endocrine/hypothalamus/pituitary Flashcards
Endocrine System
Collective term for all endocrine glands and hormone-secreting cells distributed throughout the body
Endocrine gland/Endocrine cell
Lacks a duct
Secretes their hormone into the surrounding tissue/fluid and it is taken up by the blood and carried throughout the body
Neuroendocrine cell/Neurosecretory cell
Neurons that produce and release their secretions/hormones in response to signals from the nervous system
Hormones
General
Chemical messenger secreted into the bloodstream
Produces a response only in certain target cells that possess a receptor
Control and coordinate the body’s metabolism, energy level, reproduction, growth and development, and response to injury, stress, and mood
Commonly referred to by abbreviations or acronyms
Example: TSH = thyroid stimulating hormone
Endocrine Organs
No “master control center” that regulates the entire endocrine system
Hypothalamus and pituitary gland secrete hormones and have broader effects than any other endocrine glands
Hypothalamus
Region of the forebrain located below the thalamus and posterior to the optic chiasma
Has both neural and circulatory connections with the pituitary gland
Made of a collection of nuclei within the diencephalon of the brain with a variety of functions
hypothalamus
functions
Major functions include:
Hormone regulation and secretion primarily from the pituitary gland
Autonomic regulation (HR, BP, GI secretions and motility)
Thermoregulation
Food and water intake
Sleep and circadian rhythms
Memory
Emotional behavior
Pituitary Gland (Hypophysis)
general
Seated in the sella turcica of the sphenoid bone just below the hypothalamus
Attached to the hypothalamus by a stalk-like structure called the infundibulum
Consists of two lobes:
Anterior pituitary (adenohypophysis)
Posterior pituitary (neurohypophysis)
Considered the “master endocrine gland”
Secretes several hormones and regulates the activity of other hormone-secreting glands
hypothalamus and pituitary
Paraventricular and Supraoptic nuclei
Hypothalamus is the primary regulator of thepituitary
Connected to thepituitary via nerve fibers and via circulation
Nerve fiber connections: Hypothalamohypophysial tract
Neurons in the paraventricular and supraoptic nuclei have direct projections that end in the posteriorpituitary
Secretions include:
Paraventricular nuclei: primarily produce oxytocin. located inside hypothalamus.
Stimulate uterine contractions inlabor and milkrelease duringlactation
Supraoptic nuclei: primarily produceantidiuretic hormone (ADH)
Vasoconstrictor that stimulates ↑absorption of water from the renal tubules
these hormones are made in hypothalamus but stored in pituitary by means of Hypothalamohypophysial tract
pituitary and hypothalamus
Bloodstream connections
Bloodstream connections: Hypothalamohypophysial portal system
Formed from branches off the internal carotid arteries
Arteries travel through themedian eminence (thepituitary “stalk”) →capillaries that surround cells within the anterior pituitary
Neurosecretory cells in the medial zone of the hypothalamus have projections to themedian eminence and secretehormones into the portal system:
Releasing hormones:
Corticotropin-releasing hormone (CRH)
Thyrotropin-releasing hormone (TRH)
Gonadotropin-releasing hormone (GnRH)
Growth hormone–releasing hormone (GHRH)
Release-inhibitinghormones:
Somatostatin
Dopamine
Anterior Pituitary (Adenohypophysis)
Tropic and non-tropic hormones
Constitutes ¾ of the pituitary gland
Synthesizes and secretes 6 hormones:
Non-tropic hormone: directly stimulate target cells to induce effects
Prolactin (PRL)
Growth hormone (GH)
Tropic hormone: pituitary hormone whose target organ is another endocrine gland
Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)
Thyroid-stimulating hormone (TSH)
Adrenocorticotropic hormone (ACTH)
anterior pituitary
Relationship between the pituitary, tropic hormones, and their target endocrine gland is called an axis:
Pituitary-thyroid axis
Pituitary-adrenal axis
Pituitary-gonadal axis
Posterior Pituitary (Neurohypophysis)
general
Constitutes ¼ of the pituitary gland
Not a true gland
Stores two hormones synthesized in the hypothalamus
Hormones travel down the hypothalamohypophyseal tract in the infundibulum
Antidiuretic hormone (ADH)
Oxytocin (OT)
not a true gland bc does not synthesize its own hormones
Control of Pituitary Secretion
Timing and the amount of pituitary secretion is regulated by the hypothalamus, higher brain structures, and feedback from target organs
Anterior pituitary
Connected to the hypothalamus by a complex of blood vessels (hypothalamohypophyseal portal system)
Hypothalamic hormones:
Releasing hormones
Stimulate secretion by the pituitary cells
Inhibiting hormones
Suppress secretion from the pituitary cells
Control of Posterior Pituitary Secretion
Posterior pituitary
Controlled by neuroendocrine reflexes
Release of hormones in response to signals from the nervous system
Antidiuretic hormone (ADH)
Released when there is an increase in blood plasma osmolality (2-3%) or decrease in blood volume (10-15%)
Oxytocin (OT)
Released during labor and after nipple stimulation (breastfeeding)
know difference between positive and negative feedback loops
Pitocin
Synthetic substance that mimics oxytocin
Given to induce labor or to augment labor contractions (stronger and faster)
Antidiuretic hormone (ADH)
general
Also known as vasopressin
Homeostasis: blood osmolality 275-295 mOsm/L
Increased osmolality (dehydration) is detected by the hypothalamic neurons (osmoreceptor) and will release ADH from the posterior pituitary
