Endocrinology Part 1 (8.1) Flashcards
What are the endocrine system and nervous system known as in the body?
- two major control systems of the vertebrate body
What can homeostasis be defined as?
- monitoring & coordinating of internal environment
- make appropriate adaptive changes
- regulate growth, development, senescence
- enables to respond + adapt to changes in external environment e.g. temperature change, food intake
What is the nervous system?
- network of neurons
- transmit signals along dedicated pathways
What is the endocrine system?
- hormones are chemical signaling molecules that travel through the blood + reach every part of the body
- only target cells have receptors that allows them to respond
What do organisms use homeostasis for?
- to maintain a “steady state”
- to maintain an internal balance regardless of external environment
- e.g. body temp, blood, pH + glucose conc.
- maintained at a constant level
How does homeostasis work?
- moderate changes in an internal environment
- fluctuations above/below a set point = stimulus
- detected by a sensor and trigger an immune response
- response returns variable to a set point
What is a hormone?
- chemical messenger produced and secreted by a specialised endocrine gland, transported in the bloodstream
- to a distant target, organ/cell where it elicits a physiological response
What are the 3 different classes of hormones?
- proteins/peptides, *growth hormone
- cholesterol derivatives, *steroids, vitamin D
- modified amino acids, *adrenaline, thyroid hormones
What happens in target cell recognition? - Part 2
- non lipid-soluble hormones e.g. protein hormones - cannot diffuse through the phospholipid layers
- action upon target cells must be carried out indirectly
- binding to an extra-cellular receptor + this triggers an intracellular signalling cascade - “second messenger system”
What are the stages of the second messenger model?
- the hormone itself = the first messenger
- binds to specific receptors on the cell-surface membrane of target cells
- forms a hormone complex
- activates an enzyme within the cell
- production of a chemical that acts as a second messaenger
What happens in target cell recognition?
- lipid- soluble hormones (e.g. steroid hormones) diffuse through the phospholipid bilayer
- bind to an intracellular receptor that directly activates target molecules
(changes in gene expression)
What are some hormones actions?
- affect growth, development, metabolic activity & function of tissues
- may be stimulatory/inhibitory
- may act on several tissues/ just one specific target tissue - major difference between endocrine & nervous system
- responsive tissues must have specific receptors for that hormone
What are circulating hormone levels influenced by?
- rate of secretion, *by endocrine gland
- rate of metabolism, *by target tissue, blood, liver, kidney
- serum binding proteins, *transport in blood - solubility tissue etc.
What regulates hormone secretion?
- physiological changes e.g. blood glucose and insulin
- by endogenous rhythms, e.g. infradian cycles
- by feedback mechanisms, e.g. negative feedback, which maintain homeostasis
What does endogenous mean?
“built in”
What are some causes of hypersecretion?
- functional tumour
- ectopic hormone-secreting tumour
- immunological situations
- substance abuse
What are some examples of endogenous rhythms? (in regulation of hormone secretion) - naturally occurring cycles in the body
- ultradian - cycle in minutes e.g. GnRH pulses
- circadian - daily cycles e.g. testosterone
- infradian - monthly e.g. menstrual cycle (LH in females)
What is negative feedback?
- a response to conditions in your body, in which conditions change from the ideal or set point and returns conditions to this set point
- the body does what it can to reverse the change
How is hypersecretion treated?
- surgical removal of the gland, eventually needing replacement therapy
- irradiation of gland - reduces function, will need replacement therapy
- drugs that block the actions of the hormone
What are the main types of endocrine dysfunction?
- hypo secretion
- hyper secretion
- ectopic hormone secretion, hormone made outside normal gland e.g. tumour.
What is hyposecretion caused by?
- genetics
- diet
- auto-immune disease
- cancer
- Iatrogenic (doctor caused)
- idiopathic (spontaneous/unknown)
How is hyposecretion treated?
- hormone replacement
- steroids, which are straightforward,absorbed in the GI tract with high success rates
- protein hormones, difficult, must be injected, with a specific species
