Endocrine
Thyroid Gland-clinical correlation: thyroglossal cyst
(Top) Absence of isthmus - may be associated with the presence of a pyramidal lobe. (Bottom) Accessory Thyroid Glandular Tissue - may appear anywhere along the embryonic course of the thyroglossal duct. - other variations from the movement of the thyroid
What does the thyroid gland secret?
1.Thyroid hormone (thyroglobulin, T3, T4) - regulates tissue growth and development; main calorigenic hormone (through regulation of glucose oxidation) - play an important role in determining how many calories a cell is going to utilize in a particular given amount of time 2.Calcitonin - lowers blood Calcium levels (antagonizing the effect of parathyroid hormone)
What is the Suprarenal (adrenal) gland?
An adrenal gland is located at the superomedial aspect of each kidney. The gland is triangular, flattened and embedded in adipose tissue. It includes a cortex and a medulla. The right suprarenal gland is partially overlapped by the inferior vena cava. The adrenal glands serve to maintain the constancy of the internal environment. They are indispensible. All help to maintain homeostasis during stressful situations. The adrenal glands have a cortex and medulla. The cortex synthesizes corticosteroids, including: •Mineralcorticoids - sodium/potassium (electrolyte) homeostasis •Glucocorticoids - glucose homeostasis •Gonadocorticoids - primarily androgens - The cortex is the region of the gland that has the endocrine functions
What are some structures and hormones of the pituitary gland?
Anterior pituitary - 1.Adrenocorticotropic hormone (ACTH) 2.Thyroid - stimulating hormone (TSH) 3.Follicle - stimulating hormone (FSH) 4.Luteinizing hormone (LH) 5.Growth hormone 6.Prolactin Posterior pituitary - 1.Oxytocin 2.Anti-diuretic hormone (vasopressin) The posterior pituitary (or neurohypophysis) is the posterior lobe of the pituitary gland. The posterior pituitary is not glandular as is the anterior pituitary. Instead, it is largely a collection of axonal projections from the hypothalamus that terminate behind the anterior pituitary, and serve as a site for the secretion of neurohypophysial hormones (oxytocin and vasopressin) directly into the blood. Anterior pituitary - There are cells in the hypothalamus that synthesize and release hormones into a portal system - so they are taken up by a capillary bed and go into the anterior pituitary where are there cells that will release stimulating hormones Posterior pituitary - releases through axons
What two structures are vulnerable during surgical removal of the thyroid gland?
During surgical removal of thyroid gland, several structures are vulnerable. These include: • external laryngeal n. - damage to this nerve results in hoarseness (inability to tense the vocal cords due to impaired function of the cricothyroid muscle) • recurrent laryngeal nerve - innervates laryngeal muscles (except cricothyroid). Damage results in hoarseness. Bilateral damage results in breathing difficulties and aphonia (loss of voice).
What is the cortex and medulla part of the adrenal gland?
Each adrenal gland consists of two functionally distinct regions designated cortex and medulla. The cortex responds to ACTH (adrenocorticotropic hormone) from the pituitary gland and secretes hormones (for example, cortisol and aldosterone) that control metabolism and electrolyte homeostasis. The medulla is part of the autonomic nervous system and includes a type of cell referred to as a chromaffin cell. The chromaffin cells are modified postganglionic sympathetic neurons that synthesize and secrete catecholamines (epinephrine and norepinephrine). Secretion is stimulated by preganglionic sympathetic nerve fibers. - medulla is not involved in making the hormones, it is involved in making catecholamines - chromaffin cells are connected directly by synapsis with preganglionic sympathetic fibers. When the sympathetic nervous system activates the chromaffin cells, the chromaffin cells will release epinephrine and norepinephrine
What are some examples of homeostatic imbalance?
Examples of homeostatic imbalance related to the adrenal glands: hyperadrenocorticism (Cushing Disease) is chronic over-activity of adrenal cortex • From Mayo Clinic: Left untreated, Cushing syndrome can result in exaggerated facial roundness, weight gain around the midsection and upper back, thinning of your arms and legs, easy bruising and stretch marks hypoadrenocorticism (Addison's disease) is under activity of adrenal cortex (often related to tuberculosis or some other infectious process) From Mayo Clinic: Addison's disease, also called adrenal insufficiency, is an uncommon disorder that occurs when your body doesn't produce enough of certain hormones. In Addison's disease, your adrenal glands, located just above your kidneys, produce too little cortisol and, often, too little aldosterone. Addison's disease occurs in all age groups and both sexes, and can be life-threatening. Treatment involves taking hormones to replace those that are missing.
