Intro to endocrinology, hormones and receptors, and negative feedback control

hormone

a chemical substance is released by a specific type of cell into the bloodstream to act on distant target cells

homeostasis

secretion of a hormone is triggered by a change in internal environment to stabilize or maintain the status quo and bring about __

nervism

pavlov theory of __

• until the early 20th century, pavlov’s theory that all physiological functions were controlled by nerves was accepted

Brown-sequard

• in 1855, thomas addison in london described 11 patients with weakness, tiredness, weight loss, anemia, “feebleness of the heart” and bronzed skin; at autopsy their adrenal glands were diseased bilaterally

• in paris, ___ ___ was intrigued. in the laboratory he excised both adrenal glands in several species of small animals and observed that they were essential to life, and that death was not due to hemorrhage, infection, or damage to neighboring structures. he then showed that adrenalectomized animals could be kept alive with blood transfusions from normal animals

• later reported to societe de biologie in paris

• experiments in which he had injected himself subcutaneously on 10 occasions over a 3-week period with testicular extracts derived from dogs and guinea-pigs, in an attempt to counter the effects of aging

• claimed that subjective improvements in mental concentration, physical strength and endurance, bowel habits, and urinary system

• within 2 years, the successful treatment of hypothyroidism by subcutaneous injections of thyroid extract was reported

bayliss and starling

• in 1902

• observed that acidification of the duodenum of a dog resulted in copious bicarbonate secretion from the pancreas, even though all nerves connections were severed

• theorized that a substance was released into the bloodstream to stimulate the pancreas and made extracts of intestine and injected them to mimic the effect

• named the substance secretin and coined the word “hormone” from the Greek “I arouse to activity”

functions of hormones

• metabolism

• cardiovascular function

• cell division

• cell differentiation

• body growth and maturation

• body mass

• reproduction

• behavior

endocrine system

enteroendocrine cells

gastrointestinal hormones

renal cells

secrete erythropoietin for RBC production

cardiac cells

atrial natriuretic hormone

endothelial cells

endothelin, nitric oxide

lymphocytes

interleukins, interferons

adipose cells

leptin, resistin

placental cells

multiple hormones

*

similarities in function of different types of regulators (hormones, neurotransmitters, growth factors, and immune system cytokines:

• similar receptors

• similar intracellular messengers

• feedback regulation

• similar intracellular functions

• similar substances work as agonists

amines

thyroxine and epinephrine

polypeptides and proteins

insulin and growth hormone

steroids

cortisol and estradiol

*

secretion of thyroid and steroid hormones:

• compartmentalized in the cell but not in secretory granules

• once the hormones have appeared in free form within the cytoplasm, they diffuse from the cell

response of a hormone depends on

• hormone conc

• receptor number

• duration of exposure

• intervals between consecutive exposures

• cell conditions: conc of rate-limiting enzymes, cofactors or substrates

• concurrent effects of antagonistic or synergistic (work together to produce a stronger effect) hormones

all or none

hormonal effects are not “____” phenomena

basal

intrinsic __ activity usually exists

threshold

a minimal ___ level of hormone is usually required to elicit a response

saturating concentrations of hormone define the maximal response

sensitivity

concentration for half-maximal response defines the ___ of target cell