{"id":33785,"date":"2023-11-22T11:48:45","date_gmt":"2023-11-22T10:48:45","guid":{"rendered":"http:\/\/b1be2650-54e2-4362-8519-45096818ceca"},"modified":"2023-11-22T12:36:54","modified_gmt":"2023-11-22T11:36:54","slug":"all-your-blood-questions-answered-from-why-is-it-red-to-do-all-animals-have-blood-the-answer-is-no","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcwildlife\/rss_feed\/all-your-blood-questions-answered-from-why-is-it-red-to-do-all-animals-have-blood-the-answer-is-no\/","title":{"rendered":"All your blood questions answered, from why is it red to do all animals have blood? The answer is no…"},"content":{"rendered":"

What is blood? Why is blood red? Why is it so important? Do all animals have blood? JV explains all you need to know about blood <\/p>

By JV Chamary\n <\/p>

Published: Wednesday, 22 November 2023 at 10:48 AM<\/p>

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Blood is known for transporting substances around the body. The fluid has many functions, from fighting infection to generating hydraulic force in an erect penis, but its main role is to supply oxygen and nutrients so that an animal\u2019s cells can fuel respiration and power metabolic reactions.<\/p>

Do all animals have blood?<\/strong><\/h2>

No. Many invertebrates have open circulation: instead of true blood, they use haemolymph, a fluid that empties into the body cavity and bathes cells before it reenters blood vessels. Insect haemolymph<\/a> doesn\u2019t even carry oxygen! Instead, gases move in and out of the body through air-filled tubes known as tracheae. <\/p>

This tracheal system depends on diffusion (the movement of molecules from areas of high to low concentration) for gas exchange between cells and surrounding fluid. Diffusion only works over short distances, less than 1mm, which is why insects<\/a> are small.<\/p>

All vertebrates have a closed circulatory system: blood doesn\u2019t normally leave vessels and its cargo diffuses to and from cells via a separate fluid that replaces the oxygen which cells use, and removes carbon dioxide and other waste products. This extracellular fluid is recycled back to circulation while oxygen is then replenished by breathing, via gas exchange between the air and lungs (or water and gills).<\/p>

How does blood circulate?<\/strong><\/h2>

Blood flows through a vascular system, a network of vessels such as arteries, veins and tiny capillaries. The fluid is propelled by the pressure created by squeezing the whole body, contracting vessels or pumping a dedicated organ, the heart. Octopus and other cephalopods often have multiple hearts and closed circulation, which may explain how these complex molluscs can have active lifestyles and grow so large compared to other invertebrates (one colossal squid weighed in at 495kg).<\/p>

What does blood contain?<\/strong><\/h2>

On average in vertebrates, half of the volume is plasma, a yellow liquid that\u2019s mostly water. Blood also contains three kinds of cell<\/a>: fragments of \u2018platelets\u2019 that form clots to prevent bleeding; the immune system\u2019s white blood cells; and red blood cells filled with the famous oxygen-carrying pigment haemoglobin.<\/p>

More red blood cells mean more oxygen, but more cells also means thicker blood and slower transport. So there\u2019s a trade-off and each species seems to have an optimum proportion of red cells, the \u2018haematocrit\u2019. <\/p>

The world\u2019s largest living reptile, the saltwater crocodile<\/a>, is lethargic but needs sudden bursts of speed, which is consistent with having fast-flowing blood and a haematocrit of only 19 per cent. At the other extreme, the Weddell seal stores oxygen to dive hundreds of metres for several minutes, and 63 per cent of its blood consists of red blood cells.<\/p>

Why is blood red?<\/strong><\/h2>

Blood’s red colour comes from iron at the core of the respiratory pigment, haemoglobin. Other pigments can have different metal cores. Haemocyanin contains copper so cephalopods are blue-blooded, like royalty! Though haemoglobin is packed inside red blood cells, other pigments (including haemocyanin) float freely in the plasma.<\/p>

Which animals drink blood?<\/strong><\/h2>

Sanguivory or haemoatophagy (blood eating) has evolved at least 29 times and created parasites ranging<\/a> from ticks<\/a> and tsetse flies to leeches and lampreys.<\/a> The anatomy and metabolism of sanguivores is adapted to blood-feeding: a female mosquito\u2019s mouthparts have been modified from a nectar<\/a>-sucking proboscis, while a vampire bat\u2019s saliva has anticoagulants to stop a host\u2019s blood from clotting.<\/p>