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Transportation in Humans

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Transportation in Humans - Lesson Summary

All livings beings require food, water and oxygen for their survival and to perform various activities. Food we consume is digested in to simple absorbable substances called as nutrients in the digestive system.
  • The circulatory system helps in the transport of nutrients in the glucose, amino acids and fats to different parts of the body. Every cell receives absorbed nutrients through the circulating fluid tissue called as blood.
  • Excretory system is responsible for the removal of waste from different parts of the body. Every cell releases its waste material into the blood to be carried over to excretory organs for expulsion.

Circulation in lower animals
  • In unicellular organisms like amoeba and paramecium, circulation is brought about by the process of diffusion. Nutrients are delivered to all parts of the cell by diffusion.
  • In multicellular organisms like hydra and jelly fish, nutrients are circulated in the body by water vascular system.

Circulatory System in human beings
The circulatory system is also known as the cardiovascular system. The circulatory system comprises blood, blood vessels and the heart.

Blood: Blood is a fluid tissue that flows in special tubes called as blood vessels. Different functions of blood are elucidated.
  • Blood maintains constant body temperature.
  • Blood helps in transportation of food and water from the digestive system in the body to all the cells in the body.
  • Blood helps in transportation of oxygen from the respiratory system to the cells present in all parts of the body.
  • Blood helps in transportation of harmful and unwanted wastes from the cells to the excretory organs. Blood is made up of plasma and formed elements.
  • Blood provides resistance to the body against pathogens and infections they cause in different parts of the body.

a) Plasma is the fluid part of blood which contains 90% water. It is pale yellow in colour. It carries nutrients, enzymes and waste materials in it.

b) Formed elements are made up of three different types of blood cells. These include red blood cells, white blood cells and platelets. Each of these cells performs a specific function.
  • Red blood cells - RBCs are disc-shaped cells which transport oxygen to different parts of the body. The presence of haemoglobin gives blood its red colour. Haemoglobin is an iron containing pigment that combines with oxygen to form oxyhaemoglobin. As the blood reaches the cells, oxyhaemoglobin dissociates to release oxygen which is supplied to cells. In the cells, carbon dioxide binds with haemoglobin to form carboxy-haemoglobin. In the lungs, carboxy-haemoglobin dissociates to release carbon dioxide which is expelled out.
  • White blood cells - These cells are also called as WBCs. These cells are larger than RBCs. White blood cells help in defending the body against infections. White blood cells have the capability of destroying foreign cells. WBCs can move on their own and can enter the areas of infection by passing through the membranes of blood vessels. These are of many kinds - Leucocytes, basophils, neutrophils, eosinophils etc.
  • Platelets - Platelets are the non nucleated irregularly shaped blood cells which bring about clotting of the blood. These are also called as thrombocytes as they release thromboplastin which brings about clotting of blood. Platelets immediately come to the place of injury and lyse themselves to release thromboplastin. The remnants aggregate in large amounts to form a plug on the injury preventing the blood loss.

Blood vessels: Blood flows through narrow pipe-like structures in the body known as blood vessels. These blood vessels transport food, oxygen and waste throughout the body. Blood vessels are of three types namely, arteries, veins and capillaries.

Arteries are the blood vessels which carry fresh oxygenated blood to all parts of the body.
  • Arteries carry blood away from the heart.  All the arteries except for pulmonary artery, carry fresh oxygenated blood.
  • Oxygenated blood is pumped by the heart with a great pressure into arteries, hence they have thick elastic walls.  
  • Arteries transport bright red oxygen rich blood from the heart to the other parts of the body.
  • Arteries on reaching the tissues divide into fine vessels or tubes known as capillaries
  • Pulmonary artery carries impure blood to the lungs from heart.

Veins are the blood vessels which carry deoxygenated blood from all parts of the body to tissues to the heart.
  • Veins carry blood to the heart. They carry carbon dioxide rich blood to the heart from different parts of the body. 
  • Veins have valves on their inner lining that allow blood to flow only in one direction.
  • In the tissues, number of capillaries join together to form a vein.
  • Pulmonary veins carry pure blood from lungs to the heart.

Blood capillaries are the thinnest blood vesels which are in direct contact with the cells.
  • Capillaries nourish the cells of the tissue with oxygenated blood.
  • They have thin membranes through which oxygen and nutrients get into the cells.
  • Veins inturn receive carbon dioxide and waste products from the cells.
  • Later, all these capillaries of that tissue at another end combine to form a vein.
  • This vein carries deoxygenated blood to the heart.
  • Deoxygenated blood is sent to lungs for purification.

