Untitled Flashcards Set

What is the fundamental structure of the endocrine system?

The endocrine system is a vital regulatory system composed of specialized ductless glands that secrete chemical messengers called hormones directly into the bloodstream.

What is the overarching function of the endocrine system?

Its primary function is to regulate and coordinate a wide array of long-term physiological processes throughout the body, including metabolism, growth and development, reproduction, fluid and electrolyte balance, and even mood and behavior.

What are hormones in the context of the endocrine system?

Hormones are chemical messengers secreted by endocrine glands. They travel through the bloodstream to distant target cells and organs, where they bind to specific receptors to elicit a biological response.

What is a defining characteristic of endocrine glands?

Endocrine glands are characterized by being ductless, meaning they secrete hormones directly into the surrounding interstitial fluid, from which the hormones diffuse into the bloodstream, rather than releasing them through ducts (like exocrine glands).

How do hormones primarily travel throughout the body?

Hormones are transported via the bloodstream, allowing them to reach virtually all cells in the body, but they only exert their effects on specific target cells that possess the appropriate receptor proteins.

Describe the 'lock and key' principle in hormone action.

Hormones function as highly specific chemical signals. Upon reaching their target cells, they bind to particular receptor proteins in a 'lock and key' fashion, meaning each hormone typically fits only a specific type of receptor.

What are hormone receptor proteins?

Receptor proteins are specialized molecules, usually proteins, located either on the cell surface or inside the cell, that selectively bind to hormones. This binding triggers a specific cellular response.

What happens after a hormone binds to its receptor?

The binding of a hormone to its specific receptor initiates a precise cascade of intracellular events. This can lead to various alterations in the target cell's activity, such as changes in enzyme activity, protein synthesis, gene expression, or membrane permeability.

Where are hormone receptors typically located for water-soluble vs. lipid-soluble hormones?

Water-soluble hormones bind to receptors located on the exterior surface of the target cell membrane, as they cannot easily pass through the lipid bilayer. Lipid-soluble hormones, however, bind to intracellular receptors located in the cytoplasm or nucleus, as they can diffuse directly through the cell membrane.

Name the three primary chemical classes of hormones.

The three primary types of hormones based on their chemical structure are: Steroid Hormones, Peptide/Protein Hormones, and Amino Acid Derivative Hormones.

What are steroid hormones and what is their primary chemical characteristic?

Steroid hormones are lipid-soluble hormones derived from cholesterol. Their lipid nature enables them to easily pass through cell membranes.

Provide examples of steroid hormones.

Examples of steroid hormones include cortisol, estrogen, testosterone, progesterone, and aldosterone.

What are peptide/protein hormones and what is their solubility characteristic?

Peptide/protein hormones are composed of chains of amino acids, ranging from a few amino acids (peptides) to large, complex protein structures. They are generally water-soluble.

Provide examples of peptide/protein hormones.

Common examples of peptide/protein hormones include insulin, growth hormone (GH), antidiuretic hormone (ADH), calcitonin, and parathyroid hormone (PTH).

What are amino acid derivative hormones?

Amino acid derivative hormones are modified amino acids. Their solubility varies depending on the specific hormone.

Give examples of amino acid derivative hormones and note their solubility variations.

Examples include thyroid hormones (thyroxine, T4 and triiodothyronine, T3), which are lipid-soluble, and catecholamines (epinephrine and norepinephrine), which are water-soluble.

How do lipid-soluble hormones enter a target cell?

Lipid-soluble hormones readily diffuse directly through the lipid bilayer of the target cell membrane due to their nonpolar nature.

Where do lipid-soluble hormones bind inside the cell?

Once inside the target cell, lipid-soluble hormones bind to specific intracellular receptors, which can be located either in the cytoplasm or within the nucleus.

What is the next step after a lipid-soluble hormone binds to its intracellular receptor?

The hormone-receptor complex then translocates to the nucleus (if not already there) and directly interacts with specific DNA sequences known as hormone response elements (HREs).

How do lipid-soluble hormones influence gene expression?

By binding to HREs, the hormone-receptor complex acts as a transcription factor, either promoting or inhibiting the transcription of specific genes, leading to changes in gene expression.

What is the ultimate outcome of lipid-soluble hormone action on the cell?

The altered gene expression results in the increased or decreased synthesis of specific proteins (e.g., enzymes, structural proteins), which then mediate the long-term cellular response.

Why can't water-soluble hormones directly enter target cells?

Water-soluble hormones, such as most peptide/protein hormones and catecholamines, cannot pass directly through the lipid bilayer of the cell membrane because they are polar molecules.

Where do water-soluble hormones bind on target cells?

Instead of entering the cell, water-soluble hormones bind to specific receptor proteins located on the exterior surface of the target cell membrane.

What do cell-surface receptors activate upon hormone binding?

This binding activates complex intracellular signaling pathways inside the cell. These pathways often involve intermediary molecules called second messengers.

What are second messengers in the context of hormone action?

