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hormones
a chemical that is secreted by an endocrine gland and transported in the blood, affecting the function of a cell/organ.
how do enzymes work
they work by either:
activating specific genes to produce proteins/enzymes
activating/deactivating enzymes by changing its shape/structure
change an enzyme production rate
water soluble (protein / amine) hormones
can dissolve in water
can independently travel in the bloodstream
cannot diffuse through cell membrane – must bind to receptor proteins to cross
fast, but has a quick effect
water soluble (protein / amine) hormones transportation
water soluble hormones attach to receptor proteins on the target cell membrane
this causes the secondary messenger substance to diffuse through the cell and activate particular enzymes
features of lipid soluble hormones
cannot dissolve in water
must bind to transport proteins to travel across bloodstream
can diffuse through the cell membrane
combines with receptor protein inside cell
slow, but has a long lasting effect
transportation of lipid/steroid soluble hormones
lipid hormone binds to transport proteins to travel via blood to target cells
when target cell is reached, the hormone is released and diffuse across the cell membrane
the hormone combines with receptor protein in the cytoplasm or nucleus of the cell
the hormone-receptor complex activates the gene by binding to the promoter section starting transcription and protein synthesis
compare action speed between lipid and water soluble hormones
lipid hormones have a slow effect, but it is longer lasting since the hormone-receptor complex directly alters the gene expression.
water soluble hormones have a fast effect, but short lived since it only activates enzymes, but they do not alter genetic material.
examples of steroid hormones
cortisol, testosterone, T3 , T4
examples of protein / amine hormones
insulin, adrenaline, growth hormone
hormone/receptor complex
Protein receptors are hormone specific, each type of receptor will bind with only one specific molecule.
If all protein receptors have been occupied by hormones, hormone saturation occurs; meaning an increase of hormones does not increase cell activity.
hypothalamus location and function
the hypothalamus is located in the base of the brain and regulates homeostatic functions (e.g. body temperature, water balance, heart rate)
infundibulum location and function
funnel shaped stalk that connects the pituitary gland to the hypothalamus
anterior lobe
the anterior lobe produces, stores and releases hormones
secretions by the anterior gland are controlled by releasing/inhibiting factors secreted by the hypothalamus into the extracellular fluid.
RF/IF are carried by blood to the anterior lobe, passing through a complex network of blood vessels.
posterior lobe
the posterior lobe stores and secretes hormones
hormones are produced in neurosecretory cells in the hypothalamus, then transported in vesicles to the posterior lobe via the infundibulum
follicle stimulating hormone
target: ovaries & testes
effects: stimulates growth of follicles and sperm production
luteinising hormone
target: ovaries & testes
effects: ovulation and corpus lutem formation, secretion of testosterone
growth hormone
target: all cells
effects: growth and protein synthesis
thyroid stimulating hormone
target: thyroid gland
effect: secrets thyroxine from thyroid
ACTH hormone (adrenocorticotrophic)
target: adrenal cortex
effect: secretes cortisol from adrenal cortex
Prolactin (PrL)
target: mammary glands
effect: milk production
antidiuretic hormone
posterior
target: kidneys
effect: increases the reabsorption of water
oxytocin (ot)
posterior
target: uterus & mammary gland
effects: uterine contractions & release of milk
