Unit 5 Endocrine Assignment

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1. Identify the contributions of the endocrine system to homeostasis.  Regulation of Metabolism: The endocrine system controls metabolism through hormones produced by the thyroid gland, such as thyroxine (T4) and triiodothyronine (T3). These hormones regulate the rate at which cells utilize energy and influence the body's overall metabolic rate.  Maintenance of Blood Glucose Levels: The endocrine system, particularly the pancreas, regulates blood glucose levels to ensure a constant supply of energy for cells. Insulin, produced by the beta cells of the pancreas, lowers blood glucose levels, while glucagon, produced by the alpha cells of the pancreas, raises blood glucose levels when they are too low (Big et al., 2020).  Regulation of Fluid and Electrolyte Balance: The endocrine system helps maintain the body's balance of fluids and electrolytes. Hormones such as aldosterone, produced by the adrenal glands, regulate sodium and potassium levels. In contrast, antidiuretic hormone (ADH), produced by the pituitary gland, controls water balance by regulating water reabsorption in the kidneys.  Control of Blood Pressure : Several hormones produced by different glands, including the adrenal glands and the kidneys, regulate blood pressure. For example, aldosterone helps maintain blood pressure by regulating sodium and water balance. At the same time, atrial natriuretic peptide (ANP), produced by the heart, promotes sodium and water excretion, reducing blood volume and blood pressure.  Regulation of Calcium Levels: The endocrine system, particularly the parathyroid glands, helps regulate calcium levels in the blood. Parathyroid hormone (PTH) is responsible for increasing blood calcium levels by stimulating the release of calcium from bones and enhancing its absorption in the intestines and kidneys (Big et al., 2020).

 Reproduction and Growth: The endocrine system regulates reproduction and growth. Hormones such as follicle-stimulating hormone (FSH), luteinizing hormone (LH), estrogen, and testosterone control the development and function of the reproductive organs and are essential for reproduction. Additionally, the pituitary gland's growth hormone stimulates growth and development during childhood and adolescence (Big et al., 2020). 2. Identify the major organs and tissues of the endocrine system and their location in the body.  Pituitary Gland: The pituitary gland is located at the base of the brain, below the hypothalamus, within a bony structure called the Sella turcica.  Hypothalamus: The hypothalamus is located above the pituitary gland in the brain. It is part of the brain's limbic system and is crucial in regulating various bodily functions (Kelly, 2013).  Adipose Tissue : Adipose tissue, which consists of fat cells, does produce hormones called adipokines. Adipose tissue is distributed throughout the body, primarily located beneath the skin (subcutaneous fat) and around internal organs (visceral fat). 3. Describe the chemical composition of the three major hormone groups and the mechanisms of hormone action.  Peptide or Protein Hormones : Peptide hormones are composed of amino acids and are generally water-soluble. They range in size from small peptides to larger protein molecules. Examples of peptide hormones include insulin, growth hormone, and oxytocin.  Steroid Hormones: Steroid hormones are derived from cholesterol and are lipids (fat- soluble). They are synthesized primarily by the gonads (testes and ovaries) and the

adrenal cortex. Examples of steroid hormones include estrogen, progesterone, testosterone, and cortisol.  Amine Hormones : Amine hormones are derived from the amino acid tyrosine and can be further classified into two subcategories: o Catecholamines: Catecholamines, such as epinephrine (adrenaline), norepinephrine (noradrenaline), and dopamine, are synthesized in the adrenal medulla and are water-soluble. o Thyroid Hormones: Thyroid hormones, including thyroxine (T4) and triiodothyronine (T3), are produced by the thyroid gland and are water- soluble. Hormones exert their effects through specific mechanisms of hormone action:  Receptor-Mediated Mechanism : Hormones bind to specific receptors on target cells or organs. These receptors are often located on the cell membrane (water-soluble hormones) or within the cell (lipid-soluble hormones). The hormone-receptor interaction triggers intracellular events that ultimately lead to a cellular response.  Signal Transduction: Once a hormone binds to its receptor, it initiates signal transduction pathways within the target cell. These pathways involve the activation of intracellular messengers or secondary messengers (such as cyclic adenosine monophosphate, or cAMP) that relay the hormone's signal to specific cellular enzymes or genes. This process changes cellular metabolism, gene expression, or other physiological responses.  Gene Expression Regulation : Certain hormones, such as steroid hormones, can directly enter the target cells and bind to receptors in the nucleus. This hormone- receptor complex acts as a transcription factor, regulating the expression of specific

