Coordination and homeostasis in human
Do you remember taking away your leg, when a thorn pricks your foot? This action has taken place as living beings have the ability to respond to stimuli coming from external and internal environments. That is known as irritability. Above response is due to adaptation of body according to the changes of external and internal environments. That is called coordination. The change that takes place in the external environment which is detectable by the sensory organs is called a stimulus.
The organs that can detect (sense) the stimuli are called sensory organs (receptors). Eye, nose, ear, tongue and skin act as sensory organs.
The reaction for a stimulus is known as a response. The response is done by effectors. Muscles or glands act as effectors.
Recall the incident about the thorn prick. The pain due to thorn prick is the stimulus. The receptor of that stimulus is the skin. Taking the foot away is the response to that stimulus. Responding is done using muscles of the foot and that is the effector.
You will understand that there should be a proper communication between organs/ tissues to carry out body functions smoothly. Identification of the changes in the external and internal environments and responding accordingly is done by the coordination.
For coordination, two inter connected but different systems present in the human body.
- Nervous system
- Endocrine system
The coordination done by nervous system, is called nervous cordination, and coordination by endocrine system is called chemical coordination
Nervous coordination
Due to an electro chemical change in the nerves, impulses are transmitted through nerves. A proper coordination is maintained between the receptor and the effector.
The nervous coordination takes place with the involvement of the nervous system.
The structural unit of the nervous system is the neuron. There are three types of neurons in the nervous system.
- Sensory neuron
- Motor neuron
- Inter neuron
The nervous system is mainly composed of two components. They are the central nervous system and peripheral nervous system. The structure of it can be shown by the following simplified diagram.
Central nervous system
Central nervous system is very important in controlling of activites and coordination. Brain and spinal cord belong to central nervous system. Skull provides protection to the brain and vertebral column to the spinal cord.
Brain and spinal cord covered by meninges. There is a special fluid found within the cavities of brain and between meninges. It is known as cerebro spinal fluid. The functions of cerebro spinal fluid are given below,
- Support brain and spinal cord
- Absorption of shocks and jerks
- Protection against microbial infections and dessication
- Nourishing tissues
Brain
Brain is protected by the cranium and surrounded by three linings called meninges. The brain is about 1/50 of the body weight. There are about hundred billion of neurons. Other than neurons another accessory cells called neurogloea are present in brain. The brain is composed of three main parts.
- Cerebrum
- Cerebellum
- Medulla oblongata
External view of human brain
The peripheral region of the brain is composed of grey matter made up of cell bodies and the interior with white matter made up of nerve fibres.
Cerebrum
Longitudinal section of human brain
Cerebrum is the largest and most highly developed part of the brain. It is divided into left and right hemispheres. The cortex of the cerebrum is highly convoluted to increase the surface area. The left cerebral hemisphere controls the right half of the body and the right cerebral hemisphere controls the left part of the body.
Functions of cerebrum
- Perception of impulses from receptors, identification of received sensory information and storage of those information.
- Perception of senses about pain, vision, temperature, taste and smell.
- Perform high mental activities such as learning, intelligence and thinking.
- Controlling of voluntary muscle contraction.
Cerebellum
This is located just below the latter part of the cerebrum. It consists of two hemispheres. It is of grey matter in the outer layer and white matter in the interior layer.
Functions of cerebellum
- Maintenance of body balance
- Control of voluntary muscle activity
- Involve in maintenance of body movement
Medulla Oblongata
It is located anteriorly interior to cerebellum. It is an important centre in controlling many life processes (all reflex actions and involuntary actions).
Functions of medulla oblongata
- Control the rate of heart beat
- Control the rate of respiration
- Control reflex actions such as vomitting, caughing and swallowing.
Spinal cord
Cross section of human spinal cord
It is a tubular structure starting from medulla oblongata inferiorly and runs through vertebral column.
Peripherally white matter and interiorly grey matter is present in the spinal cord. The spinal nerves start symmetrically at either side of the spinal cord.
Reflex arc
Reflex arc
We know that there is a proper co-ordination maintained by nervous system between the receptors and effectors in the body. The impulses are sent from receptors to the central nervous system and from central nervous system into the effectors. The functional unit of the nervous system that maintains the coordination is called the reflex arc.
Three types of nerve cells involve in a reflex arc. They are sensory neuron, inter neuron and motor neuron. The reflex actions take place with the involvement of the reflex arc.
Reflex actions
A sudden, involuntary response to a particular stimulus is called a reflex action. They take place without the conciousness of the involvement of the brain. The reflex actions are of two types, as spinal reflexes and cranial reflexes.
