Endocrine system

The pancreas

The pancreas is a glandular organ in the upper abdomen, but really it serves as two glands in one: a digestive exocrine gland and a hormone-producing endocrine gland. Functioning as an exocrine gland, the pancreas excretes enzymes to break down the proteins, lipids, carbohydrates, and nucleic acids in food. Functioning as an endocrine gland, the pancreas secretes the hormones insulin and glucagon to control blood sugar levels throughout the day. Both of these diverse functions are vital to the body’s survival.
Physiology of the pancreas

The exocrine portion of the pancreas plays a major role in the digestion of food. The stomach slowly releases partially digested food into the duodenum as a thick, acidic liquid called chyme. The acini of the pancreas secrete pancreatic juice to complete the digestion of chyme in the duodenum. Pancreatic juice is a mixture of water, salts, bicarbonate, and many different digestive enzymes. The bicarbonate ions present in pancreatic juice neutralize the acid in chyme to protect the intestinal wall and to create the proper environment for the functioning of pancreatic enzymes. The pancreatic enzymes each specialize in digesting specific compounds found in chyme.

- Pancreatic amylase breaks large polysaccharides like starches and glycogen into smaller sugars such as maltose, maltotriose, and glucose. Maltase secreted by the small intestine then breaks maltose into the monosaccharide glucose, which the intestines can directly absorb.
- Trypsin, chymotrypsin, and carboxypeptidase are protein-digesting enzymes that break proteins down into their amino acid subunits. These amino acids can then be absorbed by the intestines.
- Pancreatic lipase is a lipid-digesting enzyme that breaks large triglyceride molecules into fatty acids and monoglycerides. Bile released by the gallbladder emulsifies fats to increase the surface area of triglycerides that pancreatic lipase can react with. The fatty acids and monoglycerides produced by pancreatic lipase can be absorbed by the intestines.
- Ribonuclease and deoxyribonuclease are nucleases, or enzymes that digest nucleic acids. Ribonuclease breaks down molecules of RNA into the sugar ribose and the nitrogenous bases adenine, cytosine, guanine and uracil. Deoxyribonuclease digests DNA molecules into the sugar deoxyribose and the nitrogenous bases adenine, cytosine, guanine, and thymine.
The endocrine system

The endocrine system includes all of the glands of the body and the hormones produced by those glands. The glands are controlled directly by stimulation from the nervous system as well as by chemical receptors in the blood and hormones produced by other glands. By regulating the functions of organs in the body, these glands help to maintain the body’s homeostasis. Cellular metabolism, reproduction, sexual development, sugar and mineral homeostasis, heart rate, and digestion are among the many processes regulated by the actions of hormones.

The endocrine system of the head and neck

The endocrine system of the head and neck includes the vital structures responsible for governing the release of hormones to the entire body and maintaining the body’s homeostasis. Hormones released into the bloodstream from glands in the head and neck are transported throughout the body to affect every body system.

The pineal gland, a small pinecone-shaped mass of glandular tissue in the brain, plays an important role in controlling the body’s sleep cycle. The pineal gland is attached to the brain superior to the midbrain and posterior to the thalamus. Light striking the retinas of the eyes keeps the pineal gland inactive during the day, but in the absence of light the pineal gland produces the hormone melatonin. Melatonin has a sedative effect on the nervous system and helps to set the body’s sleep-wake cycle known as the circadian rhythm.
The hypothalamus

The hypothalamus is a section of the brain responsible for the production of many of the body’s essential hormones, chemical substances that help control different cells and organs. The hormones from the hypothalamus govern physiologic functions such as temperature regulation, thirst, hunger, sleep, mood, sex drive, and the release of other hormones within the body. This area of the brain houses the pituitary gland and other glands in the body.
The parathyroid glands

The parathyroid glands are four small glands that have the sole purpose of secreting parathyroid hormone to regulate the calcium level in our bodies.

The parathyroid essentially helps the nervous and muscular systems function properly. Calcium is the primary element that causes muscles to contract, and calcium levels are very important to the normal conduction of electrical currents along nerves.
The pineal gland

The pineal gland, also known as the pineal body, is an important endocrine gland that produces the hormone melatonin. Melatonin plays a key role in the sleep/wake cycle and the body’s response to sunlight.
The pituitary gland

The pituitary gland is a pea-sized gland located in the center of the skull, inferior to the hypothalamus of the brain and posterior to the bridge of the nose. It is an important link between the nervous and endocrine systems and releases many hormones which affect growth, sexual development, metabolism and human reproduction.

The pituitary gland, also known as the hypophysis, is connected to the hypothalamus of the brain by a tiny isthmus of nervous tissue called the infundibulum. It sits within a small cavity in the sphenoid bone of the skull known as the hypophyseal fossa. Thus the sphenoid bone surrounds and protects the delicate pituitary gland from damage by external forces.
The thyroid gland

The thyroid gland is a butterfly-shaped organ located in the base of your neck. It releases hormones that control metabolism—the way your body uses energy. The thyroid\'s hormones regulate vital body functions, including:

- Breathing
- Heart rate
- Central and peripheral nervous systems
- Body weight
- Muscle strength
- Menstrual cycles
- Body temperature
- Cholesterol levels

The thyroid gland is about 2-inches long and lies in front of your throat below the prominence of thyroid cartilage sometimes called the Adam\'s apple. The thyroid has two sides called lobes that lie on either side of your windpipe, and is usually connected by a strip of thyroid tissue known as an isthmus. Some people do not have an isthmus, and instead have two separate thyroid lobes.
The endocrine system of the upper torso

The endocrine system of the thorax contains only one gland, the thymus, but several other hormones are produced in this region by tissues containing endocrine cells. These hormones work to control aspects of the body’s immune, cardiovascular, and digestive systems.

The thymus gland is a small, triangular gland located deep to the sternum and superior to the heart. It forms a key component of the immune system that trains and develops T lymphocytes (T cells) to fight off infections. A class of hormones known collectively as thymosins are produced by the thymus and used to stimulate the production and development of T cells during childhood and puberty.