What are the Sense Organs?

Sense organs are specialized organs that help to perceive the world around us. They are an integral part of our lives and it is the only way that enables us to perceive the environment.

Sense organs provide the required data for interpretation through various organs and a network of nerves in response to a particular physical phenomenon. These senses govern our association and our interaction with the environment.

We have five sense organs, namely:

• Eyes
• Ears
• Nose
• Tongue
• Skin

These five sense organs contain receptors that relay information through the sensory neurons to the appropriate places within the nervous system The receptors could be classified into two parts viz. the general and special receptors. The former is present throughout the body while the latter includes chemoreceptors, photoreceptors and mechanoreceptors.

Five Sense Organs

As stated before, we have five sense organs that can receive and relay sensory information to the brain. These senses provide an organism with information crucial for perception. The different sense organs and the senses they provide are mentioned below:

Eyes – Sight or Ophthalmoception

These are the visual sensory organs in our body. These are sensitive to light images. The eyes vary in colour depending upon the amount of melanin present in our body. It helps in the sense of sight by detecting and focussing on the light images.

The iris in the eye is the coloured part that controls the size and diameter of the pupil, which directly affects the amount of light entering the eyes. Behind the lens of the eye lies the vitreous body. It is filled with a gelatinous material called the vitreous humour. This substance gives shape to the eyeball and also transmits light to the very back of the eyeball, where the retina is found.

This retina contains photoreceptors, which detect light. There are two types of cells present that perform functions distinct from each other. These are Rod and Cones.

Rods: These sensors function in low light and are found at the edges of the retina. They also aid in peripheral vision.

Cones: These types of retinal cells work best in bright light, detecting fine details and colour. There are three types of cones for detecting three primary colours of light, namely: blue, red and green. Typically, color blindness occurs when any one of these types of cones are not present.

Ears – Hearing or Audioception

Ears are the auditory sense organs of our body. They help us to perceive sounds. Our auditory system detects vibrations in the air and this is how we hear sounds. This is known as hearing or audio caption.

The ears are divided into three sections, namely, the outer ear, the inner ear, and the middle ear. All sounds are basically vibrations, so the outer ear transfers these vibrations into the ear canal, where these vibrations are transformed by the brain into meaningful sound. Apart from hearing, this sense is also important for balancing our body or equilibrium.

Tongue – Taste or Gustaoception

The tongue helps in perceiving various tastes and flavours. The taste buds are present between the papillae on the tongue—these help in sensing different tastes.

The senses of smell and taste tend to work together. If one could not smell something, they could not taste it either. The sense of taste is also known as gustaoception.

Taste buds on the tongue contain chemoreceptors that work similarly to the chemoreceptors in the nasal cavity.

However, the chemoreceptors in the nose would detect any kind of smell, whereas there are four different types of taste buds and each one can detect different types of tastes like sweetness, sourness, bitterness and saltiness.

Nose – Smell or Olfalcoception

The nose is an olfactory organ. Our olfactory system helps us to perceive different smells. This sense of organ also aids our sense of taste. The sense of smell is also known as olfaction.

The olfactory cells tend to line the top of the nasal cavity. On one end, olfactory cells have cilia that project into the nasal cavity and on the other end of the cell, are the olfactory nerve fibres.

As one breathes in, the air enters into the nasal cavity. The olfactory cells are chemoreceptors, which means that the olfactory cells have protein receptors that can detect subtle differences in chemicals. These chemicals bind to the cilia, which conducts a nerve impulse that is carried to the brain. The brain then translates these impulses into a meaningful smell. During a cold, the body produces mucus which blocks the sense of smell; this is the reason why the food which we eat tastes bland.

Skin – Touch or Tactioception

Skin is the largest organ of our body. It is related to the sense of touch. The sense of touch is also referred to as tactioception.

The skin contains general receptors which can detect touch, pain, pressure and temperature. They are present throughout the skin. Skin receptors generate an impulse, and when activated, is carried to the spinal cord and then to the brain.

