Topic 13

Nervous System General Overview

  • The nervous system is responsible for immediate responses and some sustained responses.

  • Two major components:

    • Parasympathetic nervous system

    • Sympathetic nervous system

Gastrin Example

  • Gastrin:

    • Produced in the stomach

    • Influences the release and production of digestive enzymes.

Neurotransmitters Communication

  • Neurotransmitters need to communicate effectively with target cells.

  • Required components for effective communication:

    • The target cell must have receptors for the specific neurotransmitter.

    • Communication occurs through synapses between axons and their effectors.

Axon and Effectors

  • The axon communicates with:

    • Other neurons

    • Glands (e.g., sweat glands, oil glands)

    • Endocrine glands

  • Effectors must possess receptors for the neurotransmitters being communicated.

Chain of Reactions in Effector Cells

  • Neurotransmitter interactions cause a series of reactions within effector cells.

    • Example:

    • Muscle contraction through calcium release from the sarcoplasmic reticulum.

    • Interaction between actin and myosin fibers leads to muscle contraction.

  • Hormones and endocrine factors also require specific receptors for action to occur.

Receptors and Proteins

  • Most receptors are proteins on the cell surface (cell membrane).

  • Critical review points include:

    • Protein production within the cell

    • Sustenance and structural function of proteins in the cell membrane

    • Role of molecule shape in inducing reactions.

Chemical Specificity

  • Chemicals produced in the body are tissue-specific; specific receptors are needed for each chemical.

  • Example: Acetylcholine (neurotransmitter) has a specific effect on muscle cells.

Endocrine Function

  • Endocrine glands secrete hormones via exocytosis:

    • Hormones are released into the bloodstream from vesicles within the cell.

  • High vascularity of endocrine glands is characterized by:

    • Presence of many capillaries despite glands primarily comprising epithelial tissue.

    • Connective tissue that supports blood vessels is found beneath epithelial tissue in glands.

Hormone Travel and Target Interaction

  • Hormones produced travel through the bloodstream to specific target receptors.

  • Functions of hormones include:

    • Generally regulate reaction rates,

    • Water balance,

    • Growth and development of cells.

Growth vs. Development

  • Growth: Increase in size.

  • Development: Maturation and reaching functional capacity.

Importance of Water

  • Bodies are mainly composed of water. Important because:

    • Water is vital for metabolic processes

    • Effective transport medium due to its polarity, influencing reaction rates.

Primary Endocrine Organs

  • Various endocrine organs from head to toe, showcasing the widespread nature of hormone functions throughout the body.

  • Important endocrine organs:

    • Hypothalamus:

    • Connects neurological and endocrine functions.

    • Influences the pituitary gland.

    • Pituitary Gland:

    • Produces a variety of hormones influencing numerous bodily functions.

    • Pineal Gland:

    • Regulates sleep patterns.

    • Thyroid and Parathyroid Glands:

    • Control metabolism and calcium balance.

    • Thymus Gland:

    • Plays a role in immune system programming.

    • Adrenal Glands:

    • Located atop the kidneys, produce various hormones.

Pancreas Functions

  • The pancreas has both endocrine (insulin production) and exocrine functions.

  • Pancreatic islets function in hormone production.

Types of Hormone Action

  • Two classifications:

    • Steroid Hormones:

    • Lipids that are not water-soluble.

    • Can pass through the cell membrane; receptors located inside cells.

    • Influences DNA replication and protein synthesis.

    • Non-Steroid Hormones:

    • Composed of amino acids/proteins, water-soluble.

    • Act on cell surface receptors activating G proteins, leading to second messenger systems (e.g., cyclic AMP).

    • Alters enzyme activity but does not change genetic production directly.

Regulation of Hormone Secretion

  • Hormones can be cleared from circulation through:

    • Urinary system

    • Enzymatic breakdown.

  • Regulation Methods:

    • Negative feedback: High hormone levels inhibit further release (e.g., insulin regulation).

    • Direct nervous stimulation: Nervous system's influence on hormone release.

    • Glandular responses: Hormonal response to changing physiological conditions (e.g., glucose regulation).

Feedback Mechanisms

  • Negative Feedback: Hormone levels exert opposing effects to maintain balance.

    • Example: High glucose levels lead to insulin production, lowering glucose concentration.

  • Positive Feedback: Reinforces and promotes further influence in physiological processes.

    • Example: Oxytocin during childbirth or blood clotting processes.

Pituitary Gland Overview

  • Located at the brain's base, connected to the hypothalamus

  • Two regions:

    • Posterior Pituitary: Stores hormones produced by hypothalamus (ADH, oxytocin).

    • Anterior Pituitary: Under hypothalamic control, produces multiple hormones affecting many body functions.

Hormones from Pituitary Gland

  • Hormones from the anterior pituitary oversee various bodily processes (e.g., controlling ovaries and testes).

  • Frequent hormonal interactions occur, emphasizing how glandular function is interrelated.