Describe the pharynx,oesophagus,and external structure of the stomach in the human digestive tract.

(N/A) Pharynx: The oesophagus and the trachea open into the pharynx.
The pharynx is located behind the nasal cavity,oral cavity,and larynx. It is divided into three parts:
$(i)$ Nasopharynx
$(ii)$ Oropharynx
$(iii)$ Laryngopharynx
Function: It serves as a common passage for food and air. $A$ cartilaginous flap called the epiglottis prevents the entry of food into the glottis during swallowing.
$(b)$ Oesophagus: The oesophagus is a thin,long tube. It is situated behind the trachea and in front of the vertebral column. It extends posteriorly,passing through the neck,thorax,and diaphragm,and leads to a '$J$'-shaped,bag-like structure called the stomach.
$A$ muscular gastro-oesophageal sphincter regulates the opening of the oesophagus into the stomach.
Function: It transports food into the stomach via peristaltic movements.
$(c)$ Stomach: The stomach is the most enlarged part of the digestive tract. It is located in the upper left portion of the abdominal cavity. It has three major parts:
$(i)$ Cardiac portion: The part into which the oesophagus opens.
$(ii)$ Fundic region: The main,dome-shaped part of the stomach.
$(iii)$ Pyloric portion: The distal part that opens into the first part of the small intestine (duodenum).
Function: It stores food temporarily,churns it,and mixes it with gastric juices to convert it into chyme.