Endocrine System

endocrine main function

communication + regulation

endocrine hormone regulation

endrocrine cell secretes hormone into bloodstream - binds to receptors and target cells

paracrine hormone regulation

signaling cell secretes hormone to target cells and local mediator

neuronal hormone regulation

hormone travels through neuron and is transferred to target cell at synapse

contact-dependent hormone regulation

signaling cell secretes hormone and travels to target cell via membrane-bound signal molecule

peptides (chemical structure)

chains of amino acids

steroids (chemical structure)

from cholesterol

amines (chemical structure)

biochemical modification of tyrosine

eicosanoids (chemical structure)

derived from long-chain fatty acids (prostaglandins, thromboxanes, + leukotrienes)

arachidonic acid is 1* _____

fatty acid

eicosanoids are NOT classic hormones:

• do regulate physiologic functions

• most cases act as paracrine agents

  • rapidly metabolized so limited transport

prostaglandins

• isolated in nearly all tissues (og prostate)

• several small differ in chemical structure

• varied regulatory function in tissues

  • can have opposite effect in other tissues

prostaglandins regulate ?

blood vessel diameter, inflammation, blood clotting, uterine contraction

what are NSAIDS?

non-steroidal anti-inflammatory drugs

• drugs that inhibit prostaglandin synthesis

• ex: aspirin/buprofen

‘good’ eicosanoids

• prevent blood clots

• causes dilation of blood vessels

• decrease pain + cell division

• increase immune + brain function

‘bad’ eicosanoids

• promotes blood clots

• causes constriction of blood vessels

• increase pain + cell division

• decrease immune + brain function

what is an example of hormones with multiple target organs?

insulin: liver, adipose, muscle

what does estrogen do?

increase circulation before birth

• increase oxytocin receptors in uterus

• prepares uterus for oxytocin to stimulate smooth muscle contractions

increase in receptors =

up-regulation

decrease in receptors =

down-regulation

lock and key explanation?

key (hormone) - lock (receptor) = hormone-receptor complex

peptides ____ go thru cell membrane

cannot

example of peptide hormones?

adenylyl cyclase

• increase camp act on enzymes to elicit response

• 2nd messenger

  • diacylglycerol (DAG) + inositol triphosphate (IP3)

  • Ca also (low in cytosol, ER release into cytosol)

peptide biological responses are usually ____ + _____

rapid + quickly reversed

ADH (biological response)

• acts on kidney to change water permeability

  • occurs in minutes

    • only requires activation of enzymes in the cell

    • when hormone removed - enzymes inactivated

when are peptide responses longer-lasting ?

intracellular pathways lead to DNA transcription

• prolonged due to new proteins produced

steroid and thyroid hormones are ___ soluble

lipid (pass thru membrane)

steroid+thyroid hormones

• receptors on nucleus/cytosol

• acts on transcription factors

  • influence DNA transcription

  • change mRNA - change protein synthesis

steroid+thyroid hormone response time?

slower than peptides

• effects last longer (protein synthesis)

negative feedback

• most common control of hormone release

• increase concentration elicits response to decrease release

example of negative feedback ?

B cells in pancreas

• affected by blood glucose concentrations

increase in glucose =

release insulin

• muscle (liver + adipose) cells take up glucose

what is a more complex negative feedback ?

repro (hypothalamus, pituitary, gonad)

positive feedback

hormone brings biologic response

• further increase release of the hormone

example of positive feedback

oxytocin

• smooth muscles of uterus contract

  • pushes fetus thru cervix - dilating it

  • dilating cervix —> more oxytocin

  • pushing fetus = more dilation

the pituitary is attached to the base of the hypothalamus by ?

infundibulum - stalk of nervous tissues

• cell bodies of nerves in hypothalamus

• terminate in posterior

anterior pituitary

• contains endocrine cells (not nervous tissue)

• AKA adenohypophysis pars distalis

• portal system (imp for hormone transport)

hypothalamus communicates w/Anterior via ____

hypophyseal portal system (blood)

hypothalamus communicates w/Posterior via ____

sending axon terminals

what is known as the “Master Gland”

Anterior Pituitary

anterior pituitary

• neurons in hypothalamus release ‘ hormones ‘ into 1st capillary bed

• this hormone travels via a portal vein to the 2nd capillary bed located in Anterior

• this stimulates endocrine cells of the anterior to release more hormones

what is the meaning behind the name - master gland ?

