Vascular system

Name the functional groups of the circulary system

Capillaries ( + precapillaries and postcapillaries) and venous + arterial circulary system

What are precapillaries and postcapillaries also called?

metaarterieoles & venules, respectively

The arterial side of the ciculary system is composed of what parts?

Large aka elastic, medium( muscular) and arterioles

The venous side of the circulary system is composed of what parts?

large, small+ medium and venules

Name the main components of the blood vessel wall

* endothelium ( simple squamous)
* smooth muscle
* connective tissue element → extracellular substance
* collagen reticular fibers
* elastic fibers /laminae
* connective tissue cells

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In what blood vessels are smooth muscle cells not found

cappilaries and postcappilary venules

Which vessels has the wall with the most smooth muscle cells?

Arteries

What is produced by the smooth muscle cells?

components of their own basal laminae, elastic laminae, some collagen and reticular fibers

What lines the inner side of the blood vessel?

endothelial cells

What is the origin of endothelial cells and how are they organized in the inner lining of the blood vessel?

mesenchymal origin, organized in simple squamous form but elongated with elongated nucleus

Is the endothelial layer thicker or thinner in large vessels

Thicker

What characterizes the endothelial cells in the blood vessel wall?

* very flat
* numerous pinocytotic vesicles
* weibel- palade bodies containing von willebrand (coagulation factor)
* adherent, gap and tight junctions

What are weibel Palade bodies?

Elongated secretory granules storing post synthesis products, These can be very rapidly released. The ones in vessel walls contain a coagualtion factor relating to factor 8

What are the functions of endothelial cells in the vascular system?

* provide smooth lining
* control transport of substances, particulary in cappilaries
* control of migration across vessel wall
* produce & secrete components of ex substance
* modify biological substances
* take up pathogens & cell debrid
* role in angiogenis

What molecules can freely diffuse across the endothelium of the vessel wall

Gases and hydrophobic molecules

How does ions, glucose and other simple molecules travel across the cell membrane?

via transporters /channels

How are large molecules transported across the cell membrane?

transcytosis ( combination of exocytosis & endocytosis)

How can larger molecules transport across the cell membrane uncontrollably ?

Through pinocytotic vesicles that become channels, fenestrations ( permanents) or intercellular clefts

How can leukocytes migrate across the blood vessel wall?

endothelial cells can present adhesion molecules attracting leukocytes → initiating their migrations

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aka diapedisis

Name the groups of important secretory products from endothelial cells in vessel wall

* components of basal laminae ( ex substance)
* pro and anti coagulants
* vasoconstrictors & vasorelaxants
* growth facrors

Name the pro and anti coagulants of the endothelial cells

pro :

* von willebrandt factor
* platelet activating factor

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anti aka vasodilator:

* plasminogen activator
* prostacyclin

What are endothelins?

secretory product of endothelial cells that function as a vasoconstrictor

Does nitric oxide ( NO) relax or contstrict the vesels?

relax

What is the most important growth factor that endothelial cells secrete?

VEGF = vascular endothelial growth factor, important for capillary formations

Where does new endothelial cells come from?

endothelial progenitor cells

What is the origin of endothelial progenitor cells?

mesenchymal stem cells in the bone marrow that circulated in peripheral blood

What is the function of endothelial progenitor cells?

They repair injured endothelium, promote formation of new capillaries, initiate angiogenesis

What is angiogenesis

The action of improving the blood supply of an area with restricted blood flow ( ischemia) by making a new capillary vessel

Does the number of progenitor cells increase or decrease with age?

decrease

What is the total length of capillaries?

100 000 km

What is capillaries responsible for?

the exchange of gases and substances between blood and tissue

what are the components of the capillary wall?

endothelium, basal lamina, pericytes ( on the outer surface)

Where does pericytes originate from?

mesenchymal cells

Does pericytes have cytoplasmic processes

Yes and they surround the capillary

Does pericytes produce their own basal lamina?

yes

What cells can pericytes differentiate into?

fibroblasts, chondroblasts, osteoblasts, adipocytes, smooth muscle cells

What are the 3 main groups of capillaries?

continous, fenestrated and discontinuous ( sinusoids)

What characterizes the continous group of capillaries?

* continuous endothelial lining
* continuous basal lamina
* pericytes present
* selective blood- tissue transport
* occur in most organs

does continuous capillaries have low or high permeability?

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low

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What do we mean by “fenestrated” capillaries

Capillaries with pores in them

What characterizes fenestrated capillaries

* Thin cytoplasm
* endothelial cells with pores
* usually covered by a discontinuous protein diaphram
* =some et hjul
* continuous basal lamina
* present pericytes
* nonselective transport

Does fenestrated capillaries have high or low permebility

high

Where does fenestrated capillaries occur?

intestines, kidney and endocrine organs aka organs where the exchange between blood and tissue are intensifies

What are discontinuous capillaries also called

sinusoids

what characterizes discontinuous capillaries?

* large diameter and irregular
* large pores in endothelial cells
* no pericytes = this capillary is not a barrier between blood and tissue


* discontinuous / absent basal lamina
* nonselective transport

Where are discontinuous capillaries found?

liver, spleen & bone marrow

explain the process of angiogenesis

* o Angiogenic factor bind to EC receptor on the endothelial cells
* The endothelial cells are activated and start to proliferate ( dele seg)
* The cells start to migrate, sidelengs ut fra blodåren
* These parts will elongate, form a loop and eventually connect
* the loop will be stabilized through modifications

Are metaaterioles and postcapillary venules a part of the capillary beds?

yes, functionally

What characterizes the metaarterioles / precapillaries?

