6 - Hypothalamus and Pituitary Hormones Flashcards
Describe the pituitary and hypothalamus - overview
- Function together
- Coordinate physiological responses of many different organs
- Form an interface between the central nervous system and the endocrine system
- Act to regulate multiple endocrine glands (thyroid, adrenals, gonads)
- Disruption of normal function has profound physiological consequences
What are the two types of hypothalamus neurons?
- Magnocellular neurons
- Parvivellular neurons
Describe the location and function of magnocellular neurons
- neurosecretory cells
- axons terminate in posterior lobe of pituitary
- secrete large quantities of hormone into the systemic circulation
Describe the location and function of parvicellular neurons
- neurosecretory cells
- axons terminate at the median eminence
- secrete small quantities of hormone into the portal hypophysial system
- these hormones are hypophysiotropic factors which are transported to the anterior pituitary
- they regulate hormone release from the anterior pituitary
What is feedback regulation of hormone secretion?
When the release of a given pituitary hormone is regulated in response to the level of that same hormone in the blood
Describe one of the general themes in hormone receptors
- Most of the hormones we will discuss are hydrophilic ***
- These hormones bind to receptors that are integral membrane proteins
- Many of these receptors are G-protein coupled receptors
What do G-protein coupled receptors do?
- Regulate the activity of adenylate cyclase
- Activate phospholipase C
Describe the way in which G-protein coupled receptors regulate adenylate cyclase
- They either increase or decrease the production of cAMP
- This either increases or decreases the activity of cAMP-dependent protein kinase (protein kinase A - PKA)
Describe the way in which G-protein coupled receptors activate phospholipase C
- They generate IP3 and diacylglycerol
- This increases the intracellular Ca++
- This also activates protein kinase C (PKC)
Quick reminder - What is PKA?
PKA activity is dependent on cAMP. PKA is also known as cAMP-dependent protein kinase.
Protein kinase A has several functions in the cell, including regulation of glycogen, sugar, and lipid metabolism.
Quick reminder - what is PKC?
PKCs are a family of protein kinase enzymes that are involved in controlling the function of other proteins through the phosphorylation of hydroxyl groups of serine and threonine amino acid residues on these proteins
Give a basic overview of how peptide hormones are processed
- Many hormones that we will cover are peptide hormones
- These hormones are synthesized as larger precursor proteins
- Specific proteolysis reactions release peptide fragments
Describe the peptide fragments that are released
- Peptide fragmetns are the functional hormone
- Often several distinct proteolytic fragments are generated
- The fragments may each have distinct biological activities
What are the two hormones secreted by the posterior pituitary?
- Oxytocin
- Vasopressin
Describe the synthesis and secretion of oxytocin and vasopressin
- Oxytocin and arginine vasopressin are peptide hormones that are synthesized in the cell bodies of hypothalamic magnocellular neurons
- The hormones are then secreted into systemic circulation from the posterior pituitary gland
What are oxytocin and vasopressin derived from?
- Derived from proteolytic processing of precursor polypeptide
What is the process of synthesis of oxytocin and vasopressin?
- pre-pro-hormone is synthesized on membrane associated ribosomes
- it is then translocated into the ER, signal sequence cleaved, routed through Golgi to neurosecretory vesicles, processed on route to nerve terminal
What is the function of oxytocin?
Oxytocin stimulates smooth muscle contraction
What does oxytocin target?
- Uterus during pregnancy
- Lactating breast
What does oxytocin do to the uterus during pregnancy?
Smooth muscle contractions which induce labor
What does oxytocin do to the lactating breast during pregnancy?
Promotes milk ejection
What type of receptors are found in the tissues that oxytocin targets?
G-protein coupled receptors
- Signaling for the hormone receptors occurs through the activation of phospholipase C
What stimulates the release of oxytocin?
- Mechanical stimulation of uterine cervix by the fetus
- Suckling of lactating breast
What inhibits the release of oxytocin?
- Severe pain
- Fever
- Loud noises
What is the function of arginine vasopressin?
- Stimulates water reabsorption in the kidney
- Stimulates contraction of vascular smooth muscle
What type of receptors are found in the tissue that vasopressin targets?
G-protein coupled receptors
- When a receptor is stimulated, it activates adenylate cyclase and phospholipase C
- PKA phosphorylates aquaporin 2 transporter proteins
- This leads to increased water permeability of the collecting duct (more resorption)
What does the activation of adenylate cyclase result in?
- PKA phosphorylates aquaporin 2 transporter proteins
- This leads to increased water permeability of the collecting duct (more resorption)
What does the activation of phospholipase C result in?
- There is an increase in Ca++ concentration which activates protein kinase C
- This causes smooth muscle contraction and raises the blood pressure