Human Nutrition: Body Systems and Digestion Process

How Organisms Obtain Nutrients

Unicellular Organisms: Direct Nutrient Exchange

Unicellular living organisms perform nutrition by exchanging substances directly with their surrounding environment. Nutrients and oxygen enter the cell through a plasma membrane, through which waste is also expelled.

Multicellular Organisms: Systemic Nutrition

Multicellular living organisms, such as human beings, have most cells that do not come into direct contact with the outside world and cannot exchange substances with it directly. The nutrition function is performed through the joint action of different systems that act as intermediaries between the outside world and cells.

Essential Body Systems for Human Nutrition

The Digestive System: Nutrient Absorption

The digestive system transforms food into simpler substances, which are absorbed into the bloodstream.

The Respiratory System: Gas Exchange

The respiratory system takes oxygen and transfers it to the blood. It also takes carbon dioxide from the blood and expels it out of the body.

The Circulatory System: Nutrient & Oxygen Transport

The circulatory system uses the blood to carry nutrients and oxygen to cells.

The Lymphatic System: Circulatory Support

The lymphatic system works with the circulatory system to transport substances.

The Excretory System: Waste Elimination

The excretory system extracts waste substances produced by cellular activity from the blood before expelling them from the body.

The Human Digestive System: A Closer Look

The digestive system is a set of organs that perform the task of digestion. It transforms food into simpler substances, which are then passed into the bloodstream, meanwhile eliminating any undigested material.

Digestive Enzymes: Catalysts for Food Breakdown

Digestive enzymes are a type of proteins that accelerate the breakdown of complex food substances into their simpler components.

The Mouth: Beginning of Digestion

• Teeth: Chew and grind food (mechanical digestion).
• Taste Buds: Perceive taste.
• Saliva: Initiates chemical digestion.
• Tongue: Pushes food for deglutition (swallowing).

The Pharynx: Dual Role in Digestion & Respiration

The pharynx is a tube belonging to both the digestive and respiratory systems. The epiglottis prevents food from blocking the respiratory system. It connects the mouth with the esophagus.

The Esophagus: Peristalsis and Food Movement

The esophagus connects the pharynx to the stomach. Food moves down the esophagus via peristaltic movements.

The Stomach: Churning, Juices, and Chyme Formation

The stomach is connected to the esophagus through the cardia and to the small intestine through the pylorus. Gastric glands secrete juices that digest food. The food mixed with gastric juices is called chyme. Gastric juices perform chemical digestion, while the muscles of the stomach perform mechanical digestion.