Endocrine System PDF

The Endocrine System In this lesson: p Identify the parts of endocrine system and its functions. p Enumerate the hormones secreted by the endocrine glands and its functions. p Explain the regulation mechanism of the endocrine system. p Share the importance of endocrine system. p...

The Endocrine System In this lesson: p Identify the parts of endocrine system and its functions. p Enumerate the hormones secreted by the endocrine glands and its functions. p Explain the regulation mechanism of the endocrine system. p Share the importance of endocrine system. p Relate endocrine system to the different body systems. p Cite examples of the disorders of the endocrine system. ENDOCRINE SYSTEM p isa complex network of glands and organs that secrete hormones into the bloodstream to regulate various bodily functions, including metabolism, growth, development, mood, sexual function, and homeostasis. ENDOCRINE SYSTEM p Unlike the nervous system, which uses electrical signals to communicate quickly, the endocrine system uses chemical signals (hormones) to communicate more slowly, but often over longer durations. COMPONENTS p Endocrine Glands – These are specialized organs that secrete hormones directly into the bloodstream. p Hormones – Chemical messengers produced by glands that regulate specific functions. COMPONENTS p Target Organs/Cells – Organs or cells that are affected by specific hormones. p Feedback Mechanisms – Processes that regulate hormone production and secretion. How the system communicates p The organs of the endocrine system communicate with each other and the rest of the body using hormones. p Hormones are made and stored in their originating organ. The place they are sent is called the target. p Targets can be anything from all the bones in the body to another endocrine organ. p When the hormones reach their target, they trigger events in that location.  HYPOTHALAMUS Location: A small region of the brain located just below the thalamus. Part of the diencephalon, a region of the forebrain. Function: The hypothalamus is responsible for maintaining the body's internal balance (homeostasis) and regulating the endocrine system by controlling the release of hormones from the pituitary gland.  HYPOTHALAMUS Function: it regulates the following processes p Endocrine regulation by producing a releasing and inhibiting hormones that controls the pituitary gland. p Thirst and water intake p Hunger and food intake p Autonomic nervous system regulation p Biological circadian rhythm p Body temperature p Blood pressure p Breast feeding p Learning and memory p Sexual drive p Emotional expression  HYPOTHALAMUS Hormones regulating the Anterior Pituitary: Releasing Hormones (e.g., TRH, GnRH): Stimulate hormone release from the anterior pituitary. 1. Thyrotropin-releasing hormone (TRH): Stimulates TSH release from the anterior pituitary. 2. Corticotropin-releasing hormone (CRH): Stimulates ACTH release. 3. Gonadotropin-releasing hormone (GnRH): Stimulates LH and FSH release. 4. Growth hormone-releasing hormone (GHRH): Stimulates GH Later na release.  HYPOTHALAMUS Hormones regulating the Anterior Pituitary: Inhibiting Hormones (e.g., Somatostatin): Inhibit hormone release from the anterior pituitary. 1. Somatostatin – inhibits growth hormone (GH) and thyroid- stimulating hormone (TSH) 2. Dopamine – Inhibits the release of Prolactin  HYPOTHALAMUS Hormones Released to the Posterior Pituitary 1. Oxytocin - Stimulates uterine contractions during childbirth. - Triggers milk ejection during breastfeeding. - Plays a role in bonding and trust. 2. Antidiuretic Hormone (ADH,Vasopressin) - Promotes water reabsorption in the kidneys to regulate water balance. - Constricts blood vessels, helping maintain blood pressure. HYPOTHALAMUS DISORDERS p Genetic condition HYPOTHALAMUS DISORDERS p Genetic condition Prader willi Syndrome HYPOTHALAMUS DISORDERS p SIADH VS DIABETES INSIPIDUS HYPOTHALAMUS DISORDERS p SIADH HYPOTHALAMUS DISORDERS p Hypopituitarism: Insufficient pituitary hormone secretion. p Diabetes insipidus: Deficient ADH production causing excessive urination. p Obesity or eating disorders: Resulting from appetite dysregulation. p Sleep disturbances: Due to circadian rhythm disruption.  