Class 10
Endocrine System
Note on Endocrine System
The Endocrine System
The endocrine system is a complex network of glands that produce and secrete hormones, which are chemical messengers that regulate various bodily functions. These hormones travel through the bloodstream to target cells and organs, controlling processes like growth, metabolism, and reproduction.
Endocrine vs. Exocrine Glands
| Feature | Endocrine Glands | Exocrine Glands |
|---|---|---|
| Ducts | Ductless; secrete hormones directly into the bloodstream. | Have ducts to carry secretions to a specific location. |
| Secretions | Hormones | Enzymes, sweat, saliva, etc. |
| Target | Act on distant target cells or organs. | Act locally at the site of secretion. |
| Examples | Pituitary, thyroid, adrenal glands | Salivary, sweat, and sebaceous glands |
Major Endocrine Glands
1. Adrenal Gland
- Location: A pair of pyramid-shaped glands located on top of each kidney.
- Hormones Secreted:
- Adrenal Cortex (Outer Part):
- Cortical Hormones (Corticosteroids):
- Glucocorticoids (e.g., Cortisol): Regulate metabolism, suppress inflammation, and help the body respond to stress.
- Mineralocorticoids (e.g., Aldosterone): Control the balance of water and salts in the body.
- Cortical Hormones (Corticosteroids):
- Adrenal Medulla (Inner Part):
- Adrenaline (Epinephrine) and Noradrenaline (Norepinephrine): Responsible for the "fight or flight" response, increasing heart rate, blood pressure, and glucose levels.
- Adrenal Cortex (Outer Part):
2. Pancreas
- Location: A long, flat gland located behind the stomach.
- Hormones Secreted (from the Islets of Langerhans):
- Insulin: Lowers blood glucose levels by promoting the uptake of glucose by cells.
- Glucagon: Raises blood glucose levels by stimulating the liver to release stored glucose.
3. Thyroid Gland
- Location: A butterfly-shaped gland located in the neck, in front of the trachea.
- Hormones Secreted:
- Thyroxine (T4): The main hormone produced by the thyroid. It regulates the body's metabolic rate.
4. Pituitary Gland
- Location: A pea-sized gland located at the base of the brain.
- Hormones Secreted:
- Anterior Pituitary:
- Growth Hormone (GH): Stimulates growth, cell reproduction, and regeneration.
- Tropic Hormones: Hormones that control the function of other endocrine glands.
- Thyroid-Stimulating Hormone (TSH): Stimulates the thyroid gland.
- Adrenocorticotropic Hormone (ACTH): Stimulates the adrenal cortex.
- Posterior Pituitary:
- Antidiuretic Hormone (ADH): Regulates water balance by controlling the reabsorption of water by the kidneys.
- Oxytocin: Stimulates uterine contractions during childbirth and the release of milk during breastfeeding.
- Anterior Pituitary:
Hormonal Imbalances
| Gland | Hormone | Hyposecretion (Too Little) | Hypersecretion (Too Much) |
|---|---|---|---|
| Pancreas | Insulin | Hyperglycemia (Diabetes Mellitus): High blood sugar. | Hypoglycemia: Low blood sugar. |
| Thyroid | Thyroxine | Hypothyroidism: Slow metabolism, weight gain, fatigue. | Hyperthyroidism: Rapid metabolism, weight loss, nervousness. |
| Adrenal | Cortisol | Addison's Disease: Fatigue, muscle weakness, weight loss. | Cushing's Syndrome: Weight gain, high blood pressure, mood swings. |
| Pituitary | Growth Hormone | Dwarfism in children. | Gigantism in children; Acromegaly in adults. |
Feedback Mechanism: TSH
The endocrine system is regulated by feedback mechanisms to maintain homeostasis. A key example is the regulation of thyroid hormones.
- The hypothalamus releases Thyrotropin-Releasing Hormone (TRH).
- TRH stimulates the pituitary gland to release Thyroid-Stimulating Hormone (TSH).
- TSH stimulates the thyroid gland to produce and release thyroxine.
- As thyroxine levels in the blood rise, they inhibit the release of TRH and TSH, thus reducing the production of thyroxine. This is a negative feedback loop that ensures the levels of thyroxine are kept within a narrow, stable range.
