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🧠 Human Physiology – The Digestive System (Part 3)

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🧬 The Liver – Master Chemist of the Body

The liver is the largest gland in the human body and plays a crucial role in digestion, metabolism, and detoxification.

📍 Location & Structure

• The liver is located in the upper right side of the abdominal cavity, just below the diaphragm.

• It is divided into two main lobes.

• The functional units of the liver are called hepatic lobules, each made up of hepatocytes.

🌿 Functions of the Liver in Digestion

1. Bile Production:

   • The liver produces bile, a yellowish-green alkaline fluid.

   • Bile contains bile salts, bile pigments (bilirubin and biliverdin), and cholesterol.

   • It is stored in the gallbladder and released into the duodenum.

2. Emulsification of Fats:

   • Bile salts help break down large fat globules into smaller droplets (emulsification), increasing the surface area for enzymes to act on.

3. No Enzymes in Bile:

   • Unlike other digestive juices, bile contains no digestive enzymes, but it is essential for digestion, especially of fats.

4. Other Roles:

   • Detoxifies harmful substances.

   • Stores glycogen and vitamins.

   • Synthesizes plasma proteins like albumin and fibrinogen.

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🔬 The Pancreas – Dual Role Gland

The pancreas is both an exocrine and endocrine gland.

📌 Exocrine Functions (Digestive Role)

• The exocrine pancreas secretes pancreatic juice through the pancreatic duct into the duodenum.

• This juice is alkaline and contains:

  1. Pancreatic amylase – breaks down starch into maltose.

  2. Trypsin and chymotrypsin – break down proteins into peptides.

  3. Carboxypeptidase – breaks peptides into amino acids.

  4. Lipase – digests fats into fatty acids and glycerol.

  5. Nucleases – break down nucleic acids (DNA & RNA).

📌 Endocrine Functions

• The endocrine part of the pancreas includes Islets of Langerhans, which secrete:

  • Insulin (by β-cells): lowers blood sugar.

  • Glucagon (by α-cells): raises blood sugar.

Although these hormones are not directly involved in digestion, they play a major role in metabolism and glucose homeostasis.

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⏱️ Hormonal Control of Digestive Secretions

Digestion is not just about enzymes – it’s precisely timed and regulated by several hormones.

💡 Key Hormones Involved

1. Gastrin

   • Secreted by: G-cells in the stomach.

   • Stimulates: gastric juice secretion, especially HCl and pepsinogen.

2. Secretin

   • Secreted by: duodenum in response to acidic chyme.

   • Stimulates: pancreas to release bicarbonate-rich juice to neutralize acid.

   • Inhibits: gastric secretion and motility.

3. Cholecystokinin (CCK)

   • Secreted by: duodenum.

   • Stimulates: release of bile from gallbladder and digestive enzymes from pancreas.

   • Slows down gastric emptying.

4. Enterogastrone

   • Secreted by: intestinal wall.

   • Inhibits: gastric secretions and motility, thus slowing digestion when needed.

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🧪 NEET PYQs – Liver, Pancreas & Hormonal Regulation

1. Bile helps in digestion of:

   • A) Proteins

   • B) Carbohydrates

   • C) Fats

   • D) Vitamins
     ✅ Answer: C) Fats

2. Which of the following enzymes is not present in pancreatic juice?

   • A) Lipase

   • B) Trypsin

   • C) Pepsin

   • D) Amylase
     ✅ Answer: C) Pepsin

3. Secretin hormone regulates the function of:

   • A) Stomach

   • B) Liver

   • C) Pancreas

   • D) Salivary glands
     ✅ Answer: C) Pancreas

4. Hormone that stimulates the gall bladder to release bile:

   • A) Gastrin

   • B) Secretin

   • C) CCK

   • D) Enterogastrone
     ✅ Answer: C) CCK

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🧠 Wrap-Up

In Part 3, we explored:

• The digestive role of liver and bile

• The enzymatic secretions of pancreas

• The hormones that regulate digestive activities

These glands and hormones act like a control panel, ensuring digestion is smooth, efficient, and responsive to our body’s needs.

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📘 Explore more NEET biology content at:

• biologyatease1.blogspot.com

• neetpyqall.blogspot.com