Compartmentation: Cells and Tissues

Overview of Chapter Topics

This chapter introduces the concept of compartmentation in human physiology, focusing on how the body is organized into functional compartments separated by membranes. It covers anatomical and physiological compartments, the structure and function of cell membranes, and the organization of cells and tissues.

• Functional compartments of the body

• Physiological membranes

• Intracellular compartments

• Tissues and tissue remodeling

• Organs

Body Cavities

Anatomical Compartments

The human body contains several major cavities that house vital organs and provide protection and compartmentalization.

• Cranial cavity: Contains the brain.

• Thoracic cavity: Contains the heart and lungs, subdivided into pleural and pericardial sacs.

• Abdominopelvic cavity: Includes abdominal and pelvic cavities, housing digestive, reproductive, and excretory organs.

• Fluid-filled compartments: Examples include the circulatory system, eyes, and cerebrospinal fluid (CSF) spaces.

Example: The cranial cavity protects the brain, while the thoracic cavity is separated from the abdominopelvic cavity by the diaphragm.

Lumens of Hollow Organs

Definition and Examples

Many organs in the body are hollow, with an internal space called the lumen. The lumen is the inside space of a tubular structure, such as a blood vessel or intestine.

• Heart

• Lungs

• Blood vessels

• Intestines

• Stomach

For some organs, the lumen is not considered part of the body's internal environment (e.g., the lumen of the digestive tract is technically outside the body).

Functional Fluid Compartments

Body Fluid Distribution

Body fluids are distributed into distinct compartments, each with specific functions and compositions.

• Extracellular fluid (ECF): Fluid outside cells, subdivided into:

  • Plasma: The liquid component of blood.

  • Interstitial fluid: Fluid that surrounds most cells.

• Intracellular fluid (ICF): Fluid within cells.

Example: Red blood cells contain intracellular fluid, while plasma is the extracellular fluid within blood vessels.

Separation of Compartments by Membranes

Role of Membranes

Membranes are essential for compartmentalization, separating different functional areas and regulating exchange.

• Pericardial membrane: Surrounds the heart.

• Tissue membranes: Layers of cells supported by connective tissue.

• Cell membrane: Phospholipid bilayer that encloses each cell.

Example: The pericardial sac is a membrane that isolates the heart from other thoracic structures.

Cell Membrane

Function

The cell membrane is a dynamic structure that serves several critical functions for cellular life.

• Physical isolation: Separates the cell's interior from the external environment.

• Regulation of exchange: Controls movement of substances in and out of the cell.

• Communication: Facilitates signaling between the cell and its environment.

• Structural support: Maintains cell shape and anchors cytoskeletal elements.

Example: Ion channels in the cell membrane regulate the flow of sodium and potassium, essential for nerve impulse transmission.

Cell Membrane Composition

Major Components

The cell membrane is primarily composed of lipids, proteins, and carbohydrates, organized in a fluid mosaic model.

• Lipids: Phospholipids, sphingolipids, cholesterol

• Proteins: Integral (transmembrane, lipid-anchored), peripheral

• Carbohydrates: Glycoproteins, glycolipids

Phospholipid structures in water:

• Micelle: Spherical structure with hydrophilic heads outward.

• Liposome: Spherical vesicle with a bilayer membrane.

• Bilayer: The basic structure of the cell membrane.

Example: The fluid mosaic model describes how proteins and lipids move laterally within the membrane.

Intracellular Compartments

Organization Within Cells

Cells contain various compartments and structures that perform specialized functions.

• Cytoplasm: Includes cytosol, organelles, inclusions, and protein fibers.

• Organelles: Membranous structures such as mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes.

• Inclusions: Non-membranous structures like ribosomes, lipid droplets, glycogen granules.

• Cytoskeleton: Network of protein fibers providing shape and support.

Example: Mitochondria are the site of most ATP synthesis, containing their own DNA and double membrane.

Cytoskeleton

Structure and Function

The cytoskeleton is a dynamic network of protein fibers that maintains cell shape, enables movement, and organizes cellular components.

• Microfilaments (actin): Involved in cell movement and shape.

• Intermediate filaments: Provide mechanical strength (e.g., keratin, neurofilaments).

• Microtubules: Hollow tubes for intracellular transport and cell division.

Functions:

• Maintains cell shape

• Organizes internal structures

• Facilitates intracellular transport

• Enables cell movement and division

Example: Microtubules form the mitotic spindle during cell division.

Motor Proteins

Types and Functions

Motor proteins interact with cytoskeletal fibers to produce movement within cells.

• Myosins: Responsible for muscle contraction.

• Kinesins and dyneins: Move vesicles and organelles along microtubules.

Example: Dynein is essential for the movement of cilia and flagella.

Mitochondria

Structure and Function

Mitochondria are double-membraned organelles that play a central role in energy production.

• Outer membrane and inner membrane create two compartments: the intermembrane space and the mitochondrial matrix.

• Cristae: Folds of the inner membrane increase surface area for ATP synthesis.

• Unique DNA: Mitochondria contain their own genetic material.

Function: Site of most cellular ATP production via oxidative phosphorylation.

Example: Muscle cells have many mitochondria to meet high energy demands.

Endoplasmic Reticulum (ER)

Types and Functions

The endoplasmic reticulum is a network of membranes involved in protein and lipid synthesis.

• Rough ER: Studded with ribosomes; site of protein assembly and modification.

• Smooth ER: Lacks ribosomes; synthesizes fatty acids, steroids, and lipids. Also involved in calcium storage in some cells.

Example: Liver cells have extensive smooth ER for detoxification and lipid metabolism.

Summary Table: Body Fluid Compartments

Key Equations

• Osmosis: Movement of water across a semipermeable membrane from low solute concentration to high solute concentration.

• Surface area of a sphere:

• Volume of a sphere:

Additional info: These notes expand on the provided slides with definitions, examples, and academic context to support college-level Anatomy & Physiology study.