hormones
chemicals, secreted by one cell group, that travel through the bloodstream to act on targets (receptors)
- released from endocrine glands from different organs/tissues
- regulated by feedback systems
- function: act as messengers that control and coordinate activities throughout body (e.g. regulate growth, metabolism, development)
+ exert effects on cells and tissues
1. promote cell proliferation, growth, and differentiation (e.g. sex hormones develop secondary sexual characteristics)
2. modulate cell activity (e.g. insulin regulates how body uses and stores glucose + fat)
glands: endocrine vs. exocrine
- endocrine: release hormones within body
- exocrine: use ducts to secrete fluids outside body (e.g. sweat and tears)
categories of chemical communications
- ENDOCRINE: hormone is released into the bloodstream to act on target tissues (e.g. testoterone)
- SYNAPTIC: involves chemical release and diffusion across a synapse (e.g. neurotransmitter - dopamine)
- autocrine: released chemical acts on the releasing cell
- paracrine: released chemical diffuses to nearby target cells (e.g. growth factors)
- PHEROMONE: pheromones are released into environment to facilitate communication between individuals of the same species (e.g. urine of dogs to mark territory)
- allomone: allomones are released by one species to affect behavior of another (e.g. skunk)
neural communication vs. hormonal communication
- both neurotransmitters and hormones are stored and secreted by neurons and endocrine glands, respectively
- neuroendocrine cells blend both mechanisms
- distance traveled varies for the two types of communication
1. NEURAL COMMUNICATION: - travels through synapse
- rapid speed
2. HORMONAL COMMUNICATION: - spreads throughout body through blood vessels, picked up by cells with proper receptors
- slower speed
example of function of hormone: castration
- castration: removal of gonads (usually testes) as juveniles -> behavioral and physiological change as adults
+ testes release a chemical (testosterone) into bloodstream that affects male behavior + body structure — must be present EARLY IN LIFE to have dramatic effects - chickens:
+ castrated: smaller, higher estrogen level
+ natural: bigger, aggressive, more interested in females - humans:
+ castration before puberty preserves higher voice, non-muscular build, and small genitals -> small or no sex drive (bc body stops production of sex hormones estrogen)
+ castration after puberty: reduce sex drive considerably
=> BRAIN AND BODY ARE ORGANIZED BY EXPOSURE TO HORMONES
general principles of hormone actions
- act in gradual, long lasting fashion (e.g. hormone therapy for transpeople is a long process)
- change the probability/intensity of a behavior, not turn on/off
- relationship between hormones and behaviors = reciprocal: hormones may influence behaviors and behaviors can induce hormonal activities
- only affect cells that have corresponding receptors which recognize them
- levels of hormones vary throughout the day bc hormonal system = controlled by Circadian clocks in the brain (e.g. melatonin is almost exclusively produced during evening - 6AM to 6PM)
+ testosterone varies with daily cycle, marital status, and fatherhood (to adapt with needs - seek females or rear children)
hormone types
- protein (peptide): string of amino acids
- amine (monoamine): modified amino acids
- 1 & 2 bind to specific receptors on the surface of a cell and cause release of a second messenger, which then bring about changes in cellular function
- act rapidly - steroid: 4 rings of carbon atoms - derivatives of cholesterol
- pass through cell membrane and bind to receptors inside cell
- act slowly, long-lasting effect
negative feedback system
output feeds back and inhibits further secretion of hormones
- autocrine response: endocrine gland releases hormones, which simultaneously affects target cells and returns to where they originate from
target cell feedback
hormones act on target cells and have a biological effect
- e.g. digestion
+ glucose from food enter bloodstream
+ pancreas releases insulin
+ insulin causes glucose to enter fat tissues
+ glucose induces biological responses
+ extra glucose induces negative feedback -> pancreas secretes less
endocrine system feedback
- involves hypothalamus, which can direct hormone release
- brain detects hormone’s effects and exerts negative feedback onto hypothalamus
- for more complex behaviors (e.g. fight or flight)
+ hypothalamus releases hormone to adrenal glands above the kidneys
+ adrenal gland releases epinephrine or adrenaline
+ hormones affect many target cells and trigger sympathetic nervous system
+ fight or flight response
+ negative feedback to hypothalamus
endocrine glands in brain: pituitary glands
- categories (separate functions)
1. anterior pituitary: - tropic hormones:
+ ACTH: controls production and rlease of adrenal cortex steroid hormones
+ TSH: increases thyroid hormone release
+ FSH: stimulates egg-containing follicles in females OR sperm production in males
+ LH: stimulates follicles to form the corpora lutea in females and testosterone production by the testes in males
+ prolactin: stimulates lactation in females and involved in parental behavior
+ growth hormone (GH): influences growth, mostly during sleep
2. posterior pituitary: - hypothalamus releases hormones -> posterior pituitary releases tropic hormones, which can also serve as neurotransmitters in hypothalamus
+ e.g. oxytocin - reproductive + parenting behaviors, uterine contraction, milk letdown reflect, social bonding)
+ e.g. argine vasopressin (AVP): increases blood pressure, inhibits urine formation, and influences pair-bonding social behavior (higher AVP level, more likely to be faithfful)
adrenal medulla
releases amine hormones, which bind with receptors on the surface of the cell
- epinephrine (adrenaline): increases blood circulation and heart rate, prepares muscles for action
- norepinephrine (noradrenaline): mobilize brain and body for action, especially during dangerous situations
adrenal cortex
secretes steroids, which bind with receptors inside the cell, called “adrenocorticoids” or “adrenal steroids”
- subgroup: glucocorticoids
+ cortisol: increases glucose in blood & breaks down fat & protein - suppresses immune system
hypothalamus-pituitary-adrenal (HPA) axis
main pathway to deal with stress, default response
- stress -> hypothalamus -> CRF (release corticotrophin) -> anterior pituitary -> ACTH (release adrenocorticotrophin hormone) -> adrenal glands -> cortisol -> gluconeogenesis (new glucose for energy production and use)
- cortisol exerts a negative feedback on the hypothalamus and anterior pituitary to turn off its release when the stress is dealt with
sex steroids
- production: at gonads - ovaries and testes and brain sometimes
+ hypothalamus controls gonadal hormone production by releasing gonadotropin releasing hormone (GnRH) -> stimulates anterior pituitary to release FSH or LH
+ FSH: regulates sperm production
+ LH: regulares testes to produce and secrete testosterones, which is an androgen (male hormone) - NO steroid hormone is found exclusively in one sex
+ testosterones get converted by enzyme called aromatase into estradiol (female hormone)
+ ovaries = loaded with aromatase -> females have more estradiol, testes have far less -> less/no estrogen produced - steroids levels are diffferent based on social status
steroids and social status: baboon example
- alpha males have greatest productive success (more mates and better access to resources) BUT also highest level of stress (shown through levels of testosterone and cortisol)
+ stress is highest when: hierarchy is unstable with frequent challengers, dominance through fight and intimidation, resource inequity, and breeding cycle
+ beta males are less stressed, because they don’t have to perform energetically consuming activities like maintaining dominance rank and protecting consorts - females have hierarchy also but don’t experience hormonal adjustment, because they compromise & attain dominance via inheritance + negotiation; males do it via aggression
hormonal and neural systems
- exert reciprocal influences on each other: experience affects secretion, hormones affect behavior, and behavior affects future experiences
- integrated responses
- humans:
+ low socioeconomic status correlates with worse health - chronic psychological stress of feeling poor
+ hierarchy is less strictly defined
+ stress is reduced via social bonding
