endocrine/hypothalamus/pituitary

Question 1

Endocrine System

Answer 1

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

Question 2

Hormones

General

Answer 2

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

Question 3

Endocrine Organs

Answer 3

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

Question 4

Hypothalamus

Answer 4

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

Question 5

hypothalamus

functions

Answer 5

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

Question 6

Pituitary Gland (Hypophysis)

general

Answer 6

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

Question 7

hypothalamus and pituitary

Paraventricular and Supraoptic nuclei

Answer 7

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

Question 8

pituitary and hypothalamus

Bloodstream connections

Answer 8

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

Question 9

Anterior Pituitary (Adenohypophysis)
Tropic and non-tropic hormones

Answer 9

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)

Question 10

anterior pituitary

Relationship between the pituitary, tropic hormones, and their target endocrine gland is called an axis:

Answer 10

Pituitary-thyroid axis
Pituitary-adrenal axis
Pituitary-gonadal axis

Question 11

Posterior Pituitary (Neurohypophysis)

general

Answer 11

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

Question 12

Control of Pituitary Secretion

Answer 12

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

Question 13

Question 14

Question 15

Control of Posterior Pituitary Secretion

Answer 15

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)

Question 16

Question 17

Question 18

know difference between positive and negative feedback loops

Question 19

Pitocin

Answer 19

Synthetic substance that mimics oxytocin
Given to induce labor or to augment labor contractions (stronger and faster)

Question 20

Antidiuretic hormone (ADH)

general

Answer 20

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

Question 21

Question 22

Pituitary Adenoma

general

Answer 22

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

Question 23

pituitary adenoma

classification
Size

Answer 23

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)

Question 24

Pituitary Adenoma

Epidemiology

Answer 24

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

Question 25

Pituitary Adenoma

patho

Answer 25

Growth of an adenoma will compress surrounding glandular tissue

Most adenomas will arise from a singlepituitary cell type

Question 26

Classification by hormone production

Answer 26

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

Question 27

Pituitary Adenoma

Non-secretory adenomas

Answer 27

~ 40% of allpituitary adenomas

> 80% of non-secretory cases derive from the gonadotroph cells of thepituitary

Question 28

Hypopituitarism

general

Answer 28

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

Question 29

Hypopituitarism

causes

Answer 29

Causes:
Adenoma
Infarct
Secondary empty sella syndrome (head trauma, infection, radiation therapy, pituitary surgery, Sheehan syndrome)

Question 30

pituitary adenoma

Microadenomas
Clin man

Answer 30

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

Question 31

pituitary adenoma

Macroadenomas Clin man

Answer 31

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

Question 32

Question 33

Question 34

Secretory Macroadenomas (> 10mm)

clin man

Answer 34

Macroadenomas (> 10mm)
Secretory:
Hyperpituitarism
Symptoms depend on the hormone-specific effects
Otherhormones are deficient due topituitarytissue destruction
Masseffect symptoms

Question 35

pituitary adenomas

Dx

Answer 35

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)

Question 36

pituitary adenoma

labs

Answer 36

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

Question 37

Answer 37

MRI of a patient presenting with acromegaly shows with a large pituitary adenoma

Question 38

pituitary adenoma

Tx

Answer 38

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)

Question 39

pituitary adenom

Surgery

Answer 39

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

Question 40

Prolactinoma

general

Answer 40

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

Question 41

prolactinoma

Dx and Tx

Answer 41

Diagnosis
↑ serum prolactin

First-line treatment
Dopamine agonists to suppressprolactin secretion
Cabergoline or bromocriptine