomach and oesophageal lining

Answer 14

oesophageal epithelium - light pink - wear and tear lining
stomach epi - bright red - more resistant to low pH
mucosal gel lining of the stomach provides protection against corrosive acid

Question 15

function of gastro-oesophageal sphincter

Answer 15

acid reflux stopped by the diaphragm

Question 16

failure of the gastro-oesophageal sphincter

Answer 16

in pregnancy 
stomach pushed up 
= oesophagus pushed up 
pressure difference inn thorax and abdomen 
acid reflux

Question 17

structure of the gastro-oesophageal sphincter

Answer 17

epithelia change from stratified squamous to simple columnar because need to absorb
gastric folds/rugae - allow expansion
lower sphincter is less well defined than upper sphincter - it is made of diaphragm and fold in stomach - when stomach is empty, opening is narrow

Question 18

functions of the stomach

Answer 18

digestion of macronutrients - chemical and mechanical
storage reservoir - until down stream organs are ready to receive stomach contents
immunological protection - strong acid helps to destroy ingested pathogens

Question 19

structure of stomach

Answer 19

lined with columnar epithelia and it invaginates into gastric pits - contain exocrine and endocrine celks

Question 20

anatomical regions

Answer 20

pyloric canal
pyloric antrum
body 
fundus
cardia

Question 21

where is gastric acid secreted from

Answer 21

fundus and body in high volume

Question 22

stomach wall

Answer 22

extra oblique layer of smooth muscle inside circular layer - aids in performance of complex grinding motions
in empty state - stomache contracted - mucosa and submucosa are in folds called rugae
when full - rugae are stretched -flat
rugae allow it to undertake resevoir function

Question 23

cardiac and pyloric region

Answer 23

when immediately enter and leave respectively

mucus secretion

Question 24

body and fundus

Answer 24

mucus
HCl
pepsinogen

Question 25

Antrum

Answer 25

gastrin -endocrine hormone

Question 26

purpose of HCO3- in mucus gel

Answer 26

neutralise acid that comes into contact with the cell wall
pH at epithelial surface 6-7
pH at lumen 1-2

Question 27

stomach secretions

Answer 27

2L /day

150 mM H+

Question 28

peristalsis in stomach

Answer 28

propel chime to colon
more peowerful proximally
ANS essential
‘move food from 1 end of tube to other’

Question 29

segmentation in stomach - movement

Answer 29

weaker than peristalsis
move fluid chime to pyloric sphincter - it is digested so can move onto the next bit
solid chime pushed back up
stretching activates enteric nervous system - local

Question 30

what are gastric pits

Answer 30

deep pores within stomach mucosa
lead to multiple gastric glands - house functional secretory cells of stomach
contain cells for secreting gastric juice - cocktail of hydrochloric acid, enzymes and enzyme zymogens
cells also secrete mucous, paracrine siugnals and hormones

Question 31

mucous cells

Answer 31

abundant
secrete a bicarbonate-rich mucous which helps to protect the stomach lining
keeps pH next to lining near 7 rather than 2-3
protects lining form active lipase and proteases which may interfere with lipid bilayer and membrane transporters

Question 32

parietal cells

Answer 32

acid secreting cells
quiescent until activated
then tubovesicles in the cytoplasm fuse with the small invaginations on the apical surface to make canalicular surface with large SA for acid secretion
rich in mt
secrete intrinsic factor - a glycoprotein essential for absorption of vitamin B12

Question 33

HCL function

Answer 33

kill ingested pathogens
activate protease zymogens
alter protein structure to help digestion

Question 34

chief cells

Answer 34

produce protease zymogen - pepsinogen
and a lipase - gastric lipase
pepsinogen is activated to pepsin in the presence of HCl in gastric lumen
precurser stops it autodigesting the chief cells
pepsin breaks dietry proteins into smaller peptide chains
gastric lipase is an enzyme that digests fats by removing a fatty acid from triacylglyceride molecule

Question 35

G cells

Answer 35

enteroendocrine cells
at bottom of gastric pit release hormone gastrin into blood stream in response to the presence of peptides in the stomach, and stomach distension.

