Digestive system Questions in English

(C) The hepatic lobule is the structural and functional unit of the liver. Each lobule consists of a central axis formed by a branch of the hepatic vein,which is known as the central vein or intralobular vein (a type of venule). Therefore,both terms refer to the same structure located at the center of the lobule.

(B) Along the periphery of each hepatic lobule of the liver,there are angular intervals called portal canals.
Each portal canal contains $(a)$ a branch of the hepatic portal vein,$(b)$ a branch of the hepatic artery,and $(c)$ an interlobular bile duct.
These three structures collectively form a portal triad.

(B) The spiral valve,also known as the spiral valve of Heister,is a series of mucosal folds located within the cystic duct of the gall bladder.
These folds help to keep the cystic duct open,allowing bile to flow into the gall bladder for storage or into the common bile duct for release into the duodenum.

(B) The correct matches are as follows:
$(A)$ Crypts of Lieberkuhn are found in the small intestine, specifically between the bases of villi. Thus, $A = r$.
$(B)$ The pancreas is located in the '$C$' shaped loop of the duodenum. Thus, $B = p$.
$(C)$ The adrenal glands are located on the anterior part of each kidney. Thus, $C = s$.
$(D)$ Gastric glands are present in the mucosa of the stomach. Thus, $D = q$.
Therefore, the correct combination is $A = r, B = p, C = s, D = q$.

(B) The human stomach secretes approximately $2000 \, ml$ to $3000 \, ml$ (or $2-3 \, liters$) of gastric juice per day.
Gastric juice is a mixture of water, hydrochloric acid $(HCl)$, enzymes like pepsin and gastric lipase, and mucus.
This secretion is essential for the digestion of proteins and the sterilization of food in the stomach.

(D) The stomach is divided into four major parts: the cardiac,fundus,body,and pyloric regions.
The cardiac part is where the esophagus opens into the stomach.
The fundus and body are the main central regions.
The pyloric region is the narrower distal part of the stomach that opens into the first part of the small intestine,known as the duodenum.
Therefore,the correct answer is the pylorus.

(C) The human large intestine (colon) contains a symbiotic microflora,primarily bacteria such as $Escherichia \ coli$. These bacteria synthesize several vitamins,most notably Vitamin $K$ and certain $B$ vitamins like Vitamin $B_{12}$ (Cyanocobalamine),Biotin,and Folic acid. While the primary site of absorption for Vitamin $B_{12}$ is the ileum (via intrinsic factor),the colon is capable of absorbing some of the vitamins produced by its resident bacterial population,contributing to the host's nutritional requirements.

(C) The pulp cavity is the central part of the tooth,which is filled with a soft connective tissue known as dental pulp.
This pulp contains blood vessels (capillaries),nerve fibers,and specialized cells called odontoblasts.
Among the given options,the presence of a mass of capillaries is a characteristic feature of the pulp cavity.

(D) The tooth consists of a crown,neck,and root. The central part of the tooth is the pulp cavity,which contains connective tissue,blood vessels,and nerves. This pulp cavity is surrounded by a hard,calcified tissue called dentine. Dentine forms the bulk of the tooth and is further covered by a hard layer of enamel in the crown region. Therefore,the pulp is directly covered by dentine.

(D) The characteristic pungent odour of faeces is primarily due to the presence of toxic amines such as $Indole$ and $Skatole$,which are produced by the action of intestinal bacteria on amino acids.
Additionally,various gases produced during the fermentation of carbohydrates and the putrefaction of proteins by gut microbiota also contribute significantly to the foul smell of faeces.
Therefore,all the mentioned factors contribute to the odour.

(D) Vitamin $B_{12}$ (cyanocobalamin) is known as Castle's extrinsic factor.
It is called 'extrinsic' because it must be obtained from the diet.
In the stomach, it binds to the 'intrinsic factor' (secreted by parietal cells) to facilitate its absorption in the ileum of the small intestine.

(A) Histologically,the oesophagus consists of the standard four layers: mucosa,submucosa,circular muscle layer,and longitudinal muscle layer.
In the oesophagus,the circular muscles are arranged spirally rather than in a simple circular fashion.

