Lecture 31 Flashcards
GH releasing Hormone (GHRH) targets what cell?
Somatotrope
GH releasing Hormone causes what feedback loop on hormones?
(+) GH
Somatostatin (SRIF) targets what cells?
Somatotrope and Thyrotrope
Somatostatin (SRIF) causes what feedback loop on hormones?
(-) GH and (-) TSH
Dopamine targets what cells?
Lactotrope
Dopamine causes what feedback loop on hormones?
(-) PRL
Thyrotropin releasing hormone (TRH) targets what cells?
Lactotrope
Thyrotropin releasing hormone (TRH) causes what feedback loop on hormones?
(+) PRL and (+) TSH
Gonadotropin releasing hormone (GnRH) target what cells?
Gonadotropes
Gonadotropin releasing hormone (GnRH) causes what feedback loop on hormones?
(+) FSH and (+) LH
Corticotropin Rel. Horm. (CRH) target what cells?
Corticotrope
Corticotropin Rel. Horm. (CRH) causes what feedback loop on hormones?
(+) ACTH
Function of the hypothalamic-hypophyseal portal system
To provide blood to the hypothalamus and pituitary
Function of the hypothalamo-hypophyseal tract
Provides the pituitary gland signals from the hypothalamus
The major nuclei of the hypothalamo-hypophyseal tract
Paraventricular (PVN) and Supraoptic (SON)
The nuclei that secretes oxytocin
Paraventricular (PVN)
The nuclei that secrete anti-diuretic hormone
Supraoptic (SON)
Other terms for anti-diuretic hormone
(ADH) and arginine vasopressin (AVP)
The carrier proteins of the hypothalamo-hypophyseal tract
neurophysin
The structure in which neurophysin accumulates in
axon dilations called Herring bodies
Target tissues of Vasopressin (ADH)
Kidney and vasculature
Target tissues of Oxytocin
Mammary gland and uterus
The two major cell types that release hormones into the blood (hypothalamic-hypophyseal portal system)
Acidophils and Basophils
Acidophil cells (percent in hypothalamic-hypophyseal portal system) - hormone
Somatotropes (45%) - Growth Hormone
Lactotropes (25%) - Prolactin (PRL)
Basophil cells (percent in hypothalamic-hypophyseal portal system) - hormone
Thyrotropes (5%) - Thyrotropin (TSH)
Gonadotropes (5%) - Follitropin (FSH) or Luteotropin (LH)
Corticotropes (20%) - Cotricotropin (ACTH) or Melanocyte Stimulating Hormone (MSH)
How does hormonal activity work through the body? (Hint: start at synthesis and end at biological effect)
Hormone synthesis is used to control gene expresion
Hormones are stored before being secreted (requires either a specific or non-specific secretion stimulus)
The hormones are then transported to either a target cell receptor or back to secretion cells/cells that perform hormone synthesis for feed-back control.
The target cell binds to the hormone and starts off a signal-transduction pathway, which then kicks off the biological effect
How can transport of hormones differ from taking the hormone straight to the target cell?
- Metabolism: the hormones are inactivated and recycled via digestion
- Excretion: the hormones exit the biological system
What are the three functions of hormone receptors?
Synthesis, modification, and metabolism
What is the order of pulsatile release of GnRH and the gonadotropins?
GnRH
FSH
LH
Releasing factor pathway of hormones
Hypothalamus -> pituitary gland, releases hormone A -> target organ, releases hormone B
Inhibiting factor pathway of hormones
Hormone B inhibits the pituitary gland and hypothalamus directly. Pituitary gland is also inhibited indirectly due to hypothalamus being inhibited.
Names for Oxytocin
- Love hormone
- Divorce hormone (based on defective oxytocin hormone)
Oxytocin effects other than love
Oxytocin repairs and maintains old muscle.
How does ADH interact with its target tissue in physiologically normal conditions?
ADH binds to vasopressin II receptor on collecting duct cells -> cAMP-mediated translocation of aquaporin-2 to apical surface -> increased permeability to water
What happens in the absence of ADH?
- Water cannot be reabsorbed
- Hyperosmolality (increased solute)
- Hypernatremia (high plasma [Na+])
- polyuria (excessive volume of urine + frequency of urination)
- Polydipsia (thirst and increasing drinking) occur
How does alcohol affect ADH?
Inhibits release from Supraoptic Nuclei & acts as an antagonist for ADH in kidneys, which prevents aquaporins from binding to the collecting ducts
How does pregnancy affect ADH?
Placenta secretes vasopressinase resulting in features of both central and nephrogenic DI. (Plasma level falls after delivery)
Main causes of central diabetes insipidus
- Tumors
- Trauma
- Surgery
Main causes of nephrogenic diabetes insipidus
- Renal diseases
- ADH-unresponsive kidney (ex. DM)
- Drugs (lithium based) -> lower cAMP
What does SIADH mean?
Syndrome of Inappropriate ADH secretion
How does SIADH compare to diabetes insipidus?
SIADH acts in the opposite way in terms of ADH secretion:
- High levels of ADH secretion or AVP-like substances
- Urine osmolality is inappropriately high (kidneys salvage large volumes of water.
- Total body water increases, hypo-osomolar, and hyponatremia.
What is hyponatremia?
Two mechanisms:
1. Dilution of plasma
2. increased excretion of Na+ by the kidney (usually because of expanded blasma volume, which enhances filtration and reduces reabsorption)
