Homeostatis and Response

Homeostasis is maintaining regular conditions inside your body and cells to maintain a stable internal enviroment, in response to changes in both internal and external conditions so that cells can function properly. Nervous and hormonal communication regulates this internal enviroment. They must maintain your body temperature, blood glucose level, water content and Ph level.

Negative feedback:
Your automatic control systems keep your internal enviroment stable using a mechanism called negative feedback. When a level of something (e.g. Water or glucose) gets too high or low your body uses negative feedback.

The nervous system means that humans can react to their surroundings and coordinate their behaviour.
Central nervous system (CNS) - in vertabraes this consists of the brain and spinal chord only. In mammals it is connected to the body through sensory and motor nuerones. It recieves information from the receptors and coordinates a response,which is carried out by the effectors.
Sensory neurones - carry information as electrical impulses from the receptors to the CNS.
Motor neurones - carry electrical impulses from the CNS to effectors.
Effectors - all your muscles and glands, which respond to nervous impulses, to bring about change. Muscles contract and glands secrete hormones.
Receptors - cells that detect stimuli. e.g. Taste receptors on the tongue and sound receptors in the ear. Receptors can form part of larger, complex organs, e.g. The retina of the eye is covered in light receptirs.

The connection between two neurones is called a synapse, which is transferred by chemicals which diffuse across the gap. These chemicals then set off a new electrical signal in the next neurone.
Reflexes reduce the chance of being injured and are rapid and automatic.
Examples - pupils get smaller in bright light so that less light gets to the pupil andthey dont get damaged. In a "fight or flight" situation your body releases adrenaline.

Refelex arc
The passage of information in a reflex (from receptor to effector) is called a reflex arc.

Reaction is the time it taks the body to react to a stimulus. It can be affected by age, gender or drugs.

Practicals

Effect of caffeine - caffeine can speed up the reaction. To test this you would:

1) Sit with their arm resting on the table.

2) Person 2 holds a ruler between their finger and thum at 0 and lets go without warning.

3) Person being tested tries to catch the the ruler as soon as possible.

4) The reaction time is measured by the number on the ruler where it is caught.

5) Repeat at least 3 times and calculate a mean.

6) Person A should have a caffienated drink, wait 10 minutes, the repeat steps 1-5.

Reaction time measured by a computer -

A person being tested has to click the mouse or press a key as soo as a stimulus is given on the screen.

This is more precise as t eliminates human error and more accurate as the reaction time is given in milliseconds. It is also compleately spontaneous and random.

Hormones are chemical mlecules released into the blooad and carried to particular cells.They are secreted by the endocrine glands. They often have lasting effects, slower reaction time and act in a more general way than nerves. Therfore, if a response is quick, its probably a nervous response and if the effects of the response lasts a long time (e.g. adrenaline) its proably hormonal.

 Eating foods containing high amounts of carbohydrates puts glucose into the blood through the gut whilst vigourous exercise causes the metabolism of cells to remove more glucose from the blood.

Excess glucose can be stored as glycogen in the lier and in the muscle as the level of glucose in the blood must be kept steady. The pacreas uses insulin and glcagin in a negative feedback cycle (see diagram above).

Type 1 - The pancreas produces little or no insulin, therfore the person's blood levels can rise to extreme levels. This is treated using insulin therapy, several insulin injections throughout the day, most likely at meal times. This makes sure that glucose is removed from the blood quickly once food has been digested. They must also limit the intake of food rich in simple carbohydrates and take regular exercise.

Type 2 - This is where a person becomes resistant to their own insulin, causing blood sugar levels to rise as the body cells dont respond properly to the hormone. Obesity is a major risk factor and it can be controlled by eating a cabohydrate-controlled diet and getting regular exercise.

At puberty,your body stars releasing sex hormones that trigger seecondary sexual chracteristics and cause eggs to mature in women.

• In men the main reproductie hormone is testosterone which is produced in the testes and stimulates spermproduction.
• in women the main reproductive hormone is oestrogen which is produced by the overies. This brings about physical changes and is involved in the menstual cycle.

Secondary sexual characteristics:

The stages of the Mentraul cycle:

• Stage 1, day 1-4 - The uterus lining breaks down for about 4 days (mentruation).
• Stage 2, day 4-14 - The uterus lining builds up into a thick, spongy layer, full of blood vessels, ready to recieve a fertilised egg.
• Stage 3, day 14 - An egg develops and s released from the ovary (ovulation).
• Stage 4, day 14-28 - The wall is maintained. If no fertilised egg lands on the uterus wall by day 28, the cycle starts again.

The four hormones:

• FSH (folicle-stimulating hormone) - Produced in the pituitary glands, causes egg to mature into a folicle, stimulates overies to produce oestrogen.
• Oestrogen - Produced in the overies, causes the uterus lining to grow, stimulates release of LH and inhibits release of FSH.
• LH (Luteinising hormone) - Produced by the pituartary gland, stimulates the release of an egg at ovulation.
• Progesterone - Produced in the ovaries by the remains of the folicle after ovulation, maintain the uterus lining during the second part of the cycle, inhibits the release of LH and FSH.

Adrenaline:

• Produced by the adrenal gland, just above the kidneys.
• Released in stressful situations when the brain detects fear.
• Gets your body ready for "fight or flight" by triggering mechanisms that increase the supply of oxygen and glucose to the brain and muscles/

Thyroxine:

• Released by the thyroid gland inthe neck.
• Helps regulate the basal metabloic rate (the speed at which chemical reaction acur when the body is at rest).
• Also helps in proccesses such as protein synthesis and growth and development.
• Released in response to thyroid stimulating hormone (TSH), released in th pituatary gland.
• Uses a negative feedbak system.