Tissues of the Body: Simple Columnar Epithelium

Epithelial Tissues

• Simple Cuboidal Epithelium:

  • Lining of thyroid follicles.
  • Covers kidney's convoluted tubules and small collecting tubules.
  • Found in the anterior surface of the lens and inner cells of the choroid of the eye.
  • Lines acini and small ducts of glands.
  • Forms the germinal epithelium of ovaries in newborns.

• Simple Columnar Epithelium (Non-Ciliated):

  • Composed of tall columnar cells with basal nuclei; involved in secretion and absorption.
  • In the stomach, secretes mucin; cytoplasm appears clear.
  • In the intestine, features microvilli for enhanced absorption, rich in phosphatase enzymes.
  • Lines the gall bladder, common bile duct, pancreatic duct, and large collecting tubules of the kidney.

• Simple Columnar Epithelium (Ciliated):

  • Formed of columnar cells with cilia on free borders for movement of particles.
  • Present in the central canal of the spinal cord, brain ventricles, fallopian tubes, uterus, Eustachian tube, and some bronchioles.

• Pseudo-Stratified Columnar Epithelium:

  • Appears multi-layered due to irregular cell shapes and nuclear positioning, but consists of a single layer.
  • Contains goblet cells for mucus secretion.
  • Located in upper respiratory passages, Eustachian tube, and lacrimal sac.

Connective Tissue Cells

• Histiocyte or Macrophage:

  • Present in vascular connective tissue, especially in serous membranes and alimentary canal.
  • Functions include engulfing foreign bodies, cleaning wounds, and forming multinucleated giant cells for large foreign bodies.

• Pigment Cell:

  • Found in connective tissues of the skin and eye, carries melanin pigments.
  • Responsible for synthesis of melanin to protect from UV rays; sensitive to light.

• Fat Cell (Adipocyte):

  • Originates from mesenchymal cells, presents a signet ring appearance due to large fat globule.

Hematopoietic Tissue

• Myeloid Tissue:
  • Yellow Bone Marrow: Composed of fat cells; serves as fat storage; can convert to red marrow under specific conditions.
  • Red Bone Marrow: Present in sternum, vertebrae, ribs, skull, clavicle, and pelvis; active in blood cell production.

White Blood Cells

• Granulocytes:

  • Comprise neutrophils (60-70% of leukocytes), eosinophils, and basophils; involved in immune response.
  • Neutrophils possess a segmented nucleus and are important for phagocytosis.

• Monocyte:

  • Larger leukocytes with a central, indented nucleus and abundant blue-stained cytoplasm.
  • Transform into macrophages in connective tissue and play a role in phagocytosis.

• Lymphocytes:

  • Key players in immune response; divided into T-lymphocytes (75%) and B-lymphocytes (25%).
  • Small lymphocytes have scanty cytoplasm, while large lymphocytes are more abundant with developed organelles.

Bone Cells

• Osteoblasts:

  • Derived from osteogenic cells; involved in bone formation by synthesizing collagen and minerals.
  • Active during growth and healing of bones.

• Osteocyte:

  • Mature bone cells located in lacunae, unable to divide; they maintain bone matrix and calcium levels.

• Osteoclast:

  • Large, multinucleated cells responsible for bone resorption; originates from the fusion of monocytes.
  • Plays a vital role in bone remodeling during ossification.