Endocrine System

A&P II BIO 320 Seeley TAMU

What is the main function of the endocrine system?

It releases hormones into the blood to regulate target tissues and help maintain homeostasis.

How do the nervous and endocrine systems communicate?

Both use chemical messengers and work together to regulate body processes.

How does the nervous system differ from the endocrine system in transport?

Nervous system → neurotransmitters released directly onto target cells.
Endocrine system → hormones travel through the blood

Which system responds faster?

Nervous system—milliseconds; endocrine system—seconds.

Which system has longer-lasting effects?

Endocrine system—minutes to days.

What determines the strength of an endocrine signal?

Hormone concentration.

What determines the strength of a nervous-system signal?

Frequency of action potentials.

What is an autocrine messenger?

A chemical messenger that affects the same cell that secreted it.

What is a paracrine messenger?

A chemical messenger that affects nearby cells.

What is a neurotransmitter?

A chemical messenger released by neurons into a synaptic cleft that affects a nearby postsynaptic cell.

What is an endocrine messenger?

A hormone released into the blood that travels to target tissues.

What determines whether a cell responds to a hormone?

The cell must have the specific receptor for that hormone.

What are lipid-soluble hormones?

Nonpolar hormones that can cross the cell membrane.

Examples of lipid-soluble hormones?

Steroids, thyroid hormones, and fatty-acid derivatives.

What are water-soluble hormones?

Polar hormones that cannot easily cross the cell membrane.

Examples of water-soluble hormones?

Proteins, peptides, and most amino-acid derivatives.

Where do lipid-soluble hormones bind?

Intracellular receptors, often in the cytoplasm or nucleus

Where do water-soluble hormones bind?

Receptors on the cell membrane.

What is the direct gene activation mechanism?

A lipid-soluble hormone enters the cell, binds an intracellular receptor, and the hormone-receptor complex regulates gene transcription.

What does the hormone-receptor complex do?

It acts as a transcription factor and binds DNA at hormone-response elements.

What is produced from the activated genes?

mRNA, which is translated into proteins.

Why are effects of direct gene activation relatively slow?

The cell must transcribe mRNA and synthesize new proteins.

What are the three types of membrane-bound receptors?

Ligand-gated ion channels, G protein-coupled receptors, and enzymatic receptors.

What is a second messenger?

An intracellular molecule that carries a signal from a membrane receptor into the cell.

What is the first messenger?

The hormone.

What is cAMP?

Cyclic AMP; a second messenger that carries a hormone signal inside the cell.

What does cAMP do?

It activates intracellular pathways that produce a cellular response.

Name common second messengers.

cAMP, cGMP, Ca²⁺, IP₃, and DAG.

What is signal amplification?

One hormone-receptor interaction produces many intracellular signals, creating a larger response.

Which generally produces a faster response: direct gene activation or second-messenger systems?

Second-messenger systems.

What is negative feedback?

The hormone's effects reduce further hormone secretion.

What is positive feedback?

The hormone's effects increase further hormone secretion

What is hormone half-life?

The time required for 50% of a hormone in circulation to be removed.

What are the three factors that determine the strength of a hormone's effect?

Hormone concentration, number of receptors, and receptor affinity.

What is down-regulation?

A decrease in receptor number/sensitivity after exposure to a hormone.

What is up-regulation?

An increase in receptor number that makes a cell more sensitive to a hormone.

What is a permissive interaction?

One hormone allows another hormone to produce a stronger response.

What is a synergistic interaction?

Two or more hormones work together to produce a greater response.

What is an antagonistic interaction?

Two hormones produce opposite effects.

Example of antagonistic hormones?

Insulin and glucagon regulate blood glucose in opposite directions.

What does the hypothalamus control?

It regulates secretion of the anterior pituitary and produces hormones stored in the posterior pituitary.

What are the two lobes of the pituitary gland?

Anterior pituitary and posterior pituitary.

What type of tissue makes up the posterior pituitary?

Nervous tissue.

What type of tissue makes up the anterior pituitary?

Glandular epithelium.

How does the hypothalamus control the anterior pituitary?

Through releasing and inhibiting hormones carried through the hypothalamohypophysial portal system.

How does the hypothalamus control the posterior pituitary?

Hormones produced by hypothalamic neurons travel down axons and are stored/released by the posterior pituitary.

What does GHRH do?

Increases growth hormone secretion.

What does GHIH (somatostatin) do?

