Gastric Secretion and Motility 2 Flashcards
LEARNING OBJECTIVES:
*Stomach anatomy and function
*Gastric digestive juice secretion
*HCL secretion
*3 phases of gastric secretion
*Mucosal barrier
Stomach Anatomy see slide 3 -> LEARN NB
Stomach structure - looking at specialised of a special tube
dilated and turned on its side
Lies in between oesophagus and small intestine the duodenum
Cardia: region where material comes in from oesophagus with stomach
Fundus: top
The major part of stomach is called the body
Pyloric antrum: canal in the centre which leads to opening
guarded by pyloric sphincter: muscle nerve
Opening is called the pyloric orifice
Also the pyloric sphincter, and pyloric constriction
Stomach function? 2
1) Storage and Mixing (motility-based functions)
Need to store large material that you consume
expands up to 1L of material
Real capacity to store material
Gives DS time to ingest material
It mixes material
2) Digestion (Secretory function; HCl/pepsinogen/intrinsic factor)
At the fundus: interstitial cells of Cajal: located along DT that produce a wave live motion - this contraction about 3 every minute these contractions occur down through the stomach to allow material go down the body
Storage site the 1/3 part the body
Antrum: greatest mixing of material takes place here
As a wave of contraction moves down through it becomes stronger and stronger, the muscle mass becomes larger as you go through stomach to facilitate more mixing
Pyloric sphincter is tonically opened
Material must be below 2mL in diameter to move through
stomach makes material small enough to pass through
Retropulsion and emptying?
Amount of chyme that escapes into duodenum with each peristaltic wave (fundus) before the pyloric sphincter closes depends largely on the strength of antral peristalsis
Causes it to fully close once the contraction meets it after food has gone through
Once sphincter fully closes, the material is churned on itself and this is called retropulsion and then again when it leaves and this is called emptying
Gastric Juice secretion
1. How much a day?
2. What are the 2 major collection of cells inside the stomach?
How do they differentiate
- 2 litres of gastric juice a day
- Collection of cells - inside of stomach - the inner lining of the tube: 2 major
Oxyntic mucosa: inner lining of stomach the fundus
Pyloric gland area: mucosal lining in the antrum
They contain different collection of gastric cells however they are both mucosa cells
We have gastric pits - invaginations deepening down into surface from surface into mucosa and at base of pits sis gastric glands which make different products of gastric juice
Mixed into substance of stomach from mucosa
MOST IMPORTANT SLIDE 7
The stomach mucosa and gastric glands
1. Exocrine cells: 3 and what do they secrete?
2. Endocrine/paracrine cells and what do they secrete?
- Mucous cells- line the invaginations: protective role - alkaline mucus, chief cells- inactive enzyme that becomes active, protein breakdown - pepsinogen, parietal cells-dots within submucosa, they make acid HCL is key for protein digestion it activates pepsinogen - HCL and intrinsic factor - made by parietal cells
important for filament absorption - ECL cells: Enterochromaffin like cells - histamine - activator of PARIETAL CELLS - in oxyntic mucosa
G cells - Gastrin - released into circulation and stimulates ECL parietal and chief cells, D cells - somatostatin - inhibitor, inhibits g cells and ECL and parietal cells
There is a complex between cross talk between different cell types
Where do exocrine cells secrete from?
Where do endocrine cells secrete from?
In oxyntic mucosa
In pyloric gland area
Stimulation of HCL secretion?
Diagram slide 8 shows inter talk between all cells
Gastrin, histamine + ACh all stimulate HCL secretion by stimulating parietal cells
Gastrin releasing peptide (GRP) → gastrin release
Gastrin (G) released by Gm cells → histamine (H) release from ECL cells
Ach (A) released by neurons → histamine release
Neuron make neuropeptide: makes GRP - cranial nerve: vagus the 10th one
Vagus nerve stimulates G cells
NT labelled A is seen: Ach - localised released by neurons by intrinsic nerves - the enteric NS, can also release ECL cells which is a stimulator for secretion of HCL
Vagus nerve - CN X?
Where does it arise?
Orginates in brainstem in medulla on left and right
Exits cranial cavity back of the skull goes through the body
it has abdominal branches that innervate the digestive system - it has 10 branches throughout the body
Transits output to/from viscera: 80-90% afferent
In the medulla
HCL secretion slide 10
Q - Know cellular mechanism by which HCL is actually regulated:
Parietal cells within stomach make HCL
Lumen membrane is seen curved and on the other side is the basolateral membrane
Its not plasma it is Interstitial fluid
Want to make HCL in lumen - primary active transport and secondary active transport
ATPase pump is how H ^+ ions gain entry into lumen they pump them out against this gradient vs K^+ ions
Water within the cell donates H ions for this and also donates OH ions
These cells have Ca - carbonic anhydrase which is very important it combines OH and CO2- which is taken in from plasma by diffusion or made by cellular metabolism
Product of these is HCO3 -> KEY for Cl^- gaining entry to lumen
Secondary active transport mechanism here in basolateral membrane that moves bicarbonate out down the electrochemical gradient for reaching of bringing Cl into cell against electrical gradient then Cl^- moves by diffusion by lumen membrane and once it is in lumen it combines with H ions and makes HCL in gastric lumen
VERY DEPENDENT ON ENZUME Canaliculus
Explain cephalic phase of control of gastric secretion:
Cephalic means head
This is stimulated in the head
Feedforward mechanism that prepares body for food that is being made
Stimuli in cranial region: vagus is key - vagal nerve feeds down to the stomach to stimulate G cells to make Gastrin which promote gastric secretion and indirectly it stimulates ECL cells which make histamine which makes chief parietal cells
Vagal nerve also causes positive effect on intrinsic nerves so increases Ach which stimulates chief and parietal cells to also increase gastric secretion
SHERWOOD at top the all black diagram is the 1 to know for EXAMS -> HAS MORE DETAIL
Initial stimulus of sight, smell, taste of food, chewing and swallowing causes physiological response: Increased parasympathetic activity by vagus nerve: 2 things occur -
(1) Increased ACh increases chief and parietal cells which increases gastric secretion
(2) G cells cause increased gastrin secretion and increased plasma gastrin which causes parietal and chief cells to increase acid and pepsinogen secretion and thus increase gastric secretion
SLIDE 11 SEE
With Cephalic phase what activation stimulates multiple cell responses via neurotransmitters?
Vagal Activation
See slide 13
Vagal input
Vagus is also at GRP at the right hand side
G major stimulator for many cells
What components of the gastric mucosal barrier enables the stomach to contain acid with injuring itself?
- The luminal membrane of the gastric mucosal cells are impermeable to H^+ so that HCL cannot penetrate into the cells.
- The cells are joined by tight junctions that prevent HCL from penetrating between them.
- A mucus coating over the gastric mucosa offers further protection
Protection of gastric mucosa?
Mucosal barrier - Secretion of mucus/HCO3 by epithelial cells forms a barrier that protects stomach from low pH and from digestion by pepsin
Replacement of the entire stomach lining every 3 days
