Flashcards in L28 – Histology and Functions of Blood Vessels Deck (123):
What 3 things make up the circulatory system?
Heart, Blood vessels, Lymphatic vessels
What are the roles of circulatory system? (Transport, heat... etc)
- Transport blood, nutrient, gases, waste
- Maintains and regulates blood flow and BP
- Protect body from infection
-Maintain fluid balance
What are 3 categories of blood vessels?
arteries, veins, capillaries
What are the layers of blood vessels and heart?
Heart: Endocardium, Myocardium, Epicardium
Blood vessels (expt capillaries): Tunica Intima, Tunica Media, Tunica Adventitia
3 layers to heart endocardium?
1) endothelium : simple squamous w/ basment membrane
2) sub-endothelial layer of loose connective tissue and smooth muscle cells
What is contained in subendocardium inside endocardium?
Purkinje fibers (specialized cardiac muscle cells), small coronary blood vessels, nerve fibres
How does the histology of purkinje fibres compare to regular cardiac myocytes? (think size, colour of cytoplasm and rim, features)
Larger, 1-2 nuclei
Lots of pale-staining glycogen, mitochondria in cytoplasm
Fewer myofibrils at periphery
No T-tubules, intercalated discs
What is the purpose of subendocardium?
Connects endocardium to myocardium
What is special about heart valve endocardium?
heart valves = extensions of endocardium
Dense connective tissue core (annulus fibrosus) instead of regular subendocardium.
What 2 things are found in Myocardium?
Cardiac muscle, extensive vasculature
How are myocytes in myocardium arranged?
Layers of spirally-arranged cardiac muscle fibers
Is cardiac myocyte branched or not?
Branched (unlike skeletal muscle )
What are the types of cell junctions in cardiac myocyte?
Intercalated discs connect individual cells by 3 types of cell-cell
1. Gap junctions
2. Adherens junctions
What are myocardium myocytes organised into?
bounded by connective tissue (contains coronary
vessels, nerve fibers)
What is the tissue type in epicardium?
fibroelastic loose connective tissue
What is another name for epicardium?
What epithelium covers epicardium? What does it do?
What are the components to epicardium?
fibroelastic loose connective tissue
What is Between visceral and parietal layer of serous
What is the outermost pericardium? made of?
What are the 3 layers of heart valves?
What tissue makes up heart valve spongiosa layer?
Loose connective tissue (loosely arranged collagen and elastic fibers)
covered by endothelium
What tissue makes up Fibrosa layer of heart valves?
Dense Irregular connective tissue
Fibres extend from cardiac skeleton
What tissue makes up Ventricularis of heart valves?
Dense connective tissue covered by endothelium
Many layers of elastic fibres
What structure of heart valve is continous with chordae tendineae?
4 classes of arteries and veins?
Arteries: Large Elastic, Medium Muscular, Small, Arterioles
Veins: Large, Medium, Small, Venules
Run through route of blood circulation from heart back to heart?
Aorta > Muscular arteries > small arteries and arterioles > capillaries > venules and small veins > medium veins > S/I Vena Cava > Heart
What are the three components to Tunica intima?
Simple squamous epithelium w/ basement membrane
Internal elastic membrane (In arteries and arterioles)
What is found in subendothelial layer of tunica intima?
Loose connective tissue
Sometimes smooth muscle
What is internal elastic membrane for?
Fenestrated elastic material
boundary between tunica intima and media
Is the epithelium in tunica intima continous from arteries to capillaries?
What connects the endothelial cells in tunica intima?
Endothelial cell Junctional complexes
What are the two roles of tunica media?
Regulate blood flow
Provide structural support
What are the structures of either side of tunica media in large arteries?
Internal elastic membrane
External elastic membrane
What is found in the tunica media predominantly in arteries?
Layers of vascular smooth muscle cells
What structure exists between smooth muscle cells in tunica media?
Fenestrated lamellae of elastin and collagen interposed between SM cells
Which layer of blood vessels is thickest in arteries?
Which layer of blood vessels is thickest in Veins?
What is tunica adventitia of vein mainly made of?
Longitudinally arranged loose collagen and few elastic fibres
Smooth muscle cells (can be longitudinal or circular)
What two structures are specially located in tunica adventitia?
Artery vs veins.
Thickness: Artery thicker, vein thinner
Shape: Artery more uniform and circular, vein appears irregularly shaped and weaker flaccid walls
Lumen size: Vein lumen larger than artery lumen
Valves: Only in veins
Why is artery walls thicker than veins?
