Unit 1: Human Digestive System — Long Questions

Ans. Key Points Nutrition | Main steps of Nutrition

1. Nutrition: Nutrition is how organisms get and use nutrients. It helps them to grow, stay healthy, and repair their bodies.

2. Heterotrophic Nutrition
Animals, including humans, cannot make their own food. They get it from other organisms. This is called heterotrophic nutrition.

3. Main Steps of Nutrition
In animals, nutrition takes place in the following main steps:
a. Ingestion: Taking in food and drinks through the mouth.
b. Digestion: Breaking food into smaller parts the body can absorb.
c. Absorption: Moving nutrients from the digested food into the blood or lymph.
d. Assimilation: Using the absorbed nutrients in cells and tissues.
e. Egestion: Removing undigested food and waste from the body

Ans. Key Points Digestion | Occurrence

1. Digestion: The food we eat consists of polymers i.e., large molecules like carbohydrates, proteins, and fats. They cannot pass through cell membranes. These polymers must be broken down into smaller, soluble parts called monomers - like sugars (glucose), amino acids, and fatty acids. This process is called digestion. These small molecules can enter the cells

2. Occurrence: This process happens inside our digestive system.

Ans. Key Points Parts of Alimentary Canal | Oral Cavity | Oesophagus Stomach Small Intestine | Large Intestine

Parts of Alimentary Canal

The human digestive system consists of a long tube and some helper (accessory) organs. The tube is called the alimentary canal. It starts at the mouth and ends at the anus. Alimentary canal consists of;

• Oral cavity: Involves in digestion of carbohydrates.
• Oesophagus: Responsible for the transport of food.
• Stomach: Involves in storage of food, and also involves in partial digestion of proteins.
• Small intestine: Most of the digestion and absorption of food occurs in small intestine.
• Large intestine: Egestion of waste food takes place in large intestine, absorption of water and vitamins also occur here.

The accessory organs (glands) consist of;

• Salivary glands
• Liver
• Pancreas

The salivary glands, liver, and pancreas send their juices into the alimentary canal and aid in digestion.

Ans. Key Points Oral Cavity | Mechanical Digestion | Chemical Digestion | Swallowing

(a) Oral Cavity: The space behind mouth is called oral cavity or mouth cavity. It contains taste buds on the surface of tongue for the taste of food.

(b) Functions

(i) Mechanical Digestion: The mechanical digestion of food begins in oral cavity. During mechanical digestion, the teeth cut and grind food into smaller pieces.

(ii) Chemical Digestion: In oral cavity, partial chemical digestion of carbohydrates is done by three pairs of salivary glands.

• These glands are attached with oral cavity and secrete saliva - a mixture of water, mucus, and a digestive enzyme called salivary amylase.
• Water and mucous moisten the food pieces.
• Salivary amylase breaks down the starch present in food into maltose.

(iii) Swallowing

• After the physical and partial chemical digestion, the food mass in oral cavity is called bolus.
• It is swallowed by pushing it into the pharynx.
• For swallowing, the tongue moves the bolus to the back of the oral cavity. The swallowed food enters the pharynx.
• During swallowing, the palate (roof of oral cavity) moves upward to close the opening of the nasal cavity.

Ans. Key Points Pharynx | Oesophagus | Peristalsis

1. Pharynx

(a) Introduction: Pharynx is a short tube-like part after oral cavity. It connects oral cavity to oesophagus and also connects nose to windpipe (trachea).

(b) Functions

• The process of chemical digestion that started in oral cavity continues here.
• An important function of pharynx is to prevent the entry of food particles into lungs.
• It is done with the help of an elastic cartilage tissue called epiglottis.
• When swallowed food passes through pharynx, the top of trachea (windpipe) is pushed up against epiglottis.
• In this way, the opening of trachea (glottis) closes and the swallowed food passes over it.
• These waves of muscular contraction are called peristalsis.

2. Oesophagus

(a) Introduction: Oesophagus is a long tube (about 25 cm or 9.84 inches long). It connects the pharynx to the stomach.

(b) Functions

• When food enters oesophagus, successive waves of contraction are generated in its muscular walls.
• These waves of contractions move food along the oesophagus to the stomach.
• These waves of muscular contraction are called peristalsis.

