L6 - Smooth Muscles 2 PDF - Histology Past Paper 2023-2024

ITM 101 | HISTOLOGY LESSON # 5 - Smooth Muscles 1st YEAR | A.Y. 2023-2024 | SEPTEMBER 11, 2023 DR. JOANNA MELISSA F MARQUEZ, MD, MPH, DPSP SMOOTH MUSCLE 3. PYLORUS Note: Smooth mus...

ITM 101 | HISTOLOGY LESSON # 5 - Smooth Muscles 1st YEAR | A.Y. 2023-2024 | SEPTEMBER 11, 2023 DR. JOANNA MELISSA F MARQUEZ, MD, MPH, DPSP SMOOTH MUSCLE 3. PYLORUS Note: Smooth muscle (tunica muscularis) on pyloric sphincter thickens to timing the flow of food and prevent acid reflux. Composed of fusiform (spindle-shapedI uninucleate nucleus that respond to the autonomic nervous system Elongated nucleus situated in the wider central portion Nucleus contains one or two nucleoli Chromatin distributed in small clumps 4. JEJUNUM peripheral cytoplasm contains the contractile Note: Has presence of villi which are fusiform cells, components the smooth muscle on submucosa is present as single ○ Note: not all types of muscle have the same or double. Contractile Mechanism Forms the contractile portion of the wall of the digestive tract from the middle of the esophagus to the internal sphincter of the anus. 1. ESOPHAGUS Note: 1st portion of esophagus has striated muscle. 5. SMALL INTESTINE 2. STOMACH 101 INTRODUCTION TO MEDICINE | HISTOLOGY AYURA 2027 1 ITM 101 | HISTOLOGY LESSON # 5 - Smooth Muscles 1st YEAR | A.Y. 2023-2024 | SEPTEMBER 11, 2023 DR. JOANNA MELISSA F MARQUEZ, MD, MPH, DPSP 6. LARGE INTESTINE Note: Shortened villi, has inner circular and outer longitudinal that moves in peristalsis motion. 8. BLOOD VESSELS Blood vessels also have smooth muscle in their wall that controls their caliber. Note: Vein has presence of sphincter and artery has smaller muscle. 7. LUNGS Found in the walls of respiratory passages from the trachea to the alveolar ducts. Note: No more smooth muscle on alveoli. During operation when a person is under anesthesia, the smooth muscles will be immobile, making respiration difficult. Hence, proper intubation is important. Tunica media regulates the internal diameter of the blood vessel and is important in regulating blood pressure. It is thicker in arteries than in veins. ○ Note: If the blood vessel is vasoconstricted, blood pressure increases. Clinical importance: In atherosclerosis, there is migration of smooth muscle cells from the tunica media to the tunica intima, which will then be part of formation of atherosclerotic plaques. 101 INTRODUCTION TO MEDICINE | HISTOLOGY AYURA 2027 2 ITM 101 | HISTOLOGY LESSON # 5 - Smooth Muscles 1st YEAR | A.Y. 2023-2024 | SEPTEMBER 11, 2023 DR. JOANNA MELISSA F MARQUEZ, MD, MPH, DPSP ORGANIZATIONAL DIVERSITY Their coordinated action produces peristaltic waves of Are organized in different patterns to meet local contraction that are propagated along the intestine to requirements. propel its contents. May occur: ○ Singly in loose connective tissue ○ Gathered together in slender fascicles (e.g. tiny arrector pili muscle associated with each hair bulb) ○ Annular band (e.g. constrictor pupillae muscle of the iris) Note: Arrector pili muscle contracts, resulting in goosebumps that occur in certain instances (e.g. seeing a ghost). It is located beside the root of each hair follicle. In hollow organs such as the urinary bladder, smooth muscle is not organized in distinct layers but In precapillary arterioles, single circumferentially oriented interwoven coarse bundles oriented in various fibers are spaced at intervals along the vessel. Their directions. contraction narrows the lumen, decreasing blood flow through the capillary bed. In the wall of larger arteries flow is controlled by a continuous layer of circular smooth muscle. Speakers’ note (PPT): The force generated by contraction of the fibers is transmitted through their investment of reticular fibers to the interstitial connective tissue, and thus spreads throughout the muscle mass, diminishing the size of the organ void its contents. Question by Doc: You wanted to pee and you denied yourself Note: Arterioles are smaller arteries. The