CBSE Class 10th Biology | Control and Coordination | HORMONAL SYSTEM (ENDOCRINE SYSTEM)



In addition to the nervous system, the endocrine system also helps in coordinating the activities of our body.

A group of endocrine glands which produces various hormones forms the endocrine system. It is also known as hormonal system.

The various endocrine glands in human body are – Hypothalamus, Pituitary, Thyroid, Parathyroid, Pancreas, Adrenal, Pineal, Thymus, Testes (in males) and Ovaries (in females).



Gland is a cell, tissue or an organ which secretes a specific substance in the body.




The term ‘hormone‘ was introduced by Bayliss and Starling.

Hormones are the chemical messengers which coordinate the activities of living organisms.


  1. They are secreted in small amounts by endocrine glands.
  2. They are poured directly into the blood and carried throughout the body by blood.
  3. They act on specific tissues or organs known as target organs.

Endocrine glands in human beings



Name of Gland 





Releasing hormones

Regulates the secretion of hormones from the pituitary. 



Growth hormone

Regulates the development of bones and muscles. 


Regulates the secretion of milk during lactation and regulates uterine contractions. 


Regulates the water and electrolyte balance in the body.


Regulates the function of mammary gland. 

Trophic Hormones 

Regulates the secretion of hormones from other endocrine glands like thyroid, adrenal, ovary and testis. 




Regulates the metabolism of carbohydrates, fat and proteins in the body.


Controls calcium and phosphorus balance. 



Parathormone (PTH) 

Regulates calcium and phosphorus balance in the blood.





Regulates carbohydrate, fat and protein metabolism and maintains electrolyte balance.


Regulates heart rate, breathing rate, blood pressure and carbohydrate metabolism. 




Lowers the blood sugar level 


Increases the blood sugar level




Regulates the development of male reproductive organs and accessory sexual characters like beard, moustache, etc.






Regulates the development of female reproductive organs and accessory sexual characters like development of mammary gland.


Maintenance of Pregnancy. 



Some interesting hormones and their role


(a) Adrenaline as an ‘Emergency Hormone’:


Adrenaline hormone is usually secreted in small amounts but when a person is under stress like he is frightened, it is secreted in large amounts. It prepares the body for action as it speeds up heart beat and breathing, raises the blood pressure and allows more glucose to go into the blood to give us a lot of energy to combat the stress situation.

This happens as follows : When the heart beats faster, it supplies more O2 to our muscles. The blood to the digestive system and skin is reduced due to contraction of muscles around small arteries in these organs. This diverts the blood to our skeletal muscles. The breathing rate also increases because of the contractions of the diaphragm and rib muscles. All these responses together enable the animal body to be ready to deal with the situation.

(b) Growth Hormone:


Growth hormone is one of the hormones secreted by pituitary gland. This regulates the growth and development of the body.

  1. If there is deficiency of this hormone in childhood, it leads to Dwarfism.
  2. If there is excess of this hormone in childhood, it leads to Gigantism.

(c) Thyroxin:

Thyroid gland secretes the hormone Thyroxin. Iodine is essential for the synthesis of Thyroxin by the thyroid gland. So, if iodine is deficient in our diet, less thyroxin hormone is there leading to a disease called Goitre. The main symptom of goitre is that neck of the person becomes swollen due to enlargement of thyroid gland. That is why it is advised to take iodised salt in the diet so as to prevent goitre.

(d) Insulin:


Insulin hormone, produced by pancreas functions to lower the sugar level of the blood. If it is not secreted in proper amounts, the sugar level in the blood rises causing Diabetes. Then, people suffering from diabetes are advised to take less sugar in diet. They might be taking injections of insulin as a part of treatment.

Feedback Mechanism


It is important that hormones should be secreted in precise quantities because both excess or deficiency of hormones has an harmful effect on the body. So we need a mechanism through which this is to be done. The timing and amount of hormone released by various glands are controlled by ‘Feedback mechanism’ which is inbuilt in our body.

