Circulatory system

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

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- Circulatory system
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.

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Scanning electron micrograph of human red blood cells (ca. 6–8 μm in diameter)

Red blood cell

Scanning electron micrograph of human red blood cells (ca. 6–8 μm in diameter)
There is an immense size variation in vertebrate red blood cells, as well as a correlation between cell and nucleus size. Mammalian red blood cells, which do not contain nuclei, are considerably smaller than those of most other vertebrates.
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Typical mammalian red blood cells: (a) seen from surface; (b) in profile, forming rouleaux; (c) rendered spherical by water; (d) rendered crenate (shrunken and spiky) by salt. (c) and (d) do not normally occur in the body. The last two shapes are due to water being transported into, and out of, the cells, by osmosis.
Scanning electron micrograph of blood cells. From left to right: human red blood cell, thrombocyte (platelet), leukocyte.
Two drops of blood are shown with a bright red oxygenated drop on the left and a deoxygenated drop on the right.
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.
The most common red blood cell membrane lipids, schematically disposed as they are distributed on the bilayer. Relative abundances are not at scale.
Red blood cell membrane proteins separated by SDS-PAGE and silverstained
Red blood cell membrane major proteins
Affected by Sickle-cell disease, red blood cells alter shape and threaten to damage internal organs.
Effect of osmotic pressure on blood cells
Micrographs of the effects of osmotic pressure
Variations of red blood cell shape, overall termed poikilocytosis.

Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek erythros for "red" and kytos for "hollow vessel", with -cyte translated as "cell" in modern usage), are the most common type of blood cell and the vertebrate's principal means of delivering oxygen (O2) to the body tissues—via blood flow through the circulatory system.

Arthropod

Arthropods (, (gen.

Arthropods (, (gen.

Structure of a biramous appendage.
Alignment of anterior body segments and appendages across various arthropod taxa, based on the observations until mid 2010s. Head regions in black.
Illustration of an idealized arthropod exoskeleton.
Cicada climbing out of its exoskeleton while attached to tree
Arthropod eyes
Head of a wasp with three ocelli (center), and compound eyes at the left and right
Compsobuthus werneri female with young (white)
The nauplius larva of a penaeid shrimp
Marrella, one of the puzzling arthropods from the Burgess Shale
Kylinxia
The velvet worm (Onychophora) is closely related to arthropods
Insects and scorpions on sale in a food stall in Bangkok, Thailand

The haemocoel, an arthropod's internal cavity, through which its haemolymph – analogue of blood – circulates, accommodates its interior organs; it has an open circulatory system.

Sponge

Sponges, the members of the phylum Porifera (meaning 'pore bearer'), are a basal animal clade as a sister of the Diploblasts.

Sponges, the members of the phylum Porifera (meaning 'pore bearer'), are a basal animal clade as a sister of the Diploblasts.

Sponge biodiversity and morphotypes at the lip of a wall site in 60 ft of water. Included are the yellow tube sponge, Aplysina fistularis, the purple vase sponge, Niphates digitalis, the red encrusting sponge, Spirastrella coccinea, and the gray rope sponge, Callyspongia sp.
Cells of the protist choanoflagellate clade closely resemble sponge choanocyte cells. Beating of choanocyte flagella draws water through the sponge so that nutrients can be extracted and waste removed.
Spongia officinalis, "the kitchen sponge", is dark grey when alive.
Euplectella aspergillum, a glass sponge known as "Venus' flower basket"
The carnivorous ping-pong tree sponge, Chondrocladia lampadiglobus
The freshwater sponge Spongilla lacustris
Euplectella aspergillum is a deep ocean glass sponge; seen here at a depth of 2572 m off the coast of California
Holes made by clionaid sponge (producing the trace Entobia) after the death of a modern bivalve shell of species Mercenaria mercenaria, from North Carolina
Close-up of the sponge boring Entobia in a modern oyster valve. Note the chambers which are connected by short tunnels.
Demosponge Samus anonymus (up to 50 m), hexactinellid Scleroplegma lanterna (~100–600 m), hexactinellid Aulocalyx irregularis (~550–915 m), lithistid demosponge Neoaulaxinia persicum (~500–1,700 m)
Steps of the sponge loop pathway: (1) corals and algae release exudates as dissolved organic matter (DOM), (2) sponges take up DOM, (3) sponges release detrital particulate organic matter (POM), (4) sponge detritus (POM) is taken up by sponge-associated and free-living detritivores.
The sponge holobiont is an example of the concept of nested ecosystems. Key functions carried out by the microbiome (colored arrows) influence holobiont functioning and, through cascading effects, subsequently influence community structure and ecosystem functioning. Environmental factors act at multiple scales to alter microbiome, holobiont, community, and ecosystem scale processes. Thus, factors that alter microbiome functioning can lead to changes at the holobiont, community, or even ecosystem level and vice versa, illustrating the necessity of considering multiple scales when evaluating functioning in nested ecosystems.
Raphidonema faringdonense, a fossil sponge from the Cretaceous of England
Oxygen content of the atmosphere over the last billion years. If confirmed, the discovery of fossilized sponges dating to 890 million years ago would predate the Neoproterozoic Oxygenation Event (800-500 million years BP).
A choanoflagellate
A comb jelly
Sponges made of sponge gourd for sale alongside sponges of animal origin (Spice Bazaar at Istanbul, Turkey).
Natural sponges in Tarpon Springs, Florida
Display of natural sponges for sale on Kalymnos in Greece
Halichondria produces the eribulin precursor halichondrin B

