21- Vascular Histology Flashcards
The walls of arteries and veins are composed of three layers called _________.
Tunics
Arteries branch extensively to (INCREASE/DECREASE) in diameter, while veins merge repeatedly to (INCREASE/DECREASE) in diameter.
Decrease
Increase
***Think of veins like taking a ramp onto the Interstate!
What are the three tunic layers of arteries and veins?
Tunica Intima (internal) Tunica Media (middle) Tunica Adventitia (external)
The Tunica Intima has endothelium composed of a single layer of __________ epithelial cells. The _______ _______ of the endothelial cells is a thin EC layer composed of collagen, proteoglycans, and glycoproteins.
Squamous
Basal Lamina
In the Tunica Intima, the subendothelial layer consists of loose _______.
CT
Within the Subendothelial layer of the Tunica Intima, there can be an ________ ________ ________ that is a sheet-like layer of fenestrated elastic material within arteries and arterioles.
Internal Elastic Membrane
This tunic layer is composed of circumferentially arranged layers of smooth muscle and is relatively thick in arteries. It has varying amounts of elastin, reticular fibers, and proteoglycans.
Tunica Media
The Tunica Media extends from the ________ ________ ________ to the ________ ________ ________.
Internal Elastic Membrane
External Elastic Membrane
This is a layer of elastin that separates the Tunica Media and Adventitia.
External Elastic Membrane
This Tunic layer is longitudinally arranged collagenous tissue with few elastic fibers. It will merge with the loose CT of surrounding vessels. It can range from relatively thin (arterial system) to quite thick (venules/veins).
Tunica Adventitia (also called Externa)
Why is the collagen important in the Tunica Adventitia?
It prevents over-expansion of the vessel.
These are vessels of the Tunica Adventitia that supply blood to the vascular tunics themselves. They’re basically blood vessels within blood vessels. They’re found in large arteries and veins due to the large lumen and are important for veins because they are carrying deoxygenated blood and need the extra nutrients.
Vasa Vasorum
These are in the Tunica Adventitia and provide ANS input that controls contraction of vascular smooth muscle.
Nervi Vasorum (Vascularis)
Large (_______) arteries are the largest vessels of the arterial system. Example is the Aorta.
Elastic
In Large (elastic) arteries, ________ forms concentric sheets/lamellae between the muscle cell layers. There are no ________, the smooth muscle synthesizes the collagen, elastin, and ground substance (between lamellae) of the ECM.
Elastin
Fibroblasts
***In the micrographs, the black squiggly lines is the elastin making lamellae.
Strong pressures of blood pulsating during _________ expands the arterial wall.
Systole
The artery lumen size reduces pressure and allows strong blood flow to continue during ________.
Diastole
Medium (________) arteries have more smooth muscle and less elastin than elastic arteries. They have a PROMINENT Internal Elastic Membrane, and a recognizable External Elastic Membrane.
Muscular
***On this micrograph you can see a distinct black squiggly line right by the lumen. This is the Internal Elastic Membrane!
Medium (muscular) arteries have smooth muscle arranged in a spiral fashion that produces the ECM components. It has a relatively thick Tunica ________, about the same thickness as the Tunica ________.
Adventitia
Media
Small arteries and arterioles are distinguished by the number of _______ _______ layers they have in the Tunica Media.
Smooth Muscle
(SMALL ARTERIES/ARTERIOLES) have up to eight layers of smooth muscle and will also have an Internal Elastic Membrane.
Small Arteries
(SMALL ARTERIES/ARTERIOLES) have 1-2 layers of smooth muscle and the Internal Elastic Membrane may or may not be present.
Arterioles
These are the flow regulators for capillary beds.
Arterioles
Arterioles receive sympathetic innervation to the Tunica Media that causes __________, and parasympathetic innervation to the Tunica Media that causes __________.
Vasoconstriction
Vasodilation
The smallest of all blood vessels are the _________ beds.
Capillary
Capillary beds are the site of _________ exchange and they often have a diameter even smaller than ________.
Metabolic
RBC
***This is why RBC are biconcave, so they can fold if they need to fit into smaller capillaries!
Capillaries contain cells called __________, which are perivascular (means surrounding the vessel) contractile cells with branching cytoplasmic processes.
Pericytes
Pericytes are enclosed with the basal lamina that is (DISCONTINUOUS/CONTINUOUS) with that of the endothelium.
Continuous
Pericytes are controlled by _______ ______ (endothelial cells) and promote stability of capillaries and ________ ________.
Nitric Oxide (NO) Postcapillary Venules
A single layer of _________ ________ form the innermost aspect of the Tunica Intima in capillaries. They are connected via cell-cell junctions, and the number of these junctions will vary permeability.
Endothelial Cells
Endothelial cells support the basement membrane and produce __________ for capillaries. They’re also metabolically involved in blood coagulation and thrombosis, and local vasodilation/constriction.
Collagen
This type of capillary is the most common in the body. It contains Pericytes on the continuous basal lamina, and there are endothelial cells connected via tight junctions. This is the most restrictive with what molecules are allowed to pass through it.
