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