chapter 17 endocrine anatomy

Adrenal (medulla) Epinephrine, norepinephrine Amine Stimulate fight-or-flight response

Adrenal Gland Located retroperitoneal and superior to the kidney. Composed of two distinct regions: the adrenal cortex (outer) and adrenal medulla (inner).

Alpha cells - produce glucagon

Delta cells - produce somatostatin which inhibits insulin and glucagon secretion and slows the rates of food absorption and enzyme secretion along the digestive tract.

Development and Aging of the Endocrine System Development: The endocrine system arises from all three embryonic germ layers. Endoderm: thyroid and parathyroid glands, as well as the pancreas and the thymus. Mesoderm: The endocrine glands that produce the steroid hormones, such as the gonads and adrenal cortex Ectoderm: pituitary gland, pineal gland, adrenal medulla

Direct communication -

Direct communication - via gap junctions; use ions, small solutes, and other lipid-soluble materials as chemical mediators; effects are usually limited to adjacent cells of the same type that are interconnected by connexons.

Downregulation - the presence of a significant level of a hormone circulating in the bloodstream can cause its target cells to decrease their number of receptors for that hormone, allowing cells to become less reactive to the excessive hormone levels.

Hepcidin blocks the release of iron from cells in the body, helping to regulate iron homeostasis in our body fluids.

Islets of Langerhans: endocrine cells that produce hormones.

Pancreas Insulin Protein Reduces blood glucose levels

Prolactin (PRL or luteotropic hormone) - works with other hormones to stimulate mammary gland development and the production of milk during pregnancy and during nursing. Regulated by several prolactin-releasing hormones and prolactin-inhibiting hormone (PIH).

Role of endocrine gland stimuli: Hormones can stimulate behavior or behavior may stimulate hormones. Elevated hormone levels do not equate to elevated behavior.

Thyroid Thyroxine (T4), triiodothyronine (T3) Amine Stimulate basal metabolic rate

Upregulation - cells increase their number of receptors due to the level of a hormone becoming chronically reduced.

Water-soluble = Water-soluble hormones cannot diffuse through the cell membrane. These hormones must bind to a surface cell-membrane receptor. The receptor then initiates a cell- signaling pathway within the cell involving G proteins, adenylyl cyclase, the secondary messenger cyclic AMP (cAMP), and protein kinases. In the final step, these protein kinases phosphorylate proteins in the cytoplasm. This activates proteins in the cell that carry out the changes specified by the hormone.

Zona fasciculate (middle) - produces glucocorticoids such as cortisol and cortisone which influence metabolism of glucose, protein, and fat; controlled by ACTH. Zona reticularis (inner) - produces androgens or adrenal sex hormones such as testosterone which influence masculinization.

spermagionesis takes __ days to mature

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Factors Affecting Target Cell Response. Hormones must have receptors on their target tissue.

Factors Affecting Target Cell Response. Hormones must have receptors on their target tissue. down and up regulation

Thrombopoetin stimulates the production of the blood's platelets.

Hormones and paracrine factors of the body can be divided into groups:

amino acid derivatives, lipid derivatives and peptide hormones

liver secretes four important hormones

angiotensinogen, thrombopoetin, hepcidin, insulin like growth factor somatomedin

Interactions between hormones:

antagonistic synergistic and permissive effects

production of sperm

spermatogenesis

maturation of sperm is called

spermiogenesis

transport of sperm

tubules rectus (straight tubule), retes testis, efferent ductules, epididymis

The endocrine system and nervous system are similar yet different: Both systems rely on the release of chemicals that bind to specific receptors on their target cells. Both share many chemical messengers; when released into the bloodstream they are called hormones but when released into a synapse, they are called neurotransmitters. Both systems are regulated primarily by negative feedback control. Both share a common goal: to preserve homeostasis by coordinating and regulating the activities of other cells, tissues, organs, and systems.

The endocrine system works with or in harmony with the nervous system to control and coordinate all the activities of the body and to maintain homeostasis. Endocrinology - field of medicine that focuses on the treatment of endocrine system disorders.

