MCAT Biology Chapter 5: Endocrine System Hormones and Glands

What is the primary function of the endocrine system?

To secrete hormones that regulate physiological processes and maintain homeostasis.

How do hormones travel to target tissues?

Hormones are released into the bloodstream and travel to distant target tissues.

What are the three main types of hormones based on their chemical structure?

Peptide hormones, steroid hormones, and amino acid-derived hormones.

What is the mechanism of action for peptide hormones?

Peptide hormones bind to surface receptors, acting as first messengers, and trigger a signaling cascade inside the cell.

What role does cAMP play in peptide hormone signaling?

cAMP acts as a second messenger that activates protein kinase A, leading to phosphorylation of target proteins.

What is the secretion method for peptide hormones?

Peptide hormones are released via exocytosis from endocrine cells into the bloodstream.

Why can't peptide hormones cross the cell membrane?

Because they are water-soluble and cannot pass through the hydrophobic lipid bilayer.

What is a key characteristic of steroid hormones?

Steroid hormones are lipid-soluble and can easily cross the cell membrane.

How are steroid hormones transported in the bloodstream?

Steroid hormones are carried by transport proteins in the blood.

What happens to steroid hormones when they are bound to carrier proteins?

They remain inactive and must dissociate from their carriers to exert their effects.

What is the role of the hormone-receptor complex in steroid hormone action?

It binds to specific DNA sequences in the nucleus and functions as a transcription factor to alter gene expression.

What is dimerization in the context of steroid hormones?

Dimerization is when two hormone-receptor complexes pair up to stabilize interaction with DNA.

What are amino acid-derived hormones made from?

They are made from one or two amino acids with additional modifications.

Name two important amino acid-derived hormones.

Epinephrine and norepinephrine.

What is the difference in the onset and duration of action between peptide and steroid hormones?

Peptide hormones have a rapid onset but short duration, while steroid hormones have a slower onset but longer-lasting effects.

What is the primary source of steroid hormones?

They are primarily produced by the gonads (testes and ovaries) and the adrenal cortex.

How do peptide hormones amplify their effects?

A single hormone molecule can activate many second messengers, leading to a large cellular response.

What is the function of protein kinase A in the signaling cascade?

It phosphorylates target proteins, altering their activity and leading to changes in gene expression.

What is the role of transcription factors like CREB in hormone signaling?

They modify the expression of specific genes in response to hormonal signaling.

What distinguishes the signaling mechanisms of peptide hormones from steroid hormones?

Peptide hormones use surface receptors and second messengers, while steroid hormones act directly on intracellular receptors.

What is the significance of the endocrine system in maintaining homeostasis?

It regulates various physiological processes through hormonal signaling, ensuring balance in the body.

How does the endocrine system differ from the nervous system?

The endocrine system uses slower chemical signals for long-term control, while the nervous system uses rapid electrical signals for short-term control.

What is the effect of peptide hormones on cellular behavior?

They initiate signaling cascades that can rapidly change cell behavior, often for quick physiological adjustments.

What are the implications of the lipid solubility of steroid hormones?

They can easily cross cell membranes and directly influence gene transcription inside the cell.

What is the primary difference in the mechanism of action between peptide and steroid hormones?

Peptide hormones bind to cell surface receptors, while steroid hormones bind to intracellular receptors.

What are the physiological roles of hormones released by the adrenal glands?

They regulate stress responses, metabolism, and immune function.

What is the significance of the hypothalamus in the endocrine system?

It regulates the pituitary gland and controls the release of various hormones.

How do hormones maintain homeostasis in the body?

By regulating processes such as metabolism, growth, and response to stress.

What are catecholamines?

Hormones such as epinephrine and norepinephrine that bind to receptors on the cell surface.

How do thyroid hormones behave compared to peptide hormones?

Thyroid hormones cross the membrane and bind to intracellular receptors, altering gene expression.

What is the difference between direct hormones and tropic hormones?

Direct hormones act on target cells, while tropic hormones stimulate other glands to release hormones.

Give an example of a direct hormone.

Insulin, which promotes glucose uptake in muscle cells.

What is GnRH and its function?

Gonadotropin-releasing hormone; it stimulates the release of LH from the anterior pituitary.

What role does the hypothalamus play in the endocrine system?

It regulates the pituitary gland through the release of tropic hormones.

What is the hypophyseal portal system?

A specialized blood vessel network that allows hormones from the hypothalamus to reach the anterior pituitary quickly.

What is negative feedback in the endocrine system?

A mechanism where high levels of a downstream hormone inhibit further release from the hypothalamus.

What does the anterior hypothalamus control?

Sexual behavior.

What is the function of the ventromedial hypothalamus?

It signals when you're full.

What triggers eating behavior?

The lateral hypothalamus.

What hormone does the hypothalamus release to stimulate growth hormone?

Growth hormone-releasing hormone (GHRH).

What does thyroid-releasing hormone stimulate?

The release of thyroid-stimulating hormone from the anterior pituitary.

What hormone does corticotropin-releasing factor stimulate?

Adrenocorticotropic hormone (ACTH), which promotes cortisol release.

How is prolactin regulated?

It is inhibited by prolactin-inhibiting factor (dopamine).

What is the connection between the hypothalamus and the posterior pituitary?

The posterior pituitary is connected by neurons that extend from the hypothalamus.

What hormones are released from the posterior pituitary?

Hormones synthesized by neurons in the hypothalamus, such as oxytocin and vasopressin.

What is the role of the anterior pituitary gland?

It releases hormones that act on target organs like the gonads, thyroid, or adrenal cortex.

