Human Nutrition PDF

# Human Nutrition ## Can you recall? 1. **What is nutrition?** - *Nutrition is the sum of the processes by which an organism consumes and utilizes & food substances.* 2. **Enlist life processes that provide us energy to perform different activities?** - *Life processes that provide us energy to...

# Human Nutrition ## Can you recall? 1. **What is nutrition?** - *Nutrition is the sum of the processes by which an organism consumes and utilizes & food substances.* 2. **Enlist life processes that provide us energy to perform different activities?** - *Life processes that provide us energy to perform different activities are: Nutrition, Respiration, Transportation, Excretion. * ## Think about it - **Our diet includes all necessary nutrients. Still we need to digest it. Why is it so?** - *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 the following organs:* 1. **Mouth:** Also called as oral or buccal cavity 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. 2. **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 lifetime, we get only two sets of teeth, milk teeth and permanent teeth. This is called diphyodont dentition. * We have four different types 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: 2 - 1 - 2 - 3 / 2 - 1 - 2 - 3** ### Tooth Anatomy - 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. ### Dentition The study of teeth with respect to their number, arrangement, development etc is known as dentition. ### 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. **Do you know?** 1. **Who controls the deglutition?** * *The brain controls the deglutition by coordinating the muscles involved in the process.* 2. **Is deglutition voluntary or involuntary?** * *Deglutition can be both voluntary and involuntary.* ### 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. ### 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. ### Stomach parts 1. **Cardia or Cardiac:** It is the first part in which oesophagus opens. The cardia surrounds the opening of oesophagus and stomach called cardiac sphincter. The cardiac sphincter prevents back flow or regurgitation of food from stomach to oesophagus. 2. **Fundus:** It is the dome shaped region above and left of cardia. 3. **Body:** It forms the large central portion of stomach that stores the food. 4. **Pylorus:** It is a narrow posterior region of stomach. It opens into duodenum, the initial part of small intestine. This opening is guarded by a set of sphincter muscles called pyloric sphincter. It regulates the flow of food from stomach to small intestine. * The stomach temporarily stores the food and gives the feeling of satiety. * It churns the food and helps in mixing the food with gastric juice. ### Small intestine -In human, it is about 6 meters long and 2.5 cms broad tube coiled within abdominal cavity. The coils are held together by mesenteries, supporting the blood vessels, lymph vessels and nerves. It is divided into three parts. 1. **Duodenum:** It is about 26 cm long 'U' shaped structure. The duodenum turns towards left side of abdominal cavity below the stomach. 2. **Jejunum:** It is about 2.5 meters long, coiled middle portion of small intestine. It is narrower than the duodenum. 3. **Ileum:** It is about 3.5 meters long. It is highly coiled and little broader than jejunum. The ileum opens into the caecum of large intestine at ileocaecal junction. ### Large Intestine - Ileum opens into large intestine. - It is 1.5 meters in length. It is wider in diameter and shorter than small intestine. - It consists of caecum, colon and rectum. 1. **Caecum:** Caecum is a small, blind sac present at the junction of ileum and colon. It is 6cm in length. It hosts some symbiotic microorganisms. An elongated worm like vermiform appendix arises from the coecum. Appendix is in herbivorous animals for the digestion of cellulose. 2. **Colon:** Caecum opens into colon. Colon is tube like-organ consist of three parts, ascending colon, transverse colon and descending colon. The colon is internally lined by mucosal cells. 3. **Rectum:** It is the posterior region of large intestine. It temporarily stores the undigested waste material called feces till it is egested out through anus. 4. **Anus:** Anus is the terminal opening of alimentary canal. It is guarded by sphincter. It expels fecal matter by a process called egestion or defaecation. ### 14.2 Histological structure of alimentary canal ## Find out 1. **What is heart burn? Why do we take antacids to control it?** 2. **You must have heard of appendicitis. It is inflammation of appendix. Find more information about this disorder.** ## Activity - **Make a model of human digestive system in a group.**