Maharashtra Board Class 11 Biology Chapter 14 Human Nutrition PDF Download

14. Human Nutrition

Nutrition is the sum of the processes by which an organism consumes and utilises food substances. WHO (World Health Organisation) defines nutrition as the intake of food, considered in relation to the body's dietary needs. The dietary needs of a healthy human being include carbohydrates, proteins, fats, vitamins, minerals, water and fibres in adequate amounts. The term nutrition includes the processes like ingestion, digestion, absorption, assimilation and egestion. Food provides energy and organic material for growth and tissue repair. Vitamins and minerals are also required in small quantities for nutrition. The food that is consumed needs to be processed before it is utilised.

Digestion is defined as the process by which the complex, non-diffusible and non-absorbable food substances are converted into simple, diffusible and assimilable substances.

14.1 Human Digestive System

Digestive system of man consists of alimentary canal and associated digestive glands.

Alimentary Canal

It is a long tubular structure starting from mouth and ending with anus. It is about 8-10 meters long and consists of following organs:

Mouth

Also called as oral or buccal cavity. It is bounded by fleshy lips. Its side walls are formed of cheeks, roof is formed by palate and floor by tongue. It is internally lined by a mucous membrane. Salivary glands open into the buccal cavity.

Teeth

32 teeth are present in the buccal cavity of an adult human being. Human dentition is described as thecodont, diphyodont and heterodont. It is called thecodont type because each tooth is fixed in a separate socket present in jaw bones by gomphosis type of joint. In our life time, we get only two sets of teeth, milk teeth and permanent teeth. This is called diphyodont dentition. We have four different type of teeth hence we are heterodont. Types of teeth are incisors (I) canines (C) premolars (PM) and molar (M). Each half of each jaw has two incisors, one canine, two premolars and three molars.

Thus, dental formula of adult human can be represented as \(I \frac{2}{2}, C \frac{1}{1}, PM \frac{2}{2}, M \frac{3}{3} = \frac{2,1,2,3}{2,1,2,3}\)

i.e. 8 × 2 = 16 teeth in each jaw. = 32 teeth

Teacher's Note

Humans have two sets of teeth in their lifetime - milk teeth and permanent teeth. Just like you lose your baby teeth and get new permanent teeth, other animals also change their teeth at different ages.

Exam Trick

Remember the dental formula: I-C-PM-M = 2-1-2-3. Count on your fingers: 2 incisors, 1 canine, 2 premolars, 3 molars in each half of each jaw. Multiply by 4 (both halves, both jaws) = 32 teeth total.

Points to Remember

Thecodont means each tooth is fixed in a separate socket in the jaw bone.
Diphyodont means we get only two sets of teeth in our lifetime.
Heterodont means we have four different types of teeth.
An adult human has 32 teeth total.
Dentition is the study of teeth with respect to their number, arrangement and development.

A tooth consists of the portion that projects above the gum called crown and the root that is made up of two or three projections which are embedded in gum. A short neck connects the crown with the root. The crown is covered by the hardest substance of the body called enamel. Enamel is made up of calcium phosphate and calcium carbonate. Basic shape of tooth is derived from dentin, a calcified connective tissue. The dentin encloses a cavity called pulp cavity. It is filled with connective tissue pulp. Pulp cavity contains blood vessels and nerves. Pulp cavity has extension in the root of the tooth called root canal. The dentin of the root of tooth is covered by cementum, a bone like substance that attaches the root to the surrounding socket in the gum.

Teacher's Note

The enamel on your teeth is the hardest substance in your body. It protects your teeth from breaking when you eat hard things like apples and nuts. If you do not brush your teeth, bacteria damage this enamel and cause cavities.

Exam Trick

Tooth structure from outside to inside: Enamel → Dentin → Pulp cavity. Think of it like layers of an onion - hard outer layer, softer middle, soft inside with nerves and blood vessels.

Points to Remember

Crown is the visible part of the tooth above the gum.
Root is embedded in the gum and jaw bone.
Enamel is the hardest substance in human body.
Dentin is calcified connective tissue that gives shape to tooth.
Pulp cavity contains blood vessels and nerves that keep tooth alive.

Tongue

It is a muscular, fleshy organ and roughly triangular in shape. It lies along the floor of the buccal cavity. The upper surface of the tongue bears numerous projections called papillae. Some papillae bear sensory receptors called taste buds.

Pharynx

The buccal cavity leads to a short pharynx. Pharynx is a common passage for food and air. The upper region of pharynx is called trachea. The pharynx opens into trachea through an opening called glottis. The glottis is guarded by a cartilaginous flap called epiglottis. The epiglottis closes during the swallowing (deglutition) action and prevents entry of food into the trachea. The lower region of pharynx is called oropharynx. Oropharynx opens into oesophagus through gullet.

Oesophagus

The oesophagus is a thin, muscular tube. It lies behind the trachea. This 25cm long tube passes through the neck, central aspect of rib cage, pierces the diaphragm and joins the stomach. It is lined by mucus cells. Mucus lubricates the passageway of food. Histologically, oesophagus is made up of longitudinal and circular muscles. The rhythmic wave of contraction and relaxation of these muscles is called peristalsis that helps in passage of food through oesophagus.

Teacher's Note

When you swallow food, it does not fall down to your stomach because of peristalsis. This is muscle movement that pushes food down like a wave. It is the same reason why astronauts in space can swallow and eat normally even without gravity.

Exam Trick

Peristalsis = wave-like movements. Remember: Peri = around, Stalsis = push. The muscles push food in waves from mouth to stomach, even if you are standing on your head!

Points to Remember

Oesophagus is about 25 cm long muscular tube.
It connects mouth to stomach.
Peristalsis is rhythmic wave-like contraction and relaxation of muscles.
Mucus in oesophagus lubricates food for easy passage.
Epiglottis prevents food from entering trachea during swallowing.

Stomach

The stomach is located in the upper left portion of the abdominal cavity. It is a muscular sac-like 'J' shaped organ, around 25 to 30cm in length. It is divided into upper cardiac region and lower pyloric region.

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