Circultaory Flashcards
Endocardium
A smooth, thin membrane that lines the inner surface of the heart chambers, the endocardium is composed of a thin layer of endothelial cells, which lies over a thin layer of connective tissue. This innermost layer also covers the valves of the heart, and helps to prevent resistance as blood passes through the vessels and chambers of the heart.
Myocardium:
The myocardium - the heart muscle itself, varies in thickness depending on its location, being thin in the atria and thick in the ventricles. It is composed of cardiac muscle fibers, which exhibit striations diagonally across the heart
Pericardium:
The pericardium is made up of two serous membrane layers, each composed of an epithelial lining with an underlying connective tissue. The pericardium keeps the heart in place, limits its motion, prevents it from over expanding, whilst the pericardial fluid reduces the friction between it and its surrounding structures
Pericardial cavity
Between the visceral and parietal layers is the pericardial cavity, a narrow cavity filled with a thin serous fluid, called pericardial fluid
Systole
Systole The phase of the heartbeat when the heart muscle contracts forcing blood from the chambers of the heart
Diastole
The phase of the heartbeat when the heart muscle relaxes and the heart chambers fill with blood
Capillaries
Capillaries, also referred to as exchange vessels, have a diameter varying between 5-10 μm. Red blood cells, 8 μm in diameter, must therefore fold up on themselves in order to fit through smaller capillaries
Vein:
Veins carry blood back to the heart from the extremities and organs of the body. Their size varies from about 0.5 mm in diameter to 3 cm, depending on their proximity to the heart. Veins generally have very thin walls in relation to their diameter, with large lumen. In certain regions, veins can be seen to widen, forming vascular or venous sinuses, structurally different from regular veins. They have thin endothelial walls, with a complete lack of smooth muscle, leaving them reliant upon surrounding connective tissue for support.
Artery:
Arteries carry blood away from the heart to other organs of the body. Their size and wall thickness varies depending on their proximity to the heart, i.e., large arteries with thick elastic walls carry blood being pumped directly from the heart, and arteries smaller in diameter with thinner walls deliver blood to the extremities.
Arteries have all three layers of a typical blood vessel. Their tunica media exhibits a greater muscular and elastic thickness than in veins, enabling their walls to stretch easily with a small increase in blood pressure (high compliance).
Three main types of arteries are defined
elastic arteries, muscular arteries, and arterioles
Arterioles
Arterioles, also referred to as resistance vessels, are numerous, microscopic arteries that feed blood into capillary networks. Vessel diameter varies from 15-300 μm depending on the location; wall thickness is about half the total diameter
Venules:
Venules, like arterioles, are numerous and microscopic, however, their walls are much thinner
endocrine system
The endocrine system consists of a collection of widely scattered glands and specialized cells that secrete hormones into the bloodstream. It works alongside the nervous system to regulate all aspects of body function.
Hormones are chemical messengers that circulate in the blood and act upon specific target cells to bring about specific changes in cellular function. Just as neurons are the functional units of the nervous system, specialized secretory cells and glands are the functional units of the endocrine system. Each endocrine gland releases a specific hormone, or number of hormones, that have a defined role in the control of bodily functions.
