1. Hormones Flashcards
What are hormones?
Chemicals secreted by a group of cells that travel through the bloodstream to act on targets
Release hormones within the body
Endocrine glands
Use ducts to secrete fluids such as tears
Exocrine glands
First formal study of endocrinology
Arnold Berthold in 1849
Wanted to see what happens when he removes testes via castration in chickens
1st group: control
Grew up normally
Aggressive, mounted hens, normal crowing and vocalization
2nd group: testes removed
Grew up small
Don’t mount hens, aren’t aggressive, weak crowing
3rd group: testes extracted and re-placed into the abdominal cavity (are original nerve connections required?)
Grew up normally
Findings:
Something from the testes is necessary for typical development of male roosters in terms of behavior and physical appearance
Organizational vs. activational effects of hormones
Brain and body are organized by exposure to hormones early in life
Changes can be dramatic and long-lasting
Later in life, hormones activate behaviors
But their effects tend to be less dramatic and short-lived
Synaptic communication
Involves chemical release into the synaptic cleft for action on the postsynaptic membrane
Action is limited to postsynaptic membrane
Very fast; specific path
Endocrine communication
A hormone is released into the bloodstream and acts on appropriate receptors
They can act anywhere there’s blood
Slow; way more paths for it to take
Neuroendocrine communication
Neurons that release hormones into the blood
Synaptic transmission
Neuropeptides
Can act as neuromodulators and alter sensitivity to transmitters
Neuromodulators
Chemicals that fine-tune neuron activity over time
Act slowly and have long-lasting effects
Forms of chemical communication
Paracrine function
Autocrine function
Pheromone function
Allomone function
Paracrine function
The released chemical diffuses to nearby cells
Autocrine function
A released chemical signal can feed back and send a message to the cell that produced it
Similar to an autoreceptor (communicates retrogradely)
Pheromone function
Hormones can be used to communicate between individuals of the same species
Chemicals released into the environment
Allomone function
Chemicals released by one species to affect the behavior of another species
Ex: skunk spray
Ex: female spider releases sex hormone to attract male moths that she can eat
General principles of hormone action
- hormones act gradually
- hormones act by changing the probability or intensity of a behavior occurring
- hormones do not MAKE you do anything
- the relationship between behavior and hormones is reciprocal, or bidirectional (hormones can influence behavior, and behavior can influence hormones)
- some hormones can affect more than one target, and some targets are affected by more than one hormone
More principles of hormones
- hormones often have a pulsatile release pattern (bursts, pulses)
- hormones can interact with other hormones and change their effects
- hormones can only affect cells with a receptor for that hormone
Peptide hormone or protein hormone
a string of amino acids
Amine hormones
modified amino acids (monoamine hormones)
Steroid hormones
4 rings of carbon atoms and are derived from cholesterol
Some chemicals can act as both neurotransmitters and hormones
It depends on the cells that release them, and where they are released
Peptide and protein hormones
Peptides are smaller, protein are larger (50 amino acids is the cutoff)
The most common type of hormone found in mammals
Can be stored in vesicles
They’re large and can’t diffuse in and out of cells and pass through cell membranes, so they have to bind to receptors outside of the cells
Amine hormones
Derived from amino acids
They’re single amino acids
2 classes of these affect behavior:
Indoleamines
Catecholamines
Protein and amine hormone action
Bind to specific receptors embedded within the cell membrane and cause release of a second messenger, which brings about changes in cellular function
Action is relatively fast
Steroid hormones
Derived from cholesterol
Small; can pass through cell membrane
Steroid binds to receptor inside cell, then the combo binds to DNA
Slower; effects are longer-lasting
Never stored
Some require carrier proteins (cofactors)
Steroid hormones can act as a…
Transcription factor
Can change gene expression and protein production
Recent discovery about steroid hormones
Recently, they discovered that steroid hormones can have a non-genomic effect– a rapid, brief effect involving neutral membrane receptors
Ex: estradiol can change behavior in females in a fast-acting way that cannot be explained by the traditional genomic way steroids usually act
Neurosteroids
Steroids made in the brain, including testosterone and estrogens
Aromatase
Brain produces an enzyme, aromatase, that converts testosterone into estrogens
The ovaries contain a lot of aromatase → increased release of estrogens
Negative feedback
the output goes back and shuts things off, inhibiting further secretion
Positive feedback
the output of a chemical causes more of the next thing to come out
Autocrine negative feedback loop
Endocrine cells releasing a hormone whose presence feeds back on the endocrine cells
Target cell feedback
Hormone acts on its target cell and has a biological effect
Biological effect is detected by the endocrine gland and further release is inhibited
Hypothalamus
Involved in brain regulation
Directs hormone release from endocrine glands (one of which is the pituitary gland)
The brain detects the hormone’s effects and exerts negative feedback on the hypothalamus
2 main parts of pituitary gland
Posterior and anterior pituitary
Posterior pituitary
Secretes 2 principal hormones:
Oxytocin
Vasopressin
Neurons in the supraoptic nuclei and paraventricular nuclei of the hypothalamus synthesize these hormones
Hormones travel along the pituitary stalk and into the blood supply
Anterior pituitary
Produces lots of hormones
Hypothalamus releases releasing hormones that trigger tropic hormones
Axons from cells converge on the median eminence above the pituitary stalk
Hormones secreted into blood vessels
The hypothalamic neuroendocrine cells that synthesize releasing hormones are influenced by:
Circulating messages, such as other hormones, blood sugar, and immune system products
Synaptic inputs from other brain areas
Example of complex endocrine regulation
Hypothalamic-pituitary-thyroid axis
CRH (corticotropin releasing hormone)
Tropic hormone: ACTH (adrenocortico-tropic hormone)
Target: adrenal cortex
Hormones: corticosteroids
TRH (thyrotropin releasing hormone)
Tropic hormone: TSH (thyroid-stimulating hormone)
Target: thyroid
Hormones: thyroid hormones
GnRH (gonadotropin releasing hormone)
GnIH (gonadotropin inhibiting hormone)
Topic hormones: LH (leutinizing hormone) and FSH (follicle-stimulating hormone)
Target: testes or ovaries
Hormones: androgens (testosterone) OR estrogens + progestins
Prolactin releasing peptide
Prolactin inhibiting factor (may be dopamine)
Tropic hormone: prolactin
Target: mammary glands (milk production)
Somatocrinin (stimulates)
Somatostatin (inhibits)
Tropic hormone: GH (growth hormone)
Target: bones
Example of hormones affecting the body
Oxytocin stimulates uterine contractions and is involved in milk letdown (nursing)
Example of hormones affecting behavior
Oxytocin is released during nursing interactions and during orgasm to facilitate bonding; in female prairie voles, it promotes pair-bonds
Vasopressin facilitates the formation of pair-bonds in male prairie voles
