Key things to remeber about homeostasis
- Created by: bethsibley
- Created on: 23-03-18 16:23
What is homeostasis
Homeostasis is the regulationn of the internal conditions of a cel or organism in response to internal or external changes
It keeps the conditions constant for enzyme action and cell functions
It controls:
- Blood glugose concentration
- body temperature
- water and ion levels.
They can control it through- using nerves or chemical responses via hormones
Control systems
Cells- receptors that detect the change in th environment Coordination centres- i.e. pancreas, brain, spinal cord. which receive and process info from receptors. effectors- muscle or glands which bring about a response to restore optimum levels.
The thermoregulatory centre in the brain will moniter and control body temp, it has receptors that moniter temp of blood in brain and receives imformations for temp receptors in the skin.If the body temp is too high then blood vessles will vasodilate to get more blood to the surface. more sweat is produced from the sweat glands and evaporates on the skin. If the temp is too low then blood vessles will vasoconstrict to bring vlood away from skin. sweating will stop and muscles will contract and relax wuickly (shiver) which will transer heat to the blood
The nervous system
Information from receptors passes throigh the Central Nervous System (CNS) (brain and spinal cord) which will coordinate a rseponse fro effectors i.e, muscles contracting.
- Pain stimulus is detected by receptors
- Impulses from the receptotr pass alomng the sensory neurone to the CNS
- An impulse then passes through the reay neurone
- A motor neirone carries an impulse to the effectir.
- The effector (usually a muscle) responds
Neurons are not directly attached but cmmunicate via synapes (gaps between neurons) where the electrical impulse jumps through.
The brain and the eye
Three main regiomns in the brain is the Cerebral cortex ( responsible for cpnsciousness intellegance an dmemory), Cerebellum (coordinate movemenmt and balace)and the Mendulla (controlls automatic actions i.e heart beat or breathing.)
Neuroscientists study patients with brain damage, electrically stimukating different parts of the brain amd using MRI scanning techniques.
The eye parts-
-
- Retina- contains receptor cells taht are sensitive to light and colour.
- Optic nerve- Carries impulses from the retina to the brain
- Sclera- forms a tough outer layer with transparent region at the front called a cornea
- Iris- controls the size of the pupil and the amount of light reachimg the retina
- Ciliary muscles and suspensory ligaments- change the shape of the lens to focus on near or distant objects
- Myopia (short sighted) and hyperopia (long sighted) Myopia is corrected with a concave lens and hyperopia is fixed with a convex lens.
The endocrine system
Made of glands that secrete hormones directly to blood stream.
Hormones are chemical messengers that are carried in the blood to a target organ where they broduce an effect. Compared to the nervous system th effects of hormones are slower yet act for longer.
The pituitary gland in the brain is a 'master gland' it secretes several hormones in response to body conditions. Some hormones can act to stimulate other hormones to be relesased.
- Adrenaline - produced by adrenal glands in times of fear or stress, inreases heart rate which will increase the delivery of oxygen and glucose to brain and muscles. prepares the body to 'fight or flight'
- Thyroxine - produced by the thyroid gland it increase metabolic rate and controls growth and develpment in young animals and is conrolled by negative feedback.
Blood glucose control
Concentration of glucose is controlled by the pancreas. If it is too high:
-
- Pancreas releases more insulin
- Insulin causes glucose to move from the blood into the cells
- In liver and muscle cells glucose is converted to glycogen
- If its too low
- Pancrease releases glucagon
- Glucagon stimulates glycogen to be converted back to glucose and released to blood example of negative feedback
Type 1 diabetes-caused by the pancreas failing to produce enough insulin=unconmtrolable blood glucose-treated with inlsuin injections
Type 2 diabetes-caused by the body cells no longer responding to insulin- risk of obestity- treated with carbcontrolled diet and exercise.
Water balance
Water leaves the body from lungs during breathimg. from sweat and in urine.if the concentration of blood changes then body cells will lose or gain too much water by osmosis. This balance is controlled by the kidneys. They also excrete urea as a waste product from the liver (from breaking down proteins)
The digestion of proteins from foods result in excess amino acids in the liver these are converted to ammonia in the process of deamination. ammonia is toxic so is converted to urea and sent to the kidneys for safe excretion
Urine in the kidneys is produced by Kidney failure can be treated with a transplant or Dialysis (fake kidney machine
- Filtering blood
- Selevtive reabsorption of useful substances like glucose ions and water.
- This leaves urea and excess water ions to form urine.
- This takes place in the small tubes in the kidneys called tubules.
Water levels are controled by the hormone ADH which is released in the pituitary gland when blood is too concentrated it passes in blood to the kidney tubules which causes more blood to be reabsobed to the blood.
Sex hormones
During puberty, hormones cause secondary sexual charitaristics.
-
- Oestrogen- from the ovaries- main female sex hormone-at pubery edds begin to mature and be released this is ovulation
- Testosterone-main male sex hormone produced by testes and stimulates sperm production.
- Menstrual Cycle
Reducing/increasing fertility
Various methods of contraceotion-
-
- Oral contraception (the combined pill) containing oestrogen and progesterone which inhibit FSH production so no eggs are released.
- An injection, implant or patch that slowly releases progesterone ro stop the release of eggs for a number of months or years
- Barriers like condoms and diaphrams that prvent the sperm reaching the eggs
- Spermicidal cream that kill or diable sperm.
- Surgical methods i.e. cutting sperm ducts or tying fallopian tubes.
- Increasing fertility
- Doctrs may give FSH and LH in a fertility drug if a womans hormone levels are too low to stimulate eggs to mature
- IVF
- Give woman FSH and LH to stiulate growth of many eggs
- Collect eggs from woman
- Fertilising egg with sperm from father in a lab
- Inserting one or two embryos into womeans uterus
Plant hormones
Plants respond to environment by-
-
- Roots and Shoots growing towards or away from a stimulus,
- Plants flowering at a particular time,
- Ripening of fruits.
- If a plant responds by growing in a particular direction its called tropism there are different types-
- If the stimulus is gravity then the growth of shoots grow away=nagitavely Gravitopic and the roots grow towards =positively Gravitopic,
- If the stimulus is light then the shoots will grow towards the light (positively phototropic) and the roots will grow away (negatively phototropic.)
- tropisms are controlled by auxin hormones.
- More light reaches one sie of the shoot,
- More auxin is sent down the shaded side of the shoot,
- This results in cells in the shaded side elongating more,
- The shoot therefore, grows tawardsthe light.
- In roots auxins move to the bottom of the root and causes less elongation so grow downwards
Plant hormones
Gibberellins are anther group of plant hormone and are imported in initiating seed germination
Ethene is a gas also a plant hormone it controlls cell division and ripening of fruits.
Using plant hormones-
Plant growth hormones are used by framers and gardeners auxins are used-
-
- As weed killers because they make weeds grow so rapidly that they use up all their food reserves and die
- As rooting powders, because they make cuttings produce roots when planted
- Promotiong growth in tiddue cluture.
- Ethene is used in food industry to controll ripening of fruit during storage and transport.
- Gibberellins can be used to end seed dormancy and make them germinate
- Promote flowering when there is most demand (i.e. mother day)
- Increase fruit size
complete
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