Physiology and Pharmacology Flashcards
What are the basic digestive processes?
Motility, secretion, digestion and absorption
What are the different types of movements in motility? Describe these.
Propulsive movement - directional movement of food, mouth to anus
mixing movements - non-directional, shifting food backwards and forwards
tonic contraction - large groups of smooth muscle contracting simultaneously eg defecation
What are the purposes for secretions into the lumen of the digestive tract?
protection and digestion
What is digestion?
Enzymatic hydrolysis of large complex food molecules into smaller, absorbable units.
What is absorption?
Transfer of absorbabale products of digestion (with water, vitamins and electrolytes) from lumen into enterocytes then into blood or lymph.
What are the functions of saliva?
lubrication - swallowing and speech
solvent - taste
antimicrobial - lyzozyme, lactoferrin, immunoglobulins
neutralisation of acid (bicarbonate)
facilitates suckling by infants - fluid seal
what is xerostomia?
limited saliva production resulting in rotten teeth
What are the different salivary glands and where are they found?
parotid - below ear, over masseter
submandibular - under lower edge of mandible
sublingual - floor of mouth under tongue
How is saliva produced?
primary production is in the acinar cells - Na+, Cl- and H2O
Secondary modification in duct cells - remove Na+ and Cl- and add HCO3- and K+
duct cells are impermeable to water so there is no dilution.
What is the composition of saliva?
There is less NaCl in saliva than in plasma
no glucose
High flow rate - there is more bicarbonate than in low flow rate saliva.
How does autonomic stimulation affect saliva production/composition?
parasympathetic - large volume of watery, enzyme-rich saliva. M3 muscarinic receptors, glossopharyngeal and facial nerve
sympathetic - small volume of thick and mucous rich (beta 1 - adrenoceptors)
muscarinic antagonists such as atropine cause a dry mouth
Describe swallowing (deglutation).
- Oropharyngeal stage: food bolus is forced to the back of the mouth by the tongue
this stimulates pharyngeal pressure receptors which sends afferent signals to the swallowing centre in the medulla
efferents give “All-or-nothing” reflex
oesophageal sphincter opens
food goes into the pharynx then into the oesophagus
Opening of lower oesophageal sphincter occurs within 2-3 seconds and closes after food has passed - prevents reflux
Describe the “all-or-nothing” reflex
Soft palate raises
tongue sticks to the hard palate
Uvula sticks to the back of the throat
Larynx raises
Epiglottis tilts
vocal cords close over the trachea
swallowing centre switches off the respiratory centre
pharyngeal muscles contract to force food into the oesophagus
oesophageal sphincter opens to allow food into the oesophagus.
Where is the swallowing centre?
The medulla in the brain
What is the primary peristaltic wave?
During swallowing
Controlled by medulla
Mediated by skeletal muscle (proximal) and smooth muscle (distal)
Contraction of circular muscle behind good and relaxation in front
Contraction of longitudinal muscles to shorten distance
Controlled by enteric nervous system (cholinergic)
What is the secondary peristaltic wave?
If food gets stuck - triggered locally due to stimulated pressure receptors
Also get increased saliva production
Describe the oesophageal epithelium and it’s function
Epithelium is stratified squamous - protects against mechanical damage by food bolus but not against chemical attack.
Secretes mucous for protection against gastric juices and enzymes
What nerve drives relaxation of the stomach?
Vagus
What is the function of the stomach?
Primary function is to store food before it is released into the duodenum
Starting point for protein digestion by HCl and pepsin
Mixing of food and producing chyme
Secretes about 2 litres a day of gastric juice from gastric pits in gastric mucosa
What causes gastric motility?
Pacemaker cells (interstitial cells of cajal) in the fundus generate basal electrical rhythm (BER).
Goes from fundus to pyloric sphincter through gap junctions between muscle cells
BER doesn’t always generate contraction
If BER reaches threshold, action potential in smooth muscle generated which causes contraction
What are the basic functions of the small intestine?
Digestion
Absorption
Secretion
Motility
