Tissues (Epithelium, Connective, Muscle, & Nervous) and Cell junctions (Function & Structure) (Human Anatomy)

Adhesion junctions (desmosomes)

• Structure: Disc-like plaques attached to the inside of the plasma membrane, connected by intermediate filaments (keratin).

• Function: Strong and resilient

• Cells: Found in epithelial and cardiac muscle cells.

Tight junctions

• Structure: Bands of transmembrane proteins (claudins and occludins) that encircle cells and fuse adjacent cell membranes.

• Function: Create a barrier that prevents the passage of molecules and ions between cells, maintaining tissue integrity.

• Cells: Found in epithelial cells, especially in the intestines and blood-brain barrier.

Gap junctions

• Structure: Clusters of intercellular channels made of connexin proteins, forming pores between adjacent cells.

• Function: Allow the passage of ions, nutrients, and small molecules directly between cells for communication and coordination.

• Cells: Found in cardiac and smooth muscle cells, as well as some epithelial cells.

Simple squamous epithelium

• Structure: Single layer of flat, thin cells with a central nucleus.

• Function: Facilitates diffusion and filtration.

Stratified squamous epithelium (keratinized)

• Structure: Multiple layers of cells, with surface cells being flattened and filled with keratin.

• Function: Protection against abrasion, pathogens, and water loss.

Stratified squamous epithelium (non-keratinized)

• Structure: Multiple layers of squamous cells, with surface cells being flat but not keratinized.

• Function: Protection against abrasion while remaining moist. (flexible yet resilient)

• Location: Oral cavity, esophagus, and vagina.

Simple cuboidal epithelium

• Structure: Single layer of cube-shaped cells with central round nuclei.

• Function: Secretion and absorption.

• Cells: Found in kidney tubules and glands (e.g., thyroid).

Simple columnar epithelium

• Structure: Single layer of tall, rectangular cells, often with microvilli or cilia.

• Function: Absorption and secretion, especially of mucus and enzymes

Ciliated pseudostratified columnar epithelium

• Structure: Single layer of cells that appear stratified but all cells touch the basement membrane, with cilia on the surface.

• Function: Secretion and movement of mucus via cilia.

Skeletal muscle tissue

• Structure: Long, cylindrical, multinucleated fibers with visible striations.

• Function: Voluntary movement, posture, and heat production.

• Cells: Skeletal muscle fibers (myocytes).

Smooth muscle tissue

• Structure: Spindle-shaped cells with a single central nucleus, no striations.

• Function: Involuntary control of organs such as the intestines, blood vessels, and bladder.

Cardiac muscle tissue

• Structure: Branched, striated fibers with a single nucleus, connected by intercalated discs.

• Function: Involuntary contraction to pump blood throughout the body.

Loose areolar connective tissue

• Structure: Loosely arranged collagen, elastic, and reticular fibers in a gel-like ground substance.

• Function: Wraps and cushions organs, holds tissue fluids.

• Cells: Fibroblasts, macrophages, mast cells, and some white blood cells

Dense regular collagenous connective tissue

• Structure: Tightly packed parallel collagen fibers.

• Function: Provides strong attachment between structures, resists tension in one direction.

• Cells: Fibroblasts, found in tendons and ligaments.

Dense irregular collagenous connective tissue

• Structure: Densely packed collagen fibers running in different directions.

• Function: Provides structural strength and resists tension in multiple directions.

• Cells: Fibroblasts, found in the dermis of the skin and fibrous capsules of organs and joints.

Adipose connective tissue

• Structure: Large cells filled with lipid droplets, sparse extracellular matrix.

• Function: Energy storage, insulation, and cushioning.

• Cells: Adipocytes, found under the skin, around organs.

Hyaline cartilage connective tissue

• Structure: Amorphous but firm matrix with collagen fibers, chondrocytes in lacunae.

• Function: Provides smooth surfaces for movement, flexibility, and support.

• Cells: Chondrocytes, found in the nose, trachea, larynx, and ends of long bones.

Bone connective tissue

• Structure: Hard, calcified matrix containing collagen fibers, osteocytes in lacunae.

• Function: Support, protection, and storage of calcium; site for blood cell formation.

• Cells: Osteocytes

Blood (connective tissue)

• Structure: Fluid matrix (plasma) containing red blood cells, white blood cells, and platelets.

• Function: Transport of gases, nutrients, wastes, and other substances.

• Cells: Erythrocytes (RBCs), leukocytes (WBCs), and thrombocytes (platelets), found in blood vessels.

Lymph (connective tissue)

• Structure: Clear fluid matrix, with white blood cells (mainly lymphocytes).

• Function: Transports lymph, helps in immune defense.

• Cells: Lymphocytes, found in lymphatic vessels and nodes.