Circulatory System V3

Circulatory System: Structure and Function The function of the circulatory system is to carry nutrients and wastes to and from different places in the body. The three main structures of the circulatory system are: The vessels that connect all the parts. The blood to carry dissolved nutrients and wastes. The heart to pump blood.

The Mammalian Circulatory System Mammals and other vertebrates have a closed circulatory system. In a closed circulatory system the blood stays in the blood vessels. Blood is pumped through a series of vessels. Blood moves through the parts of the circulatory system in one direction only.

Blood Circulates in 3 Cycles There are 3 major cycles or loops for blood flow. Pulmonary Circulation- the flow of blood between the heart and lungs Systemic Circulation- the route from the heart to the muscles and organs in the rest of the body Cardiac Circulation- the path taken by blood from the heart to the heart, the most common site of heart attacks.

1.Three Types of Blood Vessels The function of vessels is to direct fluid from one area to another. 1A. ARTERIES carry blood away from the heart. Most arteries carry oxygenated blood. Elastic fibres allow the artery to stretch under pressure. The thick muscle contracts to push the blood along.

1B. VEINS carry blood toward the heart 1B. VEINS carry blood toward the heart. Most veins carry deoxygenated blood. Veins have valves which stop the blood from going in the wrong direction. Broken valves cause varicose veins. When muscles surrounding the veins contract to move the body, they push the blood along the vessel.

1C. CAPILLARIES link veins with arteries 1C. CAPILLARIES link veins with arteries. All nutrients and wastes are exchanged between body cells and the blood. Nutrients go from the blood into the cells. Wastes go from the cells into the blood by diffusion.

Capillary beds are a collection of capillaries joining an arteriole to a venule. A capillary wall is only one cell thick to increase the diffusion.

2. Blood – The Transport Medium digested food red blood cells white blood cells platelets plasma carbon dioxide waste (urea) hormones oxygen BLOOD

2A. Red Blood Cells Shaped like a biconcave disc that is round and flat without a nucleus. Contain haemoglobin, a molecule specially designed to hold and carry oxygen to all the cells. A red blood cell can change shape to an amazing extent, without breaking, as it squeezes single file through the capillaries.

2B. White Blood Cells There are many different types. They all contain a big nucleus and fight infections. The two main types of white blood cells are the lymphocytes and the macrophages. Macrophages ‘eat’ and digest micro-organisms by phagocytosis. Some lymphocytes fight disease by making antibodies to destroy invaders by dissolving them.

2C. Platelets The function of platelets is to clot blood at a cut.

Types of Blood Cells

2D. Plasma About 55% of blood is a straw-coloured liquid that dissolves and carries all the non-cellular components of blood for example carbon dioxide, glucose and amino acids. It also dissolves useful substances like: carbon dioxide glucose amino acids proteins minerals vitamins hormones waste materials like urea.

3. The Heart – The Pump The heart pumps blood through the vessels. The structure and function of the heart will be covered next class.