For e.g. When we eat a carbohydrate rich meal, the sugar level of the blood rises. It is detected by the cells of pancreas, which respond by producing and secreting more insulin into the blood. In this way, blood glucose level is brought back to normal.

And if the blood sugar level falls below normal, insulin secretion by pancreas decreases automatically.



CBSE Class 10th Biology | Control and Coordination | Control and Coordination in Animals

Control and Coordination in Animals


Multicellular organisms have specialized organ system to coordinate their activities. Simple multicellular organism like Hydra consists of a network of nerve cells. Thus Hydra has only nervous system to coordinate its activities.

The control and coordination in higher animals (Human) takes place through combination of nervous system and hormonal system, i.e. neuro-endocrine system.


Nervous system of Hydra


Nervous System in Animals


Nerve cells are the fundamental unit of nervous system. They are the specialized cells responsible for carrying information across the body. A nervous system consist of millions of nerve cells communicating through neurotransmitters among themselves. It is the longest cell in the body.

Structure of Neuron


A neuron consist of two components

1. Cyton (Cell body): It is like a typical animal cell, which contains cytoplasm and nucleus. Small processes stretches out from the cell body called dendrons which may further branch into dendrites.

2. Axon: It is a cylindrical structure arising from cyton and branched at its terminal ends. It has an insulating and protective sheath of myelin (made of fat and protein) around it. It is also known as nerve fibre.

A Neuron (Nerve cell)


Receptor and Effector


    There are five sense organs in our body: eyes, ears, nose, tongue and skin. In a sense organ a receptor is present, which is a cell or group of cells sensitive to a particular type of stimulus (change in environment) such as light, heat, sound etc.

Types of receptors



Types of Stimulus 

Sense organ 


Photo receptors

Detects light 



Phono receptors 

Detects sound 



Olfactory receptors 

Detects smell 



Gustatory receptors 

Detects taste 



Thermo receptors 

Detects heat or cold



The part of a body which can respond to stimulus according to the instruction sent from the nervous system is called effector. Effectors are mainly muscles and glands.

If we touch something hot (or smell something tasty) we need to detect it and this is done by specialized tips of some nerve cells located in our sense organs. This information is then transmitted to central nervous system (brain and spinal cord) from where the response of the same is conveyed to the effector organs (muscles and glands). The whole process is done by a set of 3 neurons.

Types of Neuron


There are three types of neurons

  1. Sensory neuron: It transmits information from receptors (sense organs) towards central nervous system (brain and spinal cord).
  2. Motor neuron: It transmits information from central nervous system to effectors (muscles or glands).
  3. Inter or Relay neuron: It occurs in central nervous system and serves as link between other neurons.

Transmission of Nerve Impulse


The messages that are transmitted in the nervous system are in the form of electrical or chemical signals called nerve impulses. The nerve impulses are transmitted from one neuron to another in a nervous system. There is a microscopic gap between two neurons over which nerve impulses pass while going from one neuron to the next and it is called synapse. A chemical substance called neurotransmitter (e.g. Acetylcholine) helps in carrying nerve impulses over synapse.



Steps for transmission of nerve impulse

  • A chemical reaction followed by an electrical impulse sets off when a stimulus acts on a receptor.
  • This impulse is transmitted from the dendrite of a sensory neuron to the terminal endings of its axon.
  • At the synapse, the neurotransmitter is released which undergoes a chemical reaction resulting in initiation of a similar impulse in the next neuron.
  • This impulse is again transmitted to the terminal endings of the next neuron and the process continues till it reaches the relay neuron in spinal cord and brain.
  • From the brain and spinal cord arises a set of motor neurons which transmits electrical impulses in the similar way to the effectors like muscles and glands.

Action caused by Effectors due to Nervous Tissue


The nerve impulse received by the muscles cause action or movement (removing our hand away from a hot object). Muscles are made of muscle cells containing special proteins which change their arrangement when stimulated by electrical impulses. This causes the muscle to change shape and contract. When the muscles contract, they pull the bones and make it move.

