Monday, 16 July 2012

How The Cardiovascular, Respiratory, Neuromuscular And Energy Systems Respond To Steady State Exercise.

Cardiovascular System

During exercise your contracting muscles require a continual supply of nutrients and oxygen to support energy production. These requirements of nutrients and oxygen are more than usual so your heart has to beat faster and harder to meet the increased demands. It also beats harder and faster to remove excess carbon dioxide.

Before exercise your heart rate usually increases above its normally resting levels. This is known as the anticipatory heart rate. The sympathetic nervous system controls adrenaline and therefore increases the heart rate before exercise and during it too.  An example is a sprint. If a athlete is about to have a race the athletes heart rate is likely to increase because of the event that is about to take place.   

Exercise is detected by the medulla oblongata. The medulla is the central nervous system located in the brain. The medulla detects if the body is doing exercise and then the chemoreceptors detect carbon dioxide in the blood and sends a signal to the medulla which then sends of a signal to the sympathetic nervous system that controls adrenaline. The sympathetic nervous systems then release blood into the heart which makes it increase its flow in blood and increases in cardiac output/stroke volume.     

Stroke volume is the amount of blood pumped by one of the ventricles of the heart in one contraction. The stroke volume is not all of the blood contained in the left ventricle because the heart does not pump all the blood out.  Stroke volume and heart rate together determine the cardiac output. Stroke volume increase to its highest levels during sub maximal exercise and does not increase further during maximal exercise. Stroke volume achieves its maximum amounts at between 40 and 50 per cent of V02 max. The greatest increase in stroke volume occurs from rest to moderate exercise. During maximal exercise stroke volume does not increase because the left ventricle is already full.    

Cardiac output is the volume of blood being pumped out of the heart in one minute. It is equal to the heart rate multiplied by the stroke volume. When doing exercise stroke volume increases.  An athlete doing exercise blood flow can increase sharply. The increase in blood flow is by an increase in stroke volume which allows more oxygen get to the skeletal muscles. An increase in cardiac output has a huge benefit for trained athletes as they can move more blood to the working muscles.  
Blood pressure is the pressure of the blood against the walls of arteries which is the effect of two forces. The first one is created by the heart as it pumps blood into the arteries and the other is the force of the arteries as they resist the blood flow. During exercise both blood pressure and cardiac output increase but they act to restrict the blood pressure rise and bring it down to an efficient level. Blood pressure has two readings systole and diastole. Diastolic pressure is the lower value and is when the heart relaxes and fills with blood. Systolic pressure is when the heart beats and contracts sending blood into the blood vessels.  During steady state exercise dilation of the blood vessels in the active muscles increases the vascular area for blood flow.  The contractions and relaxation of the skeletal muscles forces blood through the vessels and returns it to the heart.   

Blood flow is controlled by pressure, this is achieved by pressure by the vasoconstriction and vasodilation. Vasodilation is the widening of blood vessels due to the relaxation of muscular vessel walls, particularly in the large and small arterioles and large veins. Vasodilation involves an increase in the diameter of the blood vessels resulting in an increased blood flow to the muscle area supplied by the vessel. Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries, small arterioles and veins. Vasoconstriction involves a decrease in the diameter of a blood vessel walls resulting in the reduction of blood flow.

Respiratory system

Respiration is a process of passive and active breathing. The active process of breathing is known as inspiration and is controlled by the external intercostals and diaphragm. Expiration is a passive process and is the product of the diaphragm and external intercostals relaxing.   

Respiratory control centre (RCC) controls breathing (pulmonary respiration) and is located in the medulla. The respiratory control centre has two main systems, inspiratory and expiratory centres.

The inspiration centre takes in air while the expiratory centre takes out air. The inspiratory system is a active process so it contracts. The inspiratory centre sends impulses to the respiratory muscles via the phrenic nerves to the diaphragm and the intercostals muscles. This signal makes the diaphragm and the external intercostals muscles contract. When the external intercostals muscles contract they cause the ribs and the sternum to move upwards and outwards. When the diaphragm contracts it causes the central part of the diaphragm to flatten. When they both contract they increase the area in chest cavity. This increased area in the chest cavity lowers the pressure in the chest which means oxygen rushers in. This means your breathing rate has increased and this increase is due to changes in temperature, chemicals or active muscles.   

