Endocrine System Overview

Endocrine System Overview

• The endocrine system is a complex network regulating feedback mechanisms for homeostasis in the human body.
• Associated with the regulation of physiological responses.
• Composed of various glands and organs.

Introduction to Endocrine System

• The endocrine system is a complex regulatory network.
• It regulates feedback mechanisms in the human body.
• It's the main gland or organ associated with homeostasis of physiological responses.
• Organs include hypothalamus, pituitary gland (anterior & posterior), adrenal gland (medulla & cortex), thymus gland, thyroid gland, parathyroid gland, pancreas, pineal gland, testis, and ovaries.

Target Cells

• Target cells have specific receptors for hormones.
• Nontarget cells lack these receptors.
• Hormones bind to their specific receptors.

Hormone Classes

• Lipid-soluble hormones (e.g., thyroid, steroid) pass through the membrane and bind to intracellular receptors.
• Water-soluble hormones (e.g., glucagon, prolactin) bind to membrane-bound receptors initiating a second messenger system.

Endocrine System: Overview

• Limbic system
• Diencephalon ("Grape-like structure")
• Hypothalamus (part of brain that controls the "little brain")
• Optic chiasm
• Pituitary gland (posterior & anterior)
• Sella turcica (of sphenoid bone)
• Kidney tubules
• Uterus smooth muscle
• Anterior pituitary hormones
• Growth hormone (GH)
• Adrenocorticotropic hormone (ACTH)
• Thyroid-stimulating hormone (TSH)
• Prolactin
• Melanocyte-stimulating hormone
• Gonadotropins (FSH & LH)
• Posterior pituitary hormones
• Antidiuretic hormone (ADH)
• Oxytocin

Anterior Pituitary Gland

• Thyroid-stimulating hormone (TSH) stimulates thyroid to produce thyroid hormones.
• Adrenocorticotropic hormone (ACTH) stimulates adrenal cortex to produce cortisol.
• Gonadotropic hormones stimulate gonads to produce sex cells and hormones.
• Prolactin (PRL) develops mammary glands for milk production after childbirth.
• Melanocyte-stimulating hormone (MSH) changes skin color.

Posterior Pituitary Gland

• Stores antidiuretic hormone (ADH) and oxytocin.
• ADH (vasopressin) regulates water balance by reabsorbing water into the bloodstream.
• Oxytocin causes uterine contractions during childbirth and milk release during nursing.

Thyroid Gland

• Iodine is needed for hormone production.
• Thyroid hormone (TH) regulates metabolism.
• Calcitonin lowers blood calcium levels.
• Thyroxine (T4) and triiodothyronine (T3) are thyroid hormones.

Thyroid Gland Disorders

• Simple goiter: Thyroid enlargement due to iodine deficiency.
• Congenital hypothyroidism: Thyroid does not develop properly, causing short stature and mental retardation.
• Myxedema: Hypothyroidism in adults, with lethargy, weight gain, hair loss, cold intolerance, and puffy skin.
• Exophthalmic goiter: Excessive thyroid hormones, enlargement, protruding eyes, hyperactivity, and insomnia.
• Thyroid tumor: Can cause hyperthyroidism.

Parathyroid Gland

• Small glands on the thyroid.
• Produces parathyroid hormone (PTH).
• PTH elevates blood calcium by stimulating osteoclast activity and kidney reabsorption.

Adrenal Gland: Medulla

• Hypothalamus stimulates hormone secretion in the adrenal medulla.
• Produces "fight-or-flight" response hormones:
• Epinephrine (adrenaline): Fast response
• Norepinephrine (noradrenaline): Slower response

Adrenal Gland: Cortex

• Produces hormones for a long term response to stress.
• Two major hormone types:
• Glucocorticoids regulate carbohydrate, protein, and fat metabolism and suppresses inflammation (e.g., cortisol, cortisone).
• Mineralocorticoids regulate salt and water balance (e.g., aldosterone).

Pancreas: Exocrine and Endocrine

• Composed of exocrine and endocrine tissues.
• The endocrine part (Islets of Langerhans) releases hormones:
• Insulin: Secreted when blood glucose is high; stimulates glucose uptake by cells (muscle and liver).
• Glucagon: Secreted when blood glucose is low; stimulates glycogen breakdown in the liver.

Pancreas: Diabetes Disorder

• Inability to control blood glucose levels.
• Symptoms include frequent urination, unusual hunger or thirst, unexplained weight change, blurred vision, slow-healing sores, and excessive fatigue.
• Normal blood sugar level: 140 mg/L (7.8 mmol/L).
• Two types: Type 1 and Type 2.
• Long-term effects can include blindness, nerve damage, kidney damage, and cardiovascular disease.

Pancreas: Diabetes Mellitus (Type 1)

• Normally early-onset autoimmune disorder.
• Pancreatic cells are attacked and cannot produce insulin.
• Insulin injections are needed.

Pancreas: Diabetes Mellitus (Type 2)

• Normally adult-onset.
• Most common type.
• Occurs often in obese, sedentary people.
• Cells do not respond to insulin.
• Diet and exercise are important for control.

Pineal Gland

• Secretes melatonin, regulating the sleep-wake cycle (circadian rhythm).
• May also regulate sexual development.

Thymus Gland

• Lies beneath the sternum.
• Largest and most active during childhood.
• T lymphocytes mature here.
• Secretes thymosins for lymphocyte differentiation.

Gonads (Testes and Ovaries)

• Testes (Leydig Cells): Produce androgens (e.g., testosterone), stimulating male sex characteristics (facial hair, larger larynx leading to voice change, muscular strength).
• Ovaries: Produce estrogen and progesterone, stimulating female secondary sex characteristics (body hair, fat distribution, development of breasts).

Explore the intricate workings of the endocrine system in this quiz. Learn about the various glands, hormones, and feedback mechanisms responsible for maintaining homeostasis in the human body. Test your knowledge on target cells, hormone classes, and their physiological roles.