Digestive system Questions in English

(A) Glisson's capsule is a thin connective tissue sheath that covers the hepatic lobules,which are the structural and functional units of the liver.
Each hepatic lobule is covered by this thin connective tissue sheath known as Glisson's capsule.
Therefore,it is specifically associated with the liver.

(D) Enamel is the hardest substance in the human body, covering the crown of the teeth. It is primarily composed of inorganic salts, specifically hydroxyapatite (calcium phosphate). Due to its highly mineralized nature, it contains very little water, approximately $3$% by weight.

(B) The esophagus is a thin,long tube that extends posteriorly,passing through the neck,thorax,and diaphragm,and finally opens into the stomach. Therefore,the correct direction of extension is posteriorly.

(C) Pernicious anemia is a type of megaloblastic anemia caused by the deficiency of vitamin $B_{12}$ (cobalamin).
This deficiency often occurs due to the lack of intrinsic factor,a protein produced by the stomach lining that is necessary for the absorption of vitamin $B_{12}$ in the small intestine.
Without sufficient vitamin $B_{12}$,the body cannot produce enough healthy red blood cells.

(D) The human stomach contains approximately $35$ million gastric pits. These pits are invaginations of the gastric mucosa. The density of these gastric pits is approximately $100$ per $mm^2$ of the mucosal surface area. Therefore,the correct option is $D$.

(B) The Sphincter of Oddi is a muscular valve that controls the flow of digestive juices (bile and pancreatic juice) through the Ampulla of Vater into the duodenum.
It regulates the entry of bile and pancreatic enzymes into the small intestine.
Therefore,it is located at the junction where the common bile duct and the main pancreatic duct join to form the Ampulla of Vater.

(D) Humans are diphyodont,meaning they develop two sets of teeth during their lifetime.
$1$. The first set is the deciduous or milk teeth,which consists of $20$ teeth.
$2$. The second set is the permanent teeth,which consists of $32$ teeth.
$3$. The teeth that grow twice are the deciduous teeth,which are replaced by permanent teeth. These are $20$ in number (incisors,canines,and premolars).
Therefore,the correct answer is $20$.

(B) The stomach of ruminants like cows is complex and consists of four chambers: the rumen,reticulum,omasum,and abomasum.
The rumen is the largest chamber of the ruminant stomach,where fermentation of plant material occurs by symbiotic microorganisms.
Therefore,the rumen is a part of the stomach.

(B) The stomach wall contains several layers. The innermost layer,the mucosa,is thrown into irregular,longitudinal folds when the stomach is empty. These folds are known as $Rugae$. $Rugae$ allow the stomach to expand significantly when food is ingested,increasing its capacity to hold food. In contrast,$Villi$ and $Microvilli$ are structures found in the small intestine for absorption,and $Fissures$ are not anatomical terms used for stomach lining.

(D) The teeth of rabbits exhibit the following characteristics:
$1$. $\text{Thecodont}$: Teeth are embedded in the sockets of the jaw bone.
$2$. $\text{Diphyodont}$: Two sets of teeth are formed during their lifetime (deciduous or milk teeth followed by permanent teeth).
$3$. $\text{Heterodont}$: Teeth are of different types (incisors, premolars, and molars) based on their structure and function.
Since rabbits possess all these characteristics, the correct option is $D$.

(B) Brunner's glands (also known as duodenal glands) are characteristic features of the submucosa of the duodenum.
These glands secrete an alkaline,mucus-rich fluid that helps to neutralize the acidic chyme coming from the stomach and protects the intestinal mucosa from damage.
Therefore,the correct answer is $B$ (Duodenum).

(C) The soft palate is the muscular part at the back of the roof of the mouth. The posterior,fleshy,finger-like extension of the soft palate that hangs down into the pharynx is known as the $Uvula$. It plays a role in preventing food from entering the nasal cavity during swallowing.

(D) Vitamin $B_{12}$ (cobalamin) is synthesized by the symbiotic bacteria present in the large intestine (colon) of the human body. While the absorption of $B_{12}$ primarily occurs in the ileum,the synthesis by gut microbiota is a well-documented biological process.

(A) The dental formula represents the arrangement of teeth in one half of the upper and lower jaw.
For a child,the set of teeth is known as deciduous or milk teeth.
$A$ $3$-year-old child has a complete set of deciduous teeth,which consists of $2$ incisors,$1$ canine,and $2$ molars in each quadrant (half of each jaw).
There are no premolars in a child's dentition.
Therefore,the dental formula is $\frac{2102}{2102}$.

