21. Regulation of Circulation Flashcards
What is membrane potential?
Membranes of cells have a charge gradient. Membrane potential in resting state is more negative inside relative to outside
What is depolarisation?
Activation of cells caused by depolarisation. The charge difference switches to being more positive inside due to ion movement
What is hyper polarisation?
Inhibition of cells is caused by hyper polarisation. Charge difference becomes more negative than resting potential and therefore harder to depolarise
How does electric charge control the cardiac muscle?
Cardiac muscle is also controlled by changes in electrical charge across the membrane. A moving wave of change in electrical charge is called an action potential
What three things control rhythmic heart contraction?
- Autorhythmicity
- Gap junctions
- Two groups of pacemaker cells: the sinoatrial node (SAN) and the atrioventricular node (AVN)
How does the atrioventricular node control rhythmic heart contractions?
- Action potentials are sent to the ventricles via the bundle of His
- They run to the ventricular apex via right and left bundle branches
- Action potentials spread through ventricles via purkinje fibers
- Ventricular sanctum
What is cardiac arrest?
The sudden loss of cardiac function, when the heart abruptly stops beating. Often referred to as “sudden death” or “sudden cardiac death”
What is the most common loss of function in cardiac arrest?
- Loss of ventricular fibrillation
- Caused by irregular electrical activity in the heart (arrhythmia)
- When this happens the heart pumps little or no blood to the body
How is cardiac arrest treated?
Defibrillation using electricity to “shock” the heart to try and restore its regular rhythm
What do survivors of cardiac arrest have?
An implantable cardiac defibrillator (ICD)
- If the heart develops an abnormal rhythm, the ICD delivers an electrical shock to the heart to return the heart rhythm to normal
Why is mean arterial pressure used to calculate blood pressure in the body?
Because the diastolic part of the cycle is twice as long as systolic, therefore we calculate the weighted average
How is MAP calculated?
(systolic)+2(diastolic)
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What are the demands on the body?
- Change in blood pressure and increased demand for oxygen
What is required in the response against a change in blood pressure?
- Rapid response
- Baroreceptros
- Baroreceptor reflex
- Autonomic nervous system
What is required in the response against an increased demand for oxygen?
- Rapid resposne
- Chemoreceptors
- Autonomic nervous system
- Hormones
In the autonomic nervous system how do systemic blood vessels change blood flow?
- Arterioles can vasoconstrict and vasodilate and change blood flow and vascular resistance
- Extrinsic (nervous and endocrine systems) factors alter arteriole and vein diameters by acting on the smooth muscle
How does norepinephrine influence vasoconstriction and vasodilation?
- Sympathic neurons
- Neural type
- Causes vasocontriction
How does endothelin influence vasoconstriction or vasodilation?
- Vascular enothelium
- Paracrine
- Vasoconstriction
How does angiotensin influence vasoconstriction or vasodilation?
- Sourced from plasma
- Endocrine
- Vasoconstriction
How does CO2 affect blood flow?
- Sourced from multiple tissues
- Metabolite
- Vasodilation
How does nitric oxide influence blood flow?
- Sourced from vascular endothelium
- Paracrine
- Vasodilation
How does bradykinin influence blood flow?
Sourced from multiple tissues
- Paracrine
- Causes vasodilation
How does noradrenalin affect vasomotor tone?
- Arteriole diameter is controlled by tonic release of noradrenaline
- If there is a change in signal rate either:
- Increased noradrenaline release onto alpha receptors so there is an increase signal rate and the blood vessel constricts OR
- Decreased noradrenaline release onto alpha receptors, decreased signal rate and the blood vessel dilates
What is the process of vasoconstriction?
- Noradrenaline, angiotensin II and Endothelin-1 act via different receptors (g-protein linked)
- Phospholipase C activation causes the formation of inositol triphosphate
- IP3 stimulates the release of calcium from the sarcoplasmic reticulum (SR)
- Increased ca2+ causes smooth muscle contraction
