Biology (Part 7: Endocrine System)

Components of Endocrine System

- Hypothalamus - Pituitary (Anterior, Intermediate, Posterior) -Thyroid - Parathyroid - Thymus - Pancreas - Testes/Ovaries - Adrenal glands

Primary vs secondary lymphoid organs

- Primary lymphoid organs are where lymphocytes are formed and mature. They provide an environment for stem cells to divide and mature into B and T cells. There are two primary lymphatic organs: the red bone marrow and the thymus gland. The development of white blood cells (haemopoesis) occurs in the red bone marrow, including T and B cells. B cells mature in the bone marrow, T cells migrate to the thymus to mature there. - Secondary lymphoid organs are arranged as a series of filters monitoring the contents of the extracellular fluids, i.e. lymph, tissue fluid and blood. The lymphoid tissue filtering each of these fluids is arranged in different ways. Secondary lymphoid tissues are also where lymphocytes are activated. These include lymph nodes, tonsils, spleen, Peyer's patches and mucosa associated lymphoid tissue (MALT).

Acidophils and Basophils

- There are two type of acidophils in the anterior pituitary gland. Somatotrophs generate Somatotropin (GH). Mammotrophs generate Prolactin. - Basophils in the anterior pituitary gland are not to be confused with basophils in the immune system. There are three types. Corticotrophs generate ACTH, Gonadotrophs generate FSH and LH, Thyrotrophs generate TSH. So Basophils generate FSH, LH, ACTH, and TSH, or B-FLAT.

Function of Endocrine System

- regulate hormones in the body - maintain widespread homeostasis - is the mechanism of the body's communication

Glucocorticoids

A class of corticosteroids, which are a class of steroid hormones. Glucocorticoids are corticosteroids that bind to the glucocorticoid receptor, which is present in almost every vertebrate animal cell. The name refers to its role in regulation of glucose metabolism, synthesis in the adrenal cortex, and its steroidal structure. A less common synonym is glucocorticosteroid.

Luteinizing hormone (LH)

A hormone produced by gonadotropic cells in the anterior pituitary gland. It is a heterodimeric glycoprotein. In females, an acute rise of LH ("LH surge") triggers ovulation and development of the corpus luteum. It also triggers estrogen and progesterone secretion. In males, where LH had also been called interstitial cell-stimulating hormone (ICSH), it stimulates Leydig cell production of testosterone. It acts synergistically (or together) with FSH.

Adrenocorticotropic hormone (ACTH)

A hormone that stimulates the adrenal cortex to synthesize and secrete glucocorticoids (like cortisol) effecting the sugar balance in body. It is released from the anterior pituitary. Corticotropin releasing factor/hormone (CRF or CRH) from the hypothalamus triggers its release. The function of the adrenal gland is determined by the ACTH stimulation test, where a dose of ACTH is administered exogenously (from outside the body). If there is an inadequate response, then the adrenal gland has reduced function. Like cortisol, levels of ACTH are generally high in the morning when we wake up and fall throughout the day. This is called a diurnal rhythm. ACTH can also be increased by a low level of circulating glucocorticoids (negative feedback) and vice versa. Patients that are on a large volume of steroids have decreased production of ACTH. It takes around a year in order to regain full function of the adrenal cortex. - small doses (5mg of prednisone) will have suppressed adrenal cortex function within a month - 20-30mg prednisone daily will have suppressed adrenal cortex function in a week - high doses for a short term will not adversely affect the function of the adrenal cortex (around 1-3 days) Adrenal insufficiency causes hyperpigmentation on the buccal and labial mucosa and other parts of the gingival. This is due to a marked increase in the production of ACTH, which stimulates melanocytes.

Glucagon

A peptide hormone used in blood glucose regulation by forcing many cells to release glucose in response to low blood sugar. The target organ is liver, which breaks down glycogen (stored glucose) to release free glucose into the blood. It increases glycogenolysis and gluconeogenesis. The main purpose of glucagon is to provide the body with the necessary mechanism to prevent hypoglycemia. Glycogen→Glucose

Insulin

A peptide hormone used to regulate blood sugar. When blood glucose levels are high, insulin tells muscles, liver, and other cells to convert glucose to glycogen and to remove glucose from blood. It increases glucose uptake into cells, increases amino acid uptake into cells, increase glycogenesis, lipogenesis, and protein production. It decreases lipolysis, gluconeogenesis. Glucose→Glycogen

