A report on Endothelium

Diagram showing the location of endothelial cells
Endothelium lines the inner wall of vessels, shown here.
Microscopic view showing endothelium (at top) inside the heart.

Single layer of squamous endothelial cells that line the interior surface of blood vessels, and lymphatic vessels.

- Endothelium
Diagram showing the location of endothelial cells

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Simple diagram of the human circulatory system

Blood vessel

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The blood vessels are the components of the circulatory system that transport blood throughout the human body.

The blood vessels are the components of the circulatory system that transport blood throughout the human body.

Simple diagram of the human circulatory system
Transmission electron micrograph of a blood vessel displaying an erythrocyte (red blood cell, E) within its lumen, endothelial cells forming its tunica intima (inner layer), and pericytes forming its tunica adventitia (outer layer).
Diagram of blood vessel structures
Constricted blood vessel.

Capillaries consist of a single layer of endothelial cells with a supporting subendothelium consisting of a basement membrane and connective tissue.

Venous (darker) and arterial (brighter) blood

Blood

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Body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells.

Body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells.

Venous (darker) and arterial (brighter) blood
Hemoglobin, a globular protein
green = haem (or heme) groups
red & blue = protein subunits
A scanning electron microscope (SEM) image of a normal red blood cell (left), a platelet (middle), and a white blood cell (right)
Vertebrate red blood cell types, measurements in micrometers
Frog red blood cells magnified 1000 times
Turtle red blood cells magnified 1000 times
Chicken red blood cells magnified 1000 times
Human red blood cells magnified 1000 times
Circulation of blood through the human heart
Basic hemoglobin saturation curve. It is moved to the right in higher acidity (more dissolved carbon dioxide) and to the left in lower acidity (less dissolved carbon dioxide)
Capillary blood from a bleeding finger
Venous blood collected during blood donation
Jan Janský is credited with the first classification of blood into four types (A, B, AB, and O)
Human blood fractioned by centrifugation: Plasma (upper, yellow layer), buffy coat (middle, thin white layer) and erythrocyte layer (bottom, red layer) can be seen.
Blood circulation: Red = oxygenated, blue = deoxygenated
Illustration depicting formed elements of blood
Two tubes of EDTA-anticoagulated blood.

4.7 to 6.1 million (male), 4.2 to 5.4 million (female) erythrocytes: Red blood cells contain the blood's hemoglobin and distribute oxygen. Mature red blood cells lack a nucleus and organelles in mammals. The red blood cells (together with endothelial vessel cells and other cells) are also marked by glycoproteins that define the different blood types. The proportion of blood occupied by red blood cells is referred to as the hematocrit, and is normally about 45%. The combined surface area of all red blood cells of the human body would be roughly 2,000 times as great as the body's exterior surface.

Heart

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Muscular organ in most animals.

Muscular organ in most animals.

Human heart during an autopsy
Computer-generated animation of a beating human heart
The human heart is in the middle of the thorax, with its apex pointing to the left.
Heart being dissected showing right and left ventricles, from above
Frontal section showing papillary muscles attached to the tricuspid valve on the right and to the mitral valve on the left via chordae tendineae.
Layers of the heart wall, including visceral and parietal pericardium
The swirling pattern of myocardium helps the heart pump effectively
Arterial supply to the heart (red), with other areas labelled (blue).
Autonomic innervation of the heart
Development of the human heart during the first eight weeks (top) and the formation of the heart chambers (bottom). In this figure, the blue and red colors represent blood inflow and outflow (not venous and arterial blood). Initially, all venous blood flows from the tail/atria to the ventricles/head, a very different pattern from that of an adult.
Blood flow through the valves
The cardiac cycle as correlated to the ECG
The x-axis reflects time with a recording of the heart sounds. The y-axis represents pressure.
Transmission of a cardiac action potential through the heart's conduction system
Conduction system of the heart
The prepotential is due to a slow influx of sodium ions until the threshold is reached followed by a rapid depolarization and repolarization. The prepotential accounts for the membrane reaching threshold and initiates the spontaneous depolarization and contraction of the cell; there is no resting potential.
3D echocardiogram showing the mitral valve (right), tricuspid and mitral valves (top left) and aortic valve (top right).
The closure of the heart valves causes the heart sounds.
Cardiac cycle shown against ECG
Heart and its blood vessels, by Leonardo da Vinci, 15th century
Animated heart
Elize Ryd making a heart sign at a concert in 2018
The tube-like heart (green) of the mosquito Anopheles gambiae extends horizontally across the body, interlinked with the diamond-shaped wing muscles (also green) and surrounded by pericardial cells (red). Blue depicts cell nuclei.
Basic arthropod body structure – heart shown in red
The human heart viewed from the front
The human heart viewed from behind
The coronary circulation
The human heart viewed from the front and from behind
Frontal section of the human heart
An anatomical specimen of the heart
Heart illustration with circulatory system
Animated Heart 3d Model Rendered in Computer

It is continuous with the endothelium of the veins and arteries of the heart, and is joined to the myocardium with a thin layer of connective tissue.

