A&P 2 Veins & Arteries
What is the function of the basement membrane of the tunica interna? What does it consist of?
(subendothelial layer) - Provides physical support for epithelial layer - Network of collagen fibers a) Provides significant tensile strength b) Also allows for some stretching and recoil - Anchors the endothelium to underlying connective tissue - Helps regulate molecular movement - Guides cell movement during tissue repair of blood vessels
What are the five types of blood vessels?
Arteries Arterioles (microcirculation) Capillaries (microcirculation) Venules (microcirculation) Veins
What is the term for when leaky valves allow flow from deep veins back into superficial veins?
Blood pooling
Where are capillaries found? Where are they not found?
Capillaries are found in nearly every cell in the body They are more prevalent in tissues that have a high metabolic need such as the liver, brain, muscles, kidneys and nervous system Capillaries are NOT found in avascular tissue such as the cornea of the eye and cartilage
What is the diameter of veins? What are the layers of veins and how do they compare to arteries?
Diameter from 0.5mm (small venules) to 30mm (venae cavae) Tunica interna (intima) Much thinner Tunica media Much thinner, much less smooth muscle and elastic fibers Tunica externa Thickest layer, consists of collagen and elastic fibers
What are the three types of capillaries?
1) Continuous 2) Fenestrated 3) Sinusoid
What does the tunica media consist of? In what vessels is it found? What is the function of the tunica media?
1) External elastic lamina Only found in arteries, not veins Separates the tunica media from the tunica externa Thins sheet of elastic fibers Has variable number of window-like openings (Swiss cheese like) These facilitate diffusion of materials through the tunica externa to tunica media 2) Smooth muscle (some elastic fibers) layer Regulates the diameter of the vessel lumen Is innervated by sympathetic nerve fibers Smooth muscle contracts and relaxes for blood flow regulation as needed Vasoconstriction Vasodilation Contracts when vessel is damaged to limit blood loss
What is another term for muscular arteries?
Also called "distributing arteries :because they branch and distribute blood to each of the organs
What is another term for elastic arteries?
Also known as "conducting arteries" because they conduct blood from the heart to medium sized muscular arteries
What is microcirculation?
Flow of blood from metarterioles through capillaries and then to venules
What are the characteristics of continuous capillaries? Where are they primarily found?
Most capillaries are continuous Plasma membranes of endothelial cells form a continuous tube interrupted only by intercellular clefts (gaps between neighboring endothelial cells) Found in CNS, lungs, skin, muscle tissue
How do varicose veins occur?
Valvular defect may occur from congenital issue or mechanical stress (prolonged standing/pregnancy) or aging
What are veins called that have leaky valves and are dilated and twisted?
Varicose
Which type of blood vessels are the smallest?
Capillaries
What are the functions of the endothelium of the tunica interna?
- Lining of the lumen of the vessel - Continuous with the endocardial lining of the heart - Inhibits platelet activation and reduces blood cell damage - Facilitates efficient blood flow by reducing friction - Secretes chemical mediators that influence contractile smooth muscle in tunica media - Assists with capillary permeability
Where are the most common places to find varicose veins?
- esophagus - anal canal - superficial veins of the lower limbs
What are the characteristics of deep veins in the lower limbs?
-Deep veins are much larger than superficial veins -Deep veins serve as principle return pathway to heart -One-way valves in small anastomosing vessels allow blood to pass from superficial to deep veins, prevent reverse flow
What are the characteristics of superficial veins in upper limbs?
-Superficial veins are much larger than the deep veins -Superficial veins serve as pathways from capillaries of upper limb back to heart
What are the characteristics of sinusoid capillaries?
-Wider and more winding than others -Incomplete or absent basement membranes -May have unusually large fenestrations -Very large intercellular clefts allowing some proteins and even blood cells to pass from tissue into blood Example: new formed blood cells pass from marrow into blood stream through these sinusoids
What are the three vessel wall layers from external to internal?
3 wall layers (external to internal): Tunica externa (adventitia) Tunica media Tunica interna (intima) Modifications of this basic design account for the five different types of blood vessels
What is a capillary bed?
A network of 10-100 capillaries that arise from a single metarteriole Capillaries from extensive branching networks that increase the surface area for rapid exchange of matt
Where are elastic arteries found?
Aorta, pulmonary trunk, brachiocephalic, subclavian, common carotid, common iliacs
What is the term for arteries that DO NOT anastomose? What happens if these arteries are obstructed?