Parathyroid hormone (PTH)

A protein hormone that is released by chief cells of the parathyroid gland. Used to regulate calcium and phosphate metabolism, and thus is involved in the process of bone remodeling. It increases blood Ca levels and decreases blood P levels. Ca levels are increased due to an increase in bone breakdown caused by PTH. PTH is stimulated by decreased Ca in the blood. It stimulates osteoclast activity to release Ca into the blood, stimulates vitamin D to increase Ca absorption in the stomach, and conserve Ca in the kidneys. With PTH, muscle wasting and fatigue result. Osteoblasts build bone (think B for Blasts and Build). Osteoclasts break down bone. ↓Ca ↑PTH (raises Ca levels) ↓P (PTH lowers phosphate levels) This is a negative feedback loop. PTH works in three ways. - increases the removal of Ca from bone storage and increases the absorption of Ca by the GI tract - acts on kidneys to decrease Ca excretion and increase P excretion in the urine. - increases vitamin D production in the kidney, which will increase the GI tracts ability to absorb Ca. Bone breakdown due to PTH is often first seen in head and neck radiographs in the dental office. If a person is deficient in Ca in their diet, PTH production and bone resorption will occur.

Cortisol

A steroid hormone produced in the adrenal cortex. It is the strongest contributor to protein catabolism. It increases lipolysis, protein catabolism, and gluconeogenesis. It's levels slowly increase during early morning because increasing light causes the release of corticotropin releasing factor (CRF) from the hypothalamus. CRF causes the release of adrenocorticotropic hormone (ACTH) from the anterior pituitary which stimulates cortisol release. Stress causes an increase of cortisol excretion. The normal average hydrocortisone excreted is around 20 mg a day, but can increase upwards of 200 mg daily.

Pineal gland

Also called the pineal body, epiphysis cerebri, epiphysis or the "third eye") is a small endocrine gland. It produces melatonin, a hormone that affects the modulation of wake/sleep patterns and photoperiodic (seasonal) functions. It is located near to the center of the brain between the two hemispheres, tucked in a groove where the two rounded thalamic bodies join. Unlike much of the rest of the brain, the pineal gland is not isolated from the body by the blood-brain barrier system.

Somatostatin

Also known as GhIH, a hormone that regulates the production and secretion of other endocrine hormones in the body. It is on a biofeedback loop that secretes hormone when endocrine hormones are low in the blood, and it is inhibited when endocrine hormones are found in excess in circulation. The major action of this hormone is to inhibit the production of insulin, glucagon, gastrin (stimulates secretion of gastric juice), and other endocrine hormones. Somatostatin is produced by neuroendocrine neurons of the hypothalamus. It is produced by many tissues in the body, principally in the nervous and digestive systems. It also regulates the activity of the gastrointestinal tract and the rapid reproduction of normal and tumour cells. It may also act as a neurotransmitter in the nervous system. It is also secreted by the pancreas in response to many factors related to food intake, such as high blood levels of glucose and amino acids.

Posterior pituitary gland

Also known as the neurohypophysis. The posterior pituitary does not produce any hormones of its own; instead, it stores and secretes two hormones made in the hypothalamus. It stores ADH and Oxytocin in neurosecretory vesicles (Herring bodies) before being secreted into the bloodstream. The hypothalamus contains neurons that control releases from the anterior and posterior pituitary glands. The hormones found here are: →ADH (antidirectic hormone, vasopressin) regulates blood pressure. →Oxytocin is involved in labor at childbirth (positive feedback cycle) and breastfeeding.

Testes and Ovaries

Although the gonads are part of the endocrine system, their primary purpose is to produce gametes. The woman's ovaries are located on both sides of the uterus below the opening of the fallopian tubes. They are oval or almond-shaped. The ovaries produce estrogen and progesterone. These two hormones affect many of the female characteristics and reproductive functions. The male's testes are egg-shaped organs that hang in a pouch of skin called the scrotum outside the male body. The testes produce testosterone, which affects many of the male characteristics and sperm production. The endocrine function of the gonads is the production of the sex hormones (estrogens and androgens). The exocrine function of the gonads is the production of the gametes. Estrogen - secondary sex characteristics, endometrial growth Progesterone - maintain uterine wall, prepare uterine wall for implantation

