Introduction to Endocrinology Flashcards Preview

MS 1 Unit VI Physiology > Introduction to Endocrinology > Flashcards

Flashcards in Introduction to Endocrinology Deck (45):

Classical endocrine hormone released

-by ductless glands into the circulating blood to influence the function of distant target cells containing specific receptors


Endocrine system regulate homeostasis

-multiple chemical messengers, in particular those controlled by the autonomic and endocrine systems, act in coordinated manner to regulate the activities of all cells, tissues and organs in the body thereby promoting growth, reproduction, and homeostasis in the face of different environmental challenged


Classic endocrine glands

pituitary (anterior and posterior lobes), thyroid, parathyroid, adrenal, pancreas (endocrine), and gonads (ovaries and testes) but several other tissues secrete hormones (GI, kidney)



-ADH-antidiuretic hormone (vasopressin)
-releasing hormones (TRH, CRH, GHRH, GnRH)


Anterior Pituitary

-ACTH adrenocorticotropic
-TSH- thyroid stimulating hormone
-GH-growth hormone
-MSH- melanocyte-stimulating hormone


Posterior Pituitary

Release of ADH and oxytocin


Pineal gland




-T3, T4



parathyroid hormone



insulin, glucagon, somatostatin


Adrenal Medulla




Erypoietin, calcitriol, renin


Adrenal Cortex

Adrenal androgens






testosterone, inhibin



-atrophy in adulthood


Digestive Tract






Corpus Luteum

Estradoil, Progesterone





Peptide Hormones

-Atrial natiuretic peptide
-ADH (vasopressin)
-Corticotropin-releasing hormone
-Follicle stimulating hormone- FSH
-Growth hormone
-INsulin like growth factors 1 and 2
-Luteinizing hormone
-parathyroid hormone
-thyrotropin releasing hormone


Amino Acid Hormones

-Thyroxine (T4)
-Triiodothyronine (T3)


Steroid Hromones



Hormones and cell receptors

-peptide and protein hormones activate receptors on the cell surface
-steroid hormones (and thyroid hormones) enter the cell and activate nuclear receptors (and sometimes cytoplasmic)
-some hormones are released by cells and act locally in a paracrine or autocrine manner
-neuroendocrine hormones are secreted by neurons into the blood to influence the function of target cells
-Hormones act at target cells by binding to specific cell membrane or cytosolic receptors, initiating a cascade of events that produces a physiological change. Binding to the receptor may result in generation of second messengers (cAMP,cGMP, IP3) or regulation of gene transcription. True hormones (endocrine secretions) are released by ductless glands and are carried by the bloodstream to their sites of action. They are part of a larger group of substance that include autocrine, paracrine, and neuronendocrine secretions


Difference between steroid and peptide/amine hormones

Storage Pools- steroids none; peptide- secretory vesicles

Interaction with cell membrane- steroid- diffusion through cell membrane, peptide- binding to receptor on cell membrane

Receptor; steriod- in cytoplasm or nucleus; peptide- on cell membrane

ACtion- Steroid-regulation of gene transcription; peptide- signal transduction cascade affect a variety of cell processes

Response time- steriod- hours to days (primarily); peptide- seconds to minutes



-molecular alterations in G proteins sometime affect certain signaling systems
-they key defect is an abnormality in a stimulatory alpha subunit of a heterotrimeric G protein
-this result is an impairment in the ability of PTH to regulate body calcium and phosphorus homeostasis
-patients have low serum calcium and high serum phosphate level, just like patient whose parathyroid glands have been surgically removed
--however these patients have increased circulating concentrations of PTH, the hormone just can't act normal on the target tissue
-aslso have increased risk of hypothyroidism, as well as of gonadal dysfunction in women- also because of same defect in signaling


Hormones released in cyclical fashion

-hypothalamic and pituitary hormone (GH) secretion throughout the day demonstrating the especially powerful effect of stenous exercise and also the high rate of GH secretion that occurs during the first few hours of deep sleep


Hyothalamic pituitary axis

-exerts control over multiple endocrine organs
-the pituitary gland, hypophysis, is highly vascularized and lies at the base of brain in the sella turcica
-secretion of pituitary hormones is regulated by the hypothalamus via vascular (anterior) and neural (posterior) connections
-the anterior (adenohypophysis_ and posterior pituitary are derived from different embryonic tissues and function as separate glands
-the posterior pituitary receives arterial blood. The anterior pituitary receives venous blood carrying neuropeptides from the hypothalamus and pituitary stalk to different cell types in the gland
-axons from hypothalamic nuclei extend to the median eminence, where they release hormones into the hypophyseal portal circulation, which carries them directly to the anterior pituitary. At the anterior pituitary, these hormones inhibit or stimulate the release of various trophic hormones into the system blood


Hypothalamus and posterior pituitary

-secretion of posterior pituitary hormones is regulated by the hypothalamus via neural connections
-axons from hypothalmuc nuclei extend to the posterior pituitary, where hormones (oxytocin_ and vasopressin) are stored until released into the systemic bloodstream
-posterior pituitary receives arterial blood
-posterior pituitary hormones are smaller molecular mass peptides that are associated with neurophysins


Hypothalamic and Pituitary Hormones

-the release of most anterior pituitary hormones is controlled by hypothalamic releasing factors (except prolactin- which is inhibited by dopamine)
-release of growth hormone is also under inhibitory control by somatostain
-hypothalmic releasing factors are delivered to the anterior pituitarty via a portal connection
-posterior pituitary hormones are synthesized in the cell bodies of neurons in the hypothalamus, then transported down axons that terminate in the posterior pituitary gland are stored in vesicles until release into the blood stream


