Ch17 Endocrine System Study Set

Nervous system vs. endocrine system transport pathways?

The nervous system uses an enclosed circuit with neurotransmitters traveling across tiny synaptic clefts over short distances and times, while the endocrine system relies on the bloodstream to carry hormones throughout systemic circulation over a longer duration.

What is the difference between ligands and hormones?

Ligands are any chemical messengers that bind to cellular receptors, while hormones are specifically endogenous messengers produced by endocrine glands and secreted into the bloodstream to reach distant targets.

What determines whether a circulating hormone can affect a target cell?

The target cell must have the correct structural receptor—a matching "key-and-lock" docking site.

What are common causes of endocrine dysfunction related to hormone signaling?

Failure of the gland to produce/secrete hormone, vascular obstructions, chemical hormone degradation in blood, or absence/modification/downregulation of target cell receptors.

What mechanism allows the endocrine system to maintain long-term physiological stability?

Negative feedback mechanisms.

What long-term developmental processes does the endocrine system regulate?

Cell division, tissue differentiation, and somatic maturation, including the onset and progression of puberty.

How does the endocrine system maintain homeostasis of blood composition and volume?

By regulating blood glucose, sodium ($Na^+$), calcium ($Ca^{2+}$), water balance, dissolved gases ($O_2$, $CO_2$), and blood pH.

Why does defecation reflect meals from previous days rather than recent meals?

Because the small intestine is ~$20\text{ feet}$ long and the large intestine is ~$5\text{ feet}$ long, causing gastrointestinal transit to span multiple days.

What does controlling reproduction manage?

Manages gametogenesis, gonadal steroid production, menstrual/luteal cycles, pregnancy, and lactation.

What triggers hormonal stimulation in endocrine glands?

The release of one hormone is triggered by another controlling hormone.

What is an example of HORmonal stimulation?

$TSH$ from the anterior pituitary stimulates thyroid follicular cells to release thyroid hormone ($TH$).

What triggers HUMoral stimulation?

Changing levels of nutrients, ions, or fluid volumes directly detected in the blood.

What is an example of humoral stimulation?

Elevated blood glucose stimulates pancreatic beta cells to secrete insulin; elevated calcium stimulates calcitonin release.

What triggers nervous system stimulation of endocrine glands?

Direct neural innervation that activates hormone release.

What is an example of nervous system stimulation?

Sympathetic neurons stimulate the adrenal medulla to release epinephrine and norepinephrine during acute stress.

What is the structural origin of steroid hormones?

They are synthesized from cholesterol and have a multi-ring carbon backbone.

What are examples of steroid hormones?

Estrogen, progesterone, testosterone, cortisol, and aldosterone.

Why do steroid hormones require carrier proteins in the bloodstream?

Because lipid-soluble molecules do not dissolve readily in water-based plasma.

How can free lipids contribute to atherosclerosis?

They adhere to hydrophobic surfaces, especially where endothelial damage or exposed collagen fibers are present.

How do lipid-soluble hormones enter target cells?

They diffuse directly through the phospholipid bilayer of the cell membrane.

What happens after steroid hormones bind intracellular receptors?

The hormone-receptor complex interacts with nuclear DNA to regulate gene expression and protein synthesis.

Which hormone type is water-soluble (except $TH$), derived from a modified amino acid, and very small in size?

Biogenic Amine.

What are examples of biogenic amines?

Catecholamines, thyroid hormone, and melatonin.

What is the solubility of biogenic amines?

Water-soluble except for thyroid hormone, which is lipid-soluble.

What is the structural composition of protein/peptide hormones?

Chains of amino acids, ranging from small peptides to large glycoproteins.

What are examples of protein/peptide hormones?

Insulin, glucagon, growth hormone, prolactin, $TSH$, $ACTH$, $FSH$, and $LH$.

Why must water-soluble hormones bind to extracellular receptors?

They cannot cross the hydrophobic phospholipid bilayer of target cell membranes.

How do water-soluble hormones alter cell activity after receptor binding?

They activate intracellular signaling cascades involving second (and tertiary) messengers.

What is the first messenger in hormone signaling?

The water-soluble hormone that initiates a series of biochemical events by binding to the extracellular membrane receptor.

