Homeostasis and Response Flashcards
Why do organisms need to respond to stimuli (changes in environment)?
In order to survive
Why don’t single-called organisms have nervous and hormonal communication systems whereas multicellular organism do?
Can just respond to its environment - cells of multicellular organisms need to communicate with each other first
What does the nervous system enable humans to do?
React to their surroundings and to coordinate their behaviour
What does Central Nervous System (CNS) consist of in vertebrates?
Brain and spinal cord only
In mammals, how is the CNS connected to the body?
By sensory neurones and motor neurones
What are sensory neurones?
Neurones carry information as electrical impulses from receptors to CNS
What are motor neurones?
Neurones that carry electrical impulses from CNS to effectors
What are effectors?
All muscles and glands which respond to nervous impulses
What is a synapse?
Connection between two neurones
Explain how synapses connect neurones
- Nerve signal is transferred by chemicals which diffuse across gap
- These chemicals set off new electrical signal in next neurone
What are receptors?
Cells that detect stimuli
What do reflexes help to prevent?
Injury
What are reflexes?
Rapid, automatic responses to certain stimuli that don’t involve conscious part of brain
What is a reflex arc?
Passage of information in a reflex (from receptor to effector)
Name the stages of a reflex arc
Stimulus → Receptor → Sensory Neurone → Central Nervous System → Motor Neurone → Effector → Response
Where do neurones in a reflex arc go through?
Spinal cord or through unconscious part of brain
When a stimulus (e.g. Painful bee sting) is detected by receptors, what happens?
Impulses are sent along a sensory neurone to CNS
Why are reflexes quicker than normal responses?
Because you don’t have to think
How do muscles respond to a nervous impulse?
Muscles contract
How do glands respond to a nervous impulse?
Glands secrete hormones
Why do conditions inside body need to be kept steady, even when external environment changes?
Because cells need right conditions in order to function properly including right conditions for enzyme action
What is homeostasis?
Maintaining a stable internal environment, in response to
changes both internal and external conditions
What do your automatic control systems use to keep the internal environment stable?
Uses a mechanism called negative feedback
How does negative feedback work?
When the level of something (e.g. Water or temperature) gets too high or too low, your body uses negative
feedback to bring it back to normal
What are receptors in the eyes sensitive to?
Light
What are receptors in the ears sensitive to?
Sound and changes in position (enables us to keep our balance)
What are receptors in the tongue and nose sensitive to?
Chemicals (enables us to taste and smell)
What are receptors in the skin sensitive to? (4 things)
Touch, pressure, pain and temperature changes
What are receptors in the brain sensitive to?
Blood temperature and concentration of water in blood
What are receptors in the pancreas sensitive to?
Concentration of glucose in blood
What does the coordination centres include?
Brain, spiral cord and pancreas
Name 4 internal conditions that are controlled
- Temperature
- Water content of body
- Ion content of body
- Blood glucose levels
What are hormones?
Chemical molecules released directly into the blood
Hormones only affect…
particular cells in particular organs (target organs)
What do hormones control?
Things in organs and cells that need constant adjustment
Where are hormones produced and secreted from?
Endocrine glands
What makes up our endocrine system?
Glands
What does the pituitary gland do?
- Produces many hormones that regulate the body
- ‘Master gland’ - these hormones produced act on other glands, directing them to release hormones (that bring about change)
What does the adrenal gland do?
Produces adrenaline (which is used to prepare body for ‘fight or flight’)
Name 5 differences between nerves and hormones
Nerves:
- Very FAST action
- Act for a very SHORT TIME
- Act on a very PRECISE AREA
- Transported through NEURONES
- ELECTRICAL messenger
Hormones:
- SLOWER action
- Act for a LONG TIME
- Act in a more GENERAL way
- Transported through BLOODSTREAM
- CHEMICAL messenger
If response is really quick, what is it likely to be?
Nervous
If response lasts for a long time, what is it likely to be?
Hormonal
Why must the inside of the body kept around 37°C?
Optimum temperature for enzymes
What does the body have to balance (temperature wise)?
Balance amount of energy gained (e.g. Through respiration) and lost to keep core body temperature constant
What controls and monitors the body temperature?
Thermoregulatory centre in brain
What does the thermoregulatory centre contain?
Contains receptors that are sensitive to temperature of blood flowing through brain
Where does the thermoregulatory centre also receive impulses from?
