Pituitary and Pineal Glands
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what's different about cell surface receptors vs. intracellular receptors?
cell surface: protein hormone binds to protein receptor - triggers secondary messenger - physiological effects
intracellular: carrier protein has a steroid hormone bound to it that can just diffuse through the membrane - bind to a steroid receptor inside the cell that will go into the nucleus and turn on transcription of particular genes - mRNA
why do lipids/steroids need carrier molecules?
because they are hydrophobic so they need a carrier to take them through the blood
what are examples of protein peptide hormones?
PTH, small organic molecules, amino acids/arachidonic acid derivatives
what are the 2 hypotheses for the lobes?
posterior lobe = neurohypothesis (more like classic neural tissue with neurons and axons)
anterior lobe = adenohypothesis (glandular tissue!)
describe the structure of the pituitary gland:
- 2 glands in one! size of a pea, gets bigger after you have kids, at the base of the brain, lies in cavity of spinoid bone
- hypothalamus leads down to the median eminence, which connects to the infundibulum which splits into the 2 lobes
- posterior lobe: pars nervosa
- anterior lobe: divided into 3 parts: pars distalis (majority - bulb part), pars intermedia (touches the posterior lobe, pars tuberalis (wraps around the infundibulum
which lobe is bigger?
how does the anterior lobe function?
- big pic: secretions into the blood
- has a portal system: vein, caps, vein, caps so that caps can pick up what the hypothalamus secretes and then the second set of caps can pick up what the anterior lobe (pars distalis) secretes
how does the posterior lobe function?
- neurosecretory cells in hypothalamus make ADH (antidiuretic hormone) and oxytocin which get transported (through axons) to the posterior part and they are STORED
- then nervous signals from the brain trigger release of these hormones
- the secretory vesicles are released at the nerve endings and picked up by the fenestrated capillaries
function of ADH and oxytocin?
- ADH - kidney tubules, regulates water retention in the kidney by inserting aquaporins
- oxytocin - mammary glands, uterine muscles, smooth muscle contraction (myoepithelial cells). milk will stay in breast but if a baby is sucking on it then release of oxytocin and milk will be released from the mammary glands, also orgasm (from mechanical stimulation)
what are the axons like that enter the posterior pituitary?
what is else is contained in the oxytocin and ADH vesicles?
ATP and specific neurophysins that bind to the ADH/oxytocin through noncovalent interactions (have to do with transport)
what causes diabetes insipidus?
lesions in the pars nervosa (posterior) that cause abnormal secretion of ADH that affects concentration of urine and glucose loss
development of the pituitary gland?
- neuroectoderm - evaginates
- oral ectoderm - outpockets and creates Rathke's pouch
- - the two grow towards each other and the developing sphenoid bone grows through it, separating it from the mouth
what are the 2 main sources of blood in the pituitary gland and where do they supply blood to?
- inferior hypophyseal artery - posterior lobe (pars nervosa), releases it into fenestrated capillary beds
- superior hypophyseal artery - goes to the hypophyseal portal veins then the hypophyseal veins then the capillaries of the hypophyseal portal system (need to look up)
give example of how thyroid is activated and the feeback loop
hypothalamus releases TRH - goes down through portal system - picked up by cells in anterior pituitary gland - pars distalis makes TSH - gets picked up by the fenestrated capillaries - goes and acts on the thryoid gland which makes thyroid hormones, which go back to the hypothalamus and inhibits production of TRH
what is the difference in histology between exocrine and endocrine glands?
- exocrine - ducts
- endocrine - clumps and cords of epithelial that are full of secretory vesicles
what is a tropic hormone?
a hormone that regulates other endocrine glands
what are the tropic and nontropic effects of the anterior lobe? nontropic and tropic effects?
