Flashcards in 13. Homeostasis and the Endocrine System Deck (36)
What is the purpose of a receptor in the control system? Name four types of receptors.
Detects the stimulus. Chemoreceptors, thermoreceptors, proprioceptors, nociceptors.
How does the receptor communicate with the control centre in a control system?
Via the nervous system (action potentials) or the endocrine system (hormones) in the afferent pathway.
What is the function of the effector in the control system? Name three examples.
It causes the change. Sweat glands, muscle and kidney.
What is negative feedback?
The response in a way to reverse the direction of change. It's the most common form of feedback.
What is positive feedback?
Response in a way as to change the variable even more in the direction of change. Only used when rapid change is desirable.
What is the biological clock in the brain?
A small group of neurones in a suprachiasmatic nucleus (cluster of neurones).
What are zeitgebers?
Cues from the environment that keep the body on a 24 hour cycle.
What can unsettle the body clock?
Jet lag, where several time zones are crossed so there is a mismatch between environmental cues and body clock.
What detects the osmotic pressures of blood plasma?
Osmoreceptors in the hypothalamus.
The number of osmoles per litre of solution.
The number of osmoles per kg of solution.
The a,punt of substance that dissolve in solution to form one mole of osmotically active particles.
What are the four main components of a control system?
The stimulus, receptor, control centre and effector.
How does ADH control raised blood osmolality?
Osmoreceptors in the hypothalamus detect the change and direct the posterior pituitary to secrete more ADH so there is more water reabsorption from urine into the blood in the collecting ducts of the kidney. This means a small volume of concentrated urine is passed, this along with the caused feeling of thirst return blood osmolality back to normal.
What is the endocrine system?
A collection of glands located throughout the body that produce the chemical signal, hormones, that travel in the bloodstream and cause an effect on other tissues.
What is the mechanism for autocrine hormonal communication?
Hormone signal acts back on the cell of origin.
What is the mechanism for paracrine hormonal communication?
Hormone signal carried to adjacent cells over a short distance via interstitial fluid.
What is the mechanism for endocrine hormonal communication?
Hormone signal released into bloodstream and carried to distant target cells.
What is the mechanism for neurocrine hormonal communication?
Hormone originates in neurone and after transport down axon, is released into bloodstream and carried to distant target cells.
What is the difference in speed of the endocrine system and the nervous system?
Endocrine is slow but nervous is fast.
What are the four classifications of hormones? Give details for each class.
Peptide/polypeptide - largest group, water soluble, short chain of amino acids.
Amino acid derivatives/ amines - synthesised form amino acids, adrenal medullary hormones are water soluble, thyroid hormones are lipid soluble.
Glycoproteins - largest protein molecules, made of subunits, carbohydrate side chain, water soluble
Steroids - derived from cholesterol, lipid soluble.
What are the roles of carrier proteins in hormone transport?
Increase the solubility of the hormone in plasma, increase the half life and readily accessible reserve.
What factors determine hormone levels in the blood?
Rate of production (most highly regulated), rate of delivery and rate of degradation.
What are the two major classes of receptors on the plasma membrane affected by water soluble hormones?
G protein coupled receptor and tyrosine kinase.
How do water soluble hormones bind to G protein coupled receptors?
There is dissociation of the G protein alpha subunit and activation of the effector protein. A second messenger is formed and the protein kinase is activated. There is phosphorylation of target proteins and this produces a cellular response.
How do water soluble proteins bind to the tyrosine kinase receptor?
Dimerisation, autophosphorylation of specific tyrosines, recruitment of adaptor proteins and signalling complex, activation of protein kinase, phosphorylation of target proteins and this causes a cellular response.
How do lipid soluble hormones work?
They pass through the lipid bilayer into the cell. Type I hormones bind to the cytoplasmic receptor and the complex enters the nucleus and binds to DNA. Type II hormones enters the nucleus and binds to pre-bound receptor on DNA, this relieves repression of gene transcription.
What is the hypothalamic pituitary axis a link between?
Endocrine and nervous system.
What are the two parts of the pituitary glands?
Anterior and posterior pituitary gland.