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.

      1. Travel through the bloodstream.

      1. 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.