Unit 4: Section 1 - Communication and Homeostasis Flashcards
Give one example of a receptor that is a protein, and one that is a cell.
Protein - glucose receptors
Cell - photoreceptors
What is homeostasis?
The maintenance of a constant internal environment, despite a changing external environment.
What is negative feedback?
Bringing the level of something that is too high or too low, back to it’s normal range.
What does positive feedback do?
Amplify a change to further increase the level away from it’s normal range.
When might positive feedback be useful?
To clot blood after an injury…
- Platelets become activated and release a chemical, this triggers more platelets to be activated, and so on
- Platelets quickly form a blood clot at the injury site
- The process ends with negative feedback, when the body detects the blood clot has been formed
What are the 3 main types of neurones and what do they do?
1) Sensory neurones transmit nerve impulses from receptors to the CNS
2) Motor neurones transmit nerve impulses from the CNS to effectors
3) Relay neurones transmit nerve impulses between sensory neurones and motor neurones
What is the general structure of a neurone?
All neurones have a cell body with a nucleus
The cell body has extensions that connect to other neurones, dendrons and dendrites carry nerve impulses towards the cell body, and axons carry impulses away from the cell body.
What is the difference in the structure of a motor neurone, and the structure of a sensory neurone?
Sensory neurones have short dendrites, one long dendron, and one short axon. Motor neurones have many short dendrites and one long axon.
What is the resting potential?
-70mV
What does the sodium potassium pump do?
Uses active transport to move 3 sodium ions out of the neurone for every two potassium ions that enter
What does the potassium ion channel do?
Allows facilitated diffusion of potassium ions out of the neurone, down their concentration gradient.
Describe the sequence of events that happen in an action potential
1) Stimulus - This excites the neurone cell membrane, causing sodium ion channels to open. The membrane becomes more permeable to sodium, so sodium ions diffuse into the neurone down the sodium ion electrochemical gradient. This makes the inside of the neurone less negative
2) Depolarisation - If the potential difference reaches -55mV voltage gated sodium ion channels open, more sodium ions diffuse into the neurone
3) Re-polarisation - At a potential difference of +30mV the sodium ion channels close and voltage gated potassium ion channels open. The membrane is more permeable to potassium so potassium ions diffuse out of the neurone, this starts to get the membrane back to its resting potential.
4) Hyperpolarisation - Potassium ion channels are slow to close so there’s a slight overshoot where too many potassium ions diffuse out of the neurone. The potential difference becomes more negative than the resting potential
5) Resting potential - The ion channels are reset, the sodium potassium pump returns the membrane to its resting potential and maintains it until the membrane is excited again
what is summation?
When the effect of neurotransmitter released from many neurones is added together.
when are hormones secreted?
When an endocrine gland is stimulated
How are glands stimulated?
By a change in concentration of a specific substance and also by electrical impulses
what do the first and second messengers do?
First - carries the chemical message the first part of the way, from the endocrine gland to the receptor
Second - carries the chemical message the second part of the way, from the receptor to other parts of the cell
Explain the cAMP example
1) The hormone adrenaline is a first messenger
2) It binds to specific receptors in the cell membranes of many cells
3) When adrenaline binds it activates an enzyme called adenylate cyclase
4) This catalyses the production of the second messenger cAMP
5) cAMP activates a cascade
What does the medulla and the cortex of adrenal gland do?
Cortex - secretes steroid hormones eg cortisol
Medulla - secretes catecholamine hormones (modified amino acids)
eg adrenaline
How can mammals lower their body temperature?
1) Sweating
2) Hairs lie flat, erector pili muscles lie flat, trapping less air, skin is cooled
3) Vasodilation
How can mammals increase their body temperature?
1) Shivering
2) Hormones - increases metabolism, so more heat produced
3) Less sweat
4) Hairs stand up - erector pili muscles contract, trapping more air, skin is warmed
5) Vasoconstriction
What is the difference between thermoreceptors in the skin, and thermoreceptors in the hypothalamus?
Skin - detect external temperature
Hypothalamus - detect internal temperature
How does insulin lower blood glucose concentration?
1) Insulin binds to specific receptors on the cell membranes of liver and muscle cells
2) It increases the permeability of the membranes to glucose, so the cells take up more glucose
3) Insulin also actives enzymes that convert glucose into glycogen
4) Glycogen can be stored in the cytoplasm of cells as an energy source
5) The process of forming glycogen from glucose is called glycogenesis
6) Insulin also increases the rate of respiration of glucose
How does glucagon raise blood glucose concentration?
1) Glucagon binds to specific receptors on the cell membranes of liver cells
2) Glucagon activates enzymes that break down glycogen into glucose
3) This is called glycogenolyisis
4) Glucagon also promotes the formation of glucose from fatty acids and amino acids, this is called gluconeogenesis
5) Glucagon decreases the rate of respiration of glucose
How do beta cells secrete insulin?
1) When blood glucose level is high, more glucose enters the beta cells by facilitated diffusion
2) This increases the rate of respiration, producing more ATP
3) The rise in ATP triggers the potassium ion channels in the beta cell membrane to close
4) This means potassium ions can’t leave the cell, making the beta cell more positive
5) This triggers calcium ion channels in the membrane to open, so calcium ions diffuse into the cell
6) This causes the vesicles to fuse with the membrane, releasing insulin (this is known as exocytosis)
What is type 1 diabetes?
1) The beta cells in the islet of langerhans don’t produce any insulin
2) After eating, the blood glucose level rises and stays high, this is called hyperglycaemia, which can result in death if left untreated
3) Usually develops in children or young adults
What is type 2 diabetes?
1) Type 2 diabetes is usually acquired later in life, and is often linked with obesity
2) It occurs when the beta cells don’t produce enough insulin or when the body’s cells don’t respond properly to insulin. This is because the insulin receptors on their membranes don’t work properly so the cells don’t take up enough glucose.
What are the advantages of using GM bacteria to produce insulin?
1) Producing insulin using GM bacteria is cheaper than extracting it from animal pancreases
2) Larger quantities of insulin can be produced using GM bacteria
3) GM bacteria make human insulin which is more effective than using pig or cattle insulin and is less likely to trigger an allergic response
4) Some people prefer insulin from GM bacteria for ethical reasons
How can stem cells be used to cure diabetes?
1) Stem cells could be grown into beta cells
2) The beta cells would then be implanted into the pancreas of a person with type 1 diabetes
3) This means the person would be able to make insulin as normal
4) The treatment is still being developed, but if it’s effective it will cure people with type 1 diabetes
