Nutrition and the Human Digestive System

What is Nutrition?

Nutrition is the process by which living organisms obtain and use food substances to support life activities such as growth, repair, and energy production. Nutrients are chemical compounds in food that the body needs in appropriate amounts.

Types of Nutrients

1. Carbohydrates – The main energy source for the body, found in rice, bread, potatoes, and sugar.

2. Proteins – Essential for growth, repair of body cells, and production of enzymes and hormones. Found in meat, fish, eggs, and legumes.

3. Fats – Provide energy storage, protect organs, and help absorb vitamins. Sources include oil, butter, nuts, and fatty meat.

4. Vitamins – Regulate body functions and maintain health. For example, Vitamin A for vision, Vitamin C for immunity, and Vitamin D for bones.

5. Minerals – Inorganic elements needed by the body, such as calcium for bones, iron for blood, and iodine for thyroid function.

6. Water – Makes up most of the body’s composition and is essential for metabolic reactions, transporting nutrients, and regulating body temperature.

Energy and Calories

The body needs energy to carry out activities such as movement, growth, and maintaining body functions. Energy is measured in calories.

• The number of calories needed depends on age, sex, body weight, and activity level.

• For example, people who exercise need more energy than those who are less active.

Example of Energy Expenditure (in Calories)

• Sleeping: about 60 cal/hour

• Studying/reading: about 90 cal/hour

• Walking: about 200 cal/hour

• Running: about 450 cal/hour

Wise Eating Habits

The Qur’an (Surah Al-A’raf: 31) reminds us:

“Eat and drink, but do not be excessive. Indeed, Allah does not like those who are excessive.”

This verse teaches us to eat in moderation, maintain balance, and avoid overeating to stay healthy.

 

Digestive Organs

The human digestive system consists of the main organs in the digestive tract and accessory (additional) organs.

Digestive Tract

Food passes through the mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus.

Accessory Organs

These organs assist digestion mechanically and chemically, including the tongue, teeth, salivary glands, liver, gallbladder, and pancreas.

• Digestive glands produce enzymes that help break down food.

   

  Table of Digestive Organs, Enzymes Produced, and Their Functions 

  Digestive Organ	Secretion Source	Juice/Enzyme Produced	Function
  Mouth	Salivary glands	Amylase, mucus, water	Breaks down starch (amylose) into maltose
  Stomach	Stomach wall	Hydrochloric acid (HCl)	Kills bacteria, activates pepsin, softens food
  		Enzyme Rennin	Converts milk protein (caseinogen) into casein
  		Enzyme Pepsin	Breaks down proteins into proteose, peptone, and polypeptides
  Pancreas	Pancreatic cells	Enzyme Amylase	Breaks down starch into maltose and other disaccharides
  		Enzyme Lipase	Breaks down fats into fatty acids and glycerol
  		Enzyme Trypsin	Breaks down proteins into simpler polypeptides
  Small Intestine	Intestinal glands	Enzyme Maltase	Breaks down maltose into glucose
  		Enzyme Sucrase	Breaks down sucrose into glucose and fructose
  		Enzyme Peptidase	Breaks down peptides into amino acids
  		Enzyme Enterokinase	Activates trypsinogen into trypsin to digest proteins
  		Enzyme Lipase	Breaks down fats into fatty acids and glycerol

   

   

   Pic taken from  2010 Encyclopedia Britannica Inc.

 

Mouth

Inside the oral cavity, there are teeth, the tongue, and salivary glands.

• Saliva contains mucus, antibacterial substances, and the enzyme amylase.

• Digestion in the mouth occurs both mechanically (chewing by teeth and tongue) and chemically (by enzymes in saliva).

  Pharynx and Esophagus

• The pharynx connects the mouth to the esophagus. At its base, there is the epiglottis, a flap that prevents food from entering the respiratory tract.

• The esophagus pushes food toward the stomach using muscular contractions called peristalsis.

   

Stomach

• In the stomach, food is digested both mechanically (churning by stomach muscles) and chemically (by gastric juice).

• Gastric juice contains hydrochloric acid (HCl), pepsin, and rennin.

• After 2–4 hours, food turns into a semi-liquid substance called chyme, which passes into the small intestine.

  Small Intestine

  The small intestine is divided into three sections:

• Duodenum – receives bile from the gallbladder and enzymes from the pancreas (lipase, amylase, trypsin).

  • Lipase digests fats.

  • Amylase digests starch.

  • Trypsin digests proteins.

• Jejunum – the site of the final digestion before absorption.

• Ileum – the site of nutrient absorption by intestinal villi.

• Glucose, amino acids, water-soluble vitamins, and minerals are absorbed into the blood.

• Fatty acids, glycerol, and fat-soluble vitamins are absorbed into the lymph vessels before entering the bloodstream.

 

Large Intestine

• Consists of the colon (ascending, transverse, descending) and ends at the anus.

• At the junction between the small and large intestines lies the cecum and appendix, which play a role in immunity.

• The large intestine absorbs water and contains Escherichia coli bacteria that produce Vitamin K and Vitamin B12

 

Digestive Glands

• Digestive glands help in chemical digestion by producing enzymes.

• The pancreas also produces insulin, which regulates blood sugar levels.

 

Disorders of the Digestive System

1. Diarrhea – caused by bacterial or viral infections.

2. Appendicitis – inflammation of the appendix due to bacterial infection.

3. Gastritis (Maag) – caused by irregular eating habits.

4. Peptic Ulcer – caused by excessive gastric acid (HCl).

5. Constipation – due to excessive water absorption in the large intestine.

6. Mumps (Parotitis) – swelling of the parotid glands caused by viral infection.

 

KUIS 1 : organs in the digestive system 

KUIS 2 : organs in the digestive system level 2 

KUIS 3 : Digestive system quiz