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B5 - Homeostasis and Response (Synapses and Reflexes (The Reflex Arc Goes…
B5 - Homeostasis and Response
Homeostasis
Homeostasis - Maintaining a Stable Internal Environment
The conditions in your body need to be constantly kept steady
Homeostasis is about the regulation of the conditions to maintain a stable internal environment
There are lots of automatic control systems in the body
The systems are made of three parts - receptors, coordination centres and effectors
Negative Feedback Counteracts Changes
Receptor detects stimulus - glucose level is too high
Coordination centre receives, processes and organises a response
Effector produces a response which counteracts the change
The effectors continue producing responses as long as the coordination centre stimulates them
The Nervous System
The Nervous System Detects and Reacts to Stimuli
It means humans can react to their surroundings
The Nervous System is made up of Different Parts
Central Nervous System
In mammals, consists of brain, spinal cord, sensory neurones and motor neurones
Sensory Neurones
Carry information from receptors to CNS
Motor Neurones
Carry impulses from CNS to effectors
Effectors
All muscles and glands which respond to impulses
Receptors and Effectors can form part of Complex Organs
Receptors - cells that detect stimuli
Many different types of receptors
Receptors form part of larger organs
Effectors respond to the impulses
Muscles and glands are effectors
Synapses and Reflexes
Synapses Connect Neurones
Connection between two neurones is a synapse
Signal is transferred by chemicals diffusing across the gap
These chemicals set off a new signal in the next neurone
Reflexes Help Prevent Injury
Reflexes are rapid responses that aren't conscious
If someone shines a bright light in your eye, the pupils get smaller
Your body releases adrenaline as soon as you get a shock
The passage of information is the reflex arc
The Reflex Arc Goes Through the Central Nervous System
1, The neurones go through the spinal cord
A stimulus detected by the sensory neurone is passed along the relay neurone
Impulses have to be passed across synapses
Same thing happens between relay and motor neurones
The impulses travel from the motor neurone to the effector
The muscle then responds to the stimulus
You don't think about it, it happens much quicker
Investigating Reaction Time :star:
Reaction Time is How Quickly You Respond
You Can Measure Reaction Time
1, The person should sit with their arm resting on a table
Hold a ruler vertically with their fingers at zero, then let go
The person should catch the ruler as quick as they can
Reaction time is measured by the number on the ruler
Repeat several times and find a mean
The person should have a caffeinated drink, wait 10 minutes and then repeat step 1 - 5
You need to control any variables
Too much caffeine can cause unpleasant side-effects
Reaction Time Can Be Measured Using a Computer
Simple computer tests are used to measure reaction time
Computers are more accurate as they remove human error
It can give a more accurate measurement
Using a computer limits ability to predict when to respond
The Endocrine System
Hormones Are Chemical Messengers Sent in the Blood
Hormones are chemical molecules released into the blood
Hormones produced by endocrine glands
Hormones have long-lasting effects
Some examples are:
The Pituitary Gland
Produces many hormones that regulate body conditions
Ovaries
Produce oestrogen
Testes
Produce testosterone
Thyroid
Produces thyroxine
Adrenal Gland
Produces adrenaline
The Pancreas
Produces insulin
Hormones and Nerves Have Differences
Nerves
Very fast action
Act for a short time
Act on a precise area
Hormones
Slower action
Act for a long time
Act more generally
If the response is quick, it's probably nervous
If it lasts for a long time, it's probably hormonal
Controlling Blood Glucose
Insulin and Glucagon Control Blood Glucose Level
Eating carbohydrates puts glucose into the blood from the gut
Normal cell metabolism removes glucose from blood
Vigorous exercise removes more glucose
Excess glucose is stored as glycogen in the liver and muscles
The level of glucose in the blood must be kept constant
With Diabetes, You Can't Control Your Blood Sugar Level
Type 1 diabetes is when the pancreas produces little or no insulin
Type 2 is when someone becomes resistant to their own insulin
Puberty and the Menstrual Cycle
Hormones Promote Sexual Characteristics at Puberty
In men, the main hormone is testosterone
In women, the main hormone is oestrogen
The Menstrual Cycle Has Four Stages
Day 1 - Menstruation starts
Day 4 - 14 - the uterus lining builds up again
Day 14 - an egg develops and is released
Until day 28 - the wall is maintained
It's Controlled by Four Hormones
FSH
Produced in pituitary gland
Causes egg to mature in the follicle
Stimulates ovaries to produce oestrogen
Oestrogen
Produced in ovaries
Causes uterus lining to grow
Stimulates release of LH and stops FSH
LH
Produced by pituitary gland
Stimulates release of egg
Progesterone
Produced in ovaries by remaining follicle
Maintains the lining of the uterus
Inhibits release of LH and FSH
Controlling Fertility
Hormones Are Used to Reduce Fertility
Oestrogen is used to prevent the release of an egg
If oestrogen is taken every day, it inhibits the production of FSH
Progesterone reduces fertility
The pill contains oestrogen and progesterone
It's over 99% effective at preventing pregnancy
There's a progesterone-only pill too
Other methods
Contraceptive patch contains oestrogen and progesterone
The contraceptive implant is inserted under the skin
The contraceptive injection contains progesterone
An IUD is inserted into the uterus to kill sperm and prevent an egg being fertilised
Barriers Stop Egg and Sperm Meeting
Non-hormonal contraception stop the sperm from reaching the egg
Condoms prevent the sperm from entering the vagina
A diaphragm is a cup that fits over the cervix
Spermicide can be used as a form of contraception
There are More Drastic Ways to Avoid Pregnancy
Sterilisation - cutting the fallopian tubes or the sperm duct
'Natural' methods - Avoiding sex when you're more fertile
More on Controlling Fertility
Hormones Are Used to Increase Fertility
Some women's FSH levels are too low to be fertile
They can be given to women to stimulate ovulation
Pros
Helps a lot of women get pregnant
Cons
Doesn't always work
Too many eggs could be stimulated
IVF Can Also Help Couples to Have Children
IVF involves collecting eggs from a female and fertilising them outside of the body
It can also involve Intra-Cytoplasmic Sperm Injection
The eggs are grown into embryos in an incubator
One or two are then transferred into the womb
FSH and LH are given beforehand to stimulate egg production
Pros
Can give an infertile couple a child
Cons
Multiple births
Success rate is low
Physically stressful for the woman
Some People Are Against IVF
The process tends to leave unused embryos
The genetic testing before implantation raises ethical issues
Adrenaline and Thyroxine
Adrenaline Prepares You for 'Fight or Flight'
Adrenaline is released by the adrenal gland
It's released in response to stressful or scary situations
It gets the body ready by triggering things that increase the supply of oxygen and glucose to cells
Hormone Release is Affected by Negative Feedback
Your body controls hormone levels using negative feedback systems
Thyroxine Regulates Metabolism
Thyroxine is released by the thyroid gland
Regulates the basal metabolic rate
Released in response to thyroid stimulating hormone
Negative feedback systems keep the thyroxine levels at the right amount