Endocrine System: Glands, Hormones, and Regulation

What are the two major control systems that regulate the human body?

The endocrine system and the nervous system.

What do endocrine glands synthesize and secrete?

Hormones.

What are target cells?

Cells that have specific receptors for a hormone.

How do hormones enter the bloodstream?

They are released from endocrine gland cells into the interstitial fluid and then enter capillaries.

What is the difference between endocrine and exocrine glands?

Endocrine glands lack ducts and release hormones directly into the blood, while exocrine glands release their secretions into ducts.

What are the two types of responses initiated by hormones?

Activating or inhibiting selective metabolic activities.

How do the nervous and endocrine systems compare in terms of response time?

The nervous system initiates responses rapidly, while the endocrine system initiates responses slowly.

What is the duration of responses in the nervous system compared to the endocrine system?

Nervous responses are short-duration, while endocrine responses are long-duration.

What is the primary function of hormones in regulating development?

They have regulatory roles in cell division and metabolism during development and growth.

How do hormones maintain blood composition and volume?

They regulate specific substances in blood plasma, including glucose and ions.

What role do hormones play in digestive processes?

They influence secretory processes and movement through the gastrointestinal tract.

What is an endocrine organ?

A single organ that is entirely endocrine in function, such as the pituitary or thyroid gland.

What are the three types of stimulation that can initiate hormone release?

Hormonal, humoral, and nervous system stimulation.

What is an example of hormonal stimulation?

Thyroid-stimulating hormone binding to the thyroid gland to release thyroid hormone.

What is humoral stimulation?

Release of hormones in response to changing levels of nutrients or ions in the blood.

What is an example of nervous system stimulation of hormone release?

Release of epinephrine and norepinephrine by the adrenal medulla.

What are circulating hormones?

Hormones that are transported within the blood.

What are the three categories of circulating hormones based on chemical structure?

Steroids, biogenic amines, and proteins.

What are local hormones?

Short-lived signaling molecules that influence nearby cells and do not circulate in the blood.

What is autocrine stimulation?

When a local hormone binds to the same cell that produced it.

What is paracrine stimulation?

When a local hormone binds to neighboring cells.

How do lipid-soluble hormones travel in the blood?

They require transport proteins due to their nonpolar nature.

What is the difference between bound and unbound hormones?

Bound hormones are attached to transport proteins, while unbound hormones are free in the blood.

How do water-soluble hormones travel in the blood?

They dissolve readily in the blood and do not generally require transport proteins.

How are water-soluble hormones transported to target cells?

They are released directly into the blood.

What is the role of transport proteins for some water-soluble hormones?

They prolong the biological half-life of these hormones.

What physiological effects do hormones exert?

They exert effects primarily as a result of their blood concentration.

What can low blood levels of thyroid hormone cause?

Decreased metabolic rate.

What condition can high blood levels of growth hormone cause?

Gigantism.

What two factors influence blood hormone concentration?

Hormone release and hormone elimination.

How does hormone release affect blood concentration?

An increase in hormone release results in higher blood concentration.

What are the three main methods of hormone elimination?

Enzymatic degradation, excretion by kidneys, and uptake into target cells.

What is the biological half-life of a hormone?

The time necessary to reduce hormone concentration in the blood to half of its original amount.

How is hormone release typically regulated?

Through negative feedback mechanisms.

What is an example of positive feedback in hormone release?

The continuous release of oxytocin during childbirth.

What is the role of the hormone-receptor complex?

It binds to a specific DNA sequence called a hormone-response element (HRE).

How do lipid-soluble hormones enter target cells?

By simple diffusion across the plasma membrane.

What initiates a signal transduction pathway for water-soluble hormones?

The binding of the hormone to a plasma membrane receptor.

What is the first messenger in a signal transduction pathway?

The hormone that binds to the receptor.

What is the role of the second messenger in a signal transduction pathway?

It modifies the activity of intracellular target proteins.

What is the function of G proteins in hormone signaling?

They bind guanine nucleotides and activate other enzymes like adenylate cyclase.

What does activated adenylate cyclase produce?

cAMP, which activates protein kinases.

What are the two secondary messenger molecules produced by phospholipase C?

DAG (diacylglycerol) and IP3 (inositol triphosphate).

What effect does IP3 have on intracellular calcium levels?

It increases intracellular calcium concentration.

How does the number of receptors on a target cell affect its response to hormones?

It influences the degree of cellular response.

What is up-regulation in the context of hormone receptors?

Increasing the number of receptors to enhance sensitivity to a hormone.

What is down-regulation in the context of hormone receptors?

Decreasing the number of receptors to reduce sensitivity to a hormone.

What factors can influence the number of hormone receptors on a target cell?

Changes in hormone concentration, developmental maturity, activity state, and cell cycle stages.

What happens to a secretory cell when it matures?

It may become less responsive to growth hormone and develop the ability to respond to hormones that stimulate it to secrete its product.

What is a synergistic interaction in hormone signaling?

