Cell Signaling and Hormone Classification

Forms of Cell Signalling

• Autocrine signalling involves a cell responding to substances that it releases itself, affecting its own activity.
• Paracrine signalling occurs when cells communicate with nearby cells through the release of signaling molecules, allowing localized effects.
• Endocrine signalling involves hormones being released into the bloodstream, affecting distant target cells and organs.

Classification of Hormones

• Class 1: Amino Acid Derivatives
  • Includes hormones derived from single amino acids, such as:
    • Thyroxine
    • Epinephrine
    • Norepinephrine
    • Dopamine
• Class 2: Large Protein Hormones
  • Composed of chains of amino acids:
    • Insulin consists of 51 amino acids.
    • Parathyroid hormone consists of 84 amino acids.
• Class 3: Cholesterol Derivatives
  • Steroid hormones derived from cholesterol, including:
    • Aldosterone
    • Cortisol
    • Testosterone
    • Estrogen
    • Progesterone
• Class 4: Vitamins
  • Some hormones are derived from vitamins, for example:
    • Vitamin A derivatives.

Hypothalamic and Pituitary Hormones

• Most anterior pituitary hormones are regulated by negative feedback mechanisms, except for LH, which sees a surge during the peak of estrogen levels.
• Hypothalamic Releasing Factors
  • Key hormones released from the hypothalamus include:
    • Thyrotropin-releasing hormone (TRH)
    • Corticotropin-releasing hormone (CRH)
    • Gonadotropin-releasing hormone (GnRH)
    • Growth hormone-releasing hormone (GHRH)
• Anterior Pituitary Hormones
  • The anterior pituitary releases several hormones in response to hypothalamic signals, such as:
    • Thyroid-stimulating hormone (TSH)
    • Adrenocorticotropic hormone (ACTH)
    • Follicle-stimulating hormone (FSH)
    • Luteinizing hormone (LH)
    • Growth hormone (GH)

Hypothalamic Inhibitory Hormones

• Prolactin releasing inhibiting hormone is known to be dopamine, which inhibits prolactin secretion.
• Growth hormone release is inhibited by somatostatin, regulating growth hormone levels.

Explore the different forms of cell signaling, including autocrine, paracrine, and endocrine signaling. This quiz also covers the classification of hormones, detailing amino acid derivatives, large protein hormones, cholesterol derivatives, and vitamins. Test your knowledge on these fundamental concepts of biology.