(C) The colon is characterized by the presence of sac-like structures called haustra.
These haustra are formed due to the contraction of the longitudinal muscle bands known as taeniae coli,which are shorter than the rest of the colon wall.
Therefore,the sacculated appearance of the colon is a result of both the presence of haustra and the structural arrangement of the taeniae coli.

(C) The inner lining of the stomach,known as the mucosa,contains numerous longitudinal folds when the stomach is empty. These folds are known as $Rugae$. They allow the stomach to expand significantly when food is ingested,increasing its capacity to hold contents without increasing the internal pressure.

(C) The pyloric constriction is a circular groove that externally marks the end of the pyloric part of the stomach.
Internally,this region corresponds to the pyloric sphincter,which regulates the passage of chyme from the stomach into the duodenum.
Therefore,it represents the narrowing of the junction between the stomach and the duodenum.

(B) The folds of Kerkring,also known as $plicae$ $circulares$,are permanent circular folds of the mucous membrane found in the small intestine.
While they begin in the distal part of the duodenum,they are most numerous,large,and well-developed in the jejunum.
These folds serve to increase the surface area for the absorption of nutrients.
Therefore,the correct answer is $B$.

(A) In humans,the $3^{rd}$ molars are commonly known as wisdom teeth.
There are a total of four $3^{rd}$ molars,with two in the upper jaw and two in the lower jaw.

(A) Meckel’s diverticulum is a congenital remnant of the vitelline duct (also known as the omphalomesenteric duct).
It is typically located in the distal part of the small intestine,specifically in the $Ileum$,usually about $2$ feet proximal to the ileocecal valve.
It is the most common congenital abnormality of the gastrointestinal tract.

(D) $Auerbach's$ plexus (also known as the myenteric plexus) is a part of the autonomic nervous system in vertebrates. It is located between the longitudinal and circular muscular layers of the intestine and is responsible for controlling its peristaltic movements.

(A) The type of attachment of teeth in which each tooth is embedded in a socket of the jaw bone is called thecodont dentition.
These bony sockets in the jaw bones are specifically known as alveoli (singular: alveolus).
Therefore,the correct term for these bony sockets is alveolus.

(C) The correct answer is $C$.
Hardness of biological substances depends upon the concentration of inorganic salts present in them.
Tooth enamel is the hardest substance in the human body because it contains approximately $93\%$ inorganic salts,primarily hydroxyapatite,which provides exceptional durability and resistance to wear.

(A) The digestive system is the only system in the human body that is derived from all three germ layers: Ectoderm,Mesoderm,and Endoderm.
- The lining of the mouth and the anal canal is derived from the Ectoderm.
- The muscular and connective tissue layers of the digestive tract are derived from the Mesoderm.
- The epithelial lining of the entire gastrointestinal tract and associated glands (like the liver and pancreas) is derived from the Endoderm.

(C) During embryonic development,the three primary germ layers are the ectoderm,mesoderm,and endoderm.
- The ectoderm gives rise to the nervous system and epidermis.
- The mesoderm gives rise to muscles,bones,the circulatory system,and the dermis.
- The endoderm gives rise to the epithelial lining of the digestive tract and its associated glands,including the liver and the pancreas.
Therefore,both the liver and the pancreas are endodermal in origin.

(C) Peristalsis is a series of wave-like muscle contractions that move food through the digestive tract.
$1$. The $Oesophagus$ exhibits strong peristaltic waves to push the bolus down to the stomach.
$2$. The $Stomach$ and $Duodenum$ show significant peristaltic activity for mixing and propelling chyme.
$3$. The $Rectum$ is primarily a storage organ for feces. While it does undergo mass movements, it exhibits the least amount of regular peristaltic activity compared to the other parts of the alimentary canal listed, as its main function is the storage and eventual expulsion of waste.

(A) The alimentary canal begins with an anterior opening,the mouth,which leads to the buccal cavity or oral cavity. This is a correct statement.
$(B)$ The majority of mammals,including humans,form a set of teeth during their life,a type of attachment called thecodont,where each tooth is embedded in a socket of the jaw bone. This is a correct statement.
$(C)$ Humans exhibit a diphyodont type of dentition,meaning they form two sets of teeth during their life: a set of temporary milk or deciduous teeth replaced by a set of permanent or adult teeth. This is a correct statement.
$(D)$ The oesophagus and the trachea open into the pharynx,not the larynx. The larynx is the cartilaginous box which helps in sound production. This is an incorrect statement.
Therefore,statements $(A)$,$(B)$,and $(C)$ are correct.

