B5 Homeostasis and response

• Homeostasis is the maintenance of a constant internal environment to keep optimum conditions for enzyme and cellular function
• Examples of conditions maintained by homeostasis in the body:

  • Blood glucose concentration
  • Body temperature
  • Water levels
• Two types of responses used in body control systems: nervous and chemical
• Three components that all control systems have:

  • Receptors
  • Coordination centres
  • Effectors
• Function of a receptor: detect changes in the environment (stimuli)
• Function of a coordination centre: obtain and process information from receptors
• Function of an effector: bring about responses to stimuli
• The function of the nervous system is to allow the body to react to its surroundings and coordinate an appropriate response
• A stimulus leads to a response being carried out by the body through the conversion of the stimulus into an electrical impulse by receptors, passing along sensory neurones to the central nervous system (CNS), which then coordinates an appropriate response and sends an electrical impulse along motor neurones to the effector
• The sequence of events describing how the nervous system works is: Stimulus → receptor → coordinator → effector → response
• A reflex action is an automatic and rapid response that does not involve any conscious input from the brain
• Reflex actions are important as they aid survival by preventing harm to the body
• The difference between a reflex pathway and a conscious pathway is that in a reflex pathway, the coordination center is a relay neurone found in the spinal cord or unconscious parts of the brain, while in a conscious pathway, the coordination center is in the conscious part of the brain
• The body's coordination system involving hormones is the endocrine system
• A hormone is a chemical messenger secreted by a gland, traveling in the blood to a target organ where it causes a response
• Glands are the type of organs that secrete hormones
• The pituitary gland is considered a 'master gland' because it secretes a wide range of hormones that may stimulate other endocrine glands
• The pituitary gland's role in the endocrine system includes:

  • Secretion of human growth hormone to control human growth
  • Stimulation of the thyroid gland
  • Stimulation of ovulation and production of estrogen in the ovaries
  • Stimulation of sperm production and testosterone in the testes
• The thyroid gland's role in the endocrine system is to secrete thyroxine, controlling metabolism, heart rate, and body temperature
• The pancreas in the endocrine system secretes insulin to control blood glucose levels
• The adrenal gland in the endocrine system secretes adrenaline, controlling the body's 'fight or flight' response
• The ovaries in the endocrine system secrete estrogen, coordinating the menstrual cycle and the development of female secondary sexual characteristics
• The testes in the endocrine system secrete testosterone, coordinating sperm production and the development of male secondary sexual characteristics
• The pancreas monitors and controls blood glucose concentration
• Blood glucose concentration is controlled using a negative feedback loop where a hormone is secreted by the pancreas to bring the concentration back to the correct level
• Treatment for Type 1 diabetes includes insulin injections, limiting carbohydrate intake, and potential pancreas or pancreatic cell transplants
• Type 2 diabetes is a disorder where the body's cells stop responding to insulin, leading to uncontrolled blood glucose concentration, often linked with increasing age and obesity
• What is the function of reproductive hormones during puberty?

  • Males: cause the development of secondary sexual characteristics
  • Females: cause the development of secondary sexual characteristics and the maturation of eggs
• What is the main male reproductive hormone?

  • Testosterone, produced by the testes, controls sperm production
• What is the main female reproductive hormone?

  • Oestrogen, produced by the ovaries, is involved in the menstrual cycle
• What is the menstrual cycle?

  • The menstrual cycle is the monthly cycle of physiological changes in females, involving the shedding of the uterus lining (menstruation) and ovulation
• Describe the events of the menstrual cycle

  • Uterus lining thickens and eggs begin to mature in the ovaries
  • An egg is released from one of the ovaries (ovulation)
  • If the egg is fertilised, pregnancy may occur; if not, both the egg and the uterus lining are shed during menstruation
• Name the four main hormones involved in the menstrual cycle

  • Oestrogen
  • Progesterone
  • Follicle stimulating hormone (FSH)
  • Luteinising hormone (LH)
• What is the role of FSH in the menstrual cycle?

  • FSH controls the maturation of eggs within the ovaries and triggers the production of oestrogen
• What is the role of LH in the menstrual cycle?

  • LH, produced as a result of oestrogen, triggers ovulation
• What is the role of progesterone in the menstrual cycle?

  • Progesterone sustains the uterus lining and inhibits FSH and LH
• What is contraception?

  • Contraception refers to any method of preventing pregnancy
• What are the two types of oral contraceptives?

  • Combined oral contraceptives
  • Progestogen-only pills
• Contraception refers to any method of preventing pregnancy
• Two types of oral contraceptives:

  • Combined contraceptive pill (contains oestrogen and progesterone)
  • Mini pill (contains only progesterone)