Other Sense Organs

Besides these five sense organs, there are another two that help to orient us with the world. They are:

Vestibular System

The vestibular system acts as a sensory system of the body and is responsible for transmitting information to our brain about the motions, head position and spatial orientation.  This system is also involved with motor functions and helps in:

1. Maintain our body posture.
2. Maintaining our body balance.
3. Stabilize our head and body during movement.
4. Identifying the orientation and posture of our bodies in relation to the environment.

Thus, the vestibular system is essential for normal movement and equilibrium.

Proprioception system

Proprioception system is described as the conscious or unconscious awareness of joint position. This system helps the body to identify the muscles, joints and limbs located in 3D space and the direction it is moving in relation to the body.

Walking or kicking without looking at our feet, balancing on one leg, touching the nose with eyes closed and the ability to sense the surface on which we are standing upon, are a few examples of proprioception system

Human Brain

 

The Human Brain

On average, an adult brain weighs between 1.0 kg – 1.5 kg.  It is mainly composed of neurons – the fundamental unit of the brain and nervous system. Recent estimates have suggested that the brain contains anywhere between 86 billion to 100 billion neurons.

The brain, along with the spinal cord, constitutes the central nervous system. It is responsible for thoughts, interpretation, and origin of control for body movements.

Brain Diagram

The brain diagram given below highlights the different lobes of the human brain.

Where is the Brain located?

The brain is enclosed within the skull, which provides frontal, lateral, and dorsal protection. The skull consists of 22 bones, 14 of which form the facial bones and the remaining 8 forms the cranial bones. Anatomically, the brain is contained within the cranium and is surrounded by cerebrospinal fluid.

The Cerebrospinal Fluid (CSF) is a fluid that circulates within the skull and spinal cord, filling up hollow spaces on the surface of the brain. Every day, the specialized ependymal cells produce around 500mL of cerebrospinal fluid.

The primary function of the CSF is to act as a buffer for the brain, cushioning mechanical shocks and dampening minor jolts. It also provides basic immunological protection to the brain.

Furthermore, CSF provides buoyancy for the brain. i.e., the brain is suspended in a layer of CSF, wherein, the weight of the brain is nearly negated. If the brain is not suspended in CSF, it would be impeded by its weight, consequently cutting off the blood supply in the lower half of the brain. It would lead to the death of neurons in the affected area.

Parts of Human Brain

Following are the major parts of the human brain:

Forebrain – The largest part of the brain

It is the anterior part of the brain. The forebrain parts include:

• Cerebrum
• Hypothalamus
• Thalamus

Forebrain Function: Controls reproductive functions, body temperature, emotions, hunger, and sleep.

Fact: The largest among the forebrain parts is the cerebrum. It is also the largest part of all vertebrate brains.

Midbrain: Smallest and central part of the brain

The midbrain consists of:

• Tectum
• Tegmentum

Hindbrain: The lower part of the brain

The hindbrain is composed of:

• Cerebellum
• Medulla
• Pons

Hindbrain functions: The three regions of the hindbrain coordinates all processes necessary for survival. These induce breathing, heartbeat, sleep, wakefulness, and motor learning.

Brain diagram highlighting various parts of the human brain

Cerebrum

The cerebrum is the largest part of the brain. It consists of the cerebral cortex and other subcortical structures. It is composed of two cerebral hemispheres that are joined together by heavy, dense bands of fiber called the corpus callosum. The cerebrum is further divided into four sections or lobes:

1. Frontal lobe: It is associated with parts of speech, planning, reasoning, problem-solving, and movements.

2. Parietal lobe: Help in movements, the perception of stimuli, and orientation.

3. Occipital lobe: It is related to visual processing.

4. Temporal lobe: This region is related to the perception and recognition of memory, auditory stimuli, and speech.

The brain consists of two types of tissues: Grey matter and White matter.

1. Grey matter mainly consists of various types of cells, which make up the bulk of the brain.
2. White matter is primarily composed of axons, which connect various grey matter areas of the brain with each other.

The exterior portion of the cerebrum is called the cortex or the cerebral mantle. The cortex is extremely convoluted, due to which, it has a large surface area.  The cerebrum also includes:

1. Sensory areas: To receive the messages.

2. Association areas: These areas integrate the incoming sensory information. It also forms a connection between sensory and motor areas.

