L2: Hypothalamus and Pituitary Gland Phys Flashcards
The interface between the nervous and endocrine systems?
Hypothalamus
Main endocrine function of the hypopthalamus? (7)
- growth
- fertility and reproduction
- osmoregulation (water balance)
- metabolism (thermoregulation)
- energy balance
- stress response
- lactation
Connections between the hypothalamus and Pituitary Gland?
Morphology and Function of each?
Magnocellular Neruons (large, long)
–large cell bodies with long axons projecting down to (posterior) pituitary
–oxytocin and vasopressin (ADH) released into systemic circulation
Parvocellular Neurons (small, short)
–small cell bodies w/ shorter axons projecting to top of pituitary stalk (infundibulum)
–6 hormones (hypophysiotropic hormones) released into Portal Circulation
Hormones secreted by Parvocellular Neurons?
Posterior Pituitary is made of __________ tissue
Pituitary gland is made of NEURAL tissue
Collection of axonal projections from the hypothalamus that serve as a site for the secretion of neurohypophysial hormones directly into the blood?
Posterior Pituitary
_____________: Unmyelinated nerve axons of neurons cells whose cell bodies are located in hypothalamus
Neurohypohysis (aka. Posterior Pituitary): Unmyelinated nerve axons of neurons cells whose cell bodies are located in hypothalamus
Another name for glial cells?
Pituicytes
______________: Secretory granules containing oxytocin and vasopressin in terminal region of axon of Posterior Pituitary
Herring bodies: Secretory granules containing oxytocin and vasopressin in terminal region of axon
Vasopressin is released from the _____________
Vasopressin is released from the Posterior Pituitary
Vasopressin’s physiological effects? (V1 vs. V2)
V1 receptors:
□ abundant in vascular smooth muscle cells
□ activation of V1 receptors => VSMC contraction (‘vasopressin’)
V2 receptors:
□ abundant in renal tubule epithelial cells
□ activation of V2 receptors => increased renal H2O reabsorption
___________ plays essential role in maintaining water balance in kidney
Vasopressin
How does Vasopressin (ADH/AVP) Function to regulate water balance?
Plasma osmolality of > 280mOsm/kg => AVP release
AVP acts on renal epithelial cells to promote reabsorption of H2O
Plasma volume is increased and its osmolality decreased
Urine volume is decreased and its osmolality is increased
Independently, thirst centers in the hypothalamus are activated increasing the urge to consume H2O
What 3 stimuli control Vasopressin Release?
- Blood Osmolality > 280mOsM (sensed by hypothalamus osmoreceptors)
- Hypovolemia (decreased atrial stretch receptor activation)
- Hypotension ( decreased carotid and aortic baroreceptor activation
ADH Action on Kidney Tubule Epithelia?
ADH acts on renal epithelial cells V2 receptors to promote reabsorption of H2O
Leads to water channels (Aquaporin II ) insertion on apical membrane => allows water to enter cell and be returned to vasculature=> Smaller volume of more concentrated urine secreted
Inability of kidney to reabsorb H2O =>excretion of large volumes of dilute urine (25l/day)?
DIabetes Insipidus (ADH Deficiency)
Types of Diabetes Insipidus?
NEURAL (cranial) DI (hypothalamus/pituitary lesion)
NEPHROGENIC DI (renal ‘resistance’ to ADH)
- Inherited -mutations in V2 receptor (X-linked) or aquaporin 2 (autosomal)
- acquired -drug-induced (amphotericin B)
Diagnosis of Diabetes Insipidus?
Water deprivation test (DI individual will not concentrate urine)
Treatment of Diabetes Insipidus?
Desmopressin (Synthetic Vasopressin)
NOT Appropriate to treat nephrogenic DI - resistant to vasopressin!!
Which drug can induce Diabetes Insipidus?
Amphotericin B
Excess ADH usually caused by GI/Pulmonary tumors that secrete ADH in unregulated function?
Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)
Physiological Role of Oxytocin?
Weak antidiuretic action (similarity to AVP)
Parturition (Childbirth)- Stimulates uterine contractions, can induce labor
Lactation- Milk letdown reflex
Social/mating/emotional behaviour (Love Hormone)
______________ triggers myoepithelial contractions to expel milk from mammary alveoli into ducts/collecting chamber. This is known as __________
Oxytocin triggers myoepithelial contractions to expel milk from mammary alveoli into ducts/collecting chambers. This is known as the milk letdown reflex
One of the few areas of the brain where the blood-brain barrier is compromised?
Hypothalamus/pituitary is one of the few areas of the brain where the blood-brain barrier is compromised because of fenestrated capillaries
All the hormones released by the anterior pituitary are ________
All are peptide hormones
Hormones that have other endocrine glands as their target?
Trophic Hormone: Triggers release of other hormones
Only major Anterior pituitary hormone that is NOT trophic
Prolactin
Regulation of Prolactin
- ________________ increases release ( ie. during pregnancy)
- ________________ inhibits prolactin release (suckling reflex)
Regulation of Prolactin
- Estrogen/progesterone increases release ( ie. during pregnancy)
- Dopamine inhibits prolactin release (suckling reflex)
Physiological roles of Prolactin
Lactation (Primary) - Breast Development/milk production in pregnancy
Immune tolerance: Prevents body from reacting to fetus
Behavioral: nurturing instinct/broodiness
High levels of ________ inhibits fertility by lowering GNIH
=> reduction of FSH and LH
High levels of PROLACTIN inhibits fertility by lowering GNIH
=> reduction of FSH and LH
What mediates the Anabolic (growth promoting) effects of Growth Hormone. Where is it produced?
Anabolic (growth promoting) effects mediated by IGF-1
Produced in the liver in response to GH
______ is a contrainsulin hormone
Growth hormone is a contrainsulin hormone
Insulin lowers plasma glucose, GH increases plasma glucose
_______ has insulin like metabolic actions
IGF-I has insulin-like metabolic actions despite being stimulated from the liver by Growth Hormone that is a contra insulin hormone
Normal age-related decline in GH (and IGF-I) of ~ _____% between the ages of 20-60?
Somatopause => ~50% decline
Linked to signs of aging
Growth Hormone Regulation?
Hypoglycemia/Grehlin => Increased GH
Exercise: vigorous exercise => Increased GH
Somatopause: age-related decline in GH (and IGF-I) ~ 50%
_________________ of GH Secretion is essential for normal growth
Pulsatile and circadian pattern of GH Secretion
When does the majority of GH secretion occur?
70% daily GH secretion coincides with the onset of deep sleep (REM4)
What causes GH Deficiency in Children?
head trauma
infections (eg, encephalitis, meningitis),
cranial irradiation
systemic diseases (eg. leukemia)
Symptoms of GH Deficiency in Children?
short stature
low growth velocity for age/pubertal stage
increased amount of fat around the waist
delayed tooth development
delayed onset of puberty
Main Causes of Adult Onset GH Deficiency?
- pituitary tumors that impair somatotroph function
- head trauma
- vascular abnormalities of hypophyseal circulation
Symtoms of Adult Onset GH Deficiency?
metabolic abnormalities
DECREASE lean body mass, INCREASE adiposity
osteoporosis
psychological disorders
________ is important in the maintenance of skeletal muscle and bone and in glucose homeostasis
Growth Hormone is important in maintenance of skeletal muscle and bone and in glucose homeostasis
Consequences of GH Hypersecretion (Congenital vs Adult)
Congenital (GH excess prior to fusion of epiphyseal growth plate)=> Acromegalic Gigantism
Adult Acquired (Growth plates fused)=> Acromegaly
- bone thickening (not lengthening)
- metabolic abnormalities similar to type 2 diabetes
- increased risk of cardiovascular disease, cancer
