Physiology II - Reproductive Hormones and Processes

Goals of Reproductive Physiology

• Understand hormone roles in reproduction and their fundamental differences.
• Learn the step-by-step processes of mitosis and meiosis.
• Explore fetal sex differentiation influenced by hormonal control and cellular development.
• Grasp oogenesis (egg development) and spermatogenesis (sperm development).
• Comprehend feedback mechanisms and supraphysiological stimulation, including downregulation.
• Study endocrine control and hormonal feedback loops.
• Understand ovulation, sperm maturation, capacitation, and fertilization events.
• Investigate early embryo development and maternal recognition of pregnancy in various species.
• Analyze placentation and species-specific differences.
• Delve into fetal maturation and endocrine controls during pregnancy.

Hormones Overview

• Hormones are chemical messengers secreted by endocrine glands and carried through the bloodstream to affect various organs and tissues.
• They regulate metabolic processes and other critical bodily functions.

Classification of Hormones

• Chemical Nature:
  • Amine hormones: Derived from amino acids (e.g., tyrosine, tryptophan); water-soluble and relatively small.
  • Protein/peptide hormones: Larger proteins or small/medium peptides that exert effects through membrane receptors.
  • Eicosanoids: Derived from polyunsaturated fatty acids and regulate inflammation and immunity.

Mechanism of Action

• Lipophilic hormones bind to intracellular receptors, forming hormone-receptor complexes.
• Hydrophilic hormones bind cell membrane receptors, activating secondary messengers that mediate biochemical functions.

Embryology Basics

• The embryo originates as a mass of cells that differentiates into layers, forming both the embryo proper and the placenta.
• During embryogenesis, cellular layers include ectoderm, mesoderm, and endoderm, which differentiate into distinct organ systems.

Developmental Layers

• Ectoderm: Forms the nervous system, skin, and reproductive tract.
• Mesoderm: Develops into gonads (testes and ovaries), muscles, blood vessels, and reproductive organs.
• Endoderm: Gives rise to the digestive system, respiratory system, and most glands.

Placentation

• The trophoblast is the outer layer of embryonic tissue leading to the formation of the placenta.
• Allantois expansion forms the allantochorion—a pivotal structure in placental development.

Embryo vs. Fetus

• An embryo is in early developmental stages without detectable anatomical features of a specific species.
• A fetus is recognizable as a member of a species, marked by the development of placentation.

Sex Differentiation

• Genetic sex is determined at fertilization (XX for female, XY for male in mammals).
• Gonadal sex is influenced by testis-determining genes (SRY, SOX9), alongside ovary-determining genes (RSPO1, WNT).
• Phenotypic sex is evidenced through morphology, development, and influenced by hormones (e.g., Anti-Müllerian Hormone, Testosterone).

Development of Reproductive Systems

• Primordial germ cells migrate from the yolk sac to the developing gonads.
• The mesonephric (Wolffian) ducts develop into male reproductive structures, while the paramesonephric (Müllerian) ducts develop into female structures.

Key Terms in Sex Determination

• Karyotype: Determines genetic sex (XY for males, XX for females).
• Testis Determining Factor (TDF): Synthesized in males, leading to the development of male sex characteristics.
• Anti-Müllerian Hormone (AMH): Promotes the degeneration of female duct systems and supports male reproductive system development.

Absence of Sexual Determinants

• Lack of TDF, AMH, and Testosterone leads to female development as a default pathway.

Hypothalamic Differences

• Distinct hormonal roles and structural differences in the hypothalamus between male and female embryonic development are critical for reproductive functions.

This quiz on Physiology II focuses on various reproductive processes such as oogenesis and spermatogenesis, as well as hormonal control during fetal sex differentiation. It also covers the differences between hormones and the stages of mitosis and meiosis. Prepare to delve into the intricate details of reproductive physiology.