The outer wall has layer of circular smooth muscle cells

What charcterizese postcapillary venules?

* larger diameter
* no muscle cells but have a layer of pericytes
* highly sensitive to proinflammatory mediators
* increases permebility = edema
* site of migration from blood to tissues

What is the function of precapillary sphincters?

* regular blood flow in capillary bed
* switching areas of the network on and of depending on the needs

How does arteriovenous anastomoses regulate blood flow

it is a direct connection between small arteries and small veins

What characterizes the standard type of AVA ( arteriovenous anastomoses?

short vessel with 3 segments; arterial, regulatory, venous

Where is the regulatory segment located in the AVA

between the arterial and venous segment, looks like a sphlincter

What characterizes the glomus type of AVA´s

* have coiled up and branched arterioles
* thick layer of smooth muscles

What regulated the arteriovenous anastomoses

The autonomic nervous system

What layers is the blood vessel walls parted into?

tunica intima, tunica media, tunica adventia

What is tunica intima layer composed of?

endothelium and a layer of loose connective tissue

What is the tunica media and tunica adventitia layers composed of?

media= smooth muscle cells + some elastic fibers

adventitia = collagen fibers

What are the different functions of the different layers of the blood vessel

intima : provides a surface for undisturbed blood flow

media: controls lumen size + blood flow rate

adventitia: mounts the vessel to the surrounding tissue

What is the most important function of vascular smooth muscle cells?

Regulate lumen, that will determine blood pressure and flow

What nerve fibers regulate the contractility of vascular smooth muscle cells?

vasomotor nerve fibers, belonging to the autonomic NS

In what layers of the blood vessel is the vasomotor fiber found?

mainly in adventitia + some in media

What other factors than nerve fibers can regulate the contractility of vascular smooth muscle cells?

Hormones and regulatory substances present in blood

Endothelins & nitric oxide from endothelial cells

What is a vasa vasorum?

a small vessel that supplies the walls of bigger vessels

In what layer of the blood vessel wall is vasa vasorum formed?

adventitia layer

In arteries and veins what are the thickest blood vessel wall?

vein: tinica adventitia

artery: tunica media

Are elastic fibers rare or common in veins

rare, they are common in arteries

Does veins or arteries have the thickest walls

arteries

What are arterioles composed of

very thin intima, 1-3 layers of smooth muscle cells

What is the function of arterioles?

regulate the blood flow to the capillary network, contribute to the vascular peripheral resistance

What are the 2 types of arteries

Muscular & elastic

What parts of muscular arteries contain elastic lamina?

inner and outer layers

What type of arteries are the biggest ones?

elastic, goes straight out of the heart. Elastic arteries will always be big but big arteries are not always elastic arteries

What does the media layer of muscular arteries contain?

compact circular array of smooth muscle cells

What does the media of elastic arteries contain?

Multiple layers elastic fibers of and smooth muscle cell

What is the function of elastic arteries versus the one for muscular arteries

elastic: reduce the difference between systolic and diastolic blood pressure

muscular: distribution of blood

What is the main cause of infarct and stroke?

Atherosclerosis

What characterizes atherosclerosis?

Changes in the tunica intima:


1. macrophages and smooth muscle cells accumulate lipids
2. increase in the amount of connective tissue
3. calcification of vascular wall
4. damage of the endothelium
5. local clotting → thrombus formation

Ending in hardening/ thickening of the artery

Does venules and medium veins have distinct or indistinct vessel walls?

both are indistinct but vary in thickness, medium is bigger

Does large veins in the thorax and abdominal cavity decrease or increase in stiffness of the wall?

They increase

What veins have no walls, only endothelium?

meningeal veins in the dura mater and trabecular veins in the spleen

How are the veins of the legs specialized?

They travel against gravity by having valves ( thin folds of intima) preventing the backflow of blood

They also have thick a muscular wall with thick media and smooth muscle cells in all layers → looks like a artery

Where are carotid and aortic bodies located?

near common carotid artery and aortic arch

What are the carotid and aoriv bodies composed of?

highly vascularized connective tissue

What types of cells are found in the carotid and aortic bodies?

glomus cells and sheath cells

What are glomus cells

sensory cells with granules and adjecent afferent nerve terminals

What are sheath cells

modified schwann cells

What is the function of glomus cells?

They monitor levels of O2, CO2, pH

How does glomus cells regulate different levels?

Via nerve fibers they send signals to the respiratory center of the CNS :

More specifically: during change in levels they will close their potassium channels → depolarizes the cell → voltage gated Calsium channels open → More calcium in the cell → triggering exocytosis of the granular content ( neurotransmitters)→ Goes to the respiratory center

What is the carotid sinus?

a dilated part of the internal carotid artery

What characterized the carotid sinus

It has a thin media and a thick adventitia with numerous nerve fibers and terminals

What function does the carotid sinus serve?

Their nerve terminals react to stretching of the arterial wall → monitoring blood pressure through baroreceptors

Name the 3 layers of the heart wall

endocardium, myocardium, epicardium ( visceral layer of pericardium

What is the endocardium of the heart composed of?

a layer of endothelium + basal lamina + a thin layer of loose connective tissue

What is the myocardium composed of?

Working heart muscle cells forming a network with a dense system of capillaries

What is the epicardium composed of

connective tissue with adipocytes + lined with simple squamous epithelium ( mesothelium

What is the origin of mesothelium ?

mesenchymal origin

What is the function of mesothelium?

* secretes phospholipids = reduce friction
* controls transport of substances to pericardial fluid
* if activated, it secretes cytokines

What are cardiac valves?

Thin connective tissue folds of endocardium lined with endothelium