• lg # of hormones secreted

• wide range of effects

• several hormones effect other glands to produce their own hormones (trophic/tropic)

hormones of adenohypophysis (Anterior)

• Adrenocorticotropic Hormone (ACTH)

• Thyroid Stimulating Hormone (TSH)

• Growth Hormone (GH - somatropin)

• Prolactin

• Gonadotropins (LH/FSH)

posterior pituitary

• neurons in hypothalamus project axons into the posterior

• the hormone is ‘synthesized’ in the cell body of the neuron (technically hypothalamus)

• hormone is ‘released’ from the posterior into blood stream

2 hormones of Nuerohypophysis (Posterior)

oxytocin + antidiuretic hormone (ADH) / vasopressin

oxytocin (nuerohypophysis)

• induces contraction of smooth muscle

• mammary gland - milk let down

  • physical stimulation stimulates oxytocin release

• uterus

  • expulsion of fetus + oxytocin release

antidiuretic hormone (ADH) / vasopressin (neurohypophysis) - released due to ?

• increase blood osmolality

• decrease in blood pressure

• both are related to hydration status

antidiuretic hormone (ADH) / vasopressin (neurohypophysis) - acts to:

• retain water at the kidney

• constriction of blood vessels (vasopressin)

the hypothalamus is the critical interface for?

• nervous + endocrine systems

• sensory information regulates endocrine (pituitary)

• can have +- feedback

hypothalamic axises focus on the connection between ___ + ___

hypothalamus + anterior

Hypothalamic Pituitary Adrenal Axis (HPA) - basic hormone explanation

hypothalamus

• Corticotropin - releasing hormone (CRH)

Anterior

• adrenocorticotropic hormone (ACTH)

target tissue

• glucocorticoids (cortisol)

corticotropin - releasing hormone - HPA

• from hypothalamus

• regulation of CRH (+ACTH) very complex

adrenocorticotropic hormone - HPA

• from Anterior

• secretion stimulated by stress of animal

  • ACTH + glucocorticoids have - feedback

• adrenal glands - secrete steroid hormones

  • travels to adrenal cortex + stimulates

    • zona fasiculata + reticularis - synthesizes and secretes glucocorticoids (1* cortisol + corticosterone)

adrenal glands comprised of?

cortex : zona glomerulosa, fasiculata, reticularis

medulla

mineralocorticoids (1* aldosterone)

• from zona glomerulosa

  • regulate Na + K balance

  • 1* in controlling loss of urine

• not regulated by ACTH

  • renin-angiotensin system + chemical messengers

medulla - secrete ?

epinephrine + norepinephrine

• released in times of stress

• sympathetic nervous system (autonomic)

• not a part of HPA axis

Hypothalamic Pituitary Thyroid Axis (HPT) - basic hormone explanation

hypothalamus

• thyrotropin releasing hormone (TRH)

Anterior

• thyroid stimulating hormone (TSH)

target tissue (thyroid)

• thyroxine (T3) + triiodothyronine (T4)

thyroid stimulating hormone (AKA thyrotropin) - HPT

• targets cells of thyroid to release thyroxine (T3) + triiodothyronine (T4)

thyroxine (T3) + triiodothyronine (T4) - HPT

• amine hormones

• # refer to # of iodine in structures

• necessary for growth of young animals (decrease physical + mental dev)

• regulate basal metabolic rate in adults

thyroid gland is associated with what two organs ?

trachea + larynx

thyroid gland

• most animals have 2 lobes - connected by isthmus

• arterial blood from branches of carotid - associated with parathyroid

thyroid gland - microscopically

• simple epithelium (cuboidal/columnar)

• filled w/gel like fluid ‘colloid’

• follicles consist of C cells

what is the colloid

• consists of protein-iodine complex - thyroglobulin

  • T3/4 stored in colloid as part - unique storage for endocrine

T3 + T4 - body circulation

• circulating in blood - bound to protein

• body fluids not bound —> subject to degration

• usually blood t4 is greater than t3

why is there more T4 than T3?

• affinity to protein is greater—>more in blood

• receptors have greater affinity for T3

• T4 can be converted to T3 in cells

which thyroid hormone is considered more biologically important ?

T3

what do thyroid hormones do for adults?

increase

• O2 consumption

• heat production (chronic cold stress Increase TSH)

• use of carbs + lipids

• BMR

hypothyroidism

underactive thyroid - weight gain, cannot tolerate the cold, depression, tired

what do C cells do?

• produce calcitonin - peptide that decreases blood Ca

  • inhibit osteoclasts

  • - feedback directly on C cells by Ca concentration

  • NOT controlled by TSH

Hypothalamic Pituitary Somatropic Axis (HPS) - basic hormone explanation

hypothalamus

• growth hormone releasing hormone - GHRH (+)

• growth hormone inhibiting hormone - GHIH (-)

Anterior

• growth hormone (GH somatropin)

target cell - liver

• insulin-like growth factors (IGFs)

growth hormone - HPS

blood concentrations greatest in young animals

• lil direct effect on bone + cartilage

• causes release of IGFs

  • older animals can release it aswell

growth hormone - regulates metabolism during:

starvation, decrease in blood glucose, hibernation

growth hormone - causes:

protein breakdown, decrease glucose use by muscle cells, increase mobilization of fatty acids from adipose

somatomedins (IGFs) - HPS

IGF1 + 2

• released by liver + cells around growth plates

• have - feedback to hypothalamus + Anterior

recombinant DNA tech led to :

human (rGH)

• used to treat pituitary dwarfism

bovine (rBST)

• increase lactation + feed efficiency

most animals have _ pair of parathyroids?

2 (4 total)

external parathyroids

one pair outside thyroid

internal parathyroids

pair buried in thyroid

chief cells in ___ produce parathyroid hormone (PTH)

parathyroid

parathyroid hormone

• major controller of blood Ca + P

• activates osteoclasts to elevate Ca

PTH - peptide (diseases?)

bone deformities (osteoporosis)

• diets w/decrease ca2+ are uncommon

  • except grain diets —> increase PTH

brain disease / bighead

• decalcified bone replaces w/soft tissue

  • especially flat bones —> head enlarges

pancreatic islets

• located adj to sm intestine

• imp exocrine gland - digestive enzyme

• anabolism

pancreatic islet cells other name?

islets of Langerhans

types of pancreatic islet cells?

• alpha cells : glucagon

• beta cells (75%) : insulin

how does insulin decrease blood glucose?

• increase glucose uptake in cells

• stimulates glycogen synthesis (liver+muscle)

• stimulates protein synthesis by muscle

• stimulates deposition of lipid in adipose

diabetes mellitus (pancreatic islets)

type 1 : decrease insulin

type 2 : resistence to insulin (decrease receptors)

what does glucagon do?

• liver to break down glycogen

• adipose to release fatty acids

• liver to make glucose

epiphysis - in fish, amphibians, and some reptiles

has photoreceptors ‘third eye’

• set daily + annual cycles based on photo period

epiphysis - mammals

located deep in braincase

• no photoreceptors

• receives light + dark information

• from hypothalamus

epiphysis (epiphysis cerebri, pineal gland) - pinealocytes

make serotonin + enzymes that converts to melatonin

epiphysis - melatonin

• exhibits diurnal rhythm

• release peaks in darkness

• likely involved w/sleep wake cycles

• likely involved w/repro

  • onset of puberty results in decreased production

ADH (type of hormone)

protein/peptide

OT (type of hormone)

protein/peptide

GHRH (type of hormone)

protein/peptide

GH (type of hormone)

protein/peptide

IGF (type of hormone)

protein/peptide

TRH (type of hormone)

protein/peptide

TSH(type of hormone)

protein/peptide

T3 T4 (type of hormone)

amine

PTH (type of hormone)

protein/peptide