The Hypothalamus and Pituitary Gland Physiology
Explain the osmolar control loop
Hypothalamus senses increased serum osmolarity and signals ADH/AVP from the posterior pituitary. ADH exerts effects, blood osmolarity decreases, hypothalamic osmoreceptors sense normal osmolarity so ADH release stops
Somatomedins
Insulin-like growth factor (IGF); peptides that promote growth- several types made by several tissues
Which hormones does the hypothalamus make that relate to the the posterior pituitary?
Oxytocin and vasopressin/ADH
What "type" of hormones (steroid, prostaglandin, peptide, protein) does the hypothalamus make?
Peptide hormones
What is the scientific name for Equine Cushings Disease
Pituitary Pars Intermedia Disfunction
What non-tropic hormone(s) are released from the anterior pituitary and what is their classification?
Prolactin and GH
Somatostatin
SS= GHIH; made in the hypothalamus
Somatotropin
ST=GH from anterior pituitary
What then may be a common clinical sign in patients with high ACTH?
Skin darkening!! Effect of MSH
Biologically what does oxytocin cause
contraction of mammary myoepithelial cells (to eject milk), contraction of uterine smooth muscle, develop and maintain pair bond/maternal care and group bond
What is syndrome of inappropriate ADH secretion caused by?
excessive or inappropriate ADH secretion causing the inability to excrete water so water retention and even intoxication occurs. This does NOT happen for excess water intake
What is the effect of stomatomedins
factors dependent on GH/ST; made mostly by the liver; CAUSE growth of bone (linear growth), cartilage, muscle (lean body mass), organ size/functions Also mediates protein, fat, carbs, calcium, PO4 metabolism
How is ADH regulated?
2 different negative feedback loops- Osmolar control loop and Blood volume control loop
What is the median eminence
A funnel-shaped, ventral EXTENSION of the hypothalamus extending towards, but not reaching, the pituitary gland
What do all individual cells in the anterior pituitary have?
A receptor for a specific releasing hormone and machinery TO MAKE one type of stimulating hormone (some also have a receptor for specific inhibiting hormone)
What is the relationship between ACTH and melanocyte-stimulating hormone
ACTH contains within its own structure, the exact structure of MSH
What is the biological activity for ADH and AVP respectively?
ADH: water retention by kidneys AVP: contraction of arteriolar smooth muscle
Target for Corticotropin (CTH/ACTH) and its effects on it's target.
Adrenal cortex; stimulates adrenal cortical growth and activity which increases plasma corticosteroids (stress hormones)
What are the endocrine target organs for the anterior pituitary's tropic hormones?
Adrenal corticies, Thyroid gland, gonads, skeletal muscle and liver
What happens in Equine PPID and why can't it be diagnosed in the same way as cushings in dogs and humans?
An Ademona (benign tumor) causes excessive secretion of ACTH; Cushings in horses cannot be diagnosed the same way as humans and dogs because it affects the ANTERIOR pituitary in hu/ca and the INTERMEDIATE pituitary in horses
Which part of the pituitary has no DIRECT arterial supply and how is this portion supplied?
Anterior pituitary, gets supplied via the hypophyseal portal system
How is oxytocin secretion regulated
POSITIVE feedback; sensory signals originate at the periphery from the target organ
What organ does TSH regulation act on?
Pituitary gland through T3/T4 negative feedback
What hormone does milk production and what hormone does milk excretion and which organs are they released from?
Posterior Pituitary produces oxytocin which does milk EJECTION Anterior Pituitary produces prolactin which does milk PRODUCTION
What promotes and inhibits the release of somatomedin?
Promotes: arrival of GH/ST at target tissue Inhibits: Detection of GH and SM inhibit GH secretion at anterior pituitary--> loss of GH(ST)= decreased SM
What is the difference between a stimulating and a releasing hormone?
Releasing: Made by the Hypothalamus; targets anterior pituitary; cause is tropic- production/release of another hormone Stimulating: Made by Anterior Pituitary; targets peripheral cells/organs; tropic and non-tropic effects- some targets will produce/release another hormone and others have non-endocrine effects
What hormone makes your bones growth?
SomatoMEDIN, stimulated by GH
Thyrotropin Releasing Factor (TRH/TRF)
Stimulates release of thyroid stimulating hormone (TSH)
Stimulating hormones are made by what? and there target is where?
Stimulating hormones are made by the anterior pituitary and their target is out in the body
What are the endpoint effects of Oxytocin?
Stimulation of milk EJECTION (not production), uterine contraction, and pair bonding/ maternal behavior
What is the target organ and effect(s) of prolactin?
Targets the mammary gland Induces and maintains milk PRODUCTION
What is one major difference between the anterior and posterior pituitaries in regards to hormone production?
