Cell Types: Quarter 1, Lesson 4

Types of Cells in the Human Body

• Human body contains numerous cell types including stem cells, blood cells, bone cells, cartilage cells, muscle cells, fat cells, nerve cells, and various epithelial cell types.
• Stem cells function as precursors that differentiate into various cell types, categorized into pluripotent and unipotent.

Stem Cells

• Pluripotent Stem Cells can differentiate into nearly all cell types except for extraembryonic tissues (placenta, amnion, chorion).
• Unipotent Stem Cells produce only one specific cell type.
• Embryonic Stem Cells are the most primitive, undifferentiated cells present in embryos.
• Hematopoietic Stem Cells generate all blood cell types, including erythrocytes (RBCs), leukocytes (WBCs), and platelets.
• Mesenchymal Stem Cells (bone marrow stromal cells) differentiate into a variety of connective tissues, including bone and fat cells.
• Neural Stem Cells give rise to neurons and supporting glial cells in the nervous system.
• Epithelial Stem Cells produce various cell types involved in lining and protecting body surfaces.

Blood Cells

• Red Blood Cells (Erythrocytes): Biconcave structure; primary function is oxygen transport via hemoglobin.
• White Blood Cells (Leukocytes): Crucial for immune defense, constituting about 1% of blood volume.
  • Granulocytes: Include neutrophils (most abundant), eosinophils (rare, combat parasites), and basophils (release histamines).
  • Agranulocytes: Comprise lymphocytes (T-cells and B-cells) involved in adaptive immunity, and monocytes, which differentiate into macrophages.
• Platelets (Thrombocytes): Fragments derived from megakaryocytes, essential for clotting; lifespan of 8-10 days.

Nerve Cells

• Neurons: Specialized for transmitting electrical impulses throughout the body.
• Neuroglial Cells: Support neurons, performing functions such as debris removal and myelin sheath formation.

Muscle Cells

• Skeletal Muscle Cells: Facilitate voluntary movement.
• Cardiac Muscle Cells (Cardiomyocytes): Form the heart muscle, responsible for involuntary contractions.
• Smooth Muscle Cells: Enable involuntary movements in various organs by contracting as sheets.

Cartilage Cells

• Chondrocytes: Primary cells found in cartilage; vital for maintaining cartilage structure and function.
• Types of cartilage include:
  • Hyaline Cartilage: Present in joints and respiratory passages.
  • Elastic Cartilage: Found in structures requiring flexibility (e.g., ears).
  • Fibrocartilage: Provides strength and support, found in intervertebral discs and knee joints.

Bone Cells

• Osteoblasts: Responsible for bone formation.
• Osteocytes: Mature bone cells embedded in bone matrix, regulate bone maintenance and remodeling.
• Osteoclasts: Specialized for bone resorption.
• Lining Cells: Maintain the bone surface and regulate calcium release into the bloodstream.

Skin Cells

• Keratinocytes: Produce keratin, forming the protective barrier of the skin.
• Melanocytes: Synthesize melanin, influencing skin pigmentation.
• Langerhans Cells: Part of the immune response in the skin.
• Merkel Cells: Involved in sensory reception.

Endothelial Cells

• Form the inner lining of blood vessels, providing a barrier between blood and surrounding tissues.

Epithelial Cells

• Constitute linings for cavities throughout the body, forming protective layers and facilitating absorption and secretion.

Fat Cells

• Adipocytes: Store energy as lipids.
  • White Fat Cells: Store excess lipids, involved in energy metabolism.
  • Brown Fat Cells: Contain multiple vacuoles, play a role in thermogenesis.

Sex Cells

• Male Gametes (Spermatozoa): Small and motile, crucial for fertilization.
• Female Gametes (Ova): Larger, round cells produced in the ovaries, involved in reproduction.

Summary of Cell Types

• Blood Cells: RBCs (Erythrocytes), WBCs (Leukocytes), Platelets (Thrombocytes)
• Bone Cells: Osteoblasts, Osteocytes, Osteoclasts, Bone Lining Cells
• Cartilage Cells: Chondrocytes
• Muscle Cells: Skeletal Myocytes, Cardiomyocytes, Smooth Myocytes
• Skin Cells: Keratinocytes, Melanocytes, Langerhans Cells, Merkel Cells
• Endothelial Cells: Line blood vessels
• Epithelial Cells: Line cavities and surfaces
• Fat Cells: White fat cells, Brown fat cells
• Sex Cells: Spermatozoa and Ova