PSYCH 360 - Quiz 5

Hormones

Chemicals secreted by one cell group that travel through the bloodstream to act on targets.

Endocrine glands

Glands that release hormones within the body.

Exocrine glands

Glands that use ducts to secrete fluids such as tears and sweat outside the body.

Major Endocrine Glands and Their Functions

Major Endocrine Gland and Their Hormones

Berthold’s experiment on testes

Demonstrated that testes release a chemical into the bloodstream (a hormone) that affects male behavior and body structure, proving this via castration and reimplantation.

Endocrine communication

A form of chemical communication where a hormone is released into the bloodstream to act on target tissues.

Synaptic communication (neurocrine function)

Involves chemical release and diffusion across a synapse.

Endocrine vs. Synaptic Communication

Autocrine communication

A released chemical acts on the releasing cell itself.

Paracrine communication

The released chemical diffuses to nearby target cells.

Pheromone communication

Hormones used to communicate between individuals of the same species by being released into the environment.

Allomone communication

Chemicals released by one species to affect the behavior of another species.

General principles of hormone actions

Hormones act gradually, change behavior probability/intensity, have a reciprocal relationship with behavior, have multiple effects, show pulsatile secretion, follow circadian rhythms, interact with other hormones, share similar structures across species, and only affect cells with specific receptor proteins.

Neuroendocrine cells

Neurons that blend neuronal and endocrine functions by releasing hormones into the blood.

Neuropeptides

Peptides used by neurons that can act as neuromodulators to alter sensitivity to transmitters.

Protein hormone (or peptide hormone)

A chemical structure of hormones consisting of a string of amino acids.

Amine hormones

Modified amino acids, also called monoamine hormones (e.g., thyroxine, melatonin).

Steroid hormones

Hormones composed of four rings of carbon atoms (e.g., testosterone, estradiol, cortisol).

Protein vs. Steroid Hormones

Protein and amine hormones act rapidly by binding to extracellular surface receptors and activating intracellular second messengers, whereas steroid hormones pass through cell membranes, bind to intracellular receptors, and act slowly to alter protein production and gene expression.

Hormones exert influences in two different ways:

1. Protein and amine hormones bind to specific surface receptors to release an intracellular second messenger.

2. Steroid hormones pass through the cell membrane and bind to internal receptors, forming a complex that acts as a transcription factor to control gene expression.

Second messengers

Intracellular signaling molecules released when protein or amine hormones bind to surface receptors, causing rapid cellular changes.

Transcription factors

Proteins like steroid-receptor complexes that bind to DNA to control gene expression and protein production.

Nongenomic effect

A rapid, brief effect of steroids (like estradiol or testosterone) involving neuronal membrane receptors distant from the nucleus.

Negative feedback

A regulatory control mechanism where hormone output feeds back to inhibit further secretion.

Target cell feedback

A feedback mechanism where the biological effect of a hormone on its target cell is detected by the endocrine gland, inhibiting further release.

Brain and pituitary regulation of hormones

A complex control system where the hypothalamus direct hormone release via releasing hormones and tropic hormones, governed by the negative feedback loops to the brain.

Knockout organisms

A technique comparing behaviors in animals lacking specific genes versus normal animals.

Radioimmunoassay (RIA)

A technique using antibodies to measure the concentration of a hormone in blood or fluid.

Autoradiography

A technique that shows the distribution of radioactively labeled chemicals in tissue slices using photographic film.

Immunocytochemistry

A technique that detects specific proteins in tissue by binding antibodies to them and visualizing the resulting product.

In situ hybridization

A technique that detects mRNA in tissue by providing a complementary labeled probe that hybridizes with the transcript of interest.

Pituitary gland (hypophysis)

An important endocrine gland connected to the hypothalamus by the pituitary stalk (infundibulum), consisting of the anterior pituitary and posterior pituitary.

Posterior pituitary hormones

Oxytocin and arginine vasopressin (AVP/antidiuretic hormone/ADH).

Hypophyseal portal system

A local system of blood vessels through which hypothalamic releasing hormones travel to the anterior pituitary.

Tropic hormones

Anterior pituitary hormones that affect other endocrine glands (e.g., ACTH, TSH, FSH, LH).

Six anterior pituitary tropic hormones

• Andrenocorticotropic hormone (ACTH) - controls the adrenal cortex and steroid release

• Thyroid-stimulating hormone (TSH) - increases thyroid hormone release

• Follicle-stimulating hormone (FSH) - stimulates egg follicles or sperm production

• Luteinizing hormone (LH) - stimulates follicles to form corpora lutea

• Prolactin - stimulates lactation and parental behavior

• Growth hormone (GH) - influences growth mostly during sleep

Gonads

The ovaries and testes that produce sex steroids. The hypothalamus controls their hormone production by releasing gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary to release FSH or LH.

Gonadal axes

The regulatory system where the hypothalamus releases gonadotropin-releasing hormone (GnRH), prompting the anterior pituitary to secrete gonadotropins (FSH and LH). These tropic hormones stimulate the gonads (testes and ovaries) to produce sex steroids (androgens, estrogens, and progestins), which then exert negative feedback control on the hypothalamus and anterior pituitary.

Gonadotropin-releasing hormone (GnRH)

A hypothalamic hormone that stimulates the anterior pituitary to release FSH and LH.

