cardiac cycle

(noun)

The term used to describe the relaxation and contraction that occur as a heart works to pump blood through the body.

Related Terms

Examples of cardiac cycle in the following topics:

  • Cardiac Cycle

    • The cardiac cycle describes the heart's phases of contraction and relaxation that drive blood flow throughout the body.
    • The cardiac cycle is the term used to describe the relaxation and contraction that occur as the heart works to pump blood through the body.
    • Heart rate is a term used to describe the frequency of the cardiac cycle.
    • Throughout the cardiac cycle, the arterial blood pressure increases during the phases of active ventricular contraction and decreases during ventricular filling and atrial systole.
    • Blood pressure is a regulated variable that is directly related to blood volume, based on cardiac output during the cardiac cycle.

  • Extremes in Blood Pressure

    • Graph showing changes in blood pressure during a single contraction-relaxation cycle of the heart.

  • Checking Circulation

    • Systolic pressure is peak pressure in the arteries, which occurs near the end of the cardiac cycle when the ventricles are contracting.
    • Diastolic pressure is minimum pressure in the arteries, which occurs near the beginning of the cardiac cycle when the ventricles are filled with blood.

  • Functions of the Brain Stem

    • The brainstem regulates vital cardiac and respiratory functions and acts as a vehicle for sensory information.
    • The brain stem also plays an important role in the regulation of cardiac and respiratory function.
    • It regulates the central nervous system (CNS) and is pivotal in maintaining consciousness and regulating the sleep cycle.
    • The medulla contains the cardiac, respiratory, vomiting, and vasomotor centers regulating heart rate, breathing, and blood pressure.
    • The midbrain (mesencephalon) is associated with vision, hearing, motor control, sleep and wake cycles, alertness, and temperature regulation.

  • Energy Requirements

    • Cardiac cells contain numerous mitochondria, which enable continuous aerobic respiration and production of adenosine triphosphate (ATP) for cardiac function.
    • Cardiac muscle tissue has among the highest energy requirements in the human body (along with the brain) and has a high level of mitochondria and a constant, rich, blood supply to support its metabolic activity.
    • Cardiac muscle cells contain larger amounts of mitochondria than other cells in the body, enabling higher ATP production.
    • Lactate, created from lactic acid fermentation, accounts for the anaerobic component of cardiac metabolism.
    • The produced pyruvate can then be burned aerobically in the citric acid cycle (also known as the tricarboxylic acid cycle or Krebs cycle), liberating a significant amount of energy.

  • Types of Muscle Tissue

    • The function of muscles is movement, but the types of movement elicited differ between skeletal, cardiac, and smooth muscle.
    • There are three kinds of muscle tissue: skeletal, smooth, and cardiac.
    • Cardiac muscle is found in the walls of the heart.
    • Although cardiac muscle is involuntary in nature, it is structurally different from smooth muscle.
    • Cardiac muscle is striated, similar to skeletal muscle, but beats involuntarily.

  • Physiological Changes

    • Increases in blood sugar, breathing, and cardiac output are all required.
    • Levels of progesterone and estrogens rise continuously throughout pregnancy, suppressing the hypothalamic axis and, subsequently, the menstrual cycle.
    • Plasma and blood volume slowly increase by 40-50% over the course of the pregnancy (due to increased aldosterone) to accommodate the changes, resulting in an increase in heart rate (15 beats/min more than usual), stroke volume, and cardiac output.
    • Cardiac output increases by about 50%, primarily during the first trimester.

  • Characteristics of Muscle Tissue

    • The three types of muscle tissue are skeletal, smooth, and cardiac.
    • Cardiac muscle tissue is found only in the heart where cardiac contractions pump blood throughout the body and maintain blood pressure.
    • Cardiac muscle can be further differentiated from skeletal muscle by the presence of intercalated discs which control the synchronized contraction of cardiac tissues.
    • Both cardiac and smooth muscle are involuntary while skeletal muscle is voluntary.
    • Differentiate among the structure and location of skeletal, smooth, and cardiac muscles

  • Microscopic Anatomy

    • Cardiac muscle appears striated due to the presence of sarcomeres, the highly-organized basic functional unit of muscle tissue.
    • Cardiac muscle, like skeletal muscle, appears striated due to the organization of muscle tissue into sarcomeres.
    • While similar to skeletal muscle, cardiac muscle is different in a few ways.
    • Cardiac muscles are composed of tubular cardiomyocytes, or cardiac muscle cells.
    • A sarcomere is the basic unit of muscle tissue in both cardiac and skeletal muscle.

  • Mechanism and Contraction Events of Cardiac Muscle Fibers

    • Cardiac muscle fibers undergo coordinated contraction via calcium-induced calcium release conducted through the intercalated discs.
    • In cardiac, skeletal, and some smooth muscle tissue, contraction occurs through a phenomenon known as excitation contraction coupling (ECC).
    • Similarly to skeletal muscle, the influx of sodium ions causes an initial depolarization; however, in cardiac muscle, the influx of calcium ions sustains the depolarization so that it lasts longer.
    • The actual mechanical contraction response in cardiac muscle occurs via the sliding filament model of contraction.
    • Calcium in the cytoplasm then binds to cardiac troponin-C, which moves the troponin complex away from the actin binding site.