Pituitary gland memorization

Anterior Pituitary: FLAT PiG FSH: Follicle stimulating hormone LH: Luteinizing hormone ACTH: Adrenocorticotropin hormone TSH: Thyroid stimulating hormone Prolactin GH: Growth hormone Posterior Pituitary: ADH & Oxytocin Intermediate lobe: MSH (Melanocyte stimulating hormone) All pituitary gland hormones together: GOAT FLAP GH Oxytocin ACTH TSH FSH LH ADH Prolactin

Calcitonin (CT)

Calcitonin is a protein hormone produced by the parafollicular cells (C-cells) of the thyroid gland. It is involved in helping to regulate levels of Ca and P in the blood, opposing the action of PTH. ↑CT ↓Ca

Adrenal insufficiency

Causes weight loss, weakness, nausea, vomiting, and orthostatic hypotention. Cardiovascular collapse can occur with patients with severe insufficiency. This is because they cannot increase steroid production in response to stress, and must have adequate steroid replacement in order to prevent adrenal crisis during surgery. Adrenal crisis must be overcome with an IV or IM injection of hydrocortisone with supportive treatments of IV fluids. Addison's Disease is a common type of adrenal insufficiency.

Testosterone

Develops secondary sex characteristics (appear during puberty), development and function of sex organs LH - ↑Testosterone (at the testes) A steroid hormone developed and secreted by the male testis. Testosterone exerts effects on the spermatogenic cells, the muscles, bone, and other tissues. The actions of testosterone include the development of male reproductive system, secondary sexual characteristics, sexual drive, and behavior characteristics. It also helps synthesize skeletal muscle proteins. Testosterone is the main male sex hormone, or androgen. There are several others. The ovaries of females secrete much lower levels of testosterone. Females are more sensitive to it. The adrenal glands of both men and women also produce a small amount of testosterone. For women, testosterone plays a vital role in bone strength, brain function and the overall development of lean muscle mass and strength. It helps contribute to a general sense of well-being and higher energy levels. It also effects a woman's libido or sex drive.

Endocrine and exocrine function of the liver

Endocrine functions - Synthesis of plasma proteins - Synthesis of glucose (gluconeogenesis) - Storage & release of glycogen, lipids & lipoproteins - Vitamin A & D storage Exocrine functions - Bile synthesis

Endocrine vs Exocrine

Endocrine: releases into the blood Exocrine: releases outside of the blood More detail (not really needed) - The endocrine system is the collection of glands which produce hormones to regulate processes such as growth and development, reproduction and sexual function, metabolism, mood and sleep. The word endocrine comes from Greek, "endo" meaning within and "crinis" meaning secrete. Endocrine glands remove materials from the blood and process and secrete necessary products for use elsewhere in the body. Hormones produced by these glands circulate throughout the body and each hormone is marked toward specific organs and tissues. - The exocrine system is made up of glands that produce and secrete substances to protect or lubricate the human body. The substances produced by exocrine glands travel through ducts. They are deposited onto epithelial surfaces. - Exocrine glands release subtances into the external environment, or outside of the body. Endocrine hormones are released into the internal environment, or inside of the body. Endocrine response is slower because hormones travel through the blood instead of ducts like in the exocrine system.

Follicle stimulating hormone (FSH)

Follicle stimulating hormone is one of the gonadotrophic hormones, the other being luteinising hormone. Both are released by the anterior pituitary gland into the bloodstream. It is a glycoprotein polypeptide hormone. It is a tropic hormone, meaning it has other endocrine glands as its target. It is regulated by the hypothalamus and secreted by basophils in the anterior pituitary gland. Follicle stimulating hormone is one of the hormones essential to pubertal development and the function of women's ovaries and men's testes. In women, this hormone stimulates the growth of ovarian follicles in the ovary before the release of an egg from one follicle at ovulation. It also increases estradiol production (estrogen secretion). In men, follicle stimulating hormone acts on the Sertoli cells of the testes to stimulate sperm production (spermatogenesis). It is involved in the first meiosis division of stermatocytes to secondary spermatocytes.

