Blood Vessel Histology Flashcards
What are the three layers of a blood vessel?
- Tunica intima
- Tunica media
- Tunica adventitia
What innervates blood vessels? What NT do these nerves release? How do they propagate impulses?
- Postganglionic, unmyelinated sympathetic fibers (stimulation causes contraction)
- They release NE
- Impulses propagated via gap junctions
What is different between the structure of an artery and a vein?
Arteries have an elastic membrane between the tunica intima and the tunica media.
What are the three layers of the heart wall?
Innermost to outermost:
- Endocardium
- Myocardium
- Epicardium
What are examples of elastic (conducting) arteries? How do they look in fresh specimens?
- Aorta; common carotid & subclavian arteries; common iliac arteries; pulmonary trunk
- Sometimes appear yellowish in fresh specimens due to abundance of elastin in arterial walls
What to know about the tunica intima of elastic arteries?
- Endothelium
- -Elongated endothelial cells; oriented in longitudinal plane
- -Cells connected by occluding junctions
- -Small vesicles associated with plasma membrane: transport of water, electrolytes, macromolecules
- -Weibel-Palade bodies
- Narrow layer of underlying connective tissue
- Internal elastic lamina
What are Weibel-Palade bodies?
- Arterial endothelial cells
- Contain von Willebrand factor
- associated with tunica intima of arteries
What to know about the tunica media of elastic arteries?
- Many fenestrated lamellae of elastin (gaps between)
- Circularly arranged smooth muscle bundles alternate with elastin
- Elastin tends to be the dominant component
- Extracellular matrix produced by smooth muscle cells
What to know about the tunica adventitia of elastic arteries?
- Relatively thin
- Contains vasa vasorum (blood vessels of the blood vessels)
- -Capillary beds spring from these vessels and supply the tunica media
What is wider in an elastic artery than other vessels?
Tunica intima
What are the components of the tunica media?
- Smooth muscle
- Collagenous fibers
- Elastic membrane (with windows)
What do sheets of elastin look like?
Pink, thick wavy structures
What are muscular (distributing) arteries?
Most of named arteries fall into this category
What is the chief characteristic of muscular (distributing) arteries?
Thick tunica media comprised primarily of smooth muscle cells
What to know about the tunica intima of muscular (distributing) arteries?
- Thinner than that of elastic arteries
- Prominent internal elastic lamina; undulating contour
What to know about the tunica media of muscular (distributing) arteries?
- Smooth muscle cells circumferentially arranged are the predominate component
- 3-40 layers of smooth muscle
- Smooth muscle cells produce the extracellular matrix
- External elastic lamina present in the larger muscular arteries
What to know about the tunica adventitia of muscular (distributing) arteries?
- Connective tissue components with some thin elastic laminae present
- -Connective tissue components produced by fibroblasts
- Vasa vasorum present
- Unmyelinated nerve endings present
What is the size of arterioles?
- Typical diameter of = 0.1 mm
- Wall diameter is often about the same as the lumen diameter
What are the three layers of arterioles?
- Tunica intima: endothelium; thin layer of c.t.; sometimes an internal elastic lamina
- Tunica media: 1-3 layers of smooth muscle
- Tunica adventitia: scant; produced by fibroblasts
On a slide, how does an arteriole look different than a venule?
Arteriole has much thicker walls than venule. Venule is much wider, larger lumen and is filled with more blood in general.
What are metarterioles?
- Smooth muscle cells are not continuous
- Smooth muscle cells can act as sphincters
- Control blood flow into capillary bed by encircling the arteriole adjacent to where a capillary arises from the arteriole
What are three specialized sensory structures in arteries?
- Carotid sinuses
- Carotid bodies
- Aortic bodies
What are carotid sinuses?
- Baroreceptors (perceive changes in blood pressure)
- In walls of internal carotid arteries (just above bifurcation of common carotid arteries)
- Adventitia is thick and innervated by sensory fibers of cranial nerve IX (glossopharyngeal)
- Tunica media thin: blood vessels distend with increasing blood pressure –> stimulates nerve endings
- Adjustments made in vasoconstriction to maintain proper blood pressure
What are carotid bodies?
- Chemoreceptors
- Located at bifurcation of common carotid arteries
- Special chemoreceptor nerve endings monitor changes in oxygen, carbon dioxide, and hydrogen ions in blood
- Sensory (afferent) fibers supplied by glossopharyngeal and vagus nerves
What are aortic bodies?
- Chemoreceptors
- Located on arch of aorta between right subclavian and right common carotid an between left common carotid and left subclavian
- Same structure and function as carotid bodies
What to know about capillaries?
- Usually short; 8-10 microns in diameter
- Single layer of elongated simple squamous endothelial cells
- -Long axis in direction of blood flow
- -Vimentin and desmin have been identified in cells
- -Pinocytotic vesicles associated with cell membrane
- -Joined together by fascia occultness
- -External surface covered by a basal lamina
Where does leukocyte migration occur most often?
-Almost all leukocytes migrate from lumen of vessel to adjacent connective tissue - post-capillary venule is place where this occurs most often
What are pericytes and what do they do?
- Found outside small capillaries and small venues
- Processes run circumferentially and longitudinally around capillary
- Sometimes form gap junctions with endothelial cells
- Probably contractile and help regulate blood flow through capillaries
- May give rise to smooth muscle cells or endothelial cells
What are the three main types of capillaries?
- Continuous capillaries
- Fenestrated capillaries
- Sinusoidal capillaries
What to know about continuous capillaries?
- No interruptions (pores/fenestrae) in walls
- Found in muscle, nervous and connective tissues
- Cells joined by fasciae occludentes
What to know about fenestrated capillaries?
