TSH stimulation causes the follicular epithelium to become more columnar. Trace amounts of iodine in the diet are needed to form thyroid hormones.
The "C" cells in the interstitium between the follicles produces calcitonin, which in humans has minimal functionality. The parathyroid glands are embryologically derived from the 3rd and 4th pharyngeal pouches. Since the thymus is also derived from the 4th pharyngeal pouches, thymic tissue may be seen adjacent to parathyroid, and parathyroid may be found in the anterior mediastinum, which is of no practical significance unless you are a surgeon trying to find a parathyroid adenoma.
There are normally four parathyroids, but there can rarely be two or six of them. A normal parathyroid gland weighs about 80 to milligrams and is an ovoid structure 2 x 3 x 5 mm in size. The parathyroid glands have a thin connective tissue capsule. There is a rich vascular supply to the stroma. The parenchyma consists of chief cells that secrete parathyroid hormone parathormone under the influence of decreasing serum calcium.
There are also variable numbers of oxyphil cells in small nodules. The pink oxyphil cells have cytoplasm packed with mitochondria, so they must be doing something, perhaps transitioning to chief cells. A variable number of steatocytes are scattered in the parathyroid parenchyma. This obscure gland resides at the base of the brain, attached near the habenula. It is a diencephalic structure, but has an endocrine function.
This 5 x 8 mm gland has rounded pinealocytes with surrounding interstitial cells that function similar to neuroglial cells. Beginning in childhood and increasing throughout life, calcified concretions "brain sand" appear in the pineal. The pinealocytes secrete the hormone melatonin, which may play a role in regulation of circadian rhythms and reproductive cycles.
Peak melatonin production occurs at night. The pineal is innervated by a circuitous pathway from postganglionic sympathetic nerves that arise in the superior cervical ganglia in the neck. As a digestive organ, the pancreas secretes pancreatic juice containing digestive enzymes that assist the absorption of nutrients and the digestion in the small intestine. Food particles are reduced to basic elements that can be absorbed by the intestine and used by the body.
These enzymes help to further break down the carbohydrates, proteins, and lipids in the chyme. The endocrine cells of the pancreas form clusters called pancreatic islets or the islets of Langerhans. The pancreatic islets contain two primary cell types: alpha cells, which produce the hormone glucagon, and beta cells, which produce the hormone insulin.
These hormones are responsible for the regulation of blood glucose levels. As blood glucose levels decline, alpha cells release glucagon to raise the blood glucose levels by increasing rates of glycogen breakdown and glucose release by the liver. When blood glucose levels rise, such as after a meal, beta cells release insulin to lower blood glucose levels by increasing the rate of glucose uptake in most body cells, and by increasing glycogen synthesis in skeletal muscles and the liver.
Islets of Langerhans : The islets of Langerhans are clusters of endocrine cells found in the pancreas; they stain lighter than surrounding cells. The alpha and beta cells produce glucagon and insulin, respectively. The pineal gland is responsible for melatonin production, while the gonads secrete hormones relating to sexual characteristic development. The pineal gland is a small endocrine gland in the brain.
It is located near the center of the brain, between the two hemispheres, tucked in a groove where the two rounded thalamic bodies join. The gland consists of two types of cells known as parenchymal and neuroglial cells. Nervous system endocrine glands: the pineal gland : The pineal gland, found in the brain, produces the hormone melatonin.
The main hormone produced and secreted by the pineal gland is melatonin. The rate of melatonin production is affected by the photoperiod. Collaterals from the visual pathways innervate the pineal gland. During the day photoperiod, little melatonin is produced; however, melatonin production increases during the dark photoperiod night. In some mammals, melatonin has an inhibitory affect on reproductive functions by decreasing production and maturation of sperm, oocytes, and reproductive organs.
Melatonin is an effective antioxidant, protecting the CNS from free radicals such as nitric oxide and hydrogen peroxide. Lastly, melatonin is involved in biological rhythms, particularly circadian rhythms such as the sleep-wake cycle and eating habits.
Pineal gland : The pineal gland is an endocrine gland located in the middle of the brain. It is responsible for the production of melatonin, a hormone which acts as an antioxidant and is involved in the regulation of biological rhythms.
The gonads are additional types of endocrine glands. They are the sex organs and include the male testes and female ovaries. Their main role is the production of steroid hormones. The testes produce androgens, which allow for the development of secondary sex characteristics and the production of sperm cells.
Testosterone, the most prominent androgen in males, stimulates the development and functioning of the primary sex organs. It also stimulates the development and maintenance of secondary male characteristics, such as hair growth on the face and the deep pitch of the voice.
Testes : The testes produce androgens, such as testosterone, which regulate primary sex organ development and function, as well as the development of secondary sex characteristics and the production of sperm cells.
