Q: Q1. Choose the correct answer among the following:\n(a) Gastric juice contains\n(i) pepsin, lipase and rennin\n(ii) trypsin, lipase and rennin\n(iii) trypsin, pepsin and lipase\n(iv) t

The correct answer is **(i) pepsin, lipase and rennin**.\n\n**Explanation:**\nGastric juice, secreted by the gastric glands in the stomach, primarily contains:\n* **Pepsinogen:** An inactive precursor (zymogen) that gets converted to active pepsin by HCl. Pepsin is a proteolytic enzyme.\n* **Gastric Lipase:** A minor fat-digesting enzyme.\n* **Prorennin:** An inactive precursor (zymogen) that gets converted to active rennin by HCl, primarily in infants, for milk protein digestion.\n* **Hydrochloric acid (HCl):** Provides an acidic medium and activates zymogens.\n\nTrypsin, on the other hand, is a pancreatic enzyme, not found in gastric juice.

Q: Q2. (b) Succus entericus is the name given to\n(i) a junction between ileum and large intestine\n(ii) intestinal juice\n(iii) swelling in the gut region\n(iv) appendix

The correct answer is **(ii) intestinal juice**.\n\n**Explanation:**\nSuccus entericus is the scientific term for the intestinal juice, which is secreted by the glands in the wall of the small intestine (Brunner's glands and crypts of Lieberkühn). It contains a variety of enzymes (e.g., disaccharidases, dipeptidases, lipases, nucleosidases) and mucus, playing a crucial role in the final stages of digestion and absorption in the small intestine.

Q: Q3. Match column I with column II\n\n**Column I** | **Column II**\n---|---\n(a) Bilirubin and biliverdin | (i) Pyloric sphincter\n(b) Hydrolysis of starch | (ii) Duodenum\n(c) Digestio

The correct matches are as follows:\n\n* **(a) Bilirubin and biliverdin - (iv) Bile pigments**\n* **(b) Hydrolysis of starch - (iii) Salivary amylase**\n* **(c) Digestion of fat - (v) Lipases**\n* **(d) Salivary gland - (ii) Duodenum**\n* **(e) Gastric gland - (i) Pyloric sphincter**\n\n**Explanation:**\n1. **Bilirubin and biliverdin** are the primary **bile pigments** formed from the breakdown of heme, giving bile its characteristic color. 2. **Hydrolysis of starch** begins in the oral cavity with the action of **salivary amylase** (also known as ptyalin). 3. **Digestion of fat** is primarily carried out by **lipases** (gastric lipase, pancreatic lipase, intestinal lipase), which break down triglycerides into fatty acids and glycerol. 4. **Gastric glands** are located in the stomach wall and secrete gastric juice. The **pyloric sphincter** is a muscular valve that regulates the passage of partially digested food (chyme) from the stomach into the duodenum. This represents an anatomical and functional association within the digestive tract. 5. The pairing of **Salivary gland** with **Duodenum** is biologically inaccurate in terms of direct function or anatomical proximity, as salivary glands are in the oral cavity and the duodenum is the first part of the small intestine. However, given the structure of the matching question where each item must be paired uniquely, and after making the most direct and accurate matches for (a), (b), (c), and (e), this is the only remaining option for (d). It's important to note this potential ambiguity in the question's design.

Q: Q13. Explain the term thecodont and diphyodont.

**Thecodont:**\nThecodont refers to the type of dentition where each tooth is embedded in a socket or groove of the jaw bone. This type of attachment provides strong anchorage for the teeth. This arrangement is characteristic of mammals, including humans, as well as crocodiles and alligators.\n\n**Diphyodont:**\nDiphyodont refers to the condition where an animal develops two sets of teeth during its lifetime. The first set is a temporary set of deciduous teeth (milk teeth or baby teeth), which are later replaced by a permanent set of adult teeth. Humans exhibit diphyodont dentition, having 20 deciduous teeth that are replaced by 32 permanent teeth.