3. Motor areas: This area is responsible for the action of the voluntary muscles.

Cerebrum Function

The cerebrum is responsible for thinking, intelligence,  consciousness, and memory. It is also responsible for interpreting touch, hearing, and vision.

Thalamus

The thalamus is a small structure, located right above the brain stem responsible for relaying sensory information from the sense organs. It is also responsible for transmitting motor information for movement and coordination. Thalamus is found in the limbic system within the cerebrum. This limbic system is mainly responsible for the formation of new memories and storing past experiences.

Hypothalamus

The hypothalamus is a small and essential part of the brain, located precisely below the thalamus. It is considered the primary region of the brain, as it is involved in the following functions:

1. Receives impulses
2. Regulates body temperature
3. Controls the mood and emotions
4. Controls the sense of taste and smell
5. Synthesises the body’s essential hormones
6. Coordinates the messages from the autonomous nervous system
7. Controls appetite, peristalsis, the rate of heartbeat, and blood pressure
8. Forms an axis with the pituitary gland which is the main link between the nervous and the endocrine systems

Tectum

The tectum is a small portion of the brain, specifically the dorsal part of the midbrain. It serves as a relay center for sensory information from the ears to the cerebrum. It also controls the reflex movements of the head, eye, and neck muscles. It provides a passage for the different neurons moving in and out of the cerebrum.

Tegmentum

Tegmentum is a region within the brainstem. It is a complex structure with various components, which isare mainly involved in body movements, sleep, arousal, attention, and different necessary reflexes. It forms the platform for the midbrain and connects with the thalamus, cerebral cortex, and spinal cord.

Cerebellum

The cerebellum is the second largest part of the brain, located in the posterior portion of the medulla and pons. The cerebellum and cerebrum are separated by the cerebellar tentorium and transverse fissure. Cortex is the outer surface of the cerebellum, and its parallel ridges are called the folia. Apart from this, the cerebellum has the cerebellar peduncles, cerebellar nuclei, anterior and posterior lobes. The cerebellum consists of two hemispheres, the outer grey cortex, and the inner white medulla.  It is mainly responsible for coordinating and maintaining the body balance during walking, running, riding, swimming, and precision control of voluntary movements. The main functions of the cerebellum include:

1. It senses equilibrium.
2. Transfers information.
3. Coordinates eye movement.
4. It enables precision control of voluntary body movements.
5. Predicts the future position of the body during a particular movement.
6. Both anterior and posterior lobes are concerned with skeletal movements.
7. The cerebellum is also essential for making fine adjustments to motor actions.
8. Coordinates and maintains body balance and posture during walking, running, riding, swimming.

Medulla Oblongata

The medulla oblongata is a small structure present in the lowest region of the brain. It mainly controls the body’s autonomic functions such as heartbeat, breathing, and digestion. It plays a primary role in connecting the spinal cord, pons, and the cerebral cortex. Also, it helps us in maintaining our posture and controlling our reflexes.

Pons

The pons is the primary structure of the brain stem present between the midbrain and medulla oblongata. It serves as a relay signal between the lower cerebellum, spinal cord, midbrain, cerebrum, and other higher parts of the brain. The main functions of the pons include:

1. Controlling sleep cycles.
2. Regulating the magnitude and frequency of respiration.
3. Transfers information between the cerebellum and motor cortex.
4. Pons is also involved in sensations, such as the sense of taste, hearing, and balance.

 

Characteristics Of Organisms

We have so many things around us, but how many of them are living? If plants are living entities, why don’t they move? If all living things move, are buses and cars living things too? The answer to all these questions is that living things exhibit certain features. These features help us decide if they are living or non-living. Following are the characteristics based on which a student can easily conclude if an entity is living or not.

Do All Organisms Need Food?

All living things need food to survive. Plants produce their own food. Human beings and animals depend on plants for their food. It gives them the energy to perform their daily activities and energy to carry out life processes inside the body.

Do All Organisms Show Growth?

We grow with time. Every living thing grows. It may not be a visible change, but with time we show changes. For example, we are taller than what we used to be in our childhood, kittens turn into cats, a chick hatches from an egg to grow into a hen or cock. etc. Plants grow into different sizes and shapes with time, right from germination up till a mature tree.

Do All Organisms Respire?

