Human Body Systems: Nutrition, Digestion, and More
Food and Nutrition
Mediterranean Diet: Emphasizes oil, grains, pulses, fish, vegetables, and fruit.
Digestive, Respiratory, and Circulatory Systems
The Digestive System: Process of Food Digestion
Digestion begins in the mouth, where food is mixed with saliva, initiating the chemical process of forming the bolus. Food is compressed and directed from the mouth to the esophagus by swallowing. From the esophagus, it moves to the stomach, where it is mixed with hydrochloric acid. The bolus is transformed into chyme. In the small intestine, bile secreted by the liver aids in the emulsion of fats, and lipases from pancreatic secretions degrade fats into fatty acids and glycerin. Pancreatic juice also contains proteases and amylases that act on proteins and carbohydrates. Most nutrients are absorbed in the small intestine. Digestion concludes with the accumulation of chyle in the large intestine, where water is absorbed, and the stool is subsequently defecated.
The Liver: Regulates most chemical levels in the blood and excretes bile, which helps carry away waste products. All blood leaving the stomach and intestines passes through the liver.
Respiratory System
Through a process called diffusion, oxygen moves from the alveoli to the blood via capillaries lining the alveolar walls. Once in the bloodstream, oxygen is picked up by hemoglobin in red blood cells.
Function of the Kidneys
The kidneys act as efficient filters, ridding the body of waste and toxic substances while returning vitamins, amino acids, glucose, hormones, and other vital substances to the bloodstream. They receive high blood flow, filtered by specialized blood vessels. Urine is formed in the kidneys through blood filtration, then passed through the ureters to the bladder for storage. During urination, urine is expelled from the bladder through the urethra.
Blood Circulation
The right ventricle pumps oxygen-poor blood to the lungs through the pulmonary valve. The left atrium receives oxygen-rich blood from the lungs and pumps it to the left ventricle through the mitral valve. The left ventricle then pumps the oxygen-rich blood through the aortic valve to the rest of the body.
Menstrual Cycle
- The thick mucus of the uterus breaks off and is released to the exterior along with blood (4 or 5 days).
- The uterine mucus is reconstructed thanks to the action of estrogens produced by the ovaries (11 days).
- The lining of the uterus reaches its maximum thickness and is prepared to host and feed the fertilized ovum, 12 days when the production of the hormone ceases.
If the ovum is fertilized, the corpus luteum continues to secrete progesterone, and the lining of the uterus does not break off.
Stages of Birth
Vaginal delivery is the most common method of childbirth. It involves three stages:
- Shortening and opening of the cervix.
- Descent and birth of the baby.
- Delivery of the placenta.
How Semen is Produced
Sperm first arrive at the ampulla, just above the prostate gland. Secretions from the seminal vesicle, located next to the ampulla, are added. The seminal fluid is then propelled forward through the ejaculatory ducts toward the urethra. As it passes the prostate gland, a milky fluid is added to form semen.