Endocrine Control System and Homoestasis

• Gametes


  • Sperm: Tail for swimming
  • Mitochondria to release energy
  • Nucleus to carry genes from Dad
  • Ovum: Cytoplasm to supply nutrients for growth
  • Nucleus to carry genes from Mum
• Fertilisation


  The fusing of the male and female nuclei
• Zygote


  Name for the fertilised egg
• Implantation


  The embedding of the embryo into the uterus lining (endometrium)
• Embryo


  Name of the baby when developing organs (first 10 weeks)
• Foetus


  Name for the baby that is complete but just growing (10 to 39 weeks)
• Placenta


  Structure made by the embryo which acts as the exchange surface between embryo/foetus and the mother
• The Menstrual Cycle


  Preparing the uterus for implantation
• The menstrual cycle is under hormonal control, rather than nervous control
• The 28 day cycle


  1. Every 28 days, the uterus prepares a new lining ready for the implantation of an embryo

  2. During this time one egg is released from an ovary

  3. If that egg is fertilised, the resulting embryo will implant in the lining and gain all the oxygen and nutrients it needs
• If fertilisation doesn't happen

  1. If the egg is not fertilised, it will die before it ever reaches the uterus

  2. The dead egg will not implant and will eventually pass out of the body through the vagina

  3. The uterus lining is also lost through the vagina if implantation does not occur

  4. This is called menstruation (a period)
• Implantation has not happened. Uterus lining is shed. A small amount of blood loss occurs (a period)

  1. Egg develops and uterus lining thickens

  2. Ovulation and possible fertilisation

  3. Uterus prepares for implantation of an embryo. The uterus lining continues to thicken
• Follicle stimulating hormone (FSH)


  • Stimulate follicle development (in ovary so ovum/egg starts to mature)
  • Stimulate ovary to produce oestrogen
• Oestrogen


  • Inhibits FSH (negative feedback). So only one egg matures in the cycle
  • Stimulates thickening of endometrium
  • At high levels stimulates LH production (positive feedback)
• Luteinising hormone (LH)


  • Stimulates ovulation, - release of ovum from follicle
  • Stimulates development of corpus luteum from follicle
• Progesterone


  • Prepares endometrium for implantation of embryo
  • Inhibits FSH & LH (negative feedback)
• It is important to keep maternal and foetal blood separate
• Successful implantation


  1. The embryo continues to grow after it has implanted in the uterus lining

  2. It forms a sac around itself called the amnion

  3. Amniotic fluid in the sac acts like a shock absorber and protects the embryo

  4. The embryo also forms a placenta – a sort of life support system

  5. The placenta allows it to transfer substances between itself and its mother
• Placenta


  • The embryo forms a plate-like structure called the placenta
  • The umbilical cord joins the fetus to the placenta
  • In the placenta food and oxygen diffuse from the mothers blood into the blood of the fetus
  • Carbon dioxide and waste products diffuse from the blood of the fetus to the mothers blood
• How does the embryo get food and oxygen and how does it get rid of waste?

  • The mother's blood does not enter the placenta but flows very close the embryo's blood
  • This allows substances to move (diffusion) between the different blood supplies without letting the blood mix together - WHY? - antigens from baby will cause immune response by mother
• Transfer between mother and embryo


  1. Oxygen and nutrients (food) diffuse from mother to embryo

  2. Carbon dioxide and other waste chemicals diffuse from embryo to mother

  3. Useful substances like antibodies also diffuse from mother to embryo

  4. However, harmful substances like nicotine can also diffuse into the embryo
• Stages of labour


  1. Dilation of cervix - Caused by prostaglandins and oxytocin

  2. Loss of mucus 'plug' in cervix

  3. Waters break – amniotic fluid escapes

  4. Contraction of uterus – expulsion of baby

  5. Expulsion of placenta (afterbirth)
• Hormones in Lactation


  • Placenta: Oestrogen, Progesterone
  • Pituitary: Anterior, posterior, Prolactin
  • Prostaglandins, oxytocin
  • Uterine contractions
  • Mammary glands: milk
  • Levels drop release prolactin hormone- maintains milk production
  • Aids milk let down reflex when baby latches on
• Colostrum


  • Colostrum is the first milk produced by the mother
  • It contains antibodies to help protect the baby before the baby can develop its own immune system
  • Also contains milk rich in polypeptides but less fat so that the baby can absorb the nutrients without much volume or digestion
• Thermoregulation


  Maintenance of constant body temperature as inputs from skin and blood using the hypothalamus as a control centre with responses in the skin
• Body temperature regulation


  • It is vital that mammalian body temperature is held at a constant, optimum value (37°C in humans)
  • Higher temperatures denature enzymes, lower temperatures slow body reactions down
• Parts of the skin involved in temperature control


  • Vasoconstriction and vasodilation of blood vessels
  • Erector pili muscles
  • Sweat glands
• Body temperature regulation


  1. Vasodilation and constriction of smooth muscle in arterioles

  2. Increase sweat from sweat glands

  3. Skin hairs stand up from erector pili muscles

  4. Shivering in skeletal muscles

  5. Increase metabolic rate from adrenal and thyroid glands
• Thermoreceptors


  • In hypothalamus detect core blood temperature
  • In skin detect skin temperature and send impulses to the hypothalamus
• When blood moves close to the skin surface

  It will lose more heat to the cooler outside
• Sweat evaporates from the skin surface


  A lot of body heat is required to convert liquid sweat into water vapour (LHV)
• Surface arterioles widen (dilate)


  Divert blood towards the skin surface in warm conditions
• When the hairs are erect


  They trap air, which is a good heat insulator
• When hairs are flat

  There is less air and less insulation
• Hair movement is not an effective temperature control mechanism in humans
• Control of body temperature


  Temperature set within CNS (hypothalamus) which can slightly modify the set point of 37°C by about 1°C - sleeping (lower) vs daytime active (higher)
• Control of body temperature


  1. Sensed (receptors) in the skin or hypothalamus

  2. Control centre in the hypothalamus

  3. Commands sent by nervous system (not hormones)

  4. Effectors in the skin (arterioles, hair erector muscles, sweat glands), skeletal muscles (heat production - shivering), liver & other metabolically active organs (heat production)
• Control of body temperature is controlled by negative feedback
• Kidney


  Organ that removes waste from the body, regulates ion content and water potential of the blood
• Functions of the kidney


  • Remove waste from the body
  • Regulate ion content of the blood
  • Regulate the water potential of the blood