B5 - Homeostasis & Response

  • Created by: Benny52
  • Created on: 23-02-19 12:45


  • Conditions in body need to be kept steady - cells need right conditions to function properly, & enzymes need right conditions. Homeostasis = the regulation of condtions inside body to maintain stable internal environment. Lots of automatic control systems in body to regulate internal environment - include nervous & hormonal communication systems. All automatic control systems made up of three main components - receptors, coordination centres & effectors.
  • Automatic control systems keep internal environment stable using negative feedback. When level of something gets too high or low body uses it to bring it back to normal:
    • Receptor detects stimulus - level too high/low.
    • Coordination centre receives & processes information then organises response.
    • Effector produces response, counteracting change & restoring optimum level - level decreases/increases.
  • Process is automatic - don't think about it.
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The Nervous System

  • Nervous system detects & reacts to stimuli. Allows humans to react to surroundings & coordinate behaviour. Made up of:
    • CNS - vertebrates - brain & spinal chord. Mammals - connected to body by sensory & motor neurones.
    • Sensory neurones - carry information as electrical impuleses from receptors to CNS.
    • Motor Neurones - carry electrical impulses from CNS to effectors.
    • Effectors - muscles & glands responding to nervous impulse.
  • Receptors - cells that detect stimuli. Can form part of larger, complex organs - retina of eye is covered in light receptor cells, etc.
  • Effectors respond to nervous impulses & bring about a change. Muscles contract & glands secrete hormones.
  • CNS - coordination centre - coordinates response.
  • Stimulus detected by receptors. Sensory neurones carry info from receptors to CNS, which decides what to do. Sends info to effectors along motor neurones, which produce response.
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Synapses & Reflexes

  • Connection between 2 neurones - synapse. Nerve signal transferred by chemicals that diffuse across gap. Chemicals then set off new electrical signal in next neurone.
  • Reflexes = rapid, automatic responses to stimuli that don't involve conscious part of brain - prevents injury. Passage of info in a reflex = reflex arc.
  • Neurones in reflex arc go through spinal chord or unconscious part of brain:
    • Stimulus detected by receptors & impulses sent along sensory neurone to relay neurone in CNS.
    • When impulse reaches synapse between sensory neurone & relay neurone, they trigger chemicals to be released - cause impulses to be sent along relay neurone.
    • When impulses reach synapse between relay neurone & motor neurone, chemicals released & causes impulses to be sent along motor neurone.
    • Impulse then reaches effector, causing response.
  • Don't have to think about response - quicker.
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The Endocrine System

  • Hormones = chemical molecules released directly into blood. Only affect particular cells in target organisms. Control things in organs & cells needing constant adjustment. Hormones produced in endocrine glands, making up endocrine system. Hormones tend to have long-lasting effects. Examples:
    • Pituitary Gland: Produces many hormones that regulate body conditions. Called 'master gland' - hormones released act on other glands, directing them to release hormones.
    • Ovaries: Produces oestrogen.
    • Testes: Produces tetosterone - controls puberty & sperm production - males.
    • Thyroid: Produces thyroxine - involved in regulating metabolism rate, heart rate, temp, etc.
    • Adrenal Gland: Produces adrenaline.
    • Pancreas: Produces insulin.
  • Nerves: Very fast action, act for very short time & act on precise area.
  • Hormones: Slower action, act for long time & act in more general way.
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Controlling Blood Glucose

  • Eating food containing carbohydrate puts glucose in blood. Excess stored as glycogen in liver & muscles. Level needs to be kept steady. Changes monitored & controlled by pancreas, using insulin & glucagon, in negative feedback cycle.
  • Blood glucose level too high - insulin secreted by pancreas. Glucose moves from blood into liver & muscle cells & insulin makes liver turn glucose into glycogen.
  • Blood glucose level too low - glucagon secreted by pancreas. Glucagon makes liver turn glycogen into glucose. Glucose released into blood by liver.
  • Diabetes = condition that affects ability to control blood sugar level. Two types:
    • Type 1 - pancreas produces little or no insulin. Blood glucose level can rise high enough to kill them. Insulin therapy needed - involves several insulin injections throughout the day - ensures glucose is removed from blood quickly once food is digested - effective. Amount injected depends on diet & how active person is. Also need to limit intake of food rich in simple carbohydrates, and take regular exercise.
    • Type 2 - resistant to own insulin. Can cause blood sugar level to rise to dangerous level. Being overweight increases chance of developing it. Controlled by eating carbohydrate controlled diet & getting regular exercise.
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Puberty & the Menstrual Cycle

