Blood & Circulatory System

 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.