Thicker walls = withstand pulsatile flow from heart and higher BP
Veins have Less elastic tissue, less smooth muscle = much thinner
Artery or veins hold more blood?
2/3 of all circulating blood
What 2 membranes are found only in arteries but not veins?
Internal and External elastic membrane surrounding tunica media
Compare the smooth muscle orientation between artery and vein tunica media and adventitia?
Tunica media: Artery= circular SM , Vein = circular SM
Tunica Externa: Vein= Longitudinal SM
What are the three types of capillaries?
Continuous, Fenestrated, Discontinuous/ Sinusoidal
Large elastic/ conducting arteries can maintain blood flow with what structure?
abundant elastic fibers in tunica media >
expand during systole , RECOIL during diastole
accommodate pressure changes
What are the two effects of high elastin content in tunica media of larger arteries?
o maintain BP, blood
flow and accommodate pressure changes
o Propel blood forward
transport blood from
heart to smaller arteries
Give examples of Large elastic arteries?
Aorta, pulmonary trunk (plus main branches e.g. bronchiocephalic artery)
What blast cell is found in tunica adventitia of both artery of vein?
Are internal and external elastic membranes easily observed in large elastic arteries?
No, hard to distinguish from nearby elastic lamellae
Is the tunica intima of large elastic arteries thick or thin? contains what?
Thick subendothelial layer but thin overall tunica intima
Contains SM, collagen, elastic fibres
How is the elastin arranged in tunica media in large elastic arteries?
Elastin arranged in Fenestrated Concentric lamellae
How many lamellae of elastin does Aorta have?
What tissue makes up tunica adventitia in large elastic arteries
Which of 4 types of arteries regulate blood distribution to organs by altering lumen size?
Medium muscular arteries
Regulate circulatory dynamics through vasoconstriction/ dilation > control distribution of blood to body parts
Compare the amount of SM and elastin between large and medium arteries.
Medium A have more SM and less elastin compared to Large A in tunica media
Compare visibility of internal and external elastic membrane between large and medium arteries?
Large = not conspicuous
Medium = Clearly distinguishable
What happens to number of SM cells and Internal/ external elastic membrane in tunica media of medium arteries when it branches?
branch and decrease in
Number of layers of
smooth muscle cells
in tunica media decreases
Internal/ external elasti laminae become much less prominent
Compare the thicknes of tunica intima in large and medium arteries?
Medium arteries have THINNER tunica intima than Large A
How may tunica intima of medium A be expanded over time?
Expanded through aging by lipid deposition
What makes up the tunica media of Medium muscular arteries?
Almost entirely spirally- arranged smooth muscle
Collagen fibres, little elastin
Compare thickness of tunica adventitia between Large and medium A?
Medium A has THICKER tunica adventitia than Large A
Which of 4 arteries can change peripheral resistance?
Small arteries and Arterioles
How can small arteries and arterioles be told apart?
By Number of smooth muscle cell layers in tunica media and size
Small arteries = 3-8 layers
Arterioles = 1-2 layers
What happens to internal and external elastic membrane in transition from small arteries to arterioles?
Membranes become less defined and disappear
Arterioles have NO external elastic membrane
Explain arteriole changing peripheral resistance?
Tunica Media consists of 1-2 layers of smooth muscle cells: vasoconstrict /
vasodilate > dramatic
changes in lumen
diameter > change
resistance to blood
flow and systemic
Arteriole smooth muscle contraction has 2 effect?
Effects on distribution of blood flow and systemic arterial pressure
Explain how arterioles can perform AV shunt?
Blood flow from metarteriole/terminal branch into capillaries,
sphincters: blood flow
blood flow through
What is the SM at the start of a capillary bed and end of arteriole?
What makes up a capillary wall?
Single layer of endothelial cells + basement membrane
Diameter of capillary?
Smaller than diameter of RBC
Role of capillaries?
Allow fluid to move between capillary and interstitial space
Where are pericytes found?
Intimately surrounding capillaries, enclosed within basal lamina
What are the roles of pericytes?
Undifferentiated mesenchymal cells:
Give rise to endothelial cells and SM cells
Provide vascular support and stability of capillaries
What is diapedesis?
Leukocytes squeezing through intact walls of capillaries to site of inflammation or tissue injury
What is the difference in basal lamina between three types of capillaries?
Continuous and fenestrated capillaries = continuous basal lamina
Discontinuous capillary = discontinuous or missing basal lamina
What is the difference between endothelial cells of three capillary types?
