Marieb Human Anatomy & Physiology Chapter 16: The Endocrine System Flashcards

Comprehensive 200-card practice deck covering Chapter 16 (The Endocrine System) from Marieb's Human Anatomy & Physiology, Twelfth Edition.

How does the endocrine system interact with the nervous system to control body functions?

It interacts with the nervous system to coordinate and integrate the activity of most body cells.

What chemical messengers does the endocrine system use to influence cellular metabolic activities?

Hormones transported in blood.

How do endocrine responses compare to nervous system responses regarding speed and duration?

Endocrine responses are slower to initiate but longer lasting than nervous system responses.

What is endocrinology defined as?

The study of hormones and endocrine organs.

How does the initiation speed of responses compare between the nervous and endocrine systems?

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

How does the duration of responses compare between the nervous system and the endocrine system?

The nervous system produces short-duration responses, whereas the endocrine system produces long-duration responses.

What mediators are used by the nervous system versus the endocrine system?

The nervous system acts via action potentials and neurotransmitters, whereas the endocrine system acts via hormones released into the blood.

How do the target locations differ between the nervous system and the endocrine system?

The nervous system acts at specific locations determined by axon pathways, while the endocrine system acts at diffuse locations wherever blood reaches.

Over what distance do neurotransmitters act compared to hormones?

Neurotransmitters act over very short distances, whereas hormones act over long distances.

How is signal strength coded in the nervous system versus the endocrine system?

Signal strength is coded by the frequency of action potentials in the nervous system and by the concentration of hormone in the endocrine system.

What five major physiological processes are controlled and integrated by the endocrine system?

Reproduction, growth and development, maintenance of electrolyte/water/nutrient balance in blood, regulation of cellular metabolism/energy balance, and mobilization of body defenses.

How do exocrine glands differ structurally and functionally from endocrine glands?

Exocrine glands produce nonhormonal substances and have ducts to membrane surfaces, whereas endocrine glands are ductless and secrete hormones directly into surrounding extracellular fluid.

Which five glands are classified strictly as pure endocrine glands?

Pituitary, thyroid, parathyroid, adrenal, and pineal glands.

Why is the hypothalamus described as a neuroendocrine organ?

Because it performs neural functions in addition to producing and secreting hormones.

What organs are noted for containing endocrine tissue within other functional systems?

Pancreas, gonads, and placenta.

Which non-endocrine organs or tissues produce hormones in addition to their primary functions?

Stomach, intestine, heart, kidneys, skin, thymus, bone, and adipose tissue.

What are autocrines?

Local chemicals that exert their effects on the same cells that secrete them.

What are paracrines?

Locally acting chemicals that affect neighboring cells other than those that secrete them.

Why are autocrines and paracrines not considered part of the endocrine system?

Because they are local chemical messengers that do not travel long distances in the blood.

What three properties of a hormone are determined by its chemical structure and water solubility?

How it is transported in the blood, how long it takes to be degraded, and which receptors it acts upon.

What are the two main chemical classes of hormones?

Amino acid–based hormones and steroids.

What chemical subcategories make up amino acid-based hormones?

Amino acid derivatives, peptides, and proteins.

What major amino acid–based hormone is an exception to the rule that amino acid hormones are water soluble?

Thyroxine (thyroid hormone).

From what organic compound are steroid hormones synthesized?

Cholesterol.

Which hormone categories are classified as steroids?

Gonadal and adrenocortical hormones.

Why are eicosanoids classified by most scientists as paracrines/autocrines rather than true hormones?

Due to their highly localized effects.

What is a target cell?

A tissue cell that possesses specific receptors for a given hormone.

List five target cell changes typically produced by hormone binding.

Altering membrane permeability/potential, stimulating protein/enzyme synthesis, activating/deactivating enzymes, inducing secretory activity, and stimulating mitosis.

How do water-soluble hormones interact with target cells?

They act on plasma membrane receptors coupled via G proteins to second messengers because they cannot cross the plasma membrane.

How do lipid-soluble hormones interact with target cells?

They diffuse across the plasma membrane and act on intracellular receptors that directly activate genes.

Which hormones are classified as lipid-soluble?

Steroid hormones and thyroid hormones.

In the cyclic AMP (cAMP) signaling mechanism, what is the first messenger?

The hormone itself.

What is the sequence of activation in the cAMP second-messenger system?