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genes. The altered gene expression leads to the synthesis of new proteins, resulting in long-term cellular responses.  Feedback Mechanisms: Feedback mechanisms often regulate hormone action to maintain homeostasis. Negative feedback loops involve inhibiting or reducing hormone release in response to increased hormone levels. Positive feedback loops amplify hormone secretion and response until a specific endpoint is reached (Kelly, 2013). 4. Compare and contrast intracellular and cell membrane-bound hormone receptors. Intracellular Hormone Receptors  Location : Intracellular hormone receptors are located inside the target cells, typically in the cytoplasm or nucleus.  Ligand Type : These receptors primarily bind to lipid-soluble hormones, such as steroid hormones (e.g., estrogen, testosterone) and thyroid hormones (T3 and T4).  Mechanism of Action : Once a hormone binds to the intracellular receptor, the hormone-receptor complex enters the nucleus and directly binds to specific DNA sequences known as hormone response elements (HREs). This binding triggers the transcription or inhibition of specific genes, leading to changes in protein synthesis and cellular responses.  Speed of Response: The response to intracellular hormone receptors is usually relatively slow, taking hours to days for noticeable effects to occur.  Examples : Examples of intracellular hormone receptors include estrogen receptors, androgen receptors, and thyroid hormone receptors (Big et al., 2020). Cell Membrane-Bound Hormone Receptors

 Location : Cell membrane-bound hormone receptors are located on the surface of target cells, typically embedded in the plasma membrane.  Ligand Type: These receptors primarily bind to water-soluble hormones, such as peptide hormones (e.g., insulin, growth hormone) and some amine hormones (e.g., epinephrine).  Mechanism of Action: When a hormone binds to the receptor on the cell membrane, it activates intracellular signaling pathways through various mechanisms, including second messenger systems (e.g., cAMP, calcium ions) or receptor tyrosine kinase activation. These pathways lead to activating or inhibiting specific enzymes or proteins within the cell, resulting in changes in cellular metabolism, gene expression, or other physiological responses.  Speed of Response: The response to cell membrane-bound hormone receptors is typically rapid, occurring within seconds to minutes.  Examples : Examples of cell membrane-bound hormone receptors include insulin receptors, adrenergic receptors, and growth hormone receptors (Big et al., 2020). 5. Identify the six hormones produced by the anterior lobe of the pituitary gland, their target cells, their principal actions, and their regulation by the hypothalamus. a) Growth Hormone (GH)  Target Cells: Various tissues, particularly bone, muscle, and adipose tissue.  Principal Actions: Stimulates growth, cell reproduction, and regeneration. Promotes protein synthesis, lipolysis (breakdown of fats), and overall tissue growth (Kelly, 2013).  Regulation by the Hypothalamus : GH release is regulated by the hypothalamic hormone called growth hormone-releasing hormone (GHRH), which stimulates GH

secretion. Additionally, growth hormone-inhibiting hormone (GHIH), also known as somatostatin, inhibits GH release (Kelly, 2013). b) Prolactin (PRL)  Target Cells : Mammary glands in the breasts.  Principal Actions : Stimulates milk production (lactation) in females after childbirth. In males, it may have a role in reproductive function and behavior.  Regulation by the Hypothalamus: Prolactin release is primarily inhibited by dopamine (also known as prolactin-inhibiting hormone or PIH) secreted by the hypothalamus. Reduced dopamine release allows prolactin levels to rise (Kelly, 2013). c) Adrenocorticotropic Hormone (ACTH)  Target Cells: Adrenal cortex (outer layer of the adrenal glands).  Principal Actions : Stimulates the release of cortisol and other glucocorticoid hormones from the adrenal cortex. It plays a role in the body's response to stress and helps regulate metabolism, immune function, and inflammation.  Regulation by the Hypothalamus: ACTH release is controlled by corticotropin- releasing hormone (CRH) from the hypothalamus. CRH stimulates ACTH secretion (Kelly, 2013). d) Thyroid-Stimulating Hormone (TSH)  Target Cells : Thyroid gland.  Principal Actions: Stimulates the synthesis and release of thyroid hormones, including thyroxine (T4) and triiodothyronine (T3), from the thyroid gland. These hormones regulate metabolism, growth, and development.  Regulation by the Hypothalamus : TSH release is regulated by thyrotropin-releasing hormone (TRH) from the hypothalamus. TRH stimulates TSH secretion (Kelly, 2013). e) Follicle-Stimulating Hormone (FSH)

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 Target Cells: Ovaries in females and testes in males.  Principal Actions: In females, FSH stimulates the growth and maturation of ovarian follicles and promotes estrogen production. In males, FSH promotes sperm production (spermatogenesis).  Regulation by the Hypothalamus : FSH release is regulated by gonadotropin-releasing hormone (GnRH) from the hypothalamus. GnRH stimulates FSH secretion (Kelly, 2013). Luteinizing Hormone (LH)  Target Cells: Ovaries in females and testes in males.  Principal Actions : In females, LH triggers ovulation and promotes the formation of the corpus luteum, which produces progesterone. In males, LH stimulates testosterone production.  Regulation by the Hypothalamus: LH release is also regulated by gonadotropin- releasing hormone (GnRH) from the hypothalamus. GnRH stimulates LH secretion (Kelly, 2013). 6. Explain the interrelationships of the anatomy and functions of the hypothalamus and the posterior and anterior lobes of the pituitary gland. The hypothalamus and the posterior and anterior lobes of the pituitary gland have a close anatomical and functional relationship. Located close to the brain, the hypothalamus and pituitary gland work together to regulate various physiological processes by releasing and controlling hormones. The hypothalamus serves as a crucial control center for the endocrine system. It produces and releases several releasing and inhibiting hormones, which are transported through the hypothalamic-pituitary portal system to the anterior pituitary gland. These releasing hormones stimulate or inhibit the release of specific hormones from the anterior pituitary.

