endocrinology Flashcards
what is endocrinology?
Endocrinology is the study of hormones and how they affect your body.
-the original 1902 definition that, to be classified as a hormone, a chemical must be produced by an organ, be released (in small amounts) into the blood, and be transported by the blood to a distant organ to exert its specific function Exceptions Paracrine hormones- Chemical communication between cells within the same Tissue or organ Autocrine hormones- Chemicals that acts on the cell that produced it Intracrine hormones- Chemicals that acts within the cell that produced it without being released
what is the endocrine system?
numerous glands, all in different parts of the body, which secrete hormones directly into the blood rather than into a duct system
-One hormone may have several effects on different target organs
-One target organ may be affected by more than one hormone
-Defined by the types of receptors expressed on/in cells
how are glands made
-derived from epithelial cells and are specialised for secretion
common features between endocrine system and nervous system
-Respond to changes in diet, environmental, chemical or physical inputs
-Release signalling molecules via exocytosis Neurones and endocrine cells (e.g. adrenal medulla) calcium is involved.
-can be depolarized- release noradrenaline/adrenaline
difference between neuronal or endocrine system
neuronal is a quick process whereas the endocrine system is slower to get to the site of action.
-neuronal system is short terms. ACTH is usually broken down from the synaptic cleft to prevent unwanted side effects whereas the endocrine system is long-term.
-neuronal= single target organ e.g. increased heart rate whereas the endocrine system has global effects e.g. sexual development or pregnancy
mechanisms for cell to cell signalling via hormones.
-autocrine= hormonal signal acts back on the cell of origin or adjacent cells of the same type..
-paracrine= Hormonal signal carried to an adjacent target cell over a short distance via interstitial fluid
-endocrine=Hormonal signal carried to distant target cells via the bloodstream
-neurocrine=Hormonal signal originates in a neurone and after axonal transport to the bloodstream, is carried to distant target cells
water soluable hormones actions
-binds to the receptor of the cell
-activates adenylate cyclase to convert ATP into cAMP.
-cAMP activates protein kinases
-protein kinases phosphorylate cellular proteins
-phosphorylated protein cause reactions that produced= physiological responses
lipid soluble hormone action
-diffuse straight into the cell
-activated recoptor-hormone complex alters gene expression
-newly formed mRNA directs synthesis of specific proteins on ribosomes
-new protein alters cell activity
what factors determine hormone levels?
-Rate of production: Synthesis & secretion, the most highly regulated aspect of hormonal control
-Rate of delivery: Higher blood flow to a particular organ will deliver more hormone
-Rate of degradation: Hormones are metabolized and excreted from the body
parathyroid hormone
- produced by principal cells
-increases plasma calcium levels and decreases plasma phosphate levels
parathroid hormone targets
-the bones=removes calcium from the bones and puts it into the blood= increase calcium concentration in the blood
-kidney= causes an increase in calcium reabsorption and increases phosphate loss
-gastrointestinal tract =increases the level of vitamin D which reacts with the intestine to stimulate the absorption of calcium and phosphate
how is the bone able to be a dynamic tissue
- contain osteoclasts and osteoblasts cells to allow remodelling of bone
-osteoclasts=take out calcium and phosphate from the bone when required and into the bloodstream
-osteoblasts= put back calcium and phosphate to make fresh bone
activation of vitamin D
-biologically inactive when first enters the blood
-becomes active in the kidneys
-lack of vitamin D leads to rickets as it is essential in controlling calcium balance
calcitonin
-Peptide hormone produced by the parafollicular cells of the thyroid gland
- Secreted in response to high level of plasma Ca2+ and also in response to gastrointestinal hormones (e.g. gastrin)
-decreases calcium levels and phosphate levels
how does calcium control levels of calcitonin and parathyroid hormones via negative feedback
-high levels of calcium in blood stimulates thyroid glands parafollicular cells to release more CT
-this promotes the movement of blood calcium into the bone matrix thus decreasing calcium levels
-low levels of calcium in the blood stimulates principal cells to release PTH.
-PTH promotes the release of calcium from bone matrix into blood and slows the loss of calcium in the urine thus increases calcium levels
-PTCH also stimulates the kidney to release calcitriol which stimulates increased absorption of calcium from foods which increases blood calcium levels
link between the endocrine and nervous systems
The hypothalamus and pituitary gland form a complex functional unit that serves as the major link
pituitary gland
-anterior pituitary gland= the front of the gland and the posterior pituitary gland = the bavk of the gland
-physically connected to the hypothalamus which is at the top
neurocrine functions of the posterior pituitary
- neurosecretory cells release ADH/oxytocin
-they are transported down neurones into posterior pituitary
-released directly into the circulation
-oxytocin=uterine contractions and milk secretion
-ADH= water homeostasis
neurocrine functions of the anterior pituitary glands
-7 different Trophic hormones produced by the hypothalamus
-released directly into circulation
-acts on endocrine cells in the anterior pituitary
-endocrine cells secrete hormones
-hormones interact with target cells/tissues
trophic hormones
- hormone that controls the release of another hormone in the target tissue
e.g. growth hormones, thyroid stimulating hormones, LH or FSH etc…
refer back to lecture slides for pictures
hormonal effect of cells
- hyperplasia= growth hormones can stimulate cells to reproduce faster and produce more cells
-hypertrophy= increases in cell size
-atrophy= decrease in cell size and number
-necrosis or apoptosis
growth hormone
-produced in the anterior pituitary
-has a signal peptide that must be cleaved off before proper folding
-effects mainly exerted indirectly via insulin-like growth factors
-liver and thee skeletal muscles usually are the ones to respond to growth hormone and produce and secrete IGF.