- tropic effects:
- FSH (follicle stimulating hormone) - testes/ovaries
- LH (luteinizing hormone) - testes/ovaries
- TSH - thryoid
- ACTH - adrenal cortex
- nontropic effects: prolactin - mammary glands, MSH - melanocytes, endorphin- pain receptors in the brain
- both: growth hormone - liver and bone
classification of staining of cells in the pars distalis:
- chromophobes (color fearing), they don't pick up stain, the nuclei obviously does though
- basophil (purple) - ACTH, TSH, FSH, LH
- acidophil (pink) - prolactin, GH
which type of cell stain is the majority?
- chromophobes - majority, they don't release anything, everything has been released
- basophil - least common,
basing cells by what they secrete:
- somatotropin: 50%, soma = acts on whole body, centrally located nuclie, produce growth hormone, hypothalamus releases GHRH, which is inhibited by somatostatin, GREHLIN (makes you hungry),
- lactotropes: PROLACTIN- stimulates maturation of mammary gland, acidic granules, 1 tissue that may never fully differentiate (only if you get preggers),
- gonadotropes: reglated by GRH by hypothalamus
- corticotropes: ACTH producing cells, produce a precurer called proopiomelanocortin that is a huge protein that gets cut into a bunch of pieces (one of those pieces makes ACTH, regulated by release of CRH in hypothalamus
what will happen if you have a tumor in a somatotrope?
- in a child - you get gigantism
- in an adult - you get acromegalgy (grow thicker because you dont have any more growth plates)
why do women that had kids have larger pituitary glands?
they made so many lactotropes that underwent hypertrophy
what's the name of the massive molecule that gets broken up and ultimately produces ACTH?
describe histology of pars intermedia
- has MSH
- lots of spaces (leftover ones from the ratkhes pouch)
- concretions: colloid follicles that can be calcified
compare staining of MSH in humans and other mammals?
MSH stains lightly in humans but darkly in other animals
what makes the neurophysins?
the big ass molecule that gets cut up and makes ACTH
functions of the pineal gland:
- regulates daily body rhythm (circadium and seasonal)
- relays light intensity and duration to endocrine activity
- secretes melatonin
- promotes rhythmic changes in secretory activities of gonads and other organs (seasonal sexual activity, menstraul cycle)
structure of the pineal gland?
- size of a tiny pine cone
- near the center of the brain
- it is covered in pia mater and connective tissue and nerves separates it into irregular lobes
- no blood brain barrier!
- profuse blood flow
- quite cellular
why is it described as neuroendocrine?
- b/c it is enervated by parasympathetic and sympathetic nervous systems
- converts nervous signals into hormone signals
what are the cells of the pineal gland?
- pinealocytes - clumps or cords in lobules, main cells, vesicles, processes surround blood vessels
- interstitial (glial) cells - 5% of the cells
- brain sand- calcified concretions that increase with age
what things are regulated by your biological clock?
sleep, appetite, body temperature, hormones, cell regulation/synthesis
what are the 2 characteristics of circadian rhythm?
- endogenous - could be in a dark room, its in your body
- entrainment - can adjust according to outside changes in light
what is a zeitgeber?
external cue that stimulates entrainment (the primary one is daylight)
how does pineal gland release melatonin?
photoreceptors in the retina relay info to the suprachiasmatic nuclei (SCN) through the retinohypothalamic system - causing the pineal to release melatonin
how does melatonin function?
- melatonin inhibits certain neurosecretory neurons in hypothalamus that produce GnRH
- GnRH is secreted by the hypothalamus and is stored in the anterior pituitary gland which then releases LH and FSH
what happens if you get a tumor in your pineal gland?
you cant make melatonin so you don't have a way to control GnRH so you get precocious puberty
histology of pineal gland?
- cellular, blood vessels, pinealocytes clumped together and glial cells
- secretory vesicles because producing melatonin and the blood vessels pick it up (can't see these on microscope though
- lots of similarities between pinealocytes and retina cells
- brain sand - calcified concretions that increase with age (clumps of debris)
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