Growth hormone (GH)

Growth hormone (GH), also called somatotropin or human growth hormone. It stimulates the growth of essentially all tissues of the body, including bone. GH is synthesized and secreted by anterior pituitary cells called somatotrophs. GH is vital for normal physical growth in children; its levels rise progressively during childhood and peak during the growth spurt that occurs in puberty. GH stimulates protein synthesis and increases fat breakdown to provide the energy necessary for tissue growth. It also antagonizes (opposes) the action of insulin. GH may act directly on tissues, but much of its effect is mediated by stimulation of the liver and other tissues to produce and release insulin-like growth factors, primarily insulin-like growth factor 1 (IGF-1; formerly called somatomedin). It increases lipolysis, glycogenolysis, protein production, and amino acid uptake. Some conditions related to abnormal amounts of GH include: Pituitary giganistm: excess GH delays fusion of epiphyseal plates (which happens in teenage years). A GH secreting tumor in a 5 year old likely results in this condition. Acromegaly: excess GH after fusion of epiphyseal plates Pituitary dwarf: insufficient GH resulting in premature fusion of epiphyseal plates

Thyroid stimulating hormone (TSH)

Hypothalamus - TRH TRH stimulates TSH release Pituitary - TSH TSH stimulates T4 and T3 release Thyroid - T4 and T3 Low thyroid hormones, TSH increases iodine uptake in blood TRH in the hypothalamus stimulates TSH in the pituitary to stimulate the thyroid to release thyroxine (T4) and triiodothyronine (T3) and uptake of iodine when blood thyroid hormone levels are low. Somatostatin in the hypothalamus decreases TSH activity. It's also involved in metabolism and thermoregulation. An excess of TSH can cause Grave's disease.

Antidiuretic hormone (ADH)

Increases permeability of collecting ducts to preserve water Also known as vasopressin, one of the most commonly tested peptide hormones. It is produced in the hypothalamus and secreted from the posterior pituitary gland. This hormone will conserve body water by reducing the amount of water lost in the urine. ADH stimulates aquaporins in the kidney tubules causing water to remain in the body. Osmoreceptors are receptors in the hypothalamus that measures that amount of solutes in the blood. If the blood is thick with solutes, the body will secrete vasopressin in order to increase the amount of water in the blood to dilute the solute thick blood. One of the major effects of increased blood volume is an increase in blood pressure. - Alcohol and caffeine will decrease ADH leading to extra need to urinate, and smoking will increase vasopressin. - Sweating causes an increase in ADH due to the loss of blood volume. - If ADH is secreted in low amounts, diabetes insipidus with increased thirst and peeing will result. This form of diabetes can also occur due to hypoactivity of the posterior pituitary gland due to loss of ADH secretion.

Insulin and Glucagon are synthesized and secreted by

Insulin is synthesized and secreted from β-cells of the islets of Langerhans. Glucagon is synthesized and secreted from α-cells of the islets of Langerhans. The islets of Langerhans are located in the endocrine portion of the pancreas.

Adrenal gland memorization

Medulla: MEN Medulla Epinephrine Norepinephrine Cortex 3 layers: Go Fred Run (GFR) Glomerulosa Fasiculata Reticularis Their hormones are: Make Good Sweets Sweets (Torta Dulce) Mineralocorticoids (aldosterone) SALT Glucocorticoids (cortisol) SWEET Sex hormone (androgen) SEX Main androgens: Testosterone and DHEA All adrenal gland hormones together CANES Cortisol Aldosterone Norepinephrine Epinephrine Sex hormone

Thymus

Most important detail: Develops lymphoid tissue and immune response in infants, atrophies at puberty. It gets replaced by adipose tissue. It still produces T lymphocytes. More detail (not really needed): The thymus gland is importance in the development of the immune system. It is active at birth and childhood, continuing to grow until puberty. The thymus produces thymosin, a hormone that stimulates T-cell (or T lymphocyte) maturation which enter the bloodstream and defend against pathogens. The thymus is a primary lymphoid organ. The bone marrow is also a primary lymphoid organ. Their role is to generate lymphocytes. The medulla of the thymus contains Hassall's corpuscles. These are concentric arrangements of flattened epithelioid cells that are acidophilic. Their purpose is currently unknown.

