smooth-muscle cells compared to skeletal muscle

Which of the following is absent in smooth-muscle cells compared to skeletal muscle cells?

• a.Troponin
• b.Calmodulin
• c.Calcium
• d.Myosin light-chain kinase
• e.Actin and tropomyosin interactions

 The answer is (a).
Smooth muscle is the least specialized type of muscle and contains no troponin. The contractile process is similar to the actin-myosin interactions that occur in motility of nonmuscle cells. In the smooth-muscle cell, actin and myosin are attached to intermediate filaments at dense bodies in the sarcolemma and cytoplasm. Dense bodies contain alpha-actinin and, therefore, resemble the Z-lines of skeletal muscle. Contraction causes cell shortening and a change in shape from elongate to globular. Contraction occurs by a sliding filament action analogous to the mechanism used by thick and thin filaments in striated muscle.

The connections to the plasma membrane allow all the smooth-muscle cells in the same region to act as a functional unit. The sarcoplasmic reticulum is not as well developed as that in the striated muscles. There are no T tubules present; however, endocytic vesicles called caveolae are believed to function in a fashion similar to the T tubule system of skeletal muscle. When intracellular calcium levels increase, the calcium is bound to the Ca2+ -binding protein, calmodulin. Ca2+-calmodulin (answers b and c) is required and is bound to myosin light-chain kinase (answer d) to form a Ca2+ -calmodulin-kinase complex. This complex catlayzes the phosphorylation of one of the two myosin light chains on the myosin heads. That phosphorylation allows the binding of actin to myosin. A specific phosphatase
dephosphorylates the myosin light chain, which returns the actin and myosin to the inactive, resting state. The actin-tropomyosin interactions (answer e) are similar in smooth and skeletal muscle.
Smooth-muscle cells (e.g., vascular smooth-muscle cells) also differ from skeletal muscle cells in that like fibroblasts, they are capable of collagen, elastin, and proteoglycan synthesis.

Stages of RBC`s production

This picture which shows the exact conversion process starting from the hemoblast & ending up with the erythrocyte. click for enlargment

The Erythrocyte production or "Erythropoiesis" begins when a hemocytoblast descendant called a Myeloid Stem Cell is transformed into proerythroblast, which in turn gives arise to the early (basophilic) erythroblasts that produce huge numbers of ribosomes, During these first 2 phases, the cells divide many times.
The Hemoglobin synthesis & iron accumulation occurs as the early erythroblast is transformed into a Late Erythroblast. The color of the cell cytoblasm changes as the Blue-Staining Ribosomes becomes masked by the pink color of Hemoglobin, In this stage & when the last cell produced "Normoblast" accumulates hemoglobin in a concentration of around 34%, most of its organelles are ejected, In addition, it’s nuclear functions ends & is pinched off. This will lead to cell collapsion "To Inward Direction" & will take at the end the bioconcave shape, so the result after assuming the bioconcave shape will be the what is called "The Reticulocyte" , those reticulocytes are considered to be the young erythrocytes which are holding that name because they still contain a network of clumped ribosomes & rough endoplasmic reticulum.
All the entire process from forming the hemocytoblast untill forming the reticulocyte will take around 3 to 5 days, The filled reticulocytes almost are filled to bursting with hemoglobin, then those reticulocytes filled with hemoglobin will enter the blood stream to begin their functions & tasks in oxygen transport. Usually they become fully matured eryhthrocytes whithin 2 days of the release of the reticulocytes, as the reticulocytes ribosomes are degraded by intracellular enzymes.

