Coordinated responses

Fight or flight response

• a combination of neuronal and hormonal responses

• controlled by the hypothalamus

• causes the release of stress hormones

  • corticotropin releasing factor and ACTH

• activates the sympathetic nervous system

  • activates smooth muscle and glands

  • adrenal medulla releases adrenaline and noradrenaline

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Adrenaline

• released from adrenal medulla

• triggers glycogenolysis in liver

  • glycogen converted to glucose

  • more glucose for respiration

  • more ATP produced

  • more energy for muscle contraction

• hydrophilic protein hormone

• adrenaline affects SAN

  • causes increase in heart rate

Action of adrenaline - second messenger model

• adrenaline binds to receptor on surface of liver cells

• activates the enzyme adenylyl cyclase

• adenylyl cyclase converts ATP into cAMP

• cAMP levels rise and cause activation of protein kinases

• protein kinases phosphorylate and activate other enzymes

• these enzymes convert glycogen into glucose

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Cascade effect

• small numbers of hormone molecules cause a large response

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Controlling heart rate

• - controlled by the autonomic nervous system

  • involuntary

• two centres within the medulla are linked to the SAN

  • sympathetic nerve - increases HR

  • parasympathetic nerve - decreases HR

• receptors in blood vessels collect information and send this to the medulla

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Types of receptor

• chemoreceptors

  • detect changes in blood pH

  • found in aorta, carotid artery and medulla

• baroreceptors

  • detect changes in pressure

  • found in aorta and carotid artery

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Increasing and decreasing heart rate mechanism (negative feedback)

• Increasing heart rate

  • exercise causes increase in CO2

  • pH falls

  • chemoreceptors in medulla, carotid body and aortic bodies detect fall in pH

  • nerve impulses are sent to the cardiovascular centre in the medulla

  • more impulse are sent from the cardiovascular centre to the SAN along the sympathetic nerve

  • SAN sends out more frequent impulses

  • heart rate increases

• Decreasing heart rate

  • carbon dioxide levels fall as heart rate increases

  • rise in pH detected by chemoreceptors

  • nerve impulses sent to cardiovascular centre in medulla

  • more impulses are sent to SAN along parasympathetic nerve

  • heart rate decreases