Alimentary Canal: Mouth, Pharynx & Oesophagus | Biology for JAMB PDF Download

Food is a fundamental necessity for all living organisms, providing essential components such as carbohydrates, proteins, fats, vitamins, and minerals. These nutrients are vital for energy production, tissue growth, and repair. Additionally, water, an essential component of food, plays a crucial role in metabolic processes and prevents dehydration. 

However, the biomacromolecules present in food cannot be directly utilized by our body. They need to be broken down and converted into simpler forms in the digestive system through a process called digestion. This complex process involves both mechanical and biochemical methods carried out by our digestive system. In this EduRev document, we will explore the importance of digestion in converting food into absorbable forms for our body's utilization.

What is Digestion?

To perform various functions of the body, energy is required, which is obtained from food. The process of conversion of complex food material into simple and diffusible forms by hydrolysis is termed as Digestion.

Human Digestive System

• All parts of the body are involved in the uptake and digestion of food along with the elimination of undigested material.

Alimentary Canal

The alimentary canal is mainly referred to as the pathway by which food enters our body and moves out through the anus after digestion. It is a tube-like structure that starts from the mouth and ends in the anus.

• The alimentary canal plays a primary role in human digestion and is also termed the digestive tract.

The following flowchart will show parts of Alimentary Canal:

1. Mouth and Buccopharyngeal Cavity

• The mouth is also called the buccal cavity or the oral cavity. In the human digestive system the mouth is the upper end of the beginning of the alimentary canal, which leads to the pharynx and to the oesophagus.
  

• In humans, both the mouth or the buccal cavity and the nasal cavity are separated by the palate. The buccal cavity mainly comprises the primary organ of the digestive system including the teeth, tongue and salivary glands.

• The mouth is an opening through which the food is taken inside the body.
  It is bounded by lips and its inner parts comprises of:
  

• The upper jaw is fixed, which forms the roof of the mouth cavity and consists of the palate, teeth, and gums surrounding the teeth. The lower jaw is movable and forms the floor of the mouth cavity, which consists of the tongue along with the teeth and gums surrounding them. 
• The mouth plays an important role in speech, helps in breathing in certain cases, when the nose is blocked and during strenuous exercise. It is also the most important part of the human body, which permits us to enjoy the food we eat and also to communicate with the rest of the world.

Different Parts of the Buccal Cavity

(i) Tongue

• It is a large, muscular organ, which occupies most of the oral cavity and can take up a variety of shapes and positions.
  
• There are 50 to 100 taste receptor cells in each taste buds, which are located in the lining of the mouth.

It is the main sense organ of human beings and is involved in:

(ii) Buccal mucosa

• It is the inner lining of the cheeks and the back of the lips. It provides a round shape to the cheeks.
  
  Question for Alimentary Canal: Mouth, Pharynx & Oesophagus

  Try yourself:This is a muscular organ in the mouth that helps position the food between the teeth and is covered in nerve endings that allow us to taste our food.

  • A.

    Tongue
  • B.

    Teeth
  • C.

    Gums
  • D.

    Soft Palate

  Explanation

  The tongue is a muscular organ in the mouth of a typical vertebrate. It manipulates food for mastication and swallowing as part of the digestive process, and is the primary organ of taste.

  Hence, the correct option is A

  NCERT Reference: Topic “Alimentary Canal” of chapter 'Digestion and Absorption' of NCERT

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(iii) Teeth 

• The teeth are the strongest and rigid substances in the human body. A normal adult has 32 teeth and is divided into incisor, canine, molars and premolars. There is a third molar, which is called the wisdom teeth, which appear in a person’s late teens or early twenties.
  
  Question for Alimentary Canal: Mouth, Pharynx & Oesophagus

  Try yourself:How many types of teeth are present in an adult?

  • A.

    2
  • B.

    3
  • C.

    4
  • D.

    5

  Explanation

  Most adults have 32 teeth, called permanent or secondary teeth, & they are of 4 types.