The neuromuscular junction i.e., the area of contact between a nerve fibre and sarcolemma is similar to axon-dendron junction or synapse. When a nerve impulse reaches the end of a nerve fibre, a neurotransmitter is released and it creates a similar electrical disturbance in the muscle cell bringing about its contraction.

Neuromuscular Junction


To sum up, the transmission of nerve impulse and action by effectors can be shown as follows.



Human Nervous System


Human nervous system is one of the most highly developed nervous system among living organisms on this planet.

The human nervous system can be further divided.



(a) Central Nervous System


It occupies the central axis of the body and enables a person to give a suitable response to various situations.

It consists of the

  1. Brain
  2. Spinal Cord


(i)    Brain: The brain is located in a bony case (skull) called cranium or brain box. Inside the cranium, the brain is further surrounded by three membranes called meninges. The space between the membranes and brain is filled with cerebrospinal fluid (CSF). The cranium, meninges and cerebrospinal fluid protects the brain from mechanical shocks.

Human brain


The brain is broadly divided into three regions.

Fore Brain: It consists of

Olfactory lobes: A pair of bodies covered by cerebrum. It is not so developed in humans. It is concerned with olfaction (smell).

Cerebrum: It forms about two-third of the brain. Different areas of cerebrum perform different functions. Association areas control learning, reasoning, intelligence, personality, thinking, memory, etc. Sensory areas give us sensation by receiving information from eyes, ears, nose, tongue, skin. Motor areas give instructions to muscles for various voluntary actions.


It controls reflex movements of the head, neck, eye muscles, etc. in response to visual or auditory stimuli.

Hind brain: It is further sub divided

Pons: It takes part in regulating respiration.

Cerebellum: It helps in maintaining posture and balance. It also coordinates smooth body movements like walking, riding, etc.

Medulla Oblongata: It controls various involuntary actions such as heart beat, breathing, peristaltic movements, etc. Medulla also controls reflex actions like, swallowing, sneezing, vomiting, etc.

Different regions of brain showing different functions

(ii)    Spinal Cord: It is rod-like structure extending downwards in continuation with medulla. It is enclosed in a bony cage called vertebral column and is also surrounded by meninges.

It is concerned with reflex actions and conduction of nerve impulses to and from the brain.

Reflex Action and Reflex Arc

Reflex action: A reflex action may be defined as a spontaneous, automatic and mechanical response to a stimulus, acting on a specific receptor, without the will of an animal.

Blinking of eyes, moving our foot away when we step on something sharp, etc. are examples of reflex action. In reflex action we are not aware of the things which is going to happen to us. In reflex action, spinal cord is involved for quick response to specific stimulus. However for thinking process, the information also goes to the brain.

The involvement of brain in reflex action is to think about the dangerous situation and the possibility of reaction. Such reflex action which involves brain are called cerebral reflexes. For example, the contraction of pupil of our eye automatically in the presence of bright light.    


Reflex arc


Reflex arc: The path taken by nerve impulses in a reflex action is called reflex arc.

When we accidentally touch something hot, the heat is sensed by the receptors present in the skin. A nerve impulse is triggered for the same in the sensory neuron which transmits message to the spinal cord. In the spinal cord, impulse is passed to the connector neuron which in turn passes it to the motor neuron. The motor neuron transmits the instruction to a muscle of our arm. The arm muscles contracts and pulls other hand away from the hot object.

(b) Peripheral Nervous System

All the nerves arising from brain and spinal cord forms the peripheral nervous system. Nerves arising from the brain are called cranial nerves which are twelve pairs. There are 31 pairs of nerves arising from the spinal cord (spinal nerve). Cranial nerves are either sensory, motor, or mixed in nature. All the spinal nerves are mixed.

(c) Autonomic Nervous System

It comprises of a set of two (sympathetic and parasympathetic) network of nerves antagonistic to each other. These nerves are attached to the smooth muscles of internal organs and controls involuntary actions.

For example: Sympathetic nerves increase the rate of heart beat and parasympathetic decrease the rate of heart beat.