Overview of anterior pituitary function

-controlled by releasing and inhibitory hormones secreted into the hypophyseal portal circulation
-these hormones reach the anterior pituitary directly through the portal circulation without entering the general circulation
-under control of these factors, specific secretory cell types of the anterior pituitary secrete six major trophic hormones (TSH, ACTH, FSH, LH, prolactin, and GH) which act on distal endocrine glands
-trophic hormones and the target gland hormones have feedback effects on these endocrine systems, designed to regulate blood levels of the target gland hormone


Cell types in the pituitary

-it is possible to distinguish between cell types in the anterior pituitary gland using size and cellular stains (e.g. large acidophilic called somatotropes represent ~30% of secreting cells and release GH, whereas basophilic cells called corticotropes represent ~20% of secreting and release ACTH
-the territories occupied by different cell types can be dynamic (lactotropes that synthesize and release prolactin increase during pregnancy)


Negative and Positive Feedback

-use positive and negative feedback to control the amounts of circulating hormones
-they are closed loop systems that can be simple or involve hierarchical control. In this manner, the system sense when it should increase or decrease its activity
-peptides that feedback on the hypothalamic-pituitary axis are able to pass the blood brain barrier
-feedback of hormones released from peripheral glands onto the hypothalamic-pituitary axis is called long loop feedback
-short loop feedback refers to anterior pituitary hormones feeding back on hypothalamus



-is the major hormone that stimulates milk production during lactation. It also promotes breast development during puberty and pregnancy, and inhibits ovulation
-under tonic inhibitory control by dopamine
-TRH (thyrotoprhic releasing hormone) stimulates prolactin release
-prolactin exerts negative feedback its own release by enhancing hypothalamic dopamine releasing via a short loop pathway
-circulating prolactin increases if the pituitary stalk is severed or an individual is taking a dopamine receptor antagonist (D2 type, certain antipsychotic agents)
-excessive prolactin secretion (hyperprolactinemia) is often treated with dopamine receptor agonists such as bromocriptine


Posterior pituitary hormones

-synthesized in large neuronal cell bodies in the hypothalamus (paraventricular and supraoptic) and stored in nerve terminals in the posterior pituitary gland
-ADH: prepropressophysin -> propressophysis -> hypothalamic-hypophyseal tract -> posterior lobe of pituitary and neurophysin II
-Oxytocin: prepro-oxyphysin -> pro-oxyphysin -> hypothalamic-hypophyseal tract -> posterior lobe of pituitary and neurophysin I



-a neuropeptide hormone that stimulates milk ejection (let-down) from the breasts in response to suckling, and uterine contractions during paturition in response to dilation of the cervix
-oxytocin can also be secreted in response to sight, small or sound of an infant; and orgasm
-the hypothalamic cell bodies that synthesize oxytocin are primarily in the paraventricular nuclei


Posterior Pituitary Function

-is synthesized mainly in the supraoptic nuclei (and also the paraventricular nuclei) of the hypothalamus and is stored and released at the posterior pituitary
-its main function is in water balance
-it is released in response to increased osmolarity of the excellular fluid and decreased blood pressure and has the major effect of promoting water reabsorption by the kidney
-ADH levels in plasma are high, a low volume of concentrated urine is produced



-major regulator of body fluid osmolarity
-ADH secretion increases in response to an increase in serum osmolarity- for example water deprivation leads to increased serum osmolarity which is sensed by osmoreceptors in the hypothalamic neurons that synthesize ADH
-ADH acts specific cells/regions of the kidney to promoter water reabsorption, thus decreasing body fluid osmolarity toward normal (homeostasis). This action involves a receptor called V2
-ADH (vasopressin) also causes contraction of vascular smooth muscle by stimulating a different (V1). This leads to an increase in total peripheral resistance
-failure of posterior pituitary to secrete ADH is called central diabetes insipidus. Affected individuals produce large volumes of dilute urine, and their body fluids become concentrated



-the inability of the pituitary gland to produce hormones or an insufficiency of hypothalamic-releasing hormone
-clinical symptoms are unspecific, but can be life threatening and lead to increased mortality. Patients with traumatic brain injury or subarachnoid hemorrhage are at high risk for hypopituitarism
-pituitary tumors or brain damage often causes



-clinical features deficiency in one or more of the following:corticotropin(ACTH) , thyrotropin (TSH), gonadotropin (FSH and LH), antiduretic hormone (ADH)
-treatment involves hormone replacement therapy


Corticotropin deficiency

-chronic: fatigue, pallot, anorexia, weight loss- hypoglycemia, hypotension, anemia, lymphocytosis, eosinophilia, hyponatremia
-acute: weakness, dizziness, nausea, vomiting, circulatory collapse, fever, shock
-Children: delayed puberty; failure to thrive


Thyrotropin deficiency

-tiredness, cold intolerance, constipation, hair loss, dry skin, hoarseness, cognitive slowing- weight gain, bradycardia, hypotension
-children: retarded development, growth retardation


Gonadotropin deficiency

-women" oligoarnenorrhea, loss of libido, dyspareunia, infertility- osteoporosis
-men- loss of libido, impaied sexual function, mood impairment, loss of facial, scotal and trunk hair- decreased muscle mass, osteoporosis, anaemia
-children: delayed puberty


Growth hormone deficiency

-decreased muscle mass and strength, visceral obesity, fatigue, decreased quality of life, impairment of attention and memory- dyslipidaemia, premature atherosclerosis
-children: growth retardation


Antidiuretic hormone deficiency

polyuria, polydipsia- decreased urine osmolality, hypernatraemia, polyuria