● `color{violet}("Food")` is one of the basic requirements of all `color{violet}("living organisms.")`

● The major components of our food are `color{brown}("carbohydrates, proteins")` and `color{brown}("fats.")`

● `color{brown}("Vitamins and minerals")` are also required in `color{violet}("small quantities.")`

● `color{violet}("Food")` provides `color{violet}("energy and organic")` materials for growth and repair of tissues.

● The `color{brown}("water")` we take in,plays an important role in `color{violet}("metabolic processes")` and also prevents `color{violet}("dehydration")` of the body.

● `color{brown}("Biomacromolecules")` in `color{violet}("food")` cannot be utilized by our body in their original form.

● They have to be broken down and converted into simple substances in the `color{violet}("digestive system.")`

● This process of conversion of `color{violet}("complex food substances")` to `color{violet}("simple absorbable")` forms is called `color{brown}("digestion")` and is carried out by our `color{violet}("digestive system")` by `color{violet}("mechanical")` and `color{violet}("biochemical methods.")`

● The human `color{violet}("digestive system")` consists of:

`star` `color{brown}("The alimentary canal")`

`star` `color{brown}("The associated glands.")`

● The `color{violet}("alimentary canal")` begins with an anterior opening – the `color{brown}("mouth,")` and it opens out posteriorly through the `color{brown}("anus.")`

`star` `color{green}("Buccal cavity:")`

● The `color{violet}("mouth leads")` to the `color{violet}("buccal cavity")` or `color{violet}("oral cavity")`.

● The `color{violet}("oral cavity")` has a number of `color{brown}("teeth")` and a `color{brown}("muscular tongue.")`

● Each `color{violet}("tooth")` is embedded in a `color{violet}("socket of jaw bone.")`

● This type of attachment is called `color{brown}("thecodont.")`

● Majority of `color{violet}("mammals")` including human being forms two sets of `color{violet}("teeth")` during their life, a set of temporary milk or `color{violet}("deciduous teeth")` replaced by a set of permanent or `color{violet}("adult teeth.")`

● This type of dentition is called `color{brown}("diphyodont.")`

● An adult human has `color{violet}("32 permanent teeth")` which are of four different types (`color{violet}("Heterodont dentition")` ), namely, incisors (`color{violet}(I)`), canine (`color{violet}(C)`), premolars (`color{violet}("PM")`) and molars (`color{violet}("M")`).

● Arrangement of teeth in each half of the upper and lower jaw in the order `color{brown}("I, C, PM, M")` is represented by a `color{violet}("dental formula")` which in human is

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● The `color{violet}("hard chewing")` surface of the `color{violet}("teeth")`, made up of `color{brown}("enamel,")` helps in the `color{violet}("mastication of food.")`

● The `color{brown}("tongue")` is a freely `color{violet}("movable muscular organ")` attached to the floor of the `color{violet}("oral cavity")` by the frenulum.

● The upper surface of the tongue has `color{violet}("small projections")` called `color{brown}("papillae,")` some of which bear taste buds.

`star` `color{green}("Pharynx:")`

● The `color{violet}("oral cavity")` leads into a short `color{brown}("pharynx")` which serves as a common passage for `color{violet}("food and air")`.

● The `color{brown}("oesophagus")` and the `color{brown}("trachea")` (wind pipe) open into the pharynx.

● A cartilaginous flap called `color{brown}("epiglottis")` prevents the entry of `color{violet}("food")` into the `color{brown}("glottis")` – opening of the wind pipe – during swallowing.

`star` `color{green}("Oesophagus:")`

● The `color{violet}("oesophagus")` is a thin, long tube which `color{violet}("extends posteriorly")` passing through the neck, thorax and diaphragm and leads to a `color{violet}("‘J’")` shaped bag like structure called `color{brown}("stomach.")`

● A muscular sphincter (`color{brown}("gastro-oesophageal")`) regulates the opening of `color{violet}("oesophagus")` into the `color{violet}("stomach.")`

`star` `color{green}("Stomach:")`

● The `color{violet}("stomach")`, located in the `color{violet}("upper left portion")` of the `color{violet}("abdominal cavity")`, has three major parts – a cardiac portion into which the `color{violet}("oesophagus")` opens, a `color{brown}("fundic")` region and a pyloric portion which opens into the first part of `color{violet}("small intestine.")`

`star` `color{green}("Small Intestine:")`

● `color{violet}("Small intestine")` is distinguishable into three regions, a `color{violet}("‘U’")` shaped `color{brown}("duodenum,")` a long coiled middle portion `color{brown}("jejunum")` and a highly coiled `color{brown}("ileum.")`

● The opening of the `color{violet}("stomach")` into the `color{violet}("duodenum")` is guarded by the `color{brown}("pyloric sphincter.")`

`star` `color{green}("Large Intestine:")`

● `color{brown}("Ileum")` opens into the `color{violet}("large intestine.")`

● It consists of `color{violet}("caecum, colon")` and `color{violet}("rectum.")`

● `color{brown}("Caecum")` is a small blind sac which hosts some `color{violet}("symbiotic micro-organisms")`.

● A narrow finger-like tubular projection, the `color{brown}("vermiform appendix")` which is a `color{violet}("vestigial organ")`, arises from the `color{violet}("caecum.")`

● The `color{violet}("caecum")` opens into the `color{violet}("colon.")`

● The `color{brown}("colon")` is divided into three parts – an `color{violet}("ascending, a transverse")` and a `color{violet}("descending")` part.

● The `color{violet}("descending part")` opens into the `color{brown}("rectum")` which opens out through the anus.