  • Incisors
  • Canines also called cuspids
  • Premolars also called bicuspids
  • Molars

  Hence, the correct option is C

  NCERT Reference: Topic “Alimentary Canal” of chapter 'Digestion and Absorption' of NCERT

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2. Pharynx

The pharynx is the common passage of the respiratory system and digestive system located in the throat. It connects the mouth to the oesophagus and the nose to the larynx. Food and water from the oral cavity and air from both the oral and nasal cavity comes to the pharynx. The pharynx is present in vertebrates and also in invertebrates such as annelids, arthropods, etc.

Location

• The pharynx is present behind the oral and nasal cavity. It is a part of the throat and a common passage for both the digestive and respiratory system.
• The pharynx opens into the oesophagus in the digestive tract and opens into the larynx in the respiratory tract.
• The pharynx is also present in some of the invertebrates. The shape and size vary in different organisms. It may be thick and muscular, rotated or turned outward.

Structure and Parts

The pharynx can be divided into three main regions according to its location. They are:

1. Nasal pharynx – As the name suggests, it is the part of the pharynx that is present posterior to the nasal cavity.
2. Oral pharynx – It is the part behind the oral cavity and continues in the throat till the hyoid bone.
3. Laryngeal pharynx – It is the lowermost part of the pharynx from the epiglottis and continues to the oesophagus.

The main features of the pharynx are:

• The wall of the pharynx consists of both longitudinal and circular muscles. These muscles determine the shape of the lumen.
• Isthmus connects the oropharynx to the nasopharynx. It is useful for breathing through the mouth and inserting food into the oesophagus through the nasal tube if required.
• The nasopharynx is lined with pseudostratified, columnar and ciliated respiratory epithelium.
• Eustachian tubes connect the middle ears to the pharynx. It helps in equalizing air pressure on the eardrum.
• The wall of the oropharynx is made up of non-keratinized, stratified squamous epithelium.
• The opening of the pharynx to the larynx is controlled by a muscular flap known as epiglottis. It is present over the larynx opening and prevents food from entering the trachea.
• The wall of the laryngopharynx consists of stratified squamous epithelium.
• Laryngopharynx regulates the movement of air to the lungs and food to the oesophagus.
• Pharyngeal, tubal, palatine and lingual tonsils present in different parts of the pharynx are called Waldeyer’s ring. These are lymphoid tissues present in the nasopharynx and oropharynx. It provides defence against the invasion of microorganisms in the digestive and respiratory tract.

Bored of reading and want to learn the concepts by watching a video? Refer this video for detailed explanation of Alimentary Canal:
Alimentary Canal: Digestion & Absorption

Function

The pharynx performs a dual function. It allows passage for both air and food. 

The main functions of the pharynx are:

• It makes air warm and humidifies it before reaching the lungs.
• It helps in the movement of food to the oesophagus. Circular muscles help in pushing the food down and longitudinal muscles help in swallowing the food by lifting and widening the walls.
• The pharynx also helps in speech, it amplifies the sound produced by the larynx or soundbox.
• Lymphoid tissues present in the pharynx are the first line of defence against foreign pathogens.

3. Oesophagus

The food we swallow passes through a pipe that leads to the stomach. This pipe is known as the food pipe or the oesophagus. Food reaches the stomach from the pharynx through peristaltic contractions.
Oesophagus

What is a Food Pipe?

• “Food pipe or oesophagus is the part of the digestive system of vertebrates with a distinct path exclusively meant for passage of food.”
• A food pipe is a muscular tube that is 25 centimetres long, passing just behind the heart region connecting the mouth to the stomach. It is made up of connective tissues and is the uppermost part of the digestive system.
• The upper part of the oesophagus is behind the windpipe. Oesophagus joins the stomach at a point called the gastro-oesophageal junction. When we swallow food, the oesophagus contracts and squeezes the food which pushes the food down towards the stomach.

