B5 - Homeostasis & Response

B5 - Homeostasis & Response

1. Homeostasis

   • Regulation of conditions inside the body to maintain stable internal environment
     • Automatic control systems, both nervous and hormonal
       • ACS made up of receptors, coordination centre and effectors
     • Maintain body temp., blood glucose and water content
   • Negative feedback
     • Counteracts changes, bringing back to normal
     • Receptor detects a stimulus, level too high
       • CC receives and processes info, organises response
         • Effector produces response, counteracts change and decreases level
           • Opposite if level too low

2. Nervous system

   • Detects and reacts to stimuli
   • CNS made up of brain and spinal cord, in mammals connected to body by sensory neurones and motor neurones
     • Sensory neurones carry info as electrical impulses from receptors to CNS
     • Motor neurones carry electrical impulses from CNS to effectors
       • RELAY NEURONES IN CNS
     • Effectors are muscles and glands, which respond to nervous impulses
   • Receptors are cells that detect stimuli
     • Can form part of larger, complex organs
   • Effectors respond to nervous impulses and bring about change
     • Muscles contract whereas glands secrete hormones

3. Synapses and reflexes

   • Synapses are a connection between two neurones, chemicals diffuse across the gap
   • Reflexes help prevent injury
     • Don't involve conscious part of brain
   • Passage of information in reflex called reflex arc
     • Neurones go through spinal cord or unconscious part of brain

4. Endocrine System

   • Hormones are chemical molecules released into the blood
   • Hormones tend to have long-lasting effects
   • Glands
     • Pituitary - many hormones which regulate body conditions, called 'master gland' because hormones act on other glands
     • Thyroid - produces thyroxine, regulating rate of metabolism, heart and temp.
     • Adrenal - produces adrenaline, 'fight or flight' response
     • Ovaries produce oestrogen for menstrual cycle, testes produce testosterone which controls puberty and sperm production
     • Pancreas - produces insulin which regulates blood glucose levels

5. Controlling blood glucose

   • Insulin and glucagon control blood sugar
     • Insulin lowers blood glucose
       • Blood has too much glucose - insulin secreted from pancreas - glucose moves from blood into liver and muscle cells - insulin makes liver turn glucose into glycogen
     • Glucagon raises blood glucose
       • Blood has too little glucose - glucagon secreted by pancreas - glucagon makes liver turn glycogen into glucose - glucose released into blood by liver
   • Diabetes
     • Type 1
       • Person produces little to no insulin, have to inject selves and think about carb intake and exercise
     • Type 2
       • Person resistant to own insulin, obesity is risk factor, have to control by eating carb-controlled diet and doing regular exercise

6. Menstrual cycle

   • Stage 1, uterus lining breaks down for 4 days, menstruation starts
     • Stage 2, lining builds up day 4 to day 14, ready to receive fertilised egg
       • Stage 3, egg released on day 14, ovulation
         • Stage 4, wall maintained from day 14-28, if no fertilised egg then cycle starts again
   • Controlled by 4 hormones
     • FSH - produced in pituitary, causes egg to mature, stimulates ovaries to produce oestrogen
     • Oestrogen - produced in ovaries, causes lining to grow, stimulates LH release, inhibits FSH
     • LH, produced by pituitary, stimulates egg release
     • Progesterone, produced in ovaries after ovulation, maintains uterus lining, inhibits LH and FSH

7. Controlling fertility

   • Hormones
     • The pill contains oestrogen and progesterone
       • Too much oestrogen stops egg development and production
       • Progesterone stimulates production of thick mucus which blocks sperm
         • 99% effective but can cause side effects, no STI protection
     • Contraceptive patch or implant, releases hormones
     • IUD kills sperm or prevents implantation of egg
   • Barriers
     • Non-hormonal methods designed to stop sperm meeting egg
     • Condoms protect against STIs
     • Diaphragm fits over cervix to form barrier, used with spermicide
   • Other methods
     • Sterilisation, cutting or tying fallopian tubes or sperm duct
     • 'Natural' methods, avoiding most fertile days
     • Abstinence, avoiding all intercourse

8. More controlling fertility

   • Increasing fertility
     • Some women have low FSH levels so don't release eggs
     • FSH and LH given in fertility drug
     • Pros - women can get pregnant Cons - doesn't always work so can be expensive, too many eggs could be stimulated so unexpected multiple births
   • IVF helps couples have children
     • Collecting eggs and fertilising them in lab
       • Can involve Intra-Cytoplasmic Sperm Injection (ICSI), which is directly injecting sperm into egg
       • Grown into embryos in lab incubator
         • When embryos are balls of cells, one or two transferred to uterus to improve chance of pregnancy
           • FSH and LH given before egg collection to stimulate several eggs to mature
   • Pros - gives infertile couple a child
   • Cons - multiple births can happen which is risky for mother and babies, low success rate around 26% so can be stressful and upsetting, also physically stressful and can have strong reaction to hormones
   • Some against IVF because unused embryos are destroyed, also could lead to designer babies

9. Adrenaline and Thyroxine

   • Adrenaline triggers mechanisms that increase oxygen and glucose supply to brain and muscle cells
   • Thyroxine regulates metabolism
     • Regulates basal metabolic rate which is speed at which chemical reactions occur while the body is at rest
     • Thyroxine stimulates protein synthesis for growth and development
     • Released in response to thyroid stimulating hormone (TSH)
       • Negative feedback system keep thyroxine levels right