Leading toward a region or structure of interest.

In the nervous system, afferent fibers (i.e., neurons) transmit information from a peripheral receptor to the spinal cord or the brainstem. Afferent neurons are also referred to as sensory neurons.

In the kidneys, the afferent arteriole carries blood to the glomerular capillaries.

Efferent

Lack of oxygen in arterial blood.

Anoxia
Hypoxia
Hypoxemia

Without a nucleus. In particular, it refers to a cell that lacks a nucleus. For example, prokaryotic cells are anucleate. In addition, red blood cells (erythrocytes) are anucleate.

The large blood vessel (artery) that receives the output of the left ventricle of the heart. The aorta is the first and largest (in diameter) artery of the systemic circulation.

Following ventricular contraction (systole), hydrostatic pressure within the ventricle exceeds the pressure in the aorta, which forces blood out of the left ventricle, through the aortic semilunar valve, and into the aorta. As the ventricle relaxes during diastole, the pressure within the left ventricle drops to a level below that in the aorta. At this point, the aortic semilunar valve closes, which prevents the backflow of blood from the aorta to the left ventricle.

The ability of a tissue or organ to regulate its own function without extrinsic neural or hormonal input.

For example, in the kidneys, autoregulation ensures relatively constant blood flow and pressure through the kidney tubules in order to maintain a fairly constant glomerular filtration rate (GFR).

Concave on both sides of a structure, usually referring to a disc or a lens.

Of particular importance to physiology is the structure of mature red blood cells (erythrocytes), which is a flattened cell that has assume a biconcave shape. It is thought that the biconcave shape of red blood cells helps with the flow property of blood through blood vessels.

The one-way valve between the left atrium and left ventricle of the heart. It is also known as the left atrioventricular valve or mitral valve.

The direction of blood flow through the bicuspid valve is from the left atrium to the left ventricle.

Left atrioventricular valve
Mitral valve

CO

Cardiac output is defined as the volume of blood pumped every minute by each (left or right) ventricle of the heart. It is generally reported in L/min or mL/min.

Cardiac output (CO) is the product of heart rate (HR) and stroke volume (SV). Thus,

CO = HR × SV

Heart rate is defined as the number of heart contractions per minute. Stroke volume is the volume of blood pumped per ventricular contraction.

For a typical resting adult human being at rest, CO is approximately 5 L/min.

CO = 70 contractions/min × 70 mL/contraction = 4,900 mL/min

CI⁻

The main anion (negatively charged ion) of the extracellular fluid.

Cloride (Cl⁻) plays an important role in several physiological processes such as the action potential of skeletal muscle cells, CO₂ transport in blood (via Cl⁻/bicarbonate exchange across the plasma membrane of red blood cells), and many other processes.

The extracellular concentration of Cl⁻ is about 110 mM. The intracellular concentration of Cl⁻ is about 10 mM.

Leading away from a region or structure of interest.

In the nervous system, efferent fibers (i.e., neurons) transmit information from the central nervous system to peripheral effector organs (i.e., muscles or glands). Therefore, the cells bodies of efferent neurons reside within the central nervous system, whereas their axonal projections exit the central nervous system to make synaptic contact with effector organs in the periphery. Efferent neurons are also referred to as motor neurons.

In the kidneys, the efferent arteriole carries blood away from the glomerular capillaries.

Afferent

Endocrine cells are responsible for producing and releasing hormone molecules into the bloodstream. Endocrine cells are typically grouped together in organs referred to as endocrine glands.

Endocrine gland
Hormone

Endocrine glands contain clusters of endocrine cells, whose function is to is to release hormones into the bloodstream.

Endocrine glands are ductless glands in that their secretions do not enter a duct (as for example with salivary glands). Rather, endocrine glands release their secretions (i.e., messenger molecules) into the interstitial fluid in highly vascularized regions, where the molecules then enter the bloodstream. The chemical messenger molecule that is released into the bloodstream is referred to as a hormone.

Endocrine cell
Hormone

A chemical messenger molecule secreted (i.e., released) by endocrine cells within endocrine glands.

By definition, a hormone molecule is released into the bloodstream and travels throughout the body to find its target cells. Teget cells may be within the intravascular compartment (i.e., within blood vessels), but most hormones have target cells in tissues outside of the blood vessels.

Endocrine cell
Endocrine gland

A state of decreased total blood volume caused by blood loss, reduction in plasma volume, or other causes.

Decreased oxygen content in arterial blood.

Anoxia
Anoxemia
Hypoxia

The tapping sounds heard through a stethoscope placed over a partially compressed peripheral artery.

