D5 Hormones and Metabolism Flashcards
What is the endocrine system comprised of and what do they do?
The endocrine system is comprised of ductless glands that release chemicals into the blood to regulate body functions
What is a hormone?
A hormone is a chemical messenger that is transported indiscriminately via the bloodstream to act on distant target cells
Are hormones non/specific?
Hormones are SPECIFIC and will only activate cells or tissues that possess the appropriate target receptor
How does the endocrine system compare to the nervous system?
The endocrine system is slower to initiate, but has a more prolonged response when compared to the nervous system
What do endocrine glands secrete?
Endocrine glands secrete their product (hormones) directly into the bloodstream, rather than through a duct (e.g. exocrine gland)
What are major endocrine glands?
Major endocrine glands include the pancreas, adrenal gland, thyroid gland, pineal gland and the gonads (ovaries and testes)
What are the roles of the hypothalamus and pituitary gland?
The hypothalamus and pituitary gland are neuroendocrine glands and function to link the nervous and endocrine systems
Can only endocrine glands secrete hormones?
NO
Some organs may also secrete hormones despite not being endocrine glands (e.g. adipose tissue secretes leptin)
What are steroid hormones, how are they transported?
Steroid hormones are lipophilic (fat-loving) – meaning they can freely diffuse across the plasma membrane of a cell
Where do steroid hormones bind?
They bind to receptors in either the cytoplasm or nucleus of the target cell, to form an active receptor-hormone complex
What will the activated receptor-hormone complex do?
This activated complex will move into the nucleus and bind directly to DNA, acting as a transcription factor for gene expression
What are examples of steroid hormones?
Examples of steroid hormones include those produced by the gonads (i.e. estrogen, progesterone and testosterone)
What are peptide hormones?
Peptide hormones are hydrophylic and lipophobic (fat-hating) – meaning they cannot freely cross the plasma membrane
Where do peptide hormones bind?
They bind to receptors on the surface of the cell, which are typically coupled to internally anchored proteins (e.g. G proteins)
What does the receptor complex activate? (peptide hormones)
The receptor complex activates a series of intracellular molecules called second messengers, which initiate cell activity
What is the process of peptide hormone signalling called?
This process is called signal transduction, because the external signal (hormone) is transduced via internal intermediaries
What are examples of second messengers?
Examples of second messengers include cyclic AMP (cAMP), calcium ions (Ca2+), nitric oxide (NO) and protein kinases
What does the use os second messengers enable?
The use of second messengers enables the amplification of the initial signal (as more molecules are activated)
What do peptide hormones include?
Peptide hormones include insulin, glucagon, leptin, ADH and oxytocin
What is the hypothalamus?
The hypothalamus is the section of the brain that links the nervous and endocrine systems in order to maintain homeostasis
Where does the hypothalamus receive signals from?
It receives information from nerves throughout the body and other parts of the brain and initiates endocrine responses
What does the hypothalamus secrete (not blood)?
It secretes neurochemicals (called releasing factors) into a portal system which target the anterior lobe of the pituitary gland
Where does the hypothalamus secrete hormones (apart from portal system)?
It also secretes hormones directly into the blood via neurosecretory cells that extend into the posterior pituitary lobe
What is the pituitary gland?
The pituitary gland lies adjacent to the hypothalamus and is in direct contact due to a portal blood system
Where does the pituitary gland receive instructions from?
The pituitary gland receives instructions from the hypothalamus and consists of two lobes (anterior and posterior lobe)
What is the anterior lobe also called?
The anterior lobe is also called the adenohypophysis (‘adeno’ = relating to glands)
What type of factors does the anterior lobe release?
The hypothalamus produces releasing factors, which are released into portal vessels by neurosecretory cells
What do releasing factors cause? (anterior pituitary)
The releasing factors cause endocrine cells in the anterior pituitary to release specific hormones into the bloodstream
What is an example of a releasing factor?
An example of a releasing factor is GnRH, which triggers the release of LH and FSH from the anterior pituitary
What is the posterior lobe also called?
The posterior lobe is also called the neurohypophysis (‘neuro’ = relating to nerves)
What does the posterior lobe secrete?
The posterior lobe releases hormones produced by the hypothalamus itself (via neurosecretory cells)
WHat is the role of the neurosecretory cells in the posterior lobe?
These neurosecretory cells extend into the posterior lobe from the hypothalamus and release hormones into the blood
What is the pituitary gland referred to as?
The pituitary gland is often referred to as the ‘master gland’, as it controls the secretion of a number of other endocrine glands
What will pituitary hormones target?
Pituitary hormones will often target endocrine glands in other organs (e.g. gonads, pancreas, thyroid, mammary gland)
What do pituitary hormones control? (body processes)
Metabolism
Adult development
Reproduction
Growth
Equilibirum/Homeostasis
What is an example of pituitary hormones involved in metabolism?
TSH activates thyroxin
What is an example of pituitary hormones involved in adult development?
LH/FSH trigger puberty
What is an example of pituitary hormones involved in reproduction?
LH/FSH control menstruation
What is an example of pituitary hormones involved in growth?
growth hormone promotes growth
What is an example of pituitary hormones involved in equilibrium/homeostasis?
ADH and water balance
What is a growth hormone?
Growth hormone (also known as somatotropin) is an anabolic peptide hormone that stimulates growth
Where do growth hormones act DIRECTLY?
It acts directly to reduce the formation of adipose cells (i.e. less nutrients stored as fat)
Where do growth hormones act INDIRECTLY?
It acts indirectly via insulin growth factor (IGF) – produced by the liver – to increase muscle mass and bone size
When can growth hormones be used?
Due to its role in promoting growth and regeneration, it is used by some athletes as a performance enhancer
where have growth hormones been banned?
The use of human growth hormone is banned in sports, with proven cases of doping strictly punished
How has anabolic peptide hormone testing changed in recent years and why?
Traditional urine testing could not detect doping, which historically made bans difficult to enforce
Recent blood tests can now identify between natural and artificial variants of growth hormone
What is lactation?
The production and secretion of milk by maternal mammary glands following birth is called lactation
What controls lactation?
It is predominantly controlled and regulated by two key hormones – oxytocin and prolactin
What is prolactin responsible for?
Prolactin is responsible for the development of the mammary glands and the production of milk
What secretes prolactin?
It is secreted by the anterior pituitary in response to the release of PRH (prolactin releasing hormone) from the hypothalamus
What inhibits prolactin?
The effects of prolactin are inhibited by progesterone, which prevents milk production from occurring prior to birth
What is oxytocin responsible for?
Oxytocin is responsible for the release of milk from the mammary glands (milk ejection reflex)
What produces oxytocin?
It is produced in the hypothalamus and secreted by neurosecretory cells that extend into the posterior pituitary
What triggers the release of oxytocin?
Oxytocin release is triggered by stimulation of sensory receptors in the breast tissue by the suckling infant
What type of feedback is oxytocin?
This creates a positive feedback loop that will result in continuous oxytocin secretion until the infant stops feeding