Parathyroid gland

Most important detail: Regulates blood calcium levels More detail: A small endocrine gland found on the posterior surface of the thyroid gland. Humans usually have four parathyroid glands. They are responsible for making and secreting parathyroid hormone in response to decreased plasma calcium levels. The chief cells of the gland secrete parathyroid hormone (PTH). Phosphate helps with bone growth, energy storage, and nerve and muscle production. Many foods contain phosphorus, especially meat and dairy. While Ca levels rise, PTH lowers P levels. PTH - ↑Ca ↑Bone resorption (breakdown) ↓P ↓Ca - ↑PTH

Thyroid gland

Most important details: Regulates metabolism, growth, maturation and body temperature. More details: Found below the larynx and in front of the trachea. It is the largest endocrine gland in the body, and the hormones formed in the thyroid control the speed at which the body can use energy, make proteins, and how sensitive the body is to other hormones. It produces mostly thyroxine (T4) and smaller amounts of triiodothyronine (T3). Iodine deficiency can cause enlargement of the thyroid gland. The thyroid gland also produces calcitonin from C-cells. Calcitonin is understood to play a role in regulating calcium levels in the body by lowering them, but its exact function in humans remains unclear. Summarized: T3 - Active form T4 - Stable form CT - ↓Blood calcium ↑Bone deposition

Endocrine portion of pancreas

Most important: Controls blood glucose and cell uptake of glucose Includes the islets of Langerhans, alpha, beta, and delta cells. The islets of Langerhans produce hormones that regulate blood sugar and regulate pancreatic secretions such as insulin and glucagon by releasing them into the bloodstream. Insulin and glucagon work together to maintain the proper level of blood glucose. PIGS are BAD (βαẟ) Insulin (β cell) Glucagon (α cell) Somatostatin (ẟ cell) Summarized: Glucagon - ↑Blood Glucose, Glycogen → Glucose (Glycogenolysis) This is during a fasting state, or when Glucose is gone (glucaGONE) Insulin - ↓Blood Glucose ↑Cell Glucose uptake This is after eating Somatostatin - Regulate production and secretion of insulin and glucagon

Exocrine portion of pancreas

Most of the pancreas consists of exocrine tissue that produces pancreatic enzymes for digestion including - trypsin, chymotrypsin and elastase to digest proteins; - amylase for the digestion of carbohydrates such as starch - pancreatic lipases (like phospholipase A2) to break down fats These enzymes are produced and transported by acinar cells and are secreted into the acinus lumen. When food enters the stomach, pancreatic juices are released into a system of ducts that culminate in the main pancreatic duct. The pancreatic juices from acinar cells and bile from the gallbladder are released into the duodenum and help the body to digest fats, carbohydrates, and proteins. The pancreas also secretes bicarbonate ions which are useful in neutralizing gastric acid to allow for effective enzymic changes.

Negative Feedback System

Negative feedback is a key regulatory mechanism for physiological function. It is a way to maintain homeostasis, like a thermostat will either cool down or heat up to maintain a temperature 75° in a house. It is regulatory mechanism in which a 'stimulus' causes an opposite 'output' in order to maintain an ideal level of whatever is being regulated. Steps of homeostasis 1) Stimulus causes a change to occur (example, the temperature in the house increases) 2) Sensor detects change (thermostat registers an increase in temperature) 3) Control, a response to the change (thermostat sends a signal to decrease the temperature) 4) Effector, or effect of the response (AC turning on to bring temp back down to normal or the heater stopping until the temp is brought back down to normal) A negative feedback loop serves to keep a certain variable in check. It involves product inhibition and acts as a self-limiting system. For example, when a lot of T4 is produced by the thyroid, T4 the product tells the hypothalamus to stop sending TRH, thus inhibiting more product. It limits itself. Another example, when blood calcium is high, this signals the parathyroid to stop producing PTH. When blood calcium is low, this signals the thyroid to stop producing Calcitonin. Levels of temperature, pH, hormone levels, blood sugar and others must be kept at homeostasis in the body. Homeostasis is the optimal internal state at which the body operates best. The hypothalamus controls most homeostasis. This is an antagonistic process, one to raise and one to lower blood calcium. Some negative feedback pathways include: - Temperature regulation - Blood pressure regulation - Blood sugar regulation - Thyroid regulation - Photosynthesis in response to increased CO₂ - Predator/prey population dynamic The main positive feedback systems in the body are uterine contractions during childbirth (oxytocin), milk letdown (prolactin), ovulation, and blood clotting, which are self-amplifying systems

Homeostasis of blood glucose levels

One of the most important hormone controlled mechanisms in the human body. Hormones used to control this system can be used in an anticipatory process. This process includes the increase of insulin in the blood in preparation for the glucose and amino acids that will be absorbed from the meal. This mechanism is primarily controlled by Gastric inhibitory peptide (GIP). GIP is secreted by the mucosa of the small intestine. When fatty acids, amino acids, and sugars are found in the small intestine, GIP is secreted in order to stop the motor activity of the stomach, and to cause a release of insulin into the blood. GIP also has an effect on fatty acid metabolism by stimulating lipoprotein lipase in adipocytes. GIP receptors are found on Beta cells in the pancreas. Type II Diabetics are not responsive to GIP.