Sponges do not have nervous, digestive or circulatory systems.

Simple diagram of the human circulatory system

Blood vessel

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.

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

Venous (darker) and arterial (brighter) blood

Blood

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.

Blood is a 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.

Human lymphatic system

Lymphatic system

Human lymphatic system
Diagram of vessels and organs in the lymphatic system
A lymph node showing afferent and efferent lymphatic vessels
Regional lymph nodes
Lymph capillaries in the tissue spaces
Nutrients in food are absorbed via intestinal vili (greatly enlarged in the picture) to blood and lymph. Long-chain fatty acids (and other lipids with similar fat solubility like some medicines) are absorbed to the lymph and move in it enveloped inside chylomicrons. They move via the thoracic duct of the lymphatic system and finally enter the blood via the left subclavian vein, thus bypassing the liver's first-pass metabolism completely.
Reed–Sternberg cells.
"Claude Galien". Lithograph by Pierre Roche Vigneron. (Paris: Lith de Gregoire et Deneux, ca. 1865)
Gabriele Falloppio
Portrait of Eustachius
Olaus Rudbeck in 1696.
Thomas Bartholin

The lymphatic system, or lymphoid system, is an organ system in vertebrates that is part of the immune system, and complementary to the circulatory system.

Blood flow diagram of the human heart. Blue components indicate de-oxygenated blood pathways and red components indicate oxygenated blood pathways.

Cardiology

Blood flow diagram of the human heart. Blue components indicate de-oxygenated blood pathways and red components indicate oxygenated blood pathways.
Tetralogy of Fallot
Blood flow through the valves
Main complications of persistent high blood pressure
Dextro-transposition of the Great Arteries

Cardiology (from Greek καρδίᾱ kardiā, "heart" and -λογία -logia, "study") is a branch of medicine that deals with disorders of the heart and the cardiovascular system.

Heart

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

The heart is a muscular organ in most animals that pumps blood through the blood vessels of the circulatory system.

The distribution of the total body water in mammals between the intracellular compartment and the extracellular compartment, which is, in turn, subdivided into interstitial fluid and smaller components, such as the blood plasma, the cerebrospinal fluid and lymph

Extracellular fluid

In cell biology, extracellular fluid (ECF) denotes all body fluid outside the cells of any multicellular organism.

In cell biology, extracellular fluid (ECF) denotes all body fluid outside the cells of any multicellular organism.

The distribution of the total body water in mammals between the intracellular compartment and the extracellular compartment, which is, in turn, subdivided into interstitial fluid and smaller components, such as the blood plasma, the cerebrospinal fluid and lymph
Cell membrane details between extracellular and intracellular fluid
Sodium-potassium pump and the diffusion between extracellular fluid and intracellular fluid
Differences in the concentrations of ions giving the membrane potential.
Formation of interstitial fluid from blood.
Diagram showing the formation of lymph from interstitial fluid (labeled here as "Tissue fluid"). The tissue fluid is entering the blind ends of lymph capillaries (shown as deep green arrows)

Extracellular fluid is the internal environment of all multicellular animals, and in those animals with a blood circulatory system, a proportion of this fluid is blood plasma.

The main veins in the human body

Vein

Veins are blood vessels in humans, and most other animals that carry blood towards the heart.

Veins are blood vessels in humans, and most other animals that carry blood towards the heart.

The main veins in the human body
Branches of inferior vena cava
Video of venous valve in action
Venous valves prevent reverse blood flow.
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

In systemic circulation oxygenated blood is pumped by the left ventricle through the arteries to the muscles and organs of the body, where its nutrients and gases are exchanged at capillaries.