ch 3

Definition: The human body is segmented into various compartments, many of which contain smaller, more specific compartments.
Example: The thoracic cavity includes:
- Pleural cavities
- Pericardial cavity
Functionality: Different compartments can possess slightly varied internal environments to cater to the unique necessities of the cells, tissues, and organs they harbor.
Specific Example: The pleural cavities are unique due to their negative pressure, which facilitates the adhesion of lungs to the thoracic cavity walls.

Separation of Fluids: The compartments extend down to a microscopic level:
- Intracellular Fluid (ICF): Fluid within cells.
- Extracellular Fluid (ECF): Fluid outside the cells, which includes:
- Plasma: The liquid component of blood contained within blood vessels.
- Interstitial Fluid: The fluid that exists outside blood vessels and surrounds tissues and cells.

Role of Membranes: All compartments are delineated by structures called biological membranes.
- Types:
- Small Scale: E.g., plasma membrane of a cell that separates ICF from ECF.
- Large Scale: E.g., pericardium encasing the heart, exhibiting multiple cellular layers.

Structure: Plasma membranes consist primarily of phospholipids:
- Phospholipid Structure:
- Phosphate 'Head': Hydrophilic (water-attracting), seeks proximity to water.
- Lipid 'Tails': Hydrophobic (water-repelling), prefers distance from water.
- Arrangement: In bilayers, heads face towards water (outer layer - ECF; inner layer - ICF) while tails congregate centrally, forming a hydrophobic barrier.

Transport Dynamics:
- Hydrophilic substances (polar molecules and ions) are lipophobic (avoid lipids) and struggle to traverse the plasma membrane's hydrophobic core.
- Hydrophobic substances (nonpolar molecules) are lipophilic (prefer lipids) and can transition through the membrane more easily.
Example:
- Glucose: A polar molecule that, despite being water-soluble, cannot enter directly through the hydrophobic core and thus requires assistance.

Functionality: To transport hydrophilic substances across membranes, specific proteins known as membrane or transport proteins are employed.
Future Discussion: These proteins and their mechanisms will be explored in detail in Chapter 5.

Implications: Membrane compositions extend to organelles in cells—allowing them to establish distinct compartments from cytosol.
Importance: This compartmentalization provides isolated environments necessary for organelles to function without interference; for example:
- Lysosomes: Contains digestive enzymes to manage waste; if released into the cytosol, these enzymes could be cytotoxic.

Cell Creation and Repair: The human body perpetually generates new cells to replace aging or damaged ones, a fundamental aspect of health.
Role of Stem Cells: New cells often emerge from stem cells, which can differentiate into varied cell types:
- Stem Cell Division:
- One daughter cell remains a stem cell.
- The other undergoes differentiation into a specialized cell, e.g., a keratinocyte from basal cells in the skin.

Universality of Stem Cells: Found in nearly every tissue for reparative purposes. Tissues with an abundance of stem cells can repair more readily.
Pluripotent Stem Cells: Present during early developmental stages, capable of transforming into any cell type; these stem cells vanish post-embryonic development.

Types of Cell Death:
- Apoptosis: A programmed, orderly death process that disassembles cells without adversely affecting surrounding tissues.
- Purpose: Facilitates space for new cells and removes defective or malfunctioning cells.
- Necrosis: An uncontrolled death resulting from severe trauma, toxins, or depletion of oxygen, leading to cell rupture and potential inflammation in the extracellular fluid.

Core Topics:
- Functional compartments of the body.
- Biological membranes.
- Intracellular compartments.
- Tissue remodeling significance and mechanisms.