IB myp 4-5 Biology – Study notes- All Topics
Topic :Metabolism-Circulation
Topic :Metabolism– Weightage : 21 %
All Questions for Topic : Nutrition,Digestion,Biochemistry and enzymes,Movement and transport,Diffusion,Osmosis,Gas exchange,Circulation,Transpiration and Translocation,Homeostasis
The circulatory system is a vast network of organs and vessels that is responsible for the flow of blood, nutrients, hormones, oxygen and other gases to and from cells. Without the circulatory system, the body would not be able to fight disease or maintain a stable internal environment — such as proper temperature and pH — known as homeostasis.
The circulatory system is an organ system that is a fluid filed network of vessels throw which materials. move between the environment of an organism.
Types of circulatory systems:
- Open:
- Insects
- Anthropods
- Closed:
- Fish and small mammals (single)
- Humans (double)
The circulatory system transports Oxygen and Glucose into cells, and removes $\mathrm{CO}_2$ and Urea:
Humans need a transport system in order to exchange substances with their environment. Our transport system is called the circulatory system and it can access all the cells in our body.
Humans have a closed circulatory system with three basic components:
– A circulatory fluid – the blood.
– A set of tubes – the blood vessels.
– A muscular pump – the heart.
Blood- The Fluid of Life
- Red Blood Cells (transport)
- White Blood cells (immune Defense)
- Platelets (clotting)
- Plasma (medium for transport)
In multicellular organisms like humans, this medium is called extracellular fluid. It contains interstitial fluid, a liquid found in the spaces between cells. This interstitial fluid is renewed by blood, which is constantly circulating around the body providing nutrients to cells and taking away waste products.
Composition of blood
The human body contains around 5 liters of blood. Blood is a viscous fluid which flows inside the vessels of the circulatory system. It consists of different kinds of blood cells suspended in a liquid called plasma.
- Plasma makes up about 55% of our blood volume. It is a yellow liquid part of the blood in which red and white blood cells as well as platelets are suspended. 95% of it consists of water with many substances dissolved in it. Plasma has several functions:
- Transports dissolved substances e.g. Carbon dioxide, glucose, salts, urea, hormones, antibodies, plasma proteins around the body
- Brings nourishment to cells and removes waste products
- Prevents blood vessels from collapsing
There are three types of blood cell:
- Red blood cells or erythrocytes are the most abundant. They contain the oxygen carrier molecule called haemoglobin, which gives blood its red colour. Red blood cells carry oxygen from the lungs to all cells of the body; additionally they carry carbon dioxide away from cells and to the lungs. They are disc shaped and have no nucleus ( in order to have more surface area to carry more oxygen). They are also small and flexible so can pass easily through blood vessels.
- White blood cells or leukocytes are in fewer numbers than red blood cells and form part of the immune system. There are several types, but lymphocytes and phagocytes are the main ones. White blood cells are larger than red blood cells and do contain a large nucleus. Lymphocytes recognize virus or bacteria as foreign and make antibodies to attack and destroy them. Phagocytes engulf virus and bacteria by phagocytosis
- Platelets or thrombocytes. These are cell fragments which contain substances that allow blood to coagulate preventing haemorrhages. They clump together forming a plug to help your blood clot.
Functions of blood
As you have read above, blood has many different functions, others include:
- It transports nutrients and oxygen to all cells.
- It collects waste products released during cell metabolism. The main waste products are urea, uric acid and carbon dioxide.
- It transports hormones around the body, which play an essential role in controlling body functions.
- It helps regulate temperature. Blood works like a central heating system, moving body heat from the warmer areas of the body to the cooler ones.
- It plays an essential role in protecting our bodies from infections.
- It prevents blood loss when a blood vessel is broken through a series of mechanisms.
Blood vessels
- Arteries (tubes carrying oxygenated blood away from the heart)
- veins (tubes carrying deoxygenated blood back to the heart.
- Capillaries (mesh of single cell thick tubes that are the actual site of diffusion).
There are three different types of blood vessels:
Arteries: These carry blood away from the heart. This blood is under high pressure as it is being pumped along by the heart every time it beats. Arteries have thick muscular walls which contain elastic fibers that allow the artery to stretch under pressure. (Arteries divide into smaller vessels called arterioles)
Capillaries: Capillaries are very narrow thin blood vessels which branch out from arteries (from the arterioles). Capillaries carry blood to and from the body’s cells. Capillaries are the site at which exchange of oxygen, carbon dioxide and nutrients takes place. The structure of capillaries makes them very well suited for this function. As capillaries are only one cell thick and have very thin permeable walls this means that substances can diffuse out of them very easily. (Fluid leaks out of the capillaries and bathes the surrounding cells, this is called tissue fluid. Useful substances such as oxygen and food diffuse out of the blood in the capillaries into the tissue fluid where it is then taken to the cells. Waste products such as carbon dioxide diffuse from the body’s cells, into the tissue fluid and are reabsorbed back into blood in the capillaries).
Veins: Veins carry blood back to the heart. The blood returning from the body is at a much lower pressure than that being pumped from the heart. Therefore veins do not have to be as strong as arteries. Veins are wider than arteries and have much thinner walls. There are valves inside the veins which prevent blood from flowing the wrong direction. (Capillaries come together to form thicker venules. The venules then from veins). veins have values so that the blood coming back from various parts of the body does not flow back. Arteries do not have valves because the blood flow rate from the heart is already very high.
Important vessels:
- Pulmonary Artery (Heart $\rightarrow$ Lungs)
- This is deoxygenated blood (only exception for artery)
- Pulmonary vein (Lungs $\rightarrow$ Heart)
- This is oxygenated blood (only exception for vein)
- Aortic arch and trunk (main arteries from heart)
- Common carotid artery (blood to brain)
- Renal venlartery – connect to kidneys
- Mesentric vein -Connect to intestine
- Hepatic Portal vein -Blood from GI tract to liver
The heart is a pump that circulates blood all around the body. It is approximately the size of a human fist and is located just to the left of the centre of a human’s chest. On average it beats between 60-70 times a minute when you are at rest.
The heart is a hollow organ made of a special type of muscle called the cardiac muscle.
The heart is in fact a double pump. The right side of the heart is considered as one pump and the left side of the heart is the second pump. A thick wall called the septum separates the two sides.
- The right side of the heart carries deoxygenated blood to the lungs to be oxygenated.
- The left side of the heart pumps oxygenated blood to the rest of the body.
Mammals have a four-chambered heart with two atria and two ventricles.
Coordinated cycles of heart contraction drive double circulation in humans (and other mammals):
RA –> RV –> LUNGS –> LA –> LV –> Body
The heart contracts and relaxes due to electrical impulses received from the Sinoatrial node, or pacemaker found in the heart.
- When the atria contract blood is pushed through the open valves into the ventricles.
- When the ventricles contract blood from the right ventricle is pumped through the pulmonary valves and onto the lungs, blood from the left ventricle is pumped through the aortic valves and onto the rest of the body.
- Both ventricles do not contract at precisely the same time, the left ventricle contracts slightly before the right. After contraction the ventricles relax, and wait for the next electric impulse. The atria fill with blood and an impulse from the pacemaker starts the cycle over again.
Blood pressure is the amount of force exerted by the blood on the arteries. There are two types of blood pressure:
- Systolic (ventricles contraction) – Normal: $110-140$
- Diastolic (expansion of ventricles) – Normal. $70: 90$