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

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po

ten

tial

(m

V)

Tension

0

-60

Tension

Mem

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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)