17.2 Hormones

Flashcards to review key concepts about hormone signaling, receptors, second messengers, regulation, and feedback mechanisms.

What is the role of a hormone receptor in cell signaling?

A protein located either inside the cell or on the cell membrane that binds the hormone and initiates signaling events leading to the target cell’s response.

Why can the same hormone cause different responses in different tissues?

Because the response depends on the target cell’s context and the receptor signaling pathways in that tissue; the same receptor type may be on different tissues and trigger different responses.

List some possible responses a target cell may have to a hormone signal.

Stimulation of protein synthesis; activation or deactivation of enzymes; changes in membrane permeability; altered rates of mitosis and cell growth; stimulation of product secretion.

Which hormones use intracellular hormone receptors, and where are these receptors located?

Steroid hormones (derived from cholesterol) and thyroid hormones that cross the cell membrane bind to intracellular receptors located in the cytosol or nucleus.

Where does a steroid hormone receptor binding occur and what is the outcome?

The receptor binds in the cytosol or nucleus; the hormone-receptor complex forms and moves to DNA to trigger transcription of target genes into mRNA.

How do lipid-soluble and water-soluble hormones differ in their mechanisms of action?

Lipid-soluble hormones (e.g., steroids) directly influence gene transcription after binding to intracellular receptors; water-soluble hormones bind surface receptors and activate second messenger cascades without directly altering transcription.

Describe the main steps of the cAMP second messenger pathway.

1) Hormone binds a membrane receptor; 2) G protein is activated; 3) Adenylyl cyclase is activated; 4) ATP is converted to cAMP; 5) cAMP activates protein kinases; 6) A phosphorylation cascade phosphorylates target proteins.

What is the role of phosphodiesterase (PDE) in the cAMP pathway?

PDE deactivates cAMP, terminating the signal so the response ceases unless new hormone arrives.

Which hormones can use a calcium-based second messenger system?

Hormones like angiotensin II and growth hormone-releasing hormone (GHRH) can activate PLC, producing DAG and IP3, with IP3 releasing Ca2+ and Ca2+ acting as a second messenger (often via calmodulin).

What happens in the calcium second messenger system after PLC is activated?

PLC cleaves membrane phospholipids into DAG and IP3; DAG activates protein kinases; IP3 releases Ca2+ from intracellular stores; Ca2+ then modulates enzymes or binds calmodulin to affect kinase activity.

What is the difference between upregulation and downregulation of receptors?

Downregulation decreases receptor numbers in response to high hormone levels; upregulation increases receptor numbers when hormone levels are chronically low, making cells more sensitive.

Define permissive, synergistic, and antagonistic hormone effects with examples.

Permissive: one hormone enables another (e.g., iodine-containing thyroid hormones). Synergistic: two hormones produce a greater combined effect (e.g., FSH and estrogens for oocyte maturation). Antagonistic: hormones have opposing effects (e.g., insulin and glucagon).

What is the role of feedback loops in hormone regulation?

Feedback loops regulate hormone secretion to maintain homeostasis; positive feedback amplifies a hormone release (e.g., oxytocin during childbirth); negative feedback inhibits further secretion to keep levels in check (e.g., glucocorticoids).

Give an example of a positive feedback loop in the endocrine system.

Oxytocin release during childbirth increases uterine contractions, which causes more oxytocin release until birth ends the loop.

Give an example of a negative feedback loop in the endocrine system.

Glucocorticoid release from the adrenal glands is inhibited by signaling from the hypothalamus and pituitary as blood glucocorticoid levels rise.

What are humoral, neural, and hormonal stimuli in endocrine control?

Humoral stimuli: changes in blood levels of chemicals (e.g., glucose) trigger hormones; Neural stimuli: nerve signals (e.g., fight-or-flight) trigger hormone release; Hormonal stimuli: hypothalamic releasing/inhibiting hormones regulate pituitary hormones.

What triggers ADH release and what effect does it have on the kidneys?

Osmoreceptors sense high blood osmolarity; hypothalamus releases ADH, which increases kidney water reabsorption, reducing urine volume and lowering osmolarity.

How is blood glucose regulated by hormones?

High blood glucose stimulates insulin release from the pancreas, increasing cellular glucose uptake and liver glycogen storage, lowering blood glucose.

What is the relationship between the hypothalamus and the pituitary in endocrine control?

The hypothalamus releases releasing and inhibiting hormones that regulate anterior pituitary hormone secretion, which in turn controls other endocrine glands.

What is the effect of iodine deficiency on thyroid hormone production and related systems?

Iodine deficiency reduces thyroid hormone production, which can disrupt permissive interactions with reproductive hormones and affect reproductive development and function.

How do steroid hormones reach chromatin targets after receptor binding?

The hormone-receptor complex binds to DNA in the chromatin, triggering transcription of target genes into mRNA, which is translated into proteins in the cytoplasm.