Endocrine System Flashcards
Diagram showing places in body that endocrine system is involved
Chemical groupings of hormones
Diagram showing how peptide hormones work
- Peptides are made through transcription and translation and packaged in vesicles and then they get released
- Usually, what comes out of transcription and translation is a longer peptide, along the way it gets cleaved into shorter segments, and eventually, you’ll get the activated peptide at the end (important in digestive enzymes)
Chemical structure of thyroid hormones
- Tyrosine is the amino acid that’s the beginning point for a lot of important hormones like norepinephrine and epinephrine
- It is also the source for T3 and T4 - the thyroid hormones. These have a profound impact on many cells throughout the body and adjust your basal metabolic rate.
- T3 and T4 are lipophilic, meaning that they are freely permeable through cell membranes
Diagram showing how cholesterol is the basis for all steroid hormones
- Cholesterol is lipid-soluble
- Cholesterol is put through a series of enzymatic steps to come up with all different types of steroid hormones (e.g. aldosterone and cortisol)
Diagram showing what hormones come from cholesterol
- Every arrow is an enzyme
- It takes a number of enzymes to get to estradiol and testosterone, and there’s one enzyme that turns testosterone into estradiol
Receptors for hormones can be in the ___ or ___
Cytosol or nucleus
Diagram explaining how steroid hormones work
- Most hydrophobic steroids are bound to plasma protein carriers. Only unbound hormones can diffuse into the cell.
- Steroid hormone receptors are in the cytoplasm or nucleus.
- The receptor-hormone complex binds to DNA and activates or represses one or more genes.
- Activated genes create new mRNA that moves back to the cytoplasm.
- Translation produces new proteins for cell processes.
- Some steroid hormones also bind to membrane receptors that use second messenger systems to create rapid cellular responses.
Diagram of pituitary gland
Posterior pituitary
- There are neurons in the hypothalamus and the pituitary dangles from the hypothalamus.
- Those axons come down and instead of releasing them into synapses, they release their chemical messengers into a capillary bed in the posterior pituitary, where it’s picked up and circulated throughout the body.
- This small number of neurons releases a pretty small large number of signaling molecules because they’re going to be diluted in the total fluid compartment that is extracellular fluid- blood plasma, interstitial fluid.
- So you need quite a few numbers of signaling molecules to reach an effecting concentration, (because extracellular fluid is in a high volume) such that receptors will find it, bind it, and cause a response.
Anterior pituitary
- The hypothalamus releases tiny amounts of releasing factor (signaling molecules) that only have to increase the concentration of a very small volume of extracellular fluid in the anterior pituitary.
- The releasing factors bind to receptors on the cells that are a true gland, and when they bind, the cells of the glands release large amounts of molecules that will go out and be diluted in all the extracellular fluid of the body, and reach a concentration that’s high enough so that receptors recognize that they’re there.
What hormones does the posterior pituitary release?
Oxytocin
- Stimulates contraction of uterus
- Stimulates milk let down
- Involved in maternal bonding with infant?
Vasopressin (ADH)
- Reabsorbtion of water in kidney
- Vasoconstriction
Diagram showing hormone released by the anterior pituitary
Feedback loop showing the control of hormone secretion
HPA Axis (hypothalamic, pituitary, adrenal)
Cortisol typically peaks (morning) and troughs (evening) throughout the day. Chronic activation through chronic stress can lead to chronically high levels of Cortisol.