Final Exam Flashcards
Synthesized from Amino Acids
Peptides and Proteins
Synthesized from Cholesterol
Steroids
Synthesized from Tyrosine
Amines
The hypothalamus secretes
TRH, CRH, GnRH, GHRH, Somatostatin, Dopamine
The anterior pituitary secretes
TSH, FSH, LH, ACTH, MSH, Growth Hormone, Prolactin
The posterior pituitary secretes
Oxytocin and ADH
Peptide and protein hormone synthesis in the nucleus
gene for the hormone is transcribed into an mRNA (template)
TRANSCRIPTION
Peptide and protein hormone synthesis in the ribosomes
mRNA is transferred to the cytoplasm and translated on the ribosomes to the first protein product, a preprohormone
TRANSLATION
Peptide and protein hormone synthesis in the ER
converting the preprohormone to a prohormone by removal of the signal peptide
Peptide and protein hormone synthesis in the Golgi apparatus
packed in secretory vesicles
Cortisol, aldosterone, estradiol and estriol, progesterone, testosterone, and 1,25-dihydroxycholecaliciferol
Derivatives of cholesterol
Synthesized and secreted by: adrenal cortex gonads corpus luteum placenta
Amine hormones catecholamines (epi, norepi, and dopamine) and thyroid hormones
derivatives of tyrosine
Neural mechanism of regulating hormone secretion
the adrenal gland
Feedback mechanisms of regulation hormone secretion
more common than neural mechanisms directly/indirectly NEGATIVE FEEDBACK (most important, more common) Positive feedback (rare)
Negative Feedback
when hormone levels are adequate or high, secretion of the hormone is inhibited
when hormone levels are inadequate or low, secretion of the hormone is stimulated
Long-loop feedback
hormone feeds back ALL THE WAY to the hypothalamic-pituitary axis
Short-loop feedback
Anterior pituitary hormone feeds back on the hypothalamus to inhibit secretion of hypothalamic-releasing hormone
Ultrashort-loop feedback
In which the hypothalamic hormone inhibits its own secretion
e.g. growth hormone-releasing hormone [GHRH] inhibits GHRH secretion
Positive Feedback
self-augmenting
explosive or self-reinforcing
Estrogen > Anterior Pituitary > ^ FSH & LH > ovary > ^ estrogen
Positive Feedback
Dilation of cervix > ^ oxytocin from posterior pituitary > uterine contraction > further dilation of the cervix
Positive Feedback
In this example, the explosive event is parturition: delivery of the fetus
Dose-response relationship
responsiveness of a target tissue to a hormone
as the hormone concentration increases, the response usually increases and then levels off
Sensitivity
hormone concentration that produces 50% of the maximal response
decreased sensitivity if more hormone is required to produce 50% of max response
Responsiveness or sensitivity can be changed by
changing of the NUMBER of receptors
changing the AFFINITY of the receptors for the hormone
Down-regulation
of receptors or the affinity of the receptors for the hormone has decreased
May occur by:
decreasing the synthesis of new receptors
increasing degradation of existing receptors
inactivating receptors
Up-regulation
of receptors or the affinity of the receptors has increased
May occur by:
increasing synthesis of new receptors
decreasing degradation of existing receptors
activating receptors
Hypothalamic-pituitary unit
regulates the functions of the thyroid, adrenal, and reproductive glands and also control growth, milk production & ejection, and osmoregulation (ADH)
Pituitary Gland Posterior lobe (posterior pituitary) Anterior lobe (anterior pituitary)
hypophysis
neurohypophysis
adenohypophysis
Infundibulum
thin stalk connecting the hypothalamus to the pituitary gland
Nucleus of Hypothalamus
Supraoptic nuclei - synthesize ADH
Paraventricular nuclei - synthesize oxytocin
Anterior Pituitary secretes 6 peptide hormones
thyroid-stimulating hormone (TSH) 5% follicle-stimulating hormone (FSH) 15% luteinizing hormone (LH) 15% growth hormone (GH) 20% prolactin 15% adrenocorticotropic hormone (ACTH) 15%
Relationship between hypothalamus and anterior pituitary
both neural and endocrine
Relationship between hypothalamus and posterior pituitary
only neural
Hypothalamic-hypophysial portal blood vessels
directly links the hypothalamus and anterior pituitary, providing most of the blood supply to the anterior lobe
Important implication of the portal blood supply
