3. GIT Function 1 Flashcards by Giorgia Tanner

What 4 ways is digestive function regulated?

Intrinsic nerve plexuses
Extrinsic nerves
Autonomic smooth muscle function
Gastrointestinal hormones

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What are the functions of the sensory nerves in the enteric nervous system?

Receive info from sensory receptors in mucosa and muscle

Detect stretch, tension and chemicals

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What are the functions of the motor nerves in the enteric nervous system?

Control motility and secretion

Carry out muscle contraction, vessel dilation

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What are the two plexuses in the enteric nervous system?

Meissner’s

Auerbach’s

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Where is Meissner’s plexus located?

Submucosa

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What does Meissner’s plexus control?

Intestinal secretions and local absorptive environment

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Where is Auerbach’s plexus located?

Between muscle layers

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What does Auerbach’s plexus control?

Intestinal smooth muscle

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What is the function of extrinsic innervation?

Modify the outgoing activity of ENS
Not essential for motility of the GIT
Alters levels of hormone secretion, can act on smooth muscle and glands

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What parasympathetic nerves are involved in extrinsic innervation?

Vagus (upper GIT)
Pelvic nerves (lower GIT)
Have pre-ganglionic efferents

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What sympathetic nerves are involved in extrinsic innervation?

Prevertebral ganglia

Have post-ganglionic efferents

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What is the name of the pacemaker cells of the GIT?

Interstitial cells of Cajal

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Where are the interstitial cells of Cajal found?

At the boundary of circular and longitudal muscle

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What type of activity do the interstitial cells of Cajal carry out?

Cyclic ‘slow waves’ caused by spontaneous changes in resting membrane potential
Membrane can move closer to or further away from the threshold
When combined with mechanical, neural or hormonal factors can cause contraction

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What are 3 enteric reflexes?

Peristalsis
Regulation of gastric emptying
Gastroilieal reflex

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How is gastric emptying regulated?

Stomach won’t empty when there is still food in the duodenum

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What is the gastroilieal reflex?

Chyme and gastric peristalsis activates gastrin

Contracts ileum and relaxes ileocaecal sphincter

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What regulates the motor action of the proximal stomach?

Receptive relaxation
Adaptive relaxation
Feedback regulation

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What is receptive relaxation?

Muscle relaxes to increase capacity when food enters

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What is adaptive relaxation?

Distension causes relaxation

Allows stomach to accommodate increased gastric pressure

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How does feedback regulate the proximal stomach?

Signals from nutrients in the duodenum relax the fundus

What can increase contractions in the distal stomach?

Vagus nerve
Hormones
Stretch

What are the two types of contractions within the stomach?

Segmentation: local, aid mixing

Propulsive movements: Peristalsis moving distally

Where does the most amount of mixing occur in the stomach?

Near pylorus

Where are oxyntic glands found?

Proximal and part of distal stomach

Which cells are stimulated by G cells?

Peptic chief cells | Oxyntic (parietal) cells

What do peptic cells produce?

Pepsinogen | -Protein digestion

What do oxyntic cells produce?

``` HCl -kill bacteria -Lower pH for pepsin Intrinsic factor -Vitamin B12 absorption ```

What do mucous neck cells produce?

Mucous, bicarbonate | -Protects stomach epithelium from acid

What do enterochromaffin-like cells produce (mast-like call)?

Histamine | -Stimulates gastric acid secretion

What do D cells produce?

Somatostatin | -Inhibits gastric acid secretion

What are the oxyntic gland cells?

``` Peptic Oxyntic Mucous Neck Enterochromaffin-like D ```

Where are the pyloric glands found?

Antral region

What are the pyloric gland cells?

Mucous G D

What do G cells produce?

Gastrin

What do surface epithelial cells produce?

Mucin and bicarbonate

What increases the secretion of pepsinogen?

ACh Gastrin Histamine

What clears pepsin?

HCl | Other pepsin

What decreases the secretion of pepsinogen?

Prostaglandins | Somatostatin

Describe how acid production is increased in an oxyntic cell

H+ out/K+ in using ATP HCO3- out/Cl- in Cl- leaves due to electrochemical gradient ACh and gastrin react with receptors to increase intracellular Ca++ Histamine reacts with its receptor to increase cellular cAMP production Ca++ and cAMP stimulate proton pump to increase acid secretion

Why is there so little absorption in the stomach?

Small surface area | Tight junctions between epithelial cells along allow small amounts of lipid-soluble compounds to be absorbed

What are the causes of gastritis and peptic ulcer disease?

Excess acid and pepsin (reflux, stress, diet, caffeine, smoking) Decreased mucus Drug adverse effects

What are COX 1 and 2 enzymes important for?

Maintaining the epithelium and mucus barrier

What happens when drugs inhibit COX 1 and 2?

1. Prostaglandin synthesis is inhibited Decreased mucosal defence and blood flow, increased acid production, causing gastric ulceration 2. Neutrophil-endothelial interactions: leukocytes adhere to mucosal endothelial cells

What bacteria often causes peptic ulcer disease?

Helicobacter pylori

What part of the stomach does helicobacter pylori infect?

Antrum

What effect does H. Pylori have on gastric mucosa?

Infiltration of leukocytes causes inflammation

How is H. Pylori treated?

2 antibiotics | Proton pump inhibitor reduces acidity

What is Zollinger-Ellison Syndrome?

Severe refractory peptic ulceration associated with increased gastrin blood concentrations

What is the cause of excess acid secretion in ZES?

Primary non-beat cell gastrin-secreting tumour in pancreas | Increased mass of parietal and enterochromaffin-like cells which can be overstimulated by gastrin