Temperature receptors in skin, giving information about skin temperature
What do antagonistic effectors do?
Oppose each other’s actions
Give an example of how antagonistic effectors work
Some effectors work antagonistically e.g. One effector heats and another cools = work at same time to achieve a very precise temperature
Why antagonistic effectors are used?
This mechanism allows a more sensitive response
What happens when you’re too hot?
- Hairs lie flat
- Sweat is produced by sweat glands
- Vasodilation
What is vasodilation?
Heat is lost by radiation from the skin
Explain how vasodilation works?
- Blood vessels supplying skin dilate so more blood flows close to surface of skin
- This helps transfer energy from skin to environment
Why is sweat is produced by sweat glands, when you’re hot?
- Heat energy is used to evaporate sweat from skin
2. This transfers energy to the environment
What happens when you’re too cold?
- Hairs stand up to (erect)
- Vasoconstriction
- You shiver
Why does your hairs erect when you’re cold?
To trap insulating layer of air
What is vasoconstriction?
Reduced heat loss by radiation from the skin
Explain how vasoconstriction works
- Blood vessels supplying skin capillaries constrict (become narrower) to close off the skin’s blood supply (blood is away from surface)
- Reducing the transfer of heat energy from skin to environment
When you’re cold why do you shiver?
Your muscles contract automatically as this needs respiration, which transfers some heat energy (by product) to warm the body
What are goosebumps the result of?
Your hairs standing up
What happens to people when they get frostbite?
Blood supply to fingers and toes is cut off to reduce amount of energy lost (this kills cells and they go black)
What removes glucose from the blood normally?
- Normal metabolism of cells
2. Exercise
What monitors and controls the blood glucose levels?
Pancreas
When blood glucose level is too high, what is released?
Insulin
When you sweat more water is lost, therefore what do you have to do to balance this loss?
More fluid has to be taken in through drink or food
What does insulin do?
- Causes excess glucose to be converted to glycogen (move from blood and into cells)
- Causes cells to take in glucose
Where is excess glucose stored as and where?
As glycogen in muscles and liver
How is excess glucose stored when the stores in the muscles and liver are full?
It’s stored as lipid
What is secreted when blood glucose level is too low?
Glucagon
What does glucagon do?
- Causes liver to convert stored glycogen back to glucose
2. Glucose is returned to the blood (& blood glucose level rises)
What is type 1 diabetes?
Is where the pancreas produces little or no insulin
Why is type 1 diabetes dangerous?
A person’s blood glucose level can rise to a level that can kill them
What do people with type 1 diabetes need?
Insulin therapy - usually involves serval injections of insulin through the day (most likely at mealtimes)
Why does insulin therapy do?
Makes sure glucose is removed from blood quickly onces food has been digested = stopping the level getting too high
Why is insulin therapy used?
Because it’s a very effective treatment
What does the amount of insulin that needs to be injected into a diabetic (type 1) person depend on?
Depends on person’s diet and how active they are
What should people with type 1 diabetes do?
Limit intake of food rich in simple carbohydrates and take regular exercise = helps remove excess glucose from blood
What is type 2 diabetes?
Is where a person becomes resistant to their own insulin
What can type 2 diabetes cause?
Can cause person’s blood sugar level to rise to a dangerous level
What can increase your chance of having type 2 diabetes?
Obesity
How can type 2 diabetes can be controlled?
By eating a carbohydrate-controlled diet and getting regular exercise + drugs that help cells respond to insulin
How is excess water removed?
Via the kidneys in the urine
What do kidneys make and how?
Make urine by taking waste products out of blood
What is filtration (kidneys)?
Substances are filtered out of blood as it passed through the kidneys
What is selective reabsorption (kidneys)?
Useful substances (glucose, some ions and right amount of water) are absorbed back into bloodstream as they’re needed by the body
How is water reabsorbed (in kidneys)?
By osmosis
How is glucose and ions reabsorbed (in kidneys)?
Active transport
What is ultrafiltration?
Due to high pressure, all small molecules are forced out of capillaries into kidneys
What are nephrons?
Tubes in kidney
What is osmoregulation?
Reabsorption of water
Proteins (and amino acids that they are broken down into) can’t be…
stored by body
What is deamination?
When excess amino acids are converted into fats and carbohydrates which can be stored
Where does deamination occur?
In the liver
What is a waste product of deamination?
