Histology Lecture Notes PDF

Histology Lecture Notes Dr. Shaimaa Kashef Bone Bone is a specialized connective tissue whose extracellular matrix is calcified. It consists of an outer layer of the periosteum (subdivided into an outer fibrous & inner cellul...

Histology Lecture Notes Dr. Shaimaa Kashef Bone Bone is a specialized connective tissue whose extracellular matrix is calcified. It consists of an outer layer of the periosteum (subdivided into an outer fibrous & inner cellular layer), similar to cartilage, but the inner cellular layer consists of osteoprogenitor cells. The periosteum is anchored to the bone by special bundles of collagen fibers known as Sharpey’s fibers. The inner medullary cavity of bone is lined with an endosteum that composed of a single layer of osteoprogenitor cells and osteoblasts (bone matrix-secreting cells). (Fig.6) Figure (6): Structure of bone https://feji.us/glqg7l Functions: 1-Bone protects and supports vital organs of the body as brain and spinal cord. 2-Bone serves as a storage site for calcium and phosphate. 3-It contains bone marrow which acts as a haemopoietic organ. 4- Bone serves as a lever for the muscles attached to it. 1 Histology Lecture Notes Dr. Shaimaa Kashef Structure of the bone: Bone is formed of: A-Solid matrix. C-Periosteum B-Bone cells D-Endosteum A- Bone Matrix is composed of organic and inorganic matters: I) Organic matter: (collagen fibers, proteoglycans and glycoproteins) II) Inorganic matter: mainly calcium phosphate (50-60%). The calcified matrix is organized into lamellae and within it, there are small cavities (lacunae) containing osteocytes. B- Bone cells are osteogenic cells, osteoblasts, osteocytes, and osteoclasts (Fig.7). Figure (7): Bone cells https://shorturl.at/FJIaA 2 Histology Lecture Notes Dr. Shaimaa Kashef 1-Osteogenic cells: Site: They are found in the periosteum and endosteum. Structure: They are spindle-shaped cells with pale elongated nuclei. Function: They are the stem cells of the bone. They can divide and differentiate into osteoblasts. 2-Osteoblasts: Site: They are located on the surface of the bone side by side, resembling epithelium. Structure: They are cuboidal cells with pale nuclei and basophilic cytoplasm. Function: They are responsible for the synthesis of organic components of bone matrix. Osteoblasts change into osteocytes when they are trapped inside lacunae (Fig.8). Figure (8): Osteoprogenitor cells, osteoblasts & osteocytes https://shorturl.at/SLLqG 3 Histology Lecture Notes Dr. Shaimaa Kashef 3-Osteocytes: Site: They are present singly in a small cavity called lacuna. They have cytoplasmic processes that pass through canaliculi within the bony matrix to be in contact with the processes of the adjacent cells. Structure: Osteocytes are flat cells with less basophilic cytoplasm and darker nucleus Function: They are responsible for maintaining bone matrix. 4- Osteoclasts: Origin: They are phagocytic cells derived from blood monocytes. Site: They are present at bony surface depression called Howship`s lacuna. Structure: They are large cells having many nuclei and acidophilic cytoplasm. The surface facing the bone is irregular (Ruffled border). (Fig.9). Function: They are responsible for the resorption and remodeling of bone during bone formation. Figure (9): Osteoclasts https://shorturl.at/K7ses 4 Histology Lecture Notes Dr. Shaimaa Kashef Test your self Q1. MCQ 1) Which one of the following cells is responsible the synthesis of protein and fibers of the matrix of the bone? A) Osteoblasts. B) Osteocytes. C) Osteoblasts. D) Osteogenic cells. 2) Which one of the following cells has a ruffled border? A) Osteoblasts. B) Osteocytes. C) Osteoblasts. D) Osteogenic cells. Q2. Match each bone cell with its correct function Cartilage type Site 1) Osteogenic cells A) Bone resorption and remodeling. 2) Osteoblasts B) Maintaining bone matrix. 3) Osteocytes C) Synthesis of bone matrix. 4) Osteoclasts D) Stem cells of bone. 1)……….. 2)………… 3)………………….. 4)………. 5