Continuous Capillary
This type of capillary has fenestrations in the endothelial cells and allows larger molecules to pass through it. It has a continuous basal lamina.
Fenestrated Capillary
This type of capillary is also known as sinusoidal. It has large fenestrations among endothelial cells and the basal lamina is discontinuous. It allows mass transport of molecules, anything can come and go.
Discontinuous Capillary
This is the first branch off of arterioles, supplying tissues.
Metarterioles
Metarterioles can connect straight through to the Postcapillary Venule via the _________ _________, or it can connect to ________ ________ where most gas exchange occurs.
Thoroughfare Channel
True Capillaries
________ ________ regulate blood flow through True Capillaries (from Thoroughfare Channel).
Precapillary Sphincters
These branch from Metarterioles and lack smooth muscle. Pericytes may be present.
True Capillaries
This is the distal end of the Metarteriole (lacks smooth muscle).
Thoroughfare Channel
***Connects to Postcapillary Venule
When the Precapillary Sphincters are contracted, they will shunt blood flow straight through the Thoroughfare Channel. This forces blood to enter venous return more quickly and prevents exchange with _______ _______. The contraction of the sphincters differentially occurs based on metabolic demand.
True Capillaries
This category of vein receives blood from capillaries and have a diameter as small as 0.1 mm.
Venules
What can venules be subclassified as?
Postcapillary Venules Muscular Venules (have more smooth muscle)
This category of vein are less than 1 mm in diameter, and are continuous with Muscular Venules.
Small Veins
This category of vein have a diameter of as much as 10 mm, and represent most of the named veins.
Medium Veins
This category of vein have a diameter of >10 mm, and examples include the Superior and Inferior Vena Cava and Hepatic Portal Vein.
Large Veins
In veins, tunics are not as distinct or well-defined, _______ and ________ veins have all three layers.
Large
Medium
In veins, the Tunica Intima may contain ________, which are semilunar flaps consisting of a thin CT core covered by endothelial cells.
Valves
Veins have (THICKER/THINNER) walls than accompanying arteries, and the lumen is (LARGER/SMALLER) than that of the artery.
Thinner
Larger
The lumen of veins are often…
Collapsed
The path of travel from Capillaries is to Postcapillary Venules — _________ Venules — ________ Veins.
Muscular
Small
These drain the capillaries and have no true Tunica Media.
Postcapillary Venules
_________ Venules have 1-2 layers of smooth muscle in the Tunica Media and the Tunica Adventitia is thin.
Muscular
________ Veins have all three tunics, the Tunica Media is 2-3 layers and the Tunica Adventitia is thicker.
Small
These veins travel with the Muscular Arteries (Medium) and have a thicker Tunica Media and Adventitia. The wall is often folded around a large lumen and it contains valves.
Medium Veins
For these veins, the thickest layer of the vessel wall is the Tunica Adventitia. It contains collagen and elastic fibers, and fibroblasts. It also contains longitudinal smooth muscle cells.
Large Veins
For Large Veins, the Tunica ________ is thin with circumferentially arranged smooth muscle cells, collagen fibers, and some fibroblasts. The Tunica ________ is thin and blends with Tunica ________.
Media
Intima
Media
Lymphatic vessels circulate _________ through most parts of the body. They serve as adjuncts to the blood vessels.
Lymph
Lymphatic vessels are ___________, conveying fluid only from tissues. They collect lymph, clean it, and return it to the venous supply. This is why they’re so important for infection.
Unidirectional
Lymphatic __________ are the smallest and consist of close-ended tubes found among capillary beds.
Capillaries
Lymphatic Capillaries have overlapping _________ cells that form 1-way valves for collecting lymph.
Endothelial
Lymphatic Capillaries have an incomplete ________ _______, which allows increased permeability.
Basal Lamina
For Lymphatic Capillaries, the openings between the endothelial cells are held in place by _________ _________. These join to form lymphatic vessels.
Anchoring Filaments
Lymphatic Capillaries lead to collecting lymphatic vessels. The size organization is similar to that of _______.
Veins
Lymphatic vessels have all vascular tunics and possess _______ like veins. The walls increase in thickness as the vessel increases in size, and the continuous tight junctions prevent leakage.
Valves
(AFFERENT/EFFERENT) lymphatic vessels bring lymph in, then it is cleaned and taken back out via (AFFERENT/EFFERENT) lymphatic vessels to the venous system.
Afferent
Efferent
Why is it important that lymph returns the fluid back to the venous system?
To maintain blood volume
Briefly describe the pathway of lymph return to the venous system, starting with the lymphatic capillaries.
Lymphatic Capillaries --- Lymphatic Vessels --- Lymphatic Trunks --- Right Lymphatic Duct --- Thoracic Duct --- Brachiocephalic Veins --- Vena Cava
The _______ _______ _______ collects lymph from the right side of the head, neck, upper limb, and thorax while the _______ _______ drains lymph from the rest of the body.
Right Lymphatic Duct
Thoracic Duct
