Kids Learning Science V Term-I

5th Standard Science Term-I

Organ Systems

We get energy for our daily activities from the food we eat.  How is the food broken down into simpler forms? It is through the process called digestion.  After we eat the food, it is digested and the waste products are removed from the body.  The process involved in removal of wastes is called excretion.  We need oxygen to survive.  Our body gets oxygen through the process called respiration.  These processes are carried out by different organs in our body.  Different organs together form an organ system.  In this lesson we will study about different organ systems in our body and their functions.

The food we eat consists of complex compounds like carbohydrates, proteins and fats.  They have to be converted into simpler molecules like glucose, amino acids, and fatty acids and glycerol respectively.  These simpler molecules are then assimilated either by blood or lymph in order to give us.  The process of conversion of complex food molecules into simpler molecules is called digestion.  The digestive system can be divided into two.

1. Digestive tract 

2. Digestive glands

1. It is a coiled muscular tube extending from the mouth to the anus.  It is about 6-9 metres long and consists of many specialized divisions.  They are sequentially arranged as mouth, buccal cavity, pharynx, esophagus, stomach, small intestine, large intestine, rectum and anus.

Three important digestive glands associated with the process of digestion are : 

1. Salivary glands 

2. Pancreas

3. Liver 

Salivary glands secrete saliva which moistens food.  Saliva contains enzymes which break down complex molecules into simple molecules.  Pancreas produces pancreatic juice which contains digestive enzymes for digesting fats, proteins and carbohydrates.  Liver produces bile for the digestion of fat.

The respiratory system provides oxygen to the tissues of the body and removes carbon dioxide from the tissues.  There are three major parts forming the respiratory system.

1. Airway

2. Lungs

3. Muscles of respiration

The airway includes the nasal cavity, pharynx, larynx, trachea, branchi and bronchioles.  It carries air between the lungs and the surrounding.

The lungs are the primary organs of the respiratory system.  They are paired, cone-shaped organs.  They are located in the thoracic chamber (rib cage) on both sides of the heart.

Muscles of respiration include diaphragm and intercostal muscles.  They help to push the air in and out of the lugs during breathing.

In this system blood is circulated to transport oxygen and nutrients to every part of the body.  Circulatory system consists of the following.

1. Heart

2. Blood vessels

3. Blood

The heart is a hollow, muscular organ.  It is somewhat conical in shape.  It is covered with double walled membrane called pericardium.  The space between the membranes is filled with pericardial fluid.  The pericardial fluid protects the heart from shock.  Heart is placed inside the thoracic chamber (rib cage) in between the two lungs.

The heart is divided into four chambers.  Two upper chambers are called atria (Singular-atrium) or auricles.  Two lower chambers are called ventricles.  The upper and lower chambers of the heart are separated by a muscular wall or tissue known as the auriculo - ventricular septum of the heart.  The right side of the heart receives deoxygenated blood from various parts of the body and pumps it to the lungs for oxygenation.  The left side of the heart receives oxygenated blood from the lungs and pumps it to different parts of the body.

Blood vessels consist of arteries, veins and capillaries.  Arteries carry oxygenated blood (except pulmonary artery which carries deoxygenated blood from the heart) and veins carry deoxygenated blood (except pulmonary vein which carries oxygenated blood to the heart).

Capillaries are thin blood vessels which connect the arteries and veins.  They help in exchange of materials between circulatory system and body tissue.

Blood transports nutrients, oxygen, wastes and hormones.  The volume of blood in human adults is 4-5 litres.  It regulates water level and the body temperature.  Blood is pumped throughout the body by the heart.  It takes oxygen to the tissues and cells and finally reaches the lungs to take oxygen again.

Excretory system removes the waste products from the body.  It also regulates water and electrolyte balance.  Kidneys, lungs, liver and skin together function as excretory organs.  Excretory system consists of the following.

1. Kidneys 

2. Ureters

3. Urinary bladder

The kidneys filter the blood to remove waste and produce urine.  The kidneys are a pair of dark red, bean shaped organs placed behind the abdomen on either side of the vertebral column.  The average adult's kidney measures about 12 cm in length, 6 cm in width and 3 cm in thickness.  Right kidney is slightly lower than the left kidney.  Each kidney is covered by a fibrous membrane called capsule.

The kidneys are made up of millions of excretory units, called nephrons, which are the structural and functional units of the kidneys.

Two ureters connect the kidneys with the urinary bladder.  Urine formed from each kidney reaches urinary bladder through ureters.

It is sac-like in shape and acts as a temporary storage organ of urine.  Urine entering the urinary bladder from the ureters slowly fill the hollow space inside the bladder.  Urine is expelled from the body through the urethra.

Nervous system is an integration of nerves and they are composed of specialised cells called neurons.  The human nervous system is divided into the following.

1. Central Nervous System (CNS)

2. Peripheral Nervous System (PNS)

Central nervous system consists of the brain, the spinal cord and the nerves.

✧ Brain

Brain controls all our activities like thinking, reading and writing.  The brain is covered by three membranes called meninges.  They are dura mater, arachnoid membrane and pia mater.  The meninges protect the CNS from mechanical shock.  It is made up of eight immovable bones.  The brain is made up of millions of functional units called neurons.

Human brain is divided into three major parts.

- Forebrain

- Midbrain

- Hindbrain

Forebrain

➜ The forebrain consists of cerebrum, thalamus and hypothalamus.

➜  It is the largest part of the brain.

➜  It is the centre of human memory.

➜  It is responsible for intelligence, imagination and reasoning.

Midbrain

➜  It lies behind the cerebrum.

➜  It co-ordinates the movements of the muscles of the body.

➜  It regulates our vision, hearing, sleep and body temperature.

Hindbrain

➜  The hindbrain comprises of pons and medulla oblongata.

➜  It is also called the brain stem.

➜  It is called 'vital knot' because it controls breathing, heart beat and other involuntary muscles.

➜  It connects the brain to the spinal cord.

✧ Spinal cord

Spinal cord is a long tube like structure which extends from the brain.  It lies within the back bone of our body.

Peripheral nervous system consists of nerves extending from the spinal cord to all parts of the body.  It is made up of two parts.

➜  Somatic Nervous System

➜  Autonomic Nervous System

Somatic nervous system carries sensations from the organs to the brain and takes messages from the brain to the organs for movements.  Autonomic nervous system controls the nerves of the inner organs of the body.