The cardinal signs of inflammation include: pain, heat, redness, swelling, and loss of function. Some of these indicators can be seen here due to an allergic reaction.

Inflammation

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Part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molecular mediators.

Part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molecular mediators.

The cardinal signs of inflammation include: pain, heat, redness, swelling, and loss of function. Some of these indicators can be seen here due to an allergic reaction.
Micrograph showing granulation tissue. H&E stain.
Infected ingrown toenail showing the characteristic redness and swelling associated with acute inflammation
Neutrophils migrate from blood vessels to the infected tissue via chemotaxis, where they remove pathogens through phagocytosis and degranulation
Inflammation is a process by which the body's white blood cells and substances they produce protect us from infection with foreign organisms, such as bacteria and viruses. The (phagocytes) white blood cells are a nonspecific immune response, meaning that they attack any foreign bodies. However, in some diseases, like arthritis, the body's defense system the immune system triggers an inflammatory response when there are no foreign invaders to fight off. In these diseases, called autoimmune diseases, the body's normally protective immune system causes damage to its own tissues. The body responds as if normal tissues are infected or somehow abnormal.
Asthma is considered an inflammatory-mediated disorder. On the right is an inflamed airway due to asthma.
Colitis (inflammation of the colon) caused by Crohn's Disease.
Acute appendicitis
Acute dermatitis
Acute infective meningitis
Acute tonsillitis

Stasis allows leukocytes to marginate (move) along the endothelium, a process critical to their recruitment into the tissues.

Blood coagulation pathways in vivo showing the central role played by thrombin

Coagulation

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Process by which blood changes from a liquid to a gel, forming a blood clot.

Process by which blood changes from a liquid to a gel, forming a blood clot.

Blood coagulation pathways in vivo showing the central role played by thrombin
Blood coagulation pathways in vivo showing the central role played by thrombin
Basic diagram showing blood clot formation, conversion of fibrin to thrombin, and scab formation
The interaction of vWF and GP1b alpha. The GP1b receptor on the surface of platelets allows the platelet to bind to vWF, which is exposed upon damage to vasculature. The vWF A1 domain (yellow) interacts with the extracellular domain of GP1ba (blue).
The classical blood coagulation pathway
Modern coagulation pathway. Hand-drawn composite from similar drawings presented by Professor Dzung Le, MD, PhD, at UCSD Clinical Chemistry conferences on 14 and 21 October 2014. Original schema from Introduction to Hematology by Samuel I. Rapaport. 2nd edition;Lippencott:1987. Dr Le added the factor XI portion based on a paper from about year 2000. Dr. Le's similar drawings presented the development of this cascade over 6 frames, like a comic.
Coagulation with arrows for negative and positive feedback.
The GP1b-IX receptor complex. This protein receptor complex is found on the surface of platelets, and in conjunction with GPV allows for platelets to adhere to the site of injury. Mutations in the genes associated with the glycoprotein Ib-IX-V complex are characteristic of Bernard–Soulier syndrome
Rivaroxaban drug bound to the coagulation factor Xa. The drug prevents this protein from activating the coagulation pathway by inhibiting its enzymatic activity.

Coagulation begins almost instantly after an injury to the endothelium lining a blood vessel.

The human circulatory system (simplified). Red indicates oxygenated blood carried in arteries. Blue indicates deoxygenated blood carried in veins. Capillaries join the arteries and veins.

Circulatory system

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System of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate.

System of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate.

