Cardiovascular Control, Capillary Exchange, and Circulatory Systems

Vocabulary practice flashcards covering circulatory autoregulation, neural reflexes, capillary exchange, venous return mechanisms, the hepatic portal system, and fetal circulation.

Metabolic Theory

A mechanism of autoregulation wherein tissue not receiving enough blood or meeting metabolic demands releases chemicals that dilate local blood vessels, increasing blood flow to deliver oxygen and nutrients while removing metabolic wastes.

Baroreflex

A negative feedback autoreflex triggered by changes in blood pressure, utilizing sensory receptors in the aortic arch and carotid bodies that send signals to the medulla oblongata to adjust sympathetic activity and vagal tone.

Baroreceptors

Special sensory receptors located within the aortic arch and carotid bodies that detect fluctuations in blood pressure.

Glossopharyngeal Nerve

The cranial nerve that transmits sensory signals from baroreceptors to the nuclei of the medulla oblongata.

Chemoreflex

An autonomic homeostatic reflex that regulates blood vessel diameter and breathing based on blood chemistry levels, primarily $O_2$, $CO_2$, and $pH$.

Chemoreceptors

Sensory receptors found in the aorta and carotid bodies that monitor the chemical composition of blood leaving the heart and heading toward the brain.

Medullary Ischemic Reflex

A neural homeostatic control mechanism initiated when the medulla oblongata senses inadequate blood perfusion and oxygen delivery to its own tissue, activating sympathetic fibers to raise heart rate, trigger vasoconstriction, and elevate systemic blood pressure.

Intercellular Clefts

Narrow gaps between adjacent endothelial cells in capillaries that allow water-soluble, hydrophilic molecules to pass between the blood and tissue fluid.

Fenestrations

Small pores or holes in capillary endothelial cells that permit the passage of specific hydrophilic molecules and nutrients.

Transcytosis

A transport process in endothelial cells combining pinocytosis or receptor-mediated endocytosis to internalize molecules on one side and exocytosis to discharge them on the opposite side.

Capillary Blood Pressure (Capillary Hydrostatic Pressure)

The outward fluid pressure exerted by blood remaining in the capillary, created by cardiac contractions, which forces water and solutes out of the capillary into the interstitial fluid.

Capillary Colloid Osmotic Pressure

An inward suction force within the bloodstream generated by plasma proteins that draws fluid from the interstitial space back into the capillary lumen.

Skeletal Muscle Pump

A mechanism of venous return where skeletal muscle contractions in the limbs compress deep veins, milking blood upward toward the heart and preventing pooling.

Thoracic Pump

A mechanism aiding venous return wherein inhalation expands the chest cavity, lowers the diaphragm, and increases abdominal pressure, squeezing abdominal veins and spurting blood toward the heart.

Cardiac Suction

A venous return mechanism occurring during the cardiac cycle when the relaxation of the atria reduces intra-atrial pressure, sucking blood from the vena cavae and pulmonary veins into the heart chambers.

Hepatic Portal System

A specialized vascular circuit in which blood from digestive system capillaries drains into a second capillary bed within the liver before returning to the heart.

Hepatic Portal Vein

The large receiving vessel formed by the confluence of abdominal digestive veins (such as the mesenteric, splenic, and gastric veins) that delivers nutrient-rich, deoxygenated blood to the liver hepatocytes.

Placenta

A temporary organ developing within the uterus that mediates the exchange of nutrients, wastes, and respiratory gases between maternal and fetal blood supplies without direct mixing.

Chorionic Villi

Branching, tree-like capillary projections of the fetal circulatory system within the placenta that are bathed in maternal blood to facilitate material exchange without cellular mixing.

Umbilical Arteries

Vessels in the umbilical cord carrying oxygen-poor, waste-laden blood away from the fetus to the placenta.

Umbilical Vein

The vessel in the umbilical cord delivering oxygen-rich, nutrient-loaded blood from the placenta to the fetus.

Ductus Venosus

A fetal vascular shunt that conveys oxygenated blood from the umbilical vein directly into the inferior vena cava, bypassing the non-functional liver.

Foramen Ovale

An aperture within the fetal interatrial septum that allows incoming blood to cross directly from the right atrium into the left atrium, bypassing the pulmonary circuit.

Fossa Ovalis

A shallow depression in the right atrium that represents the sealed remnant of the foramen ovale following birth.

Ductus Arteriosus

A fetal vascular shunt connecting the pulmonary trunk directly to the aorta, diverting blood away from the immature lungs into the systemic arterial system.

Ligamentum Arteriosum

A fibrous cord connecting the pulmonary trunk and aorta, representing the collapsed, obliterated remnant of the ductus arteriosus after birth.