Psych 230 Exam 2

Hormones

Chemicals, secreted by a group of cells (i.e., gland), that travel through the bloodstream to act on targets

Endocrine Glands vs. Exocrine Glands

Endocrine Glands: Release hormones within the body

Exocrine Glands: Use ducts to secrete fluids such as tears and sweat outside the body

Endocrinology

The study of endocrine glands and their associated hormones

Ectocrine

A chemical substance released by an organism into the external environment that influence the behavior, growth, or development of other organisms (either of the same or different species)

1st Formal Experiment of Endocrinology; COnducted by Arnold Berthold in 1849

Essentially, his study used roosters to figure out how the testes influence physical traits and behavior.

Berthold divided six young male chickens into three groups:

• Group 1 (Undisturbed): No removal

  • Chickens had large red wattles and cockscombs; would mount and mate with hens readily; would fight one another and crow loudly

• Group 2 (Castration): He removed the testes completely

  • These chickens developed small cockscombs and wattles; weakly crowed; and showed no interest in hens or fighting other males

• Group 3 (Castration + Re-implantation): He removed the testes and immediately transplanted them back into the chicken’s own abdominal cavity, but as a different, disconnected site

  • Also was another group where testes were removed and transplanted into the abdominal cavity of different castrated chicken

  • Both of these groups developed normally into full roosters

Upon later dissection of the birds, Berthold discovered that the transplanted testes had reattached to the intestines and developed a completely new network of blood vessels, but they had no nerve connections to the rest of the body

• Because the transplanted organs worked without any connection to the nervous system, Berthold concluded that the testes must release a “secretory blood-borne product” directly into the bloodstream that acts on the entire organism

  • He didn’t isolate the chemical itself, but his work laid the foundational work for the eventual discovery of testosterone

Synaptic Communication

Involves chemical release into the synaptic cleft for action of the postsynaptic membrane

Endocrine Communication

A hormone is released into the bloodstream to act on target tissues

Neuroendocrine/ Neurosecretory Cells

Neurons that release hormones into the blood

Synaptic vs. Endocrine Communication

Synaptic Communication

• Travels only across a synaptic cleft to act on receptor

• Signal travels along a laid path (circuit)

• Very fast

Endocrine Communication

• Spreads anywhere throughout the body if there is blood supply; can act on cells with the appropriate receptor

• Relatively slow

Paracrine Function

The released chemical diffuses to nearby target cells (ex; synaptic transmission)

Autocrine Function

A released chemical acts on the releasing cell (ex; autoreceptors on neurons)

Pheromone Function

Hormones can be used to communicate between individuals of the same species; pheromones are released into the environment

Allomone Function

Allomones are chemicals released by one species to affect the behavior of different species

How do Hormones Act?

Hormones act by changing the probability or intensity of a behavior; Hormones don’t make you do anything

Reciprocal/ Bidirectional Relationship

• Hormones change behavior AND behavior changes hormones

Principles of Hormone Action

• A hormone may have multiple effects, and one behavior can be affected by several hormones

• Hormones often act in a pulsatile secretion pattern

• Hormones can interact with other hormones and change their effects

• Hormones can only affect cells with a receptor for that hormone

Multiplicity of Hormone Action

• Some hormones affect more than one target

• Some targets are affected by more than one hormone

Peptide Hormone (or Protein Hormone)

• Made up a string of amino acids

• Peptide hormones: only a few amino acids in lengths

• Protein hormones: larger ones (>50 amino acids)

• Can be stored within the cell (in vesicles)

• Large (can’t pass through cell membranes)

• Ex; oxytocin, insulin, leptin

Amine Hormones

• Derived from/modified amino acids, called monoamine hormones

• Two classes of these hormones affect behavior:

  • Indoleamines (ex; serotonin)

  • Catecholamines (epinephrine, dopamine)

• Thyroid hormones are also monomines, but they don’t affect behavior

Protein and Amine Hormone Action

• Protein and amine hormones bind to specific receptors embedded within the cell membrane and cause release of a second messenger, which brings about changes in cellular function

• This action is relatively fast (effects on order of ms to min)

Steroid Hormones

• Derived from cholesterol

• Most come from the adrenal glands and gonads

• Small and lipophilic (passes through cell membrane)

• Never stored

• Some require carrier proteins, or cofactors

• Ex; estrogens, androgens

Steroid Hormone Action

• Steroid hormones pass through the cell membrane and bind to receptors inside the cell

• The steroid-receptor complex binds to DNA in the nucleus and acts as a transcription factor, controlling gene expression and protein production -hence, effects are longer lasting

• This is relatively slow (effects usually on order of hours to days)

• Called: Genomic Action

• Some steroids can have alternative actions, as well:

  • Estradiol can have rapid, brief effect involving neuronal membrane receptors; this is called nongenomic action

• Neurosteroids: steroids made in the brain, including testosterone and estrogens

• Many steroid hormones are made by combining an enzyme with a different hormone

  • For example, aromatase is an enzyme that can convert testosterone into estrogens inside a cell (androgens like testosterone into estrogens like estradiol)

Some chemicals can act as both neurotransmitters AND hormones

• Depends on the cells that release them, and where they are released

• Ex; Serotonin

Feedback Systems

• Hormones are regulated by feedback systems

  • Negative Feedback: output feeds back and inhibits further secretion

    • Much more common in terms of hormone regulation

  • Positive Feedback: output feeds back and increases further secretion

Autocrine Negative Feedback Loops

Involves endocrine cells releasing a hormone whose presence feeds back on the endocrine cells

Target Cell Feedback

The hormone acts on its target cells and has a biological effect

• The biological effect is detected by the endocrine gland and further release is inhibited

Brain and Pituitary Regulation

• A more complex endocrine system involved the brain, usually the hypothalamus

• First, the hypothalamus uses “releasing hormones” to act on the anterior pituitary

• Then the pituitary released tropic hormones that affect other endocrine cells

• Negative feedback from the endocrine cells goes to both the pituitary and the hypothalamus

Hypothalamic-Pituitary Interactions

• 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

• One primary mechanism of hypothalamic interaction is through the pituitary gland

• The pituitary gland releases hormones, and has two main but separate parts:

  • Posterior pituitary

  • Anterior pituitary

• The way in which the hypothalamus interacts with these parts of the pituitary is different

Posterior Pituitary

• Secretes two principal hormones:

  • Oxytocin

  • Vasopressin

• Neurons in the supraoptic nuclei and paraventricular nuclei of the hypothalamus synthesize these hormones

• The hormones travel along the pituitary stalk and into the blood supply in the posterior pituitary

• Because there are released into the blood supply of the posterior pituitary, they are called “posterior pituitary hormones”

Anterior Pituitary

• The hypothalamus communicates with the anterior pituitary in a different way, requiring additional steps

• Some hypothalamic neuroendocrine cells synthesize releasing hormones

• Axons from these cells coverage on the median eminence, above the pituitary stalk

• Releasing hormones are secreted into blood vessels called the hypophyseal portal system, and are carried to the anterior pituitary

• The releasing hormones stimulate specific cells in anterior pituitary to release tropic hormones into general circulation, where they’ll travel through the body to their targets

• How will the hormone know where to have action?

  • It’s looking for the correct receptor

Hormones can affect both Physiology as well as Behavior

• Physiology: Oxytocin stimulates uterine contractions and is involved in milk letdown (nursing)

• 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

Secretion of the Anterior Pituitary