Week 7: Endocrine Feedback Loops Flashcards
Describe hypothalamic and metabolic homeostasis

ACTH AKA
- Adrenocorticotropic hormone
GH AKA
growth hormone
or
STH (Somatotropic Hormone)
TSH AKA
Thyroid-stimulating hormone
Prl AKA
Prolactin
LH AKA
Luteinizing hormone
OT AKA
Oxytocin
AVP
Arginine Vasopressin
Posterior pituitary secretions and functions
- OT (Parturition & Lactation)
- AVP (Water balance)
Anterior pituitary secretions and functions
6 listed
- ACTH (response to stress)
- GH (Growth & development)
- TSH (Metabolism)
- Prl (Lactation)
- LH (Reproducion)
- FSH (Reproduction)
Describe all Anterior & Posterior Pituitary secretions and functions

Describe hypothalamic control of pituitary function

List of pituitary disorders
- Hypopituitarism
- Hormone-producing Pituitary adenomas
- Growth Hormone Insensitivity
Case discussion question

B Pituitary adenoma
can cause secretory dysfunction of the pituitary gland
Hypopituitarism Pathophysiology/etiology
Ischemic damage to the pituitary gland or hypothalamic pituitary stalk during the peripartum period leads to Sheehan syndrome
What is Sheehan Syndrome?
Hypopituitarism
Ischemic damage to the pituitary gland or hypothalamic pituitary stalk during the peripartum period leads to Sheehan syndrome
Hypopituitarism Clinical Manifestations
5 listed
- hypothyroidism
- adrenal insufficiency
- hypogonadism
- GH deficiency
- Hypoprolactinemia
Hormone-producing Pituitary adenomas epidemiology
5 listed
- Prolactinomas are the most common pituitary tumors (40-45%)
- Somatotroph adenoma (20%)
- Corticotroph adenomas (10-12%)
- Gonadotroph adenomas (15%)
- Thyotroph adenomas (1-2%)
Etiology of GH Insensitivity
Growth failure can be the result of decreased GH release, decreased GH action or GH Insensitivity Syndrome
GH Insensitivity Syndrome AKA
Laron Syndrome
Laron Syndrome AKA
GH Insensitivity Syndrome
Describe the Hypothalamus-pituitary-thyroid axis

Describe the biosynthesis of thyroid hormones

Thyroid hormone structure
Thyroid hormones are basically 2 tyrosines linked together with the critical addition of iodine at three (T3) or four (T4) positions on the aromatic rings

Hypothalamus and metabolic regulation
- decrease hepatic glucose production in the liver
- increase glycogen synthesis and glucose uptake in muscle
- Increase lipogenesis and decrease lipolysis in adipose tissue
- Can regulate the appetite
- MAYBE MORE STUFF NOT SURE

Describe the mechanisms of how the hypothalamus controls pituitary function
2 mechanisms
- Neuronal hormone secretion to the circulation and to the pituitary gland
- ACTH
- STH (GH)
- TSH
- LH
- FSH
- Prl
- direct neural synapsis from hypothalamic preganglionic to pituitary neurons postganglionic
- OT
- AVP
STH AKA
GH
What is acromegaly?
Acromegaly is a hormonal disorder that develops when your pituitary gland produces too much growth hormone during adulthood. When this happens, your bones increase in size, including those of your hands, feet and face. Acromegaly usually affects middle-aged adults
Describe the Hypothalamus-pituitary-thyroid axis
hypothalamus activation -TRH-> pituitary -TSH-> Thyroid -T3 & T4-> negative feedback (hypothalamus and the anterior pituitary gland) & increased (metabolism, growth & development and increased catecholamine effects)

Describe the biosynthesis of thyroid hormones
Thyroglobulin + Tyrosine -Thyroid peroxidase-> Diodotyrosine -Thyroid peroxidase-> thyroxine
Triiodothyronine loses an iodine and can be an active or inactive form stereoisomer
TSH drives biosynthesis of thyroid hormones