Decreases growth hormone secretion.

What does TRH do?

Increases TSH secretion.

What does CRH do?

Increases ACTH secretion.

What does GnRH do?

Increases LH and FSH secretion.

What does dopamine/PIH do?

Decreases prolactin secretion.

What are the two posterior pituitary hormones?

ADH and oxytocin.

What does ADH do?

Helps conserve water and is released when electrolytes increase, water decreases, or blood pressure decreases.

What does oxytocin do?

Stimulates uterine contractions during labor.

What does growth hormone do?

Promotes protein synthesis, fat breakdown, glycogen synthesis, and bone/cartilage growth.

What stimulates GH secretion?

GHRH.

What inhibits GH secretion?

GHIH/somatostatin.

What are IGFs?

Insulin-like growth factors produced by tissues in response to GH that stimulate growth.

What is gigantism?

Excess GH secretion during childhood.

What is acromegaly?

Excess GH secretion in adults causing enlargement of bones of the hands, feet, and face.

What is the main function of prolactin?

Milk production.

What does TSH stimulate?

Secretion and storage of T3 and T4 from the thyroid.

What does ACTH stimulate?

Cortisol secretion from the adrenal cortex.

What are LH and FSH?

Gonadotropins that regulate gonad function, gamete production, and reproductive hormones.

What hormones are produced by thyroid follicular cells?

T3 and T4.

What do T3 and T4 require for production?

Iodine and tyrosine.

Which is more potent, T3 or T4?

T3.

What do T3 and T4 do?

Increase basal metabolic rate and regulate normal growth and maturation.

What does calcitonin do?

Decreases blood Ca²⁺ levels.

What triggers calcitonin secretion?

High blood Ca²⁺.

What cells produce calcitonin?

Parafollicular (C) cells.

What happens with hypothyroidism?

Decreased metabolic rate, cold intolerance, weight gain, and slower activity.

What happens with hyperthyroidism?

Increased metabolic rate, heat intolerance, weight loss, sweating, and rapid heart rate.

What is Graves disease?

An autoimmune condition associated with hyperthyroidism, goiter, and exophthalmos.

What hormone do the chief cells of the parathyroid glands secrete?

Parathyroid hormone (PTH).

What triggers PTH release?

Low blood Ca²⁺.

What does PTH do to blood Ca²⁺?

Increases blood Ca²⁺.

How does PTH increase blood Ca²⁺?

Stimulates bone resorption, increases kidney Ca²⁺ reabsorption, and increases vitamin D synthesis → increased intestinal Ca²⁺ absorption.

What does PTH do to phosphate?

Increases phosphate excretion by the kidneys.

What are the two major regions of the adrenal gland?

Adrenal cortex and adrenal medulla.

What does the adrenal medulla secrete?

Epinephrine and norepinephrine.

What is the adrenal medulla associated with?

The sympathetic nervous system.

What are the three zones of the adrenal cortex?

Zona glomerulosa, zona fasciculata, and zona reticularis

What does the zona glomerulosa produce?

Mineralocorticoids, mainly aldosterone.

What does aldosterone do?

Increases Na⁺ and water reabsorption and increases K⁺ excretion → increases blood volume and blood pressure.

What does the zona fasciculata produce?

Glucocorticoids, mainly cortisol.

What does cortisol do?

Increases blood glucose, promotes fat/protein breakdown, and suppresses inflammation/immune responses.

What does the zona reticularis produce?

Adrenal androgens.

What does epinephrine do?

increases blood glucose, heart rate, force of contraction, and fat breakdown to prepare the body for physical activity.

What cells produce insulin?

Beta cells.

What cells produce glucagon?

Alpha cells.

What cells produce somatostatin?

Delta cells.

What does insulin do to blood glucose?

Decreases blood glucose by increasing glucose uptake into cells.

What does glucagon do to blood glucose?

Increases blood glucose by promoting glucose release from stored sources.

When does insulin secretion increase?

When blood glucose is high (hyperglycemia).

When does glucagon secretion increase?

When blood glucose is low (hypoglycemia).

What happens to insulin after a meal?

Insulin increases while glucagon decreases.

What happens to insulin and glucagon during exercise?

Sympathetic stimulation increases epinephrine and glucagon to maintain blood glucose for fuel.

What does testosterone do?

Supports spermatogenesis, reproductive-organ function, secondary sex characteristics, and sexual behavior.