4_Endocrine System I (1)

Questions and Assignments

• Any questions on Quiz #1 or Assignment #1?

Introduction to the Endocrine System

• The endocrine system is crucial in regulating hormone levels in the body.

• Visual reference: Cartoon representation highlighting concern for hormone levels.

Hormones: Introduction

Definition and Origin

• Greek origin of the word "hormone" means "to excite".

• Hormones are chemicals that are secreted by endocrine glands, which are ductless.

• The term originates from Greek "endon", meaning "within", and "krinein", meaning "to secrete".

Features of Hormones

• Hormones:

  • 1. Are secreted by endocrine glands.

  • 2. Travel through the bloodstream.

  • 3. Regulate target organs or tissues via specific receptors.

• Binding of hormones to receptors initiates a cascade of events resulting in specific cellular responses or changes in gene expression.

Hormonal vs. Neural Communication

Comparison of Signal Types

• Neural Communication vs. Hormonal Communication:

  • Signals:

    • Neural: Action potentials

    • Hormonal: Hormones

  • Pathways:

    • Neural: Transmission by neurons

    • Hormonal: Bloodstream

  • Speed:

    • Neural: Fast

    • Hormonal: Slow

  • Duration of Effect:

    • Neural: Short-lived

    • Hormonal: Short or long-lived

  • Voluntary Control:

    • Neural: Yes

    • Hormonal: No

Types of Cellular Communication

Neural and Hormonal Pathways

1. Neurocrine communication (synaptic transmission):

   • Involves presynaptic and postsynaptic neurons transmitting signals through neurotransmitters.

2. Endocrine communication:

   • Hormones from endocrine cells travel through the bloodstream to target cells.

3. Neuroendocrine communication:

   • Combination of neural and hormonal signals affecting target cells in distant sites.

Major Vertebrate Hormones

Categories of Hormones

• Protein Hormones (examples):

  • Adrenocorticotropic hormone (ACTH)

  • Follicle-stimulating hormone (FSH)

  • Insulin

  • Oxytocin

• Amine Hormones (examples):

  • Epinephrine

  • Norepinephrine

• Steroid Hormones (examples):

  • Estrogens (estradiol)

  • Androgens (testosterone)

Action Mechanisms of Hormones

Protein Hormones

• Synthesized as preprohormones with post-translational modifications producing active hormones before release.

Steroid Hormones

• Derive from cholesterol; consist of three 6-carbon rings and one conjugated 5-carbon ring.

Amine Hormones

• Derive from amino acids, examples include serotonin, dopamine, and thyroid hormones. These typically bind to cell membrane receptors.

Lipid-based Hormones

• Includes prostaglandins that are derived from fatty acids and can be produced by nearly all organs in the body.

In-Class Assignment (#3)

• Pre-Course Assessment assigned; important for course assessment, not performance grade.

Chemical Communication Mechanisms

• Chemical signals regulate intracellular events, feedback for regulation, and affect adjacent cells, traveling via the bloodstream to target cells.

• Types:

  • Intracrine

  • Autocrine

  • Paracrine

  • Endocrine

  • Ectocrine

Major Endocrine Structures

• Hypothalamus: controls hormone secretions.

• Pineal Gland: regulates body rhythms.

• Pituitary Gland: divided into anterior (adenohypophysis) and posterior (neurohypophysis) sections affecting various hormones and functions.

• Other structures: Kidneys, Thyroid, Adrenal glands affecting growth, metabolism, water, and salt balance.

Hormones of the Hypothalamus

• Releasing and inhibitory hormones including:

  • Thyrotropin-releasing hormone (TRH): stimulates thyroid-stimulating hormone (TSH).

  • Growth hormone-releasing hormone (GHRH) affecting growth hormone (GH).

  • Gonadotropin-releasing hormone (GnRH): stimulates luteinizing and follicle-stimulating hormones.

• Also includes vasopressin (water balance) and oxytocin (uterine contractions, milk letdown).

The Pituitary Gland Structure and Functions

Anterior Pituitary

• Originates as an outgrowth of the mouth roof, controlled by hypothalamic hormones.

Posterior Pituitary

• Develops from an out-pouching of the brain, secreting hormones directly into the bloodstream.

Quiz and Homework Reminder

• Homework: Read Chapter 2 of the textbook posted on iCollege by Wednesday.

• Study for Quiz #2 covering techniques lecture, Assignment #2, and content discussed during the current lecture.