lecture 4 homeostasis and signalling feedback loops Flashcards
-Understand the role of feedback loops in maintaining homeostasis (positive and negative) -Describe how cells/tissues/organs communicate with themselves and the outside world -Identify the major intracellular cells, how they are generated and what they do -Appreciate the role of pituary gland and pituitary hormones in regulating different organs (39 cards)
what is homeostasis
state of balance among all the body systems to allow them to function and survive
how do we maintain homeostasis in the body
we have mechanisms to counteract these changes (negative feedback loop). this is based on a set point (37.4 degrees in humans). there is an upper and lower limit we can survive but these kick off the negative feedback loops to maintain homeostasis.
negative vs positive feedback loops
negative: counteract changes fro meet points (body temp, blood glucose, moving it back to equilibrium
positive feedback: amplifies initial stimuli to move systems further away from its set point
endocrine system vs nervous system
nervous system: sends very fact electric messages to our body (neurons)
endocrine system: slower acting chemical based (hormones to the bloodstream) messaging system to maintain homeostasis
what is the endocrine system.
variety of organs that release hormones (chemical organs messenger made by endocrine cells) to our bloodstream that arrive at various cells in the body to respond to a change.
parts of the endocrine
endocrine: a hormone secreted by an endocrine gland that gets secreted to the bloodstream
endocrine gland: ductless gland that produces hormones discharged into the blood
exocrine: external secretion via ducts (tube) to epithelial surface
parts of the endocrine system
-brain (hypothalamus, pituitary gland and pineal gland)
-pancreas
- thymus
- adrenal glands
- thyroid
-ovaries and testes
what does the Brain do as part of the endocrine system
the hypothalamus secretes hormones while the posterior pituitary gland holds on to them and secretes them (oxtocin and antidiuretic hormone), the anterior pituitary gland can make hormones like prolactin, FSH, LH and ACTH, the pineal gland can’t make hormones but secreted melatonin
what does the pancreas do as part of the endocrine system
it releases insulin and glucagon to control blood glucose levels
adrenal glands as part of the endocrine system
Adrenal medulla- epineprine and norenephrine (body responses like fight or flight respons) and adrenal cortex- glucocorticoids like cortisol (increase blood glucose levels, plays a role in stress and inflammation and mineralocorticoids- aldosterone for reabsorption of sodium and excretion of potassium.
what are hormones and how does it help with homeostasis
hormones are proteins that are known as the primary signal, coding how the target cell will function. they bind to receptors of the target cell from the endocrine gland. eg. glucagon from pancreas to two to liver.
properties of a receptor
- high affinity so the ca be lower concentration of. hormone to stimulate it
- high specificity for the ligand
- have high specific distribution on the body- determine how the hormone is going to influence an organ. this means that organ need to have the receptor
- hormones target cells/organs expressing the specific receptor
how do we achieve specificity of the affect of a particular hormone targeting an organ
the target cell or organ needs to have a receptor so the hormone can pass through other organs that don’t have it.
how does the hormone impact the cell
the hormone coming from the extracellular space released by its endocrine gland attaches to the receptor of the cell in the plasma membrane where intracellular processes occur until a change is achieved.
what happens to the cell once it has been stimulated by the hormone
this stimulation leads to a cell response such as secretion, contraction, moving, divide, die ,survive, catabolic, etc
water soluble hormones eg. insulin
as insulin is a peptide and can’t cross the membrane on its own, it binds to a receptor (alpha unit) which sits outside the cell, which will change the confirmation of the cell, and activate the tyrosine kinase domain- enzyme that cause phosphorylation of another protein to activate it.
phosphorylation, how it works and what it does
phosphorylation is the addition of a phosphate group to a molecule. this occurs by adding a phosphate group by kinase. it takes a phosphate from the ATP (hydrolysed- break down chemical reaction with water) . this an happen very quickly and reverse very quickly too. as phosphates are negatively charged, phosphorylation of a protein alters its charge, altering its conformation and functional activity, it basically activates the protein.
explain how growth factors is an example of direct phosphorylation
timulation of growth factor
Tyrosine kinase activity causes phosphorylation of another protein
Protein phosphorylation cascade
Protein is taken to the nucleus of the cell
Transcription factor is activated by the protein and cause the gene to be activated meaning the RNA is transcribed from DNA where transcription then occurs.
what is a role of a kinase
kinase are enzymes that cause cell phosphorylation, essentially changing the activity of the cell
what are the two types of signalling
- direct phosphorylation
- G protein coupled receptors (second messengers)
what are second messengers
second messengers cause the production of other molecules like cAMP that lead to production of second messenger kinase ad then same process to signal the cell. unlike primary messengers where a hormone responds to its own receptor directly.
second messenger molecules
- the presence of the molecule cAMP is the new signal. they act as amplifiers. -amlify the response
- synthesised or released from storage or an inactive version of a molecule
- act as small ligands inside the cell.
- they are made and released by effector proteins
properties of a second messenger
- low amounts in resting state
- regulated synthesis
- regulate destruction
- activate other proteins to generate a response
how is the cyclic amp made
made by the enzyme Adenyl cyclace. the ATP molecule which has the adenosine and three phosphates, the adenyl cyclase takes two of the phosphates out making it a monophosphate, and cause cyclisation (combine) of the phosphate sugar base of the adenosine. it goes from one attachment to the adenosine to two. the product is cyclic AMP.