  • Puberty - body starts releasing sex hormones - trigger secondary sexual characteristics, & causes eggs to mature in women.
  • Men - main reproductive hormone - tetosterone. Females - oestrogen.
  • Menstrual Cycle - 4 stages:
    • 1: Day 1 - menstruation starts. Uterus lining breaks down - 4 days. Hormone released - FSH - produced in pituitary gland. Causes egg to mature in one ovary in a follicle. Stimulates ovaries to produce oestrogen.
    • 2: Uterus lining builds up again - days 4-14. Thick spongy layer full of blood vessels, ready to receive fertilised egg. Hormone - Oestrogen - causes uterus lining to grow. Stimulates release of LH & inhibits release of FSH.
    • 3. Egg develops & released from ovary - day 14 - ovulation. Hormone - LH - produced by pituitary gland. Stimulates release of egg.
    • 4. Wall maintained from day 14-28. If no fertilised egg lands on uterus wall by day 28, spongy lining starts to break down & cycle restarts. Hormone - Progesterone - produced in ovaries by remains of follicle after ovulation. Maintains uterus lining for 14 days. When levels fall, lining breaks down. Inhibits release of LH & FSH.
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Controlling Fertility

  • Oestrogen - method of contraception - if taken daily to keep levels permanently high - inhibits production of FSH - egg development & production stop.
  • Progesterone - stimulates production of thick mucus - prevents sperm from reaching egg.
  • Pill - contains oestrogen & progesterone. +99% effective at preventing pregnancy but side effects - headaches. Also doesn't protect against STD's. Also progesterone-only pill - fewer side effects & just as effective.
  • Contraceptive patch - oestrogen & progesterone - small patch stuck to skin. Lasts 1 week.
  • Contraceptive implant - under skin of arm - continuously releases progesterone - stops ovaries releasing eggs, makes it hard for sperm to swim to egg & stops fertilised egg implanting in uterus. Lasts 3 yrs.
  • Contraceptive injection - progesterone - doses - 2-3 months.
  • IUD - T-shaped device inserted into uterus to kill sperm & prevent implantation of fertilised egg. Plastic ones release progesterone & copper ones prevent sperm surviving in uterus.
  • Non-hormonal - stop sperm getting to egg - condoms. Only contraception that perevent against STD's. Diaphragm - fits over cervix to form barrier. Used with spermicide - disables/kills sperm. Spermicide alone - contraception, but not as effective.
  • Sterilisation - cutting/tying fallopian tubes in females or sperm duct in males. Permanent. However, small chance tubes can rejoin. 'Natural' methods - finding out when in menstrual cycle woman is most fertile and avoid sex then. Not very effective. Abstinence - no sex.
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More on Controlling Fertility

  • Some women - FSH levels too low to cause eggs to mature - no eggs released. FSH & LH can be taken in fertility drug to stimulate ovulation. Pros - women can get pregnant. Cons - doesn't always work & repeating it multiple times is expensive. Too many eggs can be stimulated - unexpected multiple pregnancies.
  • IVF - involves collecting eggs from woman's overies & fertilising them in lab using man's sperm. Can involve ICSI - sperm injected directly into egg - if man has low sperm count. Fertilised egg grown into embryos in incubator. Once embryos = tiny balls of cells, 1 or 2 transferred to woman's uterus to increase pregnancy chance. FSH & LH given before egg collection to stimulate several eggs to mature. Pros - Can give infertile couple child. Cons - multible births if more than one embryo grows - risk of misscarriage, stillbirth, etc. Success rate low - 26% in UK - stressful & upsetting especially if multiple failures. Can have strong reaction to hormones - abdominal pain, vomiting, etc.
  • Advances in microscopic techniques - increase success rate. Specialised micro-tools - used on eggs & sperm under microscope. Also used to remove single cells from embryo - genetic testing. Development of time-lapse imaging - growth of embryos continuously monitored - helps identify ones more likely to lead to successful pregnancy.
  • IVF - unused embryos destroyed - people think it's unethical - each embryo potential human life. Genetic testing before implantation - people think it can lead to selection of preferred characteristics.
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Adrenaline & Thyroxine

  • Adrenaline - released in response to stressful or scary situations - brain detects fear or stress & sends nervous impulses to adrenal glands - responds by secreting adrenaline. It gets body ready for 'fight or flight' - triggers mechanisms that increase supply of oxygen & glucose to cells in brain & muscles.
  • Body controls levels of hormones in blood using negative feedback systems - thyroxine - regulates basal metobolic rate - speed at which chemical reactions in body occur while body's at rest. Also important for other processes in body - stimulating protein synthesis for growth & development, etc. Thyroxine released in response to TSH - released from pituitary gland. Negative feedback system keeps amount in blood at right level. High - secretion of TSH inhibited.
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