(C) The vagus nerve ($CN$ $X$) provides parasympathetic innervation to the thoracic and abdominal viscera.
Preganglionic parasympathetic fibers from the vagus nerve synapse with postganglionic neurons located within the walls of the target organs.
These networks of neurons and fibers located within the walls of the gastrointestinal tract are specifically known as the enteric nervous system,which includes the $Auerbach's$ plexus (myenteric plexus) and the $Meissner's$ plexus (submucosal plexus).
Therefore,the network formed by these fibers is referred to as $Auerbach's$ plexus.

(A) The condition in which each tooth is embedded in a socket of the jaw bone is known as thecodont dentition. This type of dentition is a characteristic feature of mammals,including humans. In contrast,acrodont teeth are attached to the surface of the jaw,and pleurodont teeth are attached to the inner side of the jaw bone.

(B) Assertion $A$ is true because mammals possess different types of teeth (incisors,canines,premolars,and molars),which is defined as heterodont dentition.
Reason $R$ is also true because mammals typically exhibit diphyodont dentition,where a set of temporary milk teeth is replaced by a set of permanent adult teeth.
However,the reason $R$ explains the diphyodont nature of mammals,not the heterodont nature. Therefore,$R$ is not the correct explanation of $A$.

(B) In humans,the teeth that fall out during childhood and are replaced by permanent teeth are known as deciduous teeth,also called milk teeth or primary teeth.
$A$. Thecodont refers to teeth embedded in the jaw bone sockets.
$B$. Deciduous teeth are the temporary set of teeth that fall out.
$C$. Heterodont refers to the presence of different types of teeth (incisors,canines,premolars,molars).
$D$. Permanent teeth are the final set of teeth that replace the deciduous teeth and do not fall out naturally.

(B) In birds like the peacock,the digestive system includes a specialized structure called the $Crop$.
The $Crop$ is an expanded,muscular pouch located along the esophagus.
Its primary function is to store food temporarily before it passes into the stomach (proventriculus and gizzard) for digestion.
Therefore,the correct answer is $B$.

(B) The dental formula for a child (deciduous or milk teeth) is $2102/2102$,which totals $20$ teeth.
In this set,there are $8$ incisors,$4$ canines,and $8$ molars.
Premolars are completely absent in the primary (milk) dentition of a two-year-old child.
Therefore,the correct answer is $B$.

(D) The correct answer is $D$.
In humans,the primary dentition (milk teeth) consists of $20$ teeth in total,which include $8$ incisors,$4$ canines,and $8$ molars.
Premolars are completely absent in the primary dentition.
In contrast,the permanent dentition consists of $32$ teeth,which include $8$ incisors,$4$ canines,$8$ premolars,and $12$ molars.
Therefore,premolars are the type of teeth that are not present in the primary dentition.

(A) The human $Caecum$ is a small blind sac which hosts some symbiotic microorganisms. These microorganisms play a role in the digestion of certain substances and the synthesis of vitamins. While the large intestine as a whole contains a vast microbiome,the $Caecum$ is specifically noted in biological texts as a site for these symbiotic organisms.

(C) The correct answer is $C$. An adult human has $32$ permanent teeth which are of four different types (heterodont dentition),namely,incisors $(I)$,canines $(C)$,premolars $(PM)$,and molars $(M)$.
The arrangement of teeth in each half of the upper and lower jaw in the order $I, C, PM, M$ is represented by a dental formula.
For an adult human,the dental formula is $\frac{2123}{2123}$,which means $2$ incisors,$1$ canine,$2$ premolars,and $3$ molars in each half of the jaw.
This corresponds to the representation $\frac{2}{2}, \frac{1}{1}, \frac{2}{2}, \frac{3}{3}$.

(D) : The intestinal mucosal epithelium contains goblet cells which secrete mucus.
This mucus lubricates the food to facilitate its easy passage through the alimentary canal.
Therefore,if goblet cells become non-functional,it will adversely affect the smooth movement of food down the intestine.
Additionally,the mucus,along with bicarbonates from the pancreas,protects the intestinal mucosa from gastric acid and provides an alkaline medium necessary for enzymatic activities.

(A) The dental formula represents the arrangement of teeth in one half of the upper and lower jaw.
For an adult human,the total number of teeth is $32$.
The dental formula is expressed as $\frac{\text{Incisors (I)}, \text{Canines (C)}, \text{Premolars (PM)}, \text{Molars (M)}}{\text{Incisors (I)}, \text{Canines (C)}, \text{Premolars (PM)}, \text{Molars (M)}}$.
In an adult human,each half of the jaw contains $2$ incisors,$1$ canine,$2$ premolars,and $3$ molars.
Thus,the formula is $\frac{2123}{2123}$.