Question 1

Q1. Choose the correct answer among the following:
(a) Gastric juice contains
(i) pepsin, lipase and rennin
(ii) trypsin, lipase and rennin
(iii) trypsin, pepsin and lipase
(iv) t

Accepted Answer

The correct answer is **(i) pepsin, lipase and rennin**.

**Explanation:**
Gastric juice, secreted by the gastric glands in the stomach, primarily contains:
*   **Pepsinogen:** An inactive precursor (zymogen) that gets converted to active pepsin by HCl. Pepsin is a proteolytic enzyme.
*   **Gastric Lipase:** A minor fat-digesting enzyme.
*   **Prorennin:** An inactive precursor (zymogen) that gets converted to active rennin by HCl, primarily in infants, for milk protein digestion.
*   **Hydrochloric acid (HCl):** Provides an acidic medium and activates zymogens.

Trypsin, on the other hand, is a pancreatic enzyme, not found in gastric juice.

Question 2

Q2. (b) Succus entericus is the name given to
(i) a junction between ileum and large intestine
(ii) intestinal juice
(iii) swelling in the gut region
(iv) appendix

Accepted Answer

The correct answer is **(ii) intestinal juice**.

**Explanation:**
Succus entericus is the scientific term for the intestinal juice, which is secreted by the glands in the wall of the small intestine (Brunner's glands and crypts of Lieberkühn). It contains a variety of enzymes (e.g., disaccharidases, dipeptidases, lipases, nucleosidases) and mucus, playing a crucial role in the final stages of digestion and absorption in the small intestine.

Question 3

Q3. Match column I with column II

**Column I** | **Column II**
---|---
(a) Bilirubin and biliverdin | (i) Pyloric sphincter
(b) Hydrolysis of starch | (ii) Duodenum
(c) Digestio

Accepted Answer

The correct matches are as follows:

*   **(a) Bilirubin and biliverdin - (iv) Bile pigments**
*   **(b) Hydrolysis of starch - (iii) Salivary amylase**
*   **(c) Digestion of fat - (v) Lipases**
*   **(d) Salivary gland - (ii) Duodenum**
*   **(e) Gastric gland - (i) Pyloric sphincter**

**Explanation:**
1.  **Bilirubin and biliverdin** are the primary **bile pigments** formed from the breakdown of heme, giving bile its characteristic color. 2.  **Hydrolysis of starch** begins in the oral cavity with the action of **salivary amylase** (also known as ptyalin). 3.  **Digestion of fat** is primarily carried out by **lipases** (gastric lipase, pancreatic lipase, intestinal lipase), which break down triglycerides into fatty acids and glycerol. 4.  **Gastric glands** are located in the stomach wall and secrete gastric juice. The **pyloric sphincter** is a muscular valve that regulates the passage of partially digested food (chyme) from the stomach into the duodenum. This represents an anatomical and functional association within the digestive tract. 5.  The pairing of **Salivary gland** with **Duodenum** is biologically inaccurate in terms of direct function or anatomical proximity, as salivary glands are in the oral cavity and the duodenum is the first part of the small intestine. However, given the structure of the matching question where each item must be paired uniquely, and after making the most direct and accurate matches for (a), (b), (c), and (e), this is the only remaining option for (d). It's important to note this potential ambiguity in the question's design.

Question 4

Q4. Answer briefly:
(a) Why are villi present in the intestine and not in the stomach?

Accepted Answer

Villi are finger-like projections found in the inner lining (mucosa) of the small intestine, and their primary function is to vastly increase the surface area for the absorption of digested nutrients. The small intestine is the main site where the majority of nutrient absorption occurs after digestion.

In contrast, the stomach's primary functions are:
1.  **Temporary storage of food:** It holds food for several hours.
2.  **Mechanical churning:** Muscular contractions mix food with gastric juice.
3.  **Initiation of protein digestion:** Pepsin begins the breakdown of proteins.

