Cardiac Muscle Tissue. Cardiac Muscle Tissue

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1 Walls of the heart (cardia: heart); myocardium. Cardiac muscle fibers not as densely packed as skeletal cardiac muscle tissue is highly vascularized Other components; dense C.T. septa, larger blood vessels, lymphatic vessels, and small nerves. 1 Cardiac muscle fiber; 1/3 to 1/6 as wide as skeletal much shorter 5 to 10 times longer than wide. Typically branched 1-2 nuclei nuclei are larger, lighter-staining, elongate are centrally-located in the fiber 2

2 Myofibrils align with the main axis of the muscle fiber centrally-located myofibrils of the fiber swerve around the nucleus void areas just beyond the ends of the nucleus-spaces; lacking myofibrils Fibers are cross-striated. Components tend to be much shorter and smaller Cross-striation pattern is a much finer A-bands and I-bands narrower. 3 Cardiac fibers interconnect at their ends THREE-DIMENSIONAL NETWORK of fibers Ends are flat and wide Zone of gap junctions stains more darkly than crossstriations Called an intercalated disc. Spaces contain capillaries 4

3 Intercalated disc Zone of electrical connection Membrane impulse spreads through the network of fibers one huge all-or-none unit of contraction. Cardiac muscle tissue is an interconnected network of cardiocytes 5 6

4 Void in cytoplasm Cross banding pattern Central nucleus Intercalated discs Overall; more disorganized than skeletal muscle 7 Intercalated discs 8

5 Cardiac muscle fibers do not require exogenous stimulation Rhythmically self-stimulating Occurs more quickly at the sino-atrial node (the "pacemaker") Spreads rapidly, causing contraction Impulse is conducted from adjacent fibers 9 Nervous and endocrine system are able to modulate contraction speed up or slow down stronger contraction or weaker contraction. If cardiac muscle tissue has 02 and chemical energy (glucose and lactate) it will continue to rhythmically contract. 10

6 Produce ATP aerobically only Do not reach a high level of contraction Never rest for more than about 1 sec of time Highly vascularized High myoglobin concentration very dark in life compared to skeletal Contracts more slowly somewhat greater strength. 11 On low power; Bark of trunk of elm trees Branching-and-interconnecting system of cells. light-stained Nuclei, evenly distributed more oval than skeletal and smooth muscle fibers not in single-file. 12

7 Capillaries very abundant oriented obliquely to longitudinally. Cardiocytes are eosinophilic. Cross-striations very fine; not distinct. Intercalated discs not distinct w/o special staining. Septa typically scarce larger blood vessels typically scarce small to medium-sized nerves not obvious 13 Structure and appearance of cross sections of cardiac muscle tissue Variable in diameter and shape Are branched. Central nuclei, round and lightly stained One-half the diameter of the fiber 14

8 Many fibers (or fiber branches) crosssectioned at location other than at nucleus cross-section near nucleus fiber has a void Capillaries abundant mainly cross-sectioned look for isolated RBC Need special stain for intercalated discs silver, orscein, toludine blue, etc. 15 Smooth muscle tissue Smooth muscle tissue is found in the walls of tubular organs blood vessels, digestive tract, respiratory organs, urinary ducts, reproductive ducts, controls the diameter and/or the length Made of smooth muscle fibers (SMFs) Parallel, densely packed Poorly vascularized, contains CT 16

9 Smooth muscle tissue Structure and function of the smooth muscle fiber Ancient and primitive Elongate, narrow and spindle shape diameter < cardiac muscle fiber. Mono-nucleated elongate, light-staining nucleus in middle of SMF Nucleus diameter ~ 2/3 to 3/4 of SMF 17 Smooth muscle tissue Moderately eosinophilic H&E; more pink than orange collagen fibers nearby, orange cytoplasmic : slightly basophilic ; slightly violet-pink. Not cross-striated. Fiber contains myofibrils myofibrils at a slight angle to axis Different bundles, different directions SMFs contract more slowly but with greater strength per gram 18

10 Smooth muscle tissue Anaerobic low metabolic rate fewer mitochondria and lower myoglobin. Adjust tone. No T-tubule-system. 19 Smooth muscle tissue Tone ; sustained partial depolarization of the sarcolemma No full magnitude membrane impulses. Several ways to stimulated contraction Stimuli: histamine, CO 2, 0 2, prostaglandins, hormones stretching depolarization from adjacent smooth muscle fibers direct neural input (autonomic; involuntary) 20

11 Smooth muscle tissue Structural and functional types of smooth muscle tissue Vascular smooth muscle tissue Walls of blood vessels and larger lymphatic vessels. Each fiber has an autonomic nerve ending (sympathetic) electrically insulated by reticular fibers no membrane depolarization from fiber to fiber 21 Smooth muscle tissue Visceral smooth muscle tissue Walls of digestive tract organs. Autonomic nerve endings throughout tissue; not all fibers have a nerve ending membrane depolarization is conducted from fiber to fiber. 22

12 Smooth muscle tissue Structure and appearance, longitudinal Homogeneously stained eosinophilic elongate, lightly stained nuclei random distribution ; oriented in the same direction H&E: pink to violet-pink. Capillaries, CT elements, nerves, etc., very scarce to absent. 23 Structure and appearance of cross section homogeneously stained moderately eosinophilic Sparse, very small, round, light-stained nuclei H&E: pink to violet-pink. Cell membranes; not distinguishable. Capillaries, CT elements, etc., very scarce to absent. Most difficult tissues to identify Smooth muscle tissue 24

13 Smooth muscle tissue Smooth muscle fibers are sometimes found as isolated fibers; one to two fibers thick are not smooth muscle tissue, need a mass of cells several cells thick. 25