(A) The wall of the alimentary canal from the esophagus to the rectum possesses four layers: Serosa,Muscularis,Submucosa,and Mucosa.
$1$. The outermost layer is the Serosa $(A)$,which is made of a thin mesothelium with some connective tissues.
$2$. The innermost layer lining the lumen of the alimentary canal is the Mucosa $(B)$.
Therefore,$A$ represents the Serosa and $B$ represents the Mucosa.

(A) In the human digestive system, the $Cecum$ is a small blind sac which hosts some symbiotic microorganisms.
These microorganisms play a role in the digestion of cellulose and the synthesis of certain vitamins.
While the $Vermiform \text{ } appendix$ is attached to the $Cecum$, the primary site for these symbiotic bacteria in the human gut is the $Cecum$ itself.

(D) Bile is synthesized by the hepatic cells (hepatocytes) of the liver.
It travels through the hepatic ducts.
When bile does not enter the gall bladder,it flows directly through the common bile duct.
The common bile duct and the pancreatic duct join to form the hepatopancreatic duct,which opens into the duodenum.
The opening is guarded by the sphincter of Oddi.
Therefore,the correct path is: Liver $\rightarrow$ hepatic duct $\rightarrow$ common bile duct $\rightarrow$ hepatopancreatic duct $\rightarrow$ duodenum.

(D) The wall of the alimentary canal consists of four layers: Serosa,Muscularis,Submucosa,and Mucosa.
$1$. The Submucosa layer is formed of loose connective tissue containing nerves,blood,and lymph vessels.
$2$. In the duodenum,the Submucosa also contains Brunner's glands,which secrete mucus and enzymes to aid in digestion.
$3$. Therefore,the layer containing nerves,blood vessels,lymph vessels,and Brunner's glands is the Submucosa of the duodenum.

(A) Based on the cross-section of the small intestine wall,the layers from outside to inside are serosa,muscularis,submucosa,and mucosa.
In the provided figure,$X$ points to the submucosa layer.
The magnified view of the mucosa shows finger-like projections called villi.
In this magnified view,$Y$ points to the artery (part of the blood vessel network) and $Z$ points to the villi.
Therefore,the correct identification is $X-$ Sub-mucosa,$Y-$ Artery,$Z-$ Villi.

(A) Brunner's glands (also known as duodenal glands) are characteristic features of the duodenum.
These glands are located in the submucosa layer of the duodenum.
Their primary function is to secrete an alkaline,mucus-rich fluid that protects the duodenal wall from the acidic chyme coming from the stomach and provides an optimal pH for the activity of digestive enzymes.

(A) The stomach lining is protected from the highly acidic environment created by $HCl$ through a thick coating of mucus secreted by the goblet cells of the gastric epithelium.
This mucus layer acts as a physical and chemical barrier,neutralizing the acid near the cell surface and preventing the self-digestion of the stomach wall by pepsin and $HCl$.

(A) The process of mastication (chewing) involves the mechanical breakdown of food into smaller particles.
Enamel is the hardest,outermost layer of the tooth that covers the crown.
It provides the necessary hardness and durability required to crush and grind food particles during mastication.
Therefore,enamel is the part of the tooth primarily responsible for the mechanical action of chewing.

(C) The wall of the human alimentary canal is composed of $4$ main layers.
From the periphery (outermost) to the center (innermost),these layers are:
$1$. Serosa: The outermost layer made of a thin mesothelium with some connective tissues.
$2$. Muscularis: Formed by smooth muscles,usually arranged into an inner circular and an outer longitudinal layer.
$3$. Submucosa: Formed of loose connective tissues containing nerves,blood,and lymph vessels.
$4$. Mucosa: The innermost lining of the lumen,which forms irregular folds (rugae) in the stomach and villi in the small intestine.
Therefore,the correct sequence is Serosa $\rightarrow$ Muscularis $\rightarrow$ Submucosa $\rightarrow$ Mucosa.

(A) The $Crypts$ $of$ $Lieberkühn$ are tubular glands found at the base of the villi in the small intestine.
These glands are located in the $Mucosa$ layer of the small intestine.
They are responsible for secreting intestinal juice ($succus$ $entericus$),which contains various enzymes that aid in the final stages of digestion.

(A) Assertion $(A)$ is correct because the process of replacing deciduous (temporary) teeth with permanent teeth typically starts around the age of $6$ years.
Reason $(R)$ is correct because humans possess two sets of teeth during their lifetime: a set of temporary milk teeth replaced by a set of permanent or adult teeth. This type of dentition is scientifically termed as diphyodont.
Therefore,both $A$ and $R$ are correct.