(B) The mucus in saliva acts as a lubricant and helps in adhering food particles together into a bolus,which is then swallowed.

(A) The pulp cavity of the tooth contains connective tissue,blood vessels,and nerves. The inner wall of the pulp cavity is lined by a layer of specialized cells called $Odontoblasts$. These cells are responsible for the secretion of dentin,which forms the bulk of the tooth structure.

(A) The human dentition is characterized by three main features:
$1$. Heterodont: Humans possess different types of teeth (incisors,canines,premolars,and molars) to perform different functions.
$2$. Thecodont: Each tooth is embedded in a socket of the jaw bone.
$3$. Diphyodont: Humans form two sets of teeth during their life,a set of temporary milk or deciduous teeth replaced by a set of permanent or adult teeth.
Therefore,the correct sequence is Heterodont,Thecodont,and Diphyodont.

(A) The tooth enamel is the hardest substance in the human body.
It is secreted by specialized cells called $Ameloblasts$.
$Ameloblasts$ are epithelial cells that form the enamel matrix during tooth development.
In contrast,$Odontoblasts$ are responsible for the formation of dentin,$Osteoblasts$ are involved in bone formation,and $Osteoclasts$ are involved in bone resorption.

(C) 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 containing bicarbonate ions,which helps neutralize the acidic chyme coming from the stomach and protects the duodenal wall from erosion.
Therefore,the correct option is $C$.

(A) The wall of the alimentary canal from the esophagus to the rectum possesses four layers:
$1$. Mucosa (innermost layer lining the lumen).
$2$. Submucosa (layer of loose connective tissue).
$3$. Muscularis (formed by smooth muscles).
$4$. Serosa (outermost layer made of a thin mesothelium).
Therefore, the correct sequence from inside to outside is $Mucosa \rightarrow Submucosa \rightarrow Muscularis \rightarrow Serosa$.

$(B)$ The human stomach secretes gastric juice, which contains hydrochloric acid, pepsinogen, and mucus. The average volume of gastric juice secreted by an adult human stomach in a $24$-hour period is typically estimated to be between $2000 \, ml$ and $3000 \, ml$ $(2-3 \, \text{liters})$.

(A) The large intestine consists of the caecum,colon,and rectum.
The caecum is a small blind sac which hosts some symbiotic microorganisms.
It is vestigial in humans and is associated with the vermiform appendix.

(B) In humans,the dental formula consists of four types of teeth: Incisors $(I)$,Canines $(C)$,Premolars $(PM)$,and Molars $(M)$.
Incisors are the front teeth specialized for cutting and biting food.
Canines are used for tearing,while Premolars and Molars are used for grinding and crushing food.
Therefore,the correct answer is Incisors.

(A) The hepatic portal system is a specialized vascular connection that exists between the digestive tract and the liver.
Deoxygenated blood,which is rich in nutrients absorbed from the digestive system,is transported to the liver via the hepatic portal vein before it is delivered to the systemic circulation.
This arrangement allows the liver to process,detoxify,and store nutrients before they reach the rest of the body.
Therefore,the correct pathway is from the digestive system to the liver.

(D) In humans,each tooth is embedded in a socket of the jaw bone. This type of attachment is called $Thecodont$. The term $Thecodont$ refers to the condition where teeth are fixed in bony sockets (alveoli) of the jaw.

(A) Ruminant mammals,such as cows,sheep,and goats,possess a complex stomach consisting of four distinct chambers: the rumen,reticulum,omasum,and abomasum.
$1$. The $Rumen$ is the largest chamber where fermentation occurs.
$2$. The $Reticulum$ acts as a filter.
$3$. The $Omasum$ is involved in water absorption.
$4$. The $Abomasum$ is the 'true stomach' where digestive enzymes are secreted.
Therefore,the correct answer is $A$ (Four).

