Oesophagus and Structure of Stomach

Q: What are the basic layers of the wall of alimentary canal?

The wall of alimentary canal possesses four layers- serosa, muscularis, sub mucosa, and mucosa. Serosa is the outermost layer and is made up of a thin mesothelium and connective tissue. Muscularis is formed by smooth muscles usually arranged into an inner circular and an outer longitudinal layer. Sub-mucosa layer is formed of loose connective tissues containing nerves, blood and lymph vessels. Glands are also present in sub-mucosa of duodenum. Mucosa is the innermost layer lining the lumen of the alimentary canal. Mucosa forms irregular folds (rugae) in stomach and villi in small intestine.

Q: How is small intestine designed to absorb digested food?

correct answer is option D.The small intestine is the most important part of the alimentary canal for digestion and absorption of food. It has three regions a U-shaped duodenum, a long coiled middle portion jejunum and highly coiled ileum.The innermost layer lining the lumen of the alimentary canal is the mucosa. This layer forms irregular folds (rugae) in the stomach and small finger-like foldings called villi in the small intestine. These modifications increase the surface area for more absorption. Villi are supplied with a network of capillaries and a large lymph vessel called the lacteal.It transports lipid molecules. The wall of the intestine is surrounded by the blood vessels which assimilates the food molecules to the different parts of the body.

Q: Which of the following is not present in pancreatic juice?

Pancreatic juice is secreted by the pancreas, which contains a variety of enzymes, including trypsinogen, chymotrypsinogen, elastase, carboxypeptidase, pancreatic lipase and amylase. Pepsin in not present in pancreatic juice. It is secreted by the peptic cells of the stomach.

Q: The most important function of villi in the small intestine is

Villi are tiny, finger-like projections from the wall of the small intestine. They line the inner surface of the small intestine. Their role is to increase the surface area within the small intestine. This will lead to the increase of the surface area of absorption as it is the main function of the small intestine.

Q: Which of the following terms describe human dentition?

\$\textbf{Correct answer: D}\$ \$\textbf{Option (A):}\$ \$\bullet\$ Pleurodont teeth have long roots with weak attachments to the mandible. There is no socket for the teeth to be placed on the jaw. \$\bullet\$ Monophyodont teeth mean the presence of only one set of teeth for the entire lifetime.\$\bullet\$ Homodont means the presence of a single type of teeth. \$\bullet\$ None of these characters are observed in human dentition. \$\textbf{Option (B):}\$ \$\bullet\$ The thecodont teeth are the type of teeth containing the base of the tooth which is completely immersed inside the socket present on the jawbone. \$\bullet\$ Diphyodont teeth are the presence of two sets of teeth throughout the entire lifecycle. \$\bullet\$ Human dentition shows the thecodont and diphyodont character. But the homodont character is not observed.\$\textbf{Option (C):}\$ \$\bullet\$ Heterodont teeth mean the presence of different types of teeth with different functions. \$\bullet\$ Human dentition does not have the pleurodont character, but it is both diphyodont and heterodont. \$\textbf{Option (D):}\$ \$\bullet\$ Human dentition is thecodont because of the presence of sockets in the jawbone where the teeth are embedded. \$\bullet\$ Human dentition shows a diphyodont character because of the presence of two sets of teeth throughout the life cycle. The first set is called the deciduous teeth and the second set is the permanent teeth. \$\bullet\$ Human dentition shows heterodont character because of the presence of four types of teeth which are incisors, canine, premolars and molars. Hence, the correct answer is option (D).

Q: In human alimentary canal, name the site of complete digestion of various components of food. Explain the process of digestion.

Answer:i) Small intestine is the site of complete digestion of various components of a food.ii) Process of digestionFood is chewed with digestion of starch by the action of salivary amylase present in the mouth. The formed bolus passes down the esophagus into the stomach by the action of peristalsis. Gastric juices further acts on food for the digestion of proteins and forms chyme.This chyme enters the duodenum where digestive enzymes from pancreas and bile juice from liver mixes with it and then passes through the small intestine. Absorption of nutrients occurs in the small intestine. The reabsorption of water and minerals happens majorly in the large intestine.

Q: What is the role of HCl in our stomach?

HCl is one of the gastric juices secreted by stomach.HCl converts the inactive enzyme pepsinogen into its active form pepsin. Pepsin digests proteins and breaks them into amino acids. HCl also kills harmful pathogens or particles in our food when it reaches the stomach through the gastrointestinal duct.

Q: In the wall of the alimentary canal, what is the correct sequence of layers, starting from the outside to the inside?

The alimentary canal walls have four basic tunics or layers. The outermost one is the serosa which is a thin membranous covering. Inner to serosa is the muscle layer of outer longitudinal muscles and the inner layer of circular muscles.Then there is submucosa which is then followed by the innermost layer of mucosa. The mucosa is the epithelial membrane lining the lumen of the alimentary canal.So, the correct answer is (C).

Q: What are Villi ? Mention their functions.

The small intestine has millions of tiny finger-like projections called villi. These villi increase the surface area for more efficient food absorption. Within these villi, are present numerous blood vessels that absorb the digested food and carry it to the bloodstream. It is hence from the bloodstream, the absorbed food is delivered to each and every cell of the body.

Biology

definition

Oesophagus

The esophagus or the food pipe is a muscular tube and has the following features:

It starts from the pharynx to the stomach. The pharynx is present behind the trachea.
Food/bolus is pushed through the esophagus into the stomach by means of a series of contractions called peristalsis. These contractions occur in the muscles in its wall.
There is no digestion in this part.
It is also called as gullet.
The opening of the esophagus into the stomach is regulated by a muscular sphincter called gastro-esophageal sphincter.

definition

Stomach

Structure of the stomach
It is a highly muscular, J-shaped organ.
It is located in the upper left portion of the abdominal cavity.
The stomach has three parts:

Cardiac portion: The esophagus opens here.
Fundic region
Pyloric portion: It opens in the first part of small intestine.

The opening of the stomach into the duodenum is guarded by the pyloric sphincter.
The innermost layer lining the lumen is the mucosa. This layer forms irregular folds called rugae in the stomach.
Mucosa form gastric glands in the stomach.
Function of the stomach
The gastric glands present in its walls secrete gastric juice containing hydrochloric acid (HCl) and enzymes, like pepsinogen.
HCl activates pepsinogen into pepsin and kills bacteria.
Proteins are broken into smaller fragments called peptones by the enzyme called pepsin.
It eventually leads to the formation of chyme, which is moved to the intestine through pylorus.