The anterior pituitary, in turn, synthesizes and secretes hormones such as growth hormone, prolactin, adrenocorticotropic hormone, thyroid-stimulating hormone, follicle-stimulating hormone, and luteinizing hormone. These hormones act on various endocrine glands or target tissues to regulate their function and hormone production. Furthermore, the hypothalamus produces oxytocin and antidiuretic hormone (ADH), which are transported along nerve fibers and stored in the posterior pituitary. Upon stimulation from the hypothalamus, the posterior pituitary releases these hormones directly into the bloodstream. Oxytocin plays a role in labor, breastfeeding, and social bonding, while ADH regulates water balance and blood pressure. The interrelationships between the hypothalamus and the pituitary glands are reciprocal. The hypothalamus receives feedback from hormone levels in the bloodstream and adjusts its release of releasing and inhibiting hormones accordingly, regulating the activity of the pituitary gland. Additionally, the posterior pituitary receives neural signals from the hypothalamus, allowing for the release of oxytocin and ADH when needed (Big et al., 2020). 7. Identify the two hormones released from the posterior pituitary, their target cells, and their principal actions. a) Oxytocin  Target Cells: Oxytocin primarily acts on the smooth muscle cells of the uterus (myometrium) and the mammary glands.  Principal Actions: i. Uterine Contraction: Oxytocin stimulates contractions of the uterine muscles during childbirth. It plays a crucial role in initiating and enhancing labor, facilitating the progression of childbirth, and promoting the expulsion of the placenta.

ii. Milk Ejection: Oxytocin also promotes the contraction of specialized cells surrounding the milk-producing alveoli in the mammary glands. This contraction helps squeeze milk from the alveoli into the milk ducts, facilitating the ejection or let-down of milk during breastfeeding (Kelly, 2013). b) Antidiuretic Hormone (ADH), also known as Vasopressin  Target Cells: ADH primarily acts on the cells of the distal convoluted tubules and collecting ducts in the kidneys.  Principal Actions : i. Water Reabsorption: ADH increases the permeability of the renal tubules, specifically the collecting ducts, to water. This action increases water reabsorption into the bloodstream, reducing urine volume and promoting water retention. ii. Concentration of Urine: By enhancing water reabsorption, ADH helps concentrate urine, preventing excessive fluid loss and maintaining fluid balance. iii. Blood Pressure Regulation: In higher concentrations, ADH acts as a vasoconstrictor, causing constriction of blood vessels. This action helps elevate blood pressure and regulate blood volume (Kelly, 2013). 8. Discuss the hormonal regulation of the reproductive system. a) Gonadotropin-Releasing Hormone (GnRH)  Produced by the hypothalamus, GnRH regulates the release of gonadotropins from the anterior pituitary gland.  GnRH secretion is pulsatile, and its frequency and amplitude change throughout the menstrual cycle (in females) or in a cyclical pattern (in males) (Kelly, 2013). b) Follicle-Stimulating Hormone (FSH)  Produced and released by the anterior pituitary gland, FSH plays a crucial role in both males and females.

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 In females, FSH stimulates the growth and development of ovarian follicles, which contain eggs (oocytes). It also promotes the production of estrogen by the ovarian follicles.  In males, FSH stimulates the maturation of sperm cells (spermatogenesis) within the testes (Kelly, 2013). c) Luteinizing Hormone (LH)  Also produced and released by the anterior pituitary gland, LH is involved in regulating the reproductive system in both males and females.  In females, LH triggers ovulation, the release of a mature egg from the ovarian follicle. After ovulation, LH promotes the formation and function of the corpus luteum, which produces progesterone.  In males, LH stimulates the production of testosterone by the interstitial cells (Leydig cells) in the testes (Kelly, 2013). d) Estrogen  Estrogen is primarily produced by the ovaries in females (mainly by the ovarian follicles) and smaller amounts by the adrenal glands.  Estrogen plays a crucial role in the development and maintenance of female reproductive structures, including the uterus, fallopian tubes, and breasts.  It is also responsible for the development of secondary sexual characteristics and plays a role in regulating the menstrual cycle (Kelly, 2013). e) Progesterone  Progesterone is primarily produced by the corpus luteum in the ovaries after ovulation.  Progesterone prepares the uterus for potential implantation of a fertilized egg and helps maintain pregnancy.

