108 Cardiovascular Histology Flashcards
Walls of arteries and veins
The walls of arteries and veins have three basic concentric layers (tunics)
- 1.Tunica intima: endothelium (simple squamous epithelium) and a thin layer of connective tissue. Inner-most layer, closest to the lumen of the vessel.
- 2.Tunica media: smooth muscle. Thickest, middle layer.
- 3.Adventitia: connective tissue. Outer layer that blends with the surrounding tissue.
Systemic Blood Flow Path
role of arteries
role of capillaries
role of veins
Arteries are the vessels responsible for delivery of oxygen-rich blood from the heart to the tissues (with the exception of the pulmonary arteries). They are relatively smaller than veins with thicker walls and smaller lumens.
Capillaries (4-10 µm) are between the arteries and veins and are about the diameter of a single red blood cell and are the site of metabolic exchange in tissues. Capillaries consist primarily of endothelial cells that are elongated along with their nuclei in the direction of blood flow. In many capillaries, pericytes surround the endothelium. Capillaries do not have a tunica media or adventitia.
Veins are the vessels responsible for delivery of oxygen-depleted blood from the tissues to the heart (with the exception of the pulmonary veins). They have thinner walls and larger lumens than arteries. The three layers in veins are not as distinct as the layers in arteries.
Without thick muscular walls, movement of venous blood back to the heart is effected by compression from skeletal muscle contraction and negative intrathoracic pressure. Some veins (e.g. veins in the limbs) have valves that prevent retrograde flow of the blood. The valves consist of two flaps that are extensions of the intima.
Elastic artery histology
Venules
Relative sizes of vessels, wall thicknesses, and components of the walls
Fenestrated capillaries
Continuous capillaries
Muscular artery histology
Arteriole histology
Distribution of blood in the arteries/veins
Pressure in the RA
- Blood pressure decreases from arteries through veins. Mean pressure continually decreases through the system until it is less than 5% as it enters the right atrium of the heart.
- Blood vessel walls are compliant; they are not rigid tubes that function simply as a conduit for blood flow. Arteries and veins are dynamic structures that dilate and constrict in response to changes in blood pressure and volume related to the control of blood flow.
- Only 15% of the blood in the body is in systemic arteries; 5% in capillaries; and over 60% in veins. The rest is in the heart and pulmonary circulation.
Large veins
Wall of the heart histology
Cardiac Muscle
The heart also has the three basic layers
- 1.Tunica intima (endocardium): stratified squamous epithelium. Inner-most layer.
- 2.Tunica media (myocardium): cardiac muscle fibers and loose connective tissue with capillaries. The largest of the three layers.
- 3.Tunica adventitia (epicardium): fibroelastic connective tissue and adipose tissue with blood vessels and lymphatics.
Cardiac Muscle
- Cardiac muscle is similar to skeletal muscle in the presence of striations/sarcomeres and a similar mechanism of action of actin and myosin in contraction.
- Cardiac muscle differs from skeletal muscle in that the cells are shorter and branch, have central nuclei, attach to each other end to end at special junctions called intercalated discs, and have a different T-tubule structure.
- Intercalated discs are dense staining regions with intracellular junctions that are important for spreading depolarization from cell to cell. The gap junctions in cardiac muscle stimulates all cells to contract after electrical stimuli.
Discontinuous capillaries
Small and medium veins