Lecture 28 Notes

Lecture 28

Derived from mesoderm: blood cells, connective tissue cells, muscle and bone. Chapt. 22 p. 1279-1291, 1296-1308 • o o o

Derived from mesoderm: Cartilage, bone, fibrous tissue, including dermis Muscles and entire vascular system, including heart, blood vessels and blood cells Tubules, ducts and supporting tissues of kidneys and gonads

Blood cells. Fig. 22-29: Erythrocytes • O2 and CO2 transport • Remain in the blood vessels Leucocytes • Combat infection, phagocytose and digest debris • Migrate out of the blood vessels into the tissues Plateletes (thrombocytes) • Platelets are cell fragments produced from megakaryocytes. Fig 22-33 • Help to repair damaged blood vessels, aid in blood clotting

Erythrocytes • • •

Manufacture hemoglobin until it accounts for some 90% of the dry weight of the cell. Nucleus, ribosomes and mitochondria are lost in the process of maturation of erythrocyte. Fig. 22-37 The most numerous type in the blood.

Leucocytes (white blood cells) • • • • o o o

are much less numerous than red (the ratio between the two is around 1:700), have nuclei, participate in protecting the body from infection, consist of 3 types of cells: lymphocytes (reenter circulation via lymphatic system channels), monocytes (single, well defined nucleus, clear cytoplasm), granulocytes, (cytoplasm is filled with granules)

Granulocytes Fig. 22-30. Neutrophil: Phagocytose and destroy microorganisms. Granules - lysosomes Eosinophil: Destroy parasites by releasing cytotoxic granules content, modulate allergic inflammatory response Basophil: Mediate inflamatory response. Granules -secretory vesicles, contain histamine, Leucocytes • Granulocytes o neutrophils, o basophils, o eosinophils • Monocytes Once they leave the bloodstream, mature in: o Macrophages (large cell, that engulf dead and damaged cells, large microorganisms) o dendritic cells - immune response • Lymphocytes - immune response o B-lymphocytes (Bone marrow) o T-lymphocytes (Thymus) o Natural killer cells Platelets are broken pieces of megakaryocytes processes . Fig 22-33 Magakaryocyte is a giant cell with polyploid nuclei (several copies of genome). Megekaryocytes themselves are not present in blood, they reside in bone marrow, middle of the bone where blood cells are formed Migration of white blood cell out of bloodstream during inflammatory response Fig. 22-31. Production of blood cells - hemopoiesis • • • •

Occurs in bone marrow (exceptions T-lymphocytes, some macrophages) Bone marrow is the spongy tissue in the cavities of the bones It contains stem cells and different blood cells It also contains: fat cells, connective tissue cells, collagen fibers, blood sinuses (small blood vessels into which new blood is discharged)

Blood stem cells • Multipotent stem cells gives rise to to all classes of blood cells • Divide slowly and give rise to amplifying cells • Stem cell gives rise to: myeloid cell line • •

• •

erythrocytes granulocytes, Monocytes Dendritic cells

lymphoid cell line • •

Lymphocytes Dendritic cells

•

Stem cells require contact with supporting stromal cells, which provide them with specific signal proteins Fig. 22-36. Stem cells can grow in culture on top of stromal cells layer

•

Muscles and muscle cells Muscle cells, myoblasts, originate from somites. Fig. 21-70 Differentiating myoblasts fuse with one another to form multinucleate muscle fibers Fig. 21-41 Growth of muscles • • • •

The number of muscle fibers in human is attained before birth Growth in length is achieved by addition of myoblasts to the fibers Growth in size is achieved by addition of myoblasts and increase in size and numbers of contractile fibrils that each nucleus supports There is a negative control signal for the amount of muscle: myostatin

A satellite stem cell on a skeletal muscle fiber Fig. 22-44

Connective tissue cells • Fibroblasts, cartilage cells, bone cells Secrete collagen, responsible for framework of the body • Fat cells • Smooth muscle cells Fibroblasts • •

The least specialized cells in connective tissue family Dispersed throughout the body Secrete extracellular matrix, that is rich in collagen

• Help to repair damaged tissue They proliferate, migrate into the wound and produce large amounts of collagen matrix • Can differentiate (“mature”) into other connective tissue cells They can occur in more or less “mature” state throughout the body. The most immature are called mesenchymal stem cells mostly found in bone marrow (mesenchyme = mesoderm) • Can grow in culture The family of connective tissue cells. Fig. 22-45 Remodeling of the bone • Bone is a mixture of collagen fibers and calcium phosphate crystals • Bone matrix is continuously replaced Osteoclasts (clast=break) demolish old bone Osteoblasts (blast=bud, germ) deposit new bone matrix • Bone can grow only by laying down additional matrix and cells on the free surfaces of existing bone • Embryos have cartilage instead of bone, during development and growth cartilage is replaced by bones Deposition of bone matrix by osteoblasts.Fig. 22-52 Osteoblasts lie on bone surface just below the precursors, secrete osteoid, the uncalcified, organic matrix of bone. As osteoblasts differentiate into osteocytes, the osteoid is rapidly calcifed and the osteocytes get embedded in this matrix. Osteoclast in cross-section. Fig. 22-53. Giant, multinulcleated, erodes bone matrix. Ruffled border is site of secretion of acids to dissolve bone minerals and hydrolases to digest the organic components of the matrix. Can send out processes to resorb bone a multiple sites. Are specialized macrophages developed from monocytes. The remodeling of compact bone. Fig. 22-54 Osteoclasts excavate bone at 50um per day. Capillary endothelial cells and osteoblasts follow, latter fill tunnel with new bone. In mammals, 10-15% of bone is replaced per year. The development of long bones. Fig. 22-56 Long bones in the limb develop from cartilage models formed during fetal development. The cartilage is believed to be eroded by osteoclasts to make way for bone. As cartilage matures, chondrocyte in central areas enlarge, the matrix around them becomes mineralized and the swollen chondrocytes die leaving large cavities. These are invaded

by osteoclasts & blood vessels, remove residual cartilage matrix. Osteoblasts enter in their wake and begin to deposit bone. The only surviving cartilage is a the ends of the bones, for joint articulation Bone health depends on proper balance of osteoblast & osteoclast activities

Practice questions 1. Osteoporosis: low bone density, due to excessive bone erosion (osteoclast activity>osteoblast activity) 2. Osteopetrosis: abnormally high bone density (osteoblast activity>osteoclast activity) 3. What tissues come from mesoderm? 4. What are the main kinds of cells in blood? 5. What is the main function of leucocytes? 6. What is the most numerous kind of cells in blood? 7. Which of the blood cells have no nucleus? 8. What are the three types of leucocytes? 9. Which type of granulocytes is able to engulf microorganisms? 10. Which type of granulocytes can secrete histamine? 11. What is the tissue where megakaryocytes can be found? 12. Which cells come from myeloid cell line? 13. Can number of muscle fibers change in adulthood? 14. What are connective tissue cells? 15. Which cells can fibroblasts turn into? 16. What is name of the cell responsible for old bone destruction? 17. What is the cause of osteoporosis? 18. What kind of cell is adipocyte? 19. Which tissue would you select to obtain mesenchymal stem cells? Terms to know: Erythrocytes Leucocytes Plateletes (thrombocytes) Granulocytes neutrophils basophils eosinophils Monocytes megakaryocytes hemopoiesis lymphoid cell line myeloid cell line stromal cells myoblasts Fibroblasts,

Chrondrocyte (cartilage cells) Adipocyte (fat cell) Osteoclasts Osteoblasts Osteoporosis Osteopetrosis