Pituitary secretions

The posterior pituitary secretes oxytocin (reproductive/parenting behavior, milk letdown) and vasopressin/ADH (increases blood pressure, inhibits urine formation). The anterior pituitary secretes six tropic hormones: andrenocorticotropic hormone, thyroid-stimulating hormone, follicle-stimulating hormone, luteinizing hormone, prolactin, and growth hormone.

Kisspeptin and its role

A hypothalamic peptide that stimulates gonadotropin-releasing hormone (GnRH) nuerons, playing a critical role in the onset of puberty

Gonadotropin-inhibiting hormone (GnlH)

A hypothalamic hormone used to inhibit gonadotropic secretion.

Adrenal glands

Glands located on top of each kidney, consisting of an outer cortex (80%) and an inner medulla (20%).

Thyroid hormones

Hormones produced by the thyroid gland (regulated by TSH and TRH) that regulate growth and metabolic rate.

Pineal gland

A single gland on top of the brainstem that secretes the amine hormone melatonin almost exclusively at night.

Melatonin

adrdenal, only released at night

Psychosocial dwarfism (Box 5.2)

A syndrome of stress-induced reduced growth caused by emotional deprivation or severe stress suppressing growth hormone release.

Oxytocin and vasopressin in social behavior

Neuropeptides and hormones that modulate social behavior: oxytocin promotes pair-bonds and uterine contractions in females, while vasopressin facilities pair-bond formation in male prairie voles.

Definition and action of hormones

Chemical compounds secreted by endocrine glands or specialized cells that act as signals, exerting effects through specialized cells that act as signals, exerting effects through specialized receptors.

Historical background endocrinology

Folk traditions and agricultural knowledge suspected chemical factors for centuries, but most formal knowledge has developed only in the last 50 years and remains incomplete.

Continuum of chemical communication

Hormonal actions classified by distance traveled, ranging from autocrine (self) to allomone (interspecies) communication.

Temporal pattern and environmental sensitivity of hormone action

Hormones act in a subtle, gradual fashion to alter behavior probability rather than acting as a switch, and are sensitive to environmental factors.

Comparison of hormonal vs. neural messages

Hormones broadcast slowly in an analog manner across the body to affect distant/local targets, while neural messages move rapidly in a digital manner over fixed pathways.

Similarities between neural and hormonal communication systems

Both manufacture, store, and release chemical messengers, use specific receptors with second messengers, and some chemicals act as both hormones and transmitters.

Differences between neural and hormonal communication systems

1. Destination/Spread: Neural communication travels to precise destinations, whereas hormonal communication spreads throughout the body and is picked up by cells with proper receptors.

2. Neural messages are rapid, while hormonal messages are slower.

3. Distance: Neural distance is small (synaptic cleft), whereas hormones may travel over a meter.

4. Signal Nature: Neural messages are digital (all-or-none action potentials), while hormonal messages are analog (graded in strength).

5. Control: Neural communications can be under voluntary control, whereas hormones are involuntary.

Chemical structures and receptor mechanisms of hormone types

Peptide/protein and amine hormones bind membrane-bound receptors, while steroid hormones (and thyroid hormones as an exception) cross cell membranes to modulate DNA transcription via intracellular receptors.

Speed of hormone action and evolutionary origins

Peptide/hormones act quickly (seconds to minutes), steroid hormones act slowly (hours to days), and some peptides/neuropeptides have evolutionary origins in single-celled organisms.

Organizational vs. activational hormone effects

Hormones alter cell proliferation and differentiation (organizational effect) and modulate the function of already differentiated cells (activitional effect).

Feedback loop regulation of hormone levels

Governed by negative feedback loops, ranging from a gland’s own secretions regulating activity to higher centers like the pituitary regulating gland output.

Brain control of the endocrine system via hypothalamus and pituitary

Hypothalamic neurosecretory cells release hormones via the posterior pituitary or secrete releasing factors into the anterior pituitary to trigger tropic hormone release.

Multihormonal involvement in physiological systems

Endocrine influences on growth, homeostasis, metabolism, and learning/memory frequently involve more than one hormone acting together.

Integration of neural and hormonal systems in behavior

Behaviors require coordination via neural-to-neural, neural-to-endocrine, endocrine-to-endocrine, or endocrine-to-neural links.

Effects of endocrine disorders on the nervous system and development

Endocrine disorders can cause pronounced psychological disturbances and impact physical development, such as seen in psychosocial dwarfism.

Neuroendocrine mechanisms in social behavior

Social behavior is influenced by neuroendocrine mechanisms, as demonstrated by oxytocin and vasopressin and their respective brain receptors.

Brain-synthesized steroid hormones and aromatase

Aside from glands, the brain synthesizes steroid hormones; avian brains use aromatase to convert testosterone into estradiol systems like birdsong.

Vasopressin and the Monogamous Brain

Hormones play a role in social behavior:

• Vasopressin Role: In male prairie voles, vasopressin facilitates the formation of pair-bonds with females.

• Oxytocin Role: Released during nursing interactions and orgasm; in females, it promotes pair-bonds.

• Species Comparison (Voles): Prairie voles are monogamous and exhibit high vasopressin (VP) receptor expression in the brain, whereas meadow voles are not monogamous and show much lower VP receptor binding.