While some substances like water, alcohol, and certain drugs are absorbed in the stomach, its role in nutrient absorption is minimal compared to the small intestine. Therefore, the presence of villi in the stomach is not necessary, as its structure is adapted for digestion and storage, not extensive absorption. The stomach lining is characterized by gastric folds (rugae) which allow for expansion, rather than villi for absorption.

Question 5

Q5. (b) How does the bile help in the digestion of fats?

Accepted Answer

Bile, produced by the liver and stored in the gallbladder, plays a crucial role in the digestion and absorption of fats, even though it does not contain any digestive enzymes. Its primary function is **emulsification of fats**.

Here's how bile helps in the digestion of fats:

1.  **Emulsification:** Bile contains bile salts (e.g., sodium glycocholate and sodium taurocholate). These bile salts act as detergents, breaking down large fat globules (lipids) present in the chyme into smaller, microscopic fat droplets. This process is called emulsification.
2.  **Increased Surface Area:** By breaking down large fat globules into smaller ones, bile significantly increases the total surface area of the fat particles. This increased surface area is vital because fat-digesting enzymes, called lipases (e.g., pancreatic lipase), are water-soluble and can only act on the surface of fat droplets. A larger surface area allows lipases to act more efficiently, breaking down fats into fatty acids and glycerol more rapidly.
3.  **Micelle Formation:** Bile salts also help in the formation of micelles, which are small, water-soluble complexes of fatty acids, monoglycerides, and cholesterol. Micelles are essential for the absorption of these fat-soluble products across the intestinal lining.

Question 6

Q6. Write short notes on the functions of the following:
(a) Duodenum
(b) Caecum
(c) Peyer’s patches

Accepted Answer

Here are short notes on the functions of the specified parts of the digestive system:

### (a) Duodenum

The duodenum is the first and shortest part of the small intestine, approximately 25 cm long, shaped like a 'C'. It plays a crucial role in the chemical digestion of food.

**Functions:**
1.  **Receiving Chyme:** It receives the acidic chyme from the stomach through the pyloric sphincter.
2.  **Neutralization:** The duodenal wall, along with secretions from Brunner's glands, produces bicarbonate-rich mucus that helps neutralize the acidic chyme, protecting the duodenal lining and providing an optimal pH for pancreatic and intestinal enzymes.
3.  **Site of Major Chemical Digestion:** It is the primary site where digestive juices from the liver (bile) and pancreas (pancreatic juice) mix with the chyme. These juices contain enzymes essential for the digestion of carbohydrates, proteins, and fats.
    *   **Bile:** Emulsifies fats, increasing their surface area for lipase action.
    *   **Pancreatic Juice:** Contains amylase, lipase, trypsinogen, chymotrypsinogen, and procarboxypeptidase for carbohydrate, fat, and protein digestion.
    *   **Intestinal Juice (Succus Entericus):** Secreted by the intestinal glands, it contains disaccharidases, dipeptidases, lipases, and nucleosidases that complete the digestion process.
4.  **Initial Absorption:** While most absorption occurs in the jejunum and ileum, some absorption of water, minerals, and certain drugs begins in the duodenum.

### (b) Caecum

The caecum is a small, blind-ended pouch that marks the beginning of the large intestine. It is located in the lower right abdominal quadrant, connecting the ileum of the small intestine to the colon of the large intestine via the ileocaecal valve.

**Functions:**
1.  **Passage of Undigested Food:** It receives undigested food material, water, and electrolytes from the ileum.
2.  **Symbiotic Microorganism Habitat:** In many herbivores, the caecum is large and well-developed, housing a rich population of symbiotic microorganisms (bacteria and protozoa) that aid in the digestion of cellulose. In humans, its role in digestion is minimal.
3.  **Appendix Attachment:** A small, finger-like, vestigial organ called the vermiform appendix projects from the caecum. While its exact function in humans is debated, it is thought to have some lymphoid tissue and play a minor role in immunity.
4.  **Water and Electrolyte Absorption:** Like other parts of the large intestine, the caecum contributes to the absorption of water and electrolytes from the remaining chyme.

