Lecture+6.2

Module Overview

  • Focus: Pituitary and Brain Hormones

Anatomy of the Brain and Pituitary

  • Key Structures:

    • Lepithia Cell Bendings: Neuron arrangement.

    • Cerebral Cortex: Associated with sensory perception and cognition.

    • Pineal Gland: Regulates circadian rhythms.

    • Suprachiasmatic Nucleus (SCN): Master clock for circadian rhythms.

    • Optic Chiasm: X-shaped structure where optic nerves cross.

    • Pituitary Gland: Known as "hypophysis," meaning mucus/phlegm in Greek; derived from Latin "pituita."

    • Hypothalamus: Controls pituitary gland function and regulates homeostasis.

Endocrine Regulation Centers

  • Central Role in Regulation:

    • Areas outside highlighted sections are for informational context only.

    • Focus on critical hormones such as Antidiuretic Hormone (ADH).

Development of the Pituitary Gland

  • Key Features:

    • Arises from Rathke’s Pouch (from oropharynx ectoderm).

    • Neuroectoderm outgrowth from the hypothalamus.

    • Proper development influenced by surrounding structures like the sphenoid bone.

    • Divided into:

      • Anterior lobe (Adenohypophysis)

      • Posterior lobe (Neurohypophysis)

Regions of the Pituitary Gland

  • Anatomical Sections:

    • Pars Distalis: Houses majority of cell types.

    • Pars Intermedia: Intermediate region.

    • Pars Nervosa: Part of the posterior pituitary.

    • Median Eminence: Base of the hypothalamus.

    • Infundibular Stalk: Connects hypothalamus to pituitary.

    • Pars Tuberalis: Region surrounding the infundibulum.

Species Variations in Pituitary Organization

  • Comparative Anatomy: Notable differences observed between species:

    • Horses, Dogs, Pigs, Large Ruminants, Sheep, Cats.

Hormonal Secretion Association

  • Anterior Pituitary and Hypothalamus:

    • Involvement of hypothalamic releasing factors in hormone secretion.

    • Vascular connections are crucial for hormone transfer.

    • Major Hormones Released:

      • ACTH (Adrenocorticotropic Hormone)

      • TSH (Thyroid Stimulating Hormone)

      • PRL (Prolactin)

      • LH, FSH, GH (Growth Hormone)

Classification of Pituitary Cells

  • Histochemical Characterization:

    • Cell Types and Hormones:

      • Corticotroph: Produces ACTH, Basophil.

      • Thyrotroph: Produces TSH, Basophil.

      • Gonadotroph: Produces FSH and LH, Basophil.

      • Lactotroph: Produces Prolactin, Acidophil.

      • Somatotroph: Produces Growth Hormone, Acidophil.

      • Chromophobes: Function still under investigation.

Functions of Pituitary Hormones

  • Key Hormones and Their Effects:

    • FSH: Stimulates follicle development.

    • LH: Triggers ovulation and testosterone production.

    • TSH: Stimulates the thyroid gland.

    • ACTH: Stimulates adrenal cortex functioning.

    • GH: Stimulates growth and metabolism.

    • MSH: Regulates skin pigmentation.

Hypothalamic Releasing and Inhibitory Hormones

  • Important for pituitary function:

    • PRH: Prolactin Releasing Hormone.

    • PIH: Prolactin Inhibitory Hormone.

    • TRH: Thyrotropin Releasing Hormone.

    • CRH: Corticotropin Releasing Hormone.

    • GHRH: Growth Hormone Releasing Hormone.

    • GHIH: Growth Hormone Inhibitory Hormone/Somatostatin.

    • GnRH: Gonadotropin Releasing Hormone (for FSH & LH).

Tissue-Specific Functions of Pituitary Hormones

  • Neurosecretory Functions:

    • Hypothalamus houses paraventricular and supraoptic nuclei which secrete ADH and oxytocin.

    • Target Organs include kidneys (for ADH), uterus, mammary glands, adrenal cortex, thyroid, and gonads affecting growth, metabolism, and reproductive functions.

    • Hormone Functions:

      • ADH: Regulates water absorption.

      • Oxytocin: Regulates uterine contractions and milk secretion.

      • Prolactin: Stimulates milk production.

Neural Components of the Posterior Pituitary

  • Hypothalamic Tract:

    • Connection between the hypothalamus and the posterior pituitary.

    • Neurotransmitters involved include Vasopressin (ADH) and Oxytocin from the paraventricular and supraoptic nuclei.