Communication and Homeostasis Flashcards Preview

Biology > Communication and Homeostasis > Flashcards

Flashcards in Communication and Homeostasis Deck (88):

What is a stimulus?

Any change in the environment that causes a response


What is a response?

A change in the behaviour or physiology as a result of a change in the environment


Example of epithelial organs/tissues in animals and plants

Skin in animals and Bark in trees


4 things an enzyme needs to work efficiently

A suitable temperature
A suitable pH
An aqueous environment that keeps the substrates and products in solution
Freedom from toxins and excess inhibitors


A good communication system will...

Cover the whole body
Enable cells to communicate with each other
Enable specific communication
Enable rapid communication
Enable both short-term and long-term responses


What is cell signalling?

The process in which one cell will release a chemical that is detected by another cell


What two processes are involved in cell signalling?

The neural system
The hormonal system


Describe the neural system

An interconnected network or neurones that signal each other across across synapse junctions. these conduct signals very quickly and enable rapid responses to fast changing stimuli.


Describe the hormonal system

Uses blood to transport signals around the body. Cells in an endocrine organ release the signal (hormone) directly into the blood. This hormone is only recognised by specific target cells. This enables long term responses.


Define homeostasis

The maintenance of the internal environment in a constant state despite external changes.


Define negative feedback

A process that brings about a reversal of any change in conditions. It ensures that an optimum steady state can be maintained, as the internal environment is returned to its original set of conditions after any change. It is essential for homeostasis


Name the conditions in the body that must be kept constant

Blood glucose concentration
Blood salt concentration
Water potential of the blood
Blood pressure
Carbon dioxide concentration


What are sensory receptors?

These are receptors that monitor conditions inside the body such as temperature and blood glucose concentration. If a change is detected they will be stimulated to send a message.


Give an example of negative feedback

When body temperature gets too low so the body causes the muscles to contract and relax rapidly in order to produce more heat.


Define Positive Feedback

A process that increases any change detected by the receptors. It tends to be harmful and does not lead to homeostasis.


Give a beneficial example of positive feedback

At the end of pregnancy to bring about the dilation of the cervix. As the cervix stretches, signals tell the pituitary gland which is stimulated to produce oxytocin, hormone which increases uterine contractions causing the cervix to dilate further.


Give a damaging example of negative feedback

When the body gets too cold, enzymes involved in respiration are not able to work as efficiently, so respiration rate decreases, causing less heat to evolve from those reactions, causing the body to cool further. This can eventually lead to death if the body is not warmed fast.


Define 'ectotherm'

An organism that relies on external sources of heat to regulate its body temperature. Commonly and incorrectly known as 'cold blooded'.


Define 'endotherm'

An organism that uses internal sources of heat to regulate it's body temperature. Commonly and incorrectly known as 'warm blooded'.


Advantages of being an ectotherm

They need less food for respiration, meaning they can focus more on growth.
They need less food overall to survive and so can survive for longer periods without food.


Disadvantages of being an ectotherm

Less active in colder temperatures and may need to warm up in the morning putting htem at a greter risk of predation.
If they are unable to go outsiede during colder months, they need to have sufficient storage of food to survive over this period.


Adaptations of ectotherms to regulate body temperature

Expose body to the sun so that more heat is absorbed.
Orintate body to the sun so that a larger surface area is available to absorb the heat ( and vice versa).
Hide in a borrow so that they can keep out of the sun and reduce the risk of overheating.
Increasing breathing movements evaporates more water and releases heat from the body.


Advantages of being an endotherm

Fairly constant body temperature whatever the external temperature is.
Activity is possible when external temperatures are cool.
They have the ability to inhabit colder parts of the planet.


Disadvantagse of being an endotherm

Significant part of energy intake is used to maintiain the body temperature.
More food is required to survive.
Smaller proportion of evergy is use in growth.


Components of endotherms body involved in temperature regulation

Sweat glands in the skin release sweat when B.T increases, which vapourises using the body's heat.
The lungs, mouth and nose pant during increased B.T which causes more heat to be released through breathing.
The hairs of the skin stand on end when it is cold to form an insulating layer around the body and a partial wind break.
Arterioles undergo vasodilation when it is hot, and vasoconstriction when it is cold.
Liver cells increase rate of metabolism during cold times and decrease rate of metabolism during hot times.
Skeletal muscles are spontaneously contracted during cold times to produce heat through muscle contrations and increased respiration.


Behavioural mechansims of endotherms

Move into the shade or hide in a burrow when they are too hot to get out of the sun.
Orientate body to increase/decrease surface area exposed to the sun during cold/hot envirnoments.
They remain inactivein hot climates but move around more in cold climates.


What part of the brain regulates blood temperature?

The thermoregulatory centre


What helps the thermoregulatory monitor temperature?

