Smooth muscle Histology - Dr Rabia Haider.pptx

Muscle Histology Functioning

1. Smooth muscle Histology DR. RABIA HAIDER

2. Introduction Smooth muscle is a type of tissue found in the  walls of hollow organs , such as the   intestines ,  uterus  and  stomach You can also find smooth muscle in the  walls of passageways , including arteries and veins of the  cardiovascular system This type of involuntary non-striated muscle is also found in the  tracts  of the  urinary ,  respiratory  and reproductive systems

3. …. In addition to that, you can find smooth muscle in the  eyes , where it acts to change the size of the pupil and the shape of the lens The   skin  is also contains smooth muscle which allows hair to raise in response to cold temperatures or fear (erector pilli )

4. Myofila ments The smooth muscle  cell  is 3-10 µm thick and 20-200 µm long. The  cytoplasm  is homogeneously eosinophilic and consists mainly of  myofilaments The nucleus is located in the center and takes a cigar-like shape during contraction The   cell membrane  forms small pouch-like invaginations into the cytoplasm ( caveolae ) which are functionally equivalent to the T-tubules of the skeletal musculature The smooth muscle cells are anchored to the surrounding  connective tissue  by a basal lamina

5. Cytoplasm The smooth muscle  fibers  group in branching bundles As opposed to  skeletal muscle fibers  these bundles do not run strictly parallel and ordered but consist in a complex system Thus the cells can contract much stronger than  striated musculature

6. ELECTRON MICROSCOPY Sarcoplasm of S/M cell has a contractile apparatus of thin, thick filaments and a cytoskeleton of intermediate filaments The   actin  filaments  are stretched between dense bodies in the cytoplasm and attachment plaques at the cell membrane The  myosin filaments  lie between the actin filaments Furthermore  intermediate filaments  such as desmin and vimentin support the cell structure.

7. Dense bodies: They contain actin binding proteins (alpha actinin ) They are distributed in an irregular manner with in the cytoplasm and some of them may also be associated with sarcolemma Serve as actin filament binding sites Intermediate filaments of cytoskeleton are also inserted into dense bodies

8. Caveolae Plasmalemma of s/m cells has invaginations called caveolae Which contain receptors, pumps, ion channels Located closer to mitochondria and SER Serve to regulate entry or exit of calcium ions into or out of smooth muscles cells accordingly contraction or relaxation of the s/m cell

9. Myofibroblasts Myofibroblasts   represent a special type of smooth muscle cell which additionally have qualities of fibrocytes They produce connective tissue proteins such as col lagen and elastin for which reason they are also referred to as fixed (or stationary) connective tissue cells Myofibroblasts are found, among others, in alveolar septa of the  lung  and scar tissue

10. Innervation The innervation of the smooth musculature is utmost complex It lies under the influence of the  visceral nervous system  and works autonomously at the same time Furthermore, it is regulated by : neurotransmitters :   e.g. norepinephrine, acetylcholine; hormones :   e.g. estrogen, oxytocin;  tissue hormones : e.g. prostaglandins, histamine

11. …. Local changes (e.g. stretching) may have a stimulating or relaxing effect In contrast to the skeletal musculature, the smooth musculature is  contracted involuntarily

12. Functions Functionally, one differentiates between the single-unit and multi-unit type The smooth muscle cells of the single-unit type are electrically connected by  gap junctions  and contract uniformly This type of cells is found in the wall of internal organs and blood vessels (visceral smooth musculature) The   multi-unit smooth cells  are independent from each other and therefore need to be innervated individually allowing a more precise muscle control They are found, among others, in the iris and hair erector muscles

13. Regeneration Of all the three muscle types, smooth muscle has the largest ability to regenerate after injury Adult smooth muscle cells retsin this property to divide n replace damaged tissue In addition they may also develop from blood capillary pericytes

14. CLINICAL LEIOMYOMA Benign tumor developed from smooth muscle fibers