Digestion 2

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Digestion 2

• Dr Viv Rolfe

Alternative formats and large print versions of
these handouts are available upon request.
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Lecture Summary

• Extrinsic and intrinsic nervous systems
  (structures and neurotransmitters)
• Neural control of
• Regulation of food intake
• Swallowing
• 3 phases of gastric secretion
• Defecation
• Gut diseases

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The Importance of a Healthy Gut

• Process and absorb into the body, nutrients
• and energy essentialfor survival
• Absorb water for
• hydration
• Eliminate waste
• material

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Extrinsic and Intrinsic Nerves
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Extrinsic Control

• Digestive functions (motility, enzyme secretion,
  absorption) are all controlled and co-ordinated
  by nerves.
• These nerves are extrinsic of origin (external to
  the gut) or intrinsic (internal).

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Extrinsic Control

• Parasympathetic and sympathetic control from
  VAGAL, THORACO-LUMBAR and SACRAL nerves.
• Key neurotransmitters are
• and .

Acetyl choline
Noradrenaline(norepinephrine)
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Vagus Latin for wandering
Gastric Branches
Celiac Branch pancreas, spleen, kidneys,
Hepatic Branch
Mesenteric Branch
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Brainstem
Sympathetic
Parasympathetic
Cervical
(daily maintenanceof functions)
(fight, flight orfright)
Thoracic
T1-T12 L1-L2
Lumbar
Sacral
S2-4
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Intrinsic nerves

• The gut has a complex intrinsic nervous system
  called the ENTERIC nervous system (ENS).
• Also known as the little brain because it has
  as many neurones as the central nervous system
  brain and spine.
• Neurotransmitters include ACh, NA,
• 5-HT (serotonin) and many more name some
  other neurotransmitters

?
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List of gut neurotransmitters
Amino acids Aspartate, glutamate, glycine
Monoamine Dopamine, noradrenaline,
adrenaline Serotonin (5-HT), histamine
Polypeptides Bombesin, Neuropeptide Y Opiods.etc
etc
Biogenic amine ACh
Free Radicals Nitric oxide, carbon monoxide
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ENS structure
Vagus Branch
Sub-mucosal Plexus
Myenteric Plexus
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Neural Control of Gut Functions
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Food Intake

• Food intake is regulated by the FEEDING centre
  and the SATIETY centre in the ..
• These are two groups of neurones which sense
  whether a person is well fed or hungry. But this
  is a simplistic view.

hypothalamus
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But today

• Food intake is controlled by environmental,
  psychological and physiological factors.
• Feedback from the GUT itself helps regulate food
  intake, such as via the hormone CCK which induces
  satiety (feeling of being full up).
• Leptin (produced by fat cells) also is involved
  in the regulation of food intake.
• Identification of the obese gene (ob).

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Im not well fed, Im big boned.
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Deglutition or swallowing

• Swallowing occurs after the bolus is formed and
  chewing is complete.
• Swallowing is a VOLUNTARY nervous reflex in 3
  stages

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What are some of the changes?
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1. Mouth closed tongue and cheek muscles push
   bolus into pharynx.
2. A muscle reflex in the pharynx propels the bolus
   into the oesophagus, and the epiglottis closes
   the entrance into the trachea.
3. An involuntary wave of peristalsis propels the
   bolus down the oesophagus to stomach.

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Gastric Function

• Acts as a hopper (reservoire) for digested food.
• Secretion of HCl and pepsin for the digestion of
  protein.
• Mechanical breakdown.

?
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Gastric Secretion

• 2-3 litres of gastric juice secreted daily.
• It contains water, salts, mucus, HCl and enzyme
  precursors for PROTEIN digestion.
• Gastric secretion is under NEURAL and HORMONAL
  control.

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Gastric Glands
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Control of Gastric Secretion

• PHASE 1 Cephalic phase
• Triggered by the sight, smell, taste of food!
• Sensory information travels via a vagal-nerve
  reflex to influence the stomach.
• Juice to start flowing before food reaches
  stomach to prepare it for digestion.

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• PHASE 2 Gastric phase
• Triggered by presence of food the stomach and
  duodenum.
• The hormone GASTRIN is released into the blood
  which stimulates the gastric glands to produce
  more juice during the course of a meal.

