Regulation of Blood Pressure Flashcards
1
Q
Structure and Function of the Heart
A
- In the right atrial wall are a group of nerve cells that stimulate the rhythmic contraction of the heart. This is the Sinoatrial Node, the pace maker of the heart
- the SA node can regulat the heart without any stimulation from the CNS (under normal conditions) - myogenic organ
- It initiates the cardiac cycle through the following series of events:
1. Stimulates both atria to contract (systole)
2. This causes stimulation of the Atrioventricular node
3. Impulses then move through AV bundle to the fibres of the purkinje in the apex of the heart
4. This stimulates the contraction of the ventricles from the bottom in an upwards direction
2
Q
Sinoatrial Node
A
- the SA node can regulate the heart without stimulation from the CNS (under normal conditions). It initiates the cardiac cycle through the following sequence of events:
1. Stimulates both atria to contract
2. This causes stimulation of the atrioventricular node
3. the impulse then moves through the AV bundle (bundle of his) to the fibres of purkinje in the apex of the heart
4. This stimulates the contraction of the ventricles from the bottom in an upwards direction
3
Q
Autonomic Nervous System
A
- the heart is influenced by the Automic Nervous System (ANS) to maintain homeostasis
- primarily in response to changes in blood pressure (refers the force with which the blood presses on the walls of the blood vessels) detected by pressure receptors in the walls of vessels entering and leaving the heart
- the ANS has sympathetic and parasympathetic neurons that carry impulses to the SA and AV nodes and therefore atria and ventricles from the cardiovascular regulating centre in the medulla oblongata
- the cardiovascular regulating centre in th medulla oblongata is stimulated by the hypothalamus, controls the heart rate
- Sympathetic nervous = stimulation from CRC via cardiac nerve increase heart rate and stroke volume through the release of noradrenaline
- parasympathetic nervous = stimulation from CRC via vagus nerve decrease heart rate and strength of contraction through release of acetylcholine
4
Q
Factors that affect the regulation of cardiac output
A
- cardiac output can be defined as the volume of blood that leaves the heart in one minute. It can be calculated by the following formula:
- CARDIAC OUTPUT = STROKE VOLUME X HEART RATE
- Heart rate = number of beats per minute
- Stroke volume = volume of blood forced from heart per beat
- An increase in cardiac output will result in an increase in blood pressure as there is an increased force of blood pushing against the arterial walls as it leaves the heart
5
Q
Heart Rate is influenced by - Sympathetic Division
A
- via the cardiac nerve
- stimulates SA node, AV node and ventricles
- releases noradrenaline
- increases heart rate
- increases stroke volume
- dominant during exercise
- baroreceptors detect a decrease in blood pressure
- causes vasoconstriction of blood vessels
6
Q
Heart Rate is influenced by - parasympathetic division
A
- via vagus nerve
- inhibits SA node and AV node
- releases Acetylcholine
- Decreases heart rate
- Decreases stroke volume
- Dominant during rest
- Baroreceptors detect an increase in blood pressure
- Vasodilation of BV (inhibition of sympathetic neurons rather than stimulation of parasympathetic neurons)
7
Q
Changes in Blood Pressure
A
- changes in blood pressure detected by baroreceptors located in aortic and carotid bodies
- this message is then sent to the cardiovascular regulating centre by sensory impulses
- the CRC maintain a balance in BP through the inhibition and stimulation of SA node
- The CRC has two centres:
1. Cardiac centre which controls heart rate
2. Vasomotor centre which controls blood vessel diameter
8
Q
Stroke volume is effected by:
A
-
Stroke volume: is determined by the force of ventricular contraction. With an increase in the strength of contraction there is an increase in volume of blood forced from the ventricles
1. Diastole length (relaxation) = the longer the time, the more blood can fill the heart and thus more blood can be pumped out when the heart contracts
2. Venous return (the volume of blood that is returned to the heart) = an increased return stretches the fibres of the heart causing stronger ventricular contractions. The return is affected by skeletal muscle activity, lung ventilation, tone of vein walls and ease of blood flow through capillaries from arteries to veins through skeletal muscles arterioles