Thymus Gland: located posterior to the sternum and between the lungs. Large in infant, increases in size until puberty and then shrinks as the individual continues to age. The major hormonal product of the thymus gland is thymosin which appears to be essential for the normal development of T lymphocytes and the immune response.

Thyroid Calcitonin Peptide Reduces blood Ca2+ levels

Adrenal cortex produces steroid hormones from cholesterol (corticosteroids) and is divided into three regions: Zona glomerulosa (outer) - releases mineralocorticoids, principally aldosterone, which controls electrolyte balance in the kidneys.

Adrenal medulla releases hormones when the body is under stress and consists of hormone-producing cells called chromaffin cells. Epinephrine (aka adrenaline) - (80%) elevates blood sugar, regulates body during stress or anger; raises blood pressure, heart beat, glycogen breakdown and increases all other sympathetic effects of the nervous system.

Adrenocorticotropic hormone (ACTH or corticotropin) - stimulates the release of steroid hormones by the adrenal cortex. Released in response to corticotropin-releasing hormone (CRH) from the hypothalamus.

Amino acid derivatives - hormones derived from a single amino acid. Examples include: the thyroid hormones such as thyroxine and triiodothyronine; the catecholamines such as epinephrine, norepinephrine, and dopamine; and melatonin

Angiotensinogen is the precursor to angiotensin, mentioned earlier, which increases blood pressure.

Antagonistic effects - one hormone inhibits the response of another therefore they generate opposite responses; example: insulin lowers blood sugar while glucagon raises blood sugar

Beta cells - produce insulin

Between the follicles is a second population of endocrine cells called parafollicular cells, or C (clear) cells. Clear cells produce calcitonin (CT) which lowers blood calcium levels when they are too high. Calcitonin works by increasing the amount of calcium excreted in urine and increasing the deposition of calcium in bone by stimulating osteoblast activity.

Heart secretes ANP that literally means "producing salty urine. ANP Inhibits aldosterone release by the adrenal cortex. The brain also secretes BNP that performs the same job.

Hormones are chemical messengers released by endocrine cells/glands into bloodstream to be transported throughout the body to regulate the metabolic functions and activities of other cells of the body. See table at end of outline for list of endocrine glands and their related hormones.

Hormones are regulated by feedback mechanisms and hormonal interactions

Luteinizing hormone (LH) - induces ovulation in females and promotes the secretion of estrogen and progesterone. In males it stimulates the production of sex hormones called androgens, specifically testosterone. Released in response to gonadotropin-releasing hormone from the hypothalamus.

Melanocyte stimulating hormone (MSH) - stimulates melanocytes of the skin to increase their production of melanin. Non-functional in adults.

Negative feedback systems - physiological response causes a decrease in the release of the hormone; most commonly used

Neural communication

Neural communication - via synaptic clefts; use neurotransmitters as chemical mediators; effects are limited to very specific areas; target cells must have appropriate receptors.

Neurohypophysis - the posterior lobe of the pituitary gland connected to the hypothalamus by the infundibulum; contains the axons of the hypothalamic neurons. Stores and secretes hormones synthesized in the hypothalamus:

Norepinephrine (aka noradrenaline) - helps maintain blood pressure, and accounts for 20% of the hormones released by the medullary portion of the adrenal gland.

Osteocalcin, produced by osteoblasts, stimulates the pancreatic beta cells to increase insulin production. It also acts on peripheral tissues to increase their sensitivity to insulin and their utilization of glucose.

Ovaries Estrogens and progesterone Steroid Stimulate development of female secondary sex characteristics and prepare the body for childbirth

Ovaries: located in the pelvic cavity. Produce estrogen which regulates secondary sex characteristics (breast, pubic hair, etc.). Also produce progesterone which helps to stimulate the uterus to bring about thickening and vascularization of the endometrium in preparation for implantation of a fertilized egg.

Oxytocin (OXT) - stimulates the smooth muscle contractions of the uterus which initiates child birth. After delivery, stimulates the ejection of milk. In both sexes, known as the "cuddle hormone" as it surges during arousal and orgasm.