Types of hormones

Peptide Hormones - Most of the hormones in the body are polypeptide or protein hormones. There are steroid hormones, but they are not as common. Protein and polypeptide hormones are made in the cells on the rough ER. The original protein is generally large and inactive, and with the help of enzymes, the protein is cleaved into a prohormone, which is then packaged into a vesicle and transported throughout the body. Peptide hormones function through extracellular receptors and are water soluble. Protein and polypeptide hormones include GH, TSH, FSH, LH, PTH, Prolactin, ADH, Oxytocin, Insulin, and Glucagon. Lipid-Derived Hormones - Most lipid hormones are derived from cholesterol, so they are structurally similar to it and are lipid soluble. The primary class of lipid hormones in humans is the steroid hormones. They are not stored and must be utilized quickly due to rapid metabolism. They freely pass the cell membrane and act on intracellular receptors. They must be carried through the circulatory system via plasma proteins. Common steroid hormones are cortisol, aldosterone, estrogen, progesterone, and testosterone. Amino Acid-Derived Hormones - These are relatively small molecules derived from the amino acids tyrosine and tryptophan. If a hormone is amino acid-derived, its chemical name will end in "-ine". Examples of amino acid-derived hormones include epinephrine and norepinephrine, which are synthesized in the medulla of the adrenal glands, and thyroxine, which is produced by the thyroid gland. Epinephrine and norepinephrine are formed from tyrosine. The pineal gland in the brain makes and secretes melatonin, which regulates sleep cycles.

Anterior pituitary gland

Produces and releases tropic hormones, which target organs to produce hormones. The tropic hormones are FLAT. It also produces direct hormones which have a direct effect on organs. These are PEG More detail (not really needed): Also known as the adenohypophysis. The anterior pituitary regulates several physiological processes including stress, growth, reproduction and lactation. Proper functioning of the anterior pituitary and of the organs it regulates can often be ascertained via blood tests that measure hormone levels. Its secretions are controlled by the hypothalamic hormones. The hypothalamus contains neurons that control releases from the anterior and posterior pituitary glands. It contains basophils, which are cells that manufactures hormones. Stemming from Rathke's pouch, which is found at roof of the developing mouth in an embryo, the pituitary is considered the master gland, but it's hormones are regulated by the hypothalamus. The hormones found here are: (Mnemonic - FLAT PEG) Tropic hormones FSH LH ACTH TSH Direct hormones Prolactin Endorphins GH

Prolactin

Prolactin is a protein hormone that is secreted by the anterior pituitary gland from lactotropes. The primary function of prolactin is to develop the female breast tissue to promote lactation during pregnancy. This hormone is suppressed in women that are not pregnant. The hypothalamus produces dopamine, and then secretes this dopamine into the anterior pituitary gland. Dopamine acts as an inhibitory chemical to the lactotropes. Due to the decrease in dopamine levels in pregnant women, prolactin can be secreted. The increase in prolactin secreting has a positive correlation with estrogen, breast-feeding, stress, sleep, and dopamine antagonist like high blood pressure meds. Prolactin is the only anterior pituitary gland hormone that has a suppression brake from the hypothalamus. Thus, if the stalk from the hypothalamus were cut, all anterior pituitary hormone levels would decrease except for prolactin.

How hormones target cells

Receptor-mediated Endocytosis

Adrenal gland

The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline (to arouse body in times of stress) and the steroids aldosterone and cortisol. They are found above the kidneys. Each gland has an outer cortex which produces steroid hormones and an inner medulla. The adrenal cortex itself is divided into three zones: the zona glomerulosa, the zona fasciculata and the zona reticularis. The adrenal medulla is responsible for release of epinephrine and norepinephrine. The adrenal cortex releases aldosterone, cortisol, and androgens (male sex hormones). Cortex - outer layer 1) Zona Glomerulosa - Mineralocorticoids, mainly aldosterone Aldosterone - Regulate Na reabsorption (keeps more water, maintain blood volume) in DCT (distal convoluted tubule of kidney nephron) and collecting duct 2) Zona Fasciculata - Glucocorticoids, mainly cortisol, a stress hormone. Cortisol - ↑Blood sugar ↓Immune system 3) Zona Reticularis - Androgens, mainly testosterone Medulla - inner layer Catecholemines - Epinephrine - Norepinephrine

Par intermedia

The boundary between the anterior and posterior lobes of the pituitary. It contains three types of cells - basophils, chromophobes, and colloid-filled cysts. It also contains melanotrophin hormones.

