The maintenance of a constant internal environment
What homeostasis controls in the human body
Blood glucose concentration
Body temperature
Water levels
Control systems
Receptors - cells that detect stimuli
Coordination centres - process information from receptors
Effectors - bring about responses to return conditions to optimum levels
Response to a stimulus
1. Receptor cells convert stimulus into electrical impulse
2. Impulse travels along sensory neurons to central nervous system
3. Information processed and appropriate response coordinated
4. Impulse sent along motor neurons to effectors
5. Effectors carry out response
Reflex
Automatic responses which take place before you have time to think
Reflex arc
1. Stimulus detected by receptors
2. Impulses sent along sensory neuron
3. Impulse passes to relay neuron in central nervous system
4. Impulses sent along motor neuron
5. Impulse reaches effector resulting in response
Synapse
The gap between two neurons where a chemical is released to trigger the impulse in the next neuron
Reaction time
How long it takes to respond to a stimulus
Components of the brain
Cerebral cortex
Cerebellum
Medulla
Challenges in investigating brain function and treating brain damage/disease
It is complex and delicate
It is easily damaged
Drugs cannot always reach the brain
It is not fully understood which part of the brain does what
Methods used by neuroscientists to map brain function
1. Studying patients with brain damage
2. Electrically stimulating different parts of the brain
3. Using MRI scanning techniques
Structures within the eye
Retina
Optic nerve
Sclera
Cornea
Iris
Ciliary muscles and suspensory ligaments
Accommodation
To focus on near object: Ciliary muscles contract, suspensory ligaments loosen, lens becomes thicker and more curved
To focus on distant object: Ciliary muscles relax, suspensory ligaments tighten, lens becomes thinner
Myopia
Short sightedness - lens is too curved so distant objects appear blurry
Hyperopia
Long sightedness - lens is too flat so it cannot refract light enough
Treatment methods for eye defects
Spectacle lenses
Contact lenses
Laser eye surgery
Replacement lens
Thermoregulatory centre
Monitors and controls body temperature
Has receptors that monitor blood temperature and skin temperature
Mechanisms to increase body temperature
Sweating increases to evaporate from skin surface
Vasodilation - more blood flows closer to skin surface
Mechanisms to decrease body temperature
Sweating stops
Shivering to generate heat from respiration
Hairs stand on end to trap warm air
Vasoconstriction - blood does not flow as close to skin surface
Endocrine system
Communication system that sends hormones (chemical messengers) around the body
Glands in the endocrine system
Pituitary gland
Pancreas
Thyroid
Adrenal gland
Ovary
Testes
Compared to the nervous system, the hormonal system is much slower but it acts for longer
Blood glucose concentration
Needs to be kept within a certain limit as glucose is needed by cells for respiration
Eating foods that contain carbohydrates increases blood glucose concentration
Pituitary gland
Controls metabolic rate, heart rate and temperature
Adrenal gland
Secretes adrenaline
Involved in the 'fight or flight' response (the body's response to stressful situations)
Ovary
Secretes oestrogen
Is involved in the menstrual cycle and the development of female secondary sexual characteristics (different features that develop during puberty that distinguish a female from a male)
Testes
Secretes testosterone
Is involved in the production of sperm and the development of male secondary sexual characteristics
The blood transports the hormone to a target organ or tissue where it has an effect
Blood glucose concentration
The concentration of glucose in your blood needs to be kept within a certain limit because glucose is needed by cells for respiration
Negative feedback loop
When blood glucose levels increase/decrease, a hormone is secreted to oppose the change. The action of this hormone cannot occur continually because when the blood arrives at a certain glucose concentration the other hormone is produced, resulting in the opposite effect.
Type 1 diabetes
The pancreas cannot produce enough insulin
Blood glucose level can rise to a fatal amount
Glucose is excreted with urine and lots of urine is produced leaving the individual very thirsty
It is treated with insulin injections at meal times, which results in glucose being taken up from the bloodstream
It is also advised to limit the intake of simple carbohydrates which contain lots of glucose
Doctors are attempting to cure diabetes with pancreas and pancreatic cell transplants, and genetically engineering pancreatic cells from mice to make insulin
Type 2 diabetes
The body cells no longer respond to insulin
Blood glucose levels can rise to a fatal amount
Obesity is a risk factor for this disease
Treatments include reducing the number of simple carbohydrates in diet, losing weight and increasing exercise
There are also drugs to make insulin more effective on body cells, help the pancreas make more insulin or reduce the amount of glucose absorbed from the gut
Osmosis
The process by which water molecules move from a place where they are in high concentration to a place where they are in low concentration
If the water concentration of the blood increases
Cells in the body take up water
If the water concentration of the blood decreases
Cells in the body lose water
If body cells lose or gain too much water by osmosis, they do not function properly
Kidneys
Very important in maintaining the balance of water and other substances in the body
As blood moves through the body, it makes urine by filtering out the waste products and selectively reabsorbing useful substances such as glucose, ions and water
Waste products processed at the kidney
Water
Ions
Urea
Anti-diuretic hormone (ADH)
A hormone involved in the control of the loss of water as urine
It is released into the pancreas by the pituitary gland when a receptor in the brain detects that the blood is too concentrated
It travels in the bloodstream to the kidney tubules
An increased amount of ADH reaching the tubules increases their permeability to water, so more moves out of the tubule and back into the bloodstream
This results in a smaller volume of more concentrated (yellow) urine and the blood becoming less concentrated as more water moves into it