For the purpose of non-invasive blood pressure measurements, the stethoscope is usually placed on the skin overlying the brachial artery just distal to an inflated pressure cuff wrapped around the upper arm. As the pressure cuff is gradually deflated, the Korotkoff sounds result from the pulsations of the blood through the partially constricted brachial artery. With each ventricular systole, blood is forced to flow through the partially constricted brachial artery, and the turbulence in blood flow leads to the generation of the Korotkoff sounds. When the pressure cuff is fully deflated, flow through the artery resumes its normal laminar flow and, at that time, the Korotkoff sounds disappear.

The one-way valve between the left atrium and left ventricle of the heart. It is also known as the bicuspid valve or mitral valve.

The direction of blood flow through the left atrioventricular valve is from the left atrium to the left ventricle.

Bicuspid valve
Mitral valve

The one-way valve between the left atrium and left ventricle of the heart. It is also known as the left atrioventricular valve or bicuspid valve.

The direction of blood flow through the mitral valve is from the left atrium to the left ventricle.

Left atrioventricular valve
Bicuspid valve

Neurohormones are chemical messenger molecules that are released by neurons, but enter the bloodstream where they travel to distant target sites within the body. Therefore, neurohormones share characteristics with both neurotransmitters and hormones. Similar to neurotransmitters, neurohormones are released by neurons. Similar to hormones, neurohormones travel in the bloodstream.

Two well-known examples of neurohormones are oxytocin and the antidiuretic hormone (also referred to as vasopressin).

Hormone
Neurotransmitter

PCG

A recording of the sounds produced by the heart during the cardiac cycle. The main sounds recorded are those associated with turbulent blood flow caused by the closure of heart valves.

Plasma is the fluid portion of whole blood, which makes up about 40% to 60% of the total volume of whole blood. Plasma has a light yellow color and is generally obtained by separating the fluid portion from the blood formed elements through sedimentation or centrifugation. Plasma contains mostly water and, in addition, minerals, nutrients, proteins, hormones, and gases (oxygen and carbon dioxide). Unlike serum, in which fibrinogen and other clotting factors have been removed by coagulation, fibrinogen and other clotting factors remain present in plasma.

Plasma is one the main fluid compartments of the human body, making up nearly 10% of the total volume of body fluids. Plasma makes up the intravascular fluid compartment; itself a subcompartment of the extracellular fluid compartment.

Pulse pressure is defined as the arithmetic difference between the systolic pressure (the highest blood pressure) and the diastolic pressure (the lowest blood pressure) recorded at any point along the vascular bed. Therefore:

Pulse pressure = Systolic pressure - Diastolic pressure

Pulse pressure values can be reported at any point along the vasculature starting from the left ventricle and aorta all the way to the vena cava and the right atrium. As with systolic and diastolic pressure values, pulse pressure is typically reported in mm Hg (millimeters of mercury). A typical arterial pulse pressure is 40 mm Hg (120 - 80 = 40 mm Hg). This value decreases as one proceeds along the vascular bed from arteries to arterioles, capillaries, venules, and veins. The most significant drop occurs along the arterioles.

Mean Arterial Pressure Calculator

The one-way valve between the right atrium and right ventricle of the heart. It is also known as the tricuspid valve.

The direction of blood flow through the right atrioventricular valve is from the right atrium to the right ventricle.

Tricuspid valve

Secretion refers to cellular release of substances (ions and small and large molecules) to the external environment of the cell. Secretion may be accomplished by exocytosis (fusion of transport vesicles with the plasma membrane and release of vesicle contents to the external environment), by transport of molecules across the plasma membrane (via the activity of transport proteins such as pumps, transporters, and channels), or by simple diffusion of fat-soluble molecules through the plasma membrane out of the cell.

For example, endocrine cells secrete hormone molecules that then enter the bloodstream. Neurons release (i.e., secrete) neurotransmitter molecules into the synaptic cleft. Some neurons secrete neurohormones; which similar to hormones, travel in the bloodstream to reach distant target cells. Epithelial cells secrete molecules in luminal spaces, such as digestive enzymes secreted into the digestive tract by various cell types.

Excretion

The one-way valve between the right atrium and right ventricle of the heart. It is also known as the right atrioventricular valve.

The direction of blood flow through the tricuspid valve is from the right atrium to the right ventricle.

Tricuspid valve

Removal of approximately a pint of blood in a manner similar to that for donating blood. The procedure is generally used as a simple measure to reduce the number of circulating red blood cells (e.g., to treat polycythemia) or to reduce the amount of circulating iron (e.g., to treat hemochromatosis). The procedure may be repeated as needed.

It falls under procedures referred to as phlebotomy (removing blood for therapeutic or diagnostic purposes) or bloodletting (removing blood for therapeutic purposes).