Endocrine_system

FOUNDATION IN SCIENCE BIOLOGY 3

  • Prepared by CPU Biology Team

  • Topic 1: Human Physiology II Part 2: Endocrine System

  • Objectives: Inspire, Empower, Elevate

Learning Outcomes

  • By the end of the lesson, students should be able to:

    • a) Explain the mechanism of hormone action

    • b) Outline hormone production and regulation in humans

    • c) State the functions of hormones

    • d) Describe feedback control mechanisms and their roles in homeostasis

The Endocrine System

  • The endocrine system aids in maintaining homeostasis and consists of:

    • Series of glandular structures with no direct connection to other body parts (ductless glands).

    • Secretes over 50 different hormones directly into the bloodstream.

Gland Types

Endocrine vs Exocrine Glands

  • Endocrine Glands

    • Secrete hormones directly into the blood.

    • Example: hormones in blood circulation.

  • Exocrine Glands

    • Secrete substances onto the skin surface or into body cavities.

    • Example: sweat glands.

Hormones

  • Hormones are chemical messengers that coordinate body functions.

  • Produced by endocrine glands and secreted into the bloodstream.

  • The circulatory system transports hormones to target tissues.

Types of Hormones

  1. Steroid Hormones

    • Lipid-soluble, derived from cholesterol

    • Example: cortisol, testosterone, progesterone, estrogen

  2. Amines

    • Amino acid derivatives

    • Mostly water-soluble, except thyroid hormones

    • Example: thyroid hormones, adrenaline, noradrenaline, melatonin

  3. Peptides/Proteins

    • Water-soluble; largest hormone group

    • Example: glucagon, ADH, oxytocin, ACTH, calcitonin, insulin, growth hormone, prolactin, FSH, LH, TSH

Mechanism of Hormonal Action

1. Lipid-Soluble Hormones

  • Hormones diffuse directly into target cells.

  • Bind to intracellular receptors (in cytoplasm or nucleus).

  • Form receptor-hormone complexes that regulate gene transcription, impacting protein synthesis and gene expression.

2. Water-Soluble Hormones

  • Cannot diffuse across plasma membranes.

  • Bind to surface receptors on target cells, forming hormone-receptor complexes.

G-Protein Coupled Mechanisms

  • Binding of hormone activates a G protein, leading to the activation of adenylate cyclase.

  • Converts ATP to cAMP (secondary messenger) which activates protein kinases, altering cell metabolism or activity.

Endocrine System Overview

  • A network of glands that secrete hormones, regulating growth, metabolism, and other bodily functions.

Endocrine Glands and Their Hormones

  • Thyroid Gland

    • Hormones: Thyroxine (T4), Triiodothyronine (T3), Calcitonin

  • Adrenal Glands

    • Medulla: Epinephrine (E), Norepinephrine (NE)

    • Cortex: Cortisol, corticosteroids, aldosterone, androgens

  • Pancreas (Islets of Langerhans)

    • Hormones: Insulin, Glucagon

  • Gonads (Testis and Ovary)

    • Hormones: Testosterone, Estrogens, Progestins

  • Other Organs

    • Heart: Natriuretic peptides; Thymus: Thymosins; Adipose: Leptin; Digestive Tract: Various hormones;

    • Kidneys: Erythropoietin (EPO) and Calcitriol.

Feedback Control Mechanisms

1. Negative Feedback

  • Used to regulate hormone secretion in the hypothalamic-pituitary axis.

  • Restores organ/system function back to normal range, essential for homeostasis.

  • Example: Insulin regulation of blood glucose levels.

2. Positive Feedback

  • Enhances the output induced by a stimulus, moving it out of normal ranges.

  • Benefits in situations like childbirth but can lead to uncontrolled outcomes.

  • Example: Oxytocin's role during childbirth.

The Pituitary Gland: The Master Gland

  • Secretes hormones with direct or indirect effects on target organs.

  • Divided into anterior and posterior lobes controlled by the hypothalamus.

Posterior Pituitary

  • Cannot produce hormones but stores and releases hormones produced by the hypothalamus.

  • Hormones: ADH - regulates water balance; Oxytocin - stimulates childbirth and milk secretion.

Anterior Pituitary

  • Produces its own hormones regulated by releasing factors from the hypothalamus.

Thyroid Gland

  • Produces T4, T3 - controlling metabolic rate and cell growth, and Calcitonin - affects bone and muscle function.

Parathyroid Glands

  • Secrete parathyroid hormone to increase plasma calcium levels, opposing calcitonin effects.

Adrenal Glands

  • Located above each kidney; consists of cortex and medulla with specific hormone secretions.

Pancreas

  • Functions as both endocrine (hormone secretion) and exocrine (digestive enzymes).

  • Hormones: Insulin (lowers glucose levels), Glucagon (raises glucose levels).

Gonads

  • Produce sex hormones responsible for secondary sex characteristics and reproduction physiology.

Thymus Gland

  • Located in the thoracic cavity, produces thymosin for T-lymphocyte development.