PITUITARY Location: Located at the base of the brain, below the hypothalamus. Function: Often referred to as the "master gland" because it controls other endocrine glands. The pituitary secretes hormones that regulate growth, metabolism, and reproduction. PITUITARY Function The pituitary gland is vital for: p Growth and development p Metabolism regulation p Reproductive function p Stress response p Water and electrolyte balance  PITUITARY PARTS: p Anterior Pituitary (Adenohypophysis) - it synthesizes and secretes hormones under the regulation of the hypothalamus. These hormones influence growth, metabolism, and the function of other endocrine glands. p Posterior Pituitary (Neurohypophysis) - it does not produce its own hormones; instead, it stores and releases hormones synthesized by the hypothalamus ANTERIOR PITUITARY HORMONES 1. Growth Hormone (GH) Function: Stimulates growth of bones, muscles, and other tissues. Promotes protein synthesis and fat metabolism. Increases blood glucose levels by reducing glucose uptake in cells. Target: Liver, bones, muscles, and adipose tissue. 2. Prolactin (PRL) Function: Stimulates milk production in the mammary glands. Plays a role in immune regulation and reproductive health. Target: Mammary glands. ANTERIOR PITUITARY HORMONES 3. Adrenocorticotropic Hormone (ACTH) Function: Stimulates the adrenal cortex to release cortisol, which is critical for stress response, metabolism, and immune function. Target: Adrenal cortex. 4. Thyroid-Stimulating Hormone (TSH) Function: Stimulates the thyroid gland to produce thyroxine (T4) and triiodothyronine (T3), which regulate metabolism, energy production, and growth. Target: Thyroid gland. ANTERIOR PITUITARY HORMONES p 5. Luteinizing Hormone (LH) Function: In females: Triggers ovulation and stimulates the ovaries to produce estrogen and progesterone. In males: Stimulates the testes to produce testosterone. Target: Ovaries (females) and testes (males). p 6. Follicle-Stimulating Hormone (FSH) Function: In females: Stimulates growth and maturation of ovarian follicles. In males: Stimulates sperm production. Target: Ovaries (females) and testes (males). ANTERIOR PITUITARY DISORDER 1. Hypersecretion: Naglabi 1.Acromegaly/Gigantism: Excess GH. 2.Cushing's Disease: Excess ACTH. 3.Hyperprolactinemia: Excess prolactin. 2. Hyposecretion: Nagkulang 1.Dwarfism: Deficient GH in children. 2.Hypothyroidism: Low TSH secretion. 3.Hypogonadism: Low LH/FSH leading to reproductive issues. POSTERIOR PITUITARY HORMONES p 1. Oxytocin Functions: Stimulates uterine contractions during childbirth. Triggers milk ejection (let-down reflex) in breastfeeding mothers. Plays a role in bonding, trust, and social interactions. Target Organs: Uterus, Mammary glands trigger physiological stimuli: Uterine stretching during labor. Suckling of the baby at the breast. POSTERIOR PITUITARY HORMONES 2. Antidiuretic Hormone (ADH) (also called Vasopressin) Functions: Promotes water reabsorption in the kidneys, reducing urine output and maintaining water balance in the body. Helps maintain blood pressure by constricting blood vessels. Target Organs: Kidneys, Blood vessels trigger physiological stimuli: Increased blood osmolarity (dehydration). Decreased blood volume or pressure. POSTERIOR PITUITARY DISORDER Diabetes p Syndrome of Insipidus:Caused by Inappropriate ADH insufficient ADH Secretion production or action. (SIADH):Excess ADH Symptoms: Excessive release leading to urination (polyuria) water retention, low and extreme thirst blood sodium, and (polydipsia). swelling. PINEAL p a small, pea-shaped endocrine gland located in the brain. It plays a vital role in regulating biological rhythms, particularly the sleep-wake cycle, by secreting the hormone melatonin. PINEAL p It is located in a groove between the two hemispheres of the brain, nestled in a groove where the two halves of the thalamus join.It is part of the epithalamus, near the center of the brain, above the third ventricle. PINEAL FUNCTIONS p Melatonin secretion p Regulation of circadian rhythm p Role in puberty (maturation) PINEAL HORMONE p MELATONIN Functions:Regulates the sleep-wake cycle by promoting sleep. Influences seasonal biological rhythms in response to light changes. Acts as an antioxidant, protecting cells from oxidative stress. PINEAL DISORDER 1. Sleep Disorders: - Disruption in melatonin secretion can lead to insomnia, jet lag, or delayed sleep phase syndrome. 