Identify and describe the origin of the arteries that are supplying the pancreas.
Gastroduodenal arteries and branches Inferior pancreaticoduodenal arteries and branches Splenic artery and branches It is important to know that the head of the pancreas has numerous branches of supply; the body and tail are supplied more somply by branches of the splenic artery
What is Graves' disease?
Graves' disease. A goiter can sometimes occur when your thyroid gland produces too much thyroid hormone (hyperthyroidism). In Graves' disease, antibodies produced by your immune system mistakenly attack your thyroid gland, causing it to produce excess thyroxine. This overstimulation causes the thyroid to swell. - autoimmune disorder
What is Hashimoto's disease?
Hashimoto's disease. A goiter can also result from an underactive thyroid (hypothyroidism). Like Graves' disease, Hashimoto's disease is an autoimmune disorder. But instead of causing your thyroid to produce too much hormone, Hashimoto's damages your thyroid so that it produces too little.
What is goiter?
Having a goiter doesn't necessarily mean that your thyroid gland isn't working normally. Even when it's enlarged, your thyroid may produce normal amounts of hormones. It might also, however, produce too much or too little thyroid hormone (thyroxine and T-3). A number of factors can cause your thyroid gland to enlarge. Among the most common are: Iodine deficiency. Iodine, which is essential for the production of thyroid hormones, is found primarily in seawater and in the soil in coastal areas. In the developing world, people who live inland or at high elevations are often iodine deficient and can develop goiters when the thyroid enlarges in an effort to obtain more iodine. The initial iodine deficiency may be made even worse by a diet high in hormone-inhibiting foods, such as cabbage, broccoli and cauliflower. Although a lack of dietary iodine is the main cause of goiters in many parts of the world, this is not often the case in countries where iodine is routinely added to table salt and other foods Sensing a low hormone level, your pituitary gland produces more TSH to stimulate the thyroid, which then causes the gland to enlarge.
Another diagram of thyroid and parathyroid gland arterial supply and venous drainage
In this diagram of a careful dissection of the arterial supply and venous drainage of the thyroid and parathyroid gland, note the "accessory thyroid gland".
What is the difference between lingual thyroid, thyroglossal cyst and thyroglossal fistula?
Incomplete descent of the thyroid gland (during fetal development) may result in the presence of a lingual thyroid, which is a mass of tissue under the foramen cecum. - where a portion of the thyroid gland did not descend at all Failure of the thyroglossal tract to degenerate completely following descent of the thyroid gland may result in the presence of a thryoglossal cyst. - saw on previous slide If a thyroglossal cyst ruptures to the outside surface, the resulting lesion is a thyroglossal fistula (abnormal opening)
What is the thymus gland?
Located in the superior mediastinum, the thymus gland is a bi-lobed organ; it frequently extends superiorly into the root of the neck and inferiorly into the anterior mediastinum. The thymus gland is large and conspicuous in children; it diminishes in size throughout adulthood. By old age, it is composed largely of adipose and fibrous connective tissue. -In adults the thymus gland regresses Important in the fetal development and the development of the immune system: The thymus gland is involved in T lymphocyte development. It secretes peptides referred to as thymopoietins and thymosins. These molecules mostly act locally as paracrine agents.
What do pancreatic hormones do?
Pancreatic hormones: Scattered among acinar cells (the exocrine cells of the pancreas) are "pancreatic islets" (of Langerhans). Cells in these islets synthesize and secrete insulin and glucagon. Insulin is made by beta cells; glucagon is made by alpha cells. These cells are regulated by blood glucose levels (another example of a humoral stimulus). - Insulin stimulates the uptake of glucose from the blood stream into cells - Glucagon stimulates the release of insulin Both of these hormones regulate blood glucose levels. Insulin stimulates cells to take up glucose from the blood; glucagon stimulates the breakdown of glycogen into glucose that enters the blood.