Continuous cap. = Complete endothelial cells
Fenestrated cap. = fenestrated endothlial cells perforated by small pores
Discontinuous cap. = Incomplete endothelial cells perforated by large pores
Compare the permeability of three types of capillaries?
Continous cap.= very limited movement between adjacent endothelial cells
Fenestrated cap. = for rapid exchange of substances
Discontinuous cap. = Allow direct communication, most permeable, allow proteins or even cells to pass
Which capillary type is most common?
Continuous cap. found where?
How can larger molecules be transported in continuous cap.?
from blood, extracellular
space can pass via pinocytotic vesicles
Fenestrated cap. found where?
Sites of fluid and metabolite exchange (absorption and excretion):
Intestinal tract / mucosa, villi
What is the fenestrated endothelial lining pores covered by?
60- 80nm pores
covered by thin “diaphragm”, except
Discontinuous capillaries found where?
Sites of blood exchange: No barrier to blood exchange:
What cells in liver associate with discontinuous capillary in liver?
Kupffer cells =macrophages in liver
What 3 mechanisms assists venous blood return?
Musculovenous pump (external compression)
Respiratory pump (via thoracic pressure created in breathing)
Artery pulsation (smooth muscle contraction and BP)
What is the role of venules?
Drain exchanged blood from cap. to small veins
Classify venules. Typical diameters?
Postcapillary venules (smaller)
Muscular venules (larger, 1-2 layers of SM)
10 µm – 1 mm
Do venules have tunica adventitia?
Venules have subendo thelial layer?
Which type of venule has no true tunica media?
Compare small veins and muscular venules tunica adventitia?
Small vein has tunica adventitia
Size of small veins?
Compare the tunics of small vein with venules.
All three tunics intact and present in small veins
Compare layers of SM in tunica media of small vein vs venule
Muscular venules = 1-2 layers of SM
Small vein = 2-3 layers of SM
Where are most medium veins found? diameter.
Depp veins that accompany arteries, up to 10mm
Where are valves in medium veins found in body?
Inferior portion/ lower limbs
Do medium veins have internal elastic membrane and subendothelial layer?
Yes but discontinuous
Describe tunica media of medium veins.
Several layers of circularly arranged SM cells with interspersed collagen and elastin
Compare the SM layout in tunica media vs adventitia of medium veins?
SM in media = circular
SM in adventitia = longitudinal
How are Large veins classified vs medium veins?
Large vein = diameter larger than 10mm
Give three examples of large veins?
Describe tunica adventitia and role in large veins.
Longitudinally disposed SM
Force blood toward heart: contract > shorten > close valves > help venous return
Describe tunica media in Large veins.
Circumferentially arranged SM, Collagen, fibroblasts
Where are myocardial sleeves found?
Inf. Sup. Vena Cava
What are varicose veins?
Due to leaky valves, weakness in vein wall, prescence of abnormal masses
What veins in body most prone to varicose veins?
Veins of lower limb
Risk factors > varicose veins?
Difference between simple and portal system in circulatory routes?
Simple pathway = blood pass through one network of capillaries
Portal system= blood pass through 2 consecutive capillary networks
Give 2 examples of portal system circulation.
Hepatic portal system
Nephron Peritubular capillaries and Vasa Recta
What is AV shunt? What does it allow and where is it found?
Allow blood to bypass capillaries by providing direcct route
Found in node, lips, fingertips, erectile tissue of penis and clitoris
What are 2 other types of anastomosis apart from AV?
Venous and Arterial anastomosis
Role of arterial anastomosis?
Backup route for blood in case of blockage
e.g. in functional end arteries of coronary circulation, pelvis anastomosis ...etc
Which anastomosis type is most common?
Where is interstitial fluid collected?
By blind-ended lymph capillaries from interstitial spaces
Sequence of lymph drainage starting at interstitial space.
Interstitial space > Several Afferent lymphatic vessels > lymph nodes> converge to efferent lymphatic vessels > Larger lymphatics and major lymph vessels > Subclavian veins > blood stream
Describe lymphatic capillaries.
Tubes of endothelium without continuous basal lamina and tight junction
What maintains patency of lymph CAPILLARIES?
Is lymph capillary less permeable than blood capillaries?
No, lymph cap. is more permeable
Describe lymph VESSELS.
Converge from lymph cap.
Lots of valves
Continuous tight junctions
Continuous basal lamina surrounded by SM cells
What 2 mechanisms drive flow of lymphatic vessels?
Adjacent skeletal muscles
Contraction of SM layer surrounding continuous basal lamina of lymph vessels