Human Digestive and Respiratory Systems: Anatomy & Function

Posted on Mar 7, 2025 in Biology

Introduction to Nutrition and Human Body Systems

Nutrition is the life function that enables living beings to obtain matter and energy. The systems involved are:

• Digestive System: This system transforms the food we eat into nutrients, which are absorbed and passed into the bloodstream.
• Respiratory System: This system takes oxygen from the air and transfers it to the blood. It also takes carbon dioxide from the blood and expels it out of the body.
• Circulatory System: This system uses blood to carry nutrients and oxygen to the cells. It also transports cellular waste from the cells to the excretory organs, where they are expelled.
• Lymphatic System: This system works with the circulatory system to transport substances.
• Excretory System: This system extracts waste substances produced by cellular activity from the blood before expelling them from the body.

Anatomy of the Digestive System

Digestive Tract: Mouth to Anus

Mouth: A cavity containing:

• Tongue with taste buds
• Teeth to chew and grind food
• Salivary glands that produce saliva

Pharynx: A short tube belonging to both the digestive and respiratory systems. It contains a gap that closes the larynx during deglutition (swallowing).

Esophagus: Food travels down to the stomach through an opening called the cardia, thanks to peristaltic movements.

Stomach: Connected to the small intestine with an opening called the pylorus. Its walls are muscular and very strong, and they produce acids to digest food.

Small Intestine: A long tube (7-8 m) with:

• Glands that secrete intestinal juices to digest food
• Intestinal villi to absorb nutrients

Large Intestine: Wider and shorter than the small intestine. It has three parts:

• Cecum with appendix
• Colon
• Rectum and Anus

Feces are formed and expelled here.

The Accessory Glands

These glands are outside the digestive tract, where they secrete their juices. These juices contain enzymes.

• Salivary Glands (Mouth): Secrete saliva into the mouth.
• Liver: Has three functions:
  • Secretes bile to help in the digestion of fats.
  • Stores glucose, iron, and vitamins.
  • Eliminates toxic substances (e.g., alcohol).
• Pancreas: An arrowhead-shaped gland with two functions:
  • Digestive gland: Produces pancreatic juice that goes to the intestine.
  • Endocrine gland: Produces insulin, which enters the blood to control sugar levels.

Digestive Illnesses

• Celiac Disease: A gluten intolerance that damages the intestinal villi.
• Tooth Decay: Tooth enamel is destroyed by acids produced by bacteria.
• Gastritis: Inflammation of the stomach wall.
• Gastric Ulcer: Wounds in the stomach lining.
• Gastroenteritis: Inflammation of the intestinal wall caused by viruses, often from contaminated food or water.
• Hepatitis: Inflammation of the liver caused by viruses, bacteria, excessive alcohol, drugs, or medication.

Anatomy of the Respiratory System

Respiratory Tract:

Nasal passages – Pharynx – Larynx – Trachea – Bronchus/Bronchi – Bronchioles

Lungs: Located in the rib cage, separated from the abdomen by the diaphragm, and surrounded by the pleura, which is filled with pleural fluid.

It is healthier to breathe through the nose than through the mouth because nasal passages purify, heat, and humidify the air.

How the Respiratory System Works

Inhalation: Air from the atmosphere enters the lungs. The diaphragm contracts, moving *downward*, and the lungs expand. *Ribs move upward and outward.*

Exhalation: Air is expelled from the lungs. The diaphragm relaxes, moving *upward*, and the lungs reduce in volume. *Ribs move downward and inward.*

Gas Exchange:

1. O₂ passes from the alveoli to the capillaries by diffusion.
2. O₂ travels in capillaries to the cells.
3. Cells perform cellular respiration, obtaining energy and producing CO₂ (waste).
4. CO₂ passes from the cells to the capillaries by diffusion.
5. CO₂ travels in capillaries to the alveoli.
6. CO₂ is expelled through exhalation.