Examples for spinal reflexes
- Moving the hand away when it contacts with a hot surface
- Lifting the leg when you step on a thporn
Examples for cranial reflexes
- Sneezing
- Salivation
- Blinking eyelids
Autonomic Nervous System
The nervous supply from the autonomous nervous system is to the internal organs of the body which are involuntarily controlled. This nervous system coordinates involuntary activities in the body.
The coordinating centres of the autonomous nervous system are hypothalamus and medulla oblongata. The autonomous nervous system is composed of two parts.
- Sympathetic nervous system
- Parasympathetic nervous system
The sympathetic and parasympathetic nervous systems cause opposite effects. The sympathetic system activates when a person is at emergency. It causes fight or flight effects.
Fight or flight effect caused by sympathetic system
The changes that occur due to the activities of sympathetic system, will be neutralised by the parasympathetic system.
Parasympathetic and sympathetic nervous supply on body organs
Chemical co-ordination
Chemical co-ordination is also important as nervous co-ordination to the survival of organism. Hormones secreted by endocrine glands are important in chemical co-ordination. Endocrine glands or ductless glands secrete hormones, directly into blood stream. So hormones are transported through blood.
Features of hormones -
- Hormones are oraganic compounds
- They are transproted through blood
- Produced at one site and act on another site
- Stimulate target organs or target cells
- Small concetration is required
The endocrine glands of human body
There are several endocrine glands located in human body. The main endocrine glands are mentioned
below.
- Pituitary
- Thyroid
- Hpothalamus
- Pancreas
- Adrenal gland
- Gonads (testes and ovaries)
Location of endocrine glands in human body
Several hormones secreted by endocrine glands of human
Homeostasis
Maintenance of constant internal environment is called homeostasis.
The internal environment is the immediate surrounding of the cell which provides medium for the cell to survive. The tissue fluid around cells, the plasma around blood cells and lymph are included into the internal environment.
When internal environment is constant, the conditions inside cells is also constant. If there is a small change in the internal environment it highly affects the cellular activities. Therefore the internal environment should maintain stable conditions or within a narrow range, which can be tolerated by the cells. If not, automatic control system will be active with feedback mechanisms.
The factors in the internal environment that has to be regulated
- Blood glucose level
- Body temprature
- Water balance
Regulation of blood glucose level
The blood glucose level of a healthy adult is 80-120 mg/100 ml of blood. When blood glucose level is greater than the normal level beta cells in islets of langerhans in pancreas secrete more insulin. This hormone converts glucose into glycogen and then glycogen store in liver. Further excess glucose is converted to fat and stored in adipose tissue.
When blood glucose level is less than normal (when a person is starving) alpha cells in islets of langerhans in pancreas are stimulated to secrete more glucogen. This glucogen acts on glycogen stored in liver to convert it into glucose and release into blood. The blood glucose level will be increased to normal level. Due to the activities of insulin and glucogen. The blood glucose level is regulated. Due to absence of beta cells or secretion of insulin will cause diabetes.
Regulation of body temperature
Human is a homoithermic organism. Homoithermic means maintenance of constant body temperature irrespective to the fluctuations of temperature in the environment. Normal body temperature of human is 37 0C. But it can vary from 36 0C to 37.5 0C. The thermo regulatory centre of the human is present in the hypothalamus of the brain. When environmental temperature drops to avoid the decrease of body temperature, hypothalamus stimulates and carries out the activities below.
- Reduce blood supply to skin to reduce heat loss, by contracting blood capillaries in the skin.
- Reduce production of sweat in sweat glands and reduce heat loss.
- The hairs become erect and trap an air layer to act as a heat insulating layer.
- If the heat loss is high, heat is generated by shivering.
When temperature of the internal environment increases, to prevent the increase of body temperature, the hypothalamus stimulates to activate the processes as follows,
- Dialate blood vessels in the skin and thereby increase blood supply to skin and increase heat loss.
- Increase sweat production by sweat glands. When sweat is evaporated heat is absorbed by body and decrease body temperature.
Regulation of body temperature is done by the hypothalamus.
Regulation of water balance
When the water level of blood drops, pituitary secretes ADH (Antidiuresis hormone). This ADH acts on kidney to increase reabsorption of water, thereby reduce the amount of water released with urine.
When water level in blood is high, the reabsorption of water decreases and the amount of water released with urine increases. Accordingly water balance in the body is regulated.
source by internet and books
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