endocrine system Flashcards
role of the endocrine system
keeping the environment inside the body fairly constant
homeostasis
maintenance of a constant, stable
internal environment
what is the endocrine system made up of?
Made up of endocrine glands which secrete hormones into the bloodstream
what are hormones?
chemical messengers that exert a specific effect on target cells
exocrine glands function
Secrete into a duct that carries the secretion to the body surface, or one of the body cavities
exocrine gland examples
Sweat glands, mucous glands, salivary glands
endocrine gland function
Secrete hormones into the extracellular fluid that surrounds the cells that makes up the gland, secretions can pass into the capillaries to be transported by blood
hormone functions
- Activate certain genes in the nucleus so that a particular enzyme or structural protein is produced
- Change the shape or structure of an enzyme so that it is turn on or off
- Change the rate of production of an enzyme or structural protein by changing the rate of transcription or translation during protein production
what part of body hormones affect?
- All the cells of the body
- Target cells (only particular groups of cells)
- Target organs (particular organs)
what can a hormone be?
steroid hormones, protein/amine hormones
what are steroid hormones?
lipid soluble: does not dissolve in water
process of lipid soluble hormones actions
- When released into blood → bind to transport proteins → travel through bloodstream
- When target cell is reached, steroid hormones separate from transport proteins and diffuses across cell membrane
- Inside the cells, hormones combine with receptor protein in cytoplasm or nucleus (forms hormone-receptor complex)
- Hormone receptor complex enters the nucleus
- Hormone receptor complex activates the genes controlling the formation of particular proteins
- Binds to promoter section of a certain gene, either stimulating or inhibiting transcription → protein synthesis
examples of steroid hormones
oestrogen, progesterone, cortisol and aldosterone
steroid hormone effect
Slow but long-lasting effect
what are protein & amine hormones?
water soluble = dissolves in water and is unable to diffuse across the cell membrane
process of protein & amine hormones in the body
- Attaching to receptor proteins in the membrane of the target cell
- Combination of the hormone with the receptor causes a secondary messenger substance to diffuse through the cell and activate particular enzymes
examples of protein & amine hormones
insulin, human growth hormone
effect of protein & amine hormones
Quick to cause a response, but short lasting
receptor proteins are…
specific→each type of receptor will only bind with one specific molecule
lock and key for receptor protein
- Lock = receptor protein
- Key = binding molecule
number of receptor proteins in the membrane of each cell is…
limited
why is each receptor bound to a molecule?
no further increase in the rate of the cell’s activity
insulin example of receptor protein + process
When each insulin receptor in the cell membrane is bound to insulin, cells rate of glucose uptake cannot increase any further even if the amount of insulin increases→saturation (once all receptor molecules are occupied by hormone molecules, adding more hormone doesn’t produce any greater effect)
variation of receptor proteins
Different cells have different types and numbers of receptor proteins (variation in sensitivities of cells to hormones and other substances)
Enzyme amplification
one hormone molecule→activates thousands of molecules
what happens when a hormone triggers cascading effect?
the number of reacting molecules involved is increased hundreds or thousands of times for each step along the metabolic pathway
hormone clearance
- Hormones must be turned off once they’ve produced the required effect
- Breaking down the hormone molecules
- In target cells or in liver and kidneys
- Excreted in either bile or urine
what does the hypothalamus serve as?
Serves as a connection between the nervous and endocrine systems
what does the hypothalamus do with examples?
- Regulates basic functions of the body
- Body temp, water balance, HR, increasing or decreasing the sections of other glands
where is the hypothalamus located?
base of the brain
functions of the hypothalamus occur through…
the pituitary gland
functions of the hypothalamus
- secrete releasing and inhibiting factors which travel through the blood vessels to the anterior lobe of the PG, affecting the secretion of its hormones
- Other hormones produced by the hypothalamus and pass along the nerve fibres to the posterior lobe of the PG where they are released
releasing factors
stimulate the section of a hormone
inhibiting factors
slow down the secretion of a hormone
what connects the hypothalamus and pituitary gland?
infundibulum
two lobes of the pituitary gland
anterior and posterior
anterior lobe of PG structure
- No nerves connecting it to the hypothalamus
- Connected by complex network of blood vessels lying in the infundibulum
posterior lobe of PG structure
- Joined to hypothalamus by nerve fibres that come from nerve cell bodies in the hypothalamus
why is the PG not a true endocrine gland?
