Pharmacology Flashcards
Where are the parasympathetic ganglions found?
The cell bodies of pregalglionic fibres are located in the brainstem and the cell bodies of the postganglionic fibres are embedded in the walls of the bronchi and bronchioles
What does stimulation of postganglionic cholinergic fibres cause?
Bronchial smooth muscle contraction which is mediated by M3 musarinic ACh receptors on airway smooth muscle cells
Mucus secretion increases which is also mediated by M3 muscarinic ACh receptors on goblet cells
What does stimulation of postganglionic noncholinergic fibres cause?
Bronchial smooth muscle relaxation which is mediated by nitric oxide and vasoactive intestinal peptide (VIP)
What is the effect of the sympathetic division on
smooth muscle in airways?
Nothing - there is no innervation of bronchial smooth muscle in humans, but post-ganglionic fibres supply submucosal glands and smooth muscle of blood vessels
What does stimulation of the sympathetic division have on the rest of the airways?
Bronchial smooth relaxation via beta2-adrenoceptors on airway smooth muslce cells activated by adrenaline released from the adrenal glands
Decreased mucus secretion mediated by beta2-adrenoceptors on goblet cells
Increased mucociliary clearance by beta2-adrenoceptos on epithelial cells
Vascular smooth muscle contraction mediated by alpha1-adrenoceptors on vascular smooth muscle cells
What are the general mechanisms for excitation contraction coupling in smooth muscle cells
Transmitter or hormone activated a GPCR such as M3 which initiates a Gq/11 pathway that results in the influx of calcium from the sarcoplasmic reticulum to the cytoplasm via the IP3 receptor
Depolarisation can also activate a calcium channel which results in the activation of ryanodine which results in the influx of calcium from the cytoplasmic reticulum to the cytoplasm
How is contraction initiated in smooth muscle cells?
Calcium activates calmodulin which then activated MLCK (myosin light chain kinase) which then phophorylates the myosin cross bridge to allow for muscle contraction
Simply, how is contraction of muscles initated?
Contraction results from the phosphorylation of the regulatory myosin light chain in the presence of elevated calcium and ATP
Simply, how is relaxation of smooth muscles initiated?
The dephosphorylation of myosin light chain by myosin phosphatase which has consitutive activity
How is the activity of MLCK and myosin phosphatase regulated?
Extracellular signals:
Adrenaline activate a beta2-adrenoceptor which then activated Gs, which then activated cAMP which activated PKA
What can PKA do?
Phosphorylate and therefore inhibit MLCK
Phosphorylate and therefore stimulat myosin phosphatase
Causes relaxation of bronchail smooth muscle
What is the mechanism of asthma?
Increased mass of smooth muscle (hyperplasia and hypertrophy)
Accumulation of interstitial fluid (oedema)
Increased secretion of mucus
Epithelial damage exposing sensory nerve endings
Sub-epithelial fibrosis
How is the airway narrowed and what can it cause?
Inflammation and bronchoconstriction which increases airway restriction and therefore FEV1 and PERF
What is bronchial hyper-responsiveness in asthma due to?
Epithelial damage which exposes sensory nenrve endings that contribute to increased sensitivity of the airways to bronchoconstrictor influences and may cause neurogenic inflammation by the release of various peptides from sensory nerve endings
What are the 2 components to asthma?
Hypersensitivity
Hyper-reactivity
What test reveals hyper-responsiveness?
A provocation test with inhaled bronchoconstrictors (spasmogens) such as histamine or methacholine
What is FEV1?
The forced expiatory voluble in liters in one seconds
What is the mechanism in a nonatopic individual when they are exposed to an antigen?
The allergen is phagocytosed by dendritic cells which activates a low level TH1 response which is a cell-mediated immune response involving IgG and macrophages
What is the mechanism in an atopic individual when they are exposed to an antigen?
It is phagocytosed by dendritic cells but a strong TH2 response is activated which is antibody mediated and involves IgE
What happens in allergic asthma?
There is antigen presentatino by CD4+ cells which iduces the clonal expansion and maturation of B cells to IgE secreting plasma cells. This is mediated by interleukins
What happens during the development of allergic asthma?
The eosinophils differentiate and activate a response to IL-5 which is released from TH2 cells.
What do the mast cells in airways express?
IgE receptors in response to IL-4 and IL-13 released from TH2 cells