A human’s body has many glands in different parts of the body that produce different secretions like saliva, oil, hormones, etc. Broadly, these glands are divided into two categories:

• Endocrine system – It produces hormones and does not have any glands. The secretory hormones are released into the blood from where it reaches the specific organs. Thyroid glands, adrenal glands, pituitary glands are some examples of it.
• Exocrine system– Exocrine system produces sweat, mucus, sebum, and enzymes. They have ducts. The secretory content is released to the body’s external surface or an internal organ through a duct. Pancreas, liver, and salivary glands are some examples.

Hormones are chemicals that are synthesised and created by the specific glands to regulate the activities of certain cells and organs of the body. The hormones control various physiological and psychological functions of your body.

Different types of glands

Adolescence is the age when a child reaches puberty. It occurs between the age of 10 to 19. The adolescence and accompanying changes bring about a change both physically and mentally for the child.

• Change in the body – The portion below the waist of the girls widens and shoulders narrow down. Boys become muscular with broad shoulders. 
• Change in height – There is a growth in height, and the height keeps on increasing till 18.
• Change in voice – Girls develop high-pitched voices while boys develop deep and hoarse voices. This happens because of the expansion of the voice box.
• Sexual organ development – For girls, the ovaries enlarge, and they produce eggs. As for boys, the penis enlarges, and they produce sperms. Some secondary sexual developments are the growth of facial hair, hair on the chest, armpits, and pubic hair for boys. For girls, hair under armpits, pubic regions and enlargement of breasts. 

The children should be taught about personal hygiene as they slowly slide towards puberty. If proper hygiene is not maintained, it can lead to various complications in the future for them. 

They should take a balanced diet as they are in the growing stage. Girls should eat food rich in iron for the formation of RBC in their blood cells. Children should avoid drugs, alcohol, and smoking, as this is the age when they get influenced easily. Girls should maintain proper hygiene during menstruation by using proper sanitary pads. 

Exercise daily to stay fit. Yoga, meditation, proper time management for your daily activities, pursuing your hobbies, investing time in sports, and reading would help a child stay fit and slide smoothly into puberty.

The circulatory system in the human body comprises arteries, veins, and capillaries. The heart pumps blood through it to the entire body. The circulatory system comprises the heart, blood, blood vessels, and lymphatic systems. 

Heart

The heart is in between the lungs in the thoracic cavity, situated slightly left of the breastbone. The primary function of a heart is to pump blood to all parts of the body and ensure normal blood pressure.

The heart is divided into two broad parts. 

• External Structure- The external structure of the heart, which is visible, is known as the pericardium. It is a fibre membrane that acts as an external covering of the heart and secretes a serous fluid that lubricates the heart. The wall of the heart comprises – epicardium, myocardium, and endocardium. 
• Internal Structure – The internal structure of the heart has four chambers that control the flow of blood. Different animals have different chambers. The body of the human has four chambers – The left atrium, right atrium, left ventricle, and right ventricle. Atria are blood-receiving chambers, while ventricles are blood-pumping chambers. The blood from the right side flows through the pulmonary circulation, while the blood from the left chamber is pumped to the body parts.

Blood vessels

Blood vessels are the medium through which blood travels to all parts of the body. The heart has many kinds of vessels which form a network. 

• Veins – This carries the deoxygenated blood through superior and inferior vena cava to the heart and deposits it in the atriums.
• Arteries- These are muscular tubes that carry oxygenated blood from the ventricles to different parts of the body. 
• Capillaries- These are tube-shaped vessels that form a bridge between the arteries and veins.

Double circulation

The flow of blood in the human body is interesting. The blood circulates in the heart two times and hence is known as double circulation. The main advantage of double circulation is that every part of the body gets a steady supply of oxygenated blood and does not mix up with deoxygenated blood.

Blood groups

Blood groups are the grouping done for the blood based on the presence or absence of antigenic substances on the surface of RBC. There are various kinds of groups. 

The nervous system is a complex network of neurons that carry messages. The complexity of it increases as you move towards higher animals. In the body of a human, the nervous system combines all the activities of the organs based on their stimuli. This system is the combination of nerves, sensory organs, the spinal cord, and the brain.

Central Nervous system

This is the central processing unit of the body and comprises the brain and spinal cord. 

Brain

The brain is the most important organ of the body. It controls the entire nervous system and helps in discovering new things or remembering old things. It also helps you to decide, understand and memorise things. The human brain has three major parts.

• Forebrain – It is the anterior part of the brain.
• Midbrain – It is the central part of the brain and is the smallest of all the parts of the brain.
• Hindbrain – The central region of the brain. 

Spinal cord

The spinal cord is a bundle of cylindrical nerve fibres and tissues inside the spine that connects to the entire body. It is found inside the vertebral column, surrounded by meninges. It is associated with reflex actions and the transferring of nerve impulses to and from the brain.

Nerves

These are fine thread-like structures that start from the brain and spinal cord. It transmits messages all over the body. There are three types of nerves:

• Sensory nerves – It sends messages from all the senses to the brain.
• Motor nerves – The structure of a motor neuron is built to transports messages from the brain to all the muscles.
• Mixed nerves – It carries both the sensory and motor neuron.

The human body is a complex machine with many systems running efficiently so that the body works properly. When one of the systems fails to work, the body does not operate properly.