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• PHASE 3 Intestinal phase
• Triggered by partly digested food reaching the
  small intestine.
• SECRETIN CHOLECYSTOKININ slow the secretion of
  gastric juice and slows gastric motility.

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Defecation
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Colonic Function

• The colon contains FAECES - undigested food,
  bacteria, saltsand water.
• Colon resporbs water and salts.
• Bacteria ferment fibre producingenergy.
• Storage and elimination of faeces.

Rectum
Anus
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Defecation

• The colon contains FAECES - undigested food,
  bacteria, saltsand water.
• Giant peristaltic waves MASS
• MOVEMENT move faecesinto the rectum.(Can be
  triggered by COFFEE,
• EXERCISE.)

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Defecation Reflex

• Distension of the rectal wall stimulates stretch
  receptors which activates a muscle reflex to
  initiates DEFECATION.
• The external anal sphincter is under voluntary
  control so that defecation can be postponed if
  necessary!

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Digestive Diseases
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Disease Spectrum
Fatal Debilitating
Inconvenient
Cancer Bowel Oesphagus Rectum Liver Stomach
Inflammation Coeliacs disease (wheat
allergy) Crohns disease Ulcerative
colitis Pancreatitis
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Fatal Debilitating Mildly Inconvenient
Stomach Ulcers
Infections
Cancer Bowel Oesphagus Rectum Liver Stomach
Flatulence
Incontinence
Dysphagia
Piles
Irritable bowel syndrome
Food Poisoning
Inflammation Coeliacs disease (wheat
allergy) Crohns disease Ulcerative
colitis Pancreatitis
Burbulance
Acid indigestion
Some illness can be serious in susceptible groups
(the young, older people).
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Diagnosing Bowel Disease

• Difficult because individual habits vary so much.
• Habit can vary from 3 motions per day to 3 per
  week.

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Constipation

• Constipation is the occurrence of hard
  stools,excessive straining and abdominal pain.
• What factors can cause constipation?

?
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• Low fibre diet
• Lack of physical activity
• Emotional stress (irritable bowel syndrome)
• Bowel cancer
• Hirschsprungs disease (birth defect)
• Intestinal obstructions

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Dietary Cause

• Fibre is important for keeping transit regular.
  The colon requires bulk to keep peristaltic and
  segmenting (mixing) muscle contractions going.

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Congenital Defects

• Hirschsprungs disease is a genetic defect that
  manifests in childhood, sometimes associated with
  Downs syndrome.
• There are areas of enteric nerves missing from
  the large intestine, so peristalsis does not
  occur and the intestine becomes obstructed with
  faeces.
• The diseased bowel is often removed surgically.

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The two ends of gut can be resected and the bag
removed.
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Diarrhoea

• The frequent passage of watery or loose faeces
  whichcan lead to dehydration.
• Considered chronic if lasts for more than 4
  weeks.
• What factors may cause diarrhoea?

?
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• Viral infection (gastroenteritis)
• Emotional stress (irritable bowel syndrome)
• Bowel cancer
• Inflammatory bowel diseases
• Food poisoning
• Malabsorption syndromes such as lactose
  intoleranceor gluten enteropathy (wheat allergy)
• Medication such as antibiotics
• Zollinger-Ellison syndrome - tumour produces high
  levelsof gastrin in the blood

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The role of nerves

• Bacteria stimulate ENS andcause water to be
  secretedrather than absorbed.
• E.g. E coli, cholera, Clostridium difficile.
• E. coli causestravellers diarrhoea
• (Dehli Belly) and large scaleglobal death of
  children.

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Other digestive diseases
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Liver disease

• Hepatitis - liver inflammation that can be caused
  by hepatitis virus.
• Cirrhosis - chronic inflammation that can result
  from hepatitis or alcohol abuse.

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Gall bladder disease

• Cholecystitis, gall bladder inflammation, can be
  caused by gallstones which block the neck of the
  gall bladder.
• Bile gets trapped and irritates the gall
  bladder.
• Main signabdominal pain after a fatty meal.

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INFLAMMATION
Blocked bile excretion causing JAUNDICE
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www.digestivedisorders.org.uk
Source of information about different gut diseases