Human Biology

Sense Organs detect Stimuli (change in environment)

• Receptors are a group of cells which are sensitive to a stimulus, they change stimulus energy into electrical impulses

Sensory Neurones - the nerve cells that carry signals as electrical impulses from the receptors in the sense organs to the central nervous system 

Motor Neurones - nerve cells that carry signals to the effector muscle or gland

Effectors - muscles and glands are known as effectors, they respond in different ways to nerve impulses:

Muscles contract  

Glands secrete hormones

The passage of information in a reflex (receptor --> effector) is called a reflex arc

• Stimulus detected by receptor 
• Impulse is sent along a sensory neurone to the spinal cord
• In the spinal cord the impulse is passed onto a relay neurone
• It relays the impulse to a motor neurone
• Impulse travels to effector (e.g.muscle)
• Muscle contracts 

Quicker than normal responses because you don't have to think about it !!!

Synapses connect neurones

• The nerve signal is transferred by chemicals which diffuse across the gap
• The chemicals are then set off a new electrical signal in the next neurone

Chemical messengers sent in the blood, carried in the blood plasma, control things in organs and cells that need constant adjustment

Hormones have long lasting effects 

HORMONES are chemical messages which travel in the blood to activate target cells

Nerves:

• Very fast message 
• Act for a very short time
• Act on a very precise area

Hormones

• Slower message
• Act for a long time
• Act in a general way 

FSH (Follicle-Stimulating Hormone) 

• Produced by the pituitary gland
• Causes egg to mature in one of the ovaries 
• Stimulates the ovaries to produce oestrogen 

Oestrogen

• Produced in the ovaries
• Causes pituitary gland to produce LH
• Inhibits the further release of FSH

LH (Lutenising Hormone)

• Produced by the pituitary gland
• Stimulates the release of an egg at around the middle of the menstrual cycle

Oestrogen prevents the production of FSH so can be used as a method of contraception, e.g. the pill

The pill is over 99% effective and it reduces the risk of getting some types of cancer                :)

Not 100% effective, slight chance of pregnancy. It can cause side effects e.g. headaches, irregular menstrual bleeding and nausea. Doesn't protect against STDs                 :(

Some women have low levels of FSH and eggs can't mature. FSH can therefore be taken to stimulate egg production in the ovaries.

It doesn't always work and can be expensive. To many eggs stimulated resulting in multiple births     :(

IVF involves collecting eggs from the woman's ovaries and fertilizing them in a lab. These are grown into embryos and transferred into the woman's uterus.

• Hormones given before egg collection to stimulate egg production
• Oestrogen and progesterone given to make implantation of embryo more successful

BUT

• Some woman have very strong reaction to the hormones e.g. abdominal pain, vomiting and dehydration
• Some reports of increased risk of cancer

Ion content is regulated by the kidneys 

• Ions are taken into the body by food then absorbed in the blood
• Food contains too much ions then the excess needs to be removed
• Some ions lost as sweat, some are removed by the kidney --> urine

Water needs to be constantly balanced

• Lost through the skin as sweat, via lungs in breath and the kidneys as urine

Body Temp is controlled by the brain 

• Enzymes in the body work best at 37C so the body tries to maintain this temp
• Part of the brain is sensitive to blood temp and receives messages from the skin about skin temp

Blood sugar levels need to be controlled

• Glucose into the gut via the blood
• Vigorous exercise means more glucose is removed <-- this needs to be controlled