2. Pineal Tumors: - Rare tumors can impair gland function, potentially causing hormonal imbalances or vision problems. 3. Calcification: - The pineal gland often becomes calcified with age, reducing melatonin production.  PINEAL PARTS: p Anterior Pituitary - it synthesizes and secretes hormones under the regulation of the hypothalamus. These hormones influence growth, metabolism, and the function of other endocrine glands. p Posterior Pituitary - it does not produce its own hormones; instead, it stores and releases hormones synthesized by the hypothalamus THYROID a butterfly- shaped endocrine gland located in the neck, just below the larynx (voice box) and in front of the trachea (windpipe). THYROID Location: Located in the neck, below the Adam's apple. Function: Regulates metabolism, growth, and development. THYROID FUNCTIONS: 1. Metabolism 2. Growth and development 3. Temperature regulation 4. Calcium homeostasis THYROID Lobes: The gland has two lateral lobes (right and left) connected by a thin band of tissue called the isthmus. Cell Types: Follicular cells: Produce the thyroid hormones T3 (triiodothyronine) and T4 (thyroxine). Parafollicular cells (C cells): Produce calcitonin, a hormone involved in calcium homeostasis. THYROID HORMONES p 1. Thyroxine (T4) Function: Regulates metabolism, energy production, and protein synthesis. Serves as a precursor for T3. Target: All cells of the body. THYROID HORMONES p 1. Thyroxine (T4) Function: Regulates metabolism, energy production, and protein synthesis. Serves as a precursor for T3. Target: All cells of the body. THYROID HORMONES p 2. Triiodothyronine (T3) Function: More potent than T4 and has similar effects on metabolism, heart rate, and body temperature. Influences development, particularly in the nervous system during fetal and early childhood stages. Target: All cells of the body. THYROID HORMONES p 3. Calcitonin Function: Lowers blood calcium levels by inhibiting osteoclast activity (cells that break down bone). Promotes calcium storage in bones. Target: Bones, kidneys, and intestines.  REGULATION OF THYROID HORMONES SECRETION Controlled by the hypothalamus-pituitary- thyroid axis: Hypothalamus: Releases Thyrotropin-Releasing Hormone (TRH). Anterior Pituitary: Releases Thyroid-Stimulating Hormone (TSH) in response to TRH. Thyroid Gland: Produces T3 and T4 in response to TSH. Negative Feedback: Elevated levels of T3 and T4 inhibit TRH and TSH release.  THYROID DISORDERS p 1. Hypothyroidism: Cause: Underactive thyroid (e.g., Hashimoto’s thyroiditis, iodine deficiency). Symptoms: Fatigue, weight gain, cold intolerance, slow heart rate, and depression. Condition: Severe cases can lead to myxedema in adults or cretinism in children. p 2. Hyperthyroidism: Cause: Overactive thyroid (e.g., Graves’ disease, thyroid nodules). Symptoms: Weight loss, rapid heartbeat, heat intolerance, nervousness, and bulging eyes (exophthalmos in Graves’ disease).  THYROID DISORDERS p 3. Goiter: Cause: Enlarged thyroid gland, often due to iodine deficiency or autoimmune disease. Symptoms: Visible swelling in the neck. p 4. Thyroid Nodules or Cancer: Benign or malignant growths within the thyroid gland.  PARATHYROID The parathyroid is a group of small glands that are found on the thyroid and emit hormones which help regulate calcium throughout the body. If levels get too low the bones will be instructed to release more; if the levels get too high the bones are told to absorb the extra calcium. PARATHYROID are small, pea-shaped endocrine glands located on the posterior surface of the thyroid gland.  PARATHYROID Location: Small glands located on the back of the thyroid gland. Function: Regulates calcium and phosphate balance in the blood. PARATHYROID p Functions 1. Calcium Regulation: 1. PTHmaintains normal calcium levels in the blood, which is critical for muscle contraction, nerve conduction, and blood clotting. 2. Phosphorus Regulation: 1. PTH ensures phosphate levels are balanced by promoting its excretion via the kidneys.  PARATHYROID HORMONE p Parathyroid Hormone (PTH) Function: Increases blood calcium levels by acting on bones, kidneys, and the gastrointestinal tract. Target Organs: Bones: Stimulates osteoclast activity, releasing calcium and phosphate into the blood. Kidneys: Promotes calcium reabsorption and phosphate excretion. Intestines: Increases calcium absorption indirectly by stimulating the activation of vitamin D (which enhances calcium absorption from the gut).  