 It also plays a role in regulating the menstrual cycle (Kelly, 2013). f) Testosterone  Testosterone is the primary male sex hormone produced by the testes, with smaller amounts produced by the adrenal glands in both males and females.  Testosterone is crucial for the development and maintenance of male reproductive structures, including the testes, prostate gland, and seminal vesicles.  It also promotes the development of secondary sexual characteristics in males and plays a role in regulating spermatogenesis (Kelly, 2013). 9. Explain the role of the pancreatic endocrine cells in the regulation of blood glucose, Describe the location and structure of the pancreas, and the morphology and function of the pancreatic islets, then compare and contrast the functions of insulin and glucagon.  The pancreatic endocrine cells play a crucial role in regulating blood glucose levels. These cells are located in small clusters called pancreatic islets (also known as islets of Langerhans) within the pancreas. The pancreas itself is a glandular organ located in the abdominal cavity, behind the stomach. It has both exocrine and endocrine functions.  The pancreas has a unique structure that consists of lobules made up of small units called acini. The acini are responsible for producing and releasing digestive enzymes into the small intestine to aid in the digestion of food. Scattered throughout the pancreas are the pancreatic islets, which are endocrine tissue clusters. These islets contain different types of endocrine cells, including alpha cells and beta cells, which produce the hormones glucagon and insulin, respectively.  The pancreatic islets have a distinct morphology. They are made up of different types of cells, with the two main types being alpha cells and beta cells. Alpha cells produce

glucagon, a hormone that increases blood glucose levels, while beta cells produce insulin, a hormone that decreases blood glucose levels (Big et al., 2020). Function :  Insulin: Insulin facilitates the uptake of glucose from the bloodstream into various tissues (such as muscle and fat cells), promoting its storage as glycogen in the liver and muscles. It also inhibits the breakdown of glycogen into glucose (glycogenolysis) and the production of glucose by the liver (gluconeogenesis).  Glucagon: Glucagon stimulates the breakdown of glycogen into glucose (glycogenolysis) in the liver and the production of glucose from non-carbohydrate sources, such as amino acids (gluconeogenesis). It also promotes the release of glucose into the bloodstream, increasing blood glucose levels (Big et al., 2020). Regulation of Blood Glucose:  Insulin: Insulin is released when blood glucose levels are high, such as after a meal. It helps lower blood glucose levels by promoting glucose uptake and storage in tissues.  Glucagon: Glucagon is released when blood glucose levels are low, such as during fasting or exercise. It raises blood glucose levels by stimulating the breakdown of stored glycogen and the production of glucose (Big et al., 2020). Effect on Other Metabolic Processes:  Insulin: Insulin promotes protein synthesis, inhibits protein breakdown, and enhances fat storage by facilitating the uptake of fatty acids into adipose tissue.  Glucagon: Glucagon stimulates the breakdown of fats (lipolysis) in adipose tissue, releasing fatty acids into the bloodstream for energy production (Big et al., 2020). 10. Describe the location and anatomy of the thyroid gland, and describe structure and functions of triiodothyronine and thyroxine.

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The thyroid gland is a butterfly-shaped endocrine gland located in the front of the neck, just below the Adam's apple. It wraps around the trachea (windpipe) and is composed of two lobes connected by a narrow isthmus. The thyroid gland plays a crucial role in regulating metabolism and producing hormones that are essential for the body's normal functioning. The structure of the thyroid gland consists of numerous spherical structures called thyroid follicles. These follicles are lined with follicular cells, which are responsible for producing and releasing thyroid hormones. The follicles are filled with a gel-like substance called colloid, which contains a precursor molecule called thyroglobulin (Big et al., 2020). The two main hormones produced by the thyroid gland are triiodothyronine (T3) and thyroxine (T4). Triiodothyronine (T3)  Structure : Triiodothyronine, as the name suggests, contains three iodine atoms. Its chemical structure is derived from the amino acid tyrosine and consists of three iodine atoms attached to the tyrosine backbone.  Function : T3 is the biologically active form of thyroid hormone. It regulates various metabolic processes in the body, including energy production and consumption, protein synthesis, and growth and development. T3 increases the basal metabolic rate, enhances the utilization of glucose and fatty acids for energy, and affects heart rate and contraction. Thyroxine (T4)  Structure : Thyroxine, also known as tetraiodothyronine, contains four iodine atoms. Its structure is similar to T3, but it has an additional iodine atom.  Function : Thyroxine is the main hormone secreted by the thyroid gland. It acts as a precursor to T3 and is converted to T3 in peripheral tissues, such as the liver and kidneys. T4 serves as a reservoir for T3 and provides a long-lasting supply of thyroid