Doesn’t secrete substances but stores and releases hormones
function of APG
- synthesises and releases several hormones that regulate bodily activities
- Secretions of the AL are controlled by the releasing and inhibiting factors secreted by the hypothalamus
anterior lobe hormones
- follicle stimulating hormone (fsh)
- luteinising hormone
- growth hormone (somatotropin)
- thyroid stimulating hormone
- adrenocorticotropic hormone
- prolactin
gonadotropins
Hormones that affect the gonads, ovaries and tests
follicle stimulating hormone: female
target organ: ovaries
stimulates development of follicles that contain eggs
follicle stimulating hormone: male
target organ: testes
stimulate production and maturation of sperm
luteinising hormone: female
target organ: ovaries
works with FSH to bring about ovulation and form the corpus luteum
luteinising hormone: male
target organ: testes
stimulates interstitial cells to secrete male sex hormones
growth hormone (somatotropin)
target organ: all cells
- stimulates body growth
- increases rate at which amino acids are taken up by the cells -> built into proteins
- helps maintain size of organs once maturity is reached
thyroid stimulating hormone (tsh)
target organ: thyroid gland
stimulates production and release of hormones from the thyroid gland
adrenocorticotropic hormone (acth)
target organ: adrenal glands
controls production and release of hormones from cortex of adrenal glands
prolactin
target organs: mammary glands
initiate and maintain milk production in females
poster lobe pituitary gland
- Cells have long extensions that pass through infundibulum to the PL
- Hormones move down extensions and stored ready for release into blood stream
- Release of hormones triggered by nerve impulses initiated in hypothalamus and conducted along nerve cell extensions
horomes secreted by PPG
- oxytoxin
- antidiuretic horome (ADH) or vasopression
oxytocin
target organs: uterus, mammary glands
- stimulates contraction of the muscles of the uterus
- stimulates contraction of cells in mammary glands allows for secretion of milk
antidiuretic hormone (adh)
target organs: kidneys
- causes kidney to remove water from urine (returns to bloodstream)
- helps to retain fluid (reabsorption of water)
process of hormone synthesis/secretion (apg):
- neurosecretory cells synthesis RH/IH in the hypothalamus
- RH/IH travel via neurons to APG in the hypothalamus/infundibulum
- RH/IH released in capillaries in infundibulum
process of hormone synthesis/secretion (ppg):
- ADH and oxy made by neurosecretory cells in the hypothalamus and are packaged into vesicles
- they travel via axon in the infundibulum
- stored in terminals in the PPG until triggered to release hormones
thyroid gland (structure)
- Located in the neck below the larynx
- Consist of two lobes that lie on either side of the trachea
- Joined by narrow piece of tissue that lies across the front of trachea
what do follicular cells secrete in response to TSH?
thyroxine (T4) and triiodothyronine (T3)
thyroxine (T4) and triiodothyronine (T3)
increases metabolic rate (by release of energy)
- oxygen consumption
- heat production
thyroxine (T4) vs triiodothyronine (T3)
thyroxine is less active than T3 but last longer
80% is T4, 20% is T3, enzymes convert T3 to T4
thyroxine T4
- Controls body metabolism by regulating reactions
- complex molecules are broken down to release energy
- Complex molecules are synthesised from simple ones
overall effect of thyroxine
bring about the release of energy as some is released in the form of heat which maintains body temperature
hormones released by thyroid gland
T3, T4, calcitonin
calcitonin
target cells: bones, kidney
decrease calcium and phosphate levels in the blood
increase of conc of calcium in blood
TG releases calcitonin→reduces reabsorption of calcium by the kidneys and the breakdown of bone
increase of concentration of phosphate in blood
calcitonin moves phosphate into bone→reduces its reabsorption by the kidneys
parathyroid gland structure
- Located in the rear surface of the lobes of the thyroid gland
- Usually four glands – size of a small pea
what does the parathyroid gland secrete?
secrete parathyroid hormone (PTH)
parathyroid hormone (PTH)
target cells: bones and kidney
increases calcium levels in the blood
phosphate excretion in the urine
adrenal glands structure
- Two adrenal glands immediately above each kidney
- Each gland has
- Inner adrenal medulla
- Outer adrenal cortex
- Each gland is two separate endocrine glands
what does adrenal medulla produce?
Produces adrenaline (epinephrine) and noradrenaline (norepinephrine)
adrenaline and noradrenaline
target cells: most body tissues
- prepare the body for fight or flight responses
- reinforces the effects of the sympathetic nervous system
adrenal cortex
- Produces more than 20 different hormones corticosteroids
- Aldosterone
- Cortisol
Aldosterone
target cells: kidney
- reduce the amout of sodium in urine (increase reabsorption of sodium ions)
- increase the amount of potassium in urine
(excretion of potassium ions)
cortisol
target cells: most body cells
- promotes normal metabolism
- helps the body deal with stress
- promotes repair of damaged tissues
pancreas location
Lies below the stomach; alongside duodenum
pancreas is both…
an exocrine and endocrine gland
exocrine part of the pancreas
secretes digestive enzymes into the small intestine through the pancreatic duct
endocrine part of the pancreas
- made up of clusters of specials cells called islets of Langerhans (pancreatic islets) that secrete
- Insulin
- Glucagon
insulin secreted by
the beta cells of the islets of Langerhans
what does insulin do for glucose?
- Reduces the amount of glucose in the blood (blood sugar level)
- Promotes the uptake of glucose from the blood by the cells of the body
insulin effects (how does it reduce BG levels?)
- In the liver, insulin causes the conversion of glucose→glycogen and fat
- In skeletal muscles, insulin causes the formation of glycogen from glucose
- In fat storage tissues, it causes glucose to be converted to fat
what controls the level of secretion of insulin?
determine by the amount of glucose in the blood (controlled by negative feedback)
insulin target cells
most body cells
glucagon secreted by
the alpha cells of the islets of Langerhans
what does glucagon do for glucose?
Works to increase the blood glucose level
how does glucagon increase blood sugar levels?
- Promoting the breakdown of glycogen→glucose in the liver
- Stimulates the breakdown of fat in the liver and in fat storage tissue