(B) The ileocecal valve is a sphincter muscle situated at the junction of the small intestine and the large intestine.
Specifically,it connects the terminal part of the ileum (the final section of the small intestine) to the caecum (the beginning of the large intestine).
Its primary function is to prevent the backflow of fecal contents from the large intestine into the small intestine.

(B) The $Caecum$ is a small blind sac which hosts some symbiotic microorganisms.
It is a part of the large intestine and is vestigial in humans.
These microorganisms help in the digestion of cellulose in herbivores,but in humans,they are present in small numbers.

(C) Assertion $(A)$ is correct because the human digestive system is indeed composed of the alimentary canal and associated digestive glands.
Reason $(R)$ is incorrect because the pineal gland is an endocrine gland located in the brain,not a digestive gland. The primary digestive glands associated with the alimentary canal are the salivary glands,liver,and pancreas.

(C) The correct answer is $C$.
In humans,the type of attachment where each tooth is embedded in a socket of the jawbone is called 'thecodont',not 'diphyodont'.
'Diphyodont' refers to the formation of two sets of teeth during a lifetime (milk teeth and permanent teeth).
Therefore,the statement in option $C$ is scientifically incorrect.

(D) The correct answer is $D$. The colon is a part of the large intestine,but it is not divided into three parts; rather,the large intestine itself is divided into three parts: cecum,colon,and rectum. The colon is further divided into four regions: ascending,transverse,descending,and sigmoid colon. Therefore,the statement that the colon is divided into three parts is incorrect.

(A) The dental formula represents the arrangement of teeth in one half of the upper and lower jaw.
For a child of $5$ years,the primary dentition (milk teeth) is present.
The dental formula for a child is $\frac{2102}{2102}$,which means $2$ incisors,$1$ canine,$0$ premolars,and $2$ molars in each half of the jaw.
Therefore,the total number of teeth is $(2+1+0+2) \times 2 = 10$ teeth in each jaw,totaling $20$ teeth.

(D) The $Large \text{ } intestine$ is responsible for the re-absorption of water, minerals, and certain vitamins from the undigested food material.
It also plays a crucial role in the formation, preparation, and temporary storage of faeces before they are eliminated from the body through the anus.

(D) The lamina propria is a thin layer of connective tissue that forms part of the moist linings known as mucous membranes or mucosa.
It is found in various organs,including the respiratory tract,the urinary tract,and the gastrointestinal tract.
In the context of the digestive system,the lamina propria is a component of the mucosa of the intestine,providing structural support and housing blood vessels and immune cells.
Therefore,it is most directly associated with the wall of the intestine.

(A) Brunner's glands (also known as duodenal glands) are characteristic features of the duodenum.
These glands are located in the submucosal layer of the duodenum.
Their primary function is to secrete an alkaline fluid that protects the duodenal mucosa from the acidic chyme coming from the stomach and provides an optimal pH for the action of pancreatic enzymes.

(D) The human large intestine contains a symbiotic microflora,primarily consisting of bacteria such as $Escherichia \ coli$.
These bacteria play a crucial role in the synthesis of certain vitamins,most notably Vitamin $K$ and various $B$-complex vitamins (such as $B_{12}$ and biotin).
Vitamin $K$ is essential for the synthesis of blood clotting factors in the liver.
Therefore,among the given options,Vitamin $K$ is the correct answer.

(B) The enamel of the teeth is the hardest substance in the human body. It is secreted by specialized epithelial cells known as $Ameloblasts$. These cells are derived from the enamel organ during tooth development. Once the enamel is fully formed,these cells typically degenerate. In contrast,$Odontoblasts$ are responsible for the secretion of dentin,while $Osteoblasts$ are involved in bone formation.

(C) The dental formula for primary (deciduous) teeth in humans is $2102/2102$,while the dental formula for permanent teeth is $2123/2123$.
Comparing these,the primary dentition lacks premolars entirely.
Therefore,the correct answer is $C$ (Premolars).

(C) The total number of deciduous (milk) teeth in humans is $20$. The dental formula for deciduous teeth is $\frac{2102}{2102}$. According to this formula,each half of the jaw contains $2$ incisors,$1$ canine,and $2$ molars. The dental formula for permanent teeth is $\frac{2123}{2123}$,which includes premolars. Therefore,premolars are completely absent in a $2$-year-old child.

(D) Human dentition is characterized by three main features:
$1$. $Thecodont$: The teeth are embedded in the sockets of the jaw bone.
$2$. $Diphyodont$: Two sets of teeth are formed during the life of an individual,a set of temporary milk or deciduous teeth replaced by a set of permanent or adult teeth.
$3$. $Heterodont$: An adult human has different types of teeth,namely incisors $(I)$,canines $(C)$,premolars $(PM)$,and molars $(M)$,which serve different functions.