Human Body Composition and Cellular Structure
1. Levels of Organization in the Human Body
The human body is composed of several elements grouped into different levels of organization:
- Atoms: Chemical elements forming the molecules of living beings.
- Molecules: Components from which cells produce their structures.
- Cells: The basic unit of human life.
- Tissues: Sets of specialized cells working together to perform a specific function.
- Organs: Formed by different tissues and have a specific function.
- Systems: Associations of organs working together to perform a vital function.
2. The Cell: The Body’s Foundation
The cell is the basic structural and functional unit of the human body.
3. Cell Structure
All cells in different human body tissues share the same basic structure:
- Plasma Membrane: The outer boundary of the cell.
- Cytoplasm: The space between the plasma membrane and the nucleus.
- Nucleus: A detached structure within the cell.
4. Nucleus and Chromosomes
The nucleus contains the information necessary for cell function and reproduction, including genetic information and instructions for protein synthesis.
5. Tissues
Tissues are formed by similar cells and an intercellular substance.
6. Epithelial Tissue
Epithelial tissue is responsible for protection, absorption, filtration, secretion, and excretion. It can be of two types:
- Covering Epithelial Tissue: Covers the entire body, internal cavities, and ducts. It can be formed by one or multiple cell layers.
- Glandular Epithelial Tissue: Forms glands that secrete products directly into the blood, externally, or into the gut.
7. Connective Tissue
Connective tissue is the most abundant type. It supports body structure, connects other tissues, and protects internal organs. It’s formed by fibroblasts and an extracellular matrix enriched by fibers. Types include:
- Loose Connective Tissue: Extends throughout the body.
- Dense Connective Tissue: Tough and hard due to collagen fibers.
- Cartilaginous Tissue: Consists of a gelatinous matrix, collagen fibers, and elastic fibers.
- Bone Tissue: Very hard tissue.
- Blood Tissue: Consists of plasma and mobile cells.
8. Neurons
Neurons are the functional units of the nervous system. They comprise:
- A cell body containing the nucleus and cytoplasm.
- Neuronal extensions called dendrites and axons.
9. Glial Cells
Glial cells perform support functions for neurons. Various types include:
- Astrocytes: The most abundant glial cells, present in the central nervous system.
- Microglia: Small cells with extensions.
- Schwann Cells: Present in the peripheral nervous system, insulating some neurons with a myelin sheath around the axon.
10. Carbohydrates, Lipids, and Proteins
- Carbohydrates: The most important energy source for our cells. Simple carbohydrates are absorbed quickly, while complex carbohydrates require longer digestion.
- Lipids: Have energy storage, structural (cell membranes), and regulatory (vitamins and hormones) functions.
- Proteins: Have a structural function as major components of cells.