REGULATION OF PARATHYROID HORMONE p Stimulus: Low blood calcium levels (hypocalcemia) stimulate PTH secretion. p Inhibition: High blood calcium levels (hypercalcemia) suppress PTH secretion via negative feedback. p Calcitonin Interaction: Calcitonin, produced by the thyroid gland, opposes PTH by lowering blood calcium levels.  PARATHYROID DISORDER p 1. Hyperparathyroidism: Cause: Overproduction of PTH due to parathyroid adenomas, hyperplasia, or cancer. Effects: Elevated blood calcium levels (hypercalcemia). Weak bones due to excess calcium resorption (osteoporosis). Kidney stones. Fatigue, muscle weakness, and cognitive issues. p 2. Hypoparathyroidism: Cause: Insufficient PTH production due to surgical removal, autoimmune disease, or genetic disorders. Effects: Low blood calcium levels (hypocalcemia); Muscle cramps, spasms (tetany), and tingling sensations; Seizures and heart rhythm abnormalities in severe cases. p 3. Pseudohypoparathyroidism: Cause: Target tissues are resistant to PTH. Effects: Symptoms resemble hypoparathyroidism despite normal or high PTH levels. THYMUS p Size and Location: p The thymus is largest in childhood and begins to shrink in size after puberty, becoming less active with age. It is located in the upper chest, just behind the sternum.  THYMUS p Two Lobes: The thymus is divided into two lobes, and each lobe is made up of smaller lobules. p Cortex: Outer part of the thymus, where T- cell maturation begins. p Medulla: Inner part, where mature T-cells undergo selection and differentiation.  THYMUS FUNCTIONS: p T-cell Maturation and Education p Immune system development p Secretion of immune- modulating hormone THYMUS  THYMUS HORMONES 1. Thymosin n Function: Promotes the development of T-cells, which are a critical part of the immune system’s response to pathogens; Stimulates the maturation of lymphocytes (especially T-cells) in the thymus. n Target: Developing T-cells in the thymus. 2. Thymopoietin n Function: Enhances the development and differentiation of T-cells in the thymus. Plays a role in the immune response by influencing the function of mature T-cells. 3. Thymulin n Function: Promotes the activation of T-cells and helps in the differentiation of T-helper cells. n Target: T-cells, immune cells. THYMUS HORMONES  REGULATION OF THYMUS HORMONES p The function of the thymus is regulated by several factors, including: Age: The thymus is most active during childhood, after which it gradually atrophies (shrinks) and is replaced by fatty tissue. Immune System Demands: During periods of intense immune activity (e.g., infection), the thymus can become more active to generate more T-cells.  THYMUS DISORDERS p Thymic Atrophy: Occurs with age or as a result of certain diseases (e.g., HIV/AIDS), leading to a weakened immune system. Inadequate T-cell production and immune system impairment. p DiGeorge Syndrome: A genetic disorder where the thymus is either underdeveloped or absent, leading to severe immunodeficiency due to a lack of functional T-cells.  THYMUS DISORDERS p Thymomas: Tumors of the thymus, which can interfere with T-cell development and lead to autoimmune diseases, such as myasthenia gravis. p Autoimmune Diseases: Thymic dysfunction can lead to autoimmunity, where the immune system mistakenly targets the body’s tissues. ADRENAL are two small, triangular endocrine glands located on top of each kidney. Location: On top of each kidney. They play a critical role in responding to stress and maintaining homeostasis by producing various hormones involved in metabolism, immune response, blood pressure regulation, and other functions. ADRENAL FUNCTIONS They play a critical role in responding to stress and maintaining homeostasis by producing various hormones involved in metabolism, immune response, blood pressure regulation, and other functions. ADRENAL STRUCTURE: p 1. Adrenal Cortex (Outer Layer) Divided into three zones: Zona Glomerulosa: Produces mineralocorticoids (e.g., aldosterone). Zona Fasciculata: Produces glucocorticoids (e.g., cortisol). Zona Reticularis: Produces androgens (e.g., dehydroepiandrosterone, DHEA). ADRENAL STRUCTURE: p 2. Adrenal Medulla (Inner Layer) Produces catecholamines (e.g., adrenaline/epinephrine and noradrenaline/norepinephrine). ADRENAL FUNCTIONS: p Stress Response 1. The adrenal medulla manages the acute fight- or-flight response via catecholamines. 