In this report there will be an explanation of the
role of blood, blood vessels and how the blood is responsible for transporting
nutrients and waste products around the body. An explanation of what arteries,
veins and capillaries roles are in the circulatory system will be provided.

Structure of Blood

Humans male and female have roughly on average 5
litres (9pints) of blood pumping around their body at all times (Aviva, 2017).  This means that blood weighs around 8% of an
adult’s body weight and it also has a mean temperature of 38 degrees Celsius.
It also has a pH of 7.35-7.45 which means it is closer to being alkali (a pH less
than 7 is reflected as acidic) (myVMC. June, 2017). Blood has many components
that help it function properly, these components are: plasma, cellular
elements, red blood cells, white blood cells and platelets. The plasma in blood
is the liquid like portion, it’s a main role is to act as the transport
highway. This highway will be responsible transporting nutrients to the
different organs around the body and it will also transport the waste from
these organs which is created in cellular metabolism to the lungs, kidneys and
liver for excretion. Plasma also has an impact on heat around the body and it
helps distribute heat throughout the body, it also is the transport system for
blood cells and plays an important role in maintaining normal blood pressure
(Yawn, D. November, 2017). Plasma is a watery fluid that contrains dissolved
oxygen, carbon dioxide, glucose, fatty acids, salt, amino acids, hormones and
plasma proteins. Platelets are not classified as cells themselves however they
are small fragments of bone morrow cells. They help to form temporary platelet
plugs that stop bleeding, create blood clots by secreting procoagulants,
dissolve blood clots when they are no longer needed, digest and destroy
bacteria and help maintain the linings of blood vessels (myVMC. June, 2017). Inside
the stream of blood alongside plasma and platelets you can find white blood
cells, these cells help defend against diseases. White blood cells are also
known as leukocytes and lack haemoglobin. They defend the body from harmful
diseases and infections by ingesting the foreign materials and destroy them or
produce antibodies (Rogers, K. February, 2017). Red blood cells are also inside
the stream of blood that flows around the body. Red blood cells are also called
erythrocyte; they are partly responsible for the colour of blood. Their role is
too transport oxygen from the lungs to the tissues around the body. Once a
human red blood cell is mature it will be a very tiny round cell with a
biconcave centre, it will this small and flexible so it can fit through
extremely small blood vessels.  It is
covered with a membrane made up of lipids and proteins. It does not have a
nucleus however it does contain haemoglobin; a red, iron-rich protein that
binds oxygen.

Structure of Red Blood Cells

The structure of a red blood cell helps it perform
its role of transporting oxygen from lungs to all the body tissues and carbon
dioxide the waste product of metabolism back to the lungs; where it can be
excreted. The red blood cell is efficient because it lacks a nucleus, this
means that its own metabolism is very low, thus most oxygen can be transported
to the tissues. The biconcave shape of the cell allows oxygen exchange at a
constant rate over the largest surface area (Rogers, K. May, 2015). On the
inner surface there are two proteins called spectrin and actin that give the
membrane resilience and durability. This means that the red blood cell can stretch,
bend and fold as it squeezes through the small blood vessels and then after
return to its
original shape as it passes though larger vessels (myVMC. June, 2017).


Structure of Blood Vessel(s)

Blood vessels have a key role in keeping a person
alive, they are responsible for blood circulation. The arteries help take blood
away from the heart and they have small branches called arterioles. There are also
very small branches that will collect the blood from the different organs and
they are called venules, and they come together and form veins, which return
the blood to the heart. Capillaries are very thin-walled vessels that connect
the arterioles and venules; there is an exchange of oxygen, carbon dioxide, nutrients
and waste at the site of the capillaries between the blood and the body










blood vessel has a thin layer of cells known as the endothelium on its inner
surface. This endothelium is disconnected from the tough external layers of the
blood vessel by the basal lamina, this is an extracellular matrix produced by
surrounding epithelial cells. The role of the endothelium is to control the
passage of substances like nutrients and waste products to and from the blood.
Arteries and veins consist of three layers while the smaller capillaries only
have a singular layer. The inner layer is called the tunica intima, the
surrounding layer is called the tunica media and the outmost layer is the
tunica externa also known as the tunica adventitia this layer is surrounded by
an external elastic lamina which functions to attach itself to the surrounding

Function of a Blood Vessel

The main function of a blood vessel is to carry
nutrients such as oxygen throughout the body so that the tissues have nutrients
to use. They then return the waste product for example carbon dioxide back to
the lungs so it can be excreted. It does this by carrying blood, containing
nutrients or waste product, through hollow blood vessels around the body in the
circulatory system.

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