Second messengers are small, non-protein molecules that relay and amplify the signal from the hormone (the 'first messenger') from the cell surface into the cell's interior.

Name some common second messengers involved in water-soluble hormone signaling.

Common examples of second messengers include cyclic AMP (cAMP), calcium ions (Ca^{2+}), and inositol triphosphate (IP_3).

What is the general effect of second messengers inside the cell?

The second messengers then trigger a cascade of events within the cell, often involving the activation of enzymes (like protein kinases), leading to a rapid and amplified cellular response.

Which brain region is recognized as the major neuroendocrine control center?

The Hypothalamus is the central brain region that effectively serves as the chief neuroendocrine control center, acting as the critical link between the nervous system and the endocrine system.

How does the hypothalamus bridge the nervous and endocrine systems?

The hypothalamus connects the nervous and endocrine systems by receiving neural signals and translating them into hormonal signals, thereby regulating the activity of many endocrine glands.

How does the hypothalamus primarily control the anterior pituitary gland?

It directly controls the anterior pituitary by producing various releasing and inhibiting hormones that travel to the pituitary via a specialized blood vessel system.

Which two hormones does the hypothalamus produce for the posterior pituitary gland?

It synthesizes Antidiuretic Hormone (ADH) and Oxytocin in specific neurosecretory cells. These hormones are then transported via axons to the posterior pituitary for storage and release.

What specialized vascular system facilitates communication between the hypothalamus and anterior pituitary?

The communication occurs via the hypothalamo-hypophyseal portal system, a specialized network of capillaries and veins that directly connects the hypothalamus to the anterior pituitary.

What types of hormones are transported by the hypothalamo-hypophyseal portal system and why is this direct transport important?

This portal system allows hypothalamic releasing and inhibiting hormones (e.g., TRH, GnRH, GHRH) to travel directly and rapidly to the anterior pituitary, regulating its hormone secretion without entering the general circulation.

What is Growth Hormone (GH) and which gland secretes it?

Growth Hormone (GH), also known as somatotropin, is a protein hormone secreted by the anterior pituitary gland.

What are the main growth-promoting functions of Growth Hormone?

Its primary role is to promote general somatic growth throughout the body by stimulating processes like protein synthesis, cell division (mitosis), and overall tissue repair.

How does Growth Hormone influence metabolism?

Beyond growth, GH significantly influences metabolism by promoting fat breakdown (lipolysis) for energy and conserving glucose for vital organs, thereby increasing blood glucose levels.

What condition is caused by low Growth Hormone secretion in childhood?

Pituitary Dwarfism is a condition resulting from the hyposecretion (insufficient production) of Growth Hormone (GH) during childhood or adolescence.

What are the characteristics of pituitary dwarfism and when does it manifest?

It occurs before the epiphyseal growth plates of bones have closed, leading to proportionally small stature. The individual is much shorter than average, but their body proportions remain normal.

What condition results from excessive Growth Hormone secretion in adulthood?

Acromegaly is a medical condition caused by the hypersecretion (excessive production) of Growth Hormone (GH) during adulthood.

When does acromegaly typically develop in a person's life?

It occurs specifically after the epiphyseal growth plates of long bones have already fused. Therefore, longitudinal bone growth is not possible.

What are the characteristic physical signs and symptoms of acromegaly?

Acromegaly leads to the enlargement of bones in the face (e.g., jaw, nose, forehead), hands, and feet, along with the thickening of soft tissues, resulting in noticeable changes in appearance and potential organ enlargement.

How does acromegaly differ from gigantism?

Unlike gigantism (which results from GH hypersecretion in childhood, causing overall excessive height), acromegaly's effects are primarily on bone thickness and soft tissue enlargement, as long bones have already fused.

What is TSH and which gland produces it?

Thyroid-Stimulating Hormone (TSH), also known as thyrotropin, is a glycoprotein hormone secreted by the anterior pituitary gland.

What is the main function of Thyroid-Stimulating Hormone (TSH)?

Its primary function is to stimulate the thyroid gland to synthesize and release its key thyroid hormones: thyroxine (T4)** and triiodothyronine (T3).

What are the key physiological roles of the thyroid hormones stimulated by TSH?

Thyroid hormones (T3 and T4) are critical regulators of the body's basal metabolic rate (BMR), influencing energy production, cell differentiation, growth, and neurological development.

What is ACTH and where is it produced?

Adrenocorticotropic Hormone (ACTH), also known as corticotropin, is a peptide hormone secreted by the anterior pituitary gland.

What is the main target and function of Adrenocorticotropic Hormone (ACTH)?

Its primary function is to stimulate the adrenal cortex (the outer layer of the adrenal glands) to produce and secrete its own group of steroid hormones, particularly the glucocorticoids.

Which specific hormone is most notably stimulated by ACTH, and what are its key functions?

The most notable glucocorticoid stimulated by ACTH is cortisol. Cortisol plays essential roles in the body's stress response, glucose metabolism, and the modulation of inflammatory and immune reactions.