PP cells - produce the hormone pancreatic polypeptide (PP) which inhibits gallbladder contractions and regulates the production of some of the digestive enzymes.

Pancreatic amylase (almost identical to salivary amylase) - enzymes that further digest the carbohydrates, only briefly started in the mouth, into oligosaccharides and disaccharides.

Pancreatic lipase - enzyme that breaks down lipids into fatty acids and glycerol.

Pancreatic nucleases - enzymes that breaks down nucleic acids such as deoxyribonuclease (DNA) and ribonuclease (RNA).

Paracrine communication

Paracrine communication - via extracellular fluids; use paracrine factors as chemical mediators; effects are primarily limited to the local area where paracrine factor concentrations are relatively high; target cells must have appropriate receptors.

Parathyroid Parathyroid hormone (PTH) Peptide Increases blood Ca2+ levels

Peptide hormones - chains of amino acids. Examples include: Polypeptides: antidiuretic hormone (9 amino acids) and oxytocin (9 amino acids) Small proteins: insulin (51 amino acids), growth hormone (191 amino acids) and prolactin (198 amino acids) Glycoproteins: thyroid-stimulating hormone, luteinizing hormone, and follicle-stimulating hormone

Permissive effects - one hormone is needed to activate another; example: rennin stimulates the conversion of Angiotensin I into Angiotensin II

Pineal Melatonin Amine Regulates sleep cycles

Pineal Gland Located in the roof of the 3rd ventricle of the brain called the epithalamus region. Composed of special secretory cells called pinealocytes. The major product is melatonin whose concentrations rise and fall in a diurnal cycle. Levels are lowest during daylight hours and highest at night. Melatonin appears to maintain the basic circadian rhythms - daily changes in physiological processes that follow a regular day-night pattern. Melatonin protects against tissue damage by acting as an antioxidant and that protects the central nervous system from free radicals such as hydrogen peroxide. Melatonin may inhibit reproductive development and functioning

Pituitary (anterior) Growth hormone (GH) Protein Promotes growth of body tissues

Pituitary (anterior) Luteinizing hormone (LH) Glycoprotein Stimulates androgen production by gonads

Pituitary (anterior) Prolactin (PRL) Peptide Promotes milk production

Pituitary (anterior) Thyroid-stimulating hormone (TSH) Glycoprotein Stimulates thyroid hormone release

Pituitary (posterior) Antidiuretic hormone (ADH) Peptide Stimulates water reabsorption by kidneys

Pituitary (posterior) Oxytocin (OXY) Peptide Stimulates uterine contractions during childbirth

Pituitary Gland - Hypophysis Also known as the "master gland" is located within the sella turcica of the sphenoid bone. Connected to the hypothalamus via the infundibulum and a network of capillaries called the hypophyseal portal system. Divided into two lobes: an anterior lobe and a posterior lobe.

Placenta: a temporary organ only formed during pregnancy. Produces hCG hormone (human chorionic gonadotrophic) with aid in maintaining pregnancy and keeping the corpus luteum intact.

Positive feedback systems - physiological response causes an increase in the release of the hormone; rarely used

Skeleton produces at least two hormones:

Skeleton produces at least two hormones: Fibroblast growth factor 23 (FGF23) osteocalcin

Skin produces cholecalciferol, the inactive form of vitamin D.

Sodium bicarbonate - serves as a buffer of the HCl produced in the stomach.

Synergistic effects - two hormones with similar effects produce an amplified response. In some cases, two hormones are required for an adequate response. For example, two different reproductive hormones—FSH from the pituitary gland and estrogens from the ovaries—are required for the maturation of female ova (egg cells).

Testes: located in the scrotum. Secretes testosterone, the male sex hormone, which brings about development of secondary sex characteristics, normal sex behaviors, and production of sperm. Also produces inhibin which inhibits the release of FSH and GnRH when sperm counts are high.

