Circulatory System Histology

Atherosclerosis

Hyperlipidemia, smoking, hypertension and turbulent blood flow are all risk factors for what condition?

Intima

Capillaries only have a tunica ________.

Hydrostatic; lymph

Fluid is leaked out of capillaries initially due to ____________ pressure; however, once the material in the capillaries becomes increasingly concentrated, the majority of the fluid is taken back up due to osmotic pressure. The remaining 10% of fluid is taken up by the lymphatic system and is called _____________.

Metarterioles (if surrounded by smooth muscle, not capillary).

Small branches off of arterioles, that are surrounded by a discontinuous layer of smooth muscle.

Tunica intima

This layer of the vessel wall is a single layer of endothelial cells, sitting on a basal lamina.

Blood-brain barrier

Capillaries in the brain have a very tight seal, formed by extensive networks of tight junctions between the capillaries and endothelial cells. These extra tight junctions are though to be triggered embryonically via signals secreted from astrocytes in the brain. These capillaries also contain very few pinocytotic vesicles. Essential metabolites can pass through, but the exchange of anything larger than 500 daltons is essentially blocked. What is the name of this junction?

Varicose veins

Due to factors like gravity, age, load-bearing activity and obesity, the veins in the lower extremities can become distorted, damaging the valve system, causing the back-flow and pooling of blood and giving the veins a hypertrophied, tortuous appearance. What is the name of this condition, which affects women significantly more than men?

Tunica intima, tunica intermedia, and tunica adventitia

From the inside out, what are the three layers of (most) blood vessels?

Pericytes

In some capillaries, this cell type takes the place of smooth muscle, surrounding the outside of the capillary and squeezes it when necessary. These cells are also very important in the growth and regeneration of new blood vessels.

Aortic dissection

In this condition, a tear forms in the wall of the aorta, beginning at the tunica intima and ultimately separating the tunica intima from the tunica media. Mortality is 80%, with 50% of patients dying pre-hospital. Patients with Marfan's Syndrome are more predisposed to this condition.

Arterial portal system

In this sequence of micocirculation, blow flows through arterioles, into capillaries, and back through arterioles. It is most commonly seen in the kidney glomerulous.

Arteriovenous anastamosis

In this sequence of microcirculation, arterioles and venules communicate directly, without first diverting through capillaries.

Venous portal system

In this sequence of microcirculation, most notably in the liver, blood flows through venules, into capillaries and back into venules.

Thoroughfare channel

Sphincters of smooth muscle regulate blood from from arterioles into the capillaries; this process is tightly controlled. Occasionally, in situations such as blood loss or excessively cold temperatures, the blood is diverted directly from the arterioles to the venules through a _______________________, bypassing the capillary bed entirely.

Subendocardial layer

The endocardium has 2 layers: a layer of connective tissue lined with simple squamous epithelium, and a layer before the myocardium containing dense CT with blood vessels, nerves and perkinje fibers. What is the name of this second layer of endocardium?

Endocardium

The fibrous skeleton of the heart is comprised of masses of dense connective tissue in the ________________ that anchors and surrounds the two atrial-ventricular valves, giving them their shape.

Vasa vasorum

These are smaller blood vessels that supply the wall of large diameter blood vessels with O2 and nutrients; they are known as the "vessels of the vessels."

Capillaries

These very important vessels are found in most tissues (excluding collagen, some epithelium, etc) and form the location for the majority of gas and nutrient exchange with the blood and body tissues. The walls of this vessel are one cell thin, to facilitate easier exchange, and their narrow size maximizes the surface area that RBCs contact the inside of the vessel.

Athersclerosis

This condition is brought on by monocyte response to a site of arterial injury. The monocytes differentiate into macrophages, which take up circulating LDL forming thick foam cells. Eventually, smooth muscle cells migrate into the tunica intima, secrete collagen and fibroconnectin, and a fibrin cap is formed, creating a plaque.

Deep venous thrombosis (DVT)

This condition is defined as a local coagulation or clotting of the blood in a part of the circulatory system. This occurs most commonly the in lower extremities, when inactivity, and the subsequent lack of muscle contraction, does not help to propel the blood against gravity back toward the heart.

Epicardium

This is the outermost layer of the heart, and it is a visceral layer of serous pericardium. It is composed of fibrous connective tissue, with simple squamous epithelium on top of it. The coronary arteries, veins and nerves are all located in this layer.

Myocardium

This layer of heart tissue is composed of heart muscle cells arranged in complex spirals around the heart wall, interspersed with connective tissue. It is well vascularized with many capillaries, delivering O2 to contracting cardiac muscle.

Tunica intermedia

This layer of the vessel wall is comprised of concentrically arranged layers of smooth muscle cells. These muscle cells can contract, narrowing the blood vessel and increasing the blood pressure.

Tunica adventitia

This layer of the vessel wall is comprised primarily of fibroblasts, type I collagen and elastic fibers. It is continuous with the connective tissue surrounding the vessel.

Arterioles

This type of artery has neither internal nor external elastic laminas. The tunica media is comprised of just 1-2 layers of smooth muscle cells, and is surrounded by a very thin tunica aventitia

Elastic arteries

This type of artery is the largest, and is situated closest to the heart; thus, it includes the aorta and it's major branches. Because of this proximity, these arteries need to be able to withstand the pressure of systole, as well as the recoil of diastole.

Muscular arteries

This type of artery still has a some elastic laminas, but nearly as many as elastic arteries; they retain their primary elastic bands on the internal and external surface of the tunica media. As these arteries decrease in size, they initially lose their external elastic lamina first, followed by the internal elastic lamina.

Fenestrated capillary

This type of capillary is moderately leaky, and is most defined by the fenestrae lining their walls. These fenestrae, or holes, are much more permeable to water and small solutes. These capillaries are found in selective tissues where the exchange of substances is important, such as the kidneys, exocrine glands and nervous tissues. Most of the fenestrae are covered by a very thin diaphragm that separates the blood from the basal lamina.

Discontinuous/sinusoidal capillaries

This type of capillary is the leakiest, and is found in red bone marrow that lines sinusoids, as well as the liver. The fenestrae, or holes, covering the outside are large, and are surrounded by a discontinuous layer of basal lamina. There is no diaphragm covering the fenestrae. These capillaries typically have a very tortuous path, which slows the blood moving through them.

Continuous capillary

This type of capillary is the most common, and the least leaky. The lumen is formed by a single layer of endothelial cells, connected by tight junctions, sitting on a single basal lamina. There are no fenestrae on the outside of the vessel, and it is commonly found in muscle tissue, connective tissue, exocrine glands and nervous tissue.

Fibrous connective tissue

Unlike skeletal muscle, damage to the heart does not result in regeneration; instead, damaged cardiac tissue is transformed into __________________________, which cannot contract and therefore weakens the heart.

Media; adventitia

Veins have a much smaller tunica __________ than arteries of the same size. Veins also have a lot of smooth muscle in their tunica __________, which aids in constriction to move blood back toward the heart.

Intima

Veins, particularly those in your lower extremities, have a system of valves to prevent blood backflow. These valves are an extension of the tunica ____________, and are reinforced by collagen and elastic fibers.

The tunica media of muscular arteries is composed of primarily smooth muscle, while the tunica media of elastic arteries is smooth muscle intercalated by elastic laminas.

What is the major distinction between elastic arteries and muscular arteries?