Endocrine Lecture 1 overview
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Is the Endocrine system ductless?
YES! The hormones secreted by any individual endocrine organ, go to interstitial space, then intravascular space and then circulated to target organ
What system does the endocrine system work closely with?
The neuro system. Coordinates and organizes various cellular activity (micro) & organ function (macro level) to maintain homeostasis. Often involves a lot of chemical messengers (NTs) Epi and Norepi are NT and hormone (they overlap)
What is a target organ?
the organ that shows some sort of biologic response when the hormone binds to a receptor on it.
Do endocrine hormones effect only one tissue?
- It depends.
- They only effect one type of receptor but that can be found in more than one tissue. Ex: growth hormone effects more than one organ/tissue but TSH will only effect the thyroid.
True or False. Most hormones are steroid hormones.
FALSE! Most are proteins/peptides
What is the definition of a hormone?
chemical product released from cell that exerts biologic effect.
According to Guyton: a protein has more than ___ amino acids in it's structure and a peptide hormone has less than ___
Give some examples of protein/peptide hormones
TSH, ACTH, Growth hormone, ADH
Are steroid hormones usually stored in the body?
Give some examples of steroid hormones
cortisol and aldosterone
Steroid hormones are derived from _____
Amino acid derivatives (amines) hormones are synthesized from __________
amino acid tyrosine
Name some amino acid derivative hormones
include catecholamines (norepi, epi, and dopamine) as well as the thyroid hormones.
*One of the reasons the thyroid storms looks like sympathetic discharge because the structure of the thyroid hormone is similar to epi
What are the three general classifications of hormones?
- Amino acid derivatives
What does neuroendocrine mean?
Refers to NTs where hormones secreted by neurons into the circulation and then the circulation takes that hormone to another part of body to have it’s effect. As we know NT can have local effect or go through circulation and travel to distant parts of body to have its effect
Paracrine vs autocrine
- Paracrine: hormone is released from 1 cell and it’s effect is produced in neighboring cell. (not traveling too far away) Might be just a different type of cell within the same organ or tissue but traveling by interstitial space to get there.
- Autocrine: hormone is having an effect on the same cell that released it.
What is a cytokine? Give an example
Peptides that are secreted by cells into the ECF.
Ex: interleukin (involved in the immune processes) Leptin is another example of a cytokine.
Onset of hormones can be immediate or delayed. Give examples of each
- Immediate: epi and norepi
- Delayed: thyroxine or growth hormone can take months to reach maximum effect.
How do peptides get transported compared to steroid/thyroid hormones
Peptides (and catecholamines)are water soluble so they are dissolved in the plasma and so they travel in the circulation. They’ll diffuse out of the capillaries once they get to target organ, go to interstitial tissue. And to target cells.
Steroid & thyroid hormones are bound to plasma proteins. 10% are unbound (active) free portion. Just like drugs, bound fraction of the hormone acts as a reservoir. Protein binding keeps hormone away from elimination but also slows the clearance from the plasma
Name 4 ways hormone clearance occurs
- Metabolic destruction by tissues
- Binding with tissues
- Excretion into bile by the liver
- Excretion into the urine by the kidneys
Most peptide and catecholamine hormones are degraded _______________________so they really only last for a short period of time
enzymatically and rapidly degraded by the kidneys and liver
How does protein binding delay clearance of hormones?
Unbound part gets eliminated and le chatelier's principle some more of the drug will get unbind and so the hormone effect will last several hours or days.
Receptors are large proteins with ____-_____ receptors per cell
What does down regulation occur from?
results from inactivation of some of the receptor molecules. Maybe some of the signaling mechanisms that occur
What causes up regulation?
happens when the stimulating hormone causes an increased # of receptors so the target becomes more sensitive
Name 3 areas the cell receptor may be located
- Cell membrane surface: protein/peptide/catechol
- Cytoplasm: steroid
- Cell nucleus: thyroid
True or False. Positive feedback is the most common.
FALSE. Negative feedback is the most common control mechanism. It prevents over activity
Broadly there are three general mechanism for control of hormone release. Name them
- Neuro control
- Hormonal control
- Nutrient or Ion regulation
Describe hormonal control
Means when one hormone effects the release of another. The "one" hormone is referred to as a tropic hormone.
Give an example of negative feedback
Tropic hormone is TSH, it’s made by anterior pituitary which will secrete TSH which causes thyroid hormone or thyroxine to be secreted by the thyroid gland. When the thyroid hormone is present that will inhibit the anterior pituitary from secreting more TSH.
Give an example of positive feedback
- With positive feedback the release of a hormone will stimulate it’s own release.
- Less common, surge of LH from the stimulating effect of Estrogen which acts on the ant. Pituitary, the LH will act on the ovaries to stimulate additional estrogen. Causes an increase in LH, keep increasing and increasing. When appropriate concentrations of LH is reached then negative feedback takes over.
Describe a nutrient or ion regulation control example
- Commonly refers to glucose. Plasma glucose levels and insulin secretion.
- Also Parathyroid hormone release according to the plasma Ca+ levels.
Can release of a hormone be caused by more than one control mechanism (ex: hormonal and neuro?)
YES! Insulin release can be regulated by plasma glucose levels and PNS and SNS stimulation.
What is frequently the mediator in neuro control of hormone release?
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