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What is the endocrine system?

-endocrine glands and other organs with hormone secreting cells
-hormones are chemical signals
-hormones effects can occur in seconds or hours and may lawt a few minutes or several days

Visualize the human endocrine system

3 classes of hormones

1) Amines: derived from tyrosine or tryptophan
2) Proteins/peptides: most hormones
3) steroids: cholestoral derivatives, less soluble in water - use carriers

Describe amine and protein/peptide hormones

-water soluble
-not able to cross plasma membrane
-must use receptor on the cell surface

Describe hormones are lipid soluble

-diffuse across plasma membranes and acces receptors in either the cytosol or nucleus

Hormone receptors

-only cells having the proper receptors can respond to a hormone
-hormones activate only specific cells
-hormone interacts noncocalently and reversibly with the receptor - prevents cells from being permanently stimulated

Water soluble hormone receptors

-receptors on the plasma membrane - amine and protein/peptide hormones (except thyroid hormone)
-binding initiates a cascade culminating in intracellular signalling
-signaling pathways: rapid, occuring in seconds, involve activity of enzymes, a signle signalling molecule results in the production of many intracellualr messages

Lipid hormone receptors

-receptors located within the cell (in the cytosol or nucleaus)
-steroid hormone-receptor complex acts as transcriptional activator to enhance particualr genes
-transcription of gene enhance and more of that gene's product produced
-can influence a number of fenes within a single cell or in different cells

-Blood concentration of hormone can change dramatically by....?

-changing rate of hormone synthesis
-changing rate hormone removed from blood or inactivated

Protein and peptide hormones are synthsized at a steady rate in an unstimulated cell

-changing transcription rates increases or decreases the supply
-reservoir of stored hormone in secretory vesicle
-steroids are made on demand with no significan t storage

Some examples of amine hormones (tyrosine derivatives)

with one backbone can change between

Examples of major hormones derived from cholesteral

from cholesteral as a root can make....

To make hormones need precursors
Hormones are interrelated

Hormones are prevented from exerting effect indefiniately by what?

-being degraded by lysosomal enzymes
-being excreted in uring
-inactivated by liver
-negative feedback loop

Endocrine and nervous system links - 3

1) sensory stimuli detected by the nervous system can activate the endocrine system
-sensory cue preceived by a sensory receptor sends electrical stimuli to different brain areas including the hypothalamus
-hypothalamus and pituitary gland play the major roles in linking the nervous and endocrine systems

Hypothalamus and pituitary gland

hypothalamaus is a collection of seceral nuclei at the base of the brain and can talk to anterior and posterior pituitary gland

-pituitary gland made of 2 lobes: anterior and posterior
-infundibular stalk connects hypothalmus and pitutitary
-also connevted by portal veins - 2 capillary beds in series, allows for direct communication

Hypothalamus and anterior pituitary

-hypothalamic nuclei make neurohormones: any hormone made and secreted by neurons but NOT neurotransmitters
-neurons secrete neurohormones into capillaries
-travel through portal vein to anterior pituitary
-anterior pituitary then synthesizes several different hormones: 6 hormones swcreted in to general blood circulation, act on other glands or structures

Posterior pituitary gland

-blood supply not connected to hypothalamus
-does not respond to hypothalamic neurohormones
-neurons in the hypothalamus synthesize 2 hormones that have axons that terminate in the posterior pituitary and release the hormones


targes smooth muscle uterine contractions (during birth and milk ejection)

Antidiuretic hormone (ADH)

acts on collecting ducts in kidneys to increase aquaportin channels resulting in decreased urine volume

Metