Chapter 7 - Hormone Classification

Endocrine system

system of glands throughout the body releasing hormones that control growth, energy regulation, homeostasis, reproduction

Major endocrine glands include

pituitary, hypothalamus, thyroid gland, adrenal glands, ovaries/testes

how are hormones transported?

secreted by cells into blood —> targets distant target tissue receptors

Amine hormones

derived from aa / synthesized and stored as precursors

where are precursors of hormones stored

secretory vesicles

thyroid hormone receptor and activity

nuclear receptors; long half life

Catecholamines receptor and activity

cell surface receptor; short half life

protein/peptide hormones receptor and activity

cell membrane receptors (hydrophilic so it cant cross membrane into nucleus); short half life

how are protein/peptide hormones stored?

stored in vesicles as inactive prohormones (cleaved from precursors)

protein/peptide hormones synthesized as?

large inactive precursors

mechanism of protein/peptide hormones

activates second messengers —> modifies existing proteins OR stimiulates protein synthesis

phosphorylation

adding phosphate group (to usually a protein) for activation

How are steroid hormones stored?

NOT STORED! synthesized on demand from cholesterol

lipophilic

readily cross membranes

What is the rate limiting step of steroid hormone formation

conversion from choleterol of pregnenolone

What is the transport method of steroid proteins

binds to carrier proteins in blood (increases half life)

What is the solubility of steroid hormones?

lipophilic (fat-soluble)

Cytoplasmic or nuclear receptor binding steroid hormones are..

slower acting; controls gene expression throguh interference with transcription factors (binds to DNA)

cell membrane receptor binding steroid hormones are..

faster; has non-genomic effects

Two main components that control endocrine system

hypothalamus, pituitary gland

3 main pathways for endocrine system

HPT, HPA, HPG

3 target gland include:

Thyroid, adrenal, gonads

pituitary gland function

middle manager between hypothalamus and target glands

Hypothalamus function for endocrine system

master control (w CNS), releases releasing hormones

endocrine system operates through which feedback loop?

negative feedback

Regulatory (releasing) hormones

Released from hypothalamus; acts on subpopulations of cells in anterior pituitary

Stimulating (or tropic) hormones

Released from anterior pituitary; act on another target endocrine gland

Non-tropic hormones

Released from an endocrine gland; act on target cells/tissues

Target cells

repspond to SPECIFIC hormones through SPECIFIC receptors

characteristics of hormone receptors on cells

- one cell can respond to multiple hormones
- receptors on cell surface OR intracellular

Synergism

combined effect greater than the sum of individual effects

Permissiveness

need second hormone to get full effect

Antagonism

one substance opposes the action of another (ex. competitive inhibitors, functional antagonism)

which three hormones have synergistic effect for raising glucose levels?

glucagon, epinephrine, cortisol

regulatory hormones are what type of hormones

small peptide/protein hormones

Three lobes of pituitary gland

Anterior, Intermediate, Posterior

Infundibulum

stalk that connect pituitary to the brain

Posterior pituitary

extension of the neural tissue

Anterior pituitary

endocrine gland of epithelial origin

Intermediate lobe

In between posterior and anterior

Prolactin controls

milk production @mammary glands

Growth hormone (GH) controls

Growth of muscles and bones + survival @musculoskeletal system + liver

Thyroid stimulating hormone (TSH, thyrotropin) controls

Metabolism through throxine (T4) and triiodothyronine (T3) @thyroid gland

Adrenocorticotropic hormone (ACTH) controls

Stress hormone release (cortisol, androgens, minteralocorticoids) @Adrenal cortex

Gonadotropins (LH, FSH) controls

Reproductive hormones and functions @ovaries/testies

Which population of anterior pituitary cells makes GH

Somatotrophs

Which population of anterior pituitary cells makes prolactin

lactotrophs

Which population of anterior pituitary cells makes TSH

thyrotrophs

Which population of anterior pituitary cells makes FSH, LH

gonadotrophs

Which population of anterior pituitary cells makes ACTH

corticotrophs or lipotrophs

Which hormone of hypothalamus regulates release of ACTH

Corticotropin releasing hormone (CRH)

Which hormone of hypothalamus regulates release of TSH

Thyrotropin releasing hormone (TRH)

What hormones is TSH homologous to?

FSH, LH, hCG (all glycoproteins)

Which hormone of hypothalamus regulates release of LH/FSH

Gonadotropin releasing hormone (GnRH/GRH)

GRH

small peptide hormones found in all mammals

analog

human-made GRH that is stronger; Used for medical use ex) fertility treatment

what controls the feedback regulation of FSH and LH

estrogens and androgens

production of FSH and LH ______ after puberty

increase; males constant, females vary w/ menstrual cycle

FSH function in females

FSH works to grow and mature egg (oocyte) inside follicle

FSH function in male

activates sertoli cells to make androgen binding protein (helps better capture testosterone)

LH function (in general)

regulate steroid hormone production in gonads

LH function in male

acts on leydig cells —> makes testosterone

LH function in females

- LH works with FSH to grow follicles
- LH triggers ovulation —> LH stimulates formation of corpus luteum —> synthesis of progesterone

Chorionic Gonadotropin (hCG)

Hormone of human pregnancy (basis for pregnancy tests)

Chorionic Gonadotropin secreted by

placenta

Prolactin homologous to

GH (single chain glycoprotein)

why is GH and prolactin special

hypothalamus exerts both positive and negative control through hormones

What is the inhibitory hormone for prolactin

dopamine

What is the inhibitory hormone for GH (somatotropin)

somatostatin

lactation

milk production in mammary glands (breastfeeding after childbirth)

concentration for prolactin ______ during pregnancy

INCREASES A LOT

effects of prolactin

- breast development

- lactation

- blocks effects of FSH and LH (prevents menstrual cycle)

Which hormone of hypothalamus regulates release of prolactin (+)

PRH

Which hormone of hypothalamus regulates inhibition of prolactin

PRIH (dopamine)

Dopamine antagonists

blocks dopamine release —> increase prolactin secretion

Dopamine agonists

MAO inhibitors; block dopamine metabolism —> decrease prolactin secretion

Which hormone of hypothalamus regulates release of GH (+) / somatotropin

GHRH

GH is known as a stress hormone because

it raises blood sugar when body is under short-term stress (ex. exercise, fasting, trauma)

Stress hormone promotes

lipolysis, growth, anabolic action (bone/muscle)

What is the most abundant pituitary hormone?

GH with 10-15%

GH half life

short (20-25 mins); binds to plasma proteins to increase half life

Which hormone of hypothalamus regulates inhibition of GH

somatostatin / GHRIH

somatostatin also inhibits

pancreas to decrease insulin levels ; TRH —> TSH

what release pattern does GH have?

pulsatile;
Children —> most during sleep
Adolescent —> during the day

Most pronounced pulse is

just after deep sleep starts

GH levels _____ over age

decrease

how is hypoglycemia related to GH?

Low blood sugar triggers more GH release so body has enough glucose (lipolysis and save muscles rather than fat)

most GH anabolic actions (growth) mediated indirectly by

IGF-1, IGF-2 (somatomedins)

IGF-1 homologous to

insulin

insulin-like growth factors/somatomedins produced at

mostly liver
igf1 also in bone
igf2 also in fetal tissue

Major direct actions of GH (anti-insulin)

lipolysis, carbohydrate metabolism (@hepatocytes)

Major indirect actions of GH (insulin-like)

IGH synthesis —> bone growth + protein synthesis