cardiovascular

arterial vessels
distribute blood to the tissues

capillaries perfuse the tissue and exchange gases, metabolites, and waste products

venous vessels to return blood to the heart

All vessels, including the heart, are lined by endothelium, a simple squamous epithelium (type of epithelium?)

Capillaries, the tiniest vessels, are basically tubes of endothelial cells

larger vessels have
additional layers or “tunics” of muscle and connective tissue (CT).

1. Tunica intima
2. Tunica Media
3. Tunic adventitia

Simple squamous endothelial lining, basal lamina, and CT

Longitudinally in direction of blood flow

Circularly arranged smooth muscle

In the tunica media, arteries have abundant elastic fibers

Connective tissue layer

Vasa vasorum

Nerves in the adventitia

Smooth muscle

The heart is a four-chambered muscular pump with two atria and two ventricles

A connective tissue framework

1. Endocardium
2. Myocardium
3. Epicardiium

1. Inner lining of endothelium
2. Basal lamina
3. CT

Purkinje fibers are in the subendocardial connective tissue

Cardiac muscle

Thickness and fiber orientation in the myocardium varies, thickest in ventricles

1. Loose CT with adipose
2. Vessels
3. Nerves
4. Mesothelium (simple squamous)

The coronary artery is formed from the epicardium

Pericardium, a fluid filled sac that cushions and lubricates the outer
wall of the heart, reducing friction during beating

Epicardium (viseral pericardium) lined my mesothelium

Parietal pericardium lined by mesothelium

The simple squamous mesothelium produces the pericardial fluid.

Dense connective tissue

1. Separates the atria from ventricles
2. Anchors cardiac fibers
3. Forms supportive rings at base of valves

Heart valves are flaps of connective tissue (collagen and elastic) covered by endothelium.

Cardiac conducting system initiates and coordinates the rhythmic contraction of the heart

1. Sinoatrial (SA)
2. Atrioventicular (AV)
3. Atrioventricular bundle (of HIS)
4. Purkinje fibers

Purkinje fibers, located in the subendocardial CT, can be distinguished from typical cardiac muscle
cells by their greater diameter, large clear spaces, and sparse myofibrils

Purkinje fibers contain empty space histologically beause they have glycogen

Purkinje fibers spread their excitation via gap junctions.

ENDOTHELIUM, a simple squamous epithelium, lines ALL vessels

1. Selective permeability barrier, allowing solute exchange
2. Is an anti-thrombogenic surface
3. Modulates blood flow by secreting nitric oxide and endothelin
4. Helps move WBC to connective tissue
5. Secretes growth factor

The arterial system transports blood at high pressure away from the heart and distribute blood to all the parts of the body and controls of the flow of blood into capillaries

Arteries have thick walls with
the tunica media being the thickest of the 3 layers

Elastic fibers, produced by smooth muscle cells,
is prevalent in arteries

1. Elastic arteries
2. Muscular arteries
3. Arterioles

Endothelium and CT

Elastic lamellae or fenestrated sheets with circular smooth muscle

CT with abundant blood vessels and nerves

Endothelium, small amount of connective tissues, INTERNAL ELASTIC MEMBRANE

Endothelium

ONLY 1-2 layers of smooth muscle

Connective tissue

Blood pressure

The control the flow of blood into the capillary bed is done by by contracting or relaxing smooth muscle in the tunica media of arterioles

Arterioes

1. Single layer of endothelial cells
2. Basal lamina

Most capillaries
have a lumen around the size of a single red blood cell

Undifferentiated mesenchymal stem cells that wrap around capillaries and post postcapillary venules, sharing a basal lamina

1. Provide vascular support
2. Can make endothelial, smooth muscle, and mesenchyme derived cells
3. They are contractile

1. Continuous
2. Fenestrated
3. Discontinuous

Endothelial cells are attached by tight junctions (zonula occludens) and have a continuous or
complete basal lamina

muscle, connective tissue, skin, lungs, and CNS (blood brain barrier)

Endothelial cells have small pores or fenestrations that allow passage of certain size
substances, like hormones. A continuous basal lamina is present.

Endocrine glands, kidney, and intestines

Endothelial cells have large gaps between adjacent endothelial cells, fenestrations, and a
sparse, discontinuous, or incomplete basal lamina

Larger

Irregular shape

Bone marrow, liver, spleen, anterior pituitary, adrenal cortex

Terminal arterioles control flow of blood into the capillary bed by contraction of its smooth muscle by
changes the lumen size.

The terminal arteriole therefore acts as precapillary sphincter

After exchange of gases and materials in the capillaries, the blood flows into postcapillary venules.

Ateriole to venule bypassing capillary bed

Two capillary beds with a connecting or portal vessel in between

Liver and pituitary

Kidney

The venous system is a low-pressure system that collects blood from capillaries and returns it to
the heart.

