Digestion, Absorption and Assimilation of Various Food Stuffs

 

Digestion, Absorption and Assimilation of Various Food Stuffs

A clear visual diagram illustrating the human digestive system, including the mouth, stomach, liver, pancreas, and small intestine, and how each contributes to digestion, nutrient absorption through villi, and assimilation into the bloodstream.

Introduction

Digestion, absorption, and assimilation are the three key physiological processes through which our body transforms food into energy and nutrients. These processes are essential for sustaining life, enabling growth, repair, and metabolism. In this article, we’ll break down how each stage works, from the moment food enters the mouth to the point it nourishes cells.

1. Digestion:

Digestion is the mechanical and chemical breakdown of complex food substances into simpler molecules that can be absorbed.

Where It Happens:

1. Mouth: Saliva contains amylase which starts breaking down starch.

2. Stomach: Gastric juice (with pepsin) digests proteins.

3. Small Intestine: Bile (from the liver) emulsifies fats, and enzymes from the pancreas and intestinal lining finish the digestion of all macronutrients.

Key Enzymes:

Enzyme	Acts On	End Product
Amylase	Starch	Maltose
Pepsin	Proteins	Peptides
Lipase	Fats	Fatty acids + Glycerol

2. Absorption: 

Absorption is the process where digested food molecules pass through the intestinal lining into the blood or lymph.

Where It Happens:

Small Intestine (especially the ileum): It contains finger-like projections called villi and microvilli that increase surface area for absorption.

What Gets Absorbed and How:

1. Glucose and amino acids → absorbed into blood capillaries.

2. Fatty acids and glycerol → absorbed into lacteals (lymph vessels).

3. Vitamins and minerals → absorbed depending on solubility.

3. Assimilation: 

Assimilation is the utilization of absorbed nutrients by body tissues for energy, growth, and repair.

What Happens:

1. Glucose is oxidized in cells to release energy (ATP).

2. Amino acids are used to synthesize proteins (e.g., enzymes, muscle fibers).

3. Fatty acids are used to build membranes or stored as fat for energy reserves.

Organs Involved: Liver: Converts excess glucose to glycogen; detoxifies substances and Cells: Use the absorbed nutrients in metabolic processes.

References 

1. Sherwood, L. (2015). Human Physiology: From Cells to Systems (9th ed.). Cengage Learning.

2. Guyton, A. C., & Hall, J. E. (2016). Textbook of Medical Physiology (13th ed.). Elsevier.

3. Tortora, G. J., & Derrickson, B. (2018). Principles of Anatomy and Physiology (15th ed.). Wiley.

4. Chatterjee, C. C. (2018). Human Physiology Volume I. CBS Publishers & Distributors.

Frequently Asked Questions (FAQs)

Q1. What is the difference between digestion and absorption?
A: Digestion breaks down food into simpler molecules, while absorption transfers those molecules into the bloodstream.

Q2. Where does most absorption take place?
A: In the small intestine, specifically in the ileum due to the presence of villi and microvilli.

Q3. What is the role of the liver in assimilation?
A: The liver processes absorbed nutrients, converts glucose to glycogen, and detoxifies harmful substances.

Q4. Can assimilation happen without absorption?
A: No. Without absorption, nutrients cannot reach cells to be assimilated.

Q5. Why are villi important in the digestive process?
A: Villi increase the surface area of the intestine, enhancing nutrient absorption efficiency.