Sect. 11.1 - Hormone Function

Endocrinology

the study of hormones and disorders associated with abnormalities of these hormones

Hormone

secreted directly into the bloodstream for purpose of maintaining circulatory status and homeostasis

Down-Regulation

inhibition/suppression of the normal response of an organ or system

Desensitization

exposure of receptors to high concentration of hormones may decrease number of surface receptors

Specificity Spill-Over

hormones having strong affinity levels for their own receptors as well as weak affinity for receptors of another hormone

ex: aldosterone & cortisol (both from adrenal cortex)

Somatotropin

growth hormone

most abundant hormone made by anterior pituitary

Endocrine hormones

hormone synthesized in one location & released into blood; affects a distant site

Paracrine hormones

hormone synthesized in endocrine cells & released into paracrine space (interstitial cell space); acts on neighboring cells

Autocrine hormones

hormone synthesized by endocrine cells & bind to receptors of the same cell they originate from

Juxtacrine hormones

hormone synthesized by endocrine cells & acts on adjacent cells by direct cell-to-cell contact

Exocrine hormones

hormone synthesized by endocrine cells & released into gut to aid in digestion (CCK/gastrin/secretin)

Neuroendocrine hormones

hormone synthesized by CNS & released into blood; affect a distant site

on the cell surface or in the cytoplasm of cell

Target cells have receptors where on the cell that bind to hormones?

Steroids, Polypeptides, Amine

Hormones can be classified into 3 basic chemical types:

lipid based

water insoluble

chemical structure & solubility of steroids

protein based

water soluble

chemical structure & solubility of polypeptide

derived from amino acid tyrosine

can be water insoluble or solube

chemical structure & solubility of amine

cholesterol

Steroid hormones are lipid based are derived from

inside the cell; lipids can easily diffuse through the phospholipid membrane and enter the nucleus

Where is the receptor for steroid hormones located?

on the surface of cell; cannot diffuse through the cell like lipids can

Where is the receptor for polypeptide hormones located?

steriod hormones

After synthesis:

- bind to carrier molecule

- travel to their site of action

- diffuse through cell membrane & bind to receptors of cytoplasm

- enters nucleus where it undergoes replication/transcription/translation

- make proteins

- causes change

long half-life (2hrs) (take longer for action to occur)

Do steroid hormones have long or short half-life?

peptides or glycoprotein

Protein hormones are either (2)

polypeptide hormones

- bind to receptor on surface of cell

- adenylate cyclase is activated and produces cAMP (cyclic AMP)

- cAMP activates proteins/enzymes in cell

short half-life (enzyme already present in cell, just need to be activated)

Do polypeptide hormones have long or short half-life?

tyrosine

What amino acid are amine hormones derived from?

catecholamines (epinephrine, norepinephrine, dopamine)

Amine hormones share properties from both steroid and polypeptide hormones.

What are the protein-like amine hormones?

thyroid T4 (thyroxin) and T3 (triiodothyronine)

Amine hormones share properties from both steroid and polypeptide hormones.

What are the steroid-like amine hormones?

Nuclear receptors and Membrane receptors

two major classes of hormone receptors

Nuclear receptors

G protein family

- consists of guanine nucleotide-binding protein

- adenylate cyclase catalyzes formation of cAMP

- cAMP activates enzyme which regulate intracellular proteins

- requires primary & secondary messenger

primary = hormone

secondary = cAMP

What is the primary and secondary messenger?

Membrane receptors

Protein kinases

- contain tyrosine kinase activity

- phosphorylation rxn occurs

- can stimulate or depress enzyme activity

positive feedback mechanism

function of hormone A results in increase in hormone B

- original stimulus is promoted

negative feedback mechanism

concentration of hormone B can cause decrease in hormone A

- action is opposite of stimulus

1. act directly to change hormone itself

2. cause a change in a related physiological response

3. occur indirectly via another hormone

Negative feedback can exhibit 3 main actions:

positive feedback

Positive or Negative

T3/T4 is too low = thyroid releases more T3/T4

negative feedback

Positive or Negative

T3/T4 is too high = thyroid releases less T3/T4

primary: target endocrine gland

secondary: anterior pituitary

tertiary: hypothalamus

What are the primary, secondary, and tertiary hormone regulation mechanisms?

immunoassay

the most common methodology used to measure hormones

both sensitive and specific

Why are immunoassay the most common method to measure hormones?

competitive and noncompetitive

two types of immunoassay techniques

competitive immunoassay

labeled ag with a known quantity competes with pt ag for ab sites & forms hormone-ab complex

indirectly proportional

In a competitive immunoassay, the amt of analyte is __________ proportional to signal that is read

sandwich immunoassay

pt ag binds to antibody fixed onto solid phase; the second ab is labeled with a detector and binds to antigen-antibody complex

directly proportional

In a immunometric (sandwich) immunoassay, the amt of analyte is __________ proportional to signal that is read

general factors that affect hormone release & measurement

biorhythms

stress

autonomy

protein binding

heterogeneity

assay limitations

biorhythms

general factors that affect hormone release & measurement:

circadian/diurnal, may have to take multiple measurements throughout the day

stress

general factors that affect hormone release & measurement:

increases ACTH (controls cortisol) and growth hormone

autonomy

general factors that affect hormone release & measurement:

hormones acting from something other than what normally controls like (e.g. tumor)

protein binding

general factors that affect hormone release & measurement:

some hormones are bound, some are not

- bound form may not be biologically active / free unbound hormone is

heterogeneity

general factors that affect hormone release & measurement:

hormones can circulate in blood as multiple distinct immunological forms (intact vs fragments)

- immunoassay only recognize specific forms

assay limitations

general factors that affect hormone release & measurement:

some assays are not sensitive enough to differentiate low ranges from normal

- antiserum can cross-react with other hormone (overestimation)