Chapter 8 - Hormones & Sex

Definition of Hormones: Hormones are chemicals that travel through the bloodstream to act on target tissues.
Types of Glands:
- Endocrine Glands: Release hormones within the body.
- Exocrine Glands: Use ducts to secrete fluids outside the body (e.g., tears, sweat).

Peptide Hormones: Short strings of amino acids.
Amine Hormones: Modified versions of a single amino acid.
Steroid Hormones: Derived from cholesterol, characterized by four rings of carbon atoms.

Structure: Divided into anterior and posterior sections.
- Posterior Pituitary: Does not produce hormones but releases those made in the hypothalamus.
- Neuroendocrine Cells: Located in hypothalamus (specifically supraoptic and paraventricular nuclei).
- Released Hormones: Oxytocin and vasopressin.
- Anterior Pituitary: Releases tropic hormones stimulated by releasing hormones from hypothalamus.
- Function: Triggers endocrine hormones from gonads, thyroid, adrenal glands.
- Negative Feedback System: Regulates hormone levels.

Synaptic Communication: Involves neurotransmitters crossing synaptic clefts.
Endocrine Communication: Hormones released into the bloodstream affect distant target tissues.
Pheromonal Communication: Chemicals released outside the body to affect other individuals of the same species.
Allomonal Communication: Chemicals released to affect individuals of different species.

Peptide and Amine Hormones:
- Bind to specific receptors on the cell surface and activate second messengers inside the cell.
- Duration of effect: Seconds to minutes.
Steroid Hormones:
- Cross cell membrane, bind to receptors inside, and form a steroid–receptor complex that binds to DNA, controlling gene expression.
- Duration of effect: Hours to days to years.

Diverse Roles: Hormones have significant effects on behavior and bodily functions including:
- Growth, wake-sleep cycles, mood, metabolism, hunger, reproductive cycles.
- Preparation of the body for mating, fighting, fleeing, puberty, parenting, menopause.
- Regulation of other hormones.

Posterior Pituitary Function: Releases hormones made in the hypothalamus (oxytocin, vasopressin).
Anterior Pituitary Function: Makes/releases tropic hormones that modulate other endocrine glands.

Tropic Hormones:
- Prolactin: Stimulates milk production.
- Growth Hormone (GH): Affects bone and soft tissues.
Hormonal Cascades: Hormones like FSH and LH target gonads and other glands:
- HPG Axis: FSH and LH stimulate gonads (testes/ovaries), which release sex steroids.
- HPT Axis: TSH stimulates thyroid gland, which releases T3 and T4.
- HPA Axis: ACTH stimulates adrenal glands, releasing glucocorticoids.

Negative Feedback:
- Simple Feedback: Circulating hormones inhibit further secretion directly back on the endocrine gland.
- Complex Feedback: Involves indirect inhibition via the hypothalamus and pituitary.
Example of Negative Feedback: Hormone contraceptives inhibit GnRH release resulting in no ovulation.

Male Gonadotropins:
- FSH: Stimulates sperm production in testes.
- LH: Stimulates testosterone production, influences masculine traits and behaviors.
Female Gonadotropins:
- FSH: Stimulates follicle maturation and estrogen release.
- LH: Triggers ovulation and progesterone release.

Menstrual Cycle: Hormonal fluctuations influence ovarian function:
- Estrogen and progesterone variation across the ovulatory cycle, regulated by FSH and LH.

Gonadal Steroid Hormones: Necessary for reproductive behavior via both organizational and activational effects.

Definition: Developmental changes that occur during critical periods (in utero and puberty) and involve permanent changes to physical and behavioral traits.
Timing: Two critical periods are noted: in utero and during puberty.
Action: Organize the physical structure of the nervous system.

Definition: Temporary behavioral changes that occur due to the presence of hormones in adulthood.
Timing: Occurs in adulthood; effects stop upon hormone removal.

Female Rats Behavior:
- Courtship behaviors include proceptive behavior (hops, ear wiggling) when ovulating.
- Lordosis posture allows mating with males.
Neural Circuitry of Reproductive Behavior:
- VMH Role: Crucial in females for lordosis response, influenced by estrogen and progesterone.
- MPOA Role: Coordinates male copulatory behavior; impacted by pheromones through the vomeronasal organ (VNO).

Maternal Behaviors: Includes nest building, nursing, and retrieving pups, all of which are influenced by hormonal changes from pregnancy.

Chromosomal Basis: Female (XX) and Male (XY) determination based on which chromosome (X or Y) sperm contributes.
SRY Gene: Located on the Y chromosome; triggers testes development, leading to male characteristics.
Gonadal Development:
- With SRY, testes develop and produce testosterone; without SRY (XX), ovaries develop.

Indifferent Gonads: Early gonads capable of developing into either sex in all fetuses prior to exposure to hormones.
Male Development: SRY activates testes development, promoting wolffian ducts and inhibiting müllerian ducts.
Female Development: No SRY leads to ovaries; lack of testosterone causes regression of wolffian ducts.

Sexual Dimorphism: Refers to physical differences between sexes, seen in specific brain regions (e.g., SDN-POA in hypothalamus).
- Importance: Lesions in SDN impact behaviors related to mating.

Sexual Attraction: Involves courtship behaviors and signals.
Appetitive Behaviors: Promote and maintain sexual interactions.
Copulation: Coordinated response allowing for mating to occur.
Postcopulatory Behavior: Can vary by species, often includes parenting behaviors.

Sexual Response Cycle:
- Males experience a mandatory refractory period before arousal can resume.
- Females do not have a mandatory refractory period, facilitating quicker recovery.

Influence of Steroid Hormones: Organizational and activational effects are vital for reproductive behaviors, sexual differentiation, and overall hormonal regulation of bodily functions.
Neural Circuitry and Behavior: Specific brain regions and hormone interactions are crucial in mediating sexual behaviors in both males and females, showcasing the complex interplay of endocrine and nervous systems.