Human Physiology – The Digestive System (Part 2)

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🧑‍⚕️ Human Physiology – The Digestive System (Part 2)

🌿 Absorption of Nutrients in the Small Intestine

The small intestine is the main site for the absorption of nutrients from digested food. It consists of three parts: the duodenum, jejunum, and ileum. Each of these parts plays a crucial role in different stages of digestion and absorption.

Structure of the Small Intestine

  1. Villi and Microvilli: The inner walls of the small intestine are covered in tiny, finger-like projections called villi. These villi are covered in even smaller projections called microvilli, which greatly increase the surface area for absorption. The surface area of the small intestine is further enhanced by the plicae circulares, or circular folds.

  2. Absorption of Nutrients: Nutrients like glucose, amino acids, fatty acids, glycerol, vitamins, and minerals are absorbed through the walls of the small intestine and enter the bloodstream.

🌱 The Role of Enzymes in Digestion and Absorption

The process of absorption is facilitated by several digestive enzymes produced by the pancreas and the lining of the small intestine.

1. Carbohydrate Digestion and Absorption

  • Amylase: Pancreatic amylase continues the breakdown of carbohydrates (mainly starch) into simpler sugars, such as maltose.

  • Maltase: In the small intestine, maltase breaks down maltose into glucose. Glucose is then absorbed through the intestinal walls into the bloodstream.

2. Protein Digestion and Absorption

  • Proteases (Peptidases): These enzymes, like trypsin and chymotrypsin, break down proteins into smaller peptides, which are further broken down into amino acids by enzymes like aminopeptidases.

  • The amino acids are absorbed by the epithelial cells lining the villi and transported into the bloodstream.

3. Fat Digestion and Absorption

  • Bile Salts: The liver produces bile, which emulsifies fats, breaking them into smaller droplets. This increases the surface area for the enzyme lipase to act upon.

  • Lipase: This enzyme, produced by the pancreas, breaks down fats into fatty acids and glycerol.

  • The fatty acids and glycerol are absorbed through the villi and reassembled into fat molecules within the cells, which then enter the lymphatic system before reaching the bloodstream.

🌿 Transport of Absorbed Nutrients

Once absorbed into the bloodstream, nutrients are transported to various parts of the body for utilization.

1. Glucose and Amino Acids: These nutrients are transported via the hepatic portal vein to the liver, where they may be stored or processed further. Glucose is stored as glycogen in the liver or released into the bloodstream to maintain blood sugar levels.

2. Fatty Acids and Glycerol: These are transported via the lymphatic system in the form of chylomicrons, which enter the bloodstream near the heart.

🌱 The Large Intestine – Water Absorption and Defecation

After the majority of digestion and absorption occurs in the small intestine, the remaining undigested food enters the large intestine (also known as the colon). The primary function of the large intestine is the absorption of water and electrolytes, as well as the formation and excretion of feces.

Structure of the Large Intestine

The large intestine consists of several sections:

  1. Cecum: The pouch-like beginning of the large intestine, where undigested food from the small intestine enters.

  2. Colon: The longest part of the large intestine, which absorbs water and salts from the undigested food.

  3. Rectum: The final section where feces are stored before being excreted through the anus.

Water Absorption

As undigested food passes through the colon, water and electrolytes are absorbed, leaving behind solid waste. This process is essential for maintaining the body's water balance.

Formation of Feces

The remaining waste material is compacted into feces. The feces consist of water, undigested food particles, bacteria, and cells sloughed off from the lining of the digestive tract.

Defecation Reflex

When the rectum is full, stretch receptors signal the brain to initiate the defecation reflex. The anal sphincters (internal and external) relax, and feces are expelled through the anus.

⚡ NEET PYQ Alerts – Digestive System

  1. Which part of the digestive system is responsible for absorbing most of the nutrients?

    • A) Stomach

    • B) Small Intestine

    • C) Large Intestine

    • D) Esophagus

    • Answer: B) Small Intestine

  2. The majority of water absorption occurs in which part of the digestive system?

    • A) Stomach

    • B) Small Intestine

    • C) Large Intestine

    • D) Rectum

    • Answer: C) Large Intestine

  3. Which enzyme is responsible for the breakdown of fats in the small intestine?

    • A) Amylase

    • B) Lipase

    • C) Pepsin

    • D) Trypsin

    • Answer: B) Lipase

🌿 Conclusion and What’s Next?

In Part 2, we explored the process of nutrient absorption in the small intestine and discussed the role of the large intestine in water absorption and the formation of feces.

In Part 3, we will continue our journey through the digestive system and delve deeper into the liver, pancreas, and their secretions, as well as the hormonal regulation of digestion.

Stay tuned for more insights in the next blog!

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