Ammonia
What and where is ammonia converted into and why?
Ammonia is toxic so it’s converted to urea in liver
Where is urea in the liver taken to and why?
Transported to kidneys where it’s filtered out of blood and excreted from body in urine
Where is urea also lost?
From skin in sweat
Where do we lose water from?
From skin in sweat and from lungs when breathing out
How is the amount of water in our body balanced?
By amount we consume and amount removed by the kidneys in urine
How do ions get into our bloodstream?
Ions are taken into body as food and then absorbed into the blood
What happens if the ion (or water) content of body is wrong?
- Could upset balance between ions and water
- Means too much or little water is drawn into cells by osmosis
- Having wrong amount of water can damage cells or mean they don’t work as well as normal
How are some ions lost?
In sweat
How is the balance of ions in body maintained by?
The kidneys
How does the the kidneys maintain the balance of ions in body?
Right amount of ions is reabsorbed into blood after filtration and rest is removed from body in urine
What is the concentration of urine is controlled by?
An anti-diuretic hormone (ADH)
What releases ADH?
The pituitary gland
Where is ADH released into?
The bloodstream
What monitors the water content of blood?
The brain
If you are dehydrated, what happens?
- ADH secreted into blood
- Kidneys reabsorb more water
- Less urine with is more concentrated
If you are hydrated, what happens?
- Less ADH secreted into blood
- Less water is reabsorbed in kidneys
- More urine that’s more dilute
How is the production of ADH controlled?
By a negative feedback mechanism
Name 3 things that occur in the liver
- Excess animo acids deaminated to form ammonia = converted into urea for excretion
- Poisonous substances detoxified and breakdown products are excreted in urine via kidneys
- Old blood cells are broken down and iron is stored
Name 5 things healthy kidneys do
- Blood is filtered
- All glucose is reabsorbed
- Dissolved ions needed by body are reabsorbed
- As much water as body needs is reabsorbed
- Urea, excess ions and water are released as urine
What do diuretic drugs do?
Remove excess water in body
Why are diuretic drugs used?
So boxers, jockeys and weight lifters can drop a weight-class/lose weight quickly
If your kidneys don’t work properly, what happens?
- Waste substances build up in blood and you lose your ability to control levels of ions and waters in body
- Eventually, results in death
How can people with kidney failure be treated?
- With dialysis treatment
2. Have a kidney transplant
Why does dialysis have to be done regularly?
To keep concentrations of dissolved substances in blood at normals levels, and to remove waste substances
In dialysis machine, where does a person’s blood flow?
Between partially permeable membranes surrounded by dialysis fluid
What does dialysis fluid contain?
Has same concentration of dissolved ions and glucose as healthy blood
Why does dialysis fluid contain the same concentration of dissolved ions and glucose as healthy blood?
So useful dissolved ions and glucose won’t be lost from
blood during dialysis + only waste substances (e.g. Urea) and excess ions and water diffuse across barrier
How many dialysis session do patients with kidney failure have to have per week?
3
How long is each dialysis session roughly?
3-4 hours
What can dialysis cause? (harm-wise to body)
May cause blood clots, infections and/or collapsed veins
Being on a dialysis machine is _____ for NHS to run
Expensive
Why is dialysis mainly used?
To buy patient with kidney failure valuable time until donor organ is found
What is the only cure for kidney failure?
Having a kidney transplant
Who are healthy kidneys usually transplanted from?
People who have died suddenly
You could only use a dead person’s organs if the person has what?
A donor card or if they’re on organ donor register
Besides dead people, where else can kidneys be transplanted from?
From people who are still alive (as we have 2 of them)
What is the risk with a donor kidney?
Donor kidney can be rejected by patient’s immune system
How can we prevent a donor kidney being rejected?
By treating a patient with drugs to prevent it (but it can still happen)
Why might a donor kidney be rejected?
Recipient’s antibodies may attack the antigens on the donor organ as they don’t recognise them
Why should people have transplants instead of dialysis? (name 2 reasons)
- Transplants are cheaper (in long run) than dialysis
2. Puts an end to hours patients have to spend on dialysis
What is the downside of kidney transplants (excluding rejection)?
There are long waiting lists for kidneys
What detects an increase in CO2 and where does this signal go?
Receptors to brain (CNS)
What is the response to an increase in CO2?
Trigger muscles in heart to contract