Layers of Food Pipe

The food pipe or oesophagus is divided into the following layers:

• Mucosa: The innermost layer which forms irregular folds in the stomach and small finger-like foldings called villi.
  • These modifications increase surface area for maximum absorption of digested food.
  • Mucosal epithelium has Goblet cells which secrete mucus for lubrication.
  • It forms a gastric gland in the stomach.
  • It forms crypts in between the bases of villi in the intestine (crypts of Lieberkuhn) have cells called as Paneth cells which secrete antibacterial lysozyme.
• Submucosa: It is made up of loose connective tissues containing nerves, blood and lymph vessels. The layer responsible for producing secretions
• Muscularis: It is made up of smooth muscles. Food is pushed down through this layer made up of muscles.
• Serosa: Outermost layer and made up of mesothelial cells. Oesophagus is attached to the other parts through this outer layer.

Learn the Anatomy of the Alimentary Canal through this video:
Video: Anatomy of Alimentary Canal

Functions of Food Pipe

The food pipe or oesophagus performs the following important functions:

• The food we eat reaches the oesophagus after passing through the larynx.
• After the buccal cavity, the oesophagus is the next point of contact for food into the gastrointestinal tract.
• Responsible for preventing the entry of food into the windpipe by controlling the movement of the epiglottis.
• Radially symmetric contractions of the oesophagus help push food downwards known as peristalsis.
• Rhythmic contractions and relaxations of oesophageal muscles result in the swift movement of food towards the gastro-oesophageal junction.

Care needs to be taken about the health of the oesophagus or food pipe as negligence can cause severe disorders in the food pipe. One such ailment of the food pipe is Oesophageal cancer.

Structure of Teeth

There are three parts of the tooth. These are:

1. Crown: It is the outer part of the tooth, exposed outside gums.
2. Neck: It is the middle part of the tooth which is embedded inside the gums. 
3. Root: It is the part of the tooth that is inserted inside the socket of the jaw bone. (Alveoli)

• The crown part of the tooth is made up of a very hard substance called Enamel. It is the hardest material in the animal kingdom.
• Enamel is ectodermal. It is secreted by Ameloblast cells of the ectoderm. It has the maximum amount of inorganic salt (96%) in it, Inorganic salt is mainly found in the form of phosphate and carbonate of Ca, Mg, Na and K. 3% of water is found in the enamel. Along the keratin & ossein protein (1%) are also found in teeth. Ossein is a protein of bones. The remaining part of the tooth develops from the mesoderm of the embryo.
• Dentine is the main part of the tooth. Approximately 69% inorganic salts are present in dentine and 65% are present in cement. (62% inorganic salts are present in bones.) 
• Dentine surrounds a cavity called pulp-cavity. This cavity contains soft connective tissue, blood capillaries, nerve fibres. The pulp cavity is necessary for the nutrition and survival of the teeth. 
• A special type of cells from the lining of the pulp-cavity called the Odontoblast cells. These cells are the dentine secreting cells. The cytoplasmic process of odontoblasts is embedded into dentine in the form of the fine tubule. These processes are called canaliculi. These canaliculi secretes dentine. The teeth continue to grow till the odontoblast cells remain active.

Types of Teeth Found in Mammals

1. Incisor: These are long, chisel-like teeth for gnawing the food. They are more developed in gnawing animals.

• Example: lagomorphs, rodents, the tusk of elephant are modification of upper Incisor. Tusk is used to protecting from enemies, attack on enemies (not for feeding purpose)

2. Canines: These are sharp-pointed teeth meant for tearing the food. Canines are most developed in carnivorous animals. Canines are absent in herbivorous animals.

• Example: Tiger lions are carnivorous animals having canines. Rabbits do not have canines. In herbivores, the space of canine in gums is empty and this empty space is called diastema.

3. Pre Molar: These teeth are meant for chewing and crushing food, they are triangular in shape.

4. Molars (Cheek teeth): These are also meant for chewing & crushing food. They are rectangular in shape. Premolar and molar help in the mastication of food. In humans teeth of the upper jaw are attached to the maxilla bone. While teeth of the lower jaw are attached to the mandible bone.