### (c) Peyer’s patches

Peyer's patches are aggregates of lymphoid tissue found primarily in the lamina propria of the ileum, the final section of the small intestine. They are part of the Gut-Associated Lymphoid Tissue (GALT).

**Functions:**
1.  **Immune Surveillance:** Peyer's patches act as important sites for immune surveillance within the digestive tract. They monitor the intestinal lumen for pathogens and antigens.
2.  **Antigen Presentation:** They contain specialized cells called M cells (microfold cells) that sample antigens from the intestinal lumen and present them to underlying immune cells (lymphocytes, macrophages, dendritic cells).
3.  **Immune Response Initiation:** Upon encountering pathogens or antigens, Peyer's patches initiate an immune response, leading to the production of antibodies (especially IgA) and the activation of T cells. These immune cells then migrate to other parts of the gut and body to provide widespread protection.
4.  **Protection Against Pathogens:** By generating immune responses, Peyer's patches play a critical role in preventing the entry of harmful bacteria, viruses, and other pathogens from the gut into the bloodstream and other tissues, thus maintaining gut homeostasis.

Question 7

Q7. Differentiate between:
(a) Liver and Pancreas
(b) Duodenum and Ileum
(c) Afferent and Efferent arteriole
(d) Digestion and Absorption
(e) Kasa and Kwarshiorkor

Accepted Answer

Here are the differentiations between the given pairs:

### (a) Liver and Pancreas

### (b) Duodenum and Ileum

### (c) Afferent and Efferent arteriole

*Note: This question pertains to the excretory system (kidney) and is not directly related to the chapter 'Digestion and Absorption'. However, as per the instruction, the differentiation is provided.*

### (d) Digestion and Absorption

### (e) Marasmus and Kwashiorkor (Assuming 'Kasa' is a typo for Marasmus)

Question 8

Q8. Describe the process of digestion of protein in our body.

Accepted Answer

The digestion of proteins in the human body is a complex process that begins in the stomach and is completed in the small intestine. It involves various proteolytic enzymes (proteases) that break down large protein molecules into smaller peptides and ultimately into individual amino acids, which can then be absorbed.

### 1. Digestion in the Stomach

*   **Initiation:** Protein digestion begins in the stomach, where food mixes with gastric juice.
*   **Hydrochloric Acid (HCl):** The parietal cells of the gastric glands secrete HCl. HCl serves several functions:
    *   It provides an acidic pH (1.8-3.5) optimal for the action of pepsin.
    *   It denatures proteins, unfolding their complex three-dimensional structure and making them more accessible to enzymatic action.
    *   It kills most bacteria ingested with food.
*   **Pepsin:** The chief cells (or peptic cells) of the gastric glands secrete an inactive proenzyme called **pepsinogen**. HCl converts pepsinogen into its active form, **pepsin**.
    *   Pepsin is an endopeptidase that acts on proteins, breaking them down into smaller polypeptide fragments called **proteoses** and **peptones** (or peptids).
*   **Rennin (in infants):** In infants, gastric juice also contains **rennin**, an enzyme that helps in the digestion of milk proteins (casein). Rennin coagulates milk, making it easier for pepsin to act upon.

### 2. Digestion in the Small Intestine

The partially digested food (chyme), containing proteoses and peptones, moves from the stomach into the duodenum, the first part of the small intestine. Here, it mixes with pancreatic juice and intestinal juice.