How do hormones travel to their target tissues?

They are secreted into the bloodstream by endocrine glands.

What is the role of the adrenal cortex?

It produces cortisol in response to adrenocorticotropic hormone (ACTH).

What is the function of follicle-stimulating hormone (FSH)?

It stimulates the gonads to produce gametes.

What does luteinizing hormone (LH) do?

It triggers ovulation in females and testosterone production in males.

What is the significance of hormone cascades?

They involve multiple steps where one hormone stimulates another, leading to a final physiological effect.

What is the primary function of the thyroid gland?

To regulate metabolism through the release of thyroid hormones.

What physiological processes do hormones coordinate?

Metabolism, growth, stress responses, and reproduction.

What hormones are released by the posterior pituitary?

Oxytocin and antidiuretic hormone (vasopressin)

What is the role of oxytocin?

Stimulates uterine contractions during labor and promotes milk ejection during breastfeeding.

What triggers the release of antidiuretic hormone?

When the blood is too concentrated.

What is the function of antidiuretic hormone (vasopressin)?

Increases water reabsorption in the kidneys.

How does the anterior pituitary differ from the posterior pituitary?

The anterior pituitary synthesizes and secretes its own hormones, while the posterior pituitary stores and releases hormones made in the hypothalamus.

What mnemonic helps remember the tropic hormones of the anterior pituitary?

FLAT PEG

What does F stand for in the FLAT PEG mnemonic?

Follicle-stimulating hormone

What is the role of follicle-stimulating hormone in females?

Stimulates the growth of ovarian follicles.

What does L stand for in the FLAT PEG mnemonic?

Luteinizing hormone

What is the function of luteinizing hormone in males?

Stimulates Leydig cells to produce testosterone.

What does A stand for in the FLAT PEG mnemonic?

Adrenocorticotropic hormone

What is the main function of adrenocorticotropic hormone?

Stimulates the release of glucocorticoids from the adrenal cortex.

What does T stand for in the FLAT PEG mnemonic?

Thyroid-stimulating hormone

What is the role of thyroid-stimulating hormone?

Stimulates the production and release of T3 and T4 from the thyroid gland.

What are the direct hormones produced by the anterior pituitary?

Prolactin, endorphins, and growth hormone.

What is the function of prolactin?

Promotes milk production in lactating females.

What role do endorphins play in the body?

Act as natural painkillers and reduce the perception of pain.

What is the function of growth hormone?

Stimulates growth in nearly all tissues and promotes protein synthesis.

What condition results from excess growth hormone before growth plates close?

Gigantism

What condition results from low growth hormone during childhood?

Dwarfism

What happens if growth hormone levels rise after growth plates have closed?

Acromegaly occurs, causing thickening of soft tissues and certain bones.

What is the shape and location of the thyroid gland?

Butterfly-shaped and located at the front of the neck.

What are the two major functions of the thyroid gland?

Regulates metabolism and maintains calcium homeostasis.

What hormones are produced by the thyroid gland?

T3 and T4

How are T3 and T4 synthesized?

By combining iodine with the amino acid tyrosine.

What is the effect of T3 and T4 on the body?

Increase the metabolic rate in nearly every cell.

What hormone regulates the thyroid gland?

Thyroid-stimulating hormone from the anterior pituitary.

What hormone is responsible for lowering blood calcium levels?

Calcitonin

What are the primary hormones produced by the thyroid gland?

T₃ (triiodothyronine), T₄ (thyroxine), and calcitonin.

How do T₃ and T₄ affect the body's metabolic rate?

They increase the metabolic rate by enhancing cellular respiration and glucose utilization.

What is the feedback mechanism that regulates T₃ and T₄ levels?

Negative feedback that inhibits the release of thyroid-releasing hormone and thyroid-stimulating hormone when hormone levels are high.

What condition results from low levels of T₃ and T₄?

Hypothyroidism, leading to symptoms like cold intolerance, weight gain, and fatigue.

What severe condition can result from hypothyroidism in children?

Cretinism, which involves delayed growth and mental development.

What condition results from high levels of T₃ and T₄?

Hyperthyroidism, leading to symptoms like heat intolerance, weight loss, and anxiety.

What is the role of calcitonin?

To lower blood calcium levels by increasing calcium excretion by the kidneys, decreasing gut absorption, and increasing bone storage.

What hormone is secreted by the parathyroid glands?

Parathyroid hormone (PTH).

What is the primary function of parathyroid hormone?

To raise blood calcium levels.

How does parathyroid hormone increase blood calcium levels?

By stimulating bone resorption, increasing calcium reabsorption in the kidneys, and activating vitamin D.

What is the relationship between calcitonin and parathyroid hormone?

Calcitonin lowers blood calcium levels, while parathyroid hormone raises them.

What are the two main parts of the adrenal glands?

The adrenal cortex and the adrenal medulla.

What types of hormones does the adrenal cortex produce?

Glucocorticoids, mineralocorticoids, and cortical sex hormones.

What is the function of glucocorticoids?

To increase blood glucose levels, reduce protein synthesis, and suppress the immune system.

What triggers the release of glucocorticoids?

Adrenocorticotropic hormone (ACTH) from the anterior pituitary.

What is the primary mineralocorticoid produced by the adrenal cortex?

Aldosterone.

How does aldosterone affect blood pressure?

By promoting sodium reabsorption in the kidneys, which increases blood volume and pressure.

What system regulates aldosterone secretion?

The renin-angiotensin-aldosterone system.

What hormones are classified as catecholamines?

Epinephrine (adrenaline) and norepinephrine (noradrenaline).