Compared to accompanying arteries, veins have a thinner wall with loosely arranged
smooth muscle, larger and often collapsed lumen, and poorly defined tunics

Valves are present in veins.

The adventitia is the
largest layer in veins while the tunica media is the largest in arteries.

Venules, veins, and large veins

Postcapillary venules are the first and smallest venules, immediately adjacent to capillaries

1. Endothelial lining
2. Basal lamina
3. Connective tissue
4. Pericytes

Comparied to a capillary, a vein has a larger lumen

Postcapillary venules are the primary site where white blood cells leave the blood and enter
tissues at sites of infection and tissue damage.

Lymphocytes exit blood and enter the lymphatic system through high
endothelial venules (HEV), which are a special type of postcapillary venule

Blood enters veins under low pressure and moves towards the heart by contraction of smooth
muscle in the vessel wall and by external compressions from surrounding tissue.

Veins have a thin layer of tunica media with small bundles of smooth muscle cells mixed with
connective tissue. The adventitia is thicker than the media.

Veins, especially of the limbs, have valves to prevent backflow of blood.

Valves are folds of the tunica intima projecting across the lumen. They are covered by
endothelium and have a core of connective tissue rich in elastic fibers.

Large veins, like the vena cava, have a well-developed intima but only a thin media with
scattered circularly arranged smooth muscle.

Longitudinally arranged bundes of smooth muscle in the tunica adventitia

The wall of large veins is thinner than that of elastic arteries

In addition to blood vessels, there is a system of thin-walled vessels, the lymphatic vessels, that
collects excess fluid from interstitial spaces

The lymph fluid is filtered and emptied into the venous
system near the heart

Lymphatic vessels are not present in the CNS and cartilage.

1. Blind-ended vessels
2. One laye of overlapping epithelium
3. Incomplete or absent basal lamina

Interittial fluid flow in when pressure is high

No

Compared to a vein, a lymphatic vessel has a
larger lumen and a thin wall with few endothelial cell nuclei visible

Lympathic vessels have valves to keep fluid moving in one direction.

Only the largest lymphatic vessels like those next to lymph nodes have
smooth muscle in its wall

Lymphocytes are often present in lymphatic vessels because they utilize
the vessels to travel between lymphoid organ

Will not contain RBC or WBC

vasculogenesis and angiogenesis

Blood vessels form de novo, in blood islands

1. Blood islands form from mesenchyeme cells in mesoderms
2. The cells in the center give rise to primitive blood cells
3. Cells differenitae into angioblasts that give rise to endothelial cells
4. Ajacent vessels fuse

New blood vessels by growth from exisiting vessels

Angiogenesis

By recruitment of endothelial precursor cells from bone marrow

Hardening of arteries due to thickening of vessel wall. Lumen is narrowed and elasciticty is lost

1. Atherosclerosis
2. Ateriolosclerosis

Atherosclerosis – hardening of large arteries caused by growth of intimal lesions called
atherosclerotic plaques or atheroma

The plaques can cause occulsions leading to ischemia or cause blot clots

Atherosclerosis is the underlying cause of most coronary, cerebral, and peripheral vascular disease. Common arteries that develop plaques include elastic arteries
and larger muscular arteries

Atherosclerosis is a large vessel disease, Arteriolosclerosis is a small vessel disease

Arteriolosclerosis- thickening of wall of arterioles or small arteries

1. Hyaline anteriorlosclerosis
2. Hyperplastic anteriorlosclerosis

-Glassy, pink homogeneous staining due to plasma proteins leaking
-Benign hypertension and diabetes

-Concentric lamellated smooth muscle in the wall resembles an “onion” skin.
-Malignant hypertension

Localized weakening of a segment of a vessel wall leading to a dilation or bulging
outward of the vessel.

Atherosclerosis and hypertension

A tear in the intima allows blood (at high pressure) to enter the wall and
separate or “dissect” the media into layers.

MARFANS syndrome or aquired factors (hypertension, atherosclerosis, diabetes)

1. Thrombosis
2. Inadequate venous drainage

-The legs

Varicose veins – abnormally dilated torturous superficial veins produced by prolonged increase
in intraluminal pressure.

Deep vein thrombosis (DVT) – is a thrombus (blood clot) that forms in a major vein, usually in
the legs. The thrombus can restrict the return of blood to the heart and result in pain and
swelling as blood gathers behind the clot.

Deep vein thrombosis is especially dangerous because it can result in a pulmonary embolism.
This occurs when the clot detaches from the vein, travels through the heart to the lungs, and
wedges in a pulmonary vessel

Slow moving blood increases the probability of thrombus formation

IVC Filters can be placed in the inferior vena cava to “catch” any clots and prevent them from
causing a pulmonary