Ans. Key Points Stomach | Structure | Functions (Chemical and Mechanical Digestion)

Stomach

1. Shape and Location: J-shaped stomach is located in the upper left side of the abdominal cavity, below the diaphragm.

2. Structure

Cardiac End and Pyloric End: The part of stomach immediately after oesophagus is called cardiac end while the part before small intestine is called pyloric end.

Cardiac Sphincter At the junction of the oesophagus and stomach, there is sphincter (ring of muscles) called cardiac sphincter (lower oesophageal sphincter). It prevents food from flowing back from stomach into the oesophagus.

Pyloric Sphincter Similarly, pyloric sphincter is present between stomach and small intestine.

3. Functions

(a) Process of digestion in Stomach: Stomach is responsible for the mechanical and partial chemical digestion of food. It also stores food. The walls of stomach are made of thick smooth muscles. When food arrives in stomach, these muscles contract rigorously. Their contractions help in the churning (breaking down) of food into smaller particles. Heat is also produced due to this churning. This heat helps to melt the lipids.

(b) Gastric Juice: Many small gastric glands present in the inner walls of stomach secrete gastric juice. It contains hydrochloric acid, an inactive enzyme pepsinogen, and mucus.

• HCl: Hydrochloric acid converts pepsinogen into an active enzyme pepsin. Hydrochloric acid also kills pathogenic bacteria present in food.
• Pepsin: Pepsin breaks large proteins into shorter chains of amino acids called peptides.
• Mucus: The mucus forms a protective layer on the inner walls of stomach. Here, it neutralizes the HCl. So, pepsinogen cannot be activated here and the walls are protected from breakdown.

4. Chyme Formation

Food usually remains in stomach for three to four hours. Due to the actions in stomach, the food becomes a soup-like mixture called chyme.

5. Entry of Chyme into small intestine

The pyloric sphincter controls the flow of chyme. Each time the pyloric sphincter opens, about 5 to 15 ml of chyme moves into the small intestine.

Ans. Key Points Small Intestine | Digestion in small intestine | Pancreatic Juice

Small Intestine

1. Length: Small intestine is highly coiled tube and is nearly 7 m (about 23 ft) long.

2. Parts: It has three parts:

(a) Duodenum is the first part. It is about 25 cm (about 10 inches) long.
(b) Jejunum is the middle part. It is about 2.5 m (about 8 feet) long.
(c) Ileum is the last part. It is about 4 m (about 13 feet) long.

3. Digestion in small intestine

In duodenum, secretions of liver and pancreas act on food.

(a) Bile

• The secretion of liver i.e. bile enters duodenum through common bile duct.
• Bile contains salts which are produced in the liver. These bile salts break large fats into small droplets.
• Bile also contains pigments that are formed when RBCs are broken in liver. These pigments are removed from the body with faeces.
• In this way, a milky fluid is formed in which fat droplets are kept separate.

(b) Pancreatic Juice / Justify the importance of Pancreas

• The secretion of pancreas i.e., pancreatic juice enters duodenum through pancreatic duct, which joins the common bile duct before entering duodenum.
• Pancreatic juice contains many enzymes e.g., trypsin, pancreatic amylase and lipase. These enzymes digest proteins, carbohydrates and lipids respectively.
• Pancreatic juice also contains sodium bicarbonate that neutralizes the acidity of chyme.
• The glands present in the walls of small intestine also secrete enzymes for the complete digestion of all types of food.

Ans. Key Point Absorption of Food

1. Introduction: After the complete digestion of food, the end products i.e., amino acids, simple sugars, glycerol, and fatty acids etc. move from alimentary canal into the circulatory system.

2. Villi: The inner walls of small intestine are highly folded. Moreover, these folds have millions of finger-like projections called villi (singular, villus).

3. Functions of Villi: The folds and villi provide a large surface area for the absorption of food. Food molecules are absorbed through this surface through diffusion and active transport.

4. Structure of Villus: The wall of a villus is made of a single layer of cells. Inside the villus, there are blood capillaries and a lymph vessel called lacteal.

5. Absorption of Fatty Acids and Glycerol: The glycerol and fatty acids present in small intestine enter the lacteals of villi. The lacteals carry them to the main lymph vessels, which empty into the blood vessels near the heart.

6. Absorption of Sugar and Amino Acids: Amino acids and simple sugars enter the blood capillaries of villi. These capillaries join to make hepatic portal vein which carries the amino acids and sugars to liver. From liver, the hepatic vein carries these nutrients to heart and then to all parts of the body.

