PHYSIOLOGY OF THE GASTROINTESTINAL TRACT (GIT)
Main function: The GIT provides the body with a supply of water, nutrients, electrolytes,
vitamines.
Actions:
1) Digestion of the food
2) Absorption of the products of digestion
Ad 1) Digestive processes: - mechanical
- chemical
Mechanical methods: - mastication (chewing)
- swallowing (deglutition)
- movements of the GIT
(motor functions)
Chemical means (secretions): - saliva
- gastric juice
- pancreatic juice
- intestinal juice
- bile
PHYSIOLOGY OF MOUTH
Functions:
1/ Mechanical and chemical digestion of the food
2/ The source of the unconditioned reflexes
3/ Control of physical and chemical properties of the food
Ad 1 a Mechanical activity – mastication
The anterior teeth – a cutting action
The posterior teeth – a grinding action
Thee maximal closing force - incissors 15 kg
- mollars 50 kg
Inervations of the muscles of chewing – 5th, 8th, 12th cranial nerves
Centers – near the brain stem and cerebral cortex centers for taste
Act of mastication:
The movement of the lower jaw down:
- Contraction of m. biventer mandibulae (m.digastricus), m.
pterygoideus ext., m.m. infrahyoidei →
The movement – up: the drop initiates a stretch reflex
Contraction of m. masseter, m. temporalis, m. pterygoideus
Rebound of antagonists- inhibition – the jaw drops +
compression of the bolus of the food against the linings of the mouth - rebound – repetitive
actions.....
Mastication reflexive and voluntary
Function of the mastication: - grinding the food
- mixing with saliva
- prevention of excoriation of GIT
- makes easy swalowing
1
, - aids subsequent digestion
SALIVATION
Ad 1 b) Adjustment of the food by the saliva
The salivary glands: - parotid
- submandibular
- sublingual
- buccal
Secretion of the saliva: - basal - 800 – 1500 ml/day
- during intake of food
Regulation of salivary secretion
– nervous - parasympathetic
- sympathetic
Unconditioned reflexes:
Taste and tactile stimuli increase 8-20 times the basal rate of secretion
Conditioned reflexes:
Visual, olphactoric, acoustic stimuli
Centers: salivatory nuclei (at the juncture of the medulla and pons):
superior – submandibular (70%), sublingual (5%)
inferior – parotid (serous saliva)
Parasympathetic nerves: n.VII, n.IX – stimulation of the salivation.
Parasympathetic nerves – acetylcholine – kallikrein – alpha 2
globuline (plasma) – bradykinine – vasodilatation – stimulation
of the secretion of saliva (serous)
Sympathetic nerves: stimulation of the secretion of the mucinous saliva
Composition of the saliva
99.5 % - water; 0.5 % substances – organic – 0.3 %
- anorganic – 0.5 %
Organic substances: Mucin, digestive enzymes – ptyalin, lingual lipase, proteolytic
enzymes, cytochromoxidase, carbanhydrase, phosphatase, IgA, lysozyme, blood groups s....
Cells: leukocytes,epithelial cells,...
Anorganic substances: Na+, K+, Cl-, HCO3-
Functions of saliva
Saliva - keeps the mouth moist, aids speech
- facilitates swallowing
- serves as a solvent for the molecules that stimulate
the taste buds
- serves a solvent for irritating foods - helps wash away the pathogenetic
bacteria,
- destroy bacteria (thiocyanate ions, proteolytic enzymes),by proteins
antibodies
2
, can destroy oral bacteria, lysozyme = antibacterial
- keeps the mouth and teeth clean
Deficient salivation = xerostomia
Swallowing (Deglutition)
Three stages:
1) oral – voluntary – the food is squeezed into the pharynx by tongue
2) pharyngeal – automatic – cannot be stopped (1 s)
Involuntary contraction in the pharyngeal muscles – that pushes the food into the oesophagus.
Concomitant actions: Inhibition of respiration, closing of the posterior nares by the soft
palate, pulling the larynx upward (enlargement the opening of the oesophagus), glottic
closure
Control of the pharyngeal stage of swallowing -swallowing reflex:
Swallowing center – in the medulla and lower pons
Afferent nerves – Vth, VIIth, IXth, Xth
Coordination of the swallowing with respiration
3) oesophageal stage of swallowing:
Oesophagus - the first third striated muscle
- the last third smooth muscle
- the middle – mixed
Innervation – n. vagus, sympathetic nerves and others endings
Function – to transport food from the pharynx to the stomach by gravity and by
peristalsis
Peristalsis – primary = a continuation of the peristaltic wave
from pharynx
- secondary waves result from distention of the
oesophagus by the retained food. Speed 4 cm/s
The swallowing time – for a compact food 6-9 s
a fluid 4-5 s
Regulation of the oesophageal peristalsis:
- by intrinsic neural circuits – myenteric and submucosal plexus
- by vagal efferent fibers
Functions of the upper and lower oesophageal sphincters
Upper – pharyngoesophageal junction – 3 cm segment – with high resting tone – relaxes
reflexly upon swallowing
Lower – cardia – sphincter cardiae – 2-5 cm above the juncture of the oesophagus with the
stomach. Circular muscle – tonically constricted.