arterioles are not from peeing, what could happen to the signal from the brain? entirely covered by muscles, in contrast to arteries that are Like, the brain sent a signal for you to pee, and then this signal entirely covered. As seen in the picture above, there are only was ignored and then later on faded. After a few minutes, the muscle bands in an arteriole, while the artery is covered by the brain sends another signal for you to pee. (Doc did not tunica media. answer). In the wall of the intestine, smooth muscle fibers form Question by Doc in relation to the previous question: In two concentric layers with the fibers of the inner layer geriatric patients, would this be a problem with smooth or oriented circumferentially and those of the outer layer skeletal muscle? Answer: Remember, there are voluntary and longitudinally. involuntary sphincters. (Doc implies that it could be a problem Contraction of the inner layer constricts, and the outer of smooth or skeletal muscle). layer tends to shorten the intestine. 101 INTRODUCTION TO MEDICINE | HISTOLOGY AYURA 2027 3 ITM 101 | HISTOLOGY LESSON # 5 - Smooth Muscles 1st YEAR | A.Y. 2023-2024 | SEPTEMBER 11, 2023 DR. JOANNA MELISSA F MARQUEZ, MD, MPH, DPSP VARIATIONS IN FORM Three kinds of filaments can be resolved: ○ Thin actin filaments 4-8 nm in diameter ○ Thicker myosin filaments 15 nm in diameter ○ Intermediate filaments 10 nm Desmin – a cytoskeletal protein characteristic of muscle Vimentin Fibers in the urinary bladder and ductus deferens are often branched. Myoepithelial cells have myofibril-like bundles of actin and myosin filaments. The cells processes Question by Doc: Does the smooth muscle have H band, M embrace the acini of the gland and hormonally band, and Z band? Answer: None. induced contraction serves to expel the milk. Pericytes found in capillaries and postcapillary Follow up question: So how does it contract? Answer: Sliding venules; assumed to be capable of contracting to also but it does not have an organization like H band, M band, influence blood flow. and Z band. These organizations only exist in striated muscles. Doc: The myoepithelial cells here are considered as the Question by Doc: What is the function of the calcium here? smooth muscle because it has a contractile property, same Answer: It is for contraction. with the pericytes. Doc: The myoepithelial cells are smooth muscles that are not typically elongated. Rarely, spindle-like structures of these cells are captured in cuttings. But most of the time, these muscles are captured/ illustrated as round. Doc: In pathology, related to cancer cells, myoepithelial cells are always observed. Once it is breached, the myoepithelial Filaments occur in longitudinal or oblique bundles cells may go out of the epithelial cells. This will be a criteria that converge on, and attach to, the cytoplasmic for the diagnosis of cancer. However, in physiology, dense bodies and subplasmalemmal dense plaques myoepithelial cells are for contraction and help in secretion of to form robust cytoskeletal network. milk. Doc: The diagram is how smooth muscle is organized. Skeletal Doc: Pericytes found in capillaries and postcapillary venules muscles are much more organized ( H, M, Z band) than are assumed to have contractile properties. So yung smooth muscles (oblique bundles). The actin and myosin in pinapakita ko sa inyo palagi na fusiform, sa may mga smooth muscles are attached to cytoplasmic dense bodies capillaries, meron din dun siya contractile properties. (the brown circles in the diagram). The brown circles in the diagram have the same function with the H band, Z band, of ULTRASTRUCTURE OF SMOOTH MUSCLE the skeletal muscles. Cytoplasm of smooth muscle fibers contains a small Short myosin filaments seem to be intercalated golgi complex, a cluster of elongate mitochondria, a within bundles of relatively long actin filaments few short profiles of endoplasmic reticulum and The ratio of actin to myosin filaments is 12:1 to 14:1 many free ribosomes. in smooth muscle. (Compared to 2:1 or 4:1 in skeletal muscle). 