Hormone binds receptor -> Receptor activates G protein -> G protein activates adenylate cyclase -> Adenylate cyclase converts ATP to cAMP -> cAMP activates protein kinases.

What action do protein kinases perform once activated by cAMP?

They phosphorylate (add a phosphate to) other proteins, either activating or inactivating them.

What enzyme rapidly degrades cAMP to stop its intracellular response cascade?

Phosphodiesterase.

How does a second-messenger system produce a huge signal amplification effect?

Binding of 1 hormone activates multiple G proteins, which generate many cAMP molecules, activating many protein kinases that phosphorylate millions of proteins.

In the $\text{PIP}_2\text{-calcium}$ signaling mechanism, what effector enzyme is activated by the G protein?

Phospholipase C.

What two second messengers are formed when phospholipase C splits the membrane phospholipid $\text{PIP}_2$?

Diacylglycerol (DAG) and inositol trisphosphate ($\text{IP}_3$).

What is the primary intracellular role of diacylglycerol (DAG)?

It activates protein kinases.

What is the primary intracellular role of inositol trisphosphate ($\text{IP}_3$)?

It triggers the release of $\text{Ca}^{2+}$ from intracellular storage.

How do calcium ions act as second messengers in the $\text{PIP}_2\text{-calcium}$ pathway?

They alter enzyme activity and channels, or bind to the regulatory protein calmodulin to activate response-amplifying enzymes.

What compound serves as a second messenger for some hormones instead of cAMP or $\text{Ca}^{2+}$?

cGMP (cyclic guanosine monophosphate).

How does the insulin receptor signal inside cells without using a classical second-messenger system?

It is a tyrosine kinase enzyme that autophosphorylates upon insulin binding, providing docking sites for relay proteins.

What occurs when a lipid-soluble hormone-receptor complex enters the cell nucleus?

It binds to a specific region of DNA, turning on a gene and initiating DNA transcription to produce mRNA.

What is the fate of mRNA produced via direct gene activation?

It is translated in the cytoplasm into specific proteins that perform metabolic, structural, or secretory functions.

How are circulating hormone levels in the blood controlled?

By negative feedback mechanisms.

What two main categories of input trigger hormone release from endocrine glands?

Endocrine gland stimuli and nervous system modulation.

What three types of stimuli cause endocrine glands to synthesize and secrete hormones?

Humoral stimuli, neural stimuli, and hormonal stimuli.

What is a humoral stimulus?

Changing blood levels of specific ions and nutrients directly stimulating hormone release.

Give a classic example of a humoral stimulus involving blood calcium homeostasis.

Declining blood $\text{Ca}^{2+}$ concentration stimulates parathyroid glands to secrete parathyroid hormone (PTH).

What is a neural stimulus?

Nerve fibers directly stimulating hormone release.

Give an example of a neural stimulus in the endocrine system.

Sympathetic nervous system fibers stimulating the adrenal medulla to secrete catecholamines.

What is a hormonal stimulus?

Release of a hormone in response to another hormone (a tropic hormone).

Describe the hormonal stimulus feedback loop between the hypothalamus, pituitary, and target glands.

Hypothalamic hormones stimulate anterior pituitary hormone release, which stimulates target endocrine glands, whose hormones then inhibit hypothalamic and pituitary release.

How can the nervous system override normal endocrine controls?

During severe stress, the hypothalamus and sympathetic nervous system override insulin to elevate blood glucose levels for fight-or-flight energy.

What three factors govern the extent of target cell activation by a hormone?

Blood levels of the hormone, relative number of target cell receptors, and affinity of binding between hormone and receptor.

What is up-regulation?

Target cells adding receptors in response to persistently low hormone levels to increase cell sensitivity.

What is down-regulation?

Target cells removing receptors in response to persistently high hormone levels to prevent overstimulation.

Which circulating hormones travel attached to plasma proteins rather than free in blood plasma?

Steroid hormones and thyroid hormone.

What two factors determine the concentration of a hormone circulating in the blood?

Rate of hormone release and speed of inactivation/removal from the body.

What are the two primary organs responsible for removing hormones from the blood?

The liver and the kidneys.

What is defined as a hormone's half-life?

The time required for the level of a hormone in the blood to decrease by half.

What range of half-lives is observed among different body hormones?

From a fraction of a minute to a week.

