Topic 5 The Human Body

• Substances


  Gases and nutrient molecules being transported to organs/cells for metabolic reactions, as well as waste materials to be excreted
• Movement of molecules


  Controlled by partially permeable membranes, regulated by diffusion, osmosis and active transport
• Cardiac system


  • Made up of the heart and a network of blood vessels, the main transport system of the body carrying gases, nutrient molecules, hormones and other substances
• How the heart functions

  1. Deoxygenated blood enters right atrium

  2. Right atrium contracts, blood moves to right ventricle

  3. Ventricle contracts, blood exits to lungs via pulmonary artery

  4. Blood becomes oxygenated in lungs, returns to left atrium

  5. Left atrium contracts, blood moves to left ventricle

  6. Left ventricle contracts, oxygenated blood exits to aorta and around body
• Atrioventricular valves


  Bicuspid and tricuspid valves that prevent backflow between ventricles and atria
• Types of blood vessel

  • Capillaries
  • Arteries
  • Veins
• Arteries


  • Thick muscle and elastic layers to maintain and control high blood pressure, thick wall to prevent bursting
• Veins


  • Thin muscle and elastic layer, thin wall as blood is at low pressure, contain valves to prevent backflow
• Capillaries


  • Large surface area, thin diameter and lumen to decrease diffusion distance, slower blood flow to allow time for exchange
• Transport of oxygen


  1. Oxygen diffuses into capillaries at alveoli, binds to haemoglobin, transported to cells for respiration

  2. Carbon dioxide produced as waste, diffuses out of cells, carried back to lungs for excretion
• Transport of nutrients


  1. Nutrient molecules diffuse into capillaries in small intestine at villi

  2. Nutrients transported in blood to cells for metabolic reactions

  3. Substances that don't pass membrane are excreted
• Transport of waste


  1. Waste products diffuse from cells into blood

  2. Urea transported from liver to kidney, filtered and excreted as urine
• Adaptations of exchange surfaces

  • Short diffusion distance
  • Large surface area
  • Large concentration gradient
  • Moist
• Nervous system


  Controls movement and autonomic reflexes by sending electrical signals (nerve impulses) along neurones
• Types of neurone


  • Sensory
  • Relay (connector)
  • Motor (effector)
• Synapse


  Gap between presynaptic and postsynaptic neurones where neurotransmitter is released to allow impulse to continue
• Nerve cell adaptations


  • Myelin sheath for electrical insulation and faster impulses
  • Long axon to carry impulses over long distances
  • Neurotransmitter substances
  • Dendrites to pick up impulses
• Reflex arc


  1. Stimulus detected by receptor

  2. Impulse sent to spinal cord

  3. Relay neurone passes impulse to motor neurone

  4. Impulse travels to effector (e.g. muscle) which reacts
• Brain structure


  Cerebral cortex - processes signals, thought, problem solving

  Brain stem - connects brain to spinal cord, regulates involuntary actions

  Cerebellum - coordinates movement
• Research into brain structure and function could help cure diseases like Alzheimer's and Parkinson's
• Studying the brain is extremely difficult due to the complexity, need for live patients, ethical issues, and difficulty matching problems to specific damage
• Non-invasive methods like fMRI and PET scans can map some brain functions but have limitations
• Endocrine system


  Produces and secretes hormones to control growth, metabolism, homeostasis and reactions to stimuli
• Hormones


  Molecules that travel in blood and bind to receptors on target organs to stimulate a response
• Negative feedback


  Corrective mechanisms that work to move a variable back to an optimum range
• Regulation of thyroxine


  Thyroxine secreted by thyroid, travels to target organs

  Negative feedback loop - if thyroxine levels too high, release is inhibited
• Hormones


  Molecules that travel in the blood and are used for signalling in the body
• Hormones


  • Produced in glands such as the pituitary and adrenal glands
  • Excreted into the blood
  • Travel to target organs
  • Bind to receptors on cell surfaces called effectors
  • Stimulate a response from within the cell
• Negative feedback


  A response is only carried out if a certain variable moves outside of an optimum range; corrective mechanisms then work to correct the change to move the variable back to the optimum
• Negative feedback


  • Thyroxine
  • Adrenaline
• Thyroxine


  • A hormone secreted by the thyroid
  • Travels in the blood to target organs
  • Used as a catalyst to regulate a variety of functions, including metabolic rate, growth and development, and digestion
  • Release is controlled by a negative feedback loop
• Adrenaline


  • Released from the adrenal glands
  • Secreted during the 'fight or flight' response, and when stressed or excited
  • Leads to an increase in pulse rate and widened pupils
  • Causes glycogen to be converted to glucose in cells to be used in respiration for energy
  • Heart rate increases to provide more oxygen
  • Release is controlled by a negative feedback loop
• Homeostasis is the maintenance of a constant internal environment in organisms, despite external changes
• Internal conditions must be maintained between set limits and if these limits are exceeded, negative feedback mechanisms work to correct the change and restore the internal environment to the optimum
• Regulating temperature


  • Maintaining a constant temperature of 37°C in humans as this is the optimum temperature for enzyme reactions
  • If temperature is too low, rate of reaction would decrease
  • If temperature is too high, enzymes may denature and prevent reactions from occurring
  • Regulated by the hypothalamus in the brain, which receives information about internal and external temperature from thermoreceptors
• Reactions to a low internal temperature

  • Shivering - muscles contract to produce heat
  • Vasoconstriction - blood vessels constrict to reduce surface area and move away from the surface of the skin to reduce heat loss
  • Hair erection - hairs stand on end to trap warm air, reducing heat loss from the skin
• Reactions to a high internal temperature

  • Sweating- sweat evaporates from the skin, reducing the surface temperature
  • Vasodilation - blood vessels dilate, causing more heat loss to the environment
• Regulation of water balance in the blood

  • Controlled by the kidney
  • Kidneys filter water and urea from the blood into kidney tubules, where water is reabsorbed into the blood
  • Amount of water reabsorbed is controlled by the hormone ADH
  • Osmoreceptors in the hypothalamus detect changes in the amount of water in the blood and trigger the release of ADH
  • ADH controls the permeability of cells in the kidney to water, allowing more or less water to be reabsorbed
• It is important to maintain water concentration in the blood to prevent unwanted osmosis
• Hormones and the menstrual cycle

  • FSH triggers the development of an egg cell and stimulates oestrogen production
  • LH triggers ovulation and stimulates progesterone production
  • Progesterone maintains the thick uterus lining
  • Oestrogen helps repair and thicken the uterus lining, inhibits FSH, and triggers LH release which causes ovulation