#### a. Action of Pancreatic Juice

*   The pancreas secretes several inactive proteolytic enzymes into the duodenum:
    *   **Trypsinogen**
    *   **Chymotrypsinogen**
    *   **Procarboxypeptidase**
*   **Activation:**
    *   **Enterokinase** (an enzyme secreted by the intestinal mucosa) activates trypsinogen into active **trypsin**.
    *   Trypsin, in turn, activates other pancreatic proenzymes: chymotrypsinogen into **chymotrypsin** and procarboxypeptidase into **carboxypeptidase**.
*   **Enzymatic Action:**
    *   **Trypsin** and **Chymotrypsin** are endopeptidases that further hydrolyze the proteoses and peptones into smaller peptide fragments.
    *   **Carboxypeptidase** is an exopeptidase that acts on the carboxyl end of peptide chains, releasing individual amino acids.

#### b. Action of Intestinal Juice (Succus Entericus)

*   The intestinal juice, secreted by the intestinal glands, contains a final set of enzymes that complete protein digestion.
*   **Dipeptidases:** These enzymes act on the dipeptides (the smallest peptide units) produced by the action of pancreatic enzymes, breaking them down into individual **amino acids**.

### Summary of Protein Digestion Pathway:

1.  **Proteins** (in stomach, pH 1.8-3.5) $\xrightarrow{	ext{Pepsin}}$ **Proteoses + Peptones**
2.  **Proteoses + Peptones** (in small intestine, pH 7.8-8.0) $\xrightarrow{	ext{Trypsin, Chymotrypsin}}$ **Smaller Peptides**
3.  **Smaller Peptides** (in small intestine, pH 7.8-8.0) $\xrightarrow{	ext{Carboxypeptidase}}$ **Dipeptides + Amino Acids**
4.  **Dipeptides** (in small intestine, pH 7.8-8.0) $\xrightarrow{	ext{Dipeptidases}}$ **Amino Acids**

The final products of protein digestion are amino acids, which are then ready for absorption into the bloodstream.

Question 9

Q9. Give the dental formula of human beings.

Accepted Answer

The dental formula is a shorthand notation used to represent the number and arrangement of different types of teeth in each half of the upper and lower jaws. For adult human beings, the dental formula is:

**2123 / 2123**

This formula represents the teeth in one half of the upper jaw over one half of the lower jaw. The numbers correspond to the following types of teeth, from the midline outwards:

*   **I = Incisors:** 2 in each half of the upper jaw, 2 in each half of the lower jaw.
*   **C = Canines:** 1 in each half of the upper jaw, 1 in each half of the lower jaw.
*   **P = Premolars:** 2 in each half of the upper jaw, 2 in each half of the lower jaw.
*   **M = Molars:** 3 in each half of the upper jaw, 3 in each half of the lower jaw.

So, the formula 2123/2123 means:

*   **Upper Jaw (half):** 2 Incisors, 1 Canine, 2 Premolars, 3 Molars = 8 teeth
*   **Lower Jaw (half):** 2 Incisors, 1 Canine, 2 Premolars, 3 Molars = 8 teeth

Total teeth in an adult = (8 teeth in upper half + 8 teeth in lower half) x 2 (for both sides) = 32 permanent teeth.

For deciduous (milk) teeth in children, the dental formula is typically **2102 / 2102**, indicating the absence of premolars and the third molars (wisdom teeth).

Question 10

Q10. Bile juice contains no digestive enzymes, yet it is important for digestion. Why?

Accepted Answer

Bile juice, produced by the liver and stored in the gallbladder, indeed does not contain any digestive enzymes. However, it is absolutely crucial for the digestion and absorption of fats in the small intestine due to the following reasons:

1.  **Emulsification of Fats:** This is the primary and most vital function of bile. Bile salts (e.g., sodium glycocholate and sodium taurocholate) present in bile break down large fat globules into smaller, microscopic fat droplets. This process is called **emulsification**. By doing so, bile significantly increases the surface area of the fat particles, making them more accessible for the action of fat-digesting enzymes (lipases).

2.  **Activation of Lipases:** Bile salts also help in activating pancreatic lipase, the main enzyme responsible for breaking down fats into fatty acids and glycerol.