The Anterior Pituitary MAKES and RELEASES hormone The Posterior Pituitary ONLY RELEASES (doesn't make) hormones
What is a hypothalamic "factor"
a tropic hormone made by the hypothalamus that affects the production of other hormones made by the anterior pituitary
What are the alternate names for the anterior pituitary?
adenohypophysis and pars distalis
What are the 3 lobes of the pituitary gland body?
anterior, intermediate, and posterior
What is diabetes insipidis caused by?
complete or partial failure of ADH secretion or response at the renal tubules resulting in the inability to recover water in the kidney
How is prolactin regulated?
complex negative feedback with dopamine primarily involves INHIBITION or LOSS OF INHIBITION, not really stimulated
What are the METABOLIC effects of growth hormone
mobilize fat stores to spare glucose (non-growth related)
Prolactin Releasing Factor (PRF/PRH)
not well characterized, promotes release of prolactin
What is the alternative name for the intermediate pituitary?
pars intermedia
Releasing hormones/factors
peptides made by the hypothalamus controlling the anterior pituitary and cause it to produce and/or release a particular STIMULATING hormone
Inhibiting hormones/factors
peptides made by the hypothalamus controlling the anterior pituitary to INHIBIT production/release of a specific STIMULATING hormone
Gonadotropin-Releasing Factor (GnRF/GnRH)
regulates the release of BOTH FSH (follicle-stimulating hormone) and LH (luteinizing hormone)
What are the endpoint effects of ADH/AVP?
regulation of body fluid volume and osmolarity contribution to blood pressure regulation
What effects does Melanocyte-Stimulating hormone have in animals?
skin/pelage coloration and seasonal color changes (does something totally different in people)
Corticotropin Releasing Factor (CRH/CRF)
stimulates corticotropin release, adrenocorticotropic hormone ACTH
Growth Hormone releasing factor (GHRF/GHRH)
stimulates growth hormone release
How does the mammary gland regulate oxytocin secretion?
teat/mammary gland stimulated (via suckling) and signal goes to the hypothalamus and is released by posterior pituitary. myoepithelial cells contract, milk ejects, and continued sucking/stimulis= continued released. Positive feedback lost when sucking/stimulus stops
Posterior Pituitary hormones are really what?
two particular hypothalamic hormones since the posterior pituitary just stores those 2 hormones made by the hypothalamus
Why does the posterior pituitary not need releasing or inhibiting hormones?
Because the hormones are released directly into the blood to go to peripheral body tissues
What tropic hormone(s) are released from the anterior pituitary and what is their classification?
CTH/ACTH, TSH, FSH, LH, GH corticotropin (CTH or ACTH) Thyroid-stimulating hormone (TSH) Follicle-stimulating hormone (FSH) Luteinizing hormone (LH) Growth Hormone (GH)/Somatotropin (SH or GH) (The Lost Fish Got Caught anterior side)
What is the effect of Thyroid stimulating hormone and what is it's target?
Causes Thyroid hormone secretion by stimulating thyroid follicular cells
Explain the blood volume control loop
Decrease in blood pressure stimulates low-pressure receptors in heart arteries, AVP/ADH is released and AVP causes arteriole smooth muscle contraction increasing the blood pressure which is then sensed, stopping AVP release
T/F The pituitary is located in the cranial vault
FALSE; it is outside of the cranial vault but just ventral to it
What effects does FSH and LH have?
FSH: promotes ovarian follicular growth and estrogen production; promotes spermatogenesis LH: Promotes ovulation (follicular rupture) and progesterone production by ovulated follicle; promotes testosterone production
T/F The hypothalamus is its own individual organ
False; it is a part of the brain!
What is the target tissue of FSH and LH?
Gonadal tissues in BOTH genders: FSH: ovarian follicle, seminiferous tubules LH: Follicle, interstitial cells
What hormone produced by the anterior pituitary has both tropic and non-tropic effects?
Growth Hormone (GH)
What regulates GH secretion and what is the sequence of the promotion loop?
Hypothalamus integrates body signal--> hypothalamus releases GHRH into hypophyseal portal system--> GHRH to anterior pituitary--> anterior pituitary releases GH--> GH enters systemic blood and travels to target tissues--> GH stimulates somatoMEDIN release
Describe the process of getting the controlling factors made by the hypothalamus to the anterior pituitary
Hypothalamus makes appropriate hormones--> releases hormones at median eminence--> they travel through the hypophyseal portal system to the anterior pituitary to affect its function
Where does the hypothalamus release its products related to the anterior pituitary and what are the target organs for these products?
Hypothalamus sends products related to the anterior pituitary into the PITUITARY circulation and targets ENDOCRINE cells in the ANTERIOR pituitary
What regulates GH inhibition and what is the sequence of the inhibition loop? What type of feedback is this?