How is the parathyroid glands associated with the thyroid gland
Parathyroid glands have different developmental origins and different functions than the thyroid gland. However, in the adult the parathyroid glands are associated with the thyroid. The parathyroid glands, usually four in number, are located on the posterolateral surface of the thyroid gland. Parathyroid glands can be distinguished from surrounding thyroid tissue. The figure on the right illustrates sites (and frequencies) of aberrant parathyroid glands. Whereas the thyroid gland secretions regulate the general metabolic rate of all tissues (and lowers blood calcium concentration), the parathyroid secretions regulate calcium homeostasis. Falling calcium concentrations trigger the release of parathyroid hormone. This is an example of a humoral stimulus, in contrast to a neural or hormonal stimulus). The parathyroid glands are essential for life.
What is the innervation of the adrenal medulla?
The adrenal cortex is stimulated to secrete corticosteroids by hormonal signals (ACTH) arriving from the anterior pituitary gland. The adrenal medulla is regulated by autonomic (sympathetic) nerve fibers that stimulate release of catecholamines. Sympathetic fibers are supplied by abdominopelvic splanchnic nerves that arrive by way of the celiac plexus (but they do NOT synapse in this ganglion). These fibers are "preganglionic" and synapse with chromaffin cells in the adrenal medulla. The chromaffin cells in the adrenal medulla respond to nerve stimulation by secreting epinephrine and norepinephrine; this is the same response as many other sympathetic postganglionic neurons. For this reason, some authors describe chromaffin cells as acting like postganglionic sympathetic nerves - they don't actually synapse with the chromaffin cells of the medulla but the preganglionic fibers secrete transmitter which activates the chromaffin cells and release epinephrine and norepinephrine
What are some characteristics of the endocrine system?
The endocrine system includes glandular tissue in several regions of the body. - an endocrine gland is a gland that's going to produce and secrete a lot of a molecule that will regulate the activity of other cells in the body - involved in maintaining homeostasis Characteristics of an endocrine system include: - Glands that are ductless Exocrine pancreas will produce and secret digestive enzymes involved in digestion Endocrine pancreas synthesizes regulator molecules that are secreted from the endocrine cell directly into the blood stream. The blood stream will then carry these molecules throughout the body. Certain cells of the body will have receptors to detect the endocrine hormone and respond to it. Usually to maintain homeostasis in the body - Secretion of hormones directly into the blood stream Hormones that are transported through the vascular system to target tissues Target tissues that respond to the hormone by, for example, increasing or decreasing metabolic activity The endocrine system regulates basic fundamental metabolic activities, such as, for example, metabolic rate, temperature, blood glucose levels, and blood calcium concentration.
Regulation of Principal Endocrine Glands and Tissues
The pituitary gland is the "master gland" of the endocrine system, but the hypothalamus controls secretions from the pituitary gland. The nervous system and the endocrine system work together to regulate basic metabolic functions throughout the body. The hypothalamus regulates activity of the pituitary gland by synthesizing and secreting "releasing hormones" (e.g., TRH, thyrotropin releasing hormone). - TRH is released into a specific circulatory system that carries the hormone directly to the anterior pituitary gland The releasing hormones reach the anterior pituitary gland through the circulation and stimulate secretion of a hormone (e.g., TSH, thyroid stimulating hormone) The secreted stimulating hormones are detected by cells in the appropriate target, where glandular activity is regulated (e.g., TSH is detected by cells of the thyroid gland and this gland responds by releasing thyroid hormones (T3 and T4).
What is the function of the pineal gland?
The primary function of the pineal gland is to produce melatonin. Melatonin has various functions in the central nervous system, the most important of which is to help modulate sleep patterns. Melatonin production is stimulated by darkness and inhibited by light. Light sensitive nerve cells in the retina detect light and send this signal to the suprachiasmatic nucleus (SCN) of the hypothalamus, synchronizing the SCN to the day-night cycle. Nerve fibers then relay the daylight information from the SCN to the paraventricular nuclei (PVN), also part of the hypothalamus, then to the spinal cord and via the sympathetic system to superior cervical ganglia (SCG), and from there into the pineal gland. Retina --> SCN --> superior cervical ganglion --> pineal gland
What is a thyroglossal cyst?
