Understanding Human Body Tissues: Types and Functions

Tissues represent an organizational level above the cellular level. They are a set of similar cells that specialize in a particular function and are classified into four basic groups: epithelial, connective, muscular, and nervous.

1. Epithelial Tissue

Formed by epithelia, epithelial tissue has two main types based on its features:

• Epithelial tissue lining: Lines the body's surface and internal body cavities. This is further divided into two types:
  • Simple: Just one layer of cells.
  • Stratified: Many layers of cells.
• Glandular epithelial tissue: Builds secreting cells that are exchanged or clustered epithelial cells to form glands.

Examples of Epithelial Tissue:

• Simple squamous epithelium: Flattened cells, wider than they are high. Lines the heart and the inside of blood vessels.
• Simple cuboidal epithelium: Cuboidal cells, as wide as they are high, with a spherical and central nucleus. Lines the surface of the ovaries and the renal tubules.
• Simple columnar epithelium: Columnar cells, taller than they are wide, with the nucleus towards the base. Has microvilli lining the bowel.
• Stratified squamous epithelium: The deepest layers of cells are cuboidal, and as they move towards the surface, they become flattened. Found in the mouth, pharynx, esophagus, vagina, and rectum.
• Pseudostratified epithelium: A single layer of cells at different heights with a layered look. Lines the respiratory tract.

2. Connective Tissue

Connective tissue serves as a support for other body structures. Its cells are surrounded by abundant intercellular substance in which fibers are abundant. Collagen fibers provide resistance, elastin provides elasticity, and the lattice provides structural function. Connective tissue includes connective tissue proper, adipose, cartilage, and bone.

2.1 Connective Tissue Proper

Allows for support and unity of different tissues and organs. The most abundant cells are fibroblasts, which are responsible for developing the intercellular substance and collagen and elastin fibers. Two types are distinguished:

• Loose connective tissue: Predominantly elastin fibers that provide flexibility. It is the basis for settling the epithelia. Found in the dermis and around blood vessels.
• Fibrous connective tissue: Predominantly collagen fibers that provide mechanical strength. Forms the vocal cords, tendons, and ligaments.

2.2 Adipose Tissue

Stores lipid reserves. In vertebrates, besides the backup function, it is protective of organs and provides thermal insulation. It is found in yellow bone marrow. The main features are the adipose cells whose cytoplasm is occupied by a large vacuole that accumulates fat. The intercellular substance is limited.

2.3 Cartilaginous Tissue

Serves as support in the areas of the joints that form the skeleton or bone where bone has not yet formed. Its cells, called chondrocytes, have abundant intercellular substance composed of fibers that give strength and flexibility. It has no blood vessels or nerves.

2.4 Bone Tissue

The main supporting tissue of many vertebrates, forming the bones of the skeleton. The intercellular substance is solid, rich in collagen fibers that provide elasticity, and minerals that give the bone strength and fragility. The main cells are called osteocytes, which look like stars and are located in bone cavities in the matrix. Calcóformos ducts produce the exchange between blood and bone cells. Bones are surrounded by a layer of fibrous tissue called the periosteum, where tendons and ligaments attach. There are two types of bone tissue:

• Compact bone: Consists of the Haversian canal, through which blood vessels and nerves pass. It is located on the inside of the flat bones and the diaphysis of long bones.
• Spongy bone: A tissue-forming blood cells, this is located inside the long bones and within the short and flat bones.

3. Muscle Tissue

Made up of muscle fibers specialized in contraction, containing myofilaments in the cytoplasm consisting mainly of contractile proteins actin and myosin. There are three types of this tissue:

• Striated skeletal muscle: Formed by cylindrical fibers that can be grouped into several groups in their cytoplasm, containing sarcomeres.
• Striated cardiac muscle: Located in the heart. Consists of striated muscle fibers with a single nucleus.
• Smooth muscle: Forms elongated and spindle cells with a single center. In vertebrates, it lines blood vessels and the walls of internal organs.