The peripheral temperature receptors in the skin which feeds information tot he thermoregulatory centre in the hypothalamus.


What is a polarised membrane?

A membrane that has a potential difference across it. This is the resting potential.



Refer to pages 12-15


Define depolaristion

The loss of polarisation across the membrane. It refers to the period when sodium ions are entering the cell making the inside less negative with respect to the outside.


Define generator potential

A small depolarisation caused by sodium ions entering the cell.


Define action potential

Achieved when the membrane is depolarised to a value of about +40 mV. It is an all or nothing response. In the events leading up to an action potential, the membrane depolarises and reaches a threshold level, then lots of sodium ions enter the axon and an action potential is reached.


Define the resting potential

The potential difference or voltage across the neurone cell membrane while the neurone is at rest. It is about -60 mV inside the cell compared with outside the cell. Other cells may also maintain a resting potential that might change under certain circumstances.


Define Voltage-gated channels

Channels in the cell membrane that allow the passage of charged particles or ions. they have a mechanism called a gate which can open and close the channel. In these channels the gates respond to changes in the potential difference across the membrane.


Define threshold potential

A potential difference across the membrane of about -50 mV. If the depolarisation of the membrane does not reach the threshold potential then no action potential is created. If the depolarisation reaches the threshold potential then an action potential is created.


Define Local Current

The movements of ions along the neurone. The flow of ions is caused by an increase in concentration at one point, which causes diffusion away from the region of higher concentration.


Define Saltatory Conduction

'Jumping Conduction'. It refers to the way that the action potential appears to jump from one node of Ranvier to the next.


Advantages of saltatory conduction

Transmission of the action potential is sped up.
It can conduct an action potential at up to 120 ms^-1


Define Neurotransmitter

A chemical that diffuses across the cleft of the synapse to transmit a signal to the postsynaptic neurone


Define Cholinergic synapses

Synapses that use acetylcholine as their transmitter substance.


Define the synaptic knob

A swelling at the end of the presynaptic neurone


Name the features of the synaptic knob

Many mitochondria to help active processes
Large amount of smooth endoplasmic reticulum
Vesicles containing acetycholine
Voltage gated calcium ion channels in the membrane



Refer to pages 18-19


Describe and explain the purpose of the sodium channels in the post synaptic membrane

They are specialised sodium channels that respond to the transmitter substance (acetycholine). 2 of the 5 polypeptides have a complimentary shape to the acetylcholine and so open up when they come into contact with it, allow the sodium ions to pass through and the impulse to be transmitted across the membrane.


List the sequence of events during transmission across a synapse

Refer to page 19


What is the function of acetylecholinerase

An enzyme in the synaptic cleft. It breaks down the transmitter substance acetylcholine


Define all or nothing

It refers to the fact that a neurone either conducts an action potential or it does not. All action potentials are of the same magnitude, +40 mV.


Define Summation

A term that refers to the way that several small potential changes can combine to produce one larger change in potential difference across the membrane


Define Hormone

Molecules that are released by endocrine glands directly into the blood. They act as messengers, carrying a signal from the endocrine gland to a specific target organ or tissue


Define Endocrine Gland

A gland that secretes hormones directly into the blood. Endocrine glands have no ducts


Define Exocrine Gland

A gland that secretes molecules into a duct that carries the molecules to where they are used


Define Target Cell

Cells that possess a specific receptor on their plasma membrane. The shape of the receptor is complementary to the shape of the hormone molecule. Many similar cells together form a tissue.


What is Adenyl Cyclase

An enzyme associated with the receptor for many hormones, including adrenaline. It is found on the inside of the cell surface membrane.


What is the difference between the first messenger and the second messenger?

The first messenger is the hormone that transmits aq signal around the body, whereas the second messenger is cAMP which transmitts the signal inside the cell.


What is an example of an exocrine gland?

The salavary glands


What is the difference between steroid and peptaide hormones?

Peptide hormones are derivatives of amino acids whereas steroid hormoes are usually 4 carbon rings attached to each other.
Peptide hormoes are not able to pass through the phospholipid bilayer (into the cell) whereas steroid hormones can.


How does adrenaline cause an effect inside the cell?

It is an amino acid derivative so cannot enter the cell.
It binds to a complimentary receptor on the outside of the cell which is associated with adenyl cyclase.
The binding causes the adenyl cyclase to produce cAMP, from ATP, which is able to cause the effect inside the cell.
Adrenaline is the first messenger, cAMP is the second messenger.


Name the effects of adrenaline in the body

Relax smooth muscle in bronchioles
Increase stroke volume of the heart
Increase heart rate
Cause general vasoconstriction to raise blood pressure
Stimulate conversion of glycogen to glucose
Dilate pupils
Increase mental awareness
Inhibit action of the gut
Cause body hair to erect


Where are how is adrenaline released?