hormones. It regulates the metabolism of carbohydrates, proteins, and fats, and is involved in growth, development, and maintenance of body temperature. Both T3 and T4 are essential for normal growth, development, and overall metabolic balance in the body. They exert their effects by binding to specific receptors on target cells in various organs and tissues, influencing gene expression and metabolic processes. The secretion of T3 and T4 is regulated by the hypothalamus and pituitary gland through a feedback mechanism involving the hormone thyrotropin-releasing hormone (TRH) and thyroid-stimulating hormone (TSH) (Big et al., 2020). 11. Explain source, targets and functions of calcitonin. Source : Calcitonin is mainly produced by the C cells of the thyroid gland, which are located between the thyroid follicles. These cells release calcitonin in response to high levels of blood calcium. Targets : Calcitonin primarily acts on the bones, kidneys, and intestines. Functions :  Regulation of Calcium Levels: The primary function of calcitonin is to lower blood calcium levels. It does so by inhibiting the breakdown of bone tissue and the release of calcium from bones into the bloodstream. This action reduces the amount of calcium available in the blood.  Bone Health: Calcitonin helps maintain bone health by promoting calcium deposition in bones and inhibiting bone resorption. It plays a role in bone remodeling and prevents excessive bone loss.  Calcium Excretion: Calcitonin increases the excretion of calcium by the kidneys, reducing its reabsorption and promoting its elimination in the urine. This action helps further lower blood calcium levels.

 Inhibiting Intestinal Calcium Absorption: Calcitonin can also reduce the absorption of calcium from the intestines, thereby decreasing the amount of calcium entering the bloodstream through the digestive system (Kelly, 2013). 12. Describe the location and structure of the parathyroid glands, identify the hormones of the parathyroid gland, provide functions and target tissues. The parathyroid glands are small endocrine glands located near or embedded within the thyroid gland in the neck. They usually consist of four small, oval-shaped glands, two on each side of the thyroid gland. Although their location is close to the thyroid, the parathyroid glands are separate structures and have different functions. Each parathyroid gland has its own distinct structure. It consists of two main types of cells: chief cells (also known as principal cells) and oxyphil cells. Chief cells are responsible for producing and secreting the hormones of the parathyroid gland. The two primary hormones secreted by the parathyroid glands are: Parathyroid Hormone (PTH) Function : Parathyroid hormone (PTH) is the main hormone secreted by the parathyroid glands and plays a crucial role in regulating calcium and phosphate levels in the body. It acts primarily on bones, kidneys, and intestines. Target Tissues:  Bones: PTH stimulates the release of calcium from bones, promoting bone resorption. This action helps increase blood calcium levels.  Kidneys: PTH enhances the reabsorption of calcium from the renal tubules, reducing its excretion in the urine. It also promotes the excretion of phosphate ions, leading to increased serum calcium levels.

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 Intestines: PTH indirectly stimulates the absorption of calcium from the intestines by promoting the production of active vitamin D in the kidneys. Vitamin D aids in the intestinal absorption of calcium. Calcitonin (Produced by the C cells of the thyroid gland, not the parathyroid glands): Function : While not produced by the parathyroid glands themselves, calcitonin is related to calcium regulation and has opposing effects to PTH. It lowers blood calcium levels by inhibiting bone resorption and promoting calcium excretion by the kidneys. Target Tissues :  Bones: Calcitonin inhibits the breakdown of bone tissue and decreases the release of calcium from bones.  Kidneys: Calcitonin reduces the reabsorption of calcium in the renal tubules, leading to increased calcium excretion. Together, PTH and calcitonin help maintain calcium homeostasis in the body. PTH acts to increase blood calcium levels, while calcitonin acts to decrease them. These hormones work in a feedback mechanism to regulate calcium levels in response to the body's needs (Big et al., 2020). 13. Explain the hormonal control of blood calcium homeostasis. The hormonal control of blood calcium homeostasis involves the interaction of three hormones: parathyroid hormone (PTH), calcitonin, and active vitamin D (calcitriol). These hormones work together to maintain a tightly regulated balance of calcium in the bloodstream. Parathyroid Hormone (PTH) Secretion: PTH is produced and released by the parathyroid glands in response to low blood calcium levels. Function :

 Bones : PTH stimulates the activity of osteoclasts, cells responsible for breaking down bone tissue, leading to increased bone resorption. This releases calcium from the bones into the bloodstream, raising blood calcium levels.  Kidneys : PTH acts on the kidneys to increase the reabsorption of calcium in the renal tubules. It also promotes the excretion of phosphate ions, which indirectly increases blood calcium levels by reducing the formation of calcium phosphate complexes.  Intestines: PTH indirectly enhances calcium absorption from the intestines by promoting the synthesis of active vitamin D. Calcitonin : Secretion : Calcitonin is produced by the C cells (or parafollicular cells) in the thyroid gland, not the parathyroid glands. It is released in response to high blood calcium levels. Function :  Bones : Calcitonin inhibits osteoclast activity, reducing bone resorption. This decreases the release of calcium from bones into the bloodstream, thereby lowering blood calcium levels.  Kidneys : Calcitonin reduces the reabsorption of calcium in the renal tubules, promoting its excretion in the urine. Active Vitamin D (Calcitriol) Synthesis : Vitamin D is converted into its active form, calcitriol, primarily in the kidneys. The synthesis of calcitriol is stimulated by PTH. Function :  Intestines : Calcitriol enhances the absorption of dietary calcium from the intestines. It promotes the synthesis of calcium-binding proteins that facilitate the transport of calcium across the intestinal lining into the bloodstream (Big et al., 2020). 14. Describe the location and structure of the adrenal glands.

