- The heart, an extensive network of blood vessels and blood forms circulatory system.
- Blood is a red coloured fluid which flows in the blood vessels to every part of the body.
- An average person has 4.5 – 5.5 litres of blood.
- Blood consists of two components:
- Fluid component:
- Plasma
- Yellowish colour
- Contains 90% water
- It also contains electrolytes, proteins and carbohydrates.
- Solid Component:
- Red Blood Cells (Erythrocytes)
- Red in colour
- Haemoglobin is present
- Produced in bone marrow of bones
- Average lifespan is about 120 days
- Disc shaped
- White Blood Cells (Leucocytes)
- Colourless
- Irregular shape
- Lifespan is few hours to few years
- It fights against germs that enter our body
- Platelets (Thrombocytes)
- Colourless
- Round and tiny cells
- Formed in bone marrow
- Lifespan is about 8-14 days
- It helps in clotting of blood
- Blood Vessels:
- Blood flows through a network of tubes known as ‘blood vessels’.
- Three types of blood vessels:
- Arteries
- It carries blood from the heart to various parts of the body.
- Carries oxygen rich blood except pulmonary artery
- Thick and elastic walls
- Lies deep under our skin
- Veins
- It carries blood from all the parts of the body back to our heart
- Carries carbon dioxide rich blood except pulmonary vein
- Thin and less elastic muscular walls
- Less deeply situated than arteries
- Capillaries
- It connects arteries to veins
- Thin walls
- Useful substances like food and oxygen present in blood pass into the body cells through the capillaries.
- The throbbing sensation due to the flow of blood under pressure in your arteries is called pulse.
- The number of beats per minute is called the pulse rate.(72-80 beats per minute for a healthy person)
- Heart
- Pumps blood to all the parts of our body through the blood vessels.
- Located between lungs
- Size is roughly equal to the fist (about 12 cm in length and 9 cm in breadth)
- It is enclosed in a double-layered membranous sac called pericardium.
- It has 4 compartments called chambers.
- Upper two chambers-Auricles
- Lower two chambers-Ventricles
- Left side of heart has oxygen rich blood
- Right side of heart has carbon dioxide rich blood
- Left and right side of heart are separated by a wall called septum.
- Tricuspid valve is present between right atrium and right ventricle.
- Bicuspid valve is present between left atrium and left ventricle.
- The pulmonary vein brings the oxygenated blood from the lungs into the left atrium.
- When left atrium contracts, the oxygenated blood is pushed into the left ventricle.
- When left ventricle contracts, it pumps oxygenated blood into the main artery called aorta.
- Oxygenated blood from arteries passes through capillaries of the body organs and gives food and oxygen to body cells.
- Deoxygenated blood collected from the body organs enters the right atrium.
- When right atrium contracts, the deoxygenated blood is pushed into right ventricle.
- When right ventricle contracts, the deoxygenated blood is pumped into the lungs through pulmonary artery.
- In the lungs, deoxygenated blood gives out carbon dioxide and absorbs fresh oxygen from the air being breathed in.
- The contraction phase of the heart muscles is called systole.
- The relaxed phase of the heart muscles is called diastole.
- One complete rhythmic contraction of the heart followed by its relaxation is called a heartbeat.
- Average heart rate is 72-80 times per minute.
- Excretion in Animals
- The process of removal of waste products produced in the cells of the living organisms is called excretion.
- Excretory organs in various organisms:
- Amoeba, Paramecium, Hydra – Through body surface by diffusion
- Earthworms, leeches – Nephridia
- Insects – Excretory organs
- Vertebrates – Kidneys
- Excretory organs in Humans:
- Large Intestine – Undigested food is thrown out through anus in the form of faeces.
- Lungs – Carbon dioxide is removed by exhalation
- Skin – Sweat
- Kidneys – Help in removal of urea, waste salts and excess water in the form of urine.
- Excretory systems in Humans:
- When the blood reaches the two kidneys, it contains both useful and harmful substances.
- Useful substances are absorbed back in blood.
- Nephron filters harmful substances.
- Waste products dissolved in water are removed from kidney in the form of urine.
- From kidney, urine goes into urinary bladder through ureters.
- Urine is stored in urinary bladder and passed out from body through urethra.
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Published by Priya Prakash
In the midst of winter, i found there was within me an invincible summer ~ Albert Camus
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