3.  **Neutralization of Acidic Chyme:** Bile is alkaline (pH 7.6-8.6) and helps to neutralize the acidic chyme entering the duodenum from the stomach. This creates an optimal alkaline environment (pH 7.8-8.0) required for the activity of pancreatic and intestinal enzymes.

4.  **Formation of Micelles for Absorption:** After fats are digested into fatty acids and monoglycerides, these molecules are insoluble in water. Bile salts, along with phospholipids, surround these digested fat products to form tiny, water-soluble structures called **micelles**. Micelles are essential for transporting fatty acids and monoglycerides to the intestinal mucosal cells for absorption.

5.  **Excretion of Waste Products:** Bile also serves as a route for the excretion of waste products like bile pigments (bilirubin and biliverdin), cholesterol, and certain drugs from the body.

Without bile, fat digestion and absorption would be severely impaired, leading to malabsorption of fats and fat-soluble vitamins (A, D, E, K), and the presence of undigested fat in the feces (steatorrhea).

Question 11

Q11. Explain the role of the following in digestion:
(a) Bile
(b) Trypsin
(c) Mucus

Accepted Answer

The digestive system relies on various secretions and enzymes to break down complex food substances into simpler, absorbable forms. Here's the role of Bile, Trypsin, and Mucus:

**(a) Role of Bile in Digestion:**
Bile is a yellowish-green alkaline fluid produced by the liver and stored in the gallbladder. It does not contain any digestive enzymes but plays a crucial role in fat digestion and absorption.

*   **Emulsification of Fats:** Bile salts (sodium glycocholate and sodium taurocholate) reduce the surface tension of large fat globules, breaking them down into smaller droplets. This process, called emulsification, significantly increases the surface area for lipase enzymes to act upon, making fat digestion more efficient.
*   **Activation of Lipase:** Bile salts activate pancreatic lipase, the primary enzyme responsible for fat digestion.
*   **Absorption of Fats and Fat-soluble Vitamins:** Bile salts form micelles with fatty acids and monoglycerides, facilitating their absorption into the intestinal cells. They also aid in the absorption of fat-soluble vitamins (A, D, E, K).
*   **Excretion of Waste Products:** Bile also serves as a route for the excretion of bilirubin (a breakdown product of hemoglobin), cholesterol, and certain drugs.

**(b) Role of Trypsin in Digestion:**
Trypsin is a potent proteolytic enzyme (protein-digesting enzyme) secreted by the pancreas as an inactive zymogen called trypsinogen. It plays a central role in protein digestion in the small intestine.

*   **Activation:** Trypsinogen is activated into active trypsin by the enzyme enterokinase (or enteropeptidase), secreted by the intestinal mucosa. Once activated, trypsin can also auto-activate other trypsinogen molecules.
*   **Protein Digestion:** Trypsin hydrolyzes proteins and proteoses (partially digested proteins) into smaller peptides, such as dipeptides and tripeptides. It specifically cleaves peptide bonds on the carboxyl side of basic amino acids (lysine and arginine).
*   **Activation of Other Pancreatic Enzymes:** Trypsin is crucial for activating other inactive pancreatic enzymes like chymotrypsinogen (to chymotrypsin), procarboxypeptidases (to carboxypeptidases), and proelastase (to elastase), thereby initiating a cascade of protein digestion.

**(c) Role of Mucus in Digestion:**
Mucus is a viscous, slippery secretion produced by goblet cells and mucous glands throughout the alimentary canal. It is primarily composed of glycoproteins (mucins) and water.

*   **Lubrication:** Mucus lubricates the food particles, making it easier for them to pass through the digestive tract (e.g., in the esophagus and stomach).
*   **Protection:** It forms a protective layer over the epithelial lining of the gastrointestinal tract, shielding it from mechanical injury, chemical abrasion, and the corrosive action of digestive acids (like HCl in the stomach) and enzymes (like pepsin). In the stomach, the bicarbonate ions trapped within the mucus layer neutralize acid, preventing self-digestion.
*   **Binding Agent:** In the mouth, mucus helps bind food particles together to form a bolus, facilitating swallowing.
*   **Antimicrobial Properties:** Mucus contains antibodies (IgA) and lysozyme, which provide a degree of immune protection against pathogens.