What is the second messenger in hormone signaling?

An intracellular molecule (e.g., cAMP) formed to alter cellular activity.

What are local hormones made from?

Lipid-derived signaling molecules, such as prostaglandins and leukotrienes, synthesized from fatty acids in cell membranes.

How do local hormones communicate compared to endocrine hormones?

They act locally on nearby cells (paracrine) or on the same cell that secreted them (autocrine), rather than circulating through the bloodstream.

Why don't local hormones travel systemically?

Because their function is restricted to adjacent or self-targeting cells, so they do not enter systemic circulation.

What is synergistic hormone interaction?

Occurs when one hormone reinforces the activity of another hormone.

What is permissive hormone interaction?

Occurs when one hormone requires the activity of another hormone to work.

What is the hypothalamo-hypophyseal tract?

A neural pathway of unmyelinated axons extending from hypothalamic nuclei into the posterior pituitary that allows direct control of hormone release.

Which nuclei synthesize $ADH$ and Oxytocin?

The supraoptic nucleus makes $ADH$, and the paraventricular nucleus makes Oxytocin.

Why doesn't the posterior pituitary make hormones?

It only stores and releases hormones made in the hypothalamus, acting as a neurohemal organ rather than a gland.

What are the actions of $ADH$ and Oxytocin?

$ADH$ increases kidney water reabsorption and causes vasoconstriction at high levels; Oxytocin triggers uterine contractions and milk ejection.

What is the hypothalamo-hypophyseal portal system?

A two-capillary-bed vascular network connecting the hypothalamus to the anterior pituitary to deliver releasing and inhibiting hormones without dilution.

How do hypothalamic hormones reach anterior pituitary cells?

They enter the primary plexus, travel through portal veins, and bind receptors in the secondary plexus.

Why is the portal system necessary?

Systemic circulation would dilute hypothalamic hormones before they reached the pituitary; the portal system preserves their strength.

What types of hormones does the hypothalamus send through this portal system?

Releasing hormones ($RH$) and inhibiting hormones ($IH$) that regulate the six major anterior pituitary hormones.

What does $TSH$ do?

Stimulates thyroid follicular cells to produce $T_3$ and $T_4$, which regulate metabolic rate.

What cells respond to $TSH$?

Follicular cells in the thyroid gland.

How does $TSH$ relate to $TRH$?

$TRH$ from the hypothalamus stimulates the anterior pituitary to release $TSH$.

What is prolactin's main function?

$PRL$ stimulates milk production in mammary epithelial cells.

What tissue does prolactin target?

Mammary gland epithelial cells.

How is prolactin different from Oxytocin?

$PRL$ makes milk, while Oxytocin releases (ejects) it.

What does $FSH$ do in females?

Stimulates ovarian follicle development and helps oocytes mature.

What does $FSH$ do in males?

Stimulates spermatogenesis in the testes.

What organs does $FSH$ target?

The ovaries and testes.

What does $LH$ do in females?

Triggers ovulation and progesterone secretion, beginning the luteal phase.

What does $LH$ do in males?

Stimulates testosterone production in interstitial cells.

How do $LH$ and $FSH$ work together?

They coordinate gamete development and hormone production ($FSH$ prepares gametes, $LH$ triggers hormone release).

What does $ACTH$ stimulate?

Targets the adrenal cortex's zona fasciculata to release cortisol.

Why is $ACTH$ important?

It ensures the body can mobilize energy during stress.

What triggers $ACTH$ release?

$CRH$ (Corticotropin-Releasing Hormone) from the hypothalamus.

What tissues does $GH$ target?

Bone, cartilage, skeletal muscle, and the liver.

What does $GH$ stimulate?

Promotes mitosis, protein synthesis, glycogenolysis, and lipolysis.

How does $GH$ affect body structure?

Increases cell size and skeletal dimensions during childhood and adolescence.

How does $GH$ relate to $IGF$?

$GH$ stimulates the liver to produce $IGF$ (Insulin-like Growth Factor), which enhances growth effects in bone and muscle.

What does the zona glomerulosa produce?

Aldosterone, a mineralocorticoid that regulates sodium retention and potassium excretion.

What does the zona fasciculata produce?

