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 single pituitary cell type

Question 26

Classification by hormone production

Answer 26

Secretory adenomas - ~60% of all pituitary adenomas Lactotroph adenomas (40%) → increased prolactin → hyperprolactinemia Somatotroph adenomas → increased growth hormone → acromegaly or gigantism Corticotroph adenomas → increased adrenocorticotropic hormone → Cushing’s syndrome Thyrotroph adenomas (rare) → increased thyroid-stimulating hormone → secondary hyperthyroidism Adenomas derived from multiple types of pituitary 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 all pituitary adenomas   > 80% of non-secretory cases derive from the gonadotroph cells of the pituitary

Question 28

# Hypopituitarism general

Answer 28

Defined as decreased secretion of one, some, or all anterior pituitary hormones Destruction of > 75% of pituitary tissue results in the sequential loss of anterior pituitary hormones Symptoms depend on the deficient hormone(s) Most common pituitary hormone deficiencies are of gonadotropins, resulting in hypogonadism in 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 **Micro**adenomas Clin man

Answer 30

**Microadenomas (< 10 mm)** **Non-secretory:** usually asymptomatic **Secretory**: cause hyperpituitarism Symptoms depend on the effects that the excessive hormone exerts on the peripheral target organs Hyperprolactinemia Acromegaly or gigantism Cushing’s syndrome Secondary hyperthyroidism

Question 31

# pituitary adenoma **Macro**adenomas Clin man

Answer 31

Macroadenomas (> 10 mm) **Non-secretory**: **Mass effect symptoms:** **Bitemporal hemianopsia** Diminished vision 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 (> 10 mm) clin man

Answer 34

Macroadenomas (> 10 mm) Secretory: Hyperpituitarism Symptoms depend on the hormone-specific effects Other hormones are deficient due to pituitary tissue destruction Mass effect 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 to mass effect symptoms → combination suggests a pituitary 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: Basal prolactin levels to assess prolactinomas Insulin-like growth factor-1 levels to assess somatotroph adenomas 24-hour urine cortisol levels to assess corticotroph adenomas Thyrotropin-releasing hormone, thyroid-stimulating hormone, free T3 and T4 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 the tumor 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 or radiation therapy to alleviate compression 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 the pituitary gland) is used when medical therapy fails Pituitary irradiation can be used to supplement surgical resection Complications:  Postoperative/post-radiation hypopituitarism Requires life-long hormone 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 suppress prolactin secretion **Cabergoline or bromocriptine**