Location : The adrenal glands are situated on the superior (upper) poles of each kidney. They are retroperitoneal, meaning they are located behind the peritoneum (the membrane that lines the abdominal cavity). The right adrenal gland is generally pyramidal in shape, while the left adrenal gland is more crescent-shaped. Structure : The adrenal glands consist of two distinct regions: the outer adrenal cortex and the inner adrenal medulla. Adrenal Cortex:  Location : The adrenal cortex is the outer layer of the adrenal gland.  Structure: The adrenal cortex is further divided into three sub regions, or zones, each responsible for the production of specific hormones:  Zona Glomerulosa : This is the outermost zone of the adrenal cortex. It produces mineralocorticoids, primarily aldosterone, which regulates sodium and potassium balance and influences blood pressure.  Zona Fasciculata : The zona fasciculata is the middle zone of the adrenal cortex. It synthesizes glucocorticoids, mainly cortisol (hydrocortisone), which regulates metabolism, immune responses, and stress responses.  Zona Reticularis: This is the innermost zone of the adrenal cortex. It produces small amounts of various androgens, including dehydroepiandrosterone (DHEA) and androstenedione, which are precursors to male and female sex hormones (Big et al., 2020). Adrenal Medulla  Location : The adrenal medulla is the innermost region of the adrenal gland, located beneath the adrenal cortex.  Structure : The adrenal medulla consists of specialized neuroendocrine cells called chromaffin cells. These cells are responsible for producing and releasing two

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hormones, epinephrine (adrenaline) and norepinephrine (noradrenaline). These hormones play a crucial role in the body's response to stress, regulating heart rate, blood pressure, and other physiological responses. The adrenal glands are highly vascularized, receiving a rich blood supply. They also receive nerve fibers from the sympathetic nervous system, which regulate the release of hormones from the adrenal medulla (Big et al., 2020). 15. Identify the hormones produced by the adrenal cortex and adrenal medulla, and summarize their target cells and effects. Adrenal Cortex Hormones Mineralocorticoids :  Hormone: The main mineralocorticoid produced by the adrenal cortex is aldosterone.  Target Cells: Aldosterone acts primarily on the cells of the distal tubules and collecting ducts in the kidneys.  Effects: Aldosterone regulates electrolyte and fluid balance by promoting the reabsorption of sodium ions (Na+) and the excretion of potassium ions (K+) in the kidneys. It helps maintain blood pressure, blood volume, and electrolyte homeostasis. Glucocorticoids :  Hormones: The primary glucocorticoid produced by the adrenal cortex is cortisol (hydrocortisone).  Target Cells: Glucocorticoids act on a wide range of cells throughout the body.  Effects: Cortisol has numerous effects, including: a) Regulation of glucose metabolism by promoting gluconeogenesis (production of glucose from non-carbohydrate sources), inhibiting glucose uptake by cells, and promoting glycogen synthesis and storage.

b) Modulation of the immune response and inflammation by suppressing immune system activity and reducing inflammation. c) Regulation of metabolism of proteins and fats, affecting muscle function, bone metabolism, and fat storage. d) Influence on stress response, helping the body cope with physical and emotional stressors. Sex Hormones  Hormones: The adrenal cortex produces small amounts of androgens, including dehydroepiandrosterone (DHEA) and androstenedione.  Target Cells: Androgens produced by the adrenal cortex can be converted into male and female sex hormones in peripheral tissues.  Effects: While their levels are relatively low compared to the gonads, adrenal androgens contribute to the development of secondary sexual characteristics and play a role in libido and sexual function (Kelly, 2013). Adrenal Medulla Hormones Catecholamines :  Hormones: The adrenal medulla produces two main catecholamines, epinephrine (adrenaline) and norepinephrine (noradrenaline).  Target Cells: Epinephrine and norepinephrine act on various cells throughout the body, including the cardiovascular system, respiratory system, and smooth muscle.  Effects: The effects of epinephrine and norepinephrine include: a) Increased heart rate, cardiac output, and blood pressure. b) Dilation of airways to improve oxygen delivery. c) Mobilization of glucose from glycogen stores to provide energy.