Heart: The heart is the central organ for pumping the blood throughout the body. Heart is made up of strong cardiac muscles.
  • It is located in the chest cavity with its lower part pointing towards the left. Its size is that of the person’s fist. 
  • It pumps blood rich in carbon dioxide to the lungs and oxygen-rich blood to other parts of the body.
  • The heart consists of four chambers namely auricles and ventricles. The two upper chambers of the heart are known as the auricles.The two lower chambers of the heart are the ventricles.
  • Left and right parts of the heart are separated by a muscular partition called as septum.
  • Heart has number of valves which allow the blood to flow in one direction. These valves prevent the oxygenated blood mixing with de-oxygenated blood.

Purification of blood is a stepwise procedure happening in a sequence. Double circulation is observed in human beings. Blood passes twice through the heart.
  • Step 1 - Pure oxygenated blood from the lungs is carried to the left auricle through pulmonary veins. Left auricle contracts to push the pure blood into left ventricle. 
  • Step 2 – Blood from left ventricle is carried to all parts of the body through arteries. Blood gets purified in the lungs.
  • Step 3 – Deoxygenated blood from the tissues is collected by veins and transported to right auricle. Right auricle contracts to send this impure blood into right ventricle.
  • Step 4 - Right ventricle pumps deoxygenated blood into the lungs through pulmonary arteries.

Heart beat is the combined effect of contractions and relaxations of the cardiac muscles occurring in two batches.
  • Two auricles contract first to force the blood into two ventricles on either side. This produces a 'lub' sound.
  • Later, two ventricles contract to send the blood into arteries moving towards the body and pulmonary artery moving towards the lungs producing a 'dub' sound.
  • The rhythmic contraction and relaxation of the heart constitutes heartbeat.
  • Heartbeat can be felt by placing the palm on the left side of the chest.
  • Stethoscope is a device that amplifies the sound of your heartbeat.

Pulse is the throbbing sensation in the wrist region signifying the blood rushing through the arteries.
  • It is the pressure applied by blood on the walls of an artery at a particular part of the body.
  • The number of times the heart beats in a minute is the same as the pulse rate.
  • The ideal pulse rate is 70 to 80 per minute.

The process of the removal of waste produced in the cells in living organisms is called excretion. The organs that help in the process of excretion constitute the excretory system.  

Functions of excretory system
Excretion helps in eliminating different types of wastes.
  • Nitrogeneous wastes are the wastes formed in the body as a result of protein metabolism.These can be in the form of ammonia, urea or uric acid. All these nitrogeneous wastes should be eliminated from the body due to their toxic nature. Nitrogeneous wastes mix with water in the body to form urine. Urine is expelled out in periodic intervals.
  • Excess sugar from the blood is filtered and sent out through urine in case of diabetic patients.
  • Undigested wastes are passed out through anus by the process of egestion.
  • Carbon dioxide, an excretory product from every cell is expelled out through lungs.
  • Excess salts from the body are eliminated through sweat.

Excretion in lower animals
Lower organisms like amoeba, paramecium, hydra do not possess special organs for excretion. They eliminate waste products to the environment by the process of diffusion occurring through cell membrane.

Excretory system in human beings
The excretory system in human beings includes a pair of kidneys, a pair of ureters, a urinary bladder, and a urethra. This is also known as the urinary system.

a) Kidneys - The kidneys are located in the abdominal region, one on either side of the backbone.
  • Kidneys mainly act as excretory organs and also control the balance of water and mineral ions in the body.
  • Kidneys filter out nitrogenous wastes from the blood producing urine.
  • They absorb minerals into the blood. they also produce hormones to some extent.
  • Kidney is divided into two regions namely, cortex and renal medulla.
  • Kidney is made up of tiny tubules called as nephrons. Nephrons are the functional units of the kidney.
  • Each nephron consists of a corpuscle and a renal tubule. It filters out excess water, salts and urea from the blood.

b) Ureter - Ureters are tubular structures which arise from each kidney. Ureter  opens into the urinary bladder.

c) Urinary bladder - Urinary bladder is a muscular bag which has high elasting capacity to accumulate urine in it .Urinary bladder opens out to the exterior through an opening called as urethra.

d) Urethra - The urethra passes urine to the outside of the body. The urethra emerges through the penis in males and close to the vagina in females.

Urine is the liquid formed by the combination of urea with water. Urine formation occurs in three steps. A healthy human being passes out 1.5 to 2.5 litres of urine every day. Dialysis is the treatment primarily used to provide an artificial replacement for of a kidney which has become non-functional. Kidney does not function properly due to renal failure. Dialysis is eliminating nitrogenous waste and unwanted water from the blood. The material used in this technique is the dialyzing fluid which actually filters the blood to separate the wastes.


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