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Gastrointestinal physiology
Textbook of Medical Physiology,
GUYTON and HALL, 12th Ed: pp753-803, pp: 843-863. 11th ed: pp771-818, pp865-888. 10th Ed, pp 718-770, pp 803-821.
Physiological processes are Physiological processes are taking place along the taking place along the
gastrointestinal (GI) tract.gastrointestinal (GI) tract. 1. Motility.1. Motility. 2. Secretion 2. Secretion 3. Digestion.3. Digestion. 4. Absorption.4. Absorption.
Functional structures in the Functional structures in the gastrointestinal tractgastrointestinal tract
Smooth muscle cellsSmooth muscle cells Interstitial cells of CajalInterstitial cells of Cajal Secretory cellsSecretory cells
Other related structuresOther related structures
Control systems of GI functions.Control systems of GI functions.
- Neural control: - Neural control:
- Enteric nervous system- Enteric nervous system
- Autonomic nervous system- Autonomic nervous system
- Hormonal control: GI endocrine- Hormonal control: GI endocrine
Blood flow to the GI.Blood flow to the GI.
Functional structures in the Functional structures in the gastrointestinal tractgastrointestinal tract
Smooth muscle cells (SMCs)Smooth muscle cells (SMCs)
Smooth Muscle cells Smooth Muscle cells CharacteristicsCharacteristics
Electrical activityElectrical activity
- Slow waves (basic electrical rhythm)- Slow waves (basic electrical rhythm)
0
-60Mem
bra
ne
po
ten
tial
(m
V)
Tension
0
-60
Tension
Mem
bra
ne
po
ten
tial
(m
V)
Acetylcholine
Contraction of GI smooth muscle
Out
In Ca2+
(Ca2+)4. calmodulin
Inactive myosin light chain kinase
Active myosin light chain kinase
MUSCLE CONTRACTION
Myosin -(PO4)2
Calcium activates contraction
Depends on influx of calcium from extracellular space through calcium channels
Calcium- calmodulin complex activates myosin light chain kinase
Smooth Muscle cells Smooth Muscle cells CharacteristicsCharacteristics
Gap junctions:Gap junctions: Communication between Communication between
cellscells
Functional syncytiumFunctional syncytium
Chemical control of SMCsChemical control of SMCs
Control of smooth muscle cells Control of smooth muscle cells activityactivity
Electrical control:Electrical control:
- Rhythm or phasic - Rhythm or phasic contractionscontractions
Chemical control:Chemical control:
- tonic contractions- tonic contractions
Interstitial Cells of Cajal (ICCs)Interstitial Cells of Cajal (ICCs)
Characteristics of ICCsCharacteristics of ICCs
Communications:Communications:
- ICCs-ICCs gap junctions- ICCs-ICCs gap junctions
- ICCs-smooth muscle cells gab junctions- ICCs-smooth muscle cells gab junctions
- inputs from ENS- inputs from ENS
Generation of action potentials:Generation of action potentials:
pacemaker cells of the GI tractpacemaker cells of the GI tract
Secretory CellsSecretory Cells
Mucous secretion and serous secretionMucous secretion and serous secretion Solitary cellsSolitary cells PitsPits Compound glandsCompound glands Secretory organsSecretory organs
Characteristics of ENSCharacteristics of ENS
Enteric Neurons:Enteric Neurons:–Excitatory Excitatory – InhibitoryInhibitory
NeurotransmittersNeurotransmitters
Ach, SP (Substance P), VIP (Vasoactive Ach, SP (Substance P), VIP (Vasoactive intestinal peptide), CGRP (Calcitonin gene related intestinal peptide), CGRP (Calcitonin gene related peptide), GRP (Gastrin releasing peptide)…etc peptide), GRP (Gastrin releasing peptide)…etc
Autonomic Nervous System (ANS)Autonomic Nervous System (ANS)
SympatheticSympathetic
ParasympatheticParasympathetic
Myenteric plexus
Submucosal plexus
Enteric nervous system
CNS
Sympathetic ganglia
Vagal nuclei
Sacral spinal cord
Preganglionic fibres
Postganglionic fibres
Preganglionic fibres
Parasympathetic N.S Sympathetic N.S.
Smooth muscle
Secretory cells
Blood vessels
Endocrine cells
Enteric Endocrine SystemEnteric Endocrine System
GastrinGastrin Chlecystokinin (CCK)Chlecystokinin (CCK) SecretinSecretin GIP (Gastric Inhibitory peptide) or GIP (Gastric Inhibitory peptide) or
(Glucose dependent Insulinotropic (Glucose dependent Insulinotropic Polypeptide) Polypeptide)
Enteric Endocrine SystemEnteric Endocrine System
Glucagon-like peptide-1(GLP-1), Motilin, Glucagon-like peptide-1(GLP-1), Motilin, Ghrelin, Amylin, Enterostatin, Ghrelin, Amylin, Enterostatin, Neuropeptide Y (NPY), polypeptide YY, Neuropeptide Y (NPY), polypeptide YY, Pancreatic polypeptide which is closely Pancreatic polypeptide which is closely related to polypeptide YY and NPYrelated to polypeptide YY and NPY
Somatostatin,, Neurotensin, Thyrotropin Somatostatin,, Neurotensin, Thyrotropin releasing hormone (TRH), releasing hormone (TRH), Adrenocorticotropic hormone ACTH.Adrenocorticotropic hormone ACTH.
Functions of HormonesFunctions of Hormones
Control of motilityControl of motility Control of secretionControl of secretion Control of blood flowControl of blood flow Regulation of food intakeRegulation of food intake Regulation of metabolic activities in the Regulation of metabolic activities in the
bodybody
Blood Flow of the GIBlood Flow of the GI
- Related to GI activities:Related to GI activities:-Controlled by:-Controlled by: - - HormonesHormones (Secretin, CCK) (Secretin, CCK) - - ENSENS (VIP, SP, CGRP) (VIP, SP, CGRP) - - VasodilatorsVasodilators::
Kinins (Kallidin, Bradykinin)Kinins (Kallidin, Bradykinin) - - Decreased O2 concentrationDecreased O2 concentration
- - ANS ANS (Sympathetic and parasympathetic)(Sympathetic and parasympathetic)