Steroid Hormones - their effects target cells

cortisol?

this is glucocorticoid. it diffuses across cell membranes and bind to receptors in the cytosol of target cells.the cortisol receptor complex is transported to the nucleus where it binds to DNA and acts by inhibiting or stimulation the transcription of certain genes. cortisol is the main stress hormone and so when the body is under prolonged stress, it enhances noradrenaline effect on blood pressure to keep it elevated. it also increases plasma concentration of glucose by causing glucoeneogensis.

what stimulates the steroid hormone production?

when ACTH is released by the anterior pituitary gland it travels to the adrenal cortex and stimulates the production of these hormones through activation of adenyl cyclase.

non specific transport proteins?

albumins

example of specific binding

globulin binding to cortisol and sex hormones binding to globulin

specific transport proteins?

globulins

5 classes based on the receptors they bind to

glucorticoids mineralocorticoids androgens oestrogens progesterones

properties of steroid hormones?

hormones in the form of lipids so they can pass through the cell membrane to bind to nuclear receptors i.e. testosterone and progesterone do this. whilst some bind cytosolic receptors depending on the hormone. once inside the cell they cause a signalling cascade to occur. this process is regulated by a number of enzymes.

three zones in the adrenal cortex?

mineralocorticoids in the zona glomerulosa glucocorticoids in the zona fasculata. androgens are produced in the zona reticularis.

precursor for other hormones?

often they are a precursor for another hormone i.e. progesterone is a steroid hormone in its own right but it is also a precursor in the formation of glucocorticoids mineralocorticoids, testosterone and oestrogens.

estrogens?

primary female sex hormones, they are also steroid hormones. the three majorly occurring oestrogen's are estradiol, estriol and estrone.

testosterone produced in adrenal cortex?

small amounts are produced in the adrenal cortex, examples in the adrenal cortex are dehydroepiandrosterone and andostredione. their physiological actions require conversion to testosterone. testosterone had musculizing effects and increases lean body mass,

transports?

steroid hormones are bound to transport proteins when circulating they are more resistant to degradation and excretion than other hormones such as catecholamines. they also have an increased plasma half life

where are they produced?

steroid hormones are produced within the adrenal cortex they are called arenocortical hormones.

how steroid hormones are transported?

steroid hormones circulate in the blood bound to plasma proteins as they are lipid soluble. there are specific transport proteins that bind specific hormones as well as non specific hormones that bind several types of hormones simultaneously.

the relative percentages of bound and free hormones is determined by what?

the binding affinity and binding capacity of the transport protein

androgens

these are steroids that function as male sex hormone. they are produced by the leydig cells of the testes in response to the presence of LH. when testosterone defuses into blood and lymph it is bound to androgen binding hormone produced by sertoli cells. targets in the testes are the peritubular myoid cells and the sertoli cells which envelope and support developing sperm cells. in the epididymis, testosterone influences epididymal transit and further maturation spermatozoa.

storage of steroid hormones?

they cannot be stored within a cell, they are secreted immediately after formation by diffusion across the cell membrane. therefore the rate of hormone secretion is determined by the rate of hormone synthesis.

aldosterone

this is the most important mineralocorticoid. it modulates gene transcription by binding with DNA in the nucleus as part of the aldosterone-receptor complex. it stimulates the reabsorption of sodium and increases the secretion of potassium in the distal tubule and collecting ducts of the kidneys. it also increases the number of sodium potassium ATPase pumps in the basolateral membrane of the cells by modulating gene transcription. with increases absorption of sodium there is an increases absorption of water.