l16-l19: endocrine systems

endocrine systems

responsible for regulating other organ systems using hormones

primary endocrine organs

secrete hormones as their main or only function

secondary endocrine organs

secrete hormones in addition to carrying out their own primary functions

hormone

chemical messenger molecule that travels through the blood to reach its target organs

class 1 hormones (amino acid derivatives)

• synthesized by modifying amino acids

• stored in vesicles that are released when intracellular calcium levels rise

class 2 hormones (peptide hormones)

• synthesized as larger inactive proteins by ribosomes then are activated through enzymatic cleavage

• stored in large vesicles and released via exocytosis when calcium levels rise

class 3 hormones (lipid derivatives)

• synthesized on demand by modifications of lipids

• transported in blood by carrier proteins

lipid-soluble (hydrophobic) hormones

act through intracellular receptors and alter gene expression

hydrophilic hormones

act through membrane-bound (extracellular) receptors

G-protein coupled receptors (GPCRs)

metabotropic receptors that signal through soluble, mobile, second messenger molecules

enzyme-linked receptors

usually kinases which activate other proteins, but some create second messengers directly

tropic hormone

acts to affect the secretion of another hormone

trophic hormone

stimulates cell division in its target cells

effector hormone

has a direct physiological effect

hypothalamus

a collection of >20 distinct brain nuclei that serve a number of different functions

pituitary

stalk of tissue that dangles from the inferior side of the forebrain with two distinct components that each secrete hormones

oxytocin & vasopressin/ADH

effector hormones that are released directly into the systemic circulation through axon terminals in the posterior pituitary gland

pituitary portal system

capillary network that connects the hypothalamus to the anterior pituitary

gonadotropes

anterior pituitary cell type that releases FSH and LH

corticotropes

anterior pituitary cell type that releases ACTH

somatotropes

anterior pituitary cell type that releases GH

lactotropes

anterior pituitary cell type that releases PRL

thyrotropes

anterior pituitary cell type that releases TSH

hormone axis

higher order system involving multiple regulatory hormones

HPE axes

• formed by hypothalamic neurons, anterior pituitary cells, and effector endocrine organs

• regulated by negative feedback and involve releasing, pituitary, and effector hormones

metabolism

sum of all chemical and physical changes that occur in body tissues

basal metabolic rate (BMR)

amount of energy required by the body to maintain all its basic functions at rest

nutrient pool

all the nutrients that are immediately available for catabolism by the mitochondria of a cell

anabolism

building of (macro-) molecules from smaller components

direct effects on BMR

thyroid hormone receptors located in the mitochondria upregulate aerobic metabolic activity when activated

regulating nutrient mobilization and uptake/anabolism and growth

thyroid hormone receptors located in the nucleus change the expression levels of specific genes in the target cells when activated

epinephrine & glucagon

mobilize stored glucose and fatty acids

glucocorticoids & growth hormone

mobilize stored fatty acids and glucose, promote lipid use, and stimulate gluconeogenesis

glucose-sparing effect

glucocorticoids and GH promote the use of lipids for metabolism by most somatic cells, saving glucose for the CNS

embryo and infancy

life stage where growth is regulated by thyroid hormones

childhood

life stage where growth is regulated by PTH and calcitrol

puberty

life stage where growth is regulated by reproductive hormones

pancreatic islets

secrete glucagon and insulin, two peptide hormones that directly regulate blood glucose and glucose use

insulin & glucagon

use opposing negative feedback loops to help maintain a normal blood glucose level

Type I Diabetes Mellitus

endocrine disorder caused by the destruction of insulin-secreting pancreatic beta cells

Type II DIabetes Mellitus

endocrine disorder caused by insulin resistance (acquired receptor insensitivity)

stress response

begins in the brain, which classifies situations as stressful, and is passed on to the body via (neuro)endocrine systems

alarm phase

neural and endocrine release of NE/E contribute to increased physical activity and alertness

recovery phase

HPA wing of the stress response directs available nutrients and energy reserves to organ systems that are needed for short term survival

chronic stress response

triggered when moderate stress is sustained over weeks to months, affecting neural tissues, especially in the hippocampus