Endocrine System Vocabulary

Regulatory Systems

  • Main Regulatory Centers:

    • Nervous System:

    • Somatic Nervous System: Voluntary control of skeletal muscle contraction.

    • Autonomic Nervous System: Involuntary control, maintaining homeostasis.

      • Sympathetic System: "Fight-or-flight" prepares for action (e.g., physical activity).

      • Parasympathetic System: "Rest and digest" assists during quieter states (e.g., digestion).

    • Endocrine System:

    • Hormones secreted by endocrine glands travel through the bloodstream to target tissues.

    • Greek roots: "endo" (within) and "krino" (to secrete).

CNS vs Endocrine System

  • Similarities:

    • Both utilize the brain and hypothalamus.

    • Some molecules function as both neurotransmitters and hormones.

    • Both regulate bodily functions.

    • Some neurons secrete neurohormones.

  • Differences:

    • Mode of Transport:

    • Endocrine: Hormones into the bloodstream.

    • Nervous: Neurotransmitters directly to target cells.

    • Speed of Response:

    • Endocrine: Slower response than the nervous system.

    • Duration of Response:

    • Hormones: Last minutes to weeks in circulation.

    • Nervous: Active only during action potentials.

Functions of the Endocrine System

  • Key Functions:

    • Metabolism regulation.

    • Control of food intake and digestion.

    • Tissues development.

    • Ion levels and water balance.

    • Blood pressure and heart rate regulation.

    • Blood glucose and nutrient control.

    • Reproductive functions including uterine contractions and milk release.

    • Immune system regulation.

  • Classes of Chemical Messengers:

    • Autocrine: Influences the same cell that secreted it.

    • Paracrine: Secreted into extracellular fluid, affects nearby cells.

    • Neurotransmitter: Short-distance signaling by neurons in synaptic cleft.

    • Endocrine: Hormones travel through the bloodstream to distant target tissues.

Hormone Secretion Patterns

  • Chronic Secretion: Stable hormone concentrations over time (e.g., lipid-soluble hormones).

  • Acute Secretion: Irregular and dramatic concentration changes (e.g., water-soluble hormones).

  • Episodic Secretion: Regular intervals and concentrations.

Hormone Regulation

  • Neural Activation:

    • Neurons release neurotransmitters triggering hormone release from endocrine glands.

    • Neural stimulation ceases hormone release when stimulus stops.

    • Neurohormones are secreted into the blood from neurons.

  • Hormonal Activation:

    • Hormone-releasing factors stimulate other endocrine glands to release hormones.

    • Some hormones inhibit the secretion of others.

  • Humoral Control:

    • Blood-borne molecules stimulate hormone release.

    • Inhibition occurs when an opposing hormone is secreted to counteract the stimulating hormone.

Control of Hormone Release

  • Significant increases in hormone demand stimulate secretion.

  • When the hormone has done its job, it must be removed via circulation or receive an inhibitory message.

  • Regulatory Mechanisms:

    • Positive Feedback: Hormone stimulates its own production (self-propagating system).

    • Negative Feedback: Most common regulatory mechanism, inhibits hormone secretion when levels are adequate.

Receptors and Sensitivity Regulation

  • Hormones only affect cells with matching receptors.

  • Down-regulation: Decrease the number of receptors, reducing sensitivity to a hormone.

  • Up-regulation: Increased receptor synthesis enhances sensitivity to a hormone.

Endocrine Glands

  • The Hypothalamus: Major control site for nervous and endocrine systems, connects to the pituitary gland through the infundibulum.

  • Pituitary Gland:

    • Composed of anterior and posterior sections.

    • Posterior: Neurohypophysis; secretes neurohormones into the circulatory system without a portal system.

    • Anterior: Composed of glandular tissue; utilizes a hypothalamohypophysial portal system for hormone regulation.

Posterior Pituitary Hormones

  • Antidiuretic Hormone (ADH):

    • Regulates water reabsorption in kidneys based on blood osmolality.

    • Stimulated by osmoreceptors and baroreceptors responding to blood osmolality and pressure changes.

Anterior Pituitary Hormones

  • Various hormones, including:

    • Growth Hormone (GH): Involved in growth, metabolism, and regulated by GH-releasing and inhibiting hormones.

    • Thyroid-Stimulating Hormone (TSH): Stimulates thyroid hormone secretion, regulated by TRH.

    • Adrenocorticotropic Hormone (ACTH): Stimulated by corticotropin-releasing hormone to increase glucocorticoid secretion in the adrenal cortex.

Thyroid Gland

  • Major endocrine gland producing T3, T4, and calcitonin, regulates metabolism and growth/maturation of organs.

  • Hypersecretion leads to weight loss and high metabolism; Hyposecretion results in weight gain and low metabolism.

Parathyroid Glands and Hormones

  • Regulate calcium levels via Parathyroid Hormone (PTH), which increases blood calcium levels by stimulating bone resorption and renal absorption.

Adrenal Gland Structure and Hormones

  • Comprised of the outer cortex and inner medulla, secreting stress-related hormones like cortisol and epinephrine, regulating responses to stress, and influencing metabolism.

  • Cortisol affects energy metabolism and has anti-inflammatory effects while also being regulated by ACTH.

Pancreas Functions in Endocrine Regulation

  • Contains both endocrine (insulin, glucagon) and exocrine (digestive enzymes) components. Insulin decreases blood glucose while glucagon increases it. Controlled by blood glucose levels and neural signals.

  • Homeostatic feedback loops for glucose levels depend on both hormone responses and nervous system regulation.