Session 3 Gut function, swallowing and salivation

• Role of saliva?

  • Protects mouth - Wet
  • Bacteriostatic
  • Alkaline
  • High calcium
  • Lubricates food for mastication and swallowing
  • Starts digestion (of Sugars)
• If the balance between secretion and absorption is only slightly altered - Considerable loss of water and electrolytes will occur fluids - Mostly not from ingested food and water, but from body fluids - Rapid dehydration and electrolyte disturbance
• Paracrine control of the gut - Chemical messengers diffusing locally

  Example histamine in stomach
• Endocrine control of the gut - Range of hormones controlling:

  • Secretion of stomach acid
  • Alkali secretion from liver and pancreas
  • Enzyme secretion
• Individuals who may need nutritional support?

  • BMI is less than 18.5
  • Have lost more than 10% of their weight in the past 3 to 6 months without trying
  • Their BMI is less than 20 and they have lost more than 5% of your weight over the past 3 to 6 months without trying.
• Types of Nutritional Support?

  • Oral
  • Enteral Tube Feeding
  • Parenteral Nutrition
• Parenteral nutrition?

  • Feeding through central veins
  • Feeding through peripheral veins
• Enteral nutrition?

  • Nasal or oral feeding (Nasogastric, nasoduodenal, nasojejunal)
  • Gastrostomy (feeding through an artificial external opening in the stomach)
  • Jejunostomy
• Preliminary disruption of food: Mastication
• Label the mouth

  A) Parotid

  B) Salivary duct

  C) Tongue

  D) Sublingual gland

  E) Submandibular gland

  
• Tongue?

  • Stratified squamous non-keratinised epithelium, bearing dorsal papillae (some of which bear taste buds).
  • Skeletal muscle, with fibres orientated in multiple planes. Intrinsic muscles interdigitate directly with CT of tongue.
  • Serous and mucous acini of accessory salivary glands.
  • Lymphoid tissue (lingual tonsils associated with posterior third of tongue)
• Powerful muscles of mastication?

  • Masseter - elevation of the mandible
  • Temporalis: elevation and retraction of the mandible
  • Medial pterygoid: elevation and side-to-side movements of the mandible
  • Lateral pterygoid: protrusion and side-to-side movements of the mandible
• Mastication muscles are innervated by branch of trigeminal nerve (V3 mandibular nerve) but also Facial nerve.
• The major salivary glands?

  • Submandibular glands: 70% Mixed serous/mucous - Tubule-acinar glands that secrete various enzymes, including alpha amylase and lysozyme
  • Parotid glands: 25% Serous saliva - Watery secretion rich in enzymes, but little mucus. - Acinar glands that secrete a-amylase (stored as zymogen granules)
  • Sublingual glands: 5% Mucous Saliva - Branched tubule-acinar glands - Viscous secretion, No enzymes, Lots of mucus
• Saliva contains significant amounts of secretory antibodies called immunoglobulin A, which can destroy some microbes in the mouths.

  It also contains proteolytic enzymes which contains lysozyme which attacks and destroys bacteria.
• Volume of saliva determined by acinar secretion. Composition determined by ductal modification. The more rapidly saliva is produced, the less modified it is
• Saliva Composition - Resting saliva

  • Highly modified acinar secretion
  • Low volume
  • Very hypotonic
  • Neutral or slightly acid
  • Few enzymes
• Saliva composition - Stimulated Saliva

  • Less modified acinar secretion
  • High volume
  • Less hypotonic
  • More alkaline
  • Lots of enzymes
• Control of salivary secretion - Autonomic nervous system

  • Sympathetic - Superior cervical ganglion
  • Parasympathetic - Glossopharyngeal nerve IX: parotid, Facial nerve VII: sub-mandibular
• Control of salivary secretions: in detail

  • Sympathetic: Superior cervical ganglion. Produces thicker secretions, as well as reducing blood flow to glands. Contraction of myoepithelial cells surrounding acini, tubules and small ducts helps move saliva towards the oral cavity.
  • Parasympathetic: Glossopharyngeal nerve (IX), Otic ganglion & Facial nerve (VII). Submandibular ganglion stimulates release of fluid secretions and increased blood flow.
• Three stages of swallowing?

  Oral, pharyngeal, esophageal.
• Oral phase: Voluntary, Food is moistened with saliva and food bolus is formed. The tongue pushes the bolus to the back of the throat.
• Pharyngeal phase: Involuntary, parasympathetic nervous system. Starts with stimulation of tactile receptors in the oropharynx, swallow reflex is initiated. Soft palate lifts to cut off nasal airways, bolus moves over back tongue and the tongue blocks the oral cavity to prevent the food going to the oral cavity. Epiglottis is pushed backward over larynx. Larynx and vocal folds contract covering the entry of the trachea to protect airways, respiration temporary blocked. Upper oesophageal sphincter opens to allow passages to the oesophagus.
• Oesophageal Phase: Involuntary - cranial nerve X. Food bolus is propelled down the oesophagus by peristalsis. The larynx moves down back to the original position. Rapid wave of peristalsis sweeps down the oesophagus, propelling the upper and lower oesophageal sphincter to open and food passes into the stomach. Coordinated by extrinsic nerves and swallowing centre (brain stem).
• Dysphagia: Problems swallowing - muscular?

  Any condition that affects the muscles used to push food down the oesophagus and into the stomach.

  • scleroderma
  • achalasia
  • myasthenia gravis
• scleroderma – where the immune system (the body's natural defence system) attacks healthy tissue, leading to a stiffening of the throat and oesophagus muscles.
• achalasia – smooth muscle. where muscles in the oesophagus lose their ability to relax and open to allow food or liquid to enter the stomach.
• myasthenia gravis – Autoimmune attach of the Ach receptors
• Dysphagia: Problems swallowing - Neurological causes?

  Damage to the nervous system (in the brain and spinal cord) can interfere with the nerves responsible for starting and controlling swallowing.

  • stroke
  • Brain tumours
  • Neurodegenerative diseases, including Parkinson disease, MS, dementia and motor neurone disease.
• Dysphagia: Problems swallowing Obstruction?

  Conditions that cause an obstruction in the throat or a narrowing of the oesophagus (the tube that carries food from your mouth to the stomach) can make swallowing difficult.

  • mouth or throat cancer, such as–once these cancers are treated, the obstruction may no longer be an issue
  • gastro-oesophageal reflux disease (GORD)– stomach acid can cause scar tissue to develop, narrowing your oesophagus