Endocrine System: Glands, Hormones, and Reproductive Regulation

What is the endocrine system?

The endocrine system includes endocrine glands and regulates reproduction, metabolism, osmoregulation, embryonic development, growth, metamorphosis, and digestion.

What is a hormone?

A hormone is a chemical messenger that interacts with specific target tissues or cells.

What is the thyroid gland?

The thyroid gland is present in all vertebrates and arises from the outgrowth of the floor of the pharynx.

What are thyroid hormones?

Thyroid hormones include Thyroxine (T4) and Triiodothyronine (T3).

What are follicles in the thyroid?

Follicles are structures surrounded by follicular cells that produce a gelatinous colloid where hormones are stored.

What is TSH?

Thyrotropin or thyroid-stimulating hormone (TSH) stimulates the thyroid gland to release its hormones.

What is hypothyroidism?

Hypothyroidism is the underproduction of thyroid hormones, known as cretinism when present at birth.

What is hyperthyroidism?

Hyperthyroidism is the overproduction of thyroid hormones.

What is calcium homeostasis?

Calcium homeostasis is the regulation of calcium levels in the body.

What is the ultimobranchial body?

The ultimobranchial body is a paired cell mass that secretes calcitonin.

What is calcitonin?

Calcitonin is a hormone that lowers blood calcium levels by decreasing osteoclast activity.

What are parathyroid glands?

Parathyroid glands are glands embedded in or near the thyroid that regulate calcium levels.

What is PTH?

Parathyroid hormone (PTH) raises blood calcium levels by increasing kidney retention and osteoclast activity.

What are chief cells?

Chief cells are the cells in the parathyroid glands that produce PTH.

What is the adrenal gland?

The adrenal gland consists of two main parts: adrenocortical tissue and chromaffin tissue.

What is adrenocortical tissue?

Adrenocortical tissue produces corticosteroid hormones, including mineralocorticoids, glucocorticoids, and androgens.

What is chromaffin tissue?

Chromaffin tissue produces catecholamines, specifically epinephrine and norepinephrine.

What is the zona glomerulosa?

The zona glomerulosa produces mineralocorticoids, primarily aldosterone.

What is aldosterone?

Aldosterone is a hormone that increases sodium reabsorption and potassium excretion.

What is cortisol?

Cortisol is a major stress hormone that increases blood glucose and metabolism.

What is ACTH?

Adrenocorticotropic hormone (ACTH) stimulates the adrenal gland to release glucocorticoids.

What is the pancreas?

The pancreas is a composite gland with both exocrine and endocrine functions.

What are acinar cells?

Acinar cells are part of the exocrine portion of the pancreas that secrete digestive enzymes.

What are pancreatic islets?

Pancreatic islets (islets of Langerhans) are the endocrine portion of the pancreas.

What is insulin?

Insulin is produced by beta cells and lowers blood sugar by increasing glucose entry into cells.

What is hypoglycemia?

Hypoglycemia is a condition characterized by abnormally low blood sugar levels.

What is hyperglycemia?

Hyperglycemia is a condition characterized by abnormally high blood sugar levels.

What is diabetes mellitus?

Diabetes mellitus is a metabolic disorder characterized by high blood sugar levels over a prolonged period.

What is glucagon?

Glucagon is a hormone that raises blood sugar levels by promoting the release of glucose from the liver.

What is somatostatin?

Somatostatin is a hormone that inhibits the secretion of other hormones, including insulin and glucagon.

What is pancreatic polypeptide?

Pancreatic polypeptide is a hormone involved in regulating pancreatic secretions and gastrointestinal activity.

What is pancreatic polypeptide (PP)?

Produced by PP cells; it controls gastrointestinal activities like gastric juice flow.

What are blood sugar imbalances?

Hypoglycemia (low sugar), hyperglycemia (high sugar), and diabetes mellitus.

What is the pituitary gland?

Consists of two distinct parts.

What is the neurohypophysis?

The posterior pituitary formed from the infundibulum; its main part is the pars nervosa.

What is the adenohypophysis?

The anterior pituitary that originates from the ectodermal stomodeum; its main part is the pars distalis.

What are neurosecretory neurons?

Hypothalamic neurons that project into the neurohypophysis to release secretions into the blood.

What are neurohormones?

Substances secreted by the hypothalamus into the blood to regulate the adenohypophysis.

What are releasing (tropic) hormones?

Specific neurohormones that stimulate the release of hormones from the adenohypophysis.

What are inhibiting hormones?

Specific neurohormones that inhibit the release of hormones from the adenohypophysis.

What is ADH (Antidiuretic Hormone)?

Increases water reabsorption in kidneys and raises blood pressure.

What is oxytocin?

Stimulates uterine contractions, milk ejection, and bonding.

What is GH (Growth Hormone)?

Increases growth and metabolism; disorders include gigantism and acromegaly.

What does TSH do?

Stimulates the thyroid gland.

What is PRL (Prolactin)?

Stimulates milk production in mammals and brooding behavior in birds.

What are gonadotropins?

Includes FSH (stimulates follicles/sperm) and LH (promotes ovulation/corpus luteum).

What is ICSH?

LH is called interstitial cell-stimulating hormone when it stimulates interstitial cells to produce testosterone.

What is MSH (Melanophore-Stimulating Hormone)?

Changes skin darkness in lower vertebrates.

What is the pineal gland?

A midbrain evagination that detects light schedules in lower vertebrates.

What is melatonin?

Produced by the pineal gland; thought to regulate the circadian rhythm.

What is gastrin?

Stimulates gastric juice secretion.

What is secretin?

Stimulates the pancreas to secrete alkaline juice.

What is enterogastrone?

Inhibits gastric secretion and motility.

What is cholecystokinin (CCK)?

Stimulates gallbladder contraction, bile ejection, and pancreatic enzyme secretion.

What is renin?

Released when blood pressure drops; it converts angiotensinogen into angiotensin I.

What is angiotensin II?

Converted from angiotensin I; it is a vasoconstrictor and stimulates aldosterone release.

What is erythropoietin (EPO)?

Stimulates red blood cell production when oxygen levels are low.

What is testosterone?

The primary androgen that causes the development of male sex characteristics and uses negative feedback to inhibit LH overproduction.

What are granulosa cells?

Cells that surround the egg.

What is the antrum?

A fluid-filled space within granulosa cells.

What is the corpus luteum?

Forms after ovulation; if no fertilization occurs, it becomes the corpus albicans.

What is GnRH?

Gonadotropin-releasing hormone that stimulates LH secretion.

What happens if an egg is fertilized?

CG (chorionic gonadotropin) from the embryo maintains the corpus luteum.

What happens if an egg is not fertilized?

The corpus luteum degenerates.

What is a joey?

An infant kangaroo after birth.

What is embryonic diapause?

Arrested development of a blastocyst caused by a suckling joey.

What is the estrous cycle?

The reproductive cycle in most mammals, featuring estrus (heat).

What is estrus?

A period of heightened sexual behavior and receptivity.

What is premetamorphosis?

High prolactin levels stimulate growth but inhibit metamorphosis.

What is prometamorphosis?

Increasing TSH and thyroxine cause hindlimb development.

What is metamorphic climax?

Peak TSH and thyroxine stimulate the completion of metamorphosis.

What factors influence hormone effects?

Environmental factors, hormone amount, presence of other hormones, organism type, and receptor type.

How are the endocrine and nervous systems connected?

They are similar and connected through neurosecretory neurons in the hypothalamus that release hormones into the blood.