Receptive relaxation – allows propulsion of the swallowed food into the stomach. The
relaxation through VIP.
Disorders of the swallowing:
- dysphagia – pain
3
, - achalasia – weak oesoph. peristalsis, accumulation of the food in the oesophagus –
dilatation, increased tonus of cardiae. Pneumatic dilatation or myotomy
- lower oes. sphincter incompetence – gastrooesophageal reflux
(GER). Surgical treatment.
STOMACH
Anatomy and histology
- Cardia
- Fundus
- Corpus
- Antrum
- Pyloric sphincter
The smooth layers: - longitudinal – ext.
- circular - med.
- transversal - int.
Each muscle layer functions as a syncytium – gap junctions
Innervation: - myenteric plexus – outer between the longitudinal and circular layers
- submucosal plexus – inner
Vagal and sympathetic control
Gastric motility
The motor functions of the stomach:
1) storage of food
2) mixing – " – with gastric secretions – semifluid form – chyme
3) emptying of the food into duodenum
1) Storage: receptive relaxation of the stomach (P = 6 mmHg) by
- a plasticity of the smooth muscle layers
- nervous action – reduction of vagal tone
- humorally (gastrin)
Food forms concentric circles. A limit about 1.5 l.
Storage time: Fats – 6 hours, proteins – 4 hours,
sacharides – 2 hours
2) Mixing: Gastric slow waves – basal electric rhythm – 3/min – pacemaker cells – the
circular smooth muscle of the fundus
Velocity – 1- 4 cm/s – weak propulsion to move the chyme toward the antrum.
Raising intensity – peristaltic constrictor rings.
Hunger contractions – when the stomach is empty fora long time (12 hours ...) – intensive
contractions – most intense in young people – feeling of hunger – regulation of the food
intake.
4
Main function: The GIT provides the body with a supply of water, nutrients, electrolytes,
vitamines.
Actions:
1) Digestion of the food
2) Absorption of the products of digestion
Ad 1) Digestive processes: - mechanical
- chemical
Mechanical methods: - mastication (chewing)
- swallowing (deglutition)
- movements of the GIT
(motor functions)
Chemical means (secretions): - saliva
- gastric juice
- pancreatic juice
- intestinal juice
- bile
PHYSIOLOGY OF MOUTH
Functions:
1/ Mechanical and chemical digestion of the food
2/ The source of the unconditioned reflexes
3/ Control of physical and chemical properties of the food
Ad 1 a Mechanical activity – mastication
The anterior teeth – a cutting action
The posterior teeth – a grinding action
Thee maximal closing force - incissors 15 kg
- mollars 50 kg
Inervations of the muscles of chewing – 5th, 8th, 12th cranial nerves
Centers – near the brain stem and cerebral cortex centers for taste
Act of mastication:
The movement of the lower jaw down:
- Contraction of m. biventer mandibulae (m.digastricus), m.
pterygoideus ext., m.m. infrahyoidei →
The movement – up: the drop initiates a stretch reflex
Contraction of m. masseter, m. temporalis, m. pterygoideus
Rebound of antagonists- inhibition – the jaw drops +
compression of the bolus of the food against the linings of the mouth - rebound – repetitive
actions.....
Mastication reflexive and voluntary
Function of the mastication: - grinding the food
- mixing with saliva
- prevention of excoriation of GIT
- makes easy swalowing
1
, - aids subsequent digestion
SALIVATION
Ad 1 b) Adjustment of the food by the saliva
The salivary glands: - parotid
- submandibular
- sublingual
- buccal
Secretion of the saliva: - basal - 800 – 1500 ml/day
- during intake of food
Regulation of salivary secretion
– nervous - parasympathetic
- sympathetic
Unconditioned reflexes:
Taste and tactile stimuli increase 8-20 times the basal rate of secretion
Conditioned reflexes:
Visual, olphactoric, acoustic stimuli
Centers: salivatory nuclei (at the juncture of the medulla and pons):
superior – submandibular (70%), sublingual (5%)
inferior – parotid (serous saliva)
Parasympathetic nerves: n.VII, n.IX – stimulation of the salivation.
