Week 6 Lec Hist Flashcards
general features of vessel walls
tunica intima
=> Innermost layer
* endothelium (simple squamous epithelium)
* basement membrane
* loose connective tissue
tunica media
=> Middle layer
* smooth muscle
* elastic fibres
tunica adventitia
=> Outermost layer
* collagen & elastic fibres, fibroblasts
* nerves, vessels
* +/- smooth muscle
capillaries features
Endothelial lined tube
+/- basement membrane
o Pericytes (contractile connective tissue cell)
located along the wall at intervals
o Pericytes differentiate into smooth muscle
cells or fibroblasts during angiogenesis &
wound healing
Slow blood flow, large surface area, thin walls
Exchange of diffusible substances
Continuous Capillaries – skin, CNS
o zonula occludens hold endothelial cells together
o pinocytotic vesicles in cytoplasm
o Larger molecules (glucose) & water-soluble
substances selectively transported via endocytosis
& exocytosis
o Diffusion of gases & small molecules
Sinusoidal Capillaries – liver, bone marrow, endocrine glands
- gaps between endothelial cells
- pores within plasma membrane
- partially/completely absent basal lamina
- large diameter
- irregular shape
- permeable to large molecular
weight compounds & sometimes
erythrocytes & leukocytes
Q: What are the structural characteristics of elastic arteries and how do they relate to their function?
Characteristics: Thick tunica media with a high content of elastic fibers interspersed with smooth muscle cells.
Function: Elastic arteries (e.g., the aorta) can stretch and recoil, which helps to dampen the blood pressure fluctuations between heartbeats, maintaining a steady flow of blood.
Q: How are muscular arteries structurally distinct, and what is their function?
Characteristics: Well-developed tunica media dominated by smooth muscle cells, with less elastic tissue compared to elastic arteries.
Function: Muscular arteries (e.g., radial artery) regulate blood flow to specific regions of the body by constricting or dilating.
Q: What are the structural features of arterioles, and why are they important?
Characteristics: Small vessels with a thin tunica media composed of a few layers of smooth muscle cells; minimal tunica adventitia.
Function: Arterioles are key regulators of blood pressure and flow into capillary beds due to their ability to constrict and dilate.
Q: What are the three types of capillaries and how do their structures relate to their locations and functions?
Continuous Capillaries: Have an uninterrupted endothelial lining, with tight junctions. Found in muscle, skin, and the blood-brain barrier, where selective permeability is essential.
Fenestrated Capillaries: Have pores (fenestrations) in the endothelial cells, allowing for increased permeability. Located in the kidneys, intestines, and endocrine glands, where rapid exchange of substances is needed.
Discontinuous (Sinusoidal) Capillaries: Have large gaps between endothelial cells, allowing free exchange of larger molecules and cells. Found in the liver, spleen, and bone marrow.
Q: What are the structural differences between arteries and veins?
Arteries: Have thicker walls, a prominent tunica media with more smooth muscle and elastic fibers, and a smaller lumen. They maintain shape even when empty due to their thick walls.
Veins: Have thinner walls, less smooth muscle, and a larger lumen. They often contain valves to prevent backflow, especially in the limbs, and are more collapsible when empty.
Tunica Adventitia
Veins:
Thickest Layer: Tunica Adventitia is typically the thickest layer in veins. It is made up of connective tissue, which provides structural support. Veins have a thinner tunica media compared to arteries because they do not need to withstand the same high pressures.
Capillaries have only the tunica intima (a single layer of endothelial cells) and lack tunica media and tunica adventitia. This thin structure facilitates the exchange of gases, nutrients, and waste products between the blood and tissues.
Q: What are the three layers of the heart wall, and what is each composed of?
A:
Endocardium: Simple squamous epithelium (endothelium), loose connective tissue, contains Purkinje fibers.
Myocardium: Striated cardiac muscle, contains intercalated discs, thicker in ventricles due to higher pressure.
Epicardium: Visceral layer of serous pericardium, simple squamous epithelium (mesothelium), connective tissue, adipose.
Q: What is the function of the intercalated discs in the myocardium?
A: Intercalated discs are junctions between cardiac muscle cells that provide mechanical and electrical connectivity, enabling coordinated contractions.
Q: Describe the location and function of Purkinje fibers.
A: Purkinje fibers are located in the endocardium and are modified cardiac muscle cells that conduct electrical impulses, ensuring synchronized contractions of the heart.
Q: What distinguishes cardiac muscle tissue from other types of muscle tissue in terms of structure?
A: Cardiac muscle has striations, centrally located nuclei, branching fibers, and intercalated discs, which are unique to cardiac muscle.
Q: What is the pericardium, and what are its layers?
A: The pericardium is a double-walled sac surrounding the heart, consisting of:
Visceral Pericardium (Epicardium): Adheres to the heart surface.
Parietal Pericardium: Outer layer, lines the pericardial cavity.
Pericardial Cavity: Contains pericardial fluid, reduces friction.