The human circulatory system (simplified). Red indicates oxygenated blood carried in arteries. Blue indicates deoxygenated blood carried in veins. Capillaries join the arteries and veins.
Blood flow in the pulmonary and systemic circulations showing capillary networks in the torso sections
Diagram of the human heart viewed from the front
The pulmonary circulation as it passes from the heart. Showing both the pulmonary and bronchial arteries.
Capillary bed
Diagram of capillary network joining the arterial system with the venous system.
Depiction of the heart, major veins and arteries constructed from body scans
Animation of a typical human red blood cell cycle in the circulatory system. This animation occurs at a faster rate (~20 seconds of the average 60-second cycle) and shows the red blood cell deforming as it enters capillaries, as well as the bars changing color as the cell alternates in states of oxygenation along the circulatory system.
Magnetic resonance angiography of aberrant subclavian artery
The open circulatory system of the grasshopper – made up of a heart, vessels and hemolymph. The hemolymph is pumped through the heart, into the aorta, dispersed into the head and throughout the hemocoel, then back through the ostia in the heart and the process repeated.
Flatworms, such as this Pseudoceros bifurcus, lack specialized circulatory organs.
Two-chambered heart of a fish
Human anatomical chart of blood vessels, with heart, lungs, liver and kidneys included. Other organs are numbered and arranged around it. Before cutting out the figures on this page, Vesalius suggests that readers glue the page onto parchment and gives instructions on how to assemble the pieces and paste the multilayered figure onto a base "muscle man" illustration. "Epitome", fol.14a. HMD Collection, WZ 240 V575dhZ 1543.
Image of veins from William Harvey's Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus, 1628
Diagram of the human heart showing blood oxygenation to the pulmonary and systemic circulation

The blood vascular system first appeared probably in an ancestor of the triploblasts over 600 million years ago, overcoming the time-distance constraints of diffusion, while endothelium evolved in an ancestral vertebrate some 540–510 million years ago.

Transmission electron microscope image of a cross-section of a capillary occupied by a red blood cell.

Capillary

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Small blood vessel from 5 to 10 micrometres in diameter.

Small blood vessel from 5 to 10 micrometres in diameter.

Transmission electron microscope image of a cross-section of a capillary occupied by a red blood cell.
Diagram of a capillary
Depiction of the three types of capillaries. The fenestrated type in the center shows small pores called fenestrations; the sinusoidal type on the right shows intercellular gaps and an incomplete basement membrane and is also known as a discontinuous capillary.
Scanning electron micrograph of a liver sinusoid with fenestrated endothelial cells. Fenestrae are approximately 100 nm in diameter.
This is an annotated diagram of the exchange between capillary and body tissue through the exchange of materials between cells and fluid
Simplified image showing blood-flow through the body, passing through capillary networks in its path.
Depiction of the filtration and reabsorption present in capillaries.

Capillaries are composed of only the tunica intima, consisting of a thin wall of simple squamous endothelial cells.

Aggregation of thrombocytes (platelets). Platelet-rich human blood plasma (left vial) is a turbid liquid. Upon addition of ADP, platelets are activated and start to aggregate, forming white flakes (right vial)

Hemostasis

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vasoconstriction

vasoconstriction

Aggregation of thrombocytes (platelets). Platelet-rich human blood plasma (left vial) is a turbid liquid. Upon addition of ADP, platelets are activated and start to aggregate, forming white flakes (right vial)

Within seconds of a blood vessel's epithelial wall being disrupted, platelets begin to adhere to the sub-endothelium surface.

Angiogenesis following vasculogenesis

Angiogenesis

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Physiological process through which new blood vessels form from pre-existing vessels, formed in the earlier stage of vasculogenesis.

Physiological process through which new blood vessels form from pre-existing vessels, formed in the earlier stage of vasculogenesis.

Angiogenesis following vasculogenesis
3D medical animation still showing angiogenesis
Without angiogenesis a tumor cannot grow beyond a limited size

Vasculogenesis is the embryonic formation of endothelial cells from mesoderm cell precursors, and from neovascularization, although discussions are not always precise (especially in older texts).

Lymph capillaries in the tissue spaces.

Lymphatic vessel

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The lymphatic vessels (or lymph vessels or lymphatics) are thin-walled vessels (tubes), structured like blood vessels, that carry lymph.

The lymphatic vessels (or lymph vessels or lymphatics) are thin-walled vessels (tubes), structured like blood vessels, that carry lymph.

Lymph capillaries in the tissue spaces.
A still image from a 3D medical animation showing afferent vessels
Propulsion of lymph through lymph vessel
Lymphatic system
Section across portal canal of pig. X 250.

Lymph vessels are lined by endothelial cells, and have a thin layer of smooth muscle, and adventitia that binds the lymph vessels to the surrounding tissue.