Endocrine system: gonads and their hormones : The gonads are the sex organs. Male testes produce androgens, while female ovaries produce estrogen and progesterone. The ovaries produce hormones, such as estrogen and progesterone, which cause secondary sex characteristics and prepare the body for childbirth. Estrogen increases at the time of puberty, causing the growth of the uterus and vagina. Without estrogen, egg maturation would not occur.
Estrogen is also responsible for secondary sex characteristics such as female body hair and fat distribution. Estrogen and progesterone are responsible for the development of the breast and for the uterine cycle. Progesterone is a female hormone secreted by the corpus luteum after ovulation during the second half of the menstrual cycle. It prepares the lining of the uterus for implantation of a fertilized egg and allows for complete shedding of the endometrium at the time of menstruation.
In the event of pregnancy, the progesterone level remains stable beginning a week or so after conception. Ovaries : The ovaries produce estrogen and progesterone, which are hormones responsible for the development of sexual characteristics in females and the preparation of female bodies for pregnancy and childbirth.
Several organs with specialized non-endocrine functions possess endocrine roles, such as hormone production and release. There are several organs whose primary functions are non-endocrine, but that also possess endocrine functions.
These include the heart, kidneys, intestines, thymus, and adipose tissue. The heart possesses endocrine cells in the walls of the atria that are specialized cardiac muscle cells.
These cells release the hormone atrial natriuretic peptide ANP in response to increased blood volume. High blood volume causes the cells to be stretched, resulting in hormone release. ANP also reduces the amounts of renin released by the kidneys and aldosterone released by the adrenal cortex, further preventing the retention of water. ANP hormone structure : The hormone atrial natriuretic peptide ANP , released in response to increased blood volume, is produced by endocrine cells in the heart.
The gastrointestinal tract produces several hormones that aid in digestion. The endocrine cells are located in the mucus of the GI tract throughout the stomach and small intestine. Some of the hormones produced include gastrin, secretin, and cholecystokinin, which are secreted in the presence of food. They also act on other organs, such as the pancreas, gallbladder, and liver, by triggering the release of gastric juices, which help to break down and digest food in the GI tract.
While the adrenal glands associated with the kidneys are major endocrine glands, the kidneys themselves also possess endocrine function. Renin, released in response to decreased blood volume or pressure, is part of the renin-angiotensin-aldosterone system that leads to the release of aldosterone.
Erythropoietin EPO , a protein hormone produced by the kidney, triggers the formation of red blood cells in the bone marrow. EPO is released in response to low oxygen levels.
Because red blood cells are oxygen carriers, increased production results in greater oxygen delivery throughout the body. EPO has been used by athletes to improve performance as greater oxygen delivery to muscle cells allows for greater endurance. Because red blood cells increase the viscosity of blood, artificially high levels of EPO can cause severe health risks. The thymus is found behind the sternum. It is most prominent in infants, becoming smaller in size through adulthood.
The thymus produces hormones referred to as thymosins, which contribute to the development of the immune response. Thymus : The thymus, located behind the sternum, produces the hormone thymosin.
Adipose tissue is a connective tissue found throughout the body. It produces the hormone leptin in response to food intake. Leptin increases the activity of anorexigenic neurons and decreases that of orexigenic neurons, producing a feeling of satiety after eating, thus affecting appetite and reducing the urge for further eating. Leptin is also associated with reproduction.
It must be present for GnRH and gonadotropin synthesis to occur. Extremely thin females may enter puberty late; however, if adipose levels increase, more leptin will be produced, improving fertility. Privacy Policy.
Skip to main content. The Endocrine System. Search for:. Endocrine Glands. Hypothalamic-Pituitary Axis The hypothalamus, an endocrine organ, regulates the anterior pituitary gland and transports hormones along the posterior pituitary gland. Learning Objectives Describe the hormones released by the anterior posterior pituitary and their effects on the body.
Key Takeaways Key Points The endocrine system is made up by a group of endocrine glands, including the pituitary glands which are responsible for the release of hormones relating to important bodily functions and regulations. The hypothalamus instigates endocrine responses to environmental changes from messages received from the body and brain.
The hypothalamus synthesizes hormones and transports them to the posterior pituitary gland while also synthesizing and secreting regulatory hormones that control cells in the anterior pituitary gland. The anterior pituitary gland, regulated by the hypothalamus, produces seven tropic hormones which control the functioning of other organs.
Thymus regresses in adulthood. Pancreas islet cells. Insulin from beta cells. Glucose utilization; blood glucose lowers. Glucagon from alpha cells. Adrenaline Noradrenaline. Metabolism; heart rate and output; response to stress and exercise. Cortisol Corticosterone. Blood vessel smooth muscle Adrenal cortex. Blood pressure Aldosterone secretion. Reproductive development; also has effects on oestrus behaviour.
0コメント