Arteries that do not anastomose are called end-arteries - Obstruction of end-arteries interrupt the blood supply to segment of organ causing tissue necrosis - "End-Organ/Artery Damage"
What role do arterioles play in resistance?
Arterioles play key role (therefore known as resistance vessels) - Resistance is due to blood rubbing against vessel wall - When diameter is smaller, friction is higher causing greater resistance
What are the characteristics of muscular venules? What is their function?
As postcapillary venules move away from capillaries, they gain 1-2 layers of smooth muscle Become thicker walled (50-200um diameter) preventing metabolic exchange with interstitial fluid Thin walls of both postcapillary and muscular venules are most distensible elements of the entire vascular system ***Serve as reservoirs for large amounts of blood if needed*** Blood volume increases of 360% have been measured in the postcap/muscular venules
Where are deep veins found?
As superficial veins continue they form small connections with deep veins These travel between skeletal muscles
Changes in arteriole diameter cause what changes?
Cause changes to BP overall
What is the tunica externa composed of and what does it contain? What is it's function?
Composed of elastic and collagen fibers (connective tissue) Contains nerves of vessels Contains the vasa vasorum small vessels that transport O2 and nutrients to cells of blood vessel walls Easily seen on large vessels like the aorta Helps anchor vessels to surrounding tissue
What is the tunica interna composed of? What is the function of the tunica interna?
Consists of multiple layers a) internal elastic lamina layer (arterial) b) basement membrane layer (arterial, venous) c) endothelial cell layer (arterial, venous) Direct contact with blood as it flows through the lumen
What is vasomotion?
Contraction and relaxation of the pre-capillary sphincters 5-10 times per minute Regulates blood flow through the capillaries Ensures that capillaries receive blood flow during rest MOA is chemicals released from endothelial cells (NO)
What is the treatment for varicose veins?
Elastic stockings (compression) Sclerotherapy Laser occlusion Stripping...hehehe (removal of the offending vein)
What is the primary function of capillaries?
Exchange of substances between blood and interstitial space
What is another term for capillaries?
Exchange vessels
What are the characteristics of the wall layers of muscular arteries?
Has well defined internal elastic lamina but thin, ill-definied external elastic lamina Tunica externa can be thicker than the tunica media but not always Contains fibroblasts, collagen fibers, elastic fibers Longitudinally oriented
What do veins lack that arteries have? Is the lumen larger or smaller than that of arteries? Is blood pressure more or less in arteries?
Lack internal and external elastic laminae found in arteries -Distensible enough to adapt to variations in volume and pressure of blood passing through them -Not designed to withstand high pressure though Lumen of veins are larger than arteries Blood pressure in veins considerably less than that of arteries -Blood exits a lacerated vein by steady oozing flow -Blood exits a lacerated artery in spurts
Where are valves typically found? What layer are the continuous with? How do veins help with venous return?
Many veins (especially in the limbs) contain valves -Thin folds of tunica interna (intima) that form cusps -Cusps project into the lumen with the "cup" portion aiming toward the heart -Low blood pressure in veins allows blood to back up, the valves aid in venous return by helping to prevent backflow
What are arterioles? What is their function? What are the characteristics of their vessel walls?
Microscopic vessels- approximately 400 million Diameters from 15um-300um Wall thickness is ½ of the total vessel diameter 7.5um to 150um wall thickness Regulators of blood flow to systemic capillary beds Arterioles play a large role in the flow to the capillary system, and thus what comes out of the capillary system
What are the characteristics of fenestrated capillaries? Where are they primarily found?
Plasma membranes have many fenestrations allowing for easier diffusion Found in kidneys, villi of small intestine, choroid plexuses of ventricles of brain, ciliary processes of the eyes, most endocrine glands
What is the purpose/function of elastic arteries?
Propel blood onward while ventricles are in diastole As blood is expelled into aorta, the walls expand accounting for surge This expansion causes a momentary storage of mechanical energy called a pressure reservoir Elastic fibers recoil and convert stored (potential) energy into kinetic energy propelling blood forward
What are thoroughfare channels?
Provides direct route from arteriole to venule, bypassing capillaries Proximal end of metarteriole is surrounded by scattered smooth muscle fibers that contract and relax Distal end has no smooth muscle; resembles capillary, this end is called the thoroughfare channel
What is the consequence of the muscular arteries having a reduced amount of elastic fibers?
