Flashcards in Animal Physiology-Endocrinology Deck (43)
What is a hormone?
A signalling molecule that travels through the circulation to affect the actions of a target tissue
Where does the 'endocrine' type of hormone come from, travel via and what does it target?
Produced by the endocrine gland, travels via blood to distant targets/tissue
Where does the 'neuro-endocrine' type of hormone come from, travel via and what does it target?
Produced by nervous tissue, travels via blood and targets distant tissue
Where does the 'neurocrine' type of hormone come from, travel via and what does it target?
Produced by neurons, travels via synapses and targets neighbouring cells
Where does the 'paracrine' type of hormone come from, travel via and what does it target?
Produced by cells, travels via interstitial fluid and affects neighbouring cells
Where does the 'autocrine' type of hormone come from, travel via and what does it target?
Produced by cells, travels via cellular fluid and affects itself/same cell
Where does the 'pheromone' type of hormone come from, travel via and what does it target?
Produced by animals, travels via external environment and affects other animals
Are hormones always present?
Yes, they are always present in low concentrations. The change in the concentration causes the effect. This is regulated by feedback
Describe these hormone interactions in the same tissue:
Additive: A causes an effect, B causes an effect. This interaction occurs when both effects are simply added together
Synergistic: A causes an effect, B causes an effect. Both together lead to a bigger effect than if they were just added together
Non-additive: A causes an effect, B causes an effect. Both together only lead to the maximum of one of the effects
Permissive: A causes an effect but B does not cause an effect. Together, a very large effect is caused
If a hormone is lipophilic (fat loving), what properties do they display/ what are they able to do?
Lipophilic hormones such as steroids can readily go through cell membranes which are essentially made of fat
If a hormone is hydrophilic (water loving), what are they unable to do?
They are not able to enter cells on their own. e.g proteins/polypeptides/glycoproteins (can act as hormones)
Amines are amino acid derivatives (a class of hormone) from which two amino acids?
Tryptophan and tyrosine. Side note: amines are hydrophilic
Fatty acid derivatives are a class of hormone. They are usually derived from arachidonic acid and are lipophilic. Where are they produced and what sort of effects do they have?
Produced in the cell membrane and produce autocrine and paracrine effects (Self and neighbouring)
What sort of steroid hormones result from stepwise conversion of cholesterol?
Estradiol, testosterone, progesterone, cortisol and aldosterone (vitamin D and A are also produced from cholesterol)
Where are steroids produced and where does that cholesterol come from?
Steroids are produced by the gonad and adrenal glands; more specifically on the smooth ER and on the mitochondria in the adrenal glands. The cholesterol comes from LDLs in plasma (so the diet) but it is important to note that cholesterol can be synthesised de novo intracellularly if there is inadequate cholesterol in the diet
Can steroids be stored? If so what is the storage form?
Not really, they are immediately released into the blood stream. However, in the blood stream they are bound to carrier proteins and are inactive (so this is the storage form)
Which form of steroid hormone can stimulate a cell, be degraded and contributes to the feedback of the concentrations?
The active form (5-10% of all the steroid hormone in the body) which is unbound. The combination of synthesis and level of binding of the hormone is what regulates how much is circulating in the blood
Specificity in hormones is very important. Slight changes in structure can confer massive changes in response. Name two polypeptide/protein hormones which are very similar in structure and can sometimes have a residual effect on one another.
Prolactin and growth hormone.
It is possible to make cows lactate by giving them growth hormone
Are polypeptide/protein hormones synthesised in their final form?
No, they are synthesised as prehormones + signal peptides. Some have multiple units, some are glycosylated and some are synthesised as preprohormones
Can protein hormones be stored?
Yes, in secretory vesicles. They are exocytosed during secretion. This stored hormone makes the response faster than steroid hormones
Secretion of protein hormones is regulated by what?
Trophic hormones e.g GH---->IGF-1
Nervous stimuli e.g Absence of light ----> Melatonin
Levels of metabolites e.g Glucose----> Insulin
All except from IGF-1 circulate freely
Metabolism of hormones varies depending on how long term (e.g during pregnancy) or short term (e.g calcium levels). Half-life is an important concept in this. What is meant by a hormone's half life?
The time it takes for half the level of that hormone to disappear after it is inactivated
How are peptide hormones broken down?
By peptidases, deamination and reduction of disulphide bonds. This is done in lysosomes of target tissue and the liver and kidneys
How are steroid hormones broken down?
By mixed function oxidases in the liver. They are excreted via urine or bile salts
What does the rate of response depend on?
-The amount of active hormone arriving at the tissue (form)
-Rate of release of the hormone
-Rate of metabolism
-Affinity and number of receptors on the tissue
What sort of receptors are needed for hydrophilic hormones such as proteins? What is the general mechanism of such a receptor?
Cell surface receptors;
Hormone binds to receptor, activates protein kinase (often via 2nd messenger), phosphorylates specific intracellular protein, altered protein activity, response
Rapid response- uses existing proteins
What sort of receptors are needed for lipophilic hormones such as steroid and thyroid hormones? What is the general mechanism of such a receptor?
Nuclear/ intracellular receptors-acts as transcription factors;
Hormone travels through membrane, binds to receptor, translocation to nucleus, formation of a dimer hormone-receptor complex interacts with 5' end of gene, intiates transcription, response
Slow response (hours)- has to create proteins
Name the 3 most important endocrine glands found in the brain
Pineal glands, pituitary and the hypothalamus (all placed in center of brain for max. protection)
Where is the hypothalamus located in the brain and why is it the major integration centre of the brain?
The hypothalamus is located just below the 3rd ventricle, above the median eminence. It receives signals from all parts of the body and regulates most of the endocrine system (and autonomous system)
It has the suprachiasmatic nucleus located inside
It also controls hormone release from pituitary and pineal glands