Cortisol, the main glucocorticoid that manages stress and increases blood glucose.

What does the zona reticularis produce?

Adrenal androgens that support libido and tissue maintenance.

How are the adrenal cortex zones organized?

Concentric layers from outer to inner: glomerulosa, fasciculata, reticularis ("Salt, Sugar, Sex").

How does cortisol increase blood glucose?

Stimulates gluconeogenesis, lipolysis, and protein breakdown.

What anti-inflammatory effects does cortisol have?

Suppresses immune activation and cytokine release, reducing inflammation but weakening immunity.

What happens during chronic stress?

Cortisol remains elevated, causing immune suppression, high blood glucose, and increased disease risk.

How are glucocorticoids used clinically?

Cortisone injections reduce joint inflammation and swelling to relieve pain.

What happens during the alarm phase of stress?

Epinephrine and norepinephrine surge from the adrenal medulla, raising heart rate and mobilizing glucose instantly.

What happens during the resistance phase of stress?

Cortisol remains high while heart rate stabilizes to sustain long-term energy elevation.

What happens during the exhaustion phase of stress?

Energy reserves deplete and the body breaks down structural proteins from vital organs, leading to potential collapse.

What triggers stress exhaustion?

Prolonged stress without rest, running out of carbohydrates and fats.

What are thyroid follicles?

Spherical units lined by follicular cells surrounding colloid that serve as the functional units of the thyroid.

What is colloid?

A protein-rich gel containing thyroglobulin that stores precursor material for thyroid hormone synthesis.

What are parafollicular cells?

C-cells located between follicles that release calcitonin in response to high blood calcium.

What is the thyroid isthmus?

A tissue bridge connecting the right and left thyroid lobes across the anterior trachea.

What are the steps of thyroid hormone synthesis?

Iodide is transported into follicles, attached to thyroglobulin, coupled into $T_3$ and $T_4$, then endocytosed and released into blood.

Where are $T_3$ and $T_4$ formed?

Inside iodinated thyroglobulin within the colloid.

What dietary source provides iodide?

Seafood and iodized salt.

Why is iodide transport important?

It is the required first step where follicular cells actively pump iodide from the blood.

How do $T_3$/$T_4$ affect metabolism?

They increase basal metabolic rate (BMR) and accelerate chemical reactions.

How do thyroid hormones affect the heart and lungs?

They increase heart rate, contractility, and ventilation to support higher oxygen demand.

Why do thyroid hormones maintain blood glucose?

To ensure adequate fuel availability for the brain's fast neuronal signaling.

What is the calorigenic effect?

Increased ATP production generated by thyroid activity that produces body heat.

What is Hashimoto's thyroiditis?

An autoimmune destruction of thyroid tissue causing hypothyroidism (fatigue, cold intolerance, low metabolism).

What is Graves' disease?

Autoantibodies mimic $TSH$, causing excess $T_3$/$T_4$ release (heat intolerance, weight loss, exophthalmos).

What causes a goiter?

Chronic iodine deficiency preventing $T_3$/$T_4$ formation, causing the thyroid to enlarge due to persistently elevated $TSH$.

How does calcitonin affect blood calcium?

Lowers blood calcium by stimulating osteoblasts and increasing renal excretion.

What percentage of the pancreas is exocrine?

98–99% consisting of acinar cells producing digestive enzymes.

What are pancreatic islets?

Endocrine clusters (1–2% of pancreas) releasing hormones like insulin and glucagon directly into the blood.

What do alpha and beta cells produce?

Alpha cells produce glucagon; beta cells produce insulin.

What do delta and F cells produce?

Delta cells produce somatostatin; F cells produce pancreatic polypeptide.

What does insulin do?

Lowers blood glucose by increasing glycogenesis, lipogenesis, and cellular glucose uptake.

When is insulin released?

During hyperglycemia, such as after meals.

How does insulin affect muscle?

Increases amino acid uptake for cell growth and tissue repair.

How does insulin affect adipose tissue?

Promotes lipogenesis, converting glucose into stored fat.

What does glucagon do?

Raises blood glucose through glycogenolysis, gluconeogenesis, and lipolysis.

When is glucagon released?

During hypoglycemia (low blood sugar) or fasting.