Unit 5: Section 2- Exercise

A summary of the exercise topic from run for your life, Edexcel A2 biology

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Electrical Activity in the Heart 1

  • Regular heartbeat
  • 1. Impulse arrives at the sinoatrial node (SAN) in the wall of the right atrium. The SAN sends out waves of electrical activity to the atrial walls, causing the left and right atria to contract at the same time
  • 2. The waves are transferred to the atrioventricular node (AVN), as a band of non-conducting collagen prevents impulses from being transferred from atria to ventricles. The AVN transmits the wave of electrical activity to the bundle of His (with a delay to make sure atria empty before ventricles contract)
  • The bundle of His is a group of fibres which conducts the impulse to the finer muscle fibres of the left and right ventricles, called the Purkyne fibres.
  • The Purkyne fibres carry the waves into the ventricles, causing them to contract simultaneously from the bottom up
  • An electrocardiograph is a machine which records the electrical activity of the heart. The heart muscle depolarises when it contracts, and repolarises when it relaxes
  • P wave- contraction (depolarisation) of atria
  • QRS complex- contraction (depolarisation) of ventricles
  • T wave- relaxation (repolarisation) of ventricles
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Electrical Activity in the Heart 2

  • Tachycardia- the heart beat is too fast, sign of heart failure. The heart can't pump blood efficiently, so heart rate increases to ensure enough blood is pumped around the body. Can increase risk of a heart attack.
  • Problem with the AVN- Atria are contracting but the ventricles are not. May mean a problem with the AVN, as impulses are not travelling from the atria through to the ventricles
  • Fibrillation- Irregular heart beat. Both the atria and ventricles have lost their rhythm and stopped contracting properly. Atrial fibrillation can lead to chest pains, fainting and increase risk of stroke. Ventricular fibrillation can quickly cause death. It can be caused by a heart attack.
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Variations in Heart Rate and Breathing Rate 1

  • During exercise, breathing rate and depth is increased to obtain more O2 and get rid of CO2, and heart rate is increased to deliver O2 to the muscles faster and remove extra CO2 produced by increased rate of respiration in muscle cells
  • The medulla has two areas called the inspiratory and expiratory centres, which control rate of breathing
  • 1. The inspiratory centre sends nerve impulses to the intercostal and diaphragm muscles to make them contract (also impulses to inhibit expiratory centre). Lung volume increases, pressure decreases.
  • 2. Air enters the lungs to pressure difference between lungs and air 
  • 3. As the lungs inflate, stretch receptors in the lungs are stimulated. Send impulses to the medulla to inhibit the insp. centre
  • 4. The exp. centre sends impulses to intercostal and diaphragm muscles to relax. Causes lungs to deflate, expelling air. Stretch receptors become inactive, insp. no longer inhibited.
  • During exercise, CO2 in blood increases, decreasing the pH of blood. Chemoreceptors (in medulla, aortic bodies and carotid bodies) detect a decrease in pH and send impulses to the medulla to increase rate and depth of breathing.
  • Ventilation rate- volume of air breathed in and out per unit time
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Variations in Heart Rate and Breathing Rate 2

  • Medulla also controls heart rate
  • A decrease in blood pH is detected by chemoreceptors, which send impulses to the medulla, which send impulses to the SAN to increase heart rate
  • Increased bp causes a decrease in heart rate
  • 1. Baroreceptors (pressure receptors) in the aorta wall and carotid sinuses detect rise in blood pressure
  • 2. Nerve impulses are sent to the cardiovascular centre, which send impulses the SAN to slow the heart rate
  • If pressure is too low, baroreceptors send impulses to the cardiovascular centre which sends impulses to the SAN to speed up heart rate
  • Cardiac output- the volume of blood pumped by a ventricle per minute
  • Cardiac output (cm^3/min) = heart rate (beats per minute) x stroke volume (cm^3)
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Investigating Ventilation