HORMONES:
| Hormone | Origin | Hyposecretion | Hypersecretion |
|---|---|---|---|
| Insulin | Pancreas | Diabetes mellitus type 1 | Hyperinsulinism |
| Growth Hormone | Pituitary gland | Pituitary dwarfism | Acromegaly |
| Thyroxine | Thyroid gland | Hypothyroidism | Hyperthyroidism |
| Cortisol | Adrenal glands | Addison's disease | Cushing's syndrome |
| Adrenaline | Adrenal glands | Adrenal insufficiency | Pheochromocytoma |
| Estrogen | Ovaries | Primary ovarian insufficiency (POI) | Estrogen dominance |
| Testosterone | Testes | Hypogonadism | Testicular tumors (Leydig cell tumors) |
| Progesterone | Ovaries | Progesterone deficiency | Hyperprogesteronism (rare) |
| Parathyroid hormone | Parathyroid glands | Hypoparathyroidism | Hyperparathyroidism |
| Melatonin | Pineal gland | Seasonal affective disorder (SAD) | Circadian rhythm disorders |
| Oxytocin | Hypothalamus, posterior pituitary gland | Inadequate uterine contractions during labor (inadequate labor progression) | Excessive uterine contractions during labor (uterine hyperstimulation) |
| Aldosterone | Adrenal glands | Addison's disease (secondary adrenal insufficiency) | Hyperaldosteronism |
| Prolactin | Pituitary gland | Hypoprolactinemia | Hyperprolactinemia |
| Thyroid-stimulating hormone (TSH) | Pituitary gland | Hypothyroidism | Hyperthyroidism |
| Follicle-stimulating hormone (FSH) | Pituitary gland | Hypogonadism | Gonadotropin-secreting tumors |
| Luteinizing hormone (LH) | Pituitary gland | Hypogonadism | Gonadotropin-secreting tumors |
| Adrenocorticotropic hormone (ACTH) | Pituitary gland | Adrenal insufficiency (secondary adrenal insufficiency) | Cushing's disease |
| Antidiuretic hormone (ADH) | Hypothalamus | Diabetes insipidus | Syndrome of inappropriate ADH secretion (SIADH) |
| Calcitonin | Thyroid gland | Hypocalcemia | Medullary thyroid cancer |
| Glucagon | Pancreas | Hypoglycemia | Glucagonoma |
| Melanocyte-stimulating hormone (MSH) | Hypothalamus, pituitary gland, skin | Hypopituitarism | Melanosis, hyperpigmentation |
| Ghrelin | Stomach | Prader-Willi syndrome | Ghrelinoma |
| Leptin | Adipose tissue | Leptin deficiency | Leptin resistance (obesity-related) |
| Serotonin | Enterochromaffin cells | Serotonin deficiency syndrome | Serotonin syndrome |
| Vasopressin | Hypothalamus, posterior pituitary gland | Diabetes insipidus | Syndrome of inappropriate ADH secretion (SIADH) |
| Somatostatin | Pancreas, hypothalamus | Diabetes mellitus type 2 (insulin resistance) | Somatostatinoma |
| Atrial natriuretic peptide (ANP) | Heart | Sodium retention | Atrial myxoma |
| Relaxin | Ovaries, placenta | Preterm labor | Overactive relaxin production |
| Thymosin | Thymus | Reduced T cell development | Thymus gland tumors |
| Erythropoietin | Kidneys | Anemia | Polycythemia |
| Cholecystokinin | Intestines | Decreased appetite | Overproduction leading to gallbladder issues |
| Adiponectin | Adipose tissue | Insulin resistance, metabolic syndrome | Not applicable (low levels associated with obesity) |
| Norepinephrine | Adrenal glands | Low blood pressure, depression | Hypertension, anxiety |
| Glucocorticoids | Adrenal glands | Adrenal insufficiency | Cushing's syndrome |
| Inhibin | Gonads | Unknown (potential involvement in some diseases) | Granulosa cell tumors (ovaries), testicular tumors |
| Vasoinhibins | Placenta, hypothalamus | Unknown (potential involvement in various conditions) | Not applicable (no specific hypersecretion condition) |
| Neurotensin | Nervous system, digestive tract | Unknown (potential involvement in various conditions) | Neurotensin-secreting tumors |
| Secretin | Duodenum | Impaired digestion, malabsorption | Not applicable (rapidly inactivated in the body) |
| Thrombopoietin | Liver, kidneys | Thrombocytopenia | Thrombocytosis |
| Fibroblast growth factor 23 (FGF23) | Bones, kidneys | Hypophosphatemic rickets/osteomalacia | Tumor-induced osteomalacia |
| Gastrin | Stomach, duodenum | Hypogastrinemia | Zollinger-Ellison syndrome (gastrinoma) |
| Glucagon-like peptide-1 (GLP-1) | Intestines | Impaired glucose regulation | Not applicable (rapidly degraded in the body) |
| Vasopressin | Hypothalamus, posterior pituitary gland | Diabetes insipidus | Syndrome of inappropriate antidiuretic hormone (SIADH) |
| Serotonin | Enterochromaffin cells | Serotonin deficiency syndrome | Serotonin syndrome |
| Prostaglandins | Various tissues | Dysmenorrhea (painful menstruation) | Excessive menstrual bleeding (menorrhagia) |
| Vasopressin | Hypothalamus, posterior pituitary gland | Diabetes insipidus | Syndrome of inappropriate antidiuretic hormone (SIADH) |
| Natriuretic peptides | Heart | Sodium retention, hypertension | Natriuretic peptide-secreting tumors |
Location:
/Class-10/3_4_Endocrine_System.mdx