Wk. 9 L2 - Histology of Heart and Vessels 2 Flashcards
(30 cards)
What are the three main layers of a blood vessel wall?
Tunica intima, tunica media, and tunica adventitia.
What are the components of the tunica intima?
The tunica intima is composed of a single layer of endothelium, a basal lamina, and a thin layer of connective tissue.
What is the primary component of the tunica media?
The tunica media consists mainly of smooth muscle cells and elastic fibers.
What does the tunica adventitia contain?
It contains collagen and elastic fibers, fibroblasts, nerves, and in some cases, smooth muscle.
How are capillaries generally structured?
Capillaries are composed of a single layer of endothelial cells, usually surrounded by a basal lamina, which facilitates the exchange of substances.
List key features common to capillaries.
They have thin walls, support slow blood flow, contain 1–2 red blood cells at a time, provide a large surface area, and enable the diffusion of gases and solutes.
What characterizes continuous capillaries and where are they typically found?
Continuous capillaries have an uninterrupted endothelium with a continuous basal lamina and are found in the skin, CNS, muscle, lung, and connective tissue.
How do continuous capillaries facilitate selective molecular transport?
They use pinocytotic vesicles to move larger water‐soluble molecules via endocytosis and exocytosis, while small molecules and gases diffuse across the thin endothelial layer.
What defines fenestrated capillaries, and in which tissues are they common?
Fenestrated capillaries possess pores (about 80 nm in diameter, with or without a diaphragm) that enhance permeability, common in endocrine glands and the gastrointestinal tract.
What is the functional significance of the fenestrations in fenestrated capillaries?
The fenestrations allow for enhanced fluid and metabolite absorption by increasing the permeability of the capillary wall.
Describe the structure of discontinuous (sinusoidal) capillaries.
Discontinuous capillaries feature large intercellular gaps, irregular luminal diameters, and a partial or absent basal lamina.
Where are discontinuous capillaries typically located and what is their significance?
They are found in the liver, bone marrow, and spleen, which require the passage of large molecules, erythrocytes, and leukocytes.
What are the three layers of the heart wall?
The heart wall consists of the epicardium, myocardium, and endocardium.
What is the epicardium and what are its key characteristics?
The epicardium is the visceral layer of the serous pericardium; it covers the outer surface of the heart and is composed of simple squamous epithelium (mesothelium), connective tissue, and adipose tissue.
How does the myocardium differ between the atrial and ventricular walls?
The myocardium is thicker in the ventricles—reflecting the higher pressure required to pump blood—while it is thinner in the atria.
What are the main histological features of cardiac myocytes within the myocardium?
Cardiac myocytes are striated, branching cells with a single centrally located nucleus, boast abundant mitochondria and glycogen, and are interconnected by intercalated discs.
What constitutes the endocardium and what role does it play?
The endocardium lines the inner surface of the heart chambers; it is comparable to the tunica intima, consisting of a simple squamous endothelium, underlying loose connective tissue, and, in parts, Purkinje fibers for conduction.
What are Purkinje fibers, and where are they found in the heart?
Purkinje fibers are modified cardiac muscle cells with a specialized conduction function, located in the endocardium to help synchronize the heart’s contractions.
How does the structure of the endocardium support its function?
Its smooth, simple squamous epithelium minimizes resistance to blood flow, while the loose connective tissue facilitates conduction and electrical continuity via embedded Purkinje fibers.
How are the layers of the heart arranged in relation to the heart chambers?
The epicardium forms the outer surface, the myocardium makes up the thick muscular middle layer, and the endocardium lines the interior (chamber surfaces) in direct contact with blood.
How does the heart develop during embryogenesis?
The heart begins as a single tube that remodels and partitions into the multi-layered structure (epicardium, myocardium, and endocardium) of the mature heart.
What are the main components of the pericardium?
The pericardium is made up of an outer fibrous pericardium and an inner serous pericardium, which is divided into the parietal layer and the visceral layer (epicardium).
What function does the pericardial space serve?
The pericardial space, located between the parietal and visceral layers of the serous pericardium, provides lubrication to minimize friction during heart contractions.
What is the functional role of the continuous basal lamina in vessel walls?
It provides structural support to endothelial cells and serves as a selective barrier for the transfer of molecules between the blood and tissues.