Ans. Key Points Parts of Large Intestine | Egestion

1. Large Intestine

(a) Introduction: After the absorption of digested food material and some water, the remaining undigested material and water move to the large intestine by peristalsis. Absorption of more water occurs from large intestine.

(b) Parts of Large Intestine: Large intestine has 3 parts:

(i) Caecum (a pouch that forms junction with small intestine).
(ii) Colon.
(iii) Rectum.

(c) Egestion: Due to it, the undigested material solidifies and is now called faeces. The faeces contain the undigested material, large number of bacteria, broken cells of alimentary canal, bile pigments and water. Faeces are temporarily stored in the rectum. During egestion, faeces are expelled out through anus.

Ans. Key Points Location of Liver | Gall-bladder | Bile | Function of Liver

1. Role of Liver

(a) Location and Weight: Liver is a large organ located to the right of the stomach. In an adult human, it weighs about 1.5 kg.

(b) Gall-bladder: There is a sac-like organ, called gall bladder, on the ventral side of liver

(c) Bile: Liver secretes bile, which is stored in gall bladder. The common bile duct carries bile from gall bladder into duodenum. Bile does not contain enzymes but it has salts which break fats into small droplets. Bile salts also keep fat droplets separate from one another. It helps the enzymes to attack on lipids.

(d) Functions of Liver: Liver also performs many other functions in the body. For example,

(i) Stores glucose as glycogen and breaks glycogen to glucose when required.
(ii) Stores fat-soluble vitamins.
(iii) Deamination: Breaks amino acids. In this process, harmful ammonia is produced.
(iv) Detoxification: Converts ammonia into less toxic urea for excretion through urine. Breaks toxic substances e.g., alcohol.
(v) Breaks the RBCs which have completed their life spans.
(vi) Prepares vitamin-A from carotene.
(vii) Produces heat in cold temperatures by speeding up metabolism.

Ans. Key Points Diarrhoea: Causes, Symptoms, Treatment | Constipation: Causes, Symptoms, Treatment | Ulcers: Causes, Symptoms, Treatment

1. Diarrhoea

Diarrhoea is characterized by frequent, loose, or watery stools. Diarrhoea can lead to dehydration, especially in children and the adults.

(a) Signs and Symptoms: Frequent, loose, or watery stools, abdominal cramps or pain, bloating, and dehydration (thirst, dry mouth, dark urine).

(b) Causes: Infections (bacterial, viral, or parasitic), food allergies, stress, certain medications (e.g., antibiotics).

(c) Treatment: Drinking plenty of fluids, eating a balanced diet, using anti diarrheal medications, taking antibiotics or other treatments (in severe cases).

(d) Prevention: Washing hands regularly, especially before eating or after using the bathroom, avoiding contaminated food or water, avoid stress.

2. Constipation

Constipation is a condition in which faeces are not eliminated from the body at regular intervals.

(a) Signs and Symptoms: Infrequent or difficult bowel movements (less than 3 times a week), hard and dry stools, abdominal discomfort or bloating.

(b) Causes: Lack of fibre in diet, dehydration, lack of physical activity, certain medicines (e.g., painkillers, iron supplements), and other diseases (e.g., diabetes).

(c) Treatment: Increasing fibre intake (fruits, vegetables, whole grains), drinking plenty of water, regular exercise, use medicines called laxatives.

(d) Prevention: Eating a high-fibre diet, drinking plenty of fluids.

3. Ulcers

Peptic ulcers are sores that develop in the walls of alimentary canal.

(a) Types of Ulcers

(i) Ulcer usually develops in the walls of stomach and is called gastric ulcer
(ii) However, ulcers may also develop in duodenum (duodenal ulcer).
(iii) The ulcer of oesophagus is called oesophageal ulcer

(b) Signs and Symptoms: Burning stomach pain, rush of saliva after regurgitation, loss of appetite, weight loss, blood vomiting (in severe cases).

(c) Causes: Infection due to Helicobacter pylori bacteria, long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs), excessive alcohol consumption, smoking, stress (though not a direct cause, it can make symptoms worse).

(d) Treatment: Antibiotics to clear H. pylori infection, other medicines called antacids and proton pump inhibitors are also used to cure ulcer

(e) Prevention: Avoiding excessive use of painkillers (NSAIDs), avoiding spicy foods, eating a balanced diet.