Human Body: Digestion, Circulation, Respiration
Digestive System Processes
The digestive system’s mission is to transform ingested food, both physically and chemically. It breaks food down into molecules small enough for absorption and transport via the blood to all body cells.
Digestion Processes
Digestion begins in the mouth, where chewing and insalivation occur. With the help of teeth, tongue, and the muscular walls of the mouth, food is formed into a bolus.
- Mucin: A lubricant in saliva, also secreted in other parts of the alimentary tract, protects and lubricates.
- Epiglottis Function: Prevents the bolus from entering the airways by closing the entrance to the larynx during swallowing.
Stomach Function in Digestion
The stomach performs chemical and mechanical digestion. Food is dissolved by gastric juice, which is composed of mucin, hydrochloric acid, and digestive enzymes. The result of the action of gastric juice on ingested food is chyme.
Chyle is the result of the joint processing of chyme by pancreatic juice, bile, and intestinal juice, resulting in a lighter, alkaline fluid.
Circulatory System
Blood is composed of cells floating in a liquid called plasma. Its red color is due to the presence of hemoglobin, a protein located in red blood cells.
Blood Circulation Through the Heart
Blood reaches the heart via the vena cava and flows into the right atrium. It then enters the right ventricle through a valve. From the right ventricle, blood is pumped through the pulmonary arteries to the lungs, where it releases carbon dioxide and takes up oxygen. Oxygenated blood returns to the heart from the lungs through the pulmonary veins, reaching the left atrium. From the left atrium, blood passes through a valve into the left ventricle, where it is pumped out to the body via the aorta.
- Arteries: Carry oxygenated blood from the heart to all parts of the body (except the pulmonary arteries, which carry deoxygenated blood to the lungs).
- Capillaries: Microscopic vessels that form networks in contact with cells, facilitating the exchange of substances between cells and blood.
- Veins: Vessels responsible for returning deoxygenated blood to the heart (except for the pulmonary veins, which carry oxygenated blood from the lungs to the heart).
Respiratory System
The respiratory system’s mission is to capture oxygen from the air in the lungs. This oxygen is then transported by blood cells, which also collect carbon dioxide and take it to the lungs for expulsion.
Vocal Cords
Folds that protrude from the side walls of the larynx.
Air Pathway During Respiration
Air enters through the mouth or nose and travels to the lungs, passing through the larynx, trachea, and bronchi. Once in the lungs, the bronchi narrow and divide to form branches called bronchioles.
- Epithelium: Consists of two types of cells: cells with cilia and mucus-producing cells. These are found in the nasal mucosa, which retains bacteria and dust.
- Inspiration: The process by which air enters the lungs, thanks to the diaphragm lowering.
- Expiration: Occurs due to the rise of the diaphragm, which forces air out of the lungs.
- Respiratory Frequency: The number of inhalations and exhalations, which depends on the activity being performed.
Cellular Metabolism
Cellular metabolism is the set of chemical reactions that occur when molecules resulting from digestion reach the cells. There are two types: anabolism and catabolism.
- Adenosine Triphosphate (ATP): The molecule responsible for capturing and transferring energy during cellular decomposition. Also called the “universal energy currency.”
Excretory System
The main functions of the excretory system are to eliminate metabolic wastes and regulate the content of fluids and salts in the body.
The skin can be considered an excretory organ, as it removes waste products such as water, minerals, and some urea through sweat.
Excretory Organs
- Lungs: Expel air composed of water vapor and carbon dioxide.
- Skin: Expels sweat composed of water and mineral salts.
- Renal System: Expels urine, comprising water, salts, urea, and nitrogenous products.
Homeostasis
Homeostasis is the tendency of organisms to maintain a constant internal environment. Body temperature, the concentration of chemical biomolecules or compounds, osmotic pressure, and carbon dioxide content must be kept constant.