The adrenal glands are located just above the kidneys.
The cells in the adrenal medulla release the hormone is reponse to stress, pain or shock.


What is the role of the adrenal cortex?

To release steroid hormones including:
-The Mineralocorticoids to help control concentrations of sodium and potassium
-The glucocoticoids to help control the metabolism of carbohydrates and proteins in the liver.


What is special about the functions of the pancreas?

It has exocrine and edocrine functions


Define the pancreatic duct

A tube that collects all the secretions from the exocrine cells in the pacreas and carries the fluid to the small intestine.


What are the Islets of Langerhans

Small patches of tissue in the pancreas that have an endocrine function


What are Alpha and Beta cells in the pacreas?

These cells are found in the islets of Langerhans
The alpha cells secrete the hormone glucagon whereas the beta cells secrete insulin.


What is, and what is the function of, insulin?

The hormone released from the beta cells in the islets of Langerhans which cause blood glucos levels to fall


What is, and what is the function of, glucagon?

Glucagon is released from the alpha cells int he islets of Langerhans and causes blood glucose levels the rise.


What is the exocrine function of the pancreas?

To release digestive enzymes, such as amylase, trypsinogen and lipase. The cells which release these are found surrounding tiny tubules which all eventualyl join up to make the pancreatic duct which carries the fluid to the small intestine.


How does the pancreatic fluid help neutralise the contents of the digestive system?

It contains sodium hydrogencarbonate which is alkaline, and so causes the pH to rise.


What are hepatocytes?

These are liver cells. They are specialised to perform a range of metabolic functions.


What are the target cells for insulin?

The hepatocytes (liver cells)


How does insulin cause blood glucose levels to fall?

Insulin binds to receptors on the hepatocytes.
This causes cAMP to be produced in the cell
The cAMP causes:
-More glucose channels to be placed on cell membrane so more glucose enters the cell,
The glucose in the cell is converted to glycogen for storage (by glycogenesis)
-More glucose converted to fats overall and used in respiration


Define Glycogenesis

The production of glycogen from glucose in the hepatocytes


How does glucagon cause a rise in blood glucose levels?

Glucagon binds to the hepatocytes
Glucagon causes:
-The conversion of glycogen to glucose (by glycogenolysis)
-The use of more fatty acids in respiration
-The production of glucose by conversion of amino acids and fats (gluconeogenesis)


Define Glycogenolysis

The conversion of glycogen to glucose in the hepatocytes


Define Gluconeogenesis

The conversion of amino acids and fats to glucose in the hepatocytes


Define Diabetes Mellitus

A disease in which blood glucose concentrations cannot be controlled effectively


Define Hyperglycemia

The state in which the blood glucose concetration is too high (HYPERglycemia)


Define Hypoglycemia

The state in which the blood glucose concentration is too low (HYPOglycemia)


What are genetically engineered bacteria and how are they useful?

Genetically Engineered bacteria are where the DNA has been altered. Bacteria can be used to produce human insulin by inderting that gene coding for insulin into the DNA od bacteria.


What are Stem Cells?

Unspecialised cells that have the potential to develop into any other type of cell.


What are the steps involved in a beta cell regarding the control of insulin production

-Potassium ion channels are intially open and the calcium ions are intially closed
-Potassium diffuses out of the cell to maintain a PD of -70 mV across the cell membrane
-Glucose diffuses into the cell when contrations are high enough
-This is metabolised quickly to produce ATP
-The ATP causes the potassium channels to close
-The cell now becomes less negative with respect to outside the cell
-This causes calcium channels to open
-The influx of calcium ions cause vesicles containing insulin to ove toward and fuse with the membrane, releasing the insulin.


What is type 1 diabetes?

This is often called juvenile-onset diabetes. This can be caused by the body attacking its own beta cells or can result from a viral attack. The body is no longer able to produce sufficient insulin and cnnot store excess glucose as glycogen


What is type 2 diabetes?

This is where the responsiveness to the insulin beig produced declines. This is thought to be because the number of receptors on the relevant cells decline. Certain factors cause early onset such as:
-High sugar diets
-Being of Asian or Afro-Caribbean origin (Genetics)
-Family History (Genetics)


Define Cell Metabolism

The result of all the chemical reactions taking place i the cytoplasm


Define Myogenic

Muscle tissue that can initiate its own contractions


What is the Biological Pacemaker and how does it work?

A region of tissue in the right atrium wall that can generate an impulse and initiates the contraction of the chambers. This is called the sinoatrial node.
It works by sending an electrical signal as a wave of excitation over the atrial walls, through the AVN (atrioventricular node) and down the Purkyne fibres to the ventricles


What does the cardiovascular centre do?

This is a specific region of the medulla oblongata that receives sensory inputs about levels of physical activity, blood carbon dioxide concentration and blood pressure. It sends nerve impulses to the SAN in the heart to alter the frequency of excitation waves.