Describe nutrition in human and ruminants (nutrients, digestive system and processes)

The human digestive system consists of the alimentary canal (a long tube) and associated glands (liver, pancreas).

A. Digestion in the Mouth

• Ingestion: Taking food into the mouth.
• Mechanical Digestion: Teeth chew food (mastication) into smaller pieces.
• Chemical Digestion: Saliva contains salivary amylase, which begins breaking down cooked starch into maltose (a sugar).

B. Digestion in the Stomach

• Mechanical Digestion: Stomach muscles churn food (churning) to mix it with gastric juices.
• Chemical Digestion: Gastric juice contains:
  • Hydrochloric Acid (HCl): Creates an acidic environment to kill germs and activate enzymes.
  • Pepsin: Digests proteins into peptides.
  • Rennin: Coagulates milk protein.
• The semi-liquid mixture formed is called chyme.

C. Digestion in the Duodenum (Small Intestine)

• Pancreatic Juice enters here. It contains enzymes:
  • Pancreatic Amylase: Digests starch to maltose.
  • Lipase: Digests fats/oils into fatty acids and glycerol.
  • Trypsin: Digests proteins into peptides.
• Bile: Produced by the liver, stored in the gall bladder. It emulsifies fats (breaks large fat droplets into tiny ones) to increase surface area for lipase to act.

D. Digestion in the Ileum (Final Part of Small Intestine)

• Intestinal juice (Succus Entericus) completes digestion:
  • Maltase, Sucrase, Lactase: Convert disaccharides (maltose, sucrose, lactose) into simple sugars (glucose, fructose, galactose).
  • Peptidase: Converts peptides into amino acids.
  • Lipase: Completes fat digestion.

E. Absorption and Assimilation

• Villi: The inner lining of the ileum has finger-like projections called villi. They increase surface area for absorption.
• Process: Digested nutrients (glucose, amino acids) are absorbed into the blood capillaries. Fatty acids and glycerol enter the lacteals (lymphatic vessels).
• Assimilation: The blood carries these nutrients to the liver and then to all body cells for use.

F. Large Intestine

• Colon: Absorbs water from undigested material.
• Egestion: Waste (faeces) is eliminated through the anus.

Ruminants (e.g., goats, sheep, cattle) are herbivores that can digest cellulose (plant fiber) which humans cannot.

A. The Stomach Chambers

Unlike humans with one stomach, ruminants have four chambers:

1. Rumen: The largest chamber. It stores swallowed food and houses bacteria that ferment cellulose (break it down using enzymes).
2. Reticulum: Often called the "honeycomb." It helps form the cud.
3. Omasum: Absorbs water from the food.
4. Abomasum: The true stomach. It secretes gastric juices (acid and enzymes) to digest proteins, just like the human stomach.

B. The Process of Chewing the Cud

1. Ruminants swallow plant material quickly into the rumen.
2. Later, while resting, they regurgitate a soft ball of food called cud back to the mouth.
3. They chew the cud thoroughly (mastication).
4. The re-chewed food is swallowed again, bypassing the rumen and going to the reticulum, then omasum, and finally the abomasum for digestion by enzymes.

A healthy diet helps prevent nutritional disorders. We can check if a person's weight is appropriate for their height using the Body Mass Index (BMI).

Formula: $BMI = \frac{\text{Body mass (kg)}}{(\text{Height (m)})^2}$

Example: A Form 2 student in Dar es Salaam weighs 50 kg and is 1.60 m tall. $BMI = \frac{50}{(1.60)^2} = \frac{50}{2.56} = 19.53$ Interpretation: According to WHO standards, a BMI between 18.5 and 25.4 is considered a healthy (normal) weight. A BMI above 30 indicates obesity.

In Tanzania, understanding human digestion helps in planning a balanced diet. For instance, knowing that proteins (found in beans or meat) are needed for growth helps a mother ensure her child eats beans with ugali (carbohydrates) to stay healthy. Furthermore, knowing that ruminants have a four-chambered stomach helps a farmer in Dodoma understand why cattle can survive by eating grass (which humans cannot digest), while they require concentrated feeds like maize or bran to produce milk and meat efficiently.