The thyroid gland develops in the fetal pharynx and descends into the neck. During the descent a luminal connection is maintained with the pharynx. Normally, this connecting tube will become obliterated. If it remains open, a cyst may form. The child in the photo above has a thyroglossal cyst. - Early in development the thyroid gland begins in the pharynx - blue line indicates the course of the thyroid gland as the fetus begins to grow
What is the thyroid gland?
The thyroid gland in the adult regulates the rate of metabolism in cells throughout the body. It also regulates calcium concentration in extracellular fluid. The thyroid gland includes right and left lobes. The inferior border of the thyroid lies at the level of 4th or 5th tracheal ring. The two lobes are connected by an isthmus that lies anterior to 2nd, 3rd, and 4th tracheal rings. The pyramidal lobe is a normal variation. If present, it extends superiorly from the isthmus at the midline. A fibrous/muscular band connects the lobe with the hyoid bone.
What is the thyroid Ima artery?
The thyroid ima artery is a common variation (present in 10% or less of the population). It travels on the anterior surface of the trachea and supplies the isthmus of the thyroid gland. Its origin may be from either: 1.Brachiocephalic trunk 2.Arch of the aorta 3.Right common carotid artery The thyroid ima (lowest) artery can be a source of significant bleeding during tracheotomy.
What is the blood supply/lymph of the adrenal gland?
Three arteries supply branches to the adrenal glands: 1.Superior suprarenal arteries - branches of the inferior phrenic artery 2.Middle surprarenal artery - a branch from the aorta 3.Inferior suprarenal artery - branches from the renal artery Each adrenal gland is drained by a single vein. - On the right, the adrenal vein connects directly to the inferior vena cava. - On the left, the adrenal vein connects to the left renal vein, which connects to the inferior vena cava. Lymph drainage is through the lumbar lymph nodes. Each adrenal gland has a hilum from which veins and lymph vessels exit. The arteries (and nerves) do not enter at the hilum. Instead, they enter the gland from several regions along the periphery.
What is the arterial supply of the thyroid gland?
Two major arteries supply the thyroid gland: 1.Superior thyroid artery: • originates from the external carotid artery 2.Inferior thyroid artery: • arises from the thyrocervical trunk (a branch of the subclavian artery)
What is the venous drainage of the thyroid and parathyroid gland?
Venous blood is collected by a venous plexus that drains into: 1.Superior thyroid veins - drain into internal jugular vein 2.Middle thyroid vein - drain into internal jugular vein 3.Inferior thyroid vein - drain into brachiocephalic vein (usually the left) The thyroid cells are going to secrete T3 and T4 and calcitonin and those hormones are going to be taken up by the capillary beds and drained into the veins and out to the rest of the systemic circulation Once the hormones from the thyroid reach these veins they will be returned to the right side of the heart through the superior vena cava
What are some other endocrine glands and tissues?
We've considered the role of the hypothalamus and the glands dedicated solely to endocrine function. These glands include: •Pituitary •Thyroid •Parathyroid •Adrenal Many other organs contain endocrine tissue but also have other major functions. Examples would include the pancreas (considered above), gonads (to be included during sessions on genital system), and placenta. Kidneys, in addition to filtering blood, also produce a hormone (renin) important in maintaining blood volume and pressure. The heart produces a hormone (atrial natriuretic peptide) that is involved in regulating blood volume and pressure. The GI tract includes many cells described as enteroendocrine cells. Some of these hormones: somatostatin, motilin, cholecystokinin, neurotensin, vasoactive intestinal peptide, and enteroglucagon. The liver produces a number of hormones including: (Endocrine) Insulin-like Growth Factor-1 (IGF-1), angiotensinogen, thrombopoietin. - exocrine activity (bile production)
What endocrine producing organs do you see?
What regulatory functions are these organs associated with? Kidneys - blood pressure regulation, blood electrolyte balance Pancreas - blood glucose levels Intestine - many functions related to energy metabolism (feeding, etc.)
What is the pineal gland?
•Pine cone-shaped; hangs from the roof of the third ventricle •Endocrine function is a bit mysterious •Melatonin is the only major secretory product •Melatonin levels in the blood rise and fall in a diurnal cycle; peak levels occur at night; lowest levels occur around noon