101 INTRODUCTION TO MEDICINE | HISTOLOGY AYURA 2027 4 ITM 101 | HISTOLOGY LESSON # 5 - Smooth Muscles 1st YEAR | A.Y. 2023-2024 | SEPTEMBER 11, 2023 DR. JOANNA MELISSA F MARQUEZ, MD, MPH, DPSP The orientation of bundles of filaments is longitudinal or oblique. This is as opposed to the lateral myosin filaments responsible for the cross-banding of skeletal muscle. Myofibrils terminate in the cytoplasmic dense bodies and the actin filaments on the two sides of a dense body are of opposite polarity. (equivalent to z-lines of skeletal muscle). In isolated thick filaments, the projecting heads of the myosin molecules, which form cross-bridges to the surrounding actin filaments are found along their entire length. (Thick filaments of skeletal muscle have a bare central segment that is devoid of cross bridges. ) Speaker’s Note: Sarcoplasmic reticulum also has Calcium. PHYSIOLOGY OF SMOOTH MUSCLE A distinctive feature of the ultrastructure of smooth Shortening is produced by a similar sliding of actin muscle fibers is the presence of a great number of filaments with respect to the myosin filaments. vesicular invagination of the plasmalemma Contractions is slow but it can be sustained for long (caveolae). periods Speaker’s Note: Caveolae - where Calcium enters. It can shorten to one-quarter of its resting length and can generate a force, per cross section area, comparable to that of Close relationship between the caveolae and smooth striated muscle, while it is consuming less energy. endoplasmic reticulum is comparable to the interaction between T-tubules and sarcoplasmic The relatively slow speed and broad range of shortening may reticulum. be attributable to the fact that the actin filaments are considerably longer (4.6 um) than those of skeletal muscle Speaker’s Note: Skeletal muscles have T-tubules (1.6 um). instead of caveolae but their function is the same. All about calcium. 101 INTRODUCTION TO MEDICINE | HISTOLOGY AYURA 2027 5 ITM 101 | HISTOLOGY LESSON # 5 - Smooth Muscles 1st YEAR | A.Y. 2023-2024 | SEPTEMBER 11, 2023 DR. JOANNA MELISSA F MARQUEZ, MD, MPH, DPSP The force generated is believed to be transmitted to the cell - In the uterus, estrogen levels change with the surface via the attachment of the contractile units to the menstrual cycle, together with actin and myosin cytoplasmic dense bodies at nodal points in the cytoskeleton. content of the uterine smooth muscle. The tropomyosin complex that is activated by calcium ions to initiate contraction of skeletal muscle is absent in smooth muscle. Instead, calcium diffusing into the cell with depolarization of the membrane or calcium released from the subplasmalemmal reticulum, binds to a protein calmodulin. The complex, so formed, activates ATPase in the heads of the myosin molecules and cleavage of ATP induces a conformational change in the myosin heads that results in the translocation of the adjacent actin filaments. Visceral smooth muscle is also called unitary smooth muscle. - Exhibit autorhythmicity. Intrinsically generated stimuli are conducted via gap junctions, from cell to cell throughout a large area of muscle that contracts in unison. This creates a wave of peristalsis i the intestine.Same mechanism occurs in the ureters and bile duct. Smooth muscles in the arteries, ciliary body and iris of the eye and wall of the ductus deferens, described as multi unit smooth muscle. -Each fiber is innervated and contraction is relatively rapid. -Post ganglionic autonomic nerve fibers pass over the muscle surface or penetrate into it, synapsing with fibers en passant. URETER Smooth muscles in the walls of blood vessels normally maintain a state of partial contraction called muscle tonus, but this is subject to modulation by blood-borne hormones. - Norepinephrine, angiotensin and vasopressin result in vasoconstriction. - Bradykinin and prostaglandin result in loss of muscle tone or vasodilation. Response to hormones is not confined to vascular smooth muscle. 101 INTRODUCTION TO MEDICINE | HISTOLOGY AYURA 2027 6