Integrative CV responses (wk8) Flashcards
The regulation of blood pressure
-The role of baroreceptors
-Baroreceptors are receptors detecting blood pressure on beat to beat basis
-They include: internal carotid artery, external carotid artery, carotid sinus baroreceptor, aortic arch baroreceptor, common carotid arteries and afferent neurons to brainstem cardiovascular control centres
-The medulla oblongata is the primary cardiovascular control centre
-Baroreceptors and MAP (mean systemic arterial pressure) -> Baroreceptor firing frequency changes with changes in blood pressure. Normal MAP has a systolic peak and diastolic trough. There is an increase in firing rate of baroreceptors when there is an elevated MAP. During exercise, there is a shaper peak, which increases the firing rate of the baroreceptors.
-The baroreceptor are detecting when the arterial pressure is too high or too low. An increase in arterial baroreceptor firing leads to an increase in parasympathetic outflow to the heart.
The regulation of blood pressure:
-Moderate and acute responses activated to regulate blood pressure
-MAP -> A fall in blood pressure causes the carotid and aortic baroreceptors to detect a hypotensive stimulus leading to decreases in afferent baroreceptor nerve firing. This reduction in neural input to the brainstem causes a decrease in parasympathetic nerve activity to the heart and an increase in sympathetic outflow to the heart and vasculature. The converse occurs with increases in blood pressure. A hypertensive stimulus is created when a person stands up and all of the blood starts to pool at the feet/legs of the body. ‘Tilt tables’ can be used to look at the hypertensive stimulus and how the blood moves through the body.
Describe what MABP is and look at the diagrams from the lecture
MABP is the controlled variable. MAP (mean systemic arterial pressure) = CO (cardiac output) x TPR (total peripheral resistance)
-An increase in arterial pressure, increases the urinary loss of sodium and water, which decreases the plasma volume, therefore decreasing the blood volume
-Cardiac output is influenced by blood volume, skeletal muscle pump and inspiration movements
-In TPR, Local controls include: vasoconstrictors e.g. internal blood pressure and vasodilators e.g. Adenosine, Neural controls include: vasoconstrictors e.g. sympathetic nerves and vasodilators e.g. neurons that release nitric oxide and Hormonal controls include: vasoconstrictors e.g. epinephrine and vasodilators e.g. epinephrine
Draw out the diagram which is the CV response to standing (orthostatic stress)
Regulation of blood pressure during exercise
-Max and submaximal exercise tests
-Max and submaximal exercise tests -> Maximal oxygen uptake (VO2 max) = assessment of aerobic endurance or power, Submaximal exercise tests = used to assess physiological responses to a standardised workload. In a clinical setting, exercise tests are used to help diagnose health problems
Regulation of blood pressure during exercise
-Steady-state exercise
-Steady-state exercise = ‘The level of exercise at which the physiological responses remain relatively stable for an extended period of time’. Recovery is focused on, to be able to understand the processes initiated to regulate the body back to its usual levels. Important factors governing steady-state exercise include:
* The delivery of adequate oxygen to the exercising muscles
* The ability of the cells to utilise this oxygen in the aerobic process of energy metabolism
* The ability to eliminate heat
-During steady-state exercise the physiological responses of ventilation (VE), oxygen consumption (VO2), and cardiac output (Q) are similar in the sense that they involve 4 phases.
Regulation of blood pressure during exercise
-Diastolic arterial pressure
-In healthy people diastolic arterial pressure is regulated within a very narrow range. End-diastolic volume increases due to increased venous return: muscle pump, respiratory pump and sympathetic stimulation.
Regulation of blood pressure during exercise
-Mechanisms of control of ventilation
-Mechanisms of control of ventilation -> The initial rapid rise in ventilation is explained by central common (which is when the motor cortex signals the respiratory control centre to increase ventilation because there is a sudden increase in demand from the muscle). There is a sudden need in oxygen for the body. At stage 2 is where the fine tuning is mostly occurring. Mechanoreceptors in the muscles and limbs detect limb movement and physical deformation, and further supplement central command. The subsequent gradual rise in ventilation may be explained by a fine-tuning of respiratory neurons in response to central command and feedback control from arterial chemoreceptors positioned in the carotid and aortic bodies.
Regulation of blood pressure during exercise
-Mechanisms of control of cardiac output
-Mechanisms for control of cardiac output -> The initial rapid rise in cardiac output is explained firstly by central command, and secondly by the Starling Effect. Input from mechanoreceptors in muscles also contribute to the central command process by feedback control. Chemoreceptors in muscles are mainly responsible for the secondary gradual rise to steady state.
Regulation of blood pressure during exercise
-The Starling Effect
-The Starling Effect -> When venous return of the blood to the heart increases, the myofilaments (Actin and myosin) in cardiac muscle are stretched to a more optimal overlap. As a result the strength of the contraction is greater, and therefore is increased.
Regulation of blood pressure during exercise
-The Starling Effect - Metaboreflex
When exercise begins, muscle metabolism increases and metabolite (E.g. lactic acid, potassium and adenosine) accumulate in the working muscles. Receptors in the muscle detect this accumulation and afferent fibres send information to the brain (the medulla). This increases sympathetic nerve activity. There is a signal to the brain which is asking for more blood and oxygen to the body to be able to get rid of negative chemicals in the body, such as lactic acid buildup.
Regulation of blood pressure during exercise
-The Starling Effect - Sympathetic activation
- Sympathetic activation -> Exercise increases sympathetic activity. Parasympathetic activity decreases. This affects heart rate, the venules and the veins. We want to increase the venous return to the heart and this is done through decreasing the venous diameter.
Regulation of blood pressure during exercise
-The Starling Effect - Redistribution of blood flow
- Redistribution of blood flow -> Blood flow increases in skeletal muscles, the skin and the heart. Skeletal muscle (73% during strenuous exercise)-> supply of oxygen and removal of metabolic waste, Skin (11% flow during strenuous exercise)-> dissipation of heat, Heart (4% during strenuous exercise)-> Oxygen supply (cardiac muscle extracts almost all oxygen from blood even at rest). Blood flow decreases in the kidneys, digestive tract and all other parts of the body not directly involved in exercise. Blood flow through the brain remains fairly constant due to autoregulation. The fixed volume of the cranial cavity cannot accommodate large increases in blood flow.
-In healthy people, diastolic arterial pressure is regulated within a very narrow range.
Controlling mechanisms
-Local, feedback and feedforward
-Vasodilation in muscle, the heart and in the skin decreases peripheral resistance (local control mechanisms and epinephrine on B2 adrenergic receptors)
-The net effect of vasodilation and vasoconstriction in the body during exercise is a reduction in total peripheral resistance. Vasoconstriction in the rest of the body increases peripheral resistance (increase of sympathetic stimulation)
-When exercise begins, the metaboreflex increases sympathetic nerve activity and blood flow to the working muscle (local reflex and feedback)
-When exercise begins, sympathetic nerve activity increases, which increases HR, dilates arterioles to the working muscles and constricts venules and veins (feedback and feedforward)
-CV parameters and training -> CO is larger in trained people. Maximal HR is determined mainly by age and is not increased by training. However, trained people have a lower HR for a given workload. Stroke volume is greater in trained people, and is the only way of producing a higher maximal cardiac output in that group.
Draw the system for integrative CV responses