We cannot live without breathing air. Animals and human beings inhale oxygen produced by plants and exhale carbon dioxide, this process is called respiration. It is through this process that energy is finally obtained from the food we take. Some animals, however, have different breathing mechanisms, for example, earthworms breathe through their skin, fish absorb the oxygen dissolved in the water through gills.

Respiration in plants is brought about by leaves through small pores on them. In the presence of sunlight, they take in carbon dioxide and give out oxygen through the process of photosynthesis. Amount of oxygen released in the process of food preparation by plants is much more than the oxygen used in respiration.

Do All Organisms Respond To Stimuli?

We all respond to the changes that take place in our environment. For instance, we might quickly pull our hands away if we touch a very hot surface. This response to the changes is called as stimuli. For example, an octopus releases a noxious cloud of ink if it is attacked by a predator. Cockroaches begin to move when we suddenly turn on lights since they are light-sensitive. Even plants respond to stimuli too, for instance, the Mimosa plant or the ‘touch-me-not’ plant folds its leaves upon being touched.

Living Organisms And Excretion

We all need food to survive. And not all food can be fully digested by our body. Elimination of this undigested waste from our body is called excretion. Plants use a different mechanism for excretion, some secrete, while others store up these wastes in a way that they do not harm other parts of the plant.

Do All Organisms Reproduce?

All organisms reproduce and it is one of the most basic requirements to ensure the survival of their species. There are different modes of reproduction. Some lay eggs, others give birth to younger ones. Plants reproduce through pollination, budding, fragmentation, spore formation and so on.

Do All Organisms Move?

All living organisms exhibit some form of movement. It is necessary for fulfilling the various functions required for survival (such as acquiring food, escaping predation, finding mates etc). Even plants exhibit some movement, though they are anchored in the soil.

Fruit and Seed Formation Without Fertilization

Fruit and Seed Formation Without Fertilization

Fruits and seeds are not only essential  in the life cycle of flowering plants; they are also utilized as sources of food. In a few species, a special mechanism has evolved to produce seed and fruit. This mechanism can prominently be seen in Asteraceae.  Read on to explore these special mechanisms.

Apomixis

Apomixis is a type of asexual reproduction that mimics sexual reproduction to produce seeds in flowering plants. Two types of apomixis are found in flowering plants. These are as follows:

1. An unfertilized diploid egg developing into the embryo through parthenogenesis. Example: Rosaceae
2. Embryo arising directly from the nucellar cells of the ovule. Example: Citrus

Polyembryony

Polyembryony may be defined as the phenomenon of more than one embryo developing from a single ovule. It was discovered by Leeuwenhoek. Polyembryony occurs commonly in many animals and plants, Example: Nine-banded armadillo. Polyembryony is classified into two types. These are as follows:

1. True polyembryony – More than one embryo develops from a single ovule. Example: Citrus
2. False polyembryony – More than one embryo develops from different ovules. Example: Mango

Parthenocarpy

Parthenocarpy may be defined as the production of fruit from an unfertilized egg. It can be achieved by naturally or artificially. Example: seedless watermelon.

Two types of parthenocarpy are found. These are as follows:

1. Stimulative parthenocarpy – In this process, pollination is required to produce fruits. Example: Seedless watermelons.
2. Vegetative parthenocarpy – In this process, pollination is not required to produce fruits. Example: Seedless cucumbers.

Hybrid cultivation of fruits by parthenocarpy is used to increase productivity. But, parthenocarpy process is expensive. As a result, hybrid seeds and fruits become quite expensive.

Frequently Asked Questions

1. What is Apomixis?

Apomixis is a type of asexual reproduction that mimics sexual reproduction to produce seeds in flowering plants.

2. What is Polyembryony?

Polyembryony is defined as the phenomenon of more than one embryo developing from a single ovule

3. What is Parthenocarpy?

Parthenocarpy is defined as the production of fruit from an unfertilized egg.

 

Vitamins - Types, Sources, and its Significance

What are Vitamins?

The vitamins are natural and essential nutrients, required in small quantities and play a major role in growth and development, repair and healing wounds, maintaining healthy bones and tissues, for the proper functioning of an immune system, and other biological functions. These essential organic compounds have diverse biochemical functions.

