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BTEC Level 3 Applied Science | Unit 9 Human Reproduction and Regulation - Merit
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BTEC Level 3 Applied Science | Unit 9 Human Reproduction and Regulation - Merit
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Unit 9 – Human Regulation and ReproductionRegulation of the cardiovascular and respiratory system
The medulla oblongata is what controls the unconscious processes such as controlling the
heart rate as well as ventilation. There is a part of medulla oblongata called the
cardiovascular control centre, which is responsible for the changing heart rate according to
the body's ventilation and needs. This works by sending action potentials to the sympathetic
or parasympathetic neurons in which they release neurotransmitters into the sinoatrial node
(SAN), this is known as the heart pacemaker. The SAN will modify the heart rate in order to
adapt to the body's needs, such as if you are out of breath then your heart rate will increase
in order to get more oxygen in. (The Science Hive, 2021)
The pons is located beneath the medulla and the function of this is to control the rate of
involuntary respiratory.
To maintain equilibrium, the ANS specifically controls blood pressure, respiration rate, body
temperature, sweating, gastrointestinal motility and secretion, as well as other visceral
functions. With no conscious effort, the ANS runs constantly. The spinal cord, brain stem,
and hypothalamus each have control centres that govern the ANS.
Figure 6 – The Medulla (NIPF, 2019)
Chemoreceptors are sensory receptors which lay at the dendrites of sensory neurons.
During workouts, carbon dioxide levels in the blood increase due to an increased level of
respiration. Respiration takes place because we need to exhale and gain energy, which is
made by inhaling air and red blood cells picking up the oxygen. By doing so the red blood
cells travel around the body to limbs and muscles in order to diffuse the oxygen into the
mitochondria of the muscle, after that the red blood cell will pick up carbon dioxide from the
lungs and we will exhale this. Presence of carbon dioxide in the blood can form carbonic
acid, which leads to a decrease in blood pH levels. (Peers, 2016)
The concentration of carbon dioxide and oxygen is important as they control the regulation of
blood pH, respiratory system and the bond between the CO2 and haemoglobin for oxygen.
Usually, our blood level ranges between 7.35 to 7.45 with an average of 7.40pH. (Hopkins et
al,2021) When the pH of our blood decreases this means that chemoreceptors in the carotid
artery and aorta are stimulate and send impulses such as action potential to the ventilation
centre, as this will respond by sending impulses to the external intercostal muscles and the
diaphragm in order to increase the breathing rate. Hence why you would start to breathe
, Unit 9 – Human Regulation and Reproduction
Regulation of the cardiovascular and respiratory system
heavier when overusing your body muscles. (Peers, 2016, Unit 9 Human Regulation and
Reproduction).
Essentially what happens is when the carbon dioxide levels increase in the blood due to an
increase in respiration it causes the blood pH to decrease due to the presence of carbonic
acid in which chemoreceptors will send impulses to the external intercostal muscles and
diaphragm in order to increase the breathing rate leading to increasing the heart rate.
Therefore, the ventilation centre in the medulla responds by increasing the recurrence of
impulses being sent to the diaphragm and intercostal muscles.
The average resting heart rate of an adult is around 70bpm, the rhythm of the heart is
maintained by a nerve impulse. A nerve impulse begins in the pacemaker area, SAN. This
causes the atria to contract and so initiates the heartbeat. A layer of non-conducting tissue
prevents the nerve impulse from entering the ventricles. This electrical activity from the SAN
is picked up by the atrio-ventricular node (AVN). The AVN stimulates the bundle of His which
penetrates through the septum, however the AVN has a slight delay before stimulating the
bundle of His, in order to ensure that the atria has stopped contracting before the ventricles
start. After that the bundle of His is connecting tissue made up of Purkinje fibres in which the
bundle of His splits into 2 branches and conducts the impulse to the apex. At the apex, the
Purkinje fibres build a network through the walls of the ventricles on both sides, the spread
of the Purkinje fibres triggers contractions of the ventricles.
The cardiovascular control centre raises the rate of SAN firing by activating the sympathetic
nervous system when blood pressure or oxygen levels decrease. The release of the
neurotransmitter noradrenaline, binds to receptors on the SAN, causing the sympathetic
nervous system to participate in the "fight or flight" response, raising the heart rate.
The action potentials are able to conduct through the movement of positively charged Na
and K ions. Action potential obey the all-or-nothing principle. This means that the size of the
action potential is always the same despite the strength of the stimulus.
Throughout the neuron, the outside will be more positively charged rather than the inside as
3 positive charged Na go out for every 1 positive charged K. The inside of the neuron is still
positive however it has also got negative charged particles. The more positively charged Na
goes out the more positively charged the neuron becomes on the outside. The difference
between the inside and the outside potentials are called the resting potential, and it is
approximately -70mV. This means that the electrical potential inside the axon is 70mV lower
than the outside when the axon is resting.
An impulse will travel along the axon when the neuron is stimulated. When an electrical
current is applied to the axon, there is a brief change in the potential from -70mV to +35mV.
This means that the inside of the axon becomes positively charged relative to the outside.
This change in potential is called the action potential and lasts about three milliseconds.
During the action potential the axon is depolarised. If the electrodes are connected to a
cathode ray oscilloscope, the action potential shows as a peak in the trace.
When the axon is stimulated, channels in the axon membrane open. This allows sodium ions
to diffuse into the axon. This creates a positive charge on the axon and causes the action
potential. Channels then open in the membrane to allow potassium ions to diffuse out of the
axon. Sodium channels now close. This prevents any further movement of sodium ions into
the axon. This re-establishes the resting potential and the axon membrane is said to be
repolarised.
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