Flashcards in Histology of the Vascular system Deck (21):
Name the types of vessels blood flows through as it leaves the heart, reaches the capillaries then returns back to the heart.
From the heart blood is fed through a series of decreasing sized arteries: Large elastic arteries, Medium muscular distributing Arteries, Arterioles, Metarterioles and then capillaries. From here blood returns via the lymph vessels or it passes through increasing sized veins: Post capillary venules, Venules, Medium Veins and then Large Veins.
How does the speed of blood change as the overall cross sectional area changes through the vascular system?
As the blood leaves the heart the speed it travels at decreases as the surface area of the vascular bed increases and vice versa from the capillaries (although to only half of its original value even though surface area returns to its start point).
Name the three main elastic arteries
The Aorta branches out into 3 vessels the Brachiocephalic, Left common carotid and left subclavian all of these arteries are Elastic Arteries.
Describe how the histological structure of elastic arteries relates to their function.
The elasticity of the arteries allows them to act as pressure reservoirs and during diastole they act as auxiliary pumps – the blood pressure is pulsatile in the arteries closest to the heart.
Describe the general histological structure of blood vessels.
Blood vessels are made up of the Tunica intima a thin layer closest to the lumen of the vessel containing an endothelial layer, a subendothelial layer of connective tissue and an internal elastic lamina
The tunica media the largest layer consisting of fenestrated elastic membranes with smooth muscle cells and collagen in-between, followed by a thin external elastic lamina
The tunica adventitia which is a thin layer of Fibroelastic connective tissue containing vasa vasorum (vessels of vessels), lymph vessels and nerve fibres.
How does this structure change as the elastic arteries get smaller?
As the elastic arteries get smaller the same structrue persists although sometimes the Tunica Intima becomes indistinct but is still there.
What colour do the different layers stain in blood vessels?
The elastic lamella in the Tunica Media stain black whilst the collagen and matrix stain blue and the muscle stain red or pink.
Which cells lay down the elastin and collagen in blood vessels?
The smooth muscle cells not the fibroblast lay down the elastin and collagen in these vessels.
Describe dissection of the aorta and which diseases it is common in.
Disection of the aorta – blood forces its way into the layers of the tunica media. Can be catastrophic due to rupture of the aorta and is common in marfan’s sydnrome. It is treated using a large stent.
Describe the histological structure of the muscular distributing arteries
The next arteries present are muscular – distributing, in the Tunica Media there is little elastic lamella and instead contains layers of smooth muscle. The cells are connected by gap junctions for cordinated contractions.
Describe the histological structure of the arterioles
Arterioles are any arteries less than 0.1mm. They contain a few layers of smooth muscle in their TM, the external elastic lamina is completely absent and the Internal elastic lamina is sometimes present in larger arterioles. The Tunica adventita is scant and if present consists of layer(s) of fibroblasts.
Describe the histological structure of the metarterioles
Metarterioles supply the capillary beds. There are individual muscle cells (pericytes) spaced apart from each other encircling the beginning or bracnhing of a capillary. This is known as a precapillary Sphincter.
Describe the histological structure of the Capillaries
Capillaries consist of only one layer of endothelial cells and their diameter veries between 7-10um.
Describe the 3 different types of capillaries.
Continuous – most commonly located in nervous, muscular, glandular and connective tissues. They have a continuous endothelial layer joined tightly by occluding junctions
Fenestrated capillaries – found in parts of gut, endocrine glands and renal glomerulus. Have small fenestrations in their endothelial layer (which are bridged by thin diaphragms) to allow larger particles to pass through
Sinusoidal or Discontinuous Capillaries – found in liver, spleen and bone marrow. Large gaps exist in the wall allowing whole cells to move through.
Describe the histological structure of the post capillary venules
Very thin still with only a thin endothelial wall. They are even more permeable than capillaries but due to the low pressure tissue fluid tends to flow in unless there is an inflammatory response. This is where most leukocytes emigrate in and out of tissue fluid.
Describe the histological structure of the Venules
As the diameter increases above 50um Post capilliary venules become Venules which begin to develop a thin layer of smooth muscle fibres forming a tunica media. Semilunar valves are present formed from thin extensions of cells preventing retrograde transport.
Describe the histological structure of the Veins
Veins are the next rank up and are usually larger but with thinner walls than their accompanying arteries. All veins have a well defined tunica adventitia but thin Tunica media with only a few layers of smooth muscle (very few elastic fibres). Larger veins have a slightly better defined tunica intima. The only exception are the large veins of the legs which have a large muscular wall to resist distention.
Describe the histological structure of the Large Veins
Large veins have a well defined muscular layer in both the tunica adventitia (longitudial) and tunica media (circular).
Describe Venae comitantes and give examples
Venae Comitantes are when deep veins accompany arteries. Examples of this are the brachial, ulnar and tibial venae.
Describe the histological layers of the heart
The Heart consists of three layers: epicardium connective tissue covered externally by a layer of simple squamous epithelial cells
Myocardium layer of muscle which is attached to the epicardium in the subepicardial region by bundles of collagen fibres
Endocardium forms the innermost layer formed from a subendocardium of areolar tissue containing small blood vessels and nerves, a subendothelial conective tissue layer containing elastic fibres and some smooth muscle and an endothelial layer of simple squamous epithelia.