delivering high concentrations of hypothalamus hormones to the anterior pituitary without appearing in high concentration in the rest of circulatory system
Placental hormone that is structurally related to the TSH-FSH-LH family
Human Chorionic Gonadotropin (HCG)
ATCH Family
- derived from single precursor. pro-opiomelanocortin (POMC)
- includes ATCH, γ- and β-lipotropin, β-endorphin, and melanocyte-stimulating hormone (MSH)
- ACTH: only hormone of family with well-established physiological actions
- MSH: involved in pigmentation in lower vertebrates but has little activity in humans
- Endorphins: endogenous opiate
Growth Hormone (somatotrophs)
secreted throughout life
single most important hormone for normal growth to adult stature
profound effects on protein, carbohydrate, and fat metabolism
Action of GH in the Liver
generates IGF (has tyrosine kinase activity similar to the insulin receptor
polypeptides with similar sequence to insulin
has peripheral effects like GH
Direct actions of GH
Decreased glucose uptake into cells (diabetogenic)
Increased lipolysis
Increased protein synthesis in muscle
Increased body mass
Actions via IGF
Increased protein synthesis in chondrocytes and increased linear growth (pubertal growth spurt) Joint Pain
Increased protein synthesis in muscle
Increased lean body mass
Increased protein synthesis is most organs
Increased organ size
GH deficiency
dwarfism, mild obesity, delayed puberty caused by hypothalamic dysfunction (decrease GHRH) lack of anterior pituitary GH failure to generated IGF in liver GH receptor deficiency
GH excess
Adults: acromegaly (after puberty)
Increased periosteal bone grown and organ size, inhibits insulin hence hyperglycemia
Children: gigantism (before puberty)
Increased linear growth
Prolactin (lactotrophs)
stimulates lactogenesis
together with estrogen, stimulates breast development
structurally similar to GH
Actions of Prolactin
stimulates milk production
stimulates breast development
inhibits ovulation by decreasing syn. of GnRH
inhibits spermatogenesis by decreasing GnRH
Prolactin deficiency
due to destruction of anterior pituitary gland
failure to lactate
Prolactin excess
prolactinomas; most common pituitary tumor
hypothalamic destruction
loss of dopamine inhibitory effect
galactorrhea
anovulation, amenorrhea & decreased libido
due to GnHR inhibition
Rx: bromocriptine - dopamine agonist which decrease prolactin secretion
Posterior Lobe Hormones
ADH & oxytocin (produced in hypothalamus)
Synthesized by hypothalamic nuclei
Secreted by posterior pituitary
ADH
Synthesized by supraoptic nuclei
Regulates osmolarity by increasing H2O permeability of the late distal tubule and collecting ducts (V2 receptors and adenylate cyclase mechanism)
Constriction of vascular smooth muscle (V1 receptors and IP3/Ca2+ mechanism
Pathophysiology of ADH
Central diabetes insipidus
Nephrogenic diabetes insipidus
Syndrome of inappropriate ADH (SIADH)
Central Diabetes Insipidus
Failure of the post. pit. to secrete ADH
Circulating levels of ADH are low
Collecting ducts are impermeable to h2o, and urine canon be concentrated
Produce large volumes of dilute urine & body fluids become concentrated
Rx: ADH/vasopressin analogue, ddavp (desmopressin)
Nephrogenic Diabetes Insipidus
Post. pit. is normal
Principal cells of collecting duct are unresponsive to ADH (d/t defective V2 receptor, gs protein, or adenylyl cyclase)
Excretion of large volumes of dilute urine
Serum osmolarity increase
Contrast to CDI, ADH is high d/t stimulation from increased osmolarity
Rx: thiazide diuretics (inhibits Na+ reabsorption in early distal tubule=ECF vol. contraction)
Syndrome of Inappropriate ADH (SIADH)
Excess ADH secreted from post. pit. or from an autonomous site
Excess h2o reabsorption by collecting ducts
Dilutes the body fluids
Urine is INAPPROPRIATELY CONCENTRATED
Rx: water restriction, ADH antagonist (demeclocycline)
Oxytocin
Synthesized by paraventricular nuclei of hypothalamus
Lactation: contraction of myoepithelial cells in breast (milk let-down)
Uterine contraction during child-birth
Oxytocin receptors in uterus are up-regulated during child-birth (exact role is unknown)
Used to induce labor
Reduces postpartum bleeding
Regulation of Oxytocin secretion
Suckling (major stimulus for secretion)
Dilation of cervix and orgasm
