Blood &
Circulatory System
The main functions of blood are to
transport oxygen, carbon dioxide, water, nutrients, hormones and waste around
the body. Blood also fights infection and regulates temperature.
Composition of blood:
1. Plasma constitutes for about 54% of
our blood. 92% of it is water.
2. White blood cells and platelets
constitute for about 1% of our blood.
3. Red blood cells constitute for about
45% of our blood.
Red blood cells have a biconcave shape and are involved in the transportation of
oxygen by haemoglobin (haem=iron-containing), they are made in
the bone marrow, they have no nucleus, they last for approximately 120 days and are
then broken down into pigments calledbilirubin and biliverdin in the liver.(N.B. oxyhaemoglobin =oxygen rich haemoglobin,
deoxyhaemoglobin=low oxygen haemoglobin)
White blood cells are divided into 2 types: monocytes are involved in recognising anything that is foreign and ingesting
the foreign particle byphagocytosis whereas lymphocytes are involved in the production of antibodies
which inactivate and immobilise pathogens. White blood cells have nuclei and are also made in the bone marrow.
Platelets are small fragments without nuclei and last just 7 days. They are essential in
clotting blood.
Blood groups consist of A, B, AB and O groups. People in the AB blood group are known as universal recipients
because they can receive blood from any group. People in the O group are known
as universal donors because they can give blood to anybody, although the most
common blood group they can only receive blood from their own group.
Deep vein thrombosis(DVT) are swollen areas caused by unwanted clotting in veins due to a
lack of movement on long journeys’.(flight socks may prevent DVT)
Circulatory
System
Open circulatory systems allow the
blood flow out of the vessels before returning to the heart via ostia. (no
veins involved)E.g. insects
• Closed circulatory systems don’t
allow the blood to leave the blood vessels E.g. humans advantages include
faster and controlled delivery of oxygen and nutrients which allow for longer
periods of activity.
• Arteries are blood vessels that carry
blood away from the heart in powerful pulses. They have thick walls small
lumens and no valves.
• Endothelium is the innermost layer of
blood vessels that consists of just a single layer of cells.
• Veins are blood vessels that carry
blood to the heart in an even flow. They have thin walls large lumens and
valves.
• Capillaries are tiny blood vessels
with walls just one cell thick, they carry blood from arterioles to venules
through tissues releasing nutrients and removing wastes.
• The human circulatory system consists
of two circuits systemic and pulmonary.
• The coronary artery carries blood to
the heart muscle from the aorta. (coronary vein )
• The hepatic artery carries blood to
the liver. (hepatic vein)
• The renal arteries carry blood to the
kidneys. (renal veins)
• The mesenteric arteries carry blood to
the small and large intestines.
• The carotid arteries supply blood to
the head. (jugular veins)
• The subclavian arteries supply blood
to the arms. (subclavian veins)
• The iliac arteries carry blood to the
legs. (iliac veins)
• A portal system is a network of
capillaries in one organ or tissue joined to another network of capillaries in
another organ or tissue via a vein or veins.
• A pulse is the alternate contraction
and relaxation of an artery as blood passes through it.
• Blood pressure is the force blood
exerts on the walls of blood vessels.
• A sphygmomanometer is used for
measuring blood pressure(normally 120/80 mmHg)
• Atherosclerosis is the hardening of
artery walls due to a build-up of fatty deposits.
• Smoking causes heart rate and blood
pressure to increase. Diet high in saturated fats increase blood pressure and
atherosclerosis. Exercise helps lower blood pressure.
Lymphatic
System
The lymphatic system returns
extracellular fluid(ECF) or interstitial fluid caused by plasma leaking from
capillaries to the bloodstream.
Lymph is a clear liquid that is
collected around cells and is transported by the lymphatic system back to the
bloodstream. o Lymph vessels are narrow, dead ending tubes that transport lymph
and are present in every tissue and organ throughout the body.
Lymph nodes are small spherical-shaped
organs of the lymphatic system that contain many white blood cells. o Functions
of the lymphatic system:
1. Filters lymph white blood cells in lymph nodes remove bacteria and
viruses.
2. Absorb fat from small intestine lymph vessels throughout the wall
of the digestive system absorb lipids.
3. Maturation of certain white blood cells lymphocytes mature and
become fully active in the thymus.
4. Fighting infection white blood cells produce antibodies to kill
bacteria and viruses.
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