It occurs when the activity of one hormone reinforces the activity of another hormone.

Give an example of synergistic hormone interaction.

Reproductive structures are more powerfully influenced by both estrogen and progesterone than by either hormone alone.

What is a permissive interaction in hormone signaling?

It occurs when the activity of one hormone requires a second hormone to function.

Provide an example of a permissive hormone interaction.

Prolactin is required for milk production, while oxytocin is required for milk ejection.

What is an antagonistic interaction in hormone signaling?

It occurs when the activity of one hormone opposes the effects of another hormone.

Give an example of antagonistic hormone interaction.

Insulin and glucagon have opposing effects on blood glucose levels.

What is the primary role of the hypothalamus in the endocrine system?

It functions as the master control of the endocrine system by regulating hormone release from the pituitary gland.

What are the two lobes of the pituitary gland?

The posterior pituitary and the anterior pituitary.

What type of cells compose the posterior pituitary?

Neurons.

What type of cells compose the anterior pituitary?

Hormone-producing endocrine cells.

What hormones are stored in the posterior pituitary?

Antidiuretic hormone (ADH) and oxytocin.

Where are ADH and oxytocin synthesized?

In the hypothalamus.

What is the function of antidiuretic hormone (ADH)?

To help maintain fluid balance, blood volume, and blood pressure.

What are releasing hormones (RHs)?

Hormones produced by the hypothalamus that stimulate the production and secretion of specific anterior pituitary hormones.

What are inhibiting hormones (IHs)?

Hormones produced by the hypothalamus that decrease the production and secretion of specific anterior pituitary hormones.

What is growth hormone (GH) also known as?

Somatotropin.

What does growth hormone stimulate?

The liver to release insulin-like growth factors (IGF-1 and IGF-2) that promote cell growth and division.

What does thyroid-stimulating hormone (TSH) do?

Stimulates growth of the thyroid gland and the release of thyroid hormone (TH).

What is the function of adrenocorticotropic hormone (ACTH)?

Stimulates the adrenal cortex to produce and secrete glucocorticoids like cortisol.

What do follicle-stimulating hormone (FSH) and luteinizing hormone (LH) regulate?

The development of oocytes and sperm, and the release of sex hormones in the gonads.

What is the primary function of prolactin (PRL)?

To regulate mammary gland growth and breast milk production.

What are tropic hormones?

Hormones released from the anterior pituitary that target other endocrine glands.

What is the largest endocrine gland in the body?

The thyroid gland.

What are thyroid follicles?

Microscopic structures in the thyroid gland composed of follicular cells surrounding a colloid-filled lumen.

What do parafollicular cells in the thyroid gland produce?

Calcitonin.

What hormones does the adrenal medulla release?

Epinephrine and norepinephrine.

What stimulates the release of catecholamines from the adrenal medulla?

Activation by the sympathetic division during stress.

What are the three regions of the adrenal cortex?

Zona glomerulosa, zona fasciculata, and zona reticularis.

What do mineralocorticoids regulate?

The composition and concentration of electrolytes in body fluids.

What hormones do mineralocorticoids regulate?

They help regulate the composition and concentration of electrolytes in body fluids.

What is the principal mineralocorticoid?

Aldosterone

What does aldosterone regulate?

The reabsorption of sodium and the elimination of potassium.

What is the largest region of the adrenal cortex?

The zona fasciculata

What hormones are synthesized in the zona fasciculata?

Glucocorticoids, primarily cortisol and corticosterone.

What triggers the release of cortisol?

ACTH (Adrenocorticotropic hormone)

How does cortisol affect blood nutrient levels?

It increases glucose, fatty acids, and amino acids in the blood.

What is the effect of cortisol on liver cells?

It stimulates glycogenolysis and gluconeogenesis while decreasing glycogenesis.

What is the role of cortisol in adipocytes?

It increases lipolysis and decreases lipogenesis.

What is the primary function of glucagon?

To raise blood glucose levels, especially in response to low blood glucose.

What is the primary endocrine function of the pancreas?

To maintain blood glucose levels within a healthy range of 70 to 110 mg/dL.

What are the two primary hormones released from the pancreas?

Insulin and glucagon.

What type of cells in the pancreas secrete insulin?

Beta cells.

What is the function of the pineal gland?

To secrete melatonin, which regulates circadian rhythms.

What hormone does the parathyroid gland secrete?

Parathyroid hormone (PTH).

What triggers the release of parathyroid hormone?

A decrease in blood calcium levels.

What is the effect of parathyroid hormone on blood calcium levels?

It increases blood calcium levels.

What is the role of erythropoietin (EPO)?

To stimulate red bone marrow to increase erythrocyte production.

What hormone does adipose tissue release?

Leptin.

What is the function of leptin?

To regulate food intake and energy balance.

What hormone is released in response to increased stretch of the atrial wall?

Atrial natriuretic peptide (ANP).

What is the primary function of angiotensin II?

To increase blood pressure.