  • Tidal volume- volume of air in each breath
  • Breathing rate- number of breaths taken per minute
  • Ventilation rate- volume of air breathed in and out per minute. Ventilation rate = tidal volume x breathing rate
  • A spirometer gives a reading of tidal volume and breathing rate. Has an O2 filled chamber with a moveable lid, and a tube containing soda lime to absorb CO2. A person breathes through a tube into the O2 chamber, moving the lid up (breathing out) and down (breathing in)
  • These movements are recorded by a pen attached to the lid, creating a spirometer trace
  • The spirometer can be used to measure the change in breathing rate/ tidal volume before, during and after exercise. The person is connected to a spirometer using a mask, and recordings are taken.
  • During exercise, the body needs to take in more O2 and remove more CO2, so breathing rate and tidal volume increase. During recovery, the breathing rate/tidal volume is still high (to remove built up lactate), but eventually returns to rest level
  • Training decreases breathing rate at all stages as the lung muscles are strengthened, so more air taken in with each breath, so less frequent breaths needed
  • Training increases tidal vol at all stages as more air taken in with each breath
  • During recovery, breathing rate/tidal volume decreased faster due to training as the muscles are strengthened so lungs can return to normal O2 and CO2 levels quicker
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Homeostasis 1

  • Homeostasis involves control systems which maintain a constant internal environment (dynamic equilibrium). Vital for cells to function normally (eg. enzymes are sensitive)
  • Homeostatic systems have receptors which detect whether a level is too high or too low, and communicate this info via the hormonal or nervous systems to effectors. The effectors respond to counteract the change and bring the level back to normal
  • This is a negative feedback mechanism- restores the level to normal. Only works within certain limits
  • To reduce body temperature- sweating (evaporation takes heat from the body), hairs lying flat (less air trapped so less insulation) and vasodilation (more blood flows through capillaries at the surface, more heat loss by radiation)
  • To increase body temperature- shivering (more heat produced through increased respiration), hormones released (adrenaline and thyroxine increase metabolism), much less sweat (reduce heat loss), hairs stand up (trap more air, so more insulation) and vasoconstriction (less heat loss by radiation)
  • The hypothalamus receives temp info from thermorecepectors  via sensory neurones, and sends impulses along motor neurones to effectors
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Homeostasis 2

  • Transcription factors control transcription of genes. They bind to DNA near start of genes to change the rate of transcription. Activators increase rate and repressors decrease rate
  • Hormones can bind to transcription factors to change body temperature
  • 1. At cold temperatures, thyroxine binds to the thyroid hormone receptor and acts as an activator
  • 2. Transcription rate increases, producing more protein to increase the metabolic rate and increase body temperature
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Exercise and Health 1

  • Risks of too little exercise
  • Obesity- correlation between sitting down for a long time each week and being obese
  • Coronary Heart Disease (CHD)- weak correlation between too little physical exercise and an increased risk of CHD in mean aged 40-59 (only involves men of this age)
  • Type 2 Diabetes- correlation between too little physical activity and an increased risk of Type 2 diabetes in men aged 40-59 (doesn't take into account diet)
  • Risks of too much exercise
  • Wear and tear on joints- correlation between being an elite male athlete of any kind and having osteoarthritis of the hip, knee or ankle (may not be a causal link)
  • Immune system- correlation between doing a lot of exercise and getting more cases of respiratory illnesses. Also correlation between doing some exercise and getting fewer cases of respiratory illnesses
  • Keyhole surgery can repair joints damaged by doing sport. Surgeons make a small incision and insert a small video camera and specialised medical instruments. Operations are less invasive so patients lose less blood, experience less scarring, are in less pain, recover more quickly, are able to return to normal activities easily and have shorter stays in hospital.
  • Common sports injury is damage to cruciate ligaments (in middle of knee), and can be removed and replaced with a graft through a small incision in the knee
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Exercise and Health 2

  • Prostheses can replace whole limbs or parts of limbs. Allow people with disabilities to participate in sport or people with injuries to participate again
  • Damaged knee joints can be replaced by prosthetic joints. A metal device is inserted into the knee to replace damaged cartilage and bone. The knee joint and ends of the leg bone are replaced to provide a smooth joint. Allows people to move around and participate in low impact sports
  • Anabolic steroids- increase strength, speed and stamina by increasing muscle size and allowing athletes to train harder. Also increase aggression
  • Stimulants- speed up reactions, reduce fatigue and increase aggression
  • Narcotic analgesics- reduce pain so injuries don't affect performance
  • Some performance-enhancing drugs are illegal, competitions become unfair if people take drugs, there are serious health risks and athletes may not be fully informed of the risk
  • But athletes have the right to make their own decisions, drug-free sport isn't really fair anyway and athletes wanting to compete on a higher level may only be able to by using performance-enhancing drugs
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