● The activities of the gastro-intestinal tract are under `color{brown}("neural and hormonal control")` for proper coordination of different parts.

● The `color{violet}("sight, smell")` and/or the presence of food in the `color{violet}("oral cavity")` can stimulate the `color{brown}("secretion of saliva.")`

● `color{violet}("Gastric and intestinal secretions")` are also, similarly, stimulated by `color{brown}("neural signals")`.

● The `color{violet}("muscular activities")` of different parts of the alimentary canal can also be moderated by `color{violet}("neural")` mechanisms, both local and through CNS.

● `color{violet}("Hormonal control")` of the secretion of digestive juices is carried out by the local `color{violet}("hormones")` produced by the `color{violet}("gastric and intestinal mucosa.")`

● Absorption is the process by which the end products of digestion pass through the `color{violet}("intestinal mucosa")` into the `color{violet}("blood or lymph.")`

● It is carried out by `color{brown}("passive, active or facilitated")` transport mechanisms.

● Small amounts of monosacharides like glucose, amino acids and some of electrolytes like chloride ions are generally absorbed by `color{brown}("simple diffusion.")`

● The passage of these substances into the blood depends upon the concentration gradients.

● However, some of the substances like `color{violet}("fructose")` and some `color{violet}("amino acids")` are absorbed with the help of the carrier ions like `Na^+`.

● This mechanism is called the `color{brown}("facilitated transport.")`

● Transport of water depends upon the `color{brown}("osmotic gradient.")`

● `color{brown}("Active transport")` occurs against the concentration gradient and hence requires energy.

● Various nutrients like amino acids, monosacharides like glucose, electrolytes like Na+ are absorbed into the blood by this mechanism.

● Fatty acids and glycerol being insoluble, cannot be absorbed into the blood.

● They are first incorporated into small droplets called `color{brown}("micelles")` which move into the `color{violet}("intestinal mucosa")`.

● They are re-formed into very small protein coated fat globules called the `color{brown}("chylomicrons ")` which are transported into the `color{violet}("lymph vessels (lacteals)")` in the villi.

● These `color{violet}("lymph vessels")` ultimately release the absorbed substances into the blood stream.

● Absorption of substances takes place in different parts of the alimentary canal, like mouth, stomach, small intestine and large intestine.

● However, maximum absorption occurs in the `color{violet}("small intestine.")`

● The absorbed substances finally reach the `color{violet}("tissues")` which utilise them for their activities.

● This process is called `color{brown}("assimilation.")`

● The `color{violet}("digestive wastes,")` solidified into coherent faeces in the rectum initiate a `color{brown}("neural reflex")` causing an urge or `color{violet}("desire for its removal. ")`

● The `color{brown}("egestion of faeces")` to the outside through the anal opening (`color{brown}("defaecation")`) is a `color{violet}("voluntary")` process and is carried out by a `color{brown}("mass peristaltic movement.")`

● The `color{violet}("inflammation")` of the `color{violet}("intestinal tract")` is the most common ailment due to bacterial or viral infections.

The infections are also caused by the parasites of the `color{violet}("intestine")` like tape worm, round worm, thread worm, hook
● `color{violet}("worm, pin worm")`, etc.

● `color{brown}("Jaundice:")` The `color{violet}("liver")` is affected, skin and eyes turn yellow due to the deposit of bile `color{violet}("pigments.")`

● `color{brown}("Vomiting:")` It is the ejection of `color{violet}("stomach")` contents through the mouth. This reflex action is controlled by the vomit centre in the medulla. A feeling of nausea precedes `color{violet}("vomiting.")`

● `color{brown}("Diarrhoea:")` The `color{violet}("abnormal frequency")` of bowel movement and increased liquidity of the `color{violet}("faecal discharge")` is known as `color{violet}("diarrhoea")`. It reduces the absorption of food.

● `color{brown}("Constipation:")` In constipation, the faeces are retained within the `color{violet}("rectum")` as the bowel movements occur irregularly.

● `color{brown}("Indigestion:")` In this condition, the `color{violet}("food")` is not properly digested leading to a feeling of fullness. The causes of indigestion are inadequate `color{violet}("enzyme secretion,")` anxiety, food poisoning, over eating, and spicy food.