- Pores (fenestrae) in capillary walls
- -Pores covered by thin diaphragm
- -Pores occur in clusters
- Found in pancreas, intestines, and endocrine glands
What to know about sinusoidal capillaries?
- Irregularly shaped blood pools or channels
- Larger diameter than other capillary types
- Contain many fenestrae (without diaphragms); endothelial wall may be discontinuous
- -larger pores
- Basal lamina is discontinuous
- Found in bone marrow, liver, spleen, lymphoid organs and some endocrine glands
Where are continuous capillaries found?
- Muscle
- Connective tissue
- CNS
Where are fenestrated capillaries found?
- Kidney glomeruli
- Endocrine glands
- Intestinal villi
- Exocrine pancreas
Where are sinusoidal capillaries found?
- Liver
- Spleen
- Bone marrow
- Lymph nodes
What are arteriovenous anastomses?
- Occur where an artery joins a venous channel
- If shunt is open, blood largely bypasses capillary bed
- If shunt is closed, blood enters capillary bed
- Play an important role in thermoregulation
What are the three segments of arteriovenous anastomses?
- Arterial segment (structure similar to that of an artery)
- Intermediate sement: richly innervated with adrenergic and cholinergic nerve fibers
- Venous segment (structure similar to that of a vein)
What are the parts of the central channel?
- Metarterioles (proximal component of central channel): have precapillary sphincters
- -Contraction of sphincters allows blood to bypass true capillaries and enter thoroughfare channels directly
- Capillary bed (middle component of central channel)
- Thoroughfare channel (distal component of central channel)
- -Drains into venule
What is capillary histophysiology?
- Vesicle transport; transcytosis
- Leukocyte adhesion and diapedesis
- -Leukocytes bind to endothelium and pass through endothelium to extravascular spaces
- -Selectins (P,E,L)
- -Integrins
- -Other molecules
What are the steps of leukocyte recruitment?
1a. Attachment
1b. Rolling
2. Activation
3. Arrest & adhesion strengthening
4. Transendothelial migration
- Selectins are present from 1a-3
- Chemoattractants are present from 2-4
- Integrins are present from 2/3-4
What else are capillaries involved in? (histophysiology)
- Inflammation & capillary permeability (histamine & bradykinin)
- Synthetic activities: broad capabilities
- Enzymes for conversion of angiotensin I to angiotensin II
- Lipoprotein breakdown into fatty acids and triglycerides in adipose tissue
How many and how large are veins?
- Outnumber arteries
- Lumen diameter larger
- ~70% of blood volume found in veins
- Parallel arteries
- Walls tend to collapse due to thinness
- Layers: tunica intima; tunica media; tunica adventitia
What are post capillary venules?
- Receive blood from capillary bed
- Similar to capillaries
- -Thin endothelium surrounded by pericytes
- -In section look very much like sinusoidal capillaries
- Preferred site for emigration of leukocytes from vessel lumen into tissue spaces
What are Larger Venules?
- Pericytes replaced by smooth muscle
- Smooth muscle cell investment increases as venules get larger
- Much material exchanged between vascular compartment and extravascular compartment
What lines the larger venules?
Simple squamous endothelial cells
As veins get larger, pericytes are replaced with. . .
smooth muscle, wrapped circumferentially around venule
What are High endothelial venules (HEVs)?
- Specialized versions of small venues found in some lymphatic organs
- Endothelium is cuboidal rather than squamous
- Allow for migration of specific types of leukocytes through the endothelial wall into the lymphoid parenchyma
What are the three types of venules & small veins?
- Postcapillary venules
- Larger venules
- High endothelial venules (HEVs)
How large are medium veins and what do they have that smaller veins do not?
- Less than 1 cm in diameter
- Many medium veins have valves
What are the three layers of medium veins?
- Tunica intima: endothelium; basal lamina; some reticular fibers
- Tunica media: smooth muscle cells intermingled with collagen fibers and fibroblasts
- Tunica adventitia: thickest layer; collagen and elastic fibers
- Adventitia is MUCH thicker than in arteries
What are examples of large veins?
Venae cavae; pulmonary, portal, renal, internal jugular, iliac, and azygous veins
What are the three layers of large veins?
- Tunica intima: endothelium and a thick sub endothelial layers with elastic fibers
- Tunica media: not well developed– often apparent
- Tunica adventitia: collagen fibers; abundant elastic fibers; vasa vasorum; longitudinally disposed SMOOTH MUSCLE BUNDLES (e.g., inferior vena cava)
What are Varicose veins?
- Abnormally enlarged and tortous veins
- Usually affect superficial veins in legs of older individuals
- -Due to loss of muscle tone; wall degeneration; valvular incompetence
- Other common locations: lower esophagus (esophageal varices); terminus of anal canal (hemorrhoids)
What are valves?
- Found in small and medium-sized veins, especially those of the limbs
- Consist of folds of the intima
- -Endothelium
- -Connective tissue rich in elastic fibers
- Prevent back flow of blood
What are the three main components of the lymph vascular system?
- Lymph capillaries
- Collecting vessels
- Main trunks
What are lymph capillaries?
- Larger diameter than blood capillaries
- End blindly in tissue spaces
- Flimsy basal lamina
- Endothelial cells held together by a few tight junctions
What are collecting vessels?
-Vein-like structure but thinner walls and valves more closely spaced
What are main trunks?
Thoracic and right lymphatic ducts have vein-like structure
What are some functional considerations relating to pressure in the venous system?
- Pressure in vascular system forces fluids, salts and protein into extracellular compartment
- Edema will develop if substances are not returned to circulation
- Low pressure lymphatics well situated for taking up these materials
What are functional considerations of the lymph system?
- Contraction of smooth muscle in walls of vessels and adjacent skeletal muscles force lymph toward heart
- Lymph flows through lymph node where it is filtered and picks up antibodies