2. The adrenal cortex handles chronic stress via cortisol. p Metabolic Regulation p Electrolyte and Water bance p Reproductive function 1. Androgens play a role in early puberty and contribute to sex hormone levels. ADRENAL HORMONES ADRENAL DISORDERS 1. Overactivity (Hyperfunction) Cushing's Syndrome: Excess cortisol production. Symptoms: Weight gain, round face, high blood pressure, and weak bones. Hyperaldosteronism: Excess aldosterone production. Symptoms: High blood pressure and low potassium levels. Pheochromocytoma: Tumor of the adrenal medulla causing excess adrenaline and noradrenaline. Symptoms: Severe hypertension, palpitations, and anxiety. ADRENAL DISORDERS 2. Underactivity (Hypofunction) Addison's Disease: Insufficient production of cortisol and aldosterone. Symptoms: Fatigue, weight loss, low blood pressure, and skin darkening. Adrenal Crisis: Acute, life-threatening insufficiency of adrenal hormones, often triggered by stress. REGULATION TO ADRENAL HORMONES REGULATION TO ADRENAL HORMONES PANCREAS is a vital glandular organ located in the abdomen, behind the stomach. It has both endocrine and exocrine functions, making it crucial for digestion and glucose metabolism. PANCREAS Location: Located behind the stomach. Function: Regulates blood sugar levels and assists in digestion.  PANCREAS STRUCTURE STRUCTURE p Endocrine Pancreas: Consists of clusters of cells called islets of Langerhans, which secrete hormones into the bloodstream. Major cell types in the islets: Alpha (α) cells: Produce glucagon. Beta (β) cells: Produce insulin. Delta (δ) cells: Produce somatostatin. PP cells (F cells): Produce pancreatic polypeptide. Epsilon (ε) cells: Produce ghrelin. PANCREAS STRUCTURE 1. Endocrine Pancreas: n Consists of clusters of cells called islets of Langerhans, which secrete hormones into the bloodstream. n Major cell types in the islets: p Alpha (α) cells: Produce glucagon. p Beta (β) cells: Produce insulin. p Delta (δ) cells: Produce somatostatin. p PP cells (F cells): Produce pancreatic polypeptide. p Epsilon (ε) cells: Produce ghrelin. n Maintains blood glucose homeostasis by balancing insulin and glucagon actions. n Dysfunction of the endocrine pancreas leads to conditions like diabetes mellitus (hyperglycemia) or hypoglycemia. PANCREAS STRUCTURE 2. Exocrine Pancreas: n Contains acinar cells that produce digestive enzymes (e.g., amylase, lipase, protease). n Secretes these enzymes into the duodenum through the pancreatic duct. n Bicarbonate Secretion: Neutralizes stomach acid in the duodenum.; Creates an optimal pH environment (around pH 7-8) for the activation of pancreatic enzymes. n Key Role: Facilitates the digestion and absorption of nutrients in the small intestine. PANCREAS STRUCTURE 2. Exocrine Pancreas: PANCREAS STRUCTURE PANCREAS HORMONES REGULATION OF PANCREAS HORMONES p Regulation of Pancreatic Hormones 1. Blood Glucose Levels: n Insulin and glucagon secretion are tightly regulated by blood glucose concentrations. p High glucose → Insulin release (Beta cells). p Low glucose → Glucagon release (Alpha cells). 2. Feedback Mechanisms: n Insulin and glucagon work in opposition to maintain glucose homeostasis. n Somatostatin modulates the release of both insulin and glucagon. REGULATION OF PANCREAS HORMONES p Regulation of Pancreatic Hormones 3. Nervous System: n The autonomic nervous system influences pancreatic hormone secretion: p Parasympathetic stimulation (vagus nerve): Increases insulin secretion during digestion. p Sympathetic stimulation: Promotes glucagon secretion during stress. 4. Nutrient Levels: n High amino acid and fatty acid levels stimulate both insulin and glucagon secretion to manage metabolic needs. PANCREAS DISORDERS 1. Diabetes Mellitus Type 1 Diabetes: Autoimmune destruction of beta cells leading to insulin deficiency. Type 2 Diabetes: Insulin resistance in tissues and/or insufficient insulin production. Gestational Diabetes: High blood glucose during pregnancy due to hormonal changes. 2. Hypoglycemia Excessive insulin secretion or administration leading to dangerously low blood sugar levels. PANCREAS DISORDERS 3. Pancreatitis Inflammation of the pancreas caused by digestive enzyme activation within the pancreas. Can be acute or chronic. 4. Pancreatic Cancer Affects endocrine or exocrine cells; often aggressive and difficult to diagnose early. 