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By the end of this section, you will be able to:
  • Identify the primary functions of blood in transportation, defense, and maintenance of homeostasis
  • Name the fluid component of blood and the three major types of formed elements, and identify their relative proportions in a blood sample
  • Discuss the unique physical characteristics of blood
  • Identify the composition of blood plasma, including its most important solutes and plasma proteins

Recall that blood    is a connective tissue. Like all connective tissues, it is made up of cellular elements and an extracellular matrix. The cellular elements—referred to as the formed elements    —include red blood cells (RBCs)    , white blood cells (WBCs)    , and cell fragments called platelets    . The extracellular matrix, called plasma    , makes blood unique among connective tissues because it is fluid. This fluid, which is mostly water, perpetually suspends the formed elements and enables them to circulate throughout the body within the cardiovascular system.

Functions of blood

The primary function of blood is to deliver oxygen and nutrients to and remove wastes from body cells, but that is only the beginning of the story. The specific functions of blood also include defense, distribution of heat, and maintenance of homeostasis.

Transportation

Nutrients from the foods you eat are absorbed in the digestive tract. Most of these travel in the bloodstream directly to the liver, where they are processed and released back into the bloodstream for delivery to body cells. Oxygen from the air you breathe diffuses into the blood, which moves from the lungs to the heart, which then pumps it out to the rest of the body. Moreover, endocrine glands scattered throughout the body release their products, called hormones, into the bloodstream, which carries them to distant target cells. Blood also picks up cellular wastes and byproducts, and transports them to various organs for removal. For instance, blood moves carbon dioxide to the lungs for exhalation from the body, and various waste products are transported to the kidneys and liver for excretion from the body in the form of urine or bile.

Defense

Many types of WBCs protect the body from external threats, such as disease-causing bacteria that have entered the bloodstream in a wound. Other WBCs seek out and destroy internal threats, such as cells with mutated DNA that could multiply to become cancerous, or body cells infected with viruses.

When damage to the vessels results in bleeding, blood platelets and certain proteins dissolved in the plasma, the fluid portion of the blood, interact to block the ruptured areas of the blood vessels involved. This protects the body from further blood loss.

Maintenance of homeostasis

Recall that body temperature is regulated via a classic negative-feedback loop. If you were exercising on a warm day, your rising core body temperature would trigger several homeostatic mechanisms, including increased transport of blood from your core to your body periphery, which is typically cooler. As blood passes through the vessels of the skin, heat would be dissipated to the environment, and the blood returning to your body core would be cooler. In contrast, on a cold day, blood is diverted away from the skin to maintain a warmer body core. In extreme cases, this may result in frostbite.

Questions & Answers

explain respiratory centers
Tharshana Reply
which enzyme help in excretion of bile
Sakshi Reply
how conversion of Beta-carotiene into vitamin-A takes place
Sakshi
best reference books for anatomy pls suggest that
Sakshi
what is gross anatomy
Saroj Reply
The study of large structure of the body
Mablean
what is scrotum
Dakshit Reply
a bag of skin near the penis which contains the testicles
Mablean
hi
Sardar
its me Sardar from kpk pakistan
Sardar
Why are you on my digits
Mablean
hi
Kryme
how does it work?
Uriah Reply
I want to know the fertilization process in human
Nana Reply
Which plane divides the body into right and left parts
Kaeze
sagittal plane
Irvin
Thank you
Kaeze
Homestatic regulations usually involves a (n) _ that detects a particular stimulus, and a(n) _that respond to the stimulus by communicating with a (n) _whose activity has an effect on the same stimulus.
Kaeze
A cell is producing proteins to be transported out of that cell. They will be processed on ribosomes that are
Kaeze
what are diseases in the bood
Azoyenime Reply
Haemophilia
Aliyu
right hypochondriac rision how meain word
Ganesh Reply
Diabetes insipidus or diabetes mellitus would most likely be indicated by ________.
Ganesh
oral cavity how miean
Ganesh Reply
oral cavity how mean what
Suresh
seems to me every one is here a doctor and worse part is that even they donot know what to ask.
Muhammad
they know what to ask the problem is how to ask it.too much broken english.
George
dear George ongeche I think if they ask these kind questions and telling themselves as HCPs or medical student's .these are the basic ones go ask something more interesting .
Muhammad
what is blood red
Ahmad Reply
what is human anatomy?
Arpita Reply
tell me what is human anatomy?
Arpita
what is Openstax?
Arpita
arpita jana I think it's not the forum to ask such basic question...
Muhammad
study of structure of an object in this case human body.
Suresh
what are deferent between trasemicacid and vitamin k
Ubah Reply
This medication is used to treat heavy bleeding during your menstrual period. Tranexamic acid works by slowing the breakdown of blood clots, which helps to prevent prolonged bleeding. It belongs to a class of drugs known as antifibrinolytics
Muhammad
jj
John
In the body, vitamin K plays a major role in blood clotting. So it is used to reverse the effects of “blood thinning” medications when too much is given; to prevent clotting problems in newborns who don’t have enough vitamin K; and to treat bleeding caused by medications including salicylates, sulfo
Muhammad
Vitamin K plays a key role in helping the blood clot, preventing excessive bleeding. Unlike many other vitamins, vitamin K is not typically used as a dietary supplement. Vitamin K is actually a group of compounds. The most important of these compounds appears to be vitamin K1 and vitamin K2. Vitami
Muhammad
how much tha total vertebrea bone
Muhammad
26 vertebrea bone
Bhumi
wathe is blood function
dhena Reply
Blood, fluid that transports oxygen and nutrients to the cells and carries away carbon dioxide and other waste products. ... It is a tissue because it is a collection of similar specialized cells that serve particular functions. These cells are suspended in a liquid matrix (plasma), which makes the 
Ashiish
how tissue carries waste matrial
Nadeem
how many bone in human body?
Islam Reply
what is endocrin? plese help many people.
Islam
206
Nadeem
heart layers
Suresh
endoceime is the inner layer of heart
pandit
What is buffer?
Peer Reply
a buffer is a solution that resists a chemical change.
George
Yup it also balances the solutions
Peer

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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