Animal Hormones, Reproduction, and Development Study Materials Flashcards

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Hormone

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A chemical signal released into the bloodstream that travels to target cells throughout the body. Only cells with the correct receptor respond, producing specific physiological effects.

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Paracrine signaling

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Local chemical communication in which signaling molecules diffuse to nearby cells and bind receptors there. It does not involve transport through the bloodstream.

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Autocrine signaling

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A mode of signaling where a cell secretes a molecule that binds to receptors on its own surface, triggering a response in the same cell. It often regulates cell proliferation and immune responses.

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Protein (peptide) hormones

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Hormones composed of amino acids that are water-soluble and cannot cross the cell membrane. They bind cell-surface receptors and typically activate second-messenger signaling cascades.

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Steroid hormones

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Lipid-soluble hormones derived from cholesterol that can cross cell membranes and bind intracellular receptors. The hormone-receptor complex often acts as a transcription factor to alter gene expression.

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Amine hormones

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Hormones derived from the amino acid tyrosine; they can be water-soluble or lipid-soluble. Examples include epinephrine (water-soluble) and thyroxine (lipid-soluble).

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Cell-surface receptors

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Membrane proteins used by water-soluble hormones to transmit a signal to the cell interior. Hormone binding triggers second messengers and intracellular signaling cascades.

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Intracellular receptors

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Receptors located inside the cell, used by lipid-soluble hormones such as steroids. The hormone-receptor complex often alters gene transcription directly.

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Second messenger

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A small intracellular molecule (e.g., cAMP) produced or released in response to hormone binding at the cell surface. It amplifies and propagates the signal to target proteins and enzymes.

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Negative feedback loop

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A regulatory circuit where the output of a pathway inhibits an earlier step to maintain homeostasis. In endocrine axes, the final hormone typically suppresses hypothalamic and pituitary releasing hormones.

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Hypothalamic-pituitary axis

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A hierarchical endocrine pathway where the hypothalamus releases releasing hormones that stimulate the anterior pituitary to secrete tropic hormones, which then act on peripheral endocrine glands.

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TSH and TRH

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TRH (from the hypothalamus) stimulates anterior pituitary release of TSH, which in turn stimulates the thyroid to produce thyroxine. Elevated thyroxine inhibits TRH and TSH via negative feedback.

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Goiter

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An enlarged thyroid gland that occurs when iodine deficiency limits thyroxine synthesis, leading to elevated TSH and overstimulation of thyroid growth. The gland enlarges despite low thyroxine production.

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Posterior pituitary hormones

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ADH and oxytocin are synthesized in the hypothalamus and stored in the posterior pituitary. ADH regulates water balance and blood pressure while oxytocin stimulates uterine contractions and milk letdown.

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Anterior pituitary function

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The anterior pituitary produces several hormones in response to hypothalamic releasing and inhibiting hormones. It secretes tropic hormones such as TSH, ACTH, LH, and FSH that regulate other endocrine glands.

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Insulin role

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A hormone produced by pancreatic beta cells that stimulates glucose uptake by causing glucose transporters to move to the cell membrane. It lowers blood glucose and promotes storage of nutrients.

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Type I vs Type II diabetes

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Type I diabetes results from no insulin production and requires insulin replacement, while Type II is characterized by insulin resistance or reduced receptor sensitivity, causing hyperglycemia despite insulin presence.

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Cortisol effects

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A glucocorticoid released during stress that raises blood glucose and suppresses immune responses. Chronic high cortisol can cause hypertension, immune suppression, and increased cardiovascular risk.

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Blastula and gastrulation

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The blastula is a hollow ball of cells formed after cleavage; gastrulation rearranges the blastula into a three-layered embryo (ectoderm, mesoderm, endoderm), establishing the basic body plan.