Question 12

Q12. Discuss the main steps in the digestion of proteins in the alimentary canal.

Accepted Answer

Protein digestion begins in the stomach and is completed in the small intestine. It involves a series of proteolytic enzymes that break down complex proteins into simpler amino acids, which can then be absorbed.

Here are the main steps in the digestion of proteins in the alimentary canal:

**1. Digestion in the Stomach:**
*   **Initiation:** Protein digestion begins in the stomach. The gastric glands secrete hydrochloric acid (HCl) and pepsinogen.
*   **Denaturation by HCl:** Hydrochloric acid creates a highly acidic environment (pH 1.8-2.0), which denatures proteins, unfolding their complex three-dimensional structure. This makes them more accessible to enzymatic action.
*   **Activation of Pepsinogen:** HCl also activates the inactive proenzyme pepsinogen into its active form, pepsin.
*   **Action of Pepsin:** Pepsin is the primary proteolytic enzyme in the stomach. It hydrolyzes proteins into proteoses (large polypeptides) and peptones (smaller polypeptides). Pepsin is most active at an acidic pH.

**2. Digestion in the Small Intestine:**
Protein digestion continues and is completed in the duodenum and jejunum of the small intestine, involving both pancreatic and intestinal enzymes.

*   **Pancreatic Enzymes:** The pancreas secretes pancreatic juice containing inactive proteolytic enzymes: trypsinogen, chymotrypsinogen, and procarboxypeptidases.
    *   **Activation:** Trypsinogen is activated to active trypsin by the enzyme enterokinase (or enteropeptidase) secreted by the intestinal mucosa. Once formed, trypsin then activates chymotrypsinogen into chymotrypsin and procarboxypeptidases into carboxypeptidases.
    *   **Action of Trypsin and Chymotrypsin:** Trypsin and chymotrypsin are endopeptidases that act on the proteoses and peptones (from stomach digestion) and intact proteins, breaking them down into smaller peptide fragments (dipeptides, tripeptides, and oligopeptides).
    *   **Action of Carboxypeptidases:** Carboxypeptidases are exopeptidases that act on the carboxyl end of the polypeptide chains, releasing individual amino acids.

*   **Intestinal Enzymes (Brush Border Enzymes):** The intestinal mucosa secretes intestinal juice (succus entericus), which contains a variety of enzymes, including aminopeptidases and dipeptidases.
    *   **Action of Aminopeptidases:** Aminopeptidases are exopeptidases that act on the amino end of the polypeptide chains, releasing individual amino acids.
    *   **Action of Dipeptidases:** Dipeptidases hydrolyze dipeptides into their constituent individual amino acids.

**3. Final Products and Absorption:**
The final products of protein digestion are individual amino acids. These amino acids are then absorbed through the intestinal villi into the bloodstream and transported to the liver and then to other body cells for protein synthesis or energy production.

Question 13

Q13. Explain the term thecodont and diphyodont.

Accepted Answer

**Thecodont:**
Thecodont refers to the type of dentition where each tooth is embedded in a socket or groove of the jaw bone. This type of attachment provides strong anchorage for the teeth. This arrangement is characteristic of mammals, including humans, as well as crocodiles and alligators.

**Diphyodont:**
Diphyodont refers to the condition where an animal develops two sets of teeth during its lifetime. The first set is a temporary set of deciduous teeth (milk teeth or baby teeth), which are later replaced by a permanent set of adult teeth. Humans exhibit diphyodont dentition, having 20 deciduous teeth that are replaced by 32 permanent teeth.

Chapter 16: Digestion and Absorption