(D) In mammals like rabbits,the stomach and the intestine are separated by a muscular valve known as the $Pyloric$ $sphincter$.
This sphincter regulates the passage of partially digested food (chyme) from the stomach into the small intestine (duodenum).
It prevents the backflow of food and ensures that the acidic chyme is released in controlled amounts for further digestion and absorption.

(B) The dental formula of a rabbit is $I: 2/1, C: 0/0, PM: 3/2, M: 3/3$.
To calculate the total number of incisors $(I)$:
Upper jaw has $2$ incisors on each side,so $2 \times 2 = 4$.
Lower jaw has $1$ incisor on each side,so $1 \times 2 = 2$.
Total number of incisors = $4 + 2 = 6$.

(A) The tooth is composed of several layers. The outermost layer,which covers the crown of the tooth,is known as enamel. Enamel is the hardest substance in the human body,even harder than bone. It is primarily composed of calcium hydroxyapatite,which provides the necessary strength to withstand the mechanical forces of chewing and grinding food.

(D) Humans have a diphyodont dentition,meaning they have two sets of teeth during their lifetime: deciduous (milk) teeth and permanent teeth.
Total number of permanent teeth in an adult is $32$.
Out of these $32$ teeth,$20$ teeth are replaced by permanent teeth (these are the teeth that grow twice).
The remaining teeth,which grow only once in a lifetime,are the $12$ molars ($3$ molars on each side of each jaw).
Therefore,the number of teeth that grow only once is $12$.

(A) The large intestine, specifically the colon, has longitudinal muscle bands known as $Taeniae \text{ } coli$.
These bands are shorter than the rest of the colon wall, causing the colon to pucker into small sac-like structures known as $Haustra$.
$Crypts \text{ } of \text{ } Lieberkuhn$ are found in the small intestine, and $Zymogen \text{ } cells$ are involved in enzyme secretion.

(A) The dental formula represents the arrangement of teeth in one half of the upper and lower jaw.
For an adult human,the arrangement is $2$ incisors,$1$ canine,$2$ premolars,and $3$ molars on each side of both jaws.
Therefore,the dental formula is expressed as $\frac{2123}{2123}$.
This gives a total of $(2+1+2+3) \times 2 = 16$ teeth in each jaw,resulting in a total of $32$ permanent teeth.

(B) The inner wall of the stomach contains several longitudinal folds known as $Rugae$.
These folds allow the stomach to expand when it is filled with food,increasing its storage capacity.
$Villi$ are finger-like projections found in the small intestine,not the stomach.
Therefore,the correct option is $B$.

(A) The gallbladder is a small,pear-shaped organ that stores and concentrates bile produced by the liver. Anatomically,it is situated on the visceral surface of the liver,specifically within a depression or fossa located on the inferior aspect of the right lobe of the liver.

(C) In rabbits,cellulose is a major component of their diet.
Since rabbits are herbivores,they possess a specialized digestive structure called the $Caecum$ (a large,blind sac located at the junction of the small intestine and large intestine).
The $Caecum$ contains symbiotic microorganisms (bacteria) that produce the enzyme cellulase,which breaks down cellulose into simpler carbohydrates through fermentation.
Therefore,the digestion of cellulose in rabbits occurs in the $Caecum$.

(B) Peyer's patches are small masses of lymphatic tissue found throughout the ileum region of the small intestine.
They are a critical part of the immune system of the gut-associated lymphoid tissue $(GALT)$.
Their primary function is to monitor the intestinal bacteria population and prevent the growth of pathogenic bacteria.
They contain specialized cells that produce lymphocytes,which are essential for the body's immune response.

(A) Rabbits are herbivores and possess a specialized dental formula.
They lack canines,which are typically used for tearing flesh in carnivores.
Instead,they have a gap between their incisors and premolars known as the diastema,which allows them to manipulate plant material efficiently.

(D) The Crypts of Lieberkühn are tubular glands located between the villi of the small intestine.
These glands secrete intestinal juice (succus entericus),which contains various enzymes that help in the final stages of digestion.
Therefore,they are a characteristic feature of the small intestine.

(C) In rabbits,there are $4$ pairs of salivary glands present. These include the parotid,submaxillary (submandibular),sublingual,and infraorbital glands. Therefore,the correct answer is $4$ pairs.