Difference Between Milk Teeth and Permanent Teeth

• There will be two phases of dentition in one's life. i.e., primary dentition (milk teeth or deciduous teeth) and secondary dentition (permanent teeth). The permanent teeth are visible throughout a person’s lifetime. The baby teeth continue to grow till a child is about 11 years old, after that milk teeth fall and give rise to permanent teeth.

Types Of Teeth on Different Basis

1. On the Basis of Appearance in Life  

• Monophyodont: The teeth which appear only once in life.
  Example: Premolar & Last molar of man.
• Diphyodont: The teeth which appear twice in life.
  Example: Incisors, Canines, Molars of humans.

2. On the Basis of Position From Jaw

• Thecodont: The teeth which are present in the bony socket of the jaw.
  Example: Man & crocodile.

3. On the Basis of Structure and Function

• Heterodont: When the teeth are of a different type in mammals on the basis of structure and function.
  Example: Mammal.

Dental Formula

The method of expressing or describing the total number of teeth in man and animals according to the arrangement is termed as the Dental Formula. This formula is expressed using letters and figures. The letters used in this formula are based on the 4 types of teeth like– Incisor, Canine, Premolar, and Molar.

The Dental Formula is expressed as:

(The number of each type of teeth in the upper jaw) / (The number of teeth on one side of the lower jaw)

Dental Formula =  (2 incisors 1 canine 2 premolar 3 molar) / (2 incisors 1 canine 2 premolar 3 molar)

Humans have two dental formulae:

The primary dentition (20 teeth):

i2/2 c1/1m2/2=10

The permanent dentition (32 teeth):

i2/2 c1/1pm2/2m3/3=16
(2123/2123)×2=32

Where: i – Incisors, c-Canine  pm-premolar and m-Molar

Among all other mammals, both humans and apes have similar sets of teeth and dental formulae.

In humans, premolar teeth appear in the alveoli of molar teeth while permanent molar teeth are developed in new alveoli.

In this document you have learnt the following:

• The alimentary canal is divided into the following parts: Mouth and Buccopharyngeal Cavity, Oesophagus, Stomach, Small Intestine, Large Intestine.
• In humans, both the mouth or the buccal cavity and the nasal cavity are separated by the palate.
• The pharynx can be divided into three main regions according to its location - Nasal, Oral &  Laryngeal.
• Food pipe is divided into 4 layers: Mucosa, sub-mucosa, muscularis, serosa and performs different functions in the process of digestion.
• Teeth are ecto mesoderma in origin. A major portion of teeth arises from Dermis. Part of the tooth present outside the gums only is derived from ectoderm or Epidermis (Enamel part).
• Enamel is ectodermal. It is secreted by Ameloblast cells of the ectoderm. It has the maximum amount of inorganic salt (96%) in it, Inorganic salt is mainly found in the form of phosphate and carbonate of Ca, Mg, Na and K. 3% of water is found in the enamel.
• In humans, premolar teeth appear in the alveoli of molar teeth while permanent molar teeth are  developed in new alveoli.
• The dental formula in humans is:
  Dental formula = (2 incisors 1 canine 2 premolar 3 molar) / (2 incisors 1 canine 2 premolar 3 molar)

You can test your knowledge with related questions that have been asked in NEET:

Q.1. These cells of ‘Crypts of Lieberkuhn’ secrete lysozyme 
(a) Argentaffin cells 
(b) Kupffer cells 
(c) Zymogen cells 
(d) Paneth cells

Correct Answer is Option (d)
The crypts of Lieberkuhn lie between the finger-like projections of the small intestine called villi. - The cells of these glands are called paneth cells, which secrete antibacterial lysozyme.

Q.2. The cells which secrete tooth enamel are known as
(a) ameloblast
(b) dentoblast
(c) odontoblast
(d) osteoblast

Correct Answer is Option (a)
Enamel is ectodermal. It is secreted by Ameloblast cells of the ectoderm.

You can now check your understanding of this topic by giving this test:

Test: Alimentary Canal: Mouth, Pharynx & Oseophagus - 1