Hypothalamus

The master gland of the endocrine system. It contains all releasing hormones. These releasing hormones act on the anterior pituitary to release all of its hormones. Produces: (not stored here) - Oxytocin (uterine contractions, milk let down) Uterine contractions are one of the only positive feedback mechanisms in the body - Vasopressin (ADH) Releasing hormones: (cause hormones to be either released or inhibited) - Thyrotropin Releasing Hormone (TRH) Note "thyroid", stimulates release of Thyroid Stimulating Hormone (TSH) and prolactin - Dopamine/Prolactin Inhibiting Hormone (PIH) Inhibit prolactin release - Growth Hormone Releasing Hormone (GhRH) Stimulates release of Gh - Somatostatin/Growth Hormone Inhibiting Hormone (GhIH) Inhibits release of Gh - Corticotropin Releasing Hormone (CRH) Stimulates release of Adrenocorticotropic hormone (ACTH)

Menstrual cycle

The ovaries are controlled by FSH and LH. The uterus is controlled by hormones from ovaries: estrogen and progesterone. Changes that occur in the ovary is response to FSH and LH are known as the ovarian cycle; changes that occur in the uterus in response to estrogen and progesterone is known as the uterine cycle. LH spikes just before ovulation. FSH is higher at the beginning of menstrual cycle with a slight increase around ovulation. Progesterone rises after ovulation takes place. Estrogen spikes before ovulation and starts to drop during ovulation.

Hypophyseal portal system

This connects the hypothalamus and anterior pituitary gland. Its main function is to quickly transport and exchange hormones between the hypothalamus and anterior pituitary gland. The capillaries in the portal system are fenestrated (have many small channels with high vascular permeability) which allows a rapid exchange between the hypothalamus and the pituitary. The main hormones transported by the system include gonadotropin-releasing hormone (GnRH), corticotropin-releasing hormone (CRH), growth hormone-releasing hormone (GHRH), and thyrotropin-releasing hormone (TRH).

Thyrotropin-releasing hormone (TRH)

This hormone is released by the hypothalamus. It communicates with the pituitary gland that stimulates the release of thyroid-stimulating hormone (TSH). This TSH will stimulate the follicular cells of the thyroid gland to make thyroglobulin-containing tyrosine, and then secrete this substance into the colloid containing regions of the follicles in the thyroid gland. In this area, the tyrosine residues are iodinated. Iodinated tyrosine molecules bind to each other forming either triiodothyronine (T3) or thyroxine (T4). These two hormones are stored in the colloid region of the follicle. When TSH is high, T3 and T4 are transported back into the follicular cell (in the thyroid gland), and then released into circulation. - T4 is much more abundant than T3. However, T3 is much more potent. - If iodine is deficient in the diet, then thyroglobulin cannot be converted to T3 or T4, and thus an increase in thyroglobulin will be found in the blood stream. - Common signs of increased thyroid function are loss of weight, Graves' disease, heat. - The most important factor of the thyroid hormone is the growth and development of the brain.

Corticotropin-releasing hormone (CRH)

This hormone stimulates ACTH (Adrenocorticotropic hormone). Corticotropin releasing hormone in the hypothalamus stimulates ACTH in the anterior pituitary in response to stress. ACTH in turn stimulates secretion of cortisol in the adrenal cortex.

Thyroxine

Thyroxine (T4) is the main hormone secreted into the bloodstream by the thyroid gland. It is the inactive and stable form of thyroid hormone. Most of it is converted to an active form called triiodothyronine (T3) by organs such as the liver and kidneys. Thyroid hormones play vital roles in regulating the body's metabolic rate, heart and digestive functions, muscle control, brain development and maintenance of bones. It increases lipolysis, gluconeogenesis, and glycogenolysis.