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: Antidiuretic Hormone (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.