Increased GH and/or somatomedin in blood--> level communicated to hypothalamus--> hypothalamus reduces GH release (likely secretes GHIH) Long-loop negative feedback
What 2 embryologic structures form the pituitary and what parts of the pituitary are formed by each structure?
Infundibulum (out pocket from the brain) forms the infundibular stalk and the posterior pituitary The oral diverticulum forms the pars tuberalis, the intermediate lobe, and the anterior pituitary
Growth Hormone Inhibiting Factor (GHIF/H) OR Somatostatin
Inhibits growth hormone release
Prolactin Inhibiting Factor (PIF/H)
Inhibits release of prolactin
What do these releasing, inhibiting, stimulating hormones allow for?
Layers of control
What is the main product secreted by the Intermediate Pituitary
Melanocyte-Stimulating Hormone
What are the alternate names for the posterior pituitary?
NEUROhypophysis and pars nervosa
How does the uterus regulate oxytocin secretion?
Oxytocin stimulates uterine contraction stretching the uterine cervix. Stretch is sensed and sent to hypothalamus for more oxytocin release. This continues until fetus is expelled/loss of cervical stretch and oxytocin release stops
What "type(s)" of hormones are made in the anterior pituitary?
PEPTIDE, STIMULATING hormones
What is the Primary direct effect of GH/ what are the Growth-related effects of growth hormone
***cause release of somatoMEDINS***, a group of GH/ST-DEPENDENT growth factors that actually cause the growth
Overall summary of the Anterior pituitary****Know this and y0u are pretty much good****
The Anterior pituitary/adenohypophysis/pars distalis is composed of GLANDULAR tissue. It receives INDIRECT arterial supply via the HYPOPHYSEAL PORTAL SYSTEM and INDIRECT communication from the hypothalamus since no tissue connection exist between them, only vascular. The anterior pituitary is ACTED on by the hypothalamus hormones (tropic) TO MAKE hormones
How can the anterior and posterior pituitary both get their products to attain the systemic circulation?
The each have their own venous drainage
Where does the hypothalamus release its products related to the posterior pituitary what are the target organs for these products?
The hypothalamus sends products to the posterior pituitary to be released into systemic circulation to reach the peripheral body
What are the 2 parts of the pituitary stalk and what kind of tissue are they composed of?
The largest part of the pituitary stalk made up of NEURAL tissue that suspends the POSTERIOR pituitary it the infundibular stalk The portion that wraps around the infundibular stalk that is a dorsal extension of the ANTERIOR pituitary made up of GLANDULAR tissue is the pars tuberalis
What are the non-endocrine target organs for the anterior pituitary's non-tropic hormones?
The mammary gland and certain growth cells- chondrocytes and adipocytes
What is the hypophysis?
The pituitary gland, another name
What structure "suspends" the pituitary body from the brain?
The pituitary stalk
Overall summary of the Posterior pituitary****Know this and you are pretty much good****
The posterior pituitary/Neurohypophysis/pars nervosa is composed of NEURAL tissue partially made up/extention of the hypothalamus. It receives DIRECT arterial supply and communication from the hypothalamus and can STORE and RELEASE (on cue) the non-tropic HORMONES MADE FROM THE HYPOTHALAMUS to act on the peripheral body. The posterior pituitary DOES NOT make its own hormones.
Why does ADH/Vasopressin have 2 names if they are the same hormone?
The same hormone that has 2 different target tissues with tissue-specific effects
Describe how the hypophyseal portal system sends vascular supply to the anterior pituitary
There is an arterial capillary network formed in the median eminence and infundibular stalk (neural parts), this capillary bed forms venues that travel to the anterior pituitary where they re-arborize so the blood at the median eminence passes through the infundibular stalk and into the anterior pituitary
What is unique about the communication/connection between the hypothalamus and the Anterior Pituitary?
There is no tissue connection, only vascular via hypophyseal portal system
What gland is the "master" endocrine gland?
They hypothalamus and pituitary (hypophysis) together!
What are the main general roles of the hypothalamus
To control and integrate various functions: Homeostasis, some somatic functions, and a lot of endocrine activity
T/F The hypothalamus has control over the pituitary
True
T/F The hypothalamus forms part of the pituitary gland
True; extend VENTRALLY into and forms PART of the pituitary (posterior pituitary)
How can the hypothalamus control/communicate with the non-neural part of the pituitary?
Using the hypophyseal portal system, the hypothalamus can control the anterior pituitary/adenohypophysis
What are the 2 "posterior pituitary" hormones?
Vasopressin/ADH and Oxytocin
Can substances be transported from the median eminence directly to the anterior pituitary?
Yes, utilizing the hypophyseal portal system