Question 36

gastrin

Answer 36

travels through blood to receptor cells in stomach
stimulates gastric secretion and motility
stimulation of smooth muscles by gastrin leads to stronger contraction and the opening of the pyloric sphincter to move food into the duodenum
also binds to receptors on pancreas and gall bladder - increases secretion of pancreatic juice and bile

Question 37

Enterochromaffin-like cells

Answer 37

ECL
neuroendocrine cell in gastric glands
in vicinity of parietal cells
secrete histamine - stimulates the secretion of acid from the parietal cells

Question 38

D cells

Answer 38

enteroendocrine cells secrete somatostatin - inhib affect of GI func
somatostatin inhibits ECL production of histamine and parietal cell activity - both inhibit the secretion of HCl

Question 39

gastric stem cells

Answer 39

`pluripotent stem cells are capable of differentiating into all the stomach cells

Question 40

structure of chief cell

Answer 40

abundant RER
Golgi
apical secretion granules

Question 41

features of parietal cells

Answer 41

tubovesicles contain H+/K+ ATPase

internal canaliculi - internal reservoir near lumen

Question 42

parietal cell secreting

Answer 42

tubovesicles fuse with membrane and microvilli

canaliculi combine and project into the lumen of the stomach

Question 43

action of parietal cell

Answer 43

CO2 enter - carbonic anhydrase: CO2 + H2O -> HCO3- + H+
bicarbonate is exchanged for chloride
chloride diffuse into canaliculi
k enters cell in exchange for na
canaliculi absorb K for exchange
K+/H+ ATPase take H+ into canaliculi and K+ out - active transport
H+ secreted

Question 44

gastrin and histamine

Answer 44

gastrin stimulates histamine release from chromaffin cells

Question 45

3 phases of the activities of the stomach

Answer 45

cephalic phase
gastric phase
intestinal phase

Question 46

cephalic phase

Answer 46

Afferents: Sight, smell, taste and thought of food

efferents: vagus nerve stimulate secretion from mucous cells, chief cells, parietal cells and G-cells via the submucosal plexus, gastrin and histamine also stimulate parietal cell secretion
effects: small secretion for new minutes

Question 47

gastric phase

Answer 47

afferents: distention of stomach and chemoreception of nutrients and a reduced pH.
efferents: Vagus nerve (neurons secreting ACh) stimulate secretion from mucous cells, chief cells, parietal cells and G-cells via the submucosal plexus and increase motility (mixing waves) via the myenteric plexus, gastrin and histamine also stimulate parietal cell secretion
effect: 3-4 hours of gastric activity and mechajnical digestion

Question 48

intestinal phase

Answer 48

Afferents: Duodenal stretch and chemodetection of reduced pH and duodenal distension

efferents: I-cells secrete cholecystokinin (CCK) and S-cells secrete secretin into the blood. decrease parietal secretion and inhibit gastric motility and emptying, stretch receptors input into enteric nervosu system which reduces activation of the stomach
effect: Gastric emptying slows down to allow downstream organs to deal with current contents.

Question 49

cephalic phase processes

Answer 49

vagus nerve release ACh
stimulate histamine
causes cAMP to enter cell

Question 50

gastric phase processes

Answer 50

stretch and chemo receptors - activate tissue
activate muscle and gland to release mucin and acid
stomach distension - switch on vagus

Question 51

intestinal phase

Answer 51

mainly inhibitory
chime in intestine - intestine respond to pH and consistency - inhibit stomach if lipid conc is high
enterogastric reflex: inhibited by gastric inhibitory peptide, cholecytokinin, secretin, enterogastric reflex.
inhib from vagus nerve - centrally inhibited
if protein conc high - stim gastrin secretion

Question 52

pharmacology

Answer 52

ranitidine - histamine receptor antagonist

omeprazole - protein pump inhibitor