There are thirteen different types of vitamins and all are required for the metabolic processes. The discovery of the vitamins was begun in the year 1912 by a Polish American biochemist Casimir Funk. Based on his research and discoveries on vitamins, their sources, functions and deficiency disorders, he is considered as the father of vitamins and vitamin therapy.

Similar to minerals, vitamins cannot be synthesized by our body. Therefore, we need to get them from the food we consume or in extreme cases supplements to keep ourselves healthy.

Types of Vitamins

Based on the solubility, Vitamins have been classified into two different groups:

• Fat-Soluble Vitamins.
• Water-Soluble Vitamins.

Fat-soluble vitamin

Fat-soluble vitamins are stored in the fat cells and as the name suggests, these vitamins require fat in order to be absorbed. Vitamin A, D, E and K are fat-soluble vitamins.

Water-soluble vitamin

Water-soluble vitamins are not stored in our body as its excess gets excrete through the urine. Therefore, these vitamins need to be replenished constantly. Vitamin B and C are water-soluble vitamins.

Sources of Vitamins

The human body is so designed that it takes what it needs from the food we eat and then it passes out waste as excreta.

These organic substances are abundantly found in both plants and animals source and play a vital role in both growth and development and optimal health.

Listed below are the different types of vitamins along with their sources.

The best sources of fat-soluble vitamins include:

• Vitamin A: Found in potato, carrots, pumpkins, spinach, beef and eggs.
• Vitamin D: Found in fortified milk and other dairy products.
• Vitamin E: Found in fortified cereals, leafy green vegetables, seeds, and nuts.
• Vitamin K: Found in dark green leafy vegetables and in turnip or beet green.

vitamin C are abundantly found in all citrus fruits. Other sources of Vitamin B and C include:

• Vitamin B1 or Thiamin: Found in pork chops, ham, enriched grains and seeds.

• Vitamin B2 or Riboflavin: Found in whole grains, enriched grains and dairy products.

• Vitamin B3 or Niacin: Found in mushrooms, fish, poultry, and whole grains.

• Vitamin B5 or Pantothenic Acid: Found in chicken, broccoli, legumes and whole grains.

• Vitamin B6 or Pyridoxine: Found in fortified cereals and soy products.

• Vitamin B7 or Biotin: Found in many fruits like fruits and meats.

• Vitamin B9 or Folic Acid: Found in leafy vegetables.

• Vitamin B12: Found in fish, poultry, meat and dairy products.

• Vitamin C: Found in citrus fruits and juices, such as oranges and grapefruits.

Fruits - Formation, Parts and Types of Fruits

 

What is a Fruit?

Fruits are seed-bearing structures. It develops from a ripe ovary. They are a rich source of vitamins, minerals and fibers. Grapes, bananas, papaya, watermelon are some of the fruits consumed by humans. They are the main source of a balanced diet.

Let us have a detailed look at the parts, uses and types of fruits.

Parts of a Fruit

A fruit comprises the following parts:

• Pericarp
• Seeds

Pericarp

The pericarp is the wall of the ovary that develops as the wall of the fruits. The pericarp of the fruits might be fleshy as in guava, mango, etc. or might be dry as in mustard, walnut, etc. The pericarp is further differentiated into three layers, namely:

• Epicarp: Outermost layer, forms the peel.
• Mesocarp: Middle layer, fleshy, edible portion of the fruits
• Endocarp: Innermost layer, the inner rough portion where the seed is accommodated

Seeds

Seeds are ripened fertilized ovules. It is an embryonic plant enclosed in a protective outer covering.

Types of Fruits

Based on the number of ovaries and the number of flowers involved in the fruit formation, fruits are classified into three major groups namely:

Simple Fruits

These fruits develop from a single matured ovary in a single flower. Apple, banana, cherry pear, plum, tomato are few examples of simple fruits. The simple fruits are classified into the following categories:

• Drupes: These are also known as stone fruits since it contains a very hard seed inside the simple fruits. For eg., plum, cherry, peach.
• Berries: These type of fruits have a single seed in the center and are very juicy. For eg., grapes, blueberries.
• Pomes: Such fruits bloom from trees. For eg., apple, papaya
• Hesperidium and Pepos: They are slightly similar to the berries and include fruits such as watermelon, citrus fruits.