growth hormone essential for normal growth during childhood and teenage years
-GH stimulates long bone growth
-Increases length prior to epiphyseal closure
-increases width after epiphyseal closure
-IGFs stimulate both bone and cartilage growth
In adults
-GH and IGFs help maintain muscle and bone mass and promote healing and tissue repair as well as modulating metabolism and body composition
hormonal regulation of growth hormone secretion
-controlled via the hypothalamus
-GHRH(growth hormone releasing hormone )=increases growth hormone secretion
-somatostation= decreases growth hormone secretion
long loop negative feedback
-Mediated by IGFs( insulin -like growth factors)
when there is a high level of GF
-Inhibit the release of GHRH
-Inhibit the action of GHRH in the anterior pituitary
-Stimulates the release of somatostatin
short loop negative feedback
when GH hormone level rises
-Mediated by GH itself via stimulation of somatostatin release
what factors are growth hormone secretion influenced by?
- regulated metabolically by glucose and free fatty acids
-↓ in glucose or fatty acid leads to ↑ in GHsecretion
-↑ in glucose or free fatty acid leads to ↓ in GH secretion
-Fasting ↑ GH secretion - Obesity ↓ GH secretion
-CNS regulates GH secretion via inputs into the hypothalamus effecting GHRH and somatostatin levels:
-surge in GH secretion after onset of deep sleep
-Light sleep (Rapid Eye Movement (REM) sleep) ↓ GH secretion
-Stress (e.g. trauma, surgery, fever) ↑ GH secretion - Exercise ↑ GH secretion
growth hormone deficiency
- results in pituitary dwarfism and can be fixed with growth hormone replacement therapy
excess growth hormone
-gigantism. bonds are able to continue extend because ethicidal plates dont close.
- in adulthood=acromegaly
= large hands,feet and lower jaw as the bones cant extend so become wider
insulin like growth factors (IGF)
IGFs act through IGF receptors (distinct from GH receptors) to modulate
- Cell growth (Hypertrophy)
- Increases in cell numbers (Hyperplasia)
- Increase in the rate of protein synthesis
-Increase in the rate of lipolysis in adipose tissue (fat)
-Decrease glucose uptake The actions of IGFs can be paracrine and autocrine as well as endocrine
histology of thyroid tissues
- Follicular cells arranged in spheres called thyroid follicles.
-Follicles filled with colloid, a deposit thyroglobulin
-Colloid is “extracellular “even though it is inside the follicle
thyroid hormone structure
iodine is added to thyroid until
-can be mono,di,trio,dixodo,tetraiododothryronin(thyroxine) (is formed= 4 iodine attached
synthesis of thyroid hormones
-iodine is absorbed via our diet into the blood
-NA/I symporter system transfers iodide and sodium the thyroglobulin cells into colloid mixture via pendrin
-oxidation occurs iodide into iodine
-then iodination occurs where iodide is added to tyrosine
-conjugation process occurs adding the molecules together to form hormones
-endocytosis
-proteolysis
roles of thyroid peroxidase
-produces iodine at a faster rate. adds peroxide to iodide to form idodine
-adds iodine molecules on to tyrosine and does the conjugation reaction
why does the thyroid gland secrete both T3 hormone and T4
-They have different biological activity.
- we release 90% more T4 than T3
-T3 has greater avtivity
regulation of thyroid hormone secretion via a negative feedback loop
-refer back to lecture photo
What is thyroid stimulating hormone
TSH is a glycoprotein hormone composed of 2 non-covalently bound subunits (a and b).
-The a subunit is also present in FSH and LH.
-b subunit provides unique biological activity.
What roles does thyroid stimulating hormone play in the thyroid?
-increases Thyroglobulin (TG)iodination
-Increases DIT/MIT conjugation
-Promotes TG endocytosis
-increases TG proteolysis
-Stimulates T3/T4 secretion
mechanism of thyroid receptor action
-thyroid hormone released(T3 or T4)
- enters the cell membrane and binds to the receptor on the nucleus.
-removes the co repressor and requites co activators
-activation of gene transcription
-increase protein expression
biological actions of thyroid hormones
- metabolism
-growth and development
