Human Digestive, Respiratory, and Circulatory Systems
Digestive System
The digestive system is responsible for:
- Transporting food and breaking it down into nutrients.
- Absorbing nutrients into the bloodstream for distribution throughout the body.
- Expelling undigested waste.
Components of the Digestive System
- Gastrointestinal Tract:
- Mouth: Contains teeth and tongue.
- Pharynx: Connects the nose, middle ear, larynx, and esophagus.
- Esophagus: Muscular tube leading to the stomach.
- Stomach: Connects the esophagus and the small intestine.
- Small Intestine: Consists of the duodenum, jejunum, and ileum.
- Large Intestine: Includes the cecum, colon, and rectum.
- Attached Glands: Produce and secrete substances into the gastrointestinal tract.
- Salivary Glands: Sublingual, submaxillary, and parotid glands. They produce saliva, which keeps the mouth moist, facilitates speech, cleans teeth, dissolves food, lubricates the bolus, and aids in digestion of carbohydrates.
- Pancreas: Produces pancreatic juice for food digestion and controls blood glucose levels by producing hormones.
- Liver: Synthesizes plasma proteins for blood coagulation, produces bile for fat digestion, stores glucose as glycogen, metabolizes foreign molecules, regulates blood fat levels, and removes old erythrocytes.
Digestion Process
Digestion is the process by which food is broken down into nutrients.
- Mechanical Digestion: Reduces the size of food particles.
- Chemical Digestion: Breaks down nutrients into simpler molecules using enzymes.
Process of Chyme:
- Stomach walls produce gastric juices and peristaltic movements.
- The first part of the small intestine completes digestion, forming chyle.
- Intestinal juice, released by the intestinal mucosa, contains enzymes that break down proteins and fats.
- Pancreatic juice, released into the duodenum, aids in the digestion of carbohydrates, fats, and proteins.
- Bile reduces the size of fat molecules, facilitating the absorption of fats, fatty acids, and vitamins A, D, E, and K.
Respiratory System
The respiratory system is responsible for gas exchange: delivering oxygen to the blood and removing carbon dioxide.
Components of the Respiratory System
- Airway: Air enters through the nostrils, where it is warmed and moistened, and dust particles are removed. It then passes through the larynx, pharynx, trachea, and bronchi.
- Lungs: Two spongy organs covered by the pleura, which facilitates lung movement. The right lung has three lobes. The lungs contain alveoli and bronchioles.
Breathing Process
Breathing involves various muscles, including the diaphragm, rectus abdominis, and intercostals.
- Inspiration: Contraction of muscles increases the thoracic cavity, allowing oxygen-rich air to enter the lungs.
- Expiration: Air, now rich in carbon dioxide, is expelled from the lungs.
Respiratory Diseases
- Infections: Caused by bacteria or viruses, such as tuberculosis, colds, and flu, and treated with antibiotics.
- Pulmonary Emphysema: Destruction of the alveoli walls, reducing oxygen supply.
- Lung Cancer: Often linked to tobacco consumption.
Circulatory System
The circulatory system is a double and complete system, meaning blood passes through the heart twice and oxygen-rich and oxygen-poor blood do not mix.
Circuits of the Circulatory System
- Systemic Circulation: Oxygen-rich blood from the pulmonary vein enters the left atrium and ventricle, then the aorta, which distributes blood throughout the body. Arteries branch into smaller vessels, reaching capillaries in organs. Veins collect blood, increasing in size as they approach the heart, carrying carbon dioxide.
- Pulmonary Circulation: Blood from the vena cava enters the right atrium, then the right ventricle, and the pulmonary artery carries blood to the lungs. From the lungs, blood returns to the left atrium, completing the circuit.