3. Autonomic nervous system: - sympathetic stimulation: noradrenaline increases strength of ventricular contraction and therefore the heart ejects an increased blood volume
- parasympathetic stimulation: acetylcholine decreases strength of ventricular contraction and therefore the heart ejects a decreased blood volume
9
Q
Exercise and Cardiac Output/Blood Flow
A
- ventilation rate increases to provide oxygen to cells and remove more carbon dioxide
- CO increases with exercise to provide muscle cells with the nutrients they require and to remove wastes faster. Blood flow also changes with exercise. Blood flow to skeletal muscles increases and to all internal organs such as alimentary canal it decreases (as there is no change in their cellular activity)
- This occurs through the stimulation of the sympathetic nervous system which releases adrenaline in the following way:
1. Causes vasoconstriction of the BV in internal organs such as alimentary canal
2. Vasodilation of BV in skeletal muscles
10
Q
Exercise and Cardiac Output/Blood Flow 2
A
- this change in blood flow is brought on before exercise begins through anticipation stimulating the sympathetic division and causing an increase in heart rate, stroke volume and blood flow to muscles and inhibition of the parasympathic division
- the heart rate is more than stroke volume due to rapid change in the contraction of cardiac muscle and as vasoconstriction occurs in the internal organs, skeletal muscles force more blood through the heart and increase blood pressure
11
Q
Exercise and Cardiac Output/Blood Flow 3
A
- as exercise proceeds the muscle cells require more oxygen and nutrients and removal of carbon dioxide and lactic acid. These wastes act as vasodilators of arterioles and therefore result in an increased blood flow through muscle tissues.
- Heat produced through respiration increases body temperature and results in increased heart rate
- Blood flow (HR) is also affected by age (HR decreases with age), Gender (male slower than female) and emotional state
12
Q
What effects blood pressure
A
Blood pressure = refers to the force with which the blood presses on the walls of the blood vessels.
It depends on:
-
Diameter of blood vessels
- the muscle tissue received impulses from the ANS from the vasomotor centre in the CRC causing either:
- vasoconstriction (if BP is too low), through sympathetic neurons releasing noradrenaline at vessel walls = increase BP
- vasodilation (if BP is too high), through inhibition of sympathetic neurons at vessel walls = decrease BP
-
Cardiac output: the volume of blood that leaves the heart in one minute
- as cardiac output increases, blood pressure will increase
- the stroke volume is the volume of blood forced from the ventricles every contraction
- heart rate is the number of contrations per minute
13
Q
Regulation of Blood Pressure during exercise 1
A
Blood pressure = cardiac output x resistance (the resistance of arteries to blood flow)
- increases in either cardiac output or resistance will cause an increase in BP
- Resistance can be influenced by:
1. Peripheral resistance: - resistance to blood flow through the blood vessels (friction)
- increased viscosity (thickness/stickyness) of blood increases resistance
- Autonomic activity: sympathetic activity vasoconstricts blood vessels which increases resistance
14
Q
Regulation of Blood Pressure during exercise 4
A
- exercise will result in an increase in blood pressure due to the increase in cardiac output
- this is due to the increase in heart and stroke volume due to the sympathetic stimulation of the heart
- and an increased venous return as the contractions of the sketelal muscles help to push more blood in the veins back towards the heart
- this also increases stroke volume and blood pressure
15
Q
Regulation of Blood Pressure during exercise - Chemical Stimuli
A
- an increase in concentration of carbon dioxide and hydrogen ions in the blood with stimulate the cardiovascular regulating centre to increase sympathetic stimulation of the heart to increase cardiac output
- it will also result in vasoconstriction of the arterioles supplying the organs of the alimentary canal
- vasodilation of the arterioles supplying the sketal muscles