Which two hormones are classified as gonadotropins and secreted by the anterior pituitary?

The two gonadotropins secreted by the anterior pituitary gland are Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH).

What is the general role of gonadotropins?

Their general function in both males and females is to regulate the diverse functions of the gonads (the testes in males and the ovaries in females).

What are the specific functions of Follicle-Stimulating Hormone (FSH) in males and females?

In males, FSH stimulates spermatogenesis (sperm production) in the seminiferous tubules. In females, FSH promotes the development of ovarian follicles and stimulates the secretion of estrogen by these follicles.

What are the specific functions of Luteinizing Hormone (LH) in males and females?

In males, LH stimulates the Leydig cells in the testes to produce and secrete testosterone and other androgens. In females, LH triggers ovulation (release of the egg) and promotes the formation and maintenance of the corpus luteum, which secretes progesterone and some estrogen.

What is Prolactin (PRL) and which gland secretes it?

Prolactin (PRL) is a protein hormone secreted by the anterior pituitary gland.

What is the main function of Prolactin?

Its primary function is to directly stimulate and maintain milk production (lactation) in the mammary glands after childbirth.

How is Prolactin secretion uniquely regulated?

Unlike many other anterior pituitary hormones, Prolactin's secretion is largely inhibited by dopamine, which is also known as Prolactin-Inhibiting Hormone (PIH) and is released from the hypothalamus.

Which hormones are produced in the hypothalamus but stored and released by the posterior pituitary?

The two hormones synthesized by specific neurosecretory cells in the hypothalamus but released by the posterior pituitary are Antidiuretic Hormone (ADH), also known as vasopressin, and Oxytocin.

Where specifically in the hypothalamus are ADH and Oxytocin synthesized, and how do they reach the posterior pituitary?

These hormones are produced in the supraoptic and paraventricular nuclei of the hypothalamus and then transported down the axons of these neurosecretory cells to the posterior pituitary, which acts as a storage and release site.

What is the primary function of Antidiuretic Hormone (ADH)?

Antidiuretic Hormone (ADH), also known as vasopressin, is a peptide hormone whose primary function is to increase water reabsorption in the kidneys.

How does ADH increase water reabsorption in the kidneys?

ADH achieves this by promoting the insertion of specialized water channels called aquaporins into the membranes of the collecting ducts and distal convoluted tubules in the kidneys.

What are the typical physiological conditions that stimulate ADH release?

This action reduces the volume of urine produced and consequently conserves body water, which is crucial in response to increased plasma osmolarity (indicating dehydration) or decreased blood volume/pressure.

What are the two most well-known reproductive functions of Oxytocin?

Oxytocin is a peptide hormone primarily known for its roles in stimulating powerful uterine contractions during childbirth (parturition) and facilitating the milk ejection reflex (let-down reflex) during breastfeeding.

What are some lesser-known, yet significant, social roles of Oxytocin?

Beyond its reproductive roles, oxytocin is increasingly recognized for its contributions to social bonding, trust, empathy, and parental behaviors, often referred to as the 'love hormone'.

Define a 'negative feedback loop' in endocrine regulation.

A negative feedback loop is a regulatory mechanism where the output or product of a process inhibits or reduces the original stimulus, thereby stabilizing the system and maintaining homeostasis.

Provide a classic example of a negative feedback loop in the endocrine system.

The regulation of thyroid hormones provides a classic example: High levels of thyroid hormones (T3 and T4) inhibit the release of Thyrotropin-Releasing Hormone (TRH) from the hypothalamus and Thyroid-Stimulating Hormone (TSH) from the anterior pituitary.

How do thyroid hormones participate in their own negative feedback regulation?

This inhibition reduces the hypothalamic and pituitary stimulation of the thyroid gland, leading to a decrease in T3 and T4 production, thus maintaining stable thyroid hormone levels.

Define a 'positive feedback loop' in the context of endocrine regulation.

A positive feedback loop is a regulatory mechanism where the output or product of a process intensifies, amplifies, or reinforces the original stimulus, driving the physiological parameter further away from its initial set point.

What is the usual physiological purpose or outcome of a positive feedback loop?

Positive feedback loops typically lead to a rapid and escalating event or outcome, rather than maintaining equilibrium.

Provide a compelling example of a positive feedback loop in the endocrine system.

A prominent example is the release of oxytocin during childbirth: uterine contractions stimulate nerve endings that signal the hypothalamus to release more oxytocin from the posterior pituitary.

How does the oxytocin feedback loop during childbirth exemplify positive feedback?

This increased oxytocin then causes stronger and more frequent uterine contractions, which in turn leads to even more oxytocin release, creating a self-amplifying cycle.

When does the positive feedback loop of oxytocin during childbirth terminate?

This positive feedback cycle continues to build in intensity until the baby is delivered, thereby removing the initial stimulus (stretch of the cervix), and bringing the process to an end.