Human Digestive and Respiratory Systems

Posted on Apr 21, 2025 in Biology

Digestive System

The function of the digestive system is to transform food into simple compounds called nutrients.

Nutrition vs. Digestion

The difference between nutrition and digestion is that:

Nutrition: Involves all the processes by which the body takes in, digests, absorbs, and uses food.
Digestion: Is the process of breaking down food into the smallest particles that can be absorbed by the blood.

It is made up of the digestive tract (mouth, pharynx, esophagus, stomach, small intestine, and large intestine) and the accessory organs (salivary glands, liver, and pancreas).

There are two types of digestion:

Mechanical: That physically breaks up the food.
Chemical: That breaks down the food through chemical reactions.

Anatomy of the Digestive System

Mouth: Saliva, tongue, and teeth work together to mix and crush the food. The food after this process is called Bolus.
Pharynx: It is a common structure of both the digestive and respiratory systems. The epiglottis closes the trachea when you swallow to prevent choking.
Esophagus: It is a muscular tube that connects the mouth with the stomach.
Liver: Produces bile that helps to absorb fats in the intestine.
Stomach: Produces gastric juices.
Gallbladder: Its function is to store the bile produced by the liver and to secrete it into the small intestine when eating fats.
Pancreas: Produces and secretes juices to the duodenum to continue digestion, and insulin and glucagon to the blood.
Small Intestine: It is divided into the duodenum, jejunum, and ileum. Digestion and nutrient absorption take place in the small intestine.
Large Intestine: It is divided into the cecum, colon, rectum, and anal canal. The appendix is found near the cecum.
Anus: It is at the end of the large intestine. Defecation is the process of ejecting feces.

Health of the Digestive System

Common disorders include:

Tooth Decay: Some bacteria that grow inside our mouth feed on food remnants and produce acid that eats away at the tooth enamel.
Constipation: It is a disorder that includes difficulty due to infrequent bowel movements or too much water absorption.
Diarrhea: It is a disorder due to too much bowel movement. It could be the result of infections, food in poor condition, or intolerance to certain foods.
Other disorders: Gastritis, Ulcers, Cirrhosis.

Respiratory System

We obtain oxygen through breathing and we exhale carbon dioxide. The respiratory system is divided into:

Airways: Tubes that connect the exterior of the body with the lungs.
Upper Airways: Nose, pharynx, and larynx.
Lungs: They are inside the thoracic cavity and are protected by the ribs.

Anatomy of the Respiratory System

Nose: Where the air is cleaned, humidified, and heated.
Pharynx: In common with the digestive system.
Larynx: The wall is made of cartilage; inside it, you can find the vocal cords.
Trachea: The wall is made of rings of cartilage.
Bronchial Tubes and Bronchioles: The trachea splits into tubes called bronchial tubes or bronchi, which further divide into bronchioles.
Alveoli: The bronchioles finally end at small sacs called alveoli where gas exchange takes place.

Gas Exchange

Occurs by diffusion in the alveoli.

Pulmonary Ventilation

Inhalation: Your intercostal muscles and diaphragm contract and increase the volume of the thoracic cavity, drawing air in.
Exhalation: Your intercostal muscles and diaphragm relax, and the volume of the thoracic cavity decreases, pushing air out.

Health of the Respiratory System