What stimulates thyroid hormone synthesis
TSH drives biosynthesis of thyroid hormones
gPCR receptor heterotrimeric 7 transmembrane g-protein-coupled receptor -> adenylate cyclase -> cAMP -> PKA -> transcription in nucleus of thyroglobulin

Where are thyroid hormones synthesized
Follicular cells of the thyroid

Thyroid hormone precursors
Thyroglobulin & 2x Tyrosine
Describe the hypothalamus-pituitary-thyroid axis endocrine feedback loops
- Cold, acute psychosis, circadian rhythm stimulate the hypothalamic release of TRH
- Severe stress or T3 inhibits the hypothalamic release of TRH
- TRH stimulates the anterior pituitary to secrete TSH
- Corticosteroids and dopamine inhibit the anterior pituitary from secreting TSH
- TSH stimulates the thyroid to synthesize T3 & T4 and secrete them
- Low iodide stimulates the thyroid to secrete T3 & T4
- High iodide inhibits the thyroid from secreting T3 & T4

Wolff-Chaikoff effect
High iodide levels inhibit the thyroid from synthesizing and secreting T3 & T4
The Wolff–Chaikoff effect is known as an autoregulatory phenomenon that inhibits organification in the thyroid gland, the formation of thyroid hormones inside the thyroid follicle, and the release of thyroid hormones into the bloodstream. This becomes evident secondary to elevated levels of circulating iodide
Describe the action of thyroid hormone
Tyrosine is hydrophilic so it cannot passively diffuse
T3 and T4 have to bind to its transporter (thyroid hormone transporter) to enter the cell where it binds to TR (Thyroid hormone receptor) and RXR and a coactivator in the nucleus where it is able to affect gene transcription

Thyroid hormone nuclear receptors
Different types regulating different gene sequences that are Cell type-specific

Thyroid hormone functions
9 listed
- Breathing
- Heart Rate
- Central and peripheral nervous system
- body weight
- menstruation
- muscle strength
- body temperature
- Cholesterol levels
- Body growth & metabolism

Thyroid hormone effects on breathing

Thyroid hormone effects on heart rate

Thyroid hormone effects on the CNS and PNS

Thyroid hormone effects on body weight

Thyroid hormone effects on menstruation

Thyroid hormone effects on muscle strength

Thyroid hormone effects on body temperature

Thyroid hormone effects on cholesterol levels

Thyroid hormone effects on growth & metabolism

Describe the biochemistry of thyroid hormone and metabolism

WAT VS BAT
- White adipose tissue (storage)
- Brown adipose tissue (burn and release heat)
BAT & Thyroid hormones

Hypothalamic effects of thyroid hormones
5 listed
T3 & T4 can activate neurons in different nuclei of the hypothalamus

Case discussion question

A. Graves disease
hyperthyroidism is a typical feature of graves disease
Describe the hypothalamus-pituitary-adrenal axis
Hypothalamus -CRH-> anterior pituitary gland -ACTH-> adrenal gland -glucocorticoids & catecholeamines-> tissues

Hypothalamus-pituitary-adrenal axis organs targeted
immune system
Muscle
Liver
Fat cells
Heart rate

hypothalamus-pituitary-adrenal axis activation organs effects on the immune system
Altered
Hypothalamus-pituitary-adrenal axis activation organs effects on muscle
Net loss of amino acids for (glucose)
Hypothalamus-pituitary-adrenal axis activation organs effects on the liver
Deamination of proteins into amino acids and gluconeogenesis for (glucose)
Hypothalamus-pituitary-adrenal axis activation organs effects on fat cells
Free fatty acid mobilization
Hypothalamus-pituitary-adrenal axis activation organs effects on the heart rate
Increased
What is CRH?
Corticotropin-releasing hormone secreted by the hypothalamus to the pituitary to release ACTH to the adrenal glands

Describe the synthesis of steroid hormones in the adrenal cortex
