Cardiovascular physiology
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2015
Cardiac muscle cells have striations similar to those of skeletal muscle cells, being made up of sarcomeres (between Z lines) containing thick myosin filaments (in the A band) and thin actin filaments (in the I band), which are attached to the Z lines. Compared with skeletal muscle, cardiac muscle cells are shorter and thicker and form branching networks with intercalated discs between the ends of adjacent fibres that contain low electrical resistance gap junctions. Cardiac muscle operates as a functional syncytium, although it is not a true syncytium (a mass of protoplasm with many nuclei forming one cell), because each myocardial cell has its own nucleus within its own membrane. Cardiac muscle functions as a syncytium due to the presence of low-resistance connections between adjacent cells, and when an action potential is generated the atria or the ventricles contract together.
Cells, Tissues and Organs
David Sturgeon in Introduction to Anatomy and Physiology for Healthcare Students, 2018
The final type of muscle tissue is cardiac muscle or myocardium (myo + cardium = muscle + heart). This is a specialised type of striated (striped) muscle that is under involuntary control. The heart itself is essentially a muscular pump and, for obvious reasons, it is crucial that it doesn’t stop working. Unlike skeletal muscle, that is only intended to contract for a limited period of time, cardiac muscle must continue to work in an uninterrupted fashion for about 80 years or so. It can’t suddenly decide that it needs a little break and stop working for two or three minutes (occasionally it does of course – see Chapter 7). In order to ensure endurance and consistency, therefore, cardiac muscle demonstrates characteristics of both skeletal and smooth muscle. For example, it can stretch in a limited way like smooth muscle and contract (twitch only) with the force of skeletal muscle. One of the reasons it is able to endure for so long is because myocardial cells (myocardiocytes) contain a higher than normal proportion of mitochondria. These sausage-shaped organelles produce cellular energy in the form of ATP that enables the heart to continue working and step-up activity if required (e.g. in the event that an ill-tempered bear takes a dislike to you and you need to run for your life). Another unique feature of cardiac muscle is that myocardiocytes are able to generate and transmit electrical impulses (intrinsic conductivity). However, this will be discussed in more detail in Chapter 7.
ENTRIES A–Z
Philip Winn in Dictionary of Biological Psychology, 2003
Cardiac muscle is essentially skeletal muscle but with certain specific differences to do with the electrical and MEMBRANE properties of individual cells. Cardiac muscles cells have INTERCALATED DISCS (which normal skeletal muscle cells do not have) that provide the opportunity for direct electrical coupling of cells. Action potentials arriving at one site in the heart can be communicated across all cells very quickly, ensuring uniformity of action in generating heartbeats. In addition, cardiac cells can generate their own action potentials without input, being in possession of PACEMAKER CELLS with oscillatory properties (see OSCILLATION). The entire mass of cardiac muscle can be referred to as the MYOCARDIUM, which gives rise to terms such as myocardial and myocardiac: terms such as this simply refer to the musculature of the heart. Smooth muscle is not striated, the myosin and actin containing myofibrils not being organized in the same way as in skeletal muscle. It lacks the contractile power of skeletal muscle but can maintain contraction over great lengths, allowing it to develop peristaltic movements (see PERISTALSIS) to move blood through vessels or gut contents through the digestive tract.
Effect of anisotropy in myocardial electrical conductivity on lesion characteristics during radiofrequency cardiac ablation: a numerical study
Published in International Journal of Hyperthermia, 2022
Kaihao Gu, Shengjie Yan, Xiaomei Wu
Cardiac muscle is composed of myocardial fibers, which dominant the contraction of the heart [7]. Fiber orientation has been reported to affect the myocardial electrical conductivity (MEC) such that the electrical current flows preferentially along the fiber direction [8], causing the electrical conductivity throughout the heart to become anisotropic. This phenomenon influences the current distribution and thus the lesion formation of RFCA. In ablation simulation, however, to simplify the model, MEC is usually assumed to be isotropic [6]. As the electrical conductivity governs the ablation result [9], appropriate fiber orientation is essential for good accuracy. The fiber orientation can be determined using an imaging system; however, this process is time-consuming and has limited robustness [10]. Application of a rule-based method (RBM) that mathematically describes the fiber orientation based on historical observations is a more acceptable alternative, as it is more feasible for computational simulation [11–13].