Structures of the endocrine system:

Thalamus Pineal gland Pituitary gland Thyroid Thymus Adrenal Pancreas Ovaries Testes

The Endocrine Pancreas Located posterior and inferior to the stomach. A unique organ that has both and endocrine and exocrine abilities.

mechanisms of Intercellular Communication

neural, direct, paracrine, endocrine communication

Acinar cells: exocrine cells that produce enzymes and other digestive chemicals. (must know for GI chapter)

Gastrointestinal tract possesses cells that produce secretin, gastrin, CCK, GIP, VIP, ghrelin, galanin, neuropeptide Y, and many more.

Insulin and glucagon work as antagonists to maintain homeostasis of blood sugar.

Pancreas Glucagon Protein Increases blood glucose levels

Pituitary (anterior) Adrenocorticotropic hormone (ACTH) Peptide Stimulates hormone release by adrenal cortex

Pituitary (anterior) Follicle-stimulating hormone (FSH) Glycoprotein Stimulates gamete production

Proteases - secreted as inactive enzymes but become activated in the small intestine to form the activated: carboxypeptidase, chymotrypsin, and trypsin. These enzymes break down large polypeptides into oligopeptides, tripeptides, dipeptides and some amino acids.

Testes Testosterone Steroid Stimulates development of male secondary sex characteristics and sperm production

Adipose tissue releases leptin following the uptake of glucose and lipids resulting in satiety.

Adrenal (cortex) Aldosterone Steroid Increases blood Na+ levels

Adrenal (cortex) Cortisol, corticosterone, cortisone Steroid Increase blood glucose levels

Antidiuretic hormone (ADH also known as vasopressin) - increases water reabsorption within the renal tubules of the kidney. This results in a decrease in water loss from urine.

As the body ages, changes occur that affect the endocrine system, sometimes altering the production, secretion, and catabolism of hormones. For example, the structure of the anterior pituitary gland changes as vascularization decreases and the connective tissue content increases with increasing age. This restructuring affects the gland's hormone production. Certain hormones and gland production decrease with age: reduced cortisol and aldosterone from adrenal gland, lower estrogen and progesterone from ovaries, as well as lower testosterone levels.

Liver is responsible for secreting at least four important hormones or hormone precursors:

Adenohypophysis - the anterior lobe of the pituitary gland connected to the hypothalamus by the hypophyseal portal system. Controlled by regulating hormones, called releasing hormones (RH) andinhibiting hormones (IH) from the hypothalamus:

5 Parathyroid Gland Two pair of glands embedded in the posterior surfaces of the thyroid gland. Composed of two cell populations Oxyphil cells - have no known function. Chief cells - produce parathyroid hormone (PTH) which increases blood calcium levels when they are too low. PTH and calcitonin work as antagonists to maintain homeostasis of blood calcium levels. PTH specifically targets: Bones - activates osteoclasts causing calcium and phosphate ions to be released into the blood. Intestine - increases calcium absorption from food. Kidneys - promotes activation of vitamin D and increases calcium reabsorption in the kidney tubules.

Effects of Epi/NE: Signals the liver and skeletal muscle cells to convert glycogen into glucose, resulting in increased blood glucose levels. These hormones increase the heart rate, pulse, and blood pressure to prepare the body to fight the perceived threat or flee from it. Dilates the airways, raising blood oxygen levels. Prompts vasodilation, further increasing the oxygenation of important organs such as the lungs, brain, heart, and skeletal muscle. Triggers vasoconstriction to blood vessels serving less essential organs such as the gastrointestinal tract, kidneys, and skin, and downregulates some components of the immune system. Other effects include a dry mouth, loss of appetite, pupil dilation, and a loss of peripheral vision.

Endocrine communication

Endocrine communication - via the bloodstream; use hormones as chemical mediators; effects are on target cells located in other tissues or organs; target cells must have an appropriate receptor.

Fibroblast growth factor 23 (FGF23) is produced by bone cells to triggers the kidneys to inhibit the formation of calcitriol from vitamin D3 and to increase phosphorus excretion during high blood calcium levels.

Follicle stimulating hormone (FSH or gonadotropin) - promotes ovarian follicles to develop in females and, in conjunction with luteinizing hormone, stimulates the secretion of estrogens. In males FSH promotes the physical maturation in sperm. Released in response to gonadotropin-releasing hormone (GnRH) from the hypothalamus.