ADH acts on the distal tubule to reabsorb water
Lower urine volume and stimulate the sense of thirst
Pituitary Adenoma
general
Tumors that derive from one of the five types ofpituitaryhormone producing cells within the anterior lobe of the pituitary gland
> 95% are sporadic, < 5% are genetically linked
pituitary adenoma
classification
Size
Classified by size:
Microadenoma < 10 mm (functional)
Macroadenoma > or = 10 mm (mass effect) (can cause visual disturbances be it can impede on optic chiasma)
Classified by their ability to secrete hormones:
Secretory adenoma
Non-secretory adenoma
know the anatomy (sullica/optic chiasma)
Pituitary Adenoma
Epidemiology
Most commonly diagnosed between the ages of 30 and 60
> 60% arebenign, ~30% are invasive, and < 1% are carcinomas
Cause 60% of all cases ofhypopituitarism
Pituitary Adenoma
patho
Growth of an adenoma will compress surrounding glandular tissue
Most adenomas will arise from a singlepituitary cell type
Classification by hormone production
Secretory adenomas- ~60% of allpituitary adenomas
Lactotroph adenomas (40%) → increasedprolactin→hyperprolactinemia
Somatotroph adenomas → increased growth hormone →acromegaly orgigantism
Corticotroph adenomas → increasedadrenocorticotropic hormone → Cushing’s syndrome
Thyrotroph adenomas (rare) → increasedthyroid-stimulating hormone → secondaryhyperthyroidism
Adenomas derived from multiple types ofpituitary cells secrete more than 1 hormone
Most common combination is somatotroph plus lactotroph
Often atypical and/or malignant forms of adenomas, which transform into aggressive and treatment-resistant carcinomas
Pituitary Adenoma
Non-secretory adenomas
~ 40% of allpituitary adenomas
> 80% of non-secretory cases derive from the gonadotroph cells of thepituitary
Hypopituitarism
general
Defined as decreased secretion of one, some, or all anterior pituitary hormones
Destruction of > 75% ofpituitary tissue results in thesequential loss of anteriorpituitary hormones
Symptoms depend on the deficient hormone(s)
Most commonpituitary hormone deficiencies are of gonadotropins, resulting inhypogonadismin both men and women
Hypopituitarism
causes
Causes:
Adenoma
Infarct
Secondary empty sella syndrome (head trauma, infection, radiation therapy, pituitary surgery, Sheehan syndrome)
pituitary adenoma
Microadenomas
Clin man
Microadenomas (< 10mm)
Non-secretory:usually asymptomatic
Secretory:causehyperpituitarism
Symptoms depend on the effects that the excessive hormone exerts on the peripheral target organs
Hyperprolactinemia
Acromegaly orgigantism
Cushing’s syndrome
Secondaryhyperthyroidism
pituitary adenoma
Macroadenomas Clin man
Macroadenomas (> 10mm)
Non-secretory:
Mass effect symptoms:
Bitemporal hemianopsia
Diminishedvision in bilateral temporal fields
Diplopia from compression of the optic chiasma or nerve
Ophthalmoplegia
Paralysis of the extraocular muscles (CN 3, 4, and 6)
Results from the invasion of the cavernous sinus
Headache
Vomiting without nausea
Altered mental status
Pituitary apoplexy
Sudden loss of blood supply to the pituitary gland, leading to tissue necrosis and loss of function often due to sudden hemorrhage into the adenoma → excruciating headache and diplopia
Secretory Macroadenomas (> 10mm)
clin man
Macroadenomas (> 10mm)
Secretory:
Hyperpituitarism
Symptoms depend on the hormone-specific effects
Otherhormones are deficient due topituitarytissue destruction
Masseffect symptoms
pituitary adenomas
Dx
Most microadenomas are diagnosed incidentally
Clinical suspicion is based on symptoms caused by an excessive hormone in addition tomass effect symptoms → combination suggests apituitary mass
Contrast magnetic resonance imaging (MRI) is the ideal imaging test used to confirm sellar masses, size, and location
CT is used when MRI is contraindicated (patients with pacemakers, metallic implants)
pituitary adenoma
labs
Laboratory tests:
Basalprolactin levels to assess prolactinomas
Insulin-like growth factor-1 levels to assess somatotroph adenomas
24-hoururine cortisollevels to assess corticotroph adenomas
Thyrotropin-releasing hormone,thyroid-stimulating hormone, freeT3andT4 levels to assess thyrotroph adenomas
MRI of a patient presenting with acromegaly shows with a large pituitary adenoma
pituitary adenoma
Tx
Treatment strategies depend on thetumor cell type and size
Non-secretory microadenomas do not require treatment – periodic follow-up
Secretory adenomas, regardless of size, require medical therapy to counteract hormonal effects
Macroadenomas, regardless of hormone production, require surgical orradiation therapy to alleviatecompression effects (increased intracranial pressure, visual disturbances, headaches)
pituitary adenom
Surgery
Surgical resection
Transsphenoidal adenectomy (removal of the adenoma) or complete/partial hypophysectomy (removal of thepituitary gland) is used when medical therapy fails
Pituitary irradiationcan be used to supplement surgical resection
Complications:
Postoperative/post-radiationhypopituitarism
Requires life-longhormone replacement therapy
Prolactinoma
general
Functional, usually benign lactotroph cell tumor in the anterior pituitary → prolactinemia
Most common type of pituitary tumor (adenoma)
Accounts for 30% of all pituitary adenomas
May occur as part of an inherited condition called multiple endocrine neoplasia type 1 (MEN 1)
Signs/Symptoms
♀ = galactorrhea, amenorrhea
♂ = gynecomastia, erectile dysfunction
prolactinoma
Dx and Tx
Diagnosis
↑ serum prolactin
First-line treatment
Dopamine agonists to suppressprolactin secretion
Cabergoline or bromocriptine
