18. Answer in datail I

 

a. The alimentary canal is a muscular straightmuscular coiled, tubular structure. The teethmouth is the structure that leads into the buccal cavity. It is bound by threetwo soft, movable upper and lower lips.

 

b. The buccal cavity is a large space-bound above by the throatpalate, below by the palatethroat and on the sides by the jaws.

 

c. The teethmouth are hard structures, meant for cutting, grinding and crushing the food for easy digestion, known as mechanical digestion.

 

d. Human teeth are diphyodontheterodont as they develop two sets in their lifetime. The teeth that appear first in the lifetime are known as permanent teethmilk teeth. The second and permanent teethmilk teeth set develops, and they are \(16\) in each jaw (\(32\) number).

 

e. Salivary glands are endocrine glandsexocrine glands involved in producing saliva through a system of ducts in mammals. 

 

f. PharynxTongue is a muscular, sensory organ that blends food and saliva. It consists of taste budsepiglottis, which are structures that help us to recognise the taste of food. Masticated food in the buccal cavity forms a bolus, rolled by the tongue and swallowed through the pharynx and into the oesophagusstomach.

 

g. During swallowing, the food is prevented from entering into the trachea by closing a muscular flap-like structure known as the epiglottistaste buds.

 

h. TonguePharynx is a membrane-lined cavity that connects the nose and mouth to the oesophagus. It functions as a pathway for the food from the mouth to the oesophagus.

 

i. The oesophagusstomach or the food pipe is a \(22\ cm\) long muscular-membranous canal, which conducts food from the pharynx to the stomach by peristalsis.

 

j. The stomachoesophagus is a large, muscular \(J\)-shaped organ that is found between the oesophagus and the small intestine. Gastric glands secrete gastric juice in the stomach's inner walls. 

 

k. The large intestinesmall intestine is a long coiled tube measuring about \(5-7\) m, and it is the longest part of the alimentary canal. Most of the digestion occurs here.

 

l. Both digestion and absorption take place in the small intestine. FalseTrue

 

m. The liverpncreas is the body's largest digestive gland and is reddish-brown. It is divided into two primary lobes. The bile juiceintestinal juice secreted by the liver cells is temporarily deposited in the gall bladder and is released when the food reaches the small intestine.

 

n. The liverpancreas isa lobed, leabile juiceintestinal juicef-shaped gland, which is a heterocrine gland as it acts as both an exocrine and an endocrine gland. The exocrineendocrine portion of the pancreas secretes the pancreatic juice, and the exocrineendocrine portion of the pancreas secrete hormones.

 

o. The large intestinesmall intestine is a thicker tube about \(1.5\) m long. The food that hasn't been digested or consumed is transferred here. It has about  fourthree parts. The rectumcaecumcolon is found as a small blind pouch-like organ. The rectum is the last portion of the body that leads to the anus. A ring of muscles known as the anal sphincter keeps it close and opens it during passing stools.