Homeostasis and Equilibrium Flashcards
What is homeostasis?
It is the self regulated process by which a living organism maintains internal stability whilst adjusting to external conditions
What are examples of homeostasis?
Regulation of body temp
Balance between acidity and alkalines
What is negative feedback?
It is when some exrernal variable triggers a counteracting response by the body to maintain homeostasis. In essence, it reverses a derivation from the set point, thus maintaining body parameters within their normal range
What is an example of negative feedback?
In hot weather, sensors detect the heat and sends it to the brain –> sends signals to counteract this –> sweat increases, and you cool down as sweat evaporates –> lower temp
Another example is blood glucose levels, if they are too high the body releases chemicals such as insulin to assist in controlling it –> -ve feedback
What are the 3 main components to a negative feedback loop?
A sensor
A control centre
An effector
What is the function of the sensor in the negative feedback loop?
Also referred to as a receptor, it monitors a physiological value. This value is reported to the control centre
What is the function of the control centre in the negative feedback loop?
The control centre compares the value given by the sensor to the normal range. If the value deviates too much from the set point, the control centre activates an effector
What is the function of the effector in the negative feedback loop?
The effector is the component in a feedback system that causes a change to reverse the situation and return the value to the normal range
WHat is the process of the stimulus –> response in a negative feedback loop?
Stimulus –> sensor –> control –> Effector –> response
I.e.
Body temp exceeds 37 degrees –> nerve cells in skin and brain –. temp regulation in brain –> sweat gland throughout the body activated, and increased respiration to exhale heat from lungs 00> increased heat loss
What is positive feedback loop?
This is when instead of getting a counteracting response to some variable, the change is instead intensified
Here, a deviation from normal range results in more changes.
This is normal in the body, as long as there is a definite end point
What are 2 examples of positive feedback loops?
An example is seen following a pentrating wound, where the most immediate threat is excessive blood loss. This could lead to shut down of vital organs –> death. Thus, the body responds to this through releasing substances in the injured blood vessel wall that begins the process of blood clotting. As each step of clotting occurs, it stimulates more blood clotting substances –> accentuates process of clotting and seals off damaged areas –> continues on until fully repaired
Another example is seen during childbirth/child labour. Here, the head of the baby moves against the cervix –> nerve impulses from cervix transmitted to brain –> brain stimulates pituitary gland to secrete oxytocin –> oxytocin carried in bloodstream to uterus –> Oxytocin stimulates uterine contractions and passes baby towards cervix –» continues on and on (positive feedback loop)
What is the endocrine system?
It assists with homeostasis through utilising hormones to control and coordinate the body’s metabolism, energy level, growth, reproduction etc. It is responsible to make hormones and release them directly into the bloodstream, so that they can travel to a target tissue and / or organ across the body.
When the chemicals reach cells in our body, they tell those cells how to behave and act
WHat is endocrine?
An internal secretion that pertains to a gland that secretes directly into the bloodstream
What is the endocrine gland?
A ductless gland that produces internal secretion discharged into the blood or lymph, and then circulated to all parts of the body. These make the actual hormones
What are hormones?
Hormones are a chemical/organic regulatory molecule messenger made by endocrine cells. These hormones are secreted into the bloodstream and travel to various target organs on tissues where they extend their effect
They are critical in coordinating growth + development, metabolism, immune function etc.
They act as signalling molecules, transmitting info between cells and tissues to regulate certain physiological processes by transmitting signals like glucose metabolism
What is a receptor?
It is a molecule, such as proteins where a signal molecule/messenger can bind. We can find receptors on the surface of a cell membrane or in the cytoplasm/nucleus
What is the process of cell signalling? (3)
RECEPTION: Typically a signal molecule/ligand binds to a receptor. This receptor should have high specificity - only responds to that one ligand, and it should have high affinity with the ligand. It is the process by which a cell detects a signal in the environment.
TRANSDUCTION: Receptor gets activated by the binding, which means the receptor could change shape, or even invoke a whole series of molecules/proteins changing their conformation in something called a ‘signal transduction pathway’, which can amplify the original signal. The process of activating a series of proteins inside the cell from the cell membrane. It is also a series of events that converts the signal to something the target cell can respond to
CELLULAR RESPONSE: A response occurs in response to the transduction, such as transcribing a protein or DNA. This step is when the target cell responds to the signal.
Ligand means?
That it is the smaller molecule that bonds to a larger molecule
What are the 2 different types of hormones?
Water soluble hormones
Lipid soluble hormones.
What are the characteristics of a water soluble molecule. Examine the limitations of the structure, and the consequence on the signalling process
These are hydrophillic –> polar or charged. These are soluble in water.
However, because it is hydrophillic, they are repelled by the hydrophobic tails in the phospholipid bilayer. Basically, the cell membrane doesn’t allow for water soluble molecules to come in.
Thus, because it can’t go in, we need a method to still transfer the signal across the membrane, this can be achieved through a TRANS MEMBRANE RECEPTOR
What is a trans membrane receptor
These are reeptors that are embedded in the cell membrane. They act in cell signalling by receiving extracellular, water soluble hormones. This then binds to the cell surface receptors on the outside, which triggers an interceullar response
What is the first messenger?
This is the intial hormone that binds to the cell surface receptor, which triggers intracellular events leading to a cellular response.
This first messenger is typically an extracellular signalling molecule, because it only happens because it is a water soluble and can’t penetrate the membrane
What is the second messenger?
Second messengers are small molecules and ions that relay signals received by cell-surface receptors to effector proteins.
The primary function of a second messenger is to amplify the signal of a first messenger such as a hormone.
To be a second messenger, there are several characterisics it must have:
Low amounts in resting state
Regulated Synthesis
Regulated destruction
Acts through other proteins
What is a common example of a second messenger? That we study
cyclic AMP (cAMP)
What is a common example of a cell membrane receptor? That we study
G protein coupled receptors (GPCR)
Explain how water soluble hormones work, with reference to GPCR and cAMP.
The hormone comes and binds itself to the cell surface receptor (GPCR). This triggers the release of a G protein which bonds with an enzyme ‘adenylate cyclase’, and activates it.
This catalyses a reaction when ATP in the cell is converted into cAMP, which acts as a second messenger. The cAMP then acts as a catalyst for intracellular activity or biolofical effects in response to the info from the first messenger. cAMP is a common second messenger.
It could have effects such as:
Activiates proteins + enzymes
Inhibits proteins + enzymes
Altering gene expression etc.
What are lipid soluble hormones?
These are hydrophobic hormones, and they can cross the cell membrane easily. Thus, unlike water soluble hormones, they don’t need a cell surface receptor
Explain how a lipid soluble hormone works.
Their receptors are in the cytoplasm or nucleus. They are typically called ‘nuclear receptors’ . The binding of the hormone to the nucleus receptor forces ‘hormone reception complex’ which goes into the nucleus and binds with the DNA.
they DON’T need a second messenger, because they can just cross the bilayer
How do hormones allow for communication across cells?
Hormones released down bloodstream, and travel throughout the body, carrying info between cells to regulate physiological processes.
Each hormone is designed to interact with specific target cells that possess receptors for that particular hormone. These target cells can be locate d in distant organs or tissues. Thus, it allows for communication despite long distances
What are steroid hormones?
It is a steroid that acts as a hormone. They are cyclical chemical compounds made up of rings of carbon atoms that play an essential roles such as through looking at metabolism, immune response and reproductive. They are derived from cholestrol
