THE IMPROTANCE OF NERVE REFLEXES IN THE CONTROL OF THE DIGESTIVE SYSTEM Essay

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1. INTRODUCTION The digestion in humans involves the chemical and mechanical breakdown of food and it’s absorption from the gut. Stimuli around the body start the different stages of digestion. These stimuli occur in the head, stomach and small intestine. There are three phases to digestion and each stage has different nerve reflexes. These three stages are the cephalic stage (for which the stimuli occurs in the head), the gastric stage (for which the stimuli occurs in the stomach) and the intestinal phase (for which the stimuli occurs in the small intestine) This essay will focus on the three phases of digestion regarding the nerve reflexes involved and how they happen. 2. THE CEPHALIC STAGE 2.1 Stimuli from head. The cephalic phase contains those stimuli that originate from the head. By seeing, smelling or anticipating food, the brain is able to inform the stomach to prepare for a meal. These stimuli from the head encourage the mouth to ‘produce an enzyme called salivary amylase’ which initiates the first stage of chemical digestion. The brain tells the stomach to produce gastric juice (which contains hydrochloric acid and pepsin) before food arrives, when the nerves contained in the tongue and cheek are motivated. 2.2 What happens in the cephalic stage? Firstly, food is taken into the mouth and then broken down into smaller pieces by ‘mechanical digestion’ (or the using the teeth to break down food). Saliva in the mouth is produced due to the neural reponses which come about from the stimulus of the eyes, head, smell etc. An enzyme in the saliva called amylase begins the chemical digestion by breaking down ‘complex carbohydrates into simple sugars’. When the food is ready to be swallowed, the food is now called a soft mass called a ‘bolus’. This bolus is then propelled down through the pharynx and into the oesophagus. Peristalsis (alternating

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