Glucagon raises blood glucose levels by breaking down glycogen into glucose (glycogenolysis), synthesizes glucose from lactic acid and other non-carbohydrate molecules (gluconeogenesis), and releases glucose to the blood by liver cells.

Growth hormone (GH) - stimulates cell growth and reproduction by accelerating the rate of protein synthesis particularly in skeletal muscle and bone. Regulated by growth hormone-releasing hormone (GH-RH) and growth hormone-inhibiting hormone (GH-IH) from the hypothalamus.

Hypothalmus The hypothalamus provides the highest level of endocrine control. It integrates the activities of the nervous system and endocrine system. The hypothalamus accomplishes this integration through three mechanisms: The hypothalamus contains autonomic centers that exert direct neural control of the endocrine cells, called chromaffin cells, of the adrenal medulla. When the sympathetic division is activated, this direct control allows the immediate stimulation of the adrenal gland. Hypothalamic neurons synthesize two hormones - ADH and OXT - and transport them along axons within the infundibulum to the posterior lobe of the pituitary for storage and secretion. The hypothalamus secretes regulatory hormones that control the secretions of the anterior pituitary gland. These regulatory hormones, called releasing hormones (RH) and inhibiting hormones (IH), flow via a network of fenestrated capillaries called the hypophyseal portal system.

Insulin lowers blood glucose levels by enhancing membrane transport of glucose into body cells, converting excess glucose to glycogen for short-term storage (glycogenesis) and into fat for long-term storage in adipocytes (lipogenesis).

Insulin-like growth factor (somatomedin) is the immediate stimulus for growth in the body, especially of the bones.

Kidney secretes EPO for red blood cell production and rennin for activation of angiotensin II, a potent vasoconstrictor.

Lipid derivatives - consist of carbon rings and side chains built either from fatty acids chains or cholesterol. Eicosanoids - built from fatty acid chains and include: leukotrienes and prostaglandins. Steroid hormones - built from cholesterol molecules and include: testosterone, estrogen and progesterone, corticosteroids, and calcitriol.

Lipid-soluble = A steroid hormone directly initiates the production of proteins within a target cell. Steroid and thyroid hormones easily diffuse through the cell membrane. The steroid hormone binds to its receptor in the cytosol, forming a receptor-hormone complex. The receptor-hormone complex then enters the nucleus and binds to the target gene on the DNA. Thyroid hormones bind to receptors already bound to DNA. Transcription of the gene creates a messenger RNA that is translated into the desired protein within the cytoplasm.

Thyroid Gland Located in the neck just below the larynx and anterior to the trachea. Divided into a right and left lobe connected by a narrow isthmus. Regulated by TSH from the pituitary gland. The thyroid gland contains large numbers of thyroid follicles - hollow spheres lined by a simple cuboidal epithelium called the follicle cells. The follicle cells surround a cavity that holds a viscous colloid, a fluid containing a large quantity of dissolved proteins. The follicle cells synthesize a globular protein called thyroglobulin and secrete it into the colloid of the thyroid follicle. The thyroglobulin molecules contain the amino acid tyrosine. The thyroglobulin is combined with iodide ions absorbed from the diet to form the thyroid hormones: T3 (triiodothyronine) and T4(thyroxine).

Thyroid hormones have several effects in the body: Stimulates red blood cell production and thus enhanced oxygen delivery. Stimulates the activity of other endocrine tissues. Accelerates the turnover of minerals in bone. Elevates rates of oxygen consumption and energy consumption in cells; increase basal metabolic rates. Increases heart rate and force of contraction resulting in increased blood pressure. Increases sensitivity to sympathetic stimulation. Maintains the normal sensitivity of respiratory centers to changes in oxygen and carbon dioxide concentrations in the blood.

Thyroid stimulating hormone (TSH) - targets the thyroid gland; stimulates the thyroid to grow and increase its secretion of the thyroid hormones, T3 and T4. Released in response to thyrotropin-releasing hormone (TRH) from hypothalamus.

chapter 17 endocrine anatomy

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