Histology Flashcards
What are the three layers of the heart?
Epicardium (outer layer)
- simple squamous epithelium, subepicardial connective tissue, blood vessels, fat, nervous tissue
Myocardium
- muscle cells and capillaries
Endocardium (inner layer)
- endothelial layer, subendocardial connective tissue, conducting tissue
How do cardiac muscle cells coordinate contractions?
Gap junctions electrically couple cells and coordinate APs in neighbouring cells
What is the basic structure of a blood vessel?
Three layers make up the wall
- tunica intima
- tunica media
- tunica adventitia
Describe the intima
Provides the surface which contacts the blood
- lined with simple squamous epithelium
- lies on a basal lamina
- endothelial cells bulge into the lumen and are elongated in the direction of flow
What is the role of the endothelium?
Actively inhibits clotting by secreting anti-clotting factors into the blood as it passes
- at the same time secrete clotting factors into the subendothelial connective tissue so that if the endothelial layer breaks then it hits the next layer
- primes the underlying subendothelial connective tissue with VWF
- releases vasoactive substances such as endothelin and NO to regulate the diameter of blood vessels
Describe the media
Middle layer, predominantly smooth muscle arranged concentrically
- constricts the lumen
- smooth muscle secretes the connective tissue in which it is embedded
Describe the adventitia
Binds the blood vessel into the surrounding tissue
- thick layer of connective tissue with embedded fibroblasts
- has its own blood supply in larger vessels
- prevents splitting
What are elastic arteries?
Generally tend to be close to the heart - highest fluctuation in BP
- layers of elastin in the media store energy and compress the blood in the lumen
- the passive contraction means blood flow is continuous but pulsatile
What are muscular arteries?
Distribute blood to the tissue
- little elastin in media
- elastin is concentrated in the internal and external elastic laminae
- contractions of the media regulate blood pressure
What vessel contributes most to BP changes?
Arterioles
Describe capillaries
Less than the diameter of a RBC
- gets distorted as it goes through, perfect for gas exchange with tissue
- thin walled, no identifiable media, no smooth muscle
- single endothelial cell rolled into a tube sealed with a tight junction
What are fenestrated capillaries?
Found in the pancreas, intestines and endocrine glands
- regions where the outer and inner edges of a cell form a single membrane with tiny pores to facilitate exchange –> very leaky
What is the structure of veins?
Have the same layers as arteries but
- thinner media, thicker adventitia
- have valves to force one way flow
- assisted by skeletal muscle pumps
