Small Intestine: Definition, Functions and Examples

What Is The Small Intestine?

The small intestine represents an important part of the digestive system through which food is received from the stomach and then digested and absorbed. It is a long, coiled tube that starts from the stomach, ends by the large intestine, and extends to a length of about 20 feet. Its long length and structure specialisation let it efficiently process and absorb the needed nutrition for the body's functions.

Location and Extent

The small intestine lies in the abdominal cavity. Upon further division, it includes the duodenum, jejunum, and ileum. Various parts of each segment have different roles in digestion, breaking down food, and absorbing it into the bloodstream for utilisation.

Parts of the e Small Intestine

Absorption of nutrients requires a great deal of surface area within the small intestine, so its anatomy reflects this need.

Duodenum

• The first part.

• Here most of the chemical digestion is done.

Jejunum

• The middle part.

• Mainly responsible for the absorption of nutrients.

Ileum

• The last part.

• Responsible for absorption of vitamin B12 and salts of bile.

Layers of the Small Intestine

The layers of the small intestine are divided into:

Mucosa

• The innermost layer, lined with villi and microvilli

• It can increase the surface area for absorption.

Submucosa

• A supportive layer containing blood vessels, nerves and glands.

Muscularis externa

• Responsible for movements of peristalsis and segmentation.

Serosa

• Outermost protective layer.

Surface Area Adaptations

The adaptations of surface area are:

• Villi and microvilli increase surface area to promote nutrient absorption.

• Blood vessels and lymphatics are found in these structures to transport the absorbed nutrients.

Functions of the Small Intestine

The small intestine performs the important functions of digestion and food absorption.

Digestive Functions

• Secretion of enzymes: Pancreatic enzymes and intestinal enzymes break down complex molecules.

• Digestion of carbohydrates, proteins, and fats: Carbohydrates are broken down into simple sugar molecules. Proteins are broken down into amino acids and fats, into fatty acids and glycerol.

Absorptive Functions

• Nutrient Absorption: The small intestine absorbs vitamins, minerals, amino acids, and fatty acids.

• Transport Mechanisms: Nutrients will be transported through active transport, facilitated diffusion, and osmosis.

Small Intestine Digestive Process

Intrinsically related to other organs, the small intestine's digestive process is paired with definite movements for proper digestion and absorption.

Interrelationship With Other Organs

Interrelation of small intestine with other organs are:

Pancreas

• Adds enzymes such as amylase, protease, and lipase to digest the food.

Liver and gallbladder

• Produces and stores bile that emulsifies fats.

Digestive Movements of the Small Intestine

Digestive movements of the small intestine are:

Peristalsis

• Rhythmic, wave-like muscle contractions that propel food down the intestine.

Segmentation

• Periodic contractions that mix and pulverise food, thereby providing more surface area for absorption.

Diseases of The Small Intestine

The health of the small intestine is important, for it could be affected by many diseases and disorders.

Celiac Disease

• An immunological disorder in which the consumption of gluten damages the lining of the small intestine.

Crohn’s Disease

• This is one of the inflammatory bowel diseases that causes inflammation of the digested tract.

Small Intestinal Bacterial Overgrowth (SIBO)

• Too many bacteria are in the small intestine, causing bloating and diarrhoea, among other symptoms.

Prevention and Treatment

Prevention and treatment of the diseases include:

• Dietary recommendations: Ensure to have a balanced diet and an intake that has enough fiber while avoiding particular trigger foods for some conditions.

• Medications and therapies: Depending on the condition, treatments may include antibiotics, anti-inflammatory drugs, or immunosuppressants.

Small Intestine NEET MCQs (With Answers & Explanations)

Important questions asked in NEET from this topic are:

• Compartment of the ruminant stomach

• Digestion in Ruminants

Practice Questions for NEET

Q1. Identify the precise nature and origin of the enzyme Enterogastrone

1. An enzyme secreted by the gastric mucosa

2. A hormone secreted by the small intestinal mucosa

3. A hormone secreted by the duodenal mucosa

4. A secretory product of an endocrine gland associated with digestion

Correct answer: 3) A hormone secreted by the duodenal mucosa

Explanation:

Enterogastrone is a collective term for various hormones produced by the mucosa of the small intestine, primarily the duodenum. These hormones, such as secretin and cholecystokinin are released in response to the presence of chyme in the small intestine and play a role in regulating digestive processes. The term "enterogastrone" specifically emphasizes its inhibitory effect on gastric motility and acid secretion, helping to slow down the emptying of the stomach and promote efficient digestion and absorption in the small intestine.

Hence, the correct answer is option 3. A hormone secreted by the duodenal mucosa.

Q2. Assertion: The serosa is a smooth membrane made up of a thin layer of cells that release serous fluid and a thin layer of connective tissue.

Reason: Serous fluid is a lubricating fluid that minimises friction caused by muscularis action

1. Assertion and reason are both true, and reason is an accurate account of assertion.

2. Both assertion and reason are accurate, but reason does not adequately explain assertion.

3. The assertion is correct, but the reasoning is incorrect.

4. Both the assertion and reason are incorrect.

Correct answer: 1) Assertion and reason are both true, and reason is an accurate account of assertion.

Explanation:

The serosa is the outermost layer of the small intestine and is composed of a thin layer of cells that secrete serous fluid and a layer of connective tissue. The serous fluid serves as a lubricant that reduces friction caused by the movement of the muscularis layer, which helps the small intestine mix and propel its contents along its length. Therefore, both the assertion and reason are true, and reason accurately explains the assertion.

Hence, the correct answer is option 1) Assertion and reason are both true, and reason is an accurate account of assertion.

Q3. Last section of large intestine is

1. Caecum

2. Colon

3. Rectum

4. Anus

Correct answer: 3) Rectum

Explanation:

The rectum is the final part of the large intestine, situated just before the anus. It plays a vital role in the elimination of waste from the body. The rectum stores formed faeces, which are the byproducts of digestion and absorption until they are ready to be expelled from the body during defecation.

Hence, the correct answer is option 3) Rectum.

Also Read:

• MCQs on Small Intestine

• Pancreas Function in Human Body

• Intestinal Glands

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