Overview of the Endocrine System and Hormones

What is the primary function of the endocrine system?

To control growth and development, energy regulation, internal homeostasis, and reproduction through hormone release.

Name the six major glands of the endocrine system.

Hypothalamus, Pituitary gland, Thyroid gland, Adrenal glands, Ovaries, Testes.

What are hormones?

Chemical signals produced in the body that communicate from cell to cell, released into the bloodstream to target tissue receptors.

List three functions of hormones in the body.

1. Rate of enzymatic reactions 2. Transport of ions or molecules across cell membranes 3. Gene expression and protein synthesis.

What are the four types of hormones?

Amine, Peptide, Protein, Steroid.

What are Amine hormones derived from?

Amino acids, specifically tryptophan or tyrosine.

What is the difference between thyroid hormones and catecholamines?

Thyroid hormones (like T3 and T4) have mostly nuclear receptors and a long half-life, while catecholamines (like epinephrine and norepinephrine) have cell surface receptors and a short half-life.

What are peptide hormones made of?

Long chains of amino acids.

How are peptide/protein hormones synthesized and activated?

Synthesized as large precursors, stored in secretory vesicles, cleaved into prohormones, then converted to active hormones.

What type of receptors do peptide/protein hormones use?

Cell-surface receptors that activate secondary messengers or signal transduction pathways.

What are steroid hormones synthesized from?

Cholesterol.

How do steroid hormones interact with cells?

They are lipophilic, can easily cross cell membranes, and bind to nuclear or cytoplasmic receptors.

What is the rate-limiting step in steroid hormone synthesis?

The conversion of cholesterol to pregnenolone.

How do steroid hormones increase their half-life in the bloodstream?

By binding to carrier proteins.

What is the difference between genomic and non-genomic actions of steroid hormones?

Genomic actions involve binding to DNA and changing gene expression, while non-genomic actions occur quickly without altering DNA.

What happens when a steroid hormone binds to its receptor?

The hormone-receptor complex binds to DNA, activating or repressing specific genes.

What is the role of G-proteins in peptide/protein hormone signaling?

They activate secondary messenger systems or amplify enzyme activity in response to hormone binding.

What is the typical half-life of peptide/protein hormones?

Short half-life.

What is the function of oxytocin?

It is a peptide hormone involved in childbirth and lactation.

What role do catecholamines play in the body?

They are involved in the body's fight-or-flight response, affecting heart rate and energy mobilization.

What is the role of insulin in the endocrine system?

It regulates glucose levels in the blood and is a protein hormone.

What is the function of aldosterone?

It regulates sodium and potassium levels, affecting blood pressure and fluid balance.

What happens when the receptor hormone complex binds to DNA?

It activates or represses one or more genes, leading to the creation of mRNA that moves into the cytoplasm to make new proteins.

What are the three pathways of hypothalamus-pituitary control?

1. Hypothalamus-Pituitary-Thyroid (HPT) 2. Hypothalamus-Pituitary-Adrenal (HPA) 3. Hypothalamus-Pituitary-Gonadal (HPG)

What is the role of releasing/inhibiting hormones from the hypothalamus?

They act on a subpopulation of cells in the anterior pituitary to help control hormone release.

What are some examples of releasing hormones from the hypothalamus?

GHRH (Growth Hormone Releasing Hormone), CRH (Corticotropin Releasing Hormone), TRH (Thyrotropin Releasing Hormone), GnRH (Gonadotropin Releasing Hormone).

What hormones do lactotrophs produce?

Lactotrophs produce prolactin, which acts on the mammary glands.

What is the function of growth hormone (GH)?

GH stimulates growth and has anabolic actions, including raising glucose levels and promoting lipolysis.

What is the role of thyrotrophs in the endocrine system?

Thyrotrophs release TSH (Thyroid Stimulating Hormone), which stimulates the thyroid gland to release T3 and T4.

What hormones do gonadotrophs secrete, and what are their functions?

Gonadotrophs secrete LH (Luteinizing Hormone) and FSH (Follicle Stimulating Hormone), which are needed for ovulation and spermatogenesis.

How does GnRH affect FSH and LH levels?

GnRH controls the release of FSH and LH, which increase after puberty.

What is the effect of FSH in males and females?

In females, FSH promotes follicle development; in males, it stimulates spermatogenesis and acts on Sertoli cells.

What is the role of LH in the reproductive system?

LH regulates gonadal steroid hormone production, stimulates androgen production in the testes, and induces ovulation in females.

