Lymphatic system: structures involved in the transfer of lymph between tissues and the blood stream, the lymph and the nodes and vessels that transport it including the immune system: defending against disease-causing agents with leukocytes, tonsils, adenoids, thymus and spleen. Integumentary system: skin, hair and nails of mammals. Also scales of fish, reptiles, and birds, and feathers of birds. Muscular system: movement with muscles. Nervous system: collecting, transferring and processing information with brain, spinal cord and nerves. Reproductive system: the sex organs, such as ovaries, fallopian tubes, uterus, vulva, vagina, testes, vas deferens, seminal vesicles, prostate and penis. Respiratory system: the organs used for breathing, the pharynx, larynx, trachea, bronchi, lungs and diaphragm. Skeletal system: structural support and protection with bones, cartilage, ligaments and tendons. Viscera
In the study of anatomy, viscera (singular viscus) refers to the internal organs of the abdominal, thoracic, and pelvic cavities. The abdominal organs may be classed as solid organs, or hollow organs. The solid organs are the liver, pancreas, spleen, kidneys, and adrenal glands. The hollow organs are the stomach, intestines, gallbladder, bladder, and rectum. In the thoracic cavity the heart is a hollow, muscular organ. Splanchnology is the study of the viscera. The term "visceral" is contrasted with the term "parietal", meaning "of or relating to the wall of a body part, organ or cavity" The two terms are often used in describing a membrane or piece of connective tissue, referring to the opposing sides.
Parasystole is a kind of arrhythmia caused by the presence and function of a secondary pacemaker in the heart, which works in parallel with the SA node. Parasystolic pacemakers are protected from depolarization by the SA node by some kind of entrance block. This block can be complete or incomplete. Parasystolic pacemakers can exist in both the atrium or the ventricle. Atrial parasystolia are characterized by narrow QRS complexes
Two forms of ventricular parasystole have been described in the literature, fixed parasystole and modulated parasystole. Fixed ventricular parasystole occurs when an ectopic pacemaker is protected by entrance block, and thus its activity is completely independent from the sinus pacemaker activity. Hence, the ectopic pacemaker is expected to fire at a fixed rate. Therefore, on ECG, the coupling intervals of the manifest ectopic beats will wander through the basic cycle of the sinus rhythm. Accordingly, the traditional electrocardiographic criteria used to recognize the fixed form of parasystole are:

the presence of variable coupling intervals of the manifest ectopic beats;
inter-ectopic intervals that are simple multiples of a common denominator;
fusion beats.According to the modulated parasystole hypothesis, rigid constancy of a pacemaker might be expected if the entrance block were complete, but if there is an escape route available for the emergence of ectopic activity, then clearly there must be an effective ionic communication, not complete insulation, between the two tissues. If there is an electrical
communication between the two, then the depolarization of the surrounding ventricle may influence the ectopic pacemaker.