Mapa mental

Stomach

Elly Scanlon Inglés

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Stomach

Functions
- Store food
- Secrete gastric juices
- Regulates release of food into duodenum
  - Pyloric Sphincter
- Mixes food with secretions
  - Beginnign of digestion
Divisions of the stomach
- Cardia
- Fundus
- Corpus
  - Body of the stomach
    - Parietal and cheif cells present here
- Antrum
  - Thick muscle wall
    - Where all the food will be ground
      - Propelled through pylorus --> duodenum
        Contains G cells and D cells
- Pylorus
  - G and D cells
Cells of the stomach
- Mucous neck cells
  - Make mucuous and bicarbonate
- Parietal cells
  - Produce
    - Acid
      - Due to proton/potassium pump
        On apical surface
        Requires energy
        Requires alpha and beta subunit for full activity
        H+ made from breakdown of H2CO3
        H2CO3 made from H2O + CO2
        Also produces HCO3-
        Alkaline tide
        Temporary increase in pH
        Using carbonic anhydrase
        H+ combines with Cl-
        Produce HCl
    - Intrinsic factor
      - IF = important for vitamin B12 absorption
  - In corpus
  - Stimulated to produce acid
    - Histamine
      - H2 receptors
      - Produced by ECL cells
        Stimulated to release histamine
        Ach from vagus nerve
        Gastrin from G cell
      - Histamine works through PKA pathway
        activates Gs
        Activates adenylyl cyclase
        ATP --> cAMP
        cAMP activates PKA
    - Gastrin
      - Binds to cholocystokinineb receptors
      - Produced by G cells
      - Gastrin and Ach stimulate H+ secretion through PKC pathway
        M3 receptor activation - causes Ca2+ entry into parietal cell
        Binding to M3 and CCKb receptors
        Activates Gq G protein
        Activates phospholipase C
        Converts PIP3 --> DAG and IP3
        DAG
        Activates PKC
        IP3
        Causes calcium to leave ER
      - Stimulated by GRP
        Stimulated by amino acids
    - ACh
      - M3 receptors
      - Vagus nerve
- EC like cells
  - Produce histamine
- Chief cells
  - Secrete pepsinogens
- D cells
  - Produce somatostatin
    - Decreases parietal cell acid secretion
      - Antagonises the adenylyl cyclase pathway
        Activates Gi
        Inhibits adenylyl cyclase
        PKA not activated
      - Decreases HISTAMINE mediated acid production
    - Somatostain release induced by neural and hormonal mechansism
      - Induced as a consequence of low pH
        D cells in the antrum
        Endocrine
      - D cells in the corpus
        Paracrine
- G cells
  - Produce gastrin
Distension causes parasympathetic NS to
- Release ACH and GRP from Vagus nerve
Natural Inhibitors of acid secretion
- Somatostatin
- Secretin
  - Made in response to fat / low pH
  - Stimulates somatostatin release
  - Inhibits release of gastrin
- CCK
  - Is produced in response to fat
  - Antagonises gastrin mediated acid production
Pharmacological inhibitors of acid secretion
- Proton pump inhibitors
  - Target all three pathways
- H2 receptor antagonist
  - Only targets the H+ secretion by Histamine pathway
    - Less efficient
- Useful for
  - GORD
  - Barretts metaplasia
  - Zollinger ellison syndrome
- Used to do vagatomies
  - Side effects as nerves needed for motility and control of sphincters
Phases of gastric acid secretion
- Basal
  - Folows a circadian rythm
  - Acid secretion is low a.m
    - High p.m.
- Cephalic
  - Initiated by
    - Smell
    - Sight
    - Thought
    - Taste
    - Swallowing
  - Mediated by vagus nerve
  - Accounts for 30%
- Gastric
  - Accounts for 50-60% of acid secretion
    - Vagus nerve releases Ach and GRP upon distension
      - Sets of the G cell / ECL cell cascade
        Digestion of protein further stimulates G cell
        Stimulates ECL cell
- Intestinal
  - Accounts for 5-10%
    - Partially digested a.a.
      - In duodenum stimulate G cell
        Gastrin release
  - Can be inhibitory
Pepsinogens - secreted by chief cells
- Pepsinogens = proteolytic enzymes
- Acetylcholine = major trigger for pepsinogen secretion
  - Pepsinogen --> pepsin at low pH
    - Pepsin = endopeptidase which initiates protein digestion
      - Autocatalysis - more pepsin auto activates pepsinogen
Gastric mucousal protection
- Epithelium needs to be protected from harsh environment
  - Mucous layer traps HCO3- so maintains neutral environment round epithelium
    - Prostaglandins regulate this pathway
Helicobacter pylori
- Secrete urease
  - Converts urea --> ammonium ions and bicarbonate
- Lead to hypergastrinaemia in ANTRUM
  - Cause peptic ulceration
    - Break in the lining of the stomach
  - Causes G cells to hypersecrete gastin
    - Decreases somatostatin release from D cells
- Carcinogen
- Leads to atrophic gastritis
  - Lead to cancer
- Flagella = drill into mucosa
- Cause an inflammatory response
  - Causes damage --> inflammation
- Leads to hypochloridria in the CORPUS
  - Inflammatory response
    - Produces IL1- beta
      - This is the most potent acid suppressor known
      - Prevents parietal cells from secreting acid
- Treatment: Triple therapy
  - Two antibiotics and a PPI
    - As you treat for both hypochlorydria and for hyper gastrinaemia
Prostaglandins
- Phospholipid
  - Arachadonic acid
    - Prostaglandins
    - E: Cox1/Cox2
      - NSAID block these
      - Damages gastric mucosa if not selective for Cox2
        Lead to gastric ulceration
  - E : Phospholipase A2
Intrinsic factor
- Really important for vitamin B12 absorption
  - B12 normally binds with IF
  - Lack of B12 --> pernicious anaemia
    - Lack of B12 causes RBC to enlarge, can't leave bone marrow
      - Fail to loose their nuclei
- Lack of IF occurrs when parietal cells are destroyed due to auto-antibodies
  - Autoimmune disease leads to lack of B12 --> Pernicious anaemia

Información

Descripción: Mapa Mental sobre Stomach, creado por Elly Scanlon el 09/04/2017.
Creado por: Elly Scanlon · abr 2017
Actualizado: 9 abr 2017
Visitas: 3
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Stomach

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