Chapter 18: The Endocrine System Flashcards

Practice flashcards testing essential definitions, hormonal pathways, histology, and clinical values from Chapter 18 on the Endocrine System.

What are the five mechanisms of intercellular communication described in the endocrine system lecture?

1. Direct communication; 2. Paracrine communication; 3. Autocrine communication; 4. Endocrine communication; 5. Synaptic communication.

How does direct communication differ from paracrine communication?

Direct communication occurs between adjacent cells of the same type connected through gap junctions, whereas paracrine communication uses chemical mediators (paracrines) released into extracellular fluid to affect neighboring cells locally.

What are the three main chemical classes of hormones?

The three classes are amino acid derivatives, peptide hormones, and lipid derivatives.

Which hormones are derived from the amino acid tyrosine?

Thyroid hormones ($T_3$ and $T_4$) and catecholamines (epinephrine, norepinephrine, and dopamine).

Which hormones are derived from the amino acid tryptophan?

Serotonin and melatonin.

What are the two primary categories of peptide hormones?

Glycoproteins (such as TSH, LH, and FSH) and short polypeptides/small proteins (such as ADH, OXT, insulin, growth hormone, and prolactin).

What are the two major classes of lipid-derived hormones?

Eicosanoids (derived from arachidonic acid, including leukotrienes and prostaglandins) and steroid hormones (derived from cholesterol, including testosterone, estrogen, progesterone, corticosteroids, and calcitriol).

Why do bound hormones remain functional in blood circulation much longer than free hormones?

Bound hormones attach to special transport proteins in plasma, creating a substantial reserve where more than $99$ percent remain attached, protecting them from rapid filtration or degradation.

What essential role does a G protein play when a hormone binds to an extracellular receptor?

An activated G protein acts as an enzyme complex linking the first messenger (bound hormone) to the generation or activation of second messengers (such as cyclic AMP or $Ca^{2+}$) inside the cell.

What is receptor down-regulation, and what is a clinical example of it?

Down-regulation occurs when high concentrations of a hormone trigger a decrease in the number of target cell receptors, making cells less sensitive to the hormone. An example is insulin resistance in Type 2 diabetes.

What three types of stimuli trigger endocrine gland secretion?

Humoral stimuli (changes in extracellular fluid composition), hormonal stimuli (arrival or removal of specific hormones), and neural stimuli (neurotransmitters arriving at neuroglandular junctions).

Where is the pituitary gland located, and what attaches it to the hypothalamus?

The pituitary gland rests inside the sella turcica of the sphenoid bone and hangs attached to the hypothalamus by the infundibulum.

Which hypothalamic nuclei synthesize antidiuretic hormone (ADH) and oxytocin (OXT)?

The supra-optic nucleus (SON) synthesizes ADH, while the paraventricular nucleus (PVN) synthesizes oxytocin (OXT).

How are hypothalamic regulatory hormones delivered to the anterior pituitary gland?

They are secreted at the median eminence of the infundibulum and shunted directly into the anterior lobe capillaries via the hypophyseal portal system.

What seven hormones are produced and secreted by the anterior lobe of the pituitary gland?

Thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL), growth hormone (GH), and melanocyte-stimulating hormone (MSH).

What defines a tropic hormone, and which anterior pituitary hormones fit this definition?

Tropic hormones stimulate other endocrine glands to produce and release hormones. The tropic hormones are TSH, ACTH, FSH, and LH.

What are the primary metabolic effects of growth hormone (GH)?

GH stimulates liver cells to release somatomedins that promote uptake of amino acids for tissue growth, maintains blood glucose concentrations by breaking down liver glycogen, and mobilizes stored triglycerides in adipocytes.

Which two hormones are stored and released by the posterior lobe of the pituitary gland?

Antidiuretic hormone (ADH) and oxytocin (OXT).

What two key cell types make up the thyroid gland histology, and what do they produce?

Thyroid follicle cells (cuboidal epithelium surrounding colloid) produce thyroid hormones ($T_3$ and $T_4$), and C (clear or parafollicular) cells produce calcitonin.

What sequence of steps leads to thyroid hormone synthesis in follicle cells?

Follicle cells absorb iodide ions ($I^-$) from blood, convert them to iodine ($I^0$), bind iodine to tyrosine residues on thyroglobulin in colloid, link tyrosines to form $T_3$ and $T_4$, reabsorb thyroglobulin via endocytosis, and liberate free $T_3$ and $T_4$ using lysosomal enzymes.

What is the calorigenic effect of thyroid hormones?

It is an immediate increase in the rate of cellular metabolism that elevates oxygen consumption, energy expenditure, and heat generation throughout the body.

How does parathyroid hormone (PTH) respond to blood calcium concentration changes?

PTH is secreted by parathyroid (principal) cells in response to low blood $Ca^{2+}$ levels (below $8.5\,mg/dL$) to stimulate osteoclast activity, increase renal calcium reabsorption, and promote calcitriol synthesis.

What is the normal homeostatic range for blood calcium ion concentration?

$8.5\text{ to }11\,mg/dL$.

What are the three distinct structural zones of the adrenal cortex and their main secretions?

Zona glomerulosa produces mineralocorticoids (primarily aldosterone), zona fasciculata produces glucocorticoids (such as cortisol and corticosterone), and zona reticularis produces adrenal androgens.

What hormones are released by the adrenal medulla, and what relative proportions are secreted?

Epinephrine ($75\%\text{--}80\%$) and norepinephrine ($20\%\text{--}25\%$).

What hormone is secreted by pinealocytes in the pineal gland, and what triggers its synthesis?

Melatonin is synthesized and released in response to decreased ambient light to regulate circadian rhythms.

What four principal endocrine cell types are found in pancreatic islets, and what do they produce?

Alpha cells produce glucagon, Beta cells produce insulin, Delta cells produce somatostatin (GH-IH), and PP cells produce pancreatic polypeptide.

What is the normal physiological range for blood glucose level?

$70\text{ to }110\,mg/dL$.

What A1C test percentages correspond to normal, prediabetes, and diabetes diagnoses?

Normal is below $5.7\%$; prediabetes is $5.7\%\text{ to }6.4\%$; diabetes is $6.5\%$ or above.

What secondary endocrine functions are carried out by the kidneys?

The kidneys secrete calcitriol (enhances digestive calcium/phosphate absorption), erythropoietin/EPO (stimulates red blood cell production), and renin (initiates the RAAS pathway to raise blood volume and pressure).

What four possible outcomes can occur when a target cell receives two hormonal signals simultaneously?

Antagonistic effects, synergistic effects, permissive effects, and integrative effects.

What are the three sequential phases of the General Adaptation Syndrome (GAS) and their primary hormonal regulators?

The Alarm phase (dominated by epinephrine), the Resistance phase (dominated by glucocorticoids), and the Exhaustion phase (marked by systemic failure due to lipid depletion, electrolyte imbalance, and $K^+$ loss).