Fatal self-poisoning with amitriptyline: a case report and brief review of literature
Published in Journal of Substance Use, 2023
Qing Gao, Bin Lv, Weisheng Huang, Tianying Sun, Hongmei Dong
The toxic effects of amitriptyline are mainly attributed to the cardiovascular and nervous systems. Amitriptyline can block the sodium channels in myocardial cells and lead to cardiac conduction disturbances and arrhythmias (Chan & Waring, 2007). Consequently, the victims that experience amitriptyline intoxication die of severe arrhythmia and myocardial depression (Abeyaratne et al., 2016). The clinical electrocardiogram (ECG) examination may show QRS prolongation. The neurological toxicity of amitriptyline includes inhibition of norepinephrine reuptake, direct α-adrenergic block and anticholinergic action. The victims usually present with mild neurological symptoms such as agitation and then progress to convulsions and coma over time. Seizures can also be observed as reported previously (Köppel et al., 1992). The cardiovascular symptoms, such as dysrhythmia and ECG changes, and neurological symptoms, such as lethargy and seizures are considered important clinical features of amitriptyline poisoning. It is difficult to diagnose amitriptyline intoxication relying on histology due to its nonspecific morphological changes. The routine postmortem histology of the heart and brain tissue can’t reveal their dysfunction. Both our case and the experimental rat model had indicated the absence of specific morphological changes in the cardiac muscle cells and neuron (Hocaoğlu et al., 2016).
High-intensity interval training (HIIT) effectively enhances heart function via miR-195 dependent cardiomyopathy reduction in high-fat high-fructose diet-induced diabetic rats
Published in Archives of Physiology and Biochemistry, 2020
Soheyla Khakdan, Maryam Delfan, Maryam Heydarpour Meymeh, Faranak Kazerouni, Hamid Ghaedi, Mehrnoosh Shanaki, Fatemeh Kalaki-Jouybari, Sattar Gorgani-Firuzjaee, Ali Rahimipour
Since the cardiac muscle myocytes seldom proliferate, the damage of cardiac muscle cells would finally lead to compromised cardiac function (Cai et al. 2002). The present study revealed that in diabetic rats LVEF and FS are lower than those in the non-diabetic group which confirm the results of the previous studies (Gu et al. 2015, Wang et al. 2015, Huang et al. 2017). In another part of this study, the results demonstrated that HIIT effectively increases FS and LVEF and recovers cardiac function, but in the CET group no significant difference was observed. However, extensive studies have been conducted on the effects of exercise on cardiac function in diabetic myocardium. Increasing evidence has demonstrated that moderate intensity endurance exercise leads to increased EF and FS and improves cardiac performance in diabetic animals (Wang et al. 2015, Loganathan et al. 2007) that is in contradiction with the data obtained in this study. It is argued that this difference can be attributed to the duration of exercise in these studies. Increasing evidence has shown that HIIT has a significant effect compared with continuous endurance training on the improvement of cardiac function by increasing EF in type 2 diabetes mellitus and heart failure patients (Wisl⊘ff et al. 2007, Cassidy et al. 2016, Ross et al. 2016), which suggests the fact that HIIT induced a greater increase in the FS and LVEF levels.
Related Knowledge Centers
- Collagen
- Coronary Circulation
- Endocardium
- Intercalated Disc
- Muscle
- Smooth Muscle
- Striated Muscle Tissue
- Skeletal Muscle
- Extracellular Matrix
- Pericardium