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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.


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.


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

Card 5 / 12: For whom would an appreciation of the structural characteristics of the human heart come more easily: an alien who lands on Earth, abducts a human, and dissects his heart, or an anatomy and physiology student performing a dissection of the heart on her very first day of class? Why?
Gelowe Reply
what are regular shaped cells with granules in the cytoplasam
Kabita Reply
I need sylubuss of clinical officers book
Omary Reply
cholesterol normal value is
less than 200mg/dl
100 to159mg/dL
Early this wk. I had some "A & P" questions & answers unfortunately didn't save them, Is there any way I can have them back ,so as 2 save them?. Thnx.
what are the functions of the female reproductive system
Lister Reply
it produces the female egg necessary for reproduction, called the Ova or Oocytes. The system is designed to transport the Ova to the site of fertilization.
Female reproductive system was mainly functioned to produce ova(ovum) (female eggs) Into which will be fertilized by male gamete to produce zygote
absolutely right
wa qalad nimco rage iska hubi
waxwalba ka fikirbay ubaahantahay
ha wayo jawabtoda wa qabyo nimco wey ku raacdat
ha wayo jawabtoda wa qabyo nimco wey ku raacday
wxayaabaha qaarkood waaa in aan u feejignaano
asc if I try female reproductive system has two function the first is to produce egg cell and the second is to protact and nourish the offspring until birth
what is stercobilinogen
Hancerich Reply
fecal urobilinogen. Created by bacteria in the gut. a chemical that gives feces brown color.
next question pls.
The rate of diffusion increases if the
What's the answer?
it's a breaking down of haemoglobin and it's a chemical made by bacteria
Thnx Dev Raj.
yup so any more
yes I sure do need more "Questions" & "Answers". I'm learning whole lot. Thnx.
what is the greatest muscle of the body
Lungu Reply
gluteus maximus
pls!!! more "A&P" questions & answers. Thnx.
Gluteus maximus
Describe anatomy of cardiovascular system?
cardiovascular system is a group of organs coming together to perform the circulation of blood. The organs invoked are the heart and the blood vessels with blood being the tissue. The heart is a pump and it pumps oxygenated blood through the systemic circuit and deoxygenated blood through the pulmon
pulmonary circuit.
more A&P questions pls. Thnx.
If an ANOVA yields a significant F value, you could rely on ________ to test significant differences between group means.
Dane Reply
what's ANOVA
analysis of variance
plz what you mean with "ANOVA" first
anova means analysis of variance, a statistical method in which the variation in a set of observations is divided into distinct components.
M value ot test
What does it mean by M value ot test?
formation of red blood cells
Biketi Reply
explain why... lower back pain in ovarian cancer
Srijoni Reply
we says that protoplasm is the living part of us How?
Muzamil Reply
is the leaving part of our cellular structure.
it is the leaving part of our blood cellular structure also
what is receptor?
Preity Reply
an organ or cell able to respond to light, heat, or other external stimulus and transmit a signal to a sensory nerve.
Has anyone taken the first exam?
hey what is the process after your food is swallowed? how long does it take to get to the stomache until it is released as waste?
Fednise Reply
that is such a broad question. as you begin to swallow its various doses down the alimentary canal that brings the food into your stomach.then depending on whether it's a protein carbohydrate fat that dictates what function takes place in your stomach. these are all steps of digestion.
typo sorry it's peristalsis , wave-like projections that push food down your alimentary canal etc. digestion starts in your mouth ends in your large intestines (colon anus)
some of the many processes of digestion include hydrolysis dehydration synthesis denaturation of proteins etc. you have to be more specific.
there's many different contributing factors the how long it takes food to convert into waste. remember fats, triglycerides proteins and carbohydrates all breakdown two different monomers and structures. you should be looking up metabolic processes.
depending how much fiber you have in your diet dictates how much water is brought to your intestines that has to do with excretion whether fiber is insoluble or soluble. this is an anatomy and physiology app. to simply say the stomach will empty its contents in 2 to 3 hours would do you a disservice
can the study of anatomy relate to medical technologies
Lean Reply
how can I understand micro biology and anatomy better.
someone to help me understand glycogeneogenesis
what are the major branches of the aorta?
look youtube video

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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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