Unit 5: Endocrine System

Signal Transduction Pathway

• Reception:

  • Cell signals are detected by receptor proteins in the membrane.

  • Change in protein shape occurs in response to stimuli (analogous to enzymes).

• Transduction:

  • Involves multistep pathways using relay proteins and second messengers to amplify initial signals.

• Response:

  • Mechanisms include:

    • Releasing hormones or neurotransmitters.

    • Activating existing enzyme molecules.

    • Initiating transcription and translation processes, activating genes.

Importance of Cell Communication

• Reasons for Cell Communication:

  • Coordinate activities in multicellular organisms.

  • Hormonal actions and neurotransmitter functions.

  • Cell recognition (e.g., antibodies, MHCs).

  • Facilitating mating in certain species (e.g., yeast cells).

  • Regulation of pathways (turning on/off).

  • Apoptosis events in development (e.g., embryonic development).

Evolutionary Perspective

• Cell communication is ubiquitous, seen from Archaea to multicellular organisms.

• Shared chemical processes underpin evolutionary ties in cell communication.

Types of Chemical Communication

Outside the Body

• Pheromones: Chemical signals released to communicate with members of the same species (e.g., marking trails).

• Quorum Sensing: Bacteria communicate as a group using autoinducers.

Inside the Body

• Short Distance:

  • Paracrine: Signals affecting nearby cells (e.g., prostaglandin).

  • Autocrine: Signals impacting the same cell that releases them (e.g., interleukin).

• Long Distance:

  • Hormones: Released into the bloodstream to reach target cells (e.g., insulin).

Direct Contact Communication

• Occurs through:

  • Plasmodesmata in plants (openings in cell walls).

  • Gap junctions in animal cells (protein channels for molecule passage).

  • Docking: Example with immune cells (Helper T cells and Killer T cells).

Short Distance Communication

• Examples:

  • Synaptic signaling: Neurotransmitters across synapses.

  • Neuroendocrine signaling: Interactions between neurosecretory cells and the bloodstream.

Autocrine Signals

• Affect the same cells that release them (e.g., interleukin-1 in monocytes).

• Tumor cells may self-stimulate division via their own signals.

Long Distance Communication

• Hormones travel via signal transduction pathways.

• Types include:

  • Water-soluble hormones (e.g., insulin).

  • Lipid-soluble hormones (e.g., steroids).

Functions of the Endocrine System

• Hormones: Secreted by endocrine glands, influencing metabolism, growth, mood, etc.

• Branch of study: Endocrinology focuses on hormonal functions and disorders.

• Glands include pituitary, thyroid, adrenal, etc., plus secondary functions found in other organs.

Communication Features

• Secreting cell: Releases the signal (ligand).

• Receptor: Binds with the ligand to form a complex.

• Target cell: Contains the receptor to receive the signal.

Insulin Example in Cell Communication

• Insulin: Secreted from pancreatic beta cells; binds to muscle cell receptors.

• Components: Secreting cell: pancreatic beta cell, receptor: integral protein on muscle cell, target: muscle cell.

Hormonal Communication Overview

• Hormones serve as signal molecules that travel long distances in the blood.

• Process of signal transduction involves reception, transduction, and response.

Pathways for Water-Soluble and Lipid-Soluble Hormones

• Water-soluble hormones bind to cell surface receptors; lipid-soluble hormones diffuse through the membrane.

• Cyclic AMP (cAMP): A common second messenger in cellular pathways, affecting various responses.

Multiple Effects of Hormones

• Hormones like epinephrine can produce different effects based on the target cell's receptor type.

• Various responses include glycogen breakdown in liver cells and vessel dilation/constriction in blood vessels.

Regulatory Mechanisms

• Negative feedback mechanisms: Control hormone levels to maintain homeostasis (e.g., insulin and glucagon balance).

• Positive feedback mechanisms: Amplify responses (e.g., oxytocin during childbirth).

Examples of Feedback Regulation

1. Negative feedback: When blood glucose rises, insulin is secreted to reduce glucose levels.

2. Positive feedback: Oxytocin leads to increased uterine contractions during childbirth.

Hormonal Interactions in Maintaining Homeostasis

• Insulin and glucagon work against each other to stabilize blood glucose levels.

• Calcium regulation involves PTH and calcitonin to maintain necessary calcium levels in the body.