Circulation

Comprehensive vocabulary flashcards covering the physiological and mechanical concepts of circulation across vertebrates and invertebrates, including cardiac cycles, hemodynamic equations, pacemaker types, and vascular architecture.

Systole

The phase of the cardiac cycle characterized by muscular contraction of the heart chambers.

Diastole

The phase of the cardiac cycle characterized by muscular relaxation and filling of the heart chambers.

Cardiac Output

The total volume of blood pumped by the heart per unit of time, defined mathematically as $\text{Cardiac output} = \text{heart rate} \times \text{stroke volume}$ (expressed in $\text{mL/minute}$).

Stroke Volume

The volume of blood ejected by a ventricle during a single contraction or heartbeat (expressed in $\text{mL/beat}$).

Myogenic Heart

A heart whose muscle cells continue to beat rhythmically even if all nervous connections are severed, initiated by spontaneous depolarization of specialized pacemaker muscle cells.

Sinoatrial (S-A) Node

The primary myogenic pacemaker located in the wall of the right atrium in birds and mammals, possessing the highest frequency of spontaneous depolarization of all cells in the heart.

Atrioventricular (A-V) Node

A specialized conducting junction where the electrical depolarization signal is delayed between the atria and the ventricles, allowing atrial contraction to occur distinctly before ventricular contraction.

Neurogenic Heart

A heart in which the rhythmic electrical depolarization that initiates heartbeats originates within nervous tissue, causing the heart muscle to stop contracting if the ganglion is removed.

Cardiac Ganglion

A cluster of nine neurons located on the cardiac wall of decapod crustaceans whose posterior cells act as pacemakers, producing periodic bursts of impulses to drive heart contraction.

Poiseuille Equation

The physical law defining steady fluid movement through a circular vessel: $\text{Flow rate} = (P_{\text{in}} - P_{\text{out}})\left(\frac{\pi}{8}\right)\left(\frac{1}{\eta}\right)\left(\frac{r^4}{l}\right)$, demonstrating that flow is profoundly controlled by the fourth power of vessel radius ($r^4$).

Vascular Resistance

The opposition to blood flow through the vessels, defined in the relationship $\text{Flow Rate} = \frac{\Delta P}{R}$, which decreases flow rate when resistance ($R$) increases.

Laminar Flow

Fluid motion characterized by smooth, parallel fluid layers sliding over one another, where internal friction degrades kinetic energy into heat, producing zero velocity immediately adjacent to the vessel wall and maximum velocity along the central axis.

Precapillary Sphincters

Muscular valves formed by rings of smooth muscle cells at the entrance to capillary beds that contract or relax to control the distribution and entry of blood.

Arteriolar-Venular Anastomoses

Direct vascular channels connecting arterioles directly to venules that, when open, allow blood to bypass capillary networks.

Starling–Landis Hypothesis

The principle stating that fluid movement across capillary walls is determined by the balance between hydrostatic pressure difference (forcing fluid out into tissue) and colloid osmotic pressure difference (drawing fluid back into blood plasma).

Rate of Oxygen Delivery

The mathematical product describing oxygen transport to tissues: $\text{Rate of } O_2 \text{ delivery} = \text{cardiac output} \times (\text{arterial } O_2 \text{ concentration} - \text{venous } O_2 \text{ concentration})$.

Compact Myocardium

Densely packed cardiac muscle tissue characterized by organized muscle bundles supplied directly with oxygen and nutrients through coronary arteries and veins.

Spongy Myocardium

A meshwork of trabecular cardiac muscle tissue that lacks or has minimal coronary vessels and derives its oxygen directly from the luminal blood flowing through the ventricular lumen.

Air-Breathing Organ (ABO)

A specialized respiratory organ (such as a vascularized mouth cavity or gut segment) placed in parallel with systemic circulation in certain fish, allowing aerial oxygen uptake at the expense of mixing oxygenated and deoxygenated blood.

Branchial Hearts

Accessory myogenic pumps located at the base of each gill in cephalopods (such as squids and octopuses) that boost deoxygenated blood through the gill vasculature into the systemic heart.

Ostia (Crustacean Heart)

Slit-like, valved pores in the wall of the crustacean heart through which oxygenated hemolymph in the pericardial sinus is drawn into the heart during diastole.

Branchiopericardial Sinuses

Tubelike sinuses functioning like veins in decapod crustaceans that channel oxygenated blood from the gills directly into the pericardial sinus.

Open Circulatory System

A circulatory system pattern in which blood leaves discrete vessels to enter open lacunae and sinuses, directly bathing the nonvascular cells of body tissues.

Tracheal System

An internal network of branching air-filled tubules (tracheae and tracheoles) entering through spiracles in insects that delivers oxygen directly to cells, freeing the circulatory system from oxygen transport duties.