Homeostasis

Homeostasis just means the maintainance of a constant internal environment

To do this, we need to control our:

• blood glucose levels
• water levels 
• temperature

Organs in Homeostasis

• Brain - control centre
• CNS - sends signals to various parts of the body
• Pancreas - produces insulin
• Effectors/Muscles - moving, i.e. shivering
• Glands - produce hormones

The nervous system is incredibly complex and is over-laid on our muscular and spinal cord.

It consists of:

• the brain and spinal cord, which make up the Central Nervous System (CNS)
• receptors and effectors

When you pick something up (a stimuli), that signal needs to travel from wherever you picked it up from (so your fingers) to your spinal cord, and then come straight back. This is called a reflex action.

Sometime though, the signal travels to your brain, so you think about it and then react.

• The nerve cells involved in this are very long. These can send a fast electircal signal.
• However, when we want to send an electrical signal from one cell to another, things slow down a bit.
  • This is because the signal has to cross a synapse. This is going to be a slow chemical reaction, as the chemical has to be released, diffuse across the synapse and be picked back up. This then just becomes a fast electric signal.

The brain is the central control centre of the body. It makes sure everything functions properly and tells various different parts what to do.

It consists of:

• the cerebral cortex
• cerebellum
• medulla

For the brain to function properly, it needs to be inside a living person.

The eye consists of:

• Sclera - the white part of the eye
• Retina - where the image is focussed
• Optic nerve - send messages to the brain
• Ciliary muscles - change the shape of the retina
• Cronea - protecting covering
• Pupil - lets light in
• Lens - focus
• Sensory ligament - holds the lens in place

If you are:

• Short-sighted: (diverging lens)
  • can't see distant objects
  • the image focuses before the retina
• Long-sighted: (converging lens)
  • can't see near objects
  • image focuses behind the retina

Body temperature is regulated by the Thermoregulatory System in the brain

• If you are too cold:
  • the hairs on your body will stand up (to trap a layer of air)
  • stop sweating
  • vasoconstriction starts (blood vessels constrict, so that they are further away from the skin so less blood flows near to the skin, resulting in less heat loss)
  • shivering (produces energy)
• If you are too hot:
  • the hairs on your body lie flat (so as not to trap any air)
  • start sweating
  • vasodilation starts (blood vessels get wider, so that they are closer to the skin so more blood flows further away from the skin, resulting in more heat loss)

Both the male and female endocrine system consist of:

• the pituitary glands (in the brain)
  • FSH and LH
• thyroid (neck)
  • thyroxine
• adrenal gland (kidneys)
  • adrenaline
• pancreas (behing the stomach)
  • produce insulin

Ovaries are only in the female endocrine system and testies are only in the male endocrine system. Testies produce testosterone, ovaries produce oestrogen.

• If blood glucose levels get too high:
  • This is picked up by the pancreas
  • Pancreas produces insulin
  • Insulin causes the cells to remove glucose from the blood
  • Liver and muscle cells can convert glucose into glycogen and store it
  • Removing glucose from the blood will cause glucose blood levels to fall
• If blood glucose levels get too low:
  • This is picked up by the pancreas
  • The pancreas will start to produce glucagon
  • Glucose that was previously stored in liver and muscle cells returns to the blood
  • This causes blood glucose levels to rise 
• Glycogen -----> Glucose

                        glucagon         

• Glycogen is the stored form of glucose - glucagon will convert that to glucose 

There are two types of diabetes - type 1 and type 2

Type 1:

• the pancreas doesn't produce enough insulin
• loss of weight, increased need to urinate, thirst, blurry vision, fatigue, hunger
• can be treated by insulin injections

Type 2:

• cells are insensitive to insulin
• loss of weight, increased need to urinate, thirst, blurry vision, fatigue, hunger
• can be treated by:
  • controlling diet
  • excercise

The kidneys have 3 main functions: they remove urea, control iron content and they control water content

There are 3 ways we can lose water from our body: urinating, sweating and breathing out

It is important to control our water levels, as if they are too high, cells take in too much by osmosis and they might pop, but if there is too less, they enzyme reactions won't be able to take place.

The kidneys function in 3 different ways:

• Ultrafiltration:
  • Blood enters the kidneys under high pressure. Ions, urea and sugar are squeezed out into the capsule (at the start of the nephron)
• Rabsorbtion
  • As this flows along the nephron, useful items are reabsorbed.
    • all of the sugar (via active transport)
    • enough ions (via active transport)
    • enough water
• The hormone that controls how much water is absorbed is ADH (antidiuretic hormone)

• Release of waste:
  • through urine

If a perosns kidneys aren't working properly, they can undergo kidney dialysis

• the dialysis machine will take over the role of the kidney
• however, it is very time consuming
  • blood fillers take about 4 hours and have to be done 3 times a week

An alternative to a kidney dialysis would be a kidney transplant

• they have very long waiting lists
• risk of rejection

1 in 6 women find themselves in the unfortunate position where they can't have a baby.

IVF is one of the ways to have a baby, despite being infertile.

Advantages:

• you get to have a baby

Disadvantages:

• drugs have to be taken for a very long time and these have side effects
• expensive, at the least £5,000
• doesn't always work
• it's a long, painful process

Phototropism:

• grows towards the light

Geotrphism/Gravitropsim

• grows towards gravity (roots are always going to grow downwards and shoots are always going to grow upwards)

Giberellins:

• important for growth

Ethene:

• important for ripening plants

Auxins:

• important for growth towards light