Parasympathetic nerves – acetylcholine – kallikrein – alpha 2
globuline (plasma) – bradykinine – vasodilatation – stimulation
of the secretion of saliva (serous)
Sympathetic nerves: stimulation of the secretion of the mucinous saliva
Composition of the saliva
99.5 % - water; 0.5 % substances – organic – 0.3 %
- anorganic – 0.5 %
Organic substances: Mucin, digestive enzymes – ptyalin, lingual lipase, proteolytic
enzymes, cytochromoxidase, carbanhydrase, phosphatase, IgA, lysozyme, blood groups s....
Cells: leukocytes,epithelial cells,...
Anorganic substances: Na+, K+, Cl-, HCO3-
Functions of saliva
Saliva - keeps the mouth moist, aids speech
- facilitates swallowing
- serves as a solvent for the molecules that stimulate
the taste buds
- serves a solvent for irritating foods - helps wash away the pathogenetic
bacteria,
- destroy bacteria (thiocyanate ions, proteolytic enzymes),by proteins
antibodies
2
, can destroy oral bacteria, lysozyme = antibacterial
- keeps the mouth and teeth clean
Deficient salivation = xerostomia
Swallowing (Deglutition)
Three stages:
1) oral – voluntary – the food is squeezed into the pharynx by tongue
2) pharyngeal – automatic – cannot be stopped (1 s)
Involuntary contraction in the pharyngeal muscles – that pushes the food into the oesophagus.
Concomitant actions: Inhibition of respiration, closing of the posterior nares by the soft
palate, pulling the larynx upward (enlargement the opening of the oesophagus), glottic
closure
Control of the pharyngeal stage of swallowing -swallowing reflex:
Swallowing center – in the medulla and lower pons
Afferent nerves – Vth, VIIth, IXth, Xth
Coordination of the swallowing with respiration
3) oesophageal stage of swallowing:
Oesophagus - the first third striated muscle
- the last third smooth muscle
- the middle – mixed
Innervation – n. vagus, sympathetic nerves and others endings
Function – to transport food from the pharynx to the stomach by gravity and by
peristalsis
Peristalsis – primary = a continuation of the peristaltic wave
from pharynx
- secondary waves result from distention of the
oesophagus by the retained food. Speed 4 cm/s
The swallowing time – for a compact food 6-9 s
a fluid 4-5 s
Regulation of the oesophageal peristalsis:
- by intrinsic neural circuits – myenteric and submucosal plexus
- by vagal efferent fibers
Functions of the upper and lower oesophageal sphincters
Upper – pharyngoesophageal junction – 3 cm segment – with high resting tone – relaxes
reflexly upon swallowing
Lower – cardia – sphincter cardiae – 2-5 cm above the juncture of the oesophagus with the
stomach. Circular muscle – tonically constricted.
Receptive relaxation – allows propulsion of the swallowed food into the stomach. The
relaxation through VIP.
Disorders of the swallowing:
- dysphagia – pain
3
, - achalasia – weak oesoph. peristalsis, accumulation of the food in the oesophagus –
dilatation, increased tonus of cardiae. Pneumatic dilatation or myotomy
- lower oes. sphincter incompetence – gastrooesophageal reflux
(GER). Surgical treatment.
STOMACH
Anatomy and histology
- Cardia
- Fundus
- Corpus
- Antrum
- Pyloric sphincter
The smooth layers: - longitudinal – ext.
- circular - med.
- transversal - int.
Each muscle layer functions as a syncytium – gap junctions
Innervation: - myenteric plexus – outer between the longitudinal and circular layers
- submucosal plexus – inner
Vagal and sympathetic control
Gastric motility
The motor functions of the stomach:
1) storage of food
2) mixing – " – with gastric secretions – semifluid form – chyme
3) emptying of the food into duodenum
1) Storage: receptive relaxation of the stomach (P = 6 mmHg) by
- a plasticity of the smooth muscle layers
- nervous action – reduction of vagal tone
- humorally (gastrin)
Food forms concentric circles. A limit about 1.5 l.
Storage time: Fats – 6 hours, proteins – 4 hours,
sacharides – 2 hours
2) Mixing: Gastric slow waves – basal electric rhythm – 3/min – pacemaker cells – the
circular smooth muscle of the fundus
Velocity – 1- 4 cm/s – weak propulsion to move the chyme toward the antrum.
Raising intensity – peristaltic constrictor rings.
Hunger contractions – when the stomach is empty fora long time (12 hours ...) – intensive
contractions – most intense in young people – feeling of hunger – regulation of the food
intake.
4
