centered image

centered image

Control of the GI Tract: The roles of Gastrin, CCK, Secretin, Motilin and Gastric Inhibitory Peptide

Discussion in 'Physiology' started by Dr.Scorpiowoman, Jun 21, 2016.

  1. Dr.Scorpiowoman

    Dr.Scorpiowoman Golden Member

    Joined:
    May 23, 2016
    Messages:
    9,028
    Likes Received:
    414
    Trophy Points:
    13,075
    Gender:
    Female
    Practicing medicine in:
    Egypt

    d10432a09a597d9dab847d93839775c9.jpg


    Gastrin

    Source:
    - G cells (stomach antrum, duodenum)

    Action:
    - Inc: H+ secretion; gastric mucosa growth; gastric motility

    Regulation:
    - Inc: stomach distention; AAs, peptides; vagal stimulation
    - Dec: pH <1.5


    Somatostatin

    Source:
    - D cells (pancreatic islets, GI mucosa)

    Action:
    - Dec: gastric H+ and pepsinogen secretion; pancreatic and SmI fluid secretion; gallbladder contraction; insulin and glucagon release

    Reguation:
    - Inc: acid
    - Dec: vagal stimulation



    Cholecystokinin

    Source:
    - I cells (duodenum, jejunum)

    Action:
    - Inc: pancreatic secretion; gallbladder contraction; Oddi sphincter relaxation
    - Dec: gastric emptying

    Regulation:
    - Inc: fatty acids, AAs

    Notes:
    - CCK acts on neural muscarinic pathways to cause pancreatic secretion


    Secretin

    Source:
    - S cells (duodenum)

    Action:
    - Inc: pancreatic HCO3 secretion; bile secretion
    - Dec: gastric acid secretion

    Regulation:
    - Inc: acid, FA in lumen of duodenum

    Notes:
    - HCO3 neutralises gastric acid in duodenum - so pancreatic enzymes can function


    GIP

    Source:
    - K cells (duodenum, jejunum)

    Action:
    exocrine: Dec gastric H+ secretion
    endocrine: Inc insulin release

    Regulation:
    - Inc FA, AA, oral glucose

    Notes:
    - Glucose-dependent insulinotropic peptide aka gastric inhibitory peptide.


    Motilin

    Source: small intestine

    Action:
    Produces migating motor complexes

    Regulation:
    - Inc: in fasting state

    Notes:
    Motilin receptor agonists used to stimulate intestinal peristalsis.


    VIP

    Source: parasympathetic ganglia in sphincters, gallbladder, small intestine

    Action:
    - Inc: intestinal water and electrolyte secretion; relaxation of intestinal smooth muscle and sphincter

    Regulation:
    - Inc: by distention and vagal stimulation
    - Dec: by adrenergic input



    Nitric oxide

    Action:
    - Inc: smooth muscle relaxation,


    Intrinsic factor

    Source:
    - Parietal cells (stomach)

    Action:
    - binds with VitB12 - required for uptake of VitB12 in terminal ilium

    Notes:
    Autoimmune destruction of parietal cells -> chronic gastritis and pernicious anaemia


    Gastric acid

    Source:
    - parietal cells (stomach)

    Action:
    - Decreases stomach pH

    Regulation:
    - Inc: histamine, gastrin, ACh
    - Dec: somatostatin, GIP, prostoglandin, secretin

    Notes:
    - gastrinoma: gastrin-secreting tumour that cause high levels of acid and ulcers refractory to medical therapy (PPI)


    Pepsin

    Source: chief cells (stomach)

    Action: protein digestion

    Regulation:
    - Inc: vagal stimulation, local acid

    Notes: pepsinogen is inactive form; converted to pepsin (active) by stomach HCl


    HCO3-

    Source:
    Mucosal cells (stomach, duodenum, salivary glands, pancreas) and Brunner glands (duodenum)

    Action:
    neutralises acid

    Regulation:
    - Inc: by pancreatic and biliary secretion with secretin

    Notes: HCO3 is trapped in mucus that covers gastric epithelium



    Source
     

    Add Reply

Share This Page

<