Nerves and Hormones - Biology Topic 2

Keywords:

• Stimulus - Change in the environment, detected by a receptor
• Receptor - Specialized cell that detects a stimulus
• Impulse - Electrical message

Receptors and stimulus:

• Eye - light
• Ears - sound
• Tongue - chemicals/taste
• Nose - chemicals/smell
• Skin - touch, pressure, pain, temperature

Reflexes:

All reflexes are designed to protect a specific part of the body, they are also fast and automatic.

Eg. - Your pupils increase/decrease in size due to change in light

Neurone - nerve cell

Synapse - a gap between two neurones

A impulse changes to a chemical so it can cross a synapse.

The route a impulse takes:

• Sensory receptor detects stimulus
• Sends impulse along sensory neurone
• Crosses synapse
• Relay neurone
• Crosses synapse
• Impulse goes to muscle
• Muscle contracts

Glands and muscles are effectors

• Water
• Ions (salt)
• Glucose
• Temperature

Water:

Gain:

• Drink
• Food
• Respiration

Loss:

• Sweat
• Breathing out
• Urinating
• Faeces

In our bodies, the gains must balance the losses.

Salt(ions):

Gain:

• Food
• Drink

Loss:

• Sweat
• Urine - Kidney makes salt

Glucose - is always maintained for respiration

Temperature:

Glucose + O2 ---enzymes---> Co2 + H2O

Control of our internal environment = HOMEOSTASIS

Exercise:

• Water - down (sweat)
• Glucose - down (respiration)
• Temperature - up (sweat, more blood near skin)
• IONS - down (sweat)

When you sweat you save water by producing less urine. And you save IONS in the same way. When you run your temperature goes up and when you sweat it lowers. You loose glucose by burning it off and you gain more from your glucose store.

HORMONES

Hormone - Chemicals in the blood which control and coordinate a body process.

FSH - made in the pituitary gland - stimulates the ovary to produce a follicle, stimulates oestrogen production

Oestrogen - made in the follicle (ovary) - prepares the uterus for a fertilised egg, stimulates LH production + inhibits FSH production

LH - made in pituitary gland - triggers egg release

• Pituitary releases FSH
• FSH stimulates the ovary to produce a follicle (contains egg)
• Follicle produces oestrogen
• Oestrogen stimulates repair of uterus lining ready for a fertilised egg
• High oestrogen levels inhibits FSH so no more follicles develop and stimulate release of LH to trigger ovulation

Contraceptive pill:

• Early pills contained high levels of oestrogen
• Resulted in women suffering from blood clots
• Now we have two types of pill called the COMBINED and MINI pill
• Combined pill contains a low dose of oestrogen along with progestrone. Decreases chance of cancer but increases chance of blood clots

• Mini pill contains only progestrone. Fewer side effects must be taken punctually in order for it to work. Less reliable than the combined pill. Creates less blood clots

IVF:

• They inject FSH into women so that the ovary creates a follicle with creates egg release

Ethical issues against IVF:

• Spare embryos - what to do with them?
• Multiple births - Lower survival rate, risk to mother
• Mother's age - success rate lower with age, child could have to care for mother later in life

Plant hormones:

Phototrophism - Positive phototropism is when a plant grows towards the light

Gravitropism - positive gravitropism is when a plant grows towards gravity

Hydrotropism - Positive hydrotropism is when the plant grows toward water

Using plant hormones:

• selective weedkiller - kill weeds in lawn, not grass (has a plant hormone in it)
• hormone rooting powder - cuttings (dip cut plant in powder to provide roots)
• ripening fruit - ethene (bananas can ripen unripened fruit)