Satellite cells in skeletal muscle proliferate and regeneration

A 5-year-old boy sustains a tear in his gastrocnemius muscle when he is involved in a bicycle accident. Regeneration of the muscle will occur through which of the following?
a.Differentiation of satellite cells
b.Dedifferentiation of myocytes into myoblasts
c.Fusion of damaged myofibers to form new myotubes
d.Hyperplasia of existing myofibers
e.Differentiation of fibroblasts to form myocytes

 The answer is a.
Satellite cells in skeletal muscle proliferate and reconstitute the damaged part of the myofibers. They are supportive cells for maintenance of muscle and a source of new myofibers after injury or after increased load. There is no dedifferentiation of myocytes into myoblasts (answer b), or fusion of damaged myofibers to form new myotubes (answer c). Hypertrophy, not hyperplasia
(answer d),occurs in existing myofibers in response to increased load.

Proliferation of fibroblasts may occur in the damaged area but leads to fibrosis, not repair of skeletal muscle. Fibroblasts do not differentiate into myocytes (answer e). The multinucleate organization of skeletal muscle is derived developmentally by fusion and not by amitosis (failure of cytokinesis after DNA synthesis). Mitotic activity is terminated after fusion occurs. In the
development of skeletal muscle, myoblasts of mesodermal origin undergo cell proliferation. Myocyte cell division ceases soon after birth. Myoblasts, which are mononucleate cells, fuse with each other end to end to form myotubes. This process requires cell recognition between myoblasts, alignment, and subsequent fusion.

Histopathology of Osteosarcoma

Eyelid hemangioma

Eyelid hemangiomas that present congenitally or in early infancy are ususally of the capillary type ("strawberry marks"). These lesions are considered hemartomas.

Histopathologically, these lesions are densely cellular and consist of numerous small, blood-filled channels lined by plump endothelial cells with associated pericytes and little contribution from larger vessels or stroma . They may appear after birth but usually cease growing by one year of age. Complete spontaneous regression by five years of age is the rule (in 80-90%).

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Histopathology Bone--Multiple myeloma

Schwannoma (Histology)

Notice the whirly swirly pattern and how the cell nuclei are closely bunched together... almost as if they're forming a fence (Verocay bodies). Schwannomas are benign spindle cell tumors that occur along the edges of peripheral nerves. They can usually be removed without damaging the nerve itself.

Compact and Spongy Bones

The bone tissue has 2 types of differ in density......> compact and spongy

1-Compact Bone:

Compact bone consists of closely packed "osteons or haversian systems". The osteon consists of a central canal called the osteonic (haversian) canal, which is surrounded by concentric rings (lamellae) of matrix. Between the rings of matrix, the bone cells (osteocytes) are located in spaces called lacunae.
Small channels (canaliculi) radiate from the lacunae to the osteonic (haversian) canal to provide passageways through the hard matrix. In compact bone, the haversian systems are packed tightly together to form what appears to be a solid mass. The osteonic canals contain blood vessels that are parallel to the long axis of the bone. These blood vessels interconnect, by way of perforating canals, with vessels on the surface of the bone.

2-Spongy (Cancellous) Bone

Spongy (cancellous) bone is lighter and less dense than compact bone. Spongy bone consists of plates (trabeculae) and bars of bone adjacent to small, irregular cavities that contain red bone marrow. The canaliculi connect to the adjacent cavities, instead of a central haversian canal, to receive their blood supply. It may appear that the trabeculae are arranged in a haphazard manner, but they are organized to provide maximum strength similar to braces that are used to support a building. The trabeculae of spongy bone follow the lines of stress and can realign if the direction of stress changes.

Megaloblastic anaemia is a disorder of the bone marrow. There is a presence of erythroblasts in the bone marrow with delayed nuclear maturation because of defective DNA synthesis.

In megaoblastic anaemia Erythrocytes are larger and have higher nuclear-to-cytoplasmic ratios compared to normoblastic cells.
Neutrophils can be hypersegmented, and megakaryocytes are abnormal. Risk Factors for Megaloblastic anaemia are Vitamin B12 deficiency ,Folic acid deficiency and Conditions with neither B12 nor folate deficiency, e.g. orotic aciduria, where there is a defect in pyrimidine synthesis, therapy with drugs interfering with DNA synthesis and myelodysplasia.