d) Constriction of blood vessels in certain organs, such as the skin and gastrointestinal tract, to divert blood flow to critical areas. The hormones produced by the adrenal glands, both from the adrenal cortex and the adrenal medulla, play vital roles in various physiological processes, including electrolyte balance, metabolism, stress response, immune function, and cardiovascular regulation (Kelly, 2013). 16. Describe the location and structure of the pineal gland, identify the hormone, target tissues, and function.  Location : The pineal gland is situated in the posterior part of the brain, close to the center. It is positioned between the two cerebral hemispheres, above the thalamus and below the corpus callosum.  Structure : The pineal gland consists of pinealocytes, which are the main cell type found in the gland. These pinealocytes are arranged in clusters and are responsible for producing and secreting the hormone melatonin. The pineal gland is also made up of glial cells, blood vessels, and connective tissue.  Hormone : The primary hormone secreted by the pineal gland is melatonin.  Target Tissues: Melatonin acts on various tissues and cells throughout the body.  Function : a) Regulation of Circadian Rhythms: The pineal gland plays a crucial role in the regulation of circadian rhythms, which are 24-hour cycles that govern various physiological processes. Melatonin is involved in synchronizing the body's internal biological clock with external environmental cues, such as light and darkness. The gland produces melatonin primarily during periods of darkness, signaling to the body that it is nighttime and promoting sleepiness.

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b) Sleep Regulation: Melatonin helps regulate sleep-wake cycles and promotes sleep. Its secretion increases in the evening and remains elevated throughout the night, promoting the onset of sleep and maintaining sleep duration. c) Antioxidant Effects: Melatonin acts as a potent antioxidant, protecting cells and tissues from oxidative stress. It scavenges free radicals and reduces oxidative damage, which is implicated in various diseases and aging processes. d) Reproductive Function: Melatonin is involved in the regulation of reproductive function, including the timing of puberty and the control of reproductive hormones. It influences the secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus, which, in turn, affects the release of reproductive hormones such as luteinizing hormone (LH) and follicle-stimulating hormone (FSH) (Big et al., 2020). 17. Identify the hormones released by the heart, kidneys, skin, digestive glandular tissues, and adipose tissues, and list the targets and functions of each. Heart  Hormone : Atrial Natriuretic Peptide (ANP) and Brain Natriuretic Peptide (BNP).  Target and Function: ANP and BNP primarily act on the kidneys to promote sodium and water excretion, increasing urine production and decreasing blood volume and blood pressure. They also have vasodilatory effects, helping to relax and widen blood vessels (Kelly, 2013). Kidneys  Hormone : Renin and Erythropoietin (EPO).  Target and Function: a) Renin acts on the angiotensin system to regulate blood pressure and fluid balance. It converts angiotensinogen to angiotensin I, which is then converted to angiotensin II, a

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potent vasoconstrictor that stimulates the release of aldosterone and increases blood pressure. b) EPO acts on the bone marrow to stimulate the production of red blood cells, promoting the oxygen-carrying capacity of the blood (Kelly, 2013). Skin  Hormone : Vitamin D.  Target and Function : The skin plays a role in synthesizing vitamin D when exposed to ultraviolet (UV) radiation from sunlight. Vitamin D helps regulate calcium and phosphate metabolism, promoting the absorption of these minerals in the intestines for bone health (Kelly, 2013). Digestive Glandular Tissues  Hormone : Gastrin, Secretin, Cholecystokinin (CCK), and Ghrelin.  Target and Function: a) Gastrin stimulates gastric acid secretion in the stomach, aiding digestion. b) Secretin stimulates the secretion of bicarbonate-rich pancreatic juice, promoting the neutralization of stomach acid in the small intestine. c) CCK stimulates the release of digestive enzymes from the pancreas and the contraction of the gallbladder, aiding in fat digestion. d) Ghrelin stimulates appetite and promotes food intake (Kelly, 2013). Adipose Tissues  Hormone : Leptin and Adiponectin.  Target and Function : a) Leptin acts on the hypothalamus to regulate appetite and energy balance. It signals satiety and inhibits hunger.

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b) Adiponectin is involved in insulin sensitivity, lipid metabolism, and anti- inflammatory effects. It helps regulate glucose levels and lipid utilization (Kelly, 2013). 18. Describe the embryonic development of the pituitary gland. Rathke's Pouch Formation  At the early stages of embryonic development, a down growth of the oral ectoderm called Rathke's pouch forms.  Rathke's pouch appears as an invagination of the roof of the mouth, located between the oral cavity and the developing brain.  Rathke's pouch gradually elongates and migrates upwards towards the developing brain, eventually contacting the neuroectoderm (Kelly, 2013). The division into Anterior and Posterior Pituitary:  As Rathke's pouch contacts the neuroectoderm, it establishes connections with the developing hypothalamus. These connections are known as the infundibulum or pituitary stalk.  The cells in the anterior portion of Rathke's pouch differentiate into the anterior pituitary (adenohypophysis). These cells give rise to different cell types that produce and release various hormones.  The posterior portion of Rathke's pouch regresses and disappears, while the neuroectoderm-derived tissues form the posterior pituitary (neurohypophysis) (Kelly, 2013). Hormone Production and Function:  The anterior pituitary cells differentiate into distinct cell types that produce specific hormones. These include adrenocorticotropic hormone (ACTH), thyroid-stimulating