How do response onset times differ between water-soluble and steroid hormones?

Water-soluble hormone responses are often immediate, whereas steroid hormones can take hours or days to produce visible effects.

What is permissiveness in hormone interactions?

A situation where one hormone cannot exert its full effects without another hormone being present.

Provide an example of permissiveness involving reproductive hormones.

Reproductive hormones require thyroid hormone to be present to exert their full developmental effects.

What is synergism in hormone interactions?

A situation where more than one hormone produces the same effect at a target cell and their combined effects are amplified.

Provide an example of synergism in blood glucose regulation.

Glucagon and epinephrine both cause the liver to release glucose into the blood.

What is antagonism in hormone interactions?

A situation where one or more hormones oppose the action of another hormone.

Provide an example of hormonal antagonism.

Insulin lowers blood glucose, whereas glucagon raises blood glucose.

What stalk structure connects the pituitary gland to the hypothalamus?

The infundibulum.

What are the two major lobes of the pituitary gland (hypophysis)?

Posterior pituitary (neurohypophysis) and anterior pituitary (adenohypophysis).

What neural structure makes up the neurohypophysis along with the infundibulum?

The posterior lobe of the pituitary gland.

What developmental tissue gives rise to the anterior pituitary (adenohypophysis)?

Glandular tissue derived from an outpocketing of oral mucosa.

What bundle of axons connects the hypothalamus to the posterior pituitary?

The hypothalamic-hypophyseal tract.

In which hypothalamic nuclei do neuron cell bodies produce oxytocin and ADH?

Paraventricular nuclei (oxytocin) and supraoptic nuclei (ADH).

Where are oxytocin and ADH stored prior to release?

In axon terminals located within the posterior pituitary.

How are neurohormones released from the posterior pituitary?

On demand, when hypothalamic neurons fire action potentials.

What vascular network connects the hypothalamus to the anterior pituitary?

The hypophyseal portal system.

What three components comprise the hypophyseal portal system?

Primary capillary plexus, hypophyseal portal veins, and secondary capillary plexus.

How do hypothalamic releasing and inhibiting hormones reach the anterior pituitary?

They travel through the hypophyseal portal system directly to anterior pituitary cells.

What chemical structure characterizes oxytocin and antidiuretic hormone (ADH)?

Small peptides composed of nine amino acids each.

What two primary physiological actions are stimulated by oxytocin?

Strong uterine contractions during childbirth and milk ejection during breastfeeding.

What feedback mechanism and reflexes control oxytocin release during labor and lactation?

Positive feedback mechanisms involving neuroendocrine reflexes.

What second-messenger pathway is utilized by oxytocin?

The $\text{PIP}_2\text{-calcium}$ second messenger system.

What main stimulus triggers the secretion of antidiuretic hormone (ADH)?

High blood osmolarity, detected by hypothalamic osmoreceptors.

What is the primary target organ and effect of ADH?

Kidney tubule cells, stimulating them to reabsorb more water from filtrate back into the blood.

Why is ADH also known as vasopressin?

Because high concentrations cause vasoconstriction.

Name two factors that inhibit ADH release, leading to increased urinary output.

Adequate hydration and alcohol consumption.

What disorder is caused by a deficiency of ADH?

Diabetes insipidus.

What are the cardinal clinical signs of diabetes insipidus?

Intense thirst and large output of urine.

What condition is caused by hypersecretion of ADH?

Syndrome of inappropriate ADH secretion (SIADH).

What symptoms result from SIADH, and what is the primary cause of these symptoms?

Fluid retention, headache, and disorientation due to brain swelling.

How many hormones are manufactured and secreted by the anterior pituitary?

Six hormones.

List the six anterior pituitary hormones.

Growth hormone (GH), Thyroid-stimulating hormone (TSH), Adrenocorticotropic hormone (ACTH), Follicle-stimulating hormone (FSH), Luteinizing hormone (LH), and Prolactin (PRL).

What second-messenger system is used by all anterior pituitary hormones except GH?

The cAMP second-messenger system.

What are tropic hormones (tropins)?

Hormones that regulate the secretory activity of other endocrine glands.

Which four anterior pituitary hormones are classified as tropic hormones?

TSH, ACTH, FSH, and LH.

What cell type produces growth hormone (GH)?

Somatotropic cells.

What is an alternate name for growth hormone?

Somatotropin.