The expiratory centre takes out air. This system is a passive process so it recoils. It’s passive at rest but active during exercise. It recoils from the inspiratory contraction, so it’s the product of the diaphragm and external intercostals relaxing. When the diaphragm is relaxed the central part of the diaphragm rises and regains to its dome shape, when the external intercostals muscles relaxed so that means the ribs and the sternum move downwards and inwards. When all this is happening there is also a recoil. The recoil is like and elastic band or stretching a spring. When the recoil happens the chest cavity shrinks which means there’s greater pressure which causes carbon dioxide to rush out. 

As exercise intensity increases, so does your breathing rate. This increase of you breathing is to meet the demands of muscles which need oxygen. For example a trained athlete at rest might use about 250ml of oxygen per minute but they may require 3,600ml per minute during exercise. The medulla measures intensity by temperature, carbon dioxide levels and blood acidity levels.

When intensity reaches a certain point, expiration becomes more active, this will require the internal intercostals to contract. This is to help with getting rid of the carbon dioxide. When exercise reaches a level where oxygen cannot be taken in, is called your V02 max. If oxygen can be used at a constant rate it is known as steady state exercise.   

An increase in breathing rate prior to exercise is known as anticipatory rise. The anticipatory rise at the beginning of exercise is due to the release of adrenaline. This is controlled by the RCC.  When exercise begins there is an immediate and much greater increase in breathing rate. After seven minutes of aerobic exercise breathing continues to rise but at a much slower rate.

Tidal volume is the air ventilated per breath. Exercise results in an increase in minute ventilation. Minute ventilation is the volume of gas ventilated in one minute.      

Neuromuscular Junction

Neuromuscular junctions connect the end of a motor neuron to a muscle fibre. Neuromuscular junctions are attached to muscle fibres, which transmits nerve inpulses.

For a muscle to contract the central nervous system which is the medulla sends a signal to the motor neuron. The signal is action potential and could be to flex your arm. The motor neuron is a nerve that allows communication between muscles and the brain. Motor neuron attach to fibres so the bigger the muscle the more motor neurons it has. For example the quadriceps will have more motor neuron than the finger. The medullas signal also known as action potential gets sent down through the axon and arrives at the motor neuron. When the neuron gets the signal calcium gets released. Calcium gets released to help encourage the release of acetylcholine in the neuron. Acetylcholine is a neurotransmitter which transmits a signal to the muscle fibre. To transmit a signal it has to cross the synaptic cleft into the muscle fibre. When the muscle fibre gets this signal your arm will flex.    

Energy system

The body takes in chemical energy in the form of food, this is stored in the body in the form of adenosine triphosphate (ATP) which is a high energy compound that is converted into kinetic energy and used to create movement. The movement of muscles require ATP, muscles require a continued supply of ATP.

Skeletal muscles are powered by one compound ATP. The body only stores ATP in small quantities in the cells. It’s only enough to power for a few seconds of all out exercise, so the body has to replace or resynthesise ATP on a continual basis. ATP consists of a base which is called adenine and three phosphates. It is formed by a reaction between an adenosine diphospate (ADP) molecule and a phosphate. When a molecule of ATP is combined with water, the last phosphates groups splits off and energy is released.     

Creatine phosphate or Phosphocreatine or PC system. The PC system can operate with or without oxygen. During the first five seconds of exercise the PC system s relied on almost exclusively. The PC system can sustain exercise for 3 to 15 seconds at a high intensity. If the activity continues then the body must rely on another energy system. An example of a sport that users the PC system are 100m sprinters, they have to sprint intensely for 10 – 15 seconds.

Glycolysis is the breakdown of glucose. The end product of glycolysis is pyruvic acid. This can be used in the kerb cycle or converted into lactic acid. Fast glycolysis is another term used if the final product is lactic acid. Fast glycolysis can produce energy at a greater rate but the end product is lactic acid so it leads muscles to fatigue. This system last for 1-3 minutes. An example of a sport that users the lactic system is 400m runners.      

The aerobic energy system is involved with exercise at a low intensity and gets more important the longer the sport goes on. Only dehydration, lack of fuel and overheating will end exercise using this system. Aerobic systems fuelling varies according to its intensity and duration. In prolonged exercise free fatty fuel acids are used because glycogen stores are limited. For high intensity exercise the system prefers glycogen as fuel.

The kerb cycle is a series of aerobic chemical reactions occurring in the matrix in the mitochondria. The main purpose of the krebs cycle is to provide a continuous supply of electrons to feed the electron transport chain. The electron transport chain is a series of biomechanical reactions during which free energy contained within hydrogen which is derived from the kerb cycle is released so that it can be used to synthesise ATP.   

One of the three energy systems is dominant in contributing the energy required for the resynthesis of adenosine triphosphate (ATP). The contribution of each energy system is dependent on the intensity and duration of the exercise. 

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