Endocrine systems Flashcards
Function of endocrine systems
Regulation of homeostasis by slow, long-lasting chemical signalling. Hormones secreted from glands act on target organs via circulatory system and often requires activation by the nervous system
What are the 2 mechanisms for glands?
Endocrine (internal) or exocrine (external)
What is the hypothalamus?
Brain area with various physiological functions important for maintaining homeostasis by linking nervous and endocrine systems
Function of hypothalamus
Completes homeostasis
Gland
Produces hormones
Hormones
Have effects on different targets and can be secreted at different rates
A target
Acted upon by different hormones
Chemical
Acts as a hormone or neurotransmitter
Tropic vs Non-tropic hormone
Tropic: regulates production/secretion of another hormone in a gland
Non-tropic: has a direct effect on target organ
Name 3 different hormones
Peptides, amines and steroids
Peptides
Preprohormone precursor is translated and packaged into vesicles to be stored in cytosol. These vesicles fuse with plasma membrane and release the hormone into the blood
Amines
Synthesized from amino acid tyrosine by enzymes, packaged into secretory vesicles and stored until release where vesicles fuse with plasma membrane and released into blood
Steroids
Synthesized from lipid cholesterol by enzymes, diffuse across the plasma membrane into blood when synthesizes and can be converted into different hormones once in blood
Water-soluble vs Lipid soluble hormones
Water-soluble: free in blood or bind to plasma proteins and include peptides and some amines
Lipid-soluble: bound to plasma proteins and include steroids and some amines.
What are the 2 hormone receptors?
Membrane and internal
Membrane receptors
Hormone binds to receptor on outside of plasma membrane which induces enzyme activation and change in protein synthesis
Internal receptors
Free hormone diffuses across plasma membrane into cell, hormone binds to internal receptor in cytosol. Hormone-receptor complex induces response by binding to DNA to change protein synthesis
Hormone regulation
Depends on the solubility of the hormone and the nature of response induced by the hormone. Hormones secreted into circulation become diluted as only low concentration is needed for an effect on target
Neuroendocrine reflexes
Produce sudden increase in hormone secretion in response to a stimulus detected by nervous system and can be internal or external
Where are hormones inactivated?
Liver, kidney, blood and cells
Thyroid hormone
Becomes activated after metabolism
How can downregulation help with hormone response?
Decrease in receptors helps to prevent too much response if hormone levels are too high
Hormone permissiveness
For a hormone to work another hormone must be present
Hormone synergism
Combined effect of hormones is more than their separate effects
Hormone antagonism
One hormone reduces levels of receptor for another hormone
How are endocrine disorders caused?
Due to abnormal hormone secretion or abnormal response to hormone with normal hormone levels
What are the 2 types of endocrine disorders?
Hyposecretion and hypersecretion
Hyposecretion
Decrease in secretion of a hormone by a gland or of a tropic hormone
Hypersecretion
Increase in secretion of a hormone by a gland or of a tropic hormone
What are endocrine disrupting chemicals?
Chemicals made by humans in sewage and waste which effects gonadal hormones directly
Biological rhythms
Regular variations in physiology and behaviour which oscillate which can be classified as internal or external
Cortisol vs Corticosterone
Cortisol: hormones peak in the day
Corticosterone: hormones peak in the evening
Biological clocks
Maintain endogenous rhythms independently by setting patterns and getting used to changes in functions and day lengths
What is the Zeitgeber?
External cues which set biological rhythms
What is the suprachiasmatic nucleus?
Part of the hypothalamus where the rhythm of neuronal activity is maintained by clock genes
The retina
Light sets the circadian rhythm to 24 hours, activates photoreceptors which activate clock genes in neurones in the suprachiasmatic nucleus
Pineal gland
Receives light input indirectly, controls rhythmic production and secretion of melatonin hormone with high levels at night and low levels in day