Aggregate Fruits

These fruits develop from a number of matured ovaries formed in a single flower. Individual ovaries are called “fruitlets.” Blackberry, raspberry, strawberry are few examples of aggregate fruits.

Composite Fruits

These fruits develop from a complete inflorescence. these are also known as multiple fruits. Composite fruits are of two types:

• Sorosis: These are found in mulberry, jackfruits and pineapple. They develop from catkin, spikes and spadix type of inflorescence.
• Syconus: This develops from hypanthodium type of inflorescence.

Also Read: Fruit and seeds formation without Fertilization

Uses of Fruits

Fruits are rich in vitamins and minerals which are essential for a healthy human body. For instance, we know that oranges are rich in vitamin C. Vitamin C is vital to neutralize any free radicals in our body. Also, acids in citrus fruits are very effective in skin whitening and exfoliation. Besides consumption, these citrus acids can help to get rid of mineral deposits and grease on cooking utensils.

Fiber-rich fruits like raspberries are very good for digestion. The protein in papaya, called papain, can help the breakdown of proteins, and therefore aid digestion. It also reduces acidity levels and eases indigestion.

Palm dates have a low glycemic index and hence, they are very useful in blood sugar regulation. Furthermore, it is high in dietary fiber and is very helpful for digestion.

Grapes have a chemical called Resveratrol that functions similar to aspirin, giving it the properties of an analgesic (painkillers).

 

Respiration

Respiration Definition

“Respiration is defined as a metabolic process wherein, the living cells of an organism obtains energy (in the form of ATP) by taking in oxygen and liberating carbon dioxide from the oxidation of complex organic substances.”

What is Respiration?

Respiration is a metabolic process that occurs in all organisms. It is a biochemical process that occurs within the cells of organisms. In this process, the energy (ATP-Adenosine triphosphate) is produced by the breakdown of glucose which is further used by cells to perform various functions. Every living species, from a single-celled organism to a dominant multicellular organism performs respiration.

Let us have a detailed look at the different types of respiration in organisms.

Types of Respiration

There are two types of respiration:

Aerobic respiration

It is a type of cellular respiration that takes place in the presence of oxygen to produce energy. It is a continuous process that takes place within the cells of animals and plants. This process can be explained with the help of the chemical equation:

Glucose(C6H12O6) + Oxygen(6O2) → Carbon dioxide(6CO2) + Water(6H2O)+  Energy (ATP)

Anaerobic respiration

It is a type of cellular respiration that takes place in the absence of oxygen to produce energy. The chemical equation for anaerobic respiration is

Glucose(C6H12O6) → Alcohol 2(C2H5O H) + Carbon dioxide 2(CO2) + Energy (ATP )

Phases of Respiration in Organisms

Respiration occurs in the cytosol and around the plasma membrane in prokaryotic cells. In eukaryotic cells, respiration takes place in the mitochondria, which is also considered the powerhouse of the cells.

This process is very much similar to the internal combustion of the car engine, wherein organic compounds and oxygen go in, while water and carbon dioxide comes out. The energy that is liberated powers the automotive (or cell).

The three phases of Respiration are:

Glycolysis

The molecules of glucose get converted into pyruvic acid which is oxidized to carbon dioxide and water, leaving two carbon molecules, known as acetyl-CoA. During the process of glycolysis, two molecules of ATP and NADH are produced. Pyruvate enters the inner matrix of mitochondria and undergoes oxidation in Kreb’s cycle

Oxidative Phosphorylation

Oxidative phosphorylation is the process in which ATP molecules are formed as a result of the transfer of electrons from NADH or FADH2 to O2 by a series of electron carriers. This process takes place within the mitochondria of a cell.

Citric Acid Cycle

This is also known as the tricarboxylic acid cycle or Kreb’s cycle. Two ATP molecules are produced in each phase of the citric acid cycle and it takes place within the mitochondrial matrix of a cell. The electrons generated in Kreb’s cycle move across the mitochondrial matrix.