5. Hyperinsulinism Excess insulin secretion leads to recurrent hypoglycemia. GONADS Location: Ovaries are in the female pelvic cavity, testes are in the male scrotum. Function: Control sexual development and reproductive function.  GONADS (testes in males and ovaries in females) are essential components of the endocrine system. They serve dual roles as endocrine glands and reproductive organs, producing sex hormones that regulate sexual development, reproductive functions, and secondary sexual characteristics.  GONADS p Key Roles in the Endocrine System: Control of reproduction. Regulation of sexual development. Maintenance of secondary sexual characteristics. Support of pregnancy (in females).  GONADS p Importance of Gonads: Essential for reproduction and fertility. Influence physical development and sexual characteristics during puberty. Play a role in overall hormonal balance and health. GONADS (TESTES – MALE) The testes produce androgens (male sex hormones), primarily testosterone, under the regulation of the hypothalamic- pituitary-gonadal (HPG) axis. GONADS (TESTES – MALE) p Located in the scrotum. p Produce sperm cells through spermatogenesis. p Secrete testosterone and smaller amounts of other androgens. GONADS (TESTES – MALE) p Hormones Secreted: 1. Testosterone n Produced by: Leydig cells in the testes. n Functions: p Promotes the development of male reproductive organs (penis, scrotum) during fetal development. p Regulates spermatogenesis (sperm production) in the seminiferous tubules. p Stimulates the development of secondary sexual characteristics (deep voice, muscle mass, facial hair). p Maintains libido and influences male behavior. GONADS (TESTES – MALE) p Hormones Secreted: 2. Inhibin n Produced by: Sertoli cells in the seminiferous tubules. n Functions: p Inhibitsthe secretion of follicle- stimulating hormone (FSH) from the anterior pituitary. p Regulates spermatogenesis by providing negative feedback to the hypothalamus and pituitary. GONADS (OVARIES – FEMALE) The ovaries produce estrogens, progesterone, and small amounts of androgens under the regulation of the HPG axis. GONADS (OVARIES – FEMALE) p Located in the pelvic cavity. p Produce eggs (ova) through oogenesis. p Secrete estrogen and progesterone. GONADS (OVARIES – FEMALE) p Hormones Secreted: 1. Estrogens (e.g., Estradiol) n Produced by: Granulosa cells of ovarian follicles. n Functions: p Regulates the development of female reproductive organs. p Promotes the menstrual cycle, particularly the proliferation of the uterine lining during the follicular phase. p Stimulates secondary sexual characteristics (breast development, distribution of body fat). GONADS (OVARIES – FEMALE) p Hormones Secreted: 2. Progesterone Produced by: Corpus luteum (a temporary structure formed after ovulation) and, during pregnancy, by the placenta. Functions: Prepares the endometrium (uterine lining) for implantation of a fertilized egg. Maintains pregnancy by preventing uterine contractions. Regulates the luteal phase of the menstrual cycle. GONADS (OVARIES – FEMALE) p Hormones Secreted: 3. Inhibin Produced by: Granulosa cells in the ovaries. Functions: Suppresses FSH secretion to regulate follicular development. 4. Relaxin Produced by: Corpus luteum and placenta during pregnancy. Functions: Relaxes the uterine muscles to prevent premature contractions. Loosens the pelvic ligaments and cervix to facilitate childbirth. GONADS HORMONES  REGULATION OF GONADS HORMONES p HPG Axis Overview: Regulation of gonadal hormones involves the hypothalamic- pituitary-gonadal (HPG) axis. p Role of Hypothalamus: Releases gonadotropin-releasing hormone (GnRH), stimulating the pituitary gland. p Pituitary Function: Secretes luteinizing hormone (LH) and follicle-stimulating hormone (FSH). p In Males: LH stimulates Leydig cells to produce testosterone. FSH supports spermatogenesis via Sertoli cells. p In Females: LH triggers ovulation and progesterone production. FSH promotes follicular growth and estrogen synthesis. p Negative Feedback Mechanism: Sex hormones (testosterone, estrogen, and progesterone) and inhibin regulate GnRH, LH, and FSH secretion to maintain hormonal balance. p Functions: This system controls reproduction, sexual development, and secondary sexual characteristics. REGULATION OF GONADS HORMONES p The HPG axis ensures hormonal balance, adapting to developmental stages (e.g., puberty, reproductive years, and menopause). p Hormonal fluctuations are tightly coordinated during the menstrual cycle in females. p Disorders in the axis (e.g., hypogonadism or PCOS) can disrupt hormone levels, leading to infertility or other health issues.  