BIOL10002 Lecture Notes - Lecture 16: Orthostatic Hypotension, Myosin Light-Chain Kinase, Mean Arterial Pressure
Lecture 16
Regulation of the circulatory system
Heart contraction and relaxation
Pacemaker cells shoot action potentials – two clusters; SAN and AVN
SAN - Spontaneous, rhythmic depolarisation (approx. 100 times/min if independent of nervous control)
Heart rate is controlled by how often the SAN sends a signal, but the AVN is more important (syncytium).
heart = 37.5⁰C to spontaneously contract = heart transplants possible, cos heart won’t up its O2 and die.
Factors influencing vasoconstriction and vasodilation
Substance Source Type Effect
Norepinephrin
e
Sympathetic
neurons
Neural
Vasoconstrictio
n
Endothelin Vascular
Endothelium
Paracrine
Angiotensin II Plasma Endocrine
CO2Multiple Metabolite
Vasodilation
Nitric Oxide Vascular
endothelium
Paracrine
Bradykinin Multiple Paracrine
Vasodilation and Vasoconstriction
Mean Arterial Pressure (MAP); blood pressure varies in body in response to changes to MAP
Baroreceptors are stretch receptors – found in aorta detect changes in blood pressure
Chemoreceptors detect changes in chemical concentration – e.g. an increased demand for oxygen:
Arterial chemoreceptors – primarily detect changes in blood composition
Medullary chemoreceptors – detect changes in CO2 levels.
Parasympathetic N.S = rest or digest
if BP is high, causes vasoconstriction
Sympathetic N.S = fight or flight
if BP is low, causes vasodilation
- contraction tone is regulated by conc. of calcium:
Noradrenaline increases intracellular [calcium] in smooth muscle cells greater contractions of the smooth muscle
cells
Muscle Contraction
1. Calcium released binds with calmodulin, creates complex
3. Activates enzyme (myosin light chain kinase - MLCK)
4. MLCK phosphorylates myosin head which causes contraction
muscle contraction is driven by calcium but ultimately by MLCK phosphorylating myosin head.
G-protein linked receptors are always present in signals that causes vasoconstriction
Vasodilation
1. Receptor calcium increase in endothelial cells release of potassium ions out of cell hyperpolarised muscle
cells unresponsive to neurons causes relaxation
2. Endothelial cells release nitric oxide release GTP converted to cGMP causes hyperpolarisation
unresponsiveness to neurons from the sympathetic nervous system causes relaxation
Autonomic innervation of the heart - How easily the SAN will depolarise and thus contract
- Parasympathetic (vagal) nerves: Acetylcholine (ACh) Muscarinic receptor (M2)
SAN cells are made less responsive, so it takes longer for them to depolarise decreases heartrate
- Sympathetic nerves: NA and adrenaline B1 adrenoceptors
Increasing intracellular [calcium] so the SAN cells are more likely to depolarize increases heart rate
Stuff that shouldn’t happen
Cardiac arrest
function loss in ventricles due to irregular electrical activity in the heart = limited blood going to the body
brain is highly sensitive to O2 loss and blood flow, so there is only 4-6 minutes before major damage
Treatable by a defibrillator can be implanted in the body (ICD – sends electrical shock to ‘reset’ the heart)
find more resources at oneclass.com
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Document Summary
Pacemaker cells shoot action potentials two clusters; san and avn. Heart rate is controlled by how often the san sends a signal, but the avn is more important (syncytium). Heart = 37. 5 c to spontaneously contract = heart transplants possible, cos heart won"t up its o 2 and die. Mean arterial pressure (map); blood pressure varies in body in response to changes to map. Baroreceptors are stretch receptors found in aorta detect changes in blood pressure. Chemoreceptors detect changes in chemical concentration e. g. an increased demand for oxygen: Arterial chemoreceptors primarily detect changes in blood composition. Medullary chemoreceptors detect changes in co2 levels. Contraction tone is regulated by conc. of calcium: Noradrenaline increases intracellular [calcium] in smooth muscle cells greater contractions of the smooth muscle cells. Muscle contraction: calcium released binds with calmodulin, creates complex, activates enzyme (myosin light chain kinase - mlck, mlck phosphorylates myosin head which causes contraction.