 

Respiratory system

Respiratory System Definition

“Human Respiratory System is a network of organs and tissues that helps us breathe. The primary function of this system is to introduce oxygen into the body and expel carbon dioxide from the body.”

What is the Respiratory System?

As defined above, the human respiratory system consists of a group of organs and tissues that help us to breathe. Aside from the lungs, there are also muscles and a vast network of blood vessels that facilitate the process of respiration.

Human Respiratory System Diagram

To gain a clearer understanding, we have illustrated the human respiratory system and its different parts involved in the process.

Human Respiratory System Diagram showing different parts of the Respiratory Tract

Features of the Human Respiratory System

The respiratory system in humans has the following important features:

• The energy is generated by the breakdown of glucose molecules in all living cells of the human body.
• Oxygen is inhaled and is transported to various parts and is used in the process of burning food particles (breaking down glucose molecules) at the cellular level in a series of chemical reactions.
• The obtained glucose molecules are used for discharging energy in the form of ATP- (adenosine triphosphate)

Respiratory System Parts and Functions

Let us have a detailed look at the different parts of the respiratory system and their functions.

Nose

Humans have exterior nostrils, which are divided by a framework of a cartilaginous structure called the septum. This is the structure that separates the right nostril from the left nostril. Tiny hair follicles that cover the interior lining of nostrils act as the body’s first line of defense against foreign pathogens. Furthermore, they provide additional humidity for inhaled air.

Larynx

Two cartilaginous chords lay the framework for the larynx. It is found in front of the neck and is responsible for vocals as well as aiding respiration. Hence, it is also informally called the voice box. When food is swallowed, a flap called the epiglottis folds over the top of the windpipe and prevents food from entering into the larynx.

Pharynx

The nasal chambers open up into a wide hollow space called the pharynx. It is a common passage for air as well as food. It functions by preventing the entry of food particles into the windpipe. The epiglottis is elastic cartilage, which serves as a switch between the larynx and the esophagus by allowing the passage of air into the lungs, and food in the gastrointestinal tract.

Have you ever wondered why we cough when we eat or swallow?

Talking while we eat or swallow may sometimes result in incessant coughing. The reason behind this reaction is the epiglottis. It is forced to open for the air to exit outwards and the food to enter into the windpipe, triggering a cough.

Trachea

The trachea or the windpipe rises below the larynx and moves down to the neck. The walls of the trachea comprise C-shaped cartilaginous rings which give hardness to the trachea and maintain it by completely expanding. The trachea extends further down into the breastbone and splits into two bronchi, one for each lung.

Bronchi

The trachea splits into two tubes called the bronchi, which enter each lung individually. The bronchi divide into secondary and tertiary bronchioles, and it further branches out into small air-sacs called the alveoli. The alveoli are single-celled sacs of air with thin walls. It facilitates the exchange of oxygen and carbon dioxide molecules into or away from the bloodstream.

Lungs

Lungs are the primary organs of respiration in humans and other vertebrates. They are located on either side of the heart, in the thoracic cavity of the chest. Anatomically, the lungs are spongy organs with an estimated total surface area between 50 to 75 sq meters. The primary function of the lungs is to facilitate the exchange of gases between the blood and the air. Interestingly, the right lung is quite bigger and heavier than the left lung.

Also Read: Respiration

Respiratory Tract

The respiratory tract in humans is made up of the following parts:

• External nostrils – For the intake of air.
• Nasal chamber – which is lined with hair and mucus to filter the air from dust and dirt.
• Pharynx – It is a passage behind the nasal chamber and serves as the common passageway for both air and food.
• Larynx – Known as the sound box as it houses the vocal cords, which are paramount in the generation of sound.
• Epiglottis – It is a flap-like structure that covers the glottis and prevents the entry of food into the windpipe.
• Trachea – It is a long tube passing through the mid-thoracic cavity.
• Bronchi – The trachea divides into left and right bronchi.
• Bronchioles – Each bronchus is further divided into finer channels known as bronchioles.
• Alveoli – The bronchioles terminate in balloon-like structures known as the alveoli.
• Lungs – Humans have a pair of lungs, which are sac-like structures and covered by a double-layered membrane known as pleura.

