Animal Hormones Flashcards

Key Concepts

39.1 Hormones Circulate Around the Body and Affect Cells That Have Receptors
The endocrine system uses hormones as signals, reaching almost all cells, but only affecting target cells with specific hormone receptors.

Hormones: Travel in blood to activate target cells.

Paracrines: Affect nearby target cells.

Autocrines: Regulate the same cells that secrete them.

Exocrine glands: Secrete substances through ducts outside the body.

Endocrine glands: Hormone-secreting cell aggregations inside the body.

Endocrines: Chemical signals secreted into the extracellular fluid (ECF) and enter the blood for circulation.

Neuroendocrines: Secreted by neurons and transported through the circulation.

Pheromones: Influence behavior/physiology of other animals.
Three classes of hormones:

Peptide and protein hormones: Water-soluble, transported in blood, released via exocytosis.

Steroid hormones: Lipid-soluble, pass through cell membranes, bound to carrier molecules in the blood.

Amine hormones: Solubility and release modes vary.

39.2 The Endocrine System and Nervous System Work Together
Neural signals are fast and quickly turned off. Endocrine signals are slow and sustained.
Blood hormone levels are controlled by negative feedback systems.:star: This is super important for maintaining homeostasis.

Humoral: Changing levels of ions or nutrients stimulate hormone secretion.

Neural: Stimulation by nerves.

Hormonal: Stimulation from other hormones.
The pituitary gland connects the nervous and endocrine systems.

Posterior pituitary releases neurohormones (ADH, oxytocin).

Anterior pituitary secretes tropic hormones (TSH, LH, FSH, corticotropin, GH).

39.3 Hormones Play Important Roles in Development
Hormones coordinate developmental processes.
Three hormones regulate molting and maturation in insects: PTTH, ecdysone, and juvenile hormone.
In vertebrates, androgens and estrogens determine sex development.
Gonadotropins (LH, FSH) control gonad activity.

39.4 Hormones Regulate Metabolism and the Internal Environment
The thyroid gland secretes thyroxine (metabolism) and calcitonin (blood calcium regulation).
Regulation of calcium levels is controlled by calcitonin, parathyroid hormone (PTH), and Vitamin D.
Diabetes mellitus is caused by a lack of insulin.
Pancreatic islets produce insulin, glucagon, and somatostatin.
The adrenal gland has two parts:

The adrenal medulla produces epinephrine and norepinephrine.

The adrenal cortex produces mineralocorticoids

Okay, let's delve deeper into what specific hormones do and how they connect to the bigger picture of bodily functions:

Insulin: Secreted by the pancreatic islets, insulin is crucial for regulating blood glucose levels. After you eat, blood glucose rises, prompting insulin release. Insulin then enables cells to absorb glucose from the blood, either using it for energy or storing it as glycogen in the liver and muscles. In the bigger picture, insulin ensures that cells have the energy they need and prevents hyperglycemia, which can damage organs over time.

Glucagon: Also produced by the pancreatic islets, glucagon has the opposite effect of insulin. When blood glucose levels drop too low, glucagon is released. It stimulates the liver to break down stored glycogen into glucose, which is then released into the bloodstream. This raises blood glucose levels back to normal. Together, insulin and glucagon work in a negative feedback loop to maintain glucose homeostasis.

Thyroxine (T4): Secreted by the thyroid gland, thyroxine is essential for regulating metabolism. It increases the basal metabolic rate, affecting almost every cell in the body. Thyroxine influences heart rate, digestion, muscle function, brain development, and bone maintenance. In the broader context, thyroxine ensures that the body's energy usage is balanced and supports overall growth and development.

Calcitonin: Also from the thyroid gland, calcitonin helps regulate blood calcium levels. When calcium levels are too high, calcitonin stimulates calcium deposition into bones and reduces calcium absorption in the kidneys. This lowers blood calcium and protects against hypercalcemia, which can impair nerve and muscle function.

Parathyroid Hormone (PTH): Produced by the parathyroid glands, PTH counteracts calcitonin. When blood calcium levels are too low, PTH stimulates the release of calcium from bones into the bloodstream, increases calcium absorption in the intestines, and reduces calcium loss in the kidneys. PTH is vital for preventing hypocalcemia and maintaining proper nerve and muscle function.

Epinephrine (Adrenaline) and Norepinephrine (Noradrenaline): Secreted by the adrenal medulla, these hormones are part of the "fight or flight" response. They increase heart rate, blood pressure, and blood glucose levels, preparing the body for immediate action. Epinephrine and norepinephrine also divert blood flow to muscles and the brain, enhancing alertness and physical performance.

Mineralocorticoids (e.g., Aldosterone): Produced by the adrenal cortex, mineralocorticoids regulate electrolyte balance, particularly sodium and potassium. Aldosterone increases sodium reabsorption in the kidneys, which in turn increases water retention and blood volume. This is crucial for maintaining blood pressure and fluid balance.

Glucocorticoids (e.g., Cortisol): Also from the adrenal cortex, glucocorticoids have a wide range of effects, including regulating metabolism, immune function, and stress response. Cortisol increases blood glucose levels, suppresses inflammation, and helps the body cope with stress. However, chronic elevation of cortisol can have negative effects, such as immune suppression and bone loss.

Androgens and Estrogens: These sex hormones, produced by the gonads (testes and ovaries) and adrenal cortex, are responsible