GONADS DISORDER 1. Male Gonadal Disorders (Testes): Hypogonadism: Primary Hypogonadism: The testes themselves fail to produce adequate testosterone or sperm. Causes include: Klinefelter syndrome (extra X chromosome). Testicular injury or infection. Varicocele (enlargement of veins in the scrotum). Undescended testes (cryptorchidism). Secondary Hypogonadism: A problem in the hypothalamus or pituitary gland leads to insufficient production of LH and FSH, impairing testosterone and sperm production. Infertility: Testicular Cancer: Erectile Dysfunction:  GONADS DISORDER Polycystic Ovary Syndrome (PCOS): A common endocrine disorder causing irregular menstrual cycles, elevated androgen levels, and ovarian cysts. It can lead to infertility, acne, weight gain, and excess hair growth. Premature Ovarian Insufficiency (POI) (formerly known as premature menopause): The ovaries stop functioning before the age of 40, leading to early menopause symptoms such as irregular periods, hot flashes, and infertility. Ovarian Cancer: Cancer of the ovaries, that may affect hormone production and fertility. Anovulation: A condition where the ovaries do not release an egg (ovulate), leading to infertility. Endometriosis: A condition where tissue similar to the lining of the uterus grows outside the uterus, often affecting the ovaries and fallopian tubes, leading to pain and infertility.  GONADS DISORDER p 3. General Gonadal Disorders: Gonadal Dysgenesis: A condition where gonads do not develop properly, leading to ambiguous genitalia or underdeveloped reproductive organs. Congenital Adrenal Hyperplasia (CAH):A genetic condition affecting the adrenal glands that leads to imbalances in sex hormones. It may cause virilization (development of male characteristics) in females and affect fertility.  GONADS DISORDER p 3. General Gonadal Disorders: Klinefelter Syndrome (Males): A genetic disorder where males have an extra X chromosome (XXY). It leads to small testes, low testosterone levels, infertility, and sometimes learning difficulties. Turner Syndrome (Females): A genetic disorder where females have only one X chromosome (X0). It leads to ovarian failure, short stature, and infertility, among other features. GONADS DISORDER Klinefelter syndrome HORMONAL FEEDBACK MECHANISM p The feedback mechanism is a vital process that regulates the release of hormones in the endocrine system, helping to maintain homeostasis (the body's internal balance). Feedback mechanisms act like a control system, ensuring that hormone levels stay within a normal range. There are two primary types of feedback mechanisms: negative feedback and positive feedback.  HORMONAL FEEDBACK MECHANISM Negative Feedback Most common feedback loop in the endocrine system. A hormone's action reduces the stimulus for its own production. This helps maintain homeostasis by preventing overproduction of hormones. Example: Thyroid hormone regulation The hypothalamus releases TRH (Thyrotropin- releasing hormone), which stimulates the pituitary gland to release TSH (Thyroid-stimulating hormone). TSH stimulates the thyroid to produce T3 and T4 (thyroid hormones). Elevated levels of T3 and T4 feedback to the hypothalamus and pituitary to reduce TRH and TSH production, stopping further thyroid hormone HORMONAL FEEDBACK MECHANISM 2. Positive Feedback Increases the stimulus for hormone production. Less common but essential in specific situations where a rapid and amplified response is needed. Example: ChildbirthOxytocin is released during labor, which stimulates uterine contractions. Contractions stimulate further oxytocin release, intensifying the contractions until the baby is delivered. FEEDBACK MECHANISM FEEDBACK MECHANISM p Regulate vital processes such as blood pressure, body temperature, and hormone levels. p Prevent overproduction or underproduction of hormones, which can lead to disorders like hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). p Ensure proper growth, development, and reproduction, such as during the menstrual cycle or childbirth.