Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

The circulatory system


Includes the blood and lymphatic systems



Blood vascular system
o

Heart – pumps blood

o

Arteries – efferent vessels, get smaller as they branch, carry blood
containing O2 and nutrients to body tissues

o

Capillaries – smallest vessels, complex network with extensive
branching, exchange between blood and tissues

o

Veins – capillaries converge to larger channels, get larger as they
approach the heart, transport blood from tissues to the heart

o

Blood - liquid composed mainly of plasma, also erythrocytes that carry
oxygen, immune cells, dissolved nutrients, hormones etc
...
1mm diameter (muscular and elastic arteries,
larger arterioles, muscular veins)



Microvasculature – arterioles, capillaries, and post-capillary venules; seen only
with microscope

The heart


The heart is a muscular organ that contracts rhythmically to transport blood
through the circulatory system
o

Four chambers; 2 atria and 2 ventricles

o

Right and left atria receive blood from the body and pulmonary veins
respectively; pump blood into the ventricles

o

Right and left ventricles pump blood into the lungs or rest of the body
respectively

o


Atria are separated from the ventricles by atrio-ventricular valves

Histology of the heart
o

Endocardium: single layer of squamous epithelial cells on a thin layer
of loose connective tissue (elastic, collagen and smooth muscle)

o

Subendocardial layer: connective tissue layer (contains veins, nerves
and branches of impulse conducting system) that connects
endocardium to myocardium

o

Myocardium: thickest tunic, contains layers of cardiac muscle cells;
thicker in the ventricles vs
...
blogspot
...
uk/2012_06_01_archive
...
g
...
g
...


Tunica media

Very thick
...
Contains:


External elastic lamina

Smooth muscle especially in



Smooth muscle

muscular arteries





Collagen fibres

Elastic fibres mainly in elastic arteries

Present in elastic arteries

None

Tunica externa

Very thin

Relatively thick

Diameter

Small lumen

Larger lumen

Vasculature


The vasculature is a tube like system that carries blood supplying the whole
body with oxygen and nutrients and removes waste products

Large elastic arteries


Often the large arteries emanating from the heart e
...
aorta and pulmonary
artery



Thicker intima than a muscular artery; media has elastic fibers and lamellae;
adventitia is relatively underdeveloped



Elasticity allows them to extend during systole (ventricles pumping) and
contract during diastole (ventricles filling), keeping blood pressure relatively
constant



Arterial blood pressure and velocity decrease and become less variable
further away from the heart

Medical application
Arterial degenerative alterations








Arteries undergo changes during ageing
Atherosclerotic lesions are focal thickening of the intima, with proliferation
of smooth muscle cells and connective tissue, with deposition of
cholesterol in smooth muscle cells and macrophages
Macrophages loaded with lipids are known as foam cells – form visible
fatty streaks of atherosclerosis
Obstruction of blood supply in smaller vessels can lead to necrosis of tissue
– can cause infarcts where low oxygen supply to certain organs e
...
heart,
kidneys
o In the skin, arteries anastomise so blockage doesn’t stop supply
Weakening of the artery by embryonic defect, disease or lesion, may get
excessive dilation of the artery – aneurysm
o Rupture of an aneurysm can be fatal

Muscular arteries


Common in arteries that supply organs and the peripheries; control blood
flow by contraction and relaxation of tunica media



Extensive musculature in the media (up to 40 layers of muscle cells) allows
the blood flow in this area to be tightly regulated by the ANS



External elastic lamina in larger arteries



Lymphatic vessels, vaso vasorum in the adventitia which may penetrate into
the media

Arterial sensory structures


Carotid sinuses are dilations of the carotid arteries containing baroreceptors –
detect changes in BP
o

Tunica media is thinner in these sinuses – greater distension when BP
rises

o

Intima and adventitia innervated by sensory nerve fibres from cranial
nerve 9 (glossopharyngeal nerve)

o


Similar ones in aortic arch

Carotid bodies are small, ganglia-like structures near bifurcation of common
carotid into internal and external carotid
o

Contain chemoreceptors sensitive to O2 and CO2 and H+

o

Network of sinusoidal capillaries and glomus cells containing
dopamine, serotonin, adrenaline

o

Glomus cells synapsed by glossopharyngeal nerve

o

Aortic bodies in aortic arch are similar

Arterioles and metarterioles


Smallest arteries branch into arterioles



Made up of 1-2 layers of muscles cells; marks the beginning of the
microvasculature where exchange between blood and tissue fluid occurs



Due to their small diameter, arterioles account for approx
...
g
...
g
...
org, Capillary, available athttps://en
...
org/wiki/Capillary

Venules


Capillaries flow into post-capillary venules which are similar in structure to
capillaries but have a diameter of 15-20um
o



Site at which WBCs leave circulation in infection/damage

Post-capillary venules converge into collecting venules that have more
muscle cells in their tunica media



Greater sized venules have more defined media – muscular venules



All venules have large lumen versus wall size

Medical application



Venules are the loosest part of the vasculature
This allows leukocytes to access sites of inflammation
...
g
...
Another
example is the hypothylamic-hypophyseal portal system in the brain



Arteriovenous anastomosis – an anastemosis is a connection between 2
vessels
o

In some cases e
...
in skin for temperature control, the blood can
bypass the capillary bed and flow straight from the arteriole into the
vein; this is arteriovenous anastomosis



True capillaries branch off from metarterioles
...
This relaxes cyclically 510 times a minute to allow blood into capillary bed

Taken from Junqueira’s Basic Histology: text and Atlas, Twelfth Edition

Lymphatic vascular system


In addition to blood vasculature the body has a system which gathers
interstitial fluid and is a major distributor of lymphocytes, antibodies and other
immune components



This system is made up of lymph and lymph vessels



Lymph
o

Excess interstitial fluid collected from tissue spaces and returned to the
blood

o

Does not contain red blood cells (although lymphocytes may be
present) and is rich in proteins



Lymphatic vessels (lymphatics)
o

Lymph fluid is carried in the lymph vessels

o

Lymph capillaries are closed ended vessels consisting of a single layer
of very thin endothelial cells on an incomplete basal lamina

o

The opening between cells allow for drainage of interstitial fluid, and
the folds in the cells prevent backflow

o

These openings are held open by anchoring filaments that bind the
vessels to the surrounding connective tissue

o

Capillaries converge to lymphatic vessels which resemble veins in
structure

o

Contraction of smooth muscle, alongside valves, allows for a
unidirectional flow of lymph

o

The lymphatic vessels converge into two trunks, the thoracic duct and
right lymphatic duct, and both empty lymph back into the blood

o

The thoracic enters the CV system near the junction of the left jugular
and subclavian vein, and the lymphatic between the confluence of
the right jugular and subclavian vein

o

The structure of these ducts is similar to a large vein with reinforced
smooth muscle

Taken from 123RF
...
123rf
...
html



Lymph nodes
o

Small oval structures arranged in groups or chains along lymphatic
vessels throughout the body

o

Lymph nodes help to remove and filter possible harmful substances

Taken from The Lymph Guy, The Lymphatic System, available
athttp://thelymphguy
...
Mescher, Junqueira’s Basic Histology: Text and Atlass
...




---