Reduced amount of elastic fibers causes reduction in ability to propel blood Muscular tunica media performs the majority of the work in these arteries This muscle contracts and maintains a state of partial contraction
Where are sinusoid capillaries primarily found?
Sinusoids also contain specialized lining cells adapted to function of the tissue Example: liver sinusoids have phagocytes cells that remove bacteria and other debris Spleen, anterior pituitary, parathyroids and adrenal glands also have sinusoids
What are the characteristics of postcapillary venules? What is their function?
Small veins that receive blood flow directly from capillary beds 10-50um in diameter Walls of the smallest venules are very porous allowing phagocytic WBCs to pass through to inflamed or infected tissue Function as significant sites of exchange of nutrients and wastes as well ***Last site of metabolic exchange***
What is the function of a portal system? What are some examples of portal systems in the body?
Some parts of the body blood may pass from one capillary network into another network through a vein called a portal vein This is called a portal system Examples: hepatic portal circulation (liver), hypophyseal portal system (pituitary)
What are anastomotic veins and where are they typically found?
Some veins are paired and accompany medium-to-small sized muscular arteries These paired veins escort arteries and connect with one another via these anastomotic veins Greatest # of these occur in the limbs Large one in the brain called superior anastomotic vein
Why are veins seen as blue on a person's skin when the blood is deep-dark red?
Superficial veins- blue colored tubes passing under the skin -Venous blood is deep-dark red but their thin walls and the tissue of the skin absorbs red-light wavelengths -This allow blue light to pass through the surface to our eyes where we see them as blue
What is the term for a terminal end arteriole? What does it taper to? What is the function of the capillary sphincter?
Terminal end is called metarteriole 1) This tapers toward capillary junction 2) Distal-most muscle cell forms the precapillary sphincter -This sphincter monitors blood flow into the capillary -The other muscle cells in arteriole regulate resistance to blood flow
Why do capillaries in tissues that are at rest, only receive a small amount of blood?
The need for metabolic exchange is low
What is the tunica media layer of elastic arteries composed of? What are the other major characteristics?
The tunica media layer has: -More elastic fibers called elastic lamellae than other vessels -Less smooth muscle than smaller arteries and arterioles Largest diameter among the arteries Vessel walls relatively thin (1/10th total diameter)
What is the tunica media layer of muscular arteries composed of?
The tunica media layer: Contains more smooth muscle but LESS elastic fibers (when compared to elastic arteries) Constitutes ¾ of the mass of the artery making these walls very thick Makes these arteries capable of greater vasoconstriction and vasodilation Helps to adjust rate of flow of blood
how many layers do capillaries consist of? Why do they lack a tunica media and tunica externa?
They consist of a single endothelial cell layer and a basement membrane only They only have thin, basic layers because they provide an area for nutrient, gas and waste diffusion
Maintaining a state of partial contraction is also called what?
This is called vascular tone Stiffens the vessel wall and helps maintain vessel pressure and efficient blood flow
What is the function of the arteries? How are they different from the veins? What are the two major types of arteries?
Transport blood (mostly oxygenated) from the heart to tissues throughout the body Much thicker tunica media layer than veins Plentiful elastic fibers lending to high compliance Walls stretch and expand easily without tearing in response to pressure increases/decreases Two major types of arteries a) Elastic b) Muscular
What are anastomoses and what is their function?
Union of branches of two or more arteries supplying blood to same region of body - Provide alternate routes for blood to reach an organ - This alternative route is called collateral circulation Anastomoses may also occur between veins, between arterioles and between venules
What is a vascular sinus? What is it composed of? What are some examples?
Vein with thin endothelial wall, no smooth muscle Surrounding dense connective tissue replaces the tunica media and tunica externa in providing support Examples: dural venous sinuses, coronary sinus
Where are superficial veins found?
Veins that lie within the subcutaneous layer of the skin Unaccompanied (no arteries)
What are some examples/areas where muscular arteries are found?
brachial, femoral, axillary arteries Pencil sized femorals and axillaries to string sized arteries entering organs (as small as 0.5mm in diameter)
What is the tunica externa of arterioles composed of? What is its function?
consists of areolar connective tissue containing abundant unmyelinated sympathetic nerves Along with the local chemical mediators, these nerves can alter diameter of the arterioles This varies the blood rate and resistance through these vessels