Long, greyish-white organ behind and underneath the stomach. Functions: Produces hormones (insulin & glucagon) that regulate the amount of glucose in the bloodstream. Secretes pancreatic juice which contains digestive enzymes & sodium bicarbonate.
How Digestion Works
Most digestive processes take place in the small intestine. Digestion produces nutrients that cells need:
- Monosaccharides (simple sugars): obtained from complex carbohydrates.
- Glycerol & fatty acids: obtained from fats.
- Amino acids: obtained from proteins.
Nutrients pass from the small intestine into the bloodstream through absorption and then are delivered to cells by the blood. The inside wall of the small intestine is covered in folds that are lined with thousands of finger-like structures called villi. These villi are full of capillaries. The plasma membrane of villi cells is covered in microvilli which increase the surface area of the intestine.
Cells in our body need oxygen in order to perform cell respiration. As a result of cell respiration, waste products are created. Oxygen is obtained from the air and provides it to the blood stream. Respiratory track: are tubes or airways that collect oxygen and prepare it for cell consumption (nasal cavities, pharynx, larynx, trachea, bronchi and bronchioles). Inside the larynx, we can find the vocal cords. They create sounds when air passes though them. The sound changes depending on the tongue, teeth and lips position and the way the air passes though the mouth or nasal passages. Lungs: this is where the gas exchange between blood and air takes place.
Nasal cavity: Air enters the nose. Capillaries in the nose put the air at the same temperature as the body because they contain blood that has the same temperature as the body. Nooks and crannies make longer the journey of the air though the body, so that it gets warmer. Mucus purifies and humidifies the air. The pharynx: common area to the respiratory and the digestive tract. Its walls contain tonsils, which generate white blood cells. The larynx: its entry is regulated by the epiglottis, which closes and opens when food in been ingested to prevent chocking of suffocating. It is formed of cartilage. The trachea: it is a 12-centimeter tube that connects the epiglottis to the lungs. It has open cartilage rings at the back. It contains cilia (cells with vibrating filaments that move mucus to the larynx, where it is redirected to the esophagus and stomach. Bronchi and bronchioles: Bronchi are the two branches of the trachea. At the same time, they divide into bronchioles. Bronchioles end in pulmonary alveoli.
Lungs are formed by bronchi, bronchioles, alveoli and capillaries. They are elastic bodies that look like sponges. The right lung contains three lobes and the left lung only contains two. The pleura is a sheet composed of two membranes where there is a liquid that helps them to stay together and slide smoothly. Oxygen reaches the alveoli where gas exchange occurs. Alveoli have a layer of flat cells (endothelium), they are covered by capillaries that facilitate gas exchange. Breathing = pulmonary ventilation. Air in the alveoli needs to be constantly renewed. Gas exchange = diffusion: Oxygen travels from the higher concentration area (alveoli) to the lower (blood). Because of this, carbon dioxide higher concentration area is blood and the lower is alveoli. Oxygen in the air goes to the blood passing though alveolar and capillary wall to be transported to the body´s cells. Carbon dioxide passes to the alveoli where it is mixed with oxygen. Oxygen is then released as exhale.
Pulmonary Ventilation (Breathing)
The intercostal muscles and the diaphragm are responsible for pulmonary ventilation. It has two stages inspiration and expiration. Inspiration: it is the respiratory movement in which air enters the lungs. The diaphragm flattens and lowers as the ribs rise outwards, increasing the capacity of the ribcage. Its walls pull from the pleura. The lungs increase their volume and the air enters them. Expiration: respiratory movement that releases air from the lungs. The diaphragm relaxes, curves and rises reducing the ribcage capacity. The ribcage shrinks and its walls pull from the pleura, forcing the lungs to reduce their volume and release the air inside them. Pulmonary ventilation can be 8 to 10 times frequent if we exercise. Pulmonary ventilations transports about 8 liters of air every minute, but it can transport up to 100 liters. Our body regulates oxygen demands adequately using precise mechanisms. When more oxygen is needed, pulmonary ventilation accelerates and it decreases when less oxygen is needed.