Lecture 8 Flashcards
(21 cards)
What are the two parts of the pituitary gland? What is the major organ responsible for responding to internal/external signals from the body, deciding what to do, and then telling the pituitary gland what hormones to release?
The hypothalamus is responsible for telling the anterior and posterior pituitary glands what to do.
Where are oxytocin and vasopressin produced? How are these hormones released?
Oxytocin and vasopressin are produced in the posterior pituitary and released into the bloodstream through neurons.
What do oxytocin and vasopressin promote in the body?
Oxytocin: promotes contraction of smooth muscle of the uterus during labor and milk let down
Vasopressin: water reabsorption in the kidneys. Antidiuretic to maintain salt balance
Why is the posterior pituitary an extension of the hypothalamus?
The secretory neurons come down from the hypothalamus where production of the hormones occur. They are then released in the posterior pituitary. The neurons have nerve endings in the posterior pituitary and different neuronal receptors synapse on the cell body and will begin the process of precursor molecules becoming antidiuretic or oxytocin.
How are the effects of oxytocin mediated?
GPCR activation of adenylyl cyclase
In terms of the positive feedback loops which concern oxytocin, what causes the end of the positive feedback loop?
When the baby comes out during labor, oxytocin is signaled to stop being produced.
The action of suckling during milk letdown
How do sex hormones influence the effect of oxytocin on target tissues?
They allow for the differentiation of oxytocin target tissues. These are required in order for oxytocin effects to be exerted
How can the secretion of oxytocin be stimulated indirectly?
When mothers hear/see their babies crying, it enables the milk letdown to occur.
What are the effects of vasopressin and why is it released? What region of the body does vasopressin exert its main effect and how is the secretion ceased? What are the effects of vasopressin at extremely high concentrations?
It’s an antidiuretic hormone. Kidneys start to retain more water and produce less urine (increase in plasma osmolarity.) Its main effect is on the kidneys, mediated through cAMP. After blood tonicity levels have gone down to appropriate levels, it will signal for the end of the release of vasopressin. At extremely high concentration, vasopressin constricts blood vessels.
What would be the effect of a total lack of vasopressin hormone?
If there’s no ADH, your body will not absorb the water that it is supposed to. As a result, you will end up urinating a lot more than usual.
Explain how the kidneys filter fluid from your blood.
Ions get transported into these ducts along with water and your body decides whether or not you need the water to be absorbed. Water has the potential to diffuse out of the tubules such that the fluid will either become more concentrated. If you are well hydrated and your body doesn’t need to absorb a lot of water, you will have a low amount of ADH, therefore your urine will note get very concentrated.
If you’re dehydrated, your body will release ADH, signaling for your kidneys to reabsorb more water. This will help offset the concentration of ions present in the body.
What other kinds of feedback loops are associated with osmoreceptors?
Thirst: increase in plasma tonicity = increase of thirst = hold onto more liquid
Low plasma tonicity = decrease in thirst = decrease in ADH
What would occur as a result of insufficiency of ADH in the body?
Insufficiency of ADH can lead to diabetes insipidus (arginine vasopressin deficiency. This leads to polyuria (peeing a lot)
What other hormone regulates body fluid volume? Where is this hormone secreted from, and how does it function?
Aldosterone (secreted by the adrenal cortex) regulated body fluid through the regulation of sodium levels.
Where are vasopressin and oxytocin genes located? Where and in what form are these two hormones released initially, and what modifications do they undergo in order to convert them into hormones?
They are close on chromosome 20 and are initially released as prohormones in secretory neurons. Prohormones must form disulfide bonds and modify C-terminus to add nitrogen group in order to be activated. They will then be released from the posterior pituitary.
Explain the difference in the way that hormones are released from the anterior versus the posterior pituitary.
The posterior pituitary contains the axon ends of the hypothalamus. Signals come in to the hypothalamus and gets processed in the axon of the hypothalamus secretory neuron. The end of the axon is synapsed on capillaries in the posterior pituitary. So, hormones released in the posterior pituitary are made in the hypothalamus but released by the posterior pituitary.
The anterior pituitary is an endocrine organ, so it must receive releasing factors from the hypothalamus and then the anterior pituitary itself. Releasing factors from the hypothalamus are sent to the anterior pituitary through arteries. Once they enter the anterior pituitary, they affect the cells and then it releases the specific hormone based on the signal. They enter the capillaries in the anterior pituitary and they circulate through the rest of the body and activate second targets.
What enables hypothalamic secretory neurons such that they are able to synthesize and secrete specific releasing/inhibitory hormones directed towards the anterior pituitary?
Different sensory neurons will synapse in the hypothalamus to signal the release of hormones. Different neurotransmitters will come in and they will signal the hypothalamic secretory cells to release hormones into the capillaries near it. The anterior pituitary will produce hormones that it needs to respond to the stimuli.
What are the primary hypothalamic regulatory hormones, where do they signal, and what signal do they release?
1) Thyrotropin-releasing hormone (TRH): acts on thyrotrope cells and stimulates the release of thyroid stimulating hormone (TSH) - acts on thyroid cells
2) Gonadotropin-releasing hormone (GnRH): acts on gonadotrophs to release Luteinizing hormone (LH) and Follicle stimulating hormone (FSH)
3) Corticotropin-releasing hormone (CRH): acts on corticotropes to release adrenocorticotropic hormone (ACTH)
4) Growth hormone-releasing hormone (GHRH): acts on somatotrophs to release growth hormone (GH)
5) Somatostatin (SST): acts on somatotrophs and other cells to inhibit the release of their hormone
6) Dopamine: acts on lactotrophs to inhibit the release of prolactin (PRL)
What is the role of somatostatin? Where is it produced?
Inhibits the release of a lot of hormones; produced by the hypothalamus and pancreas
What is the role of dopamine in milk production?
prevents the release of prolactin by lactotrophs, which prevents the production of milk
What is the classification of the hypothalamic releasing hormones? Are they steroid hormones, protein hormones, peptide hormones, eicosanoids, or amino acid derivatives? What kind of modifications do these hormones have?
Peptide hormones; some have c-terminal amides, some have pyroglutamyl attached to n-terminus, some have both, and some have neither.