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hormone (TSH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), growth hormone (GH), prolactin, and melanocyte-stimulating hormone (MSH).  The posterior pituitary does not produce hormones but serves as a storage and release site for two hormones produced in the hypothalamus: oxytocin and antidiuretic hormone (ADH), also known as vasopressin.  The hormones released by the anterior and posterior pituitary regulate various physiological processes, including growth, reproduction, metabolism, and stress response (Kelly, 2013). 19. Identify the most important hormones produced by the testes and ovaries, name the hormones produced by the placenta, and state the functions of each hormone. Testes (Male) Testosterone  Function : Testosterone is the primary male sex hormone. It is responsible for the development of male reproductive organs, secondary sexual characteristics (such as facial hair and deep voice), and the maintenance of reproductive function. Testosterone also plays a role in muscle mass, bone density, and overall well-being (Kelly, 2013). Ovaries (Female) Estrogen  Function : Estrogen refers to a group of hormones, including estradiol, estrone, and estriol. Estrogen plays a key role in developing and regulating the female reproductive system, including the growth of the uterus and breasts. It also influences secondary sexual characteristics, such as body fat distribution, and is involved in the menstrual cycle. Progesterone

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 Function : Progesterone primarily prepares and maintains the uterus for pregnancy. It helps regulate the menstrual cycle and is essential for the successful implantation and maintenance of pregnancy. Progesterone also affects breast development and lactation (Kelly, 2013). Placenta Human Chorionic Gonadotropin (hCG)  Function : hCG is produced by the placenta during pregnancy. It plays a crucial role in supporting pregnancy by stimulating progesterone production by the corpus luteum (a temporary endocrine structure formed after ovulation). hCG helps maintain the uterine lining, preventing menstruation and supporting the developing embryo. Estrogen and Progesterone  Function : The placenta produces estrogen and progesterone during pregnancy. These hormones support fetal development, regulate uterine blood flow, and maintain the pregnancy by preventing contractions of the uterine muscles. They also contribute to the growth and development of the breasts in preparation for lactation (Kelly, 2013). 20. Discuss the effects of aging on the endocrine system.  Decreased Hormone Production: Several endocrine glands may exhibit reduced hormone production with age. For example: a) The pituitary gland's production of growth hormone (GH) tends to decline, leading to decreased muscle mass, bone density, and overall growth. b) The production of sex hormones, such as estrogen in women and testosterone in men, gradually declines, resulting in changes in sexual function, reproductive capacity, and bone health. c) The production of thyroid hormones by the thyroid gland may decrease, leading to a slower metabolic rate and potential symptoms of hypothyroidism.

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 Altered Hormone Regulation: Aging can disrupt the feedback mechanisms involved in hormone regulation. For instance: a) The sensitivity of target tissues to hormones may decrease, requiring higher hormone levels to elicit the same response. b) The production and release of regulatory hormones, such as those from the hypothalamus and pituitary gland, may become less efficient, leading to hormone production and regulation imbalances.  Increased Risk of Endocrine Disorders: Aging is associated with a higher risk of developing certain endocrine disorders, including: a) Menopause in women is characterized by the cessation of menstrual cycles due to reduced ovarian function and hormone production. b) Andropause in men involves a gradual decline in testosterone levels and may result in symptoms such as decreased libido, fatigue, and mood changes. c) Osteoporosis, a condition characterized by decreased bone density and increased risk of fractures, is often linked to hormonal changes, especially estrogen deficiency in postmenopausal women. d) Diabetes mellitus, as aging, can affect insulin production and sensitivity, contributing to the development of type 2 diabetes.  Impact on Metabolism and Body Composition: Aging can lead to changes in metabolism and body composition, often influenced by hormonal alterations: a) Basal metabolic rate may decrease, resulting in reduced calorie expenditure and a higher likelihood of weight gain. b) Changes in body composition, including increased fat mass and decreased muscle mass, may occur, which can affect metabolism, physical performance, and overall health.

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 Impact on Stress Response and Immune Function: Aging can influence the endocrine system's response to stress and immune function: a) The hypothalamic-pituitary-adrenal (HPA) axis, which regulates the stress response, may become less responsive, affecting the body's ability to handle stressors. b) Immune system function may decline with age, potentially impacting the production and regulation of various immune-related hormones (Kelly, 2013). References: Big, L. M., Dawson, S., Harwell, A., Hopkins, R., Kaufmann, J., LeMaster, M., ... & Runyeon, J. (2020). Anatomy & physiology. OpenStax/Oregon State University. Kelly A. Young (author), J. A. (2013). Anatomy and Physiology by OpenStax 1st Edition. XanEdu Publishing Inc.

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Unit 5 Endocrine Assignment

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