The Endocrine System

• The endocrine system consists of glands which release hormones directly into the bloodstream.
• Hormones travel in the blood, leading to a response in targeted organs.
• Compared to the nervous system, the endocrine system is slower, but its effects last longer.
• The nervous system delivers fast electrical impulses with fleeting effects.
• The pituitary gland, located in the brain, is the "master gland".
• The pituitary gland produces hormones that regulate other endocrine glands.

Key Endocrine Glands and Their Functions

• The pituitary gland regulates other glands including growth and water balance.
• The pancreas regulates blood glucose with insulin (lowering) and glucagon (raising).
• The thyroid gland produces thyroxine, that regulates metabolism, growth, and development.
• The adrenal glands produce adrenaline, that prepares the body for "fight or flight".
• The ovaries produce oestrogen and progesterone, which impact the menstrual cycle and female puberty.
• The testes produce testosterone, which impacts sperm production and male puberty.

Reproductive Hormones and Puberty

• Testosterone is the primary male hormone, produced by the testes.
• Testosterone stimulates sperm production.
• Testosterone promotes development of male secondary sexual characteristics, for example facial hair, deep voice, and muscle growth.
• Oestrogen is the main female hormone, produced by the ovaries.
• Oestrogen regulates the menstrual cycle.
• Oestrogen promotes development of female secondary sexual characteristics, for example breast development, and the widening of hips.

The Menstrual Cycle and Hormone Regulation

• Follicle-Stimulating Hormone (FSH) is produced by the pituitary gland.
• FSH stimulates egg maturation in the ovaries, which then triggers oestrogen production.
• Oestrogen is produced by the ovaries.
• Oestrogen thickens the uterus lining.
• Oestrogen inhibits FSH production to prevent multiple egg maturations.
• Oestrogen stimulates Luteinising Hormone (LH) production.
• LH is released by the pituitary gland.
• LH triggers ovulation, which is the release of a mature egg.
• After ovulation, the ovaries produce progesterone.
• Progesterone maintains the uterus lining.
• Progesterone inhibits FSH and LH production to prevent further ovulation.

Contraception Methods

• Barrier methods like condoms and diaphragms, prevent sperm from reaching the egg.
• Intrauterine devices (IUDs) either prevent embryo implantation or release hormones to inhibit ovulation.
• Spermicidal agents kill or disable sperm.
• Surgical sterilisation permanently prevents pregnancy.
• In females, the fallopian tubes are cut/sealed.
• In males, the vas deferens is cut/sealed.
• Abstinence avoids intercourse during ovulation.
• Oral contraceptive pills contain hormones that inhibit FSH, stopping egg maturation.
• Injections, implants, and skin patches release progesterone, preventing ovulation for months or years.

Infertility Treatments

• Fertility drugs contain FSH and LH.
• Fertility drugs stimulate egg production in women who struggle to conceive naturally.
• In Vitro Fertilisation (IVF) helps infertile couples to conceive.
• A woman is given FSH and LH to stimulate the maturation of multiple eggs.
• The eggs are collected from the ovaries and fertilised with sperm in a laboratory.
• Fertilised eggs develop into embryos.
• One or two embryos are implanted into the uterus.

Ethical and Social Concerns about IVF

• IVF is emotionally and physically stressful.
• IVF success rates are low, meaning multiple attempts may be needed.
• IVF can result in multiple births, increasing risks for babies and mothers.
• Unused embryos raise ethical concerns, as some may be discarded or designated for research.

Hormonal Regulation

• Adrenaline is produced by the adrenal glands during stress or fear.
• Adrenaline increases heart rate.
• Adrenaline dilates airways.
• Adrenaline increases oxygen and glucose supply to the brain and muscles for "fight or flight".
• Thyroxine is produced by the thyroid gland.
• Thyroxine regulates basal metabolic rate, growth, and development.

Negative Feedback Mechanism

• If thyroxine levels are high, the pituitary gland stops releasing Thyroid-Stimulating Hormone (TSH).
• Stopping the release of TSH causes thyroxine levels to drop.
• If thyroxine levels are low, the pituitary gland produces more TSH.
• Increased production of TSH stimulates thyroxine production.

Plant Hormones

• Plants use hormones to control growth and responses to the environment.
• Auxins regulate phototropism (response to light) and gravitropism/geotropism (response to gravity).

Auxins and Plant Growth

• In shoots, auxins accumulate on the shaded side.
• Auxin accumulation on the shaded side causes faster growth which bends shoots towards the light.
• In roots, auxins accumulate on the lower side.
• Auxin accumulation on the lower side slows down the growth, and makes roots grow downward.

Required Practical 8: Investigating Light Intensity on Seedlings

• This experiment tests the effect of light direction on seedling growth.
• Place seedlings in a container with light coming from one direction.
• Observe how seedlings bend towards the light due to unequal auxin distribution.
• Compare seedlings kept in uniform light to those with directional light exposure.
• Light causes unequal auxin distribution, leading to phototropic growth in shoots.

Commercial Uses of Plant Hormones

• Gibberellins stimulate seed germination.
• Gibberellins stimulates flowering.
• Gibberellins increases fruit size.
• Ethene controls fruit ripening.
• Ethene is used to ripen fruit during storage and transport.

Auxins have multiple applications

• Used as weed killers by disrupting plant growth.
• Used in rooting powders to help cuttings grow into new plants.
• Used in tissue culture to encourage cell growth.

Impact of Hormonal Weed Killers on Biodiversity

• Weed killers target broad-leaved plants, which encompasses many wildflowers.
• Reducing wild plants impacts insects and animals that depend on them which then contributes to biodiversity loss.