Chapter_8_Book

Overview of Gender and Hormones

• Development of Gender: Understanding the biological and hormonal basis of gender identity.

• Key Question: How do biological and social forces shape male and female development?

The Complexity of Development

• Baby Formation: The development of a baby is a complex process that typically occurs without complications.

• Cloacal Exstrophy: A rare condition occurring in 1 in 400,000 births; characterized by a split pelvis and exposed bladder/intestines.

  • Impact on Gender Identity: Affected individuals often face difficult choices regarding gender assignment due to the external presentation of genitalia.

Biological vs. Social Influences on Gender

• Debate on Gender Identity: The extent to which gender identity is shaped by biology versus socialization.

• Behavioural Differences: Discusses why men and women behave differently, considering genetic versus environmental factors.

  • Research Focus: Studies suggest both biological (i.e., hormonal influences) and environmental (i.e., socialization) cues shape gender behaviors.

Hormonal Influences on Gender and Behaviour

• Hormonal Mechanisms: Hormones influence not only physical development but also behavior associated with gender roles.

• Development of Sexual Behaviors: Hormones affect sexual and parental behaviors through mechanisms acting on specific brain regions.

• Prenatal Hormonal Effects: Evidence shows that prenatal exposure to hormones significantly affects sexual identity and orientation.

Understanding Hormones

• Hormones Defined: Chemical signals secreted by endocrine glands and distributed via the bloodstream to regulate body functions.

• Types of Hormones:

  • Peptide Hormones: Chains of amino acids (e.g., insulin).

  • Amine Hormones: Modified amino acids (e.g., epinephrine).

  • Steroid Hormones: Derived from cholesterol (e.g., testosterone).

Endocrine Glands and Functions

• Major Endocrine Glands:

  • Hypothalamus: Regulates hormone secretion.

  • Pituitary Gland: Releases tropic hormones affecting other glands.

  • Adrenal Cortex: Manages stress response and metabolism.

  • Gonads (Ovaries/Testes): Produce sex steroids and gametes.

Historical Perspective on Hormones

• Foundational Studies: Historical experiments led to the discovery of hormones; e.g., Arnold Berthold's study with castrated roosters demonstrating the role of testes in masculinization via hormones.

Mechanisms of Hormone Action

• Peptide and Amine Hormones: Act on cell membranes through second messengers, usually eliciting rapid responses.

• Steroid Hormones: Pass through cell membranes and act on intracellular receptors to influence gene expression, leading to longer-term changes.

Hormonal Regulation Systems

• Feedback Mechanisms: Hormonal systems are regulated via feedback from hormones acting on the hypothalamus and pituitary, maintaining homeostasis.

• Negative Feedback: Common control mechanism where hormone output suppresses its own production.

Sexual Behavior Regulation

• Sexual Response in Animals: Explains how hormones govern sexual behavior, detailing circuits involved (e.g., lordosis in females, copulation in males).

• Role of Brain Structures:

  • mPOA (Medial Preoptic Area): Critical for male copulatory behavior.

  • VMH (Ventromedial Hypothalamus): Key for female sexual behaviors.

Maternal Behaviors

• Influence of Hormones on Parenting: Examines how hormonal changes influence maternal behaviors in animals, with implications for human parenting.

Human Sexuality and Diversity

• Kinsey Studies: Groundbreaking work that revealed the complexity of human sexual behaviors and orientations.

• Masters and Johnson Model: Illustrates the phases of human sexual response emphasizing hormonal influence.

Sexual Orientation and Prenatal Hormones

• Impact of Prenatal Hormones: Discusses how exposure to different levels of androgens influences sexual orientation and behavior in humans.

• Fraternal Birth Order Effect: Research showing that having older brothers increases the likelihood of a boy being gay, indicating a biological basis.

Summary Points and Considerations

1. Influence of Hormones: Acknowledge the dual role of biological and social influences on gender identity and behavior.

2. Ongoing Research: Continuous investigation into how hormones and experience shape sexual behavior and identity in both animals and humans.