Air is inhaled with the help of nostrils, and in the nasal cavity, the air is cleansed by the fine hair follicles present within them. The cavity also has a group of blood vessels that warm the air. This air then passes to the pharynx, then to the larynx, and into the trachea.

The trachea and the bronchi are coated with ciliated epithelial cells and goblet cells (secretory cells) which discharge mucus to moisten the air as it passes through the respiratory tract. It also traps the fine bits of dust or pathogen that escaped the hair in the nasal openings. The motile cilia beat in an ascending motion, such that the mucus and other foreign particles are carried back to the buccal cavity where it may either be coughed out (or swallowed.)

Once the air reaches the bronchus, it moves into the bronchioles, and then into the alveoli.

Respiratory System Functions

The functions of the human respiratory system are as follows:

Inhalation and Exhalation

The respiratory system helps in breathing (also known as pulmonary ventilation.) The air inhaled through the nose moves through the pharynx, larynx, trachea, and lungs. The air is exhaled back through the same pathway. Changes in the volume and pressure in the lungs aid in pulmonary ventilation.

Exchange of Gases between Lungs and Bloodstream

Inside the lungs, the oxygen and carbon dioxide enter and exit respectively through millions of microscopic sacs called alveoli. The inhaled oxygen diffuses into the pulmonary capillaries, binds to hemoglobin, and is pumped through the bloodstream. The carbon dioxide from the blood diffuses into the alveoli and is expelled through exhalation.

Exchange of Gases between Bloodstream and Body Tissues

The blood carries the oxygen from the lungs around the body and releases the oxygen when it reaches the capillaries. The oxygen is diffused through the capillary walls into the body tissues. The carbon dioxide also diffuses into the blood and is carried back to the lungs for release.

The Vibration of the Vocal Cords

While speaking, the muscles in the larynx move the arytenoid cartilage. These cartilages push the vocal cords together. During exhalation, when the air passes through the vocal cords, it makes them vibrate and creates sound.

Olfaction or Smelling

During inhalation, when the air enters the nasal cavities, some chemicals present in the air bind to it and activate the receptors of the nervous system on the cilia. The signals are sent to the olfactory bulbs via the brain.

Respiration is one of the metabolic processes which plays an essential role in all living organisms. However, lower organisms like the unicellular do not “breathe” like humans – instead, they utilize the process of diffusion. Annelids like earthworms have a moist cuticle which helps them in gaseous exchange. Respiration in fish occurs through special organs called gills. Most of the higher organisms possess a pair of lungs for breathing.

To learn more about respiration, check out the video below:

      

Frequently Asked Questions

What is the human respiratory system?

The human respiratory system is a system of organs responsible for inhaling oxygen and exhaling carbon dioxide in humans. The important respiratory organs in living beings include- lungs, gills, trachea, and skin.

What are the important respiratory system parts in humans?

The important human respiratory system parts include- Nose, larynx, pharynx, trachea, bronchi, and lungs.

What is the respiratory tract made up of?

The respiratory tract is made up of nostrils, nasal chamber, larynx, pharynx, epiglottis, trachea, bronchioles, bronchi, alveoli, and lungs.

What are the main functions of the respiratory system?

The important functions of the respiratory system include- inhalation and exhalation of gases, exchange of gases between bloodstream and lungs, the gaseous exchange between bloodstream and body tissues, olfaction, and vibration of vocal cords.

What are the different types of respiration in humans?

The different types of respiration in humans include- internal respiration, external respiration, and cellular respiration. Internal respiration includes the exchange of gases between blood and cells, external respiration is the breathing process, whereas cellular respiration is the metabolic reactions taking place in the cells to produce energy.

What are the different stages of aerobic respiration?

Aerobic respiration is the process of breaking down glucose to produce energy. It occurs in the following different stages- glycolysis, pyruvate oxidation, citric acid cycle or Krebs cycle, and electron transport system.

Why do the cells need oxygen?

Our body cells require oxygen to release energy. The oxygen inhaled during respiration is used to break down the food to release energy.

What is the main difference between breathing and respiration in humans?

Breathing is the physical process of inhaling oxygen and exhaling carbon dioxide in and out of our lungs. On the contrary, respiration is the chemical process where oxygen is utilized to break down glucose to generate energy to carry out different cellular processes.