What is Chorionic Gonadotropin (hCG) and its significance?

hCG is the human pregnancy hormone secreted by the placenta after embryo implantation and is the basis for most pregnancy tests.

What is the primary function of prolactin?

Prolactin is responsible for lactation and is controlled by the hypothalamus, which exerts both positive and negative control over its release.

How does prolactin concentration change during pregnancy?

Prolactin concentration increases 20 to 40 times to prepare the mammary glands for lactation.

What is the relationship between prolactin and dopamine?

Dopamine inhibits prolactin secretion; dopamine antagonists increase prolactin levels, while agonists decrease it.

What is somatotropin?

Somatotropin is another name for growth hormone, which acts as a stress hormone and has anabolic effects.

What are the effects of dopamine antagonists on prolactin levels?

Dopamine antagonists, such as opiates and antipsychotics, increase prolactin secretion.

What are the effects of dopamine agonists on prolactin levels?

Dopamine agonists, such as levodopa and bromocriptine, decrease prolactin secretion.

What is the role of corticotrophs in the endocrine system?

Corticotrophs synthesize and release ACTH (Adrenocorticotropic Hormone), which stimulates the adrenal cortex.

How do peptide hormones from the anterior pituitary enter the bloodstream?

They are released into the capillaries of the portal system and then enter the bloodstream to act on target organs.

What is the function of the hypothalamus in the neuroendocrine system?

The hypothalamus releases regulatory hormones that control the release of hormones from the anterior pituitary.

What is the significance of the hypothalamus-pituitary axis?

It is a critical regulatory system that controls various endocrine functions and maintains homeostasis in the body.

What is the primary function of growth hormone (GH)?

To raise glucose levels, promote lipolysis, and support anabolic actions.

What percentage of pituitary hormones does growth hormone represent?

10-15%.

What is the half-life of growth hormone?

20-25 minutes.

How does growth hormone increase its half-life for transport?

By binding to specific plasma proteins.

What regulates the secretion of growth hormone?

The hypothalamus.

What is the role of Growth Hormone Releasing Hormone (GHRH)?

It stimulates the release of growth hormone by binding to receptors on somatotrophs in the anterior pituitary.

What factors can increase growth hormone secretion?

Decreased blood glucose, increased blood amino acids (especially arginine and leucine), GHRH, TRH, ADH, ghrelin, glucagon, dopamine, exercise, stress, sleep, and puberty.

What is the function of somatostatin (GHRIH) in relation to growth hormone?

It blocks growth hormone release and inhibits various endocrine and exocrine glands.

What feedback mechanism decreases growth hormone levels?

Increased levels of somatostatin and IGF-1, along with increased blood glucose.

What are some conditions that can lead to decreased growth hormone levels?

Dopamine antagonists, emotional deprivation in children, and aging.

How often is growth hormone released throughout the day?

6-8 discrete pulses per day.

When is the most pronounced pulse of growth hormone release observed?

After the onset of deep sleep.

What physiological effects does growth hormone have on growth?

It promotes growth in tissues except for the brain and eyes, makes bones longer, builds cartilage, collagen, and muscle.

How does growth hormone affect protein synthesis?

It increases amino acid utilization to build proteins and decreases urea loss, promoting a positive nitrogen balance.

What is the effect of growth hormone on carbohydrate and fat metabolism?

It burns fat for energy, increases lipolysis, and raises blood sugar levels.

How does growth hormone's action compare to insulin?

Growth hormone raises blood sugar, while insulin lowers blood sugar and promotes fat storage.

What stimulates the release of growth hormone?

Exercise and low blood sugar (hypoglycemia).

Where is growth hormone produced and stored?

In somatotrophs in the anterior pituitary.

What are insulin-like growth factors (IGFs) and their role?

IGFs are hormones that mediate the growth effects of GH, primarily produced in the liver.

What are the two main types of IGFs?

IGF-1 and IGF-2.

What is the significance of IGF-1 in fetal development?

It is important for growth in bones and body and supports brain, liver, and kidney function in adults.

Which hormones stimulate IGF-1 production?

Prolactin, insulin, thyroid hormone, glucocorticoids, estrogen, and testosterone.

What are the three types of hormones based on their action on target cells?

Regulatory hormones (from hypothalamus), tropic hormones (from anterior pituitary), and non-tropic hormones (from endocrine glands).

What is synergism in hormone action?

The combined effect of hormones is greater than the individual effects.

What is permissiveness in hormone action?

A second hormone is needed to achieve the full effect of the first hormone.

What is antagonism in hormone action?

One substance opposes another, which can involve competitive inhibitors or functional antagonism.