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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

what is the difference between cardiovascular and respiratory system
Bokenana Reply
cardiovascular deals with blood,blood vessels and heart while respiratory system deal with gas exchange
Erick
send me your app line
Erick
just make a class group and have online classes take turns in teaching
maz
send yo app lines so I make a group
Erick
ok
Erick
you're simply saying no to teaching one another
maz
what's an epithelial tissue
Romantic Reply
epithelial tissue are thin tissues that covers all the exposed surfaces of the body
Ireen
is anyone from high school?
Sahil
yes
Sulaiman
Final year
Royleen
med student
brian
South Africa
brian
final year too
brian
INDIA
Sahil
describe the structure of the human body in terms of six levels of organisation
Chulufya Reply
list the muscles of abdomen and their functions
HANNAH Reply
list the neck muscles and their functions
HANNAH
list the thy muscles and their functions
HANNAH
four muscles in facial expression
nah
describe flow of blood
osoma Reply
are arteries do pumping action to get are blood flow
isaiah
causes of occasional female muscle weakness and body pain
sammy
hey Venus ulcers description
patrick
what is conduction in the heart occur
Daud Reply
what is anatomy
Prin Reply
anatomy is the study of human body.?
Sittie
anatomy is the study of scientific human body's structure.
Sittie
Anatomy is the study of the structure of the human body and the physical relationship between its constituent parts.
Maina
Anatomy is the study of the structures of body parts
Nepi
what are the principles of public health nursing?
tribel
Anatomy is the scientific study of human body parts .
Shakinah
Anatomy is the study of structure and relationship of the body structure
Stephen
Anatomy is the study of the structure and movement of the human body
renukha
energy generation molecular transport reproduction.
Sarah
Anatomy is the study of budy structures and their relationship.
Denis
is haemoglobin considered as body fluid?
Bonnie Reply
yes
Musi
yes
Given
No
Stephen
Given plz support yo answer
Bonnie
no
Stephen
it's a pigment found on blood
Stephen
Haemoglobin is a protein found in RBCs. Seeing as it is a protein (solid) it isn't a fluid.
jason
circulation of blood through the left side of the heart
Dorothy Reply
explain features of epithelial tissue
Ghati Reply
describe with the help of a well level diagram the structure of a nephron's
Okello Reply
can't draw a diagram
Sanjith
function of animal cell
Ghati
how bones formed
Hyden Reply
Endochondral ossification involves the replacement of hyaline cartilage with bony tissue. Most of the bones of the skeleton are formed in this manner. These bones are called endochondral bones. In this process, the future bones are first formed as hyaline cartilage models.
Sanjith
function of human cell
judith Reply
what is the function of the human cell
ABIGAIL
cell is the basic structural unit of an organism ie it the basis of all the biological life
Ochiel
controls what enter and leaves d body
Jude
what causes smelling of discharge and wat hormones is responsible for that and what are the drugs to use to prevent it
Smart
It is basic structural and fundamental unit of life and help in growth, generation, and repair of our body
Deepika
structure of the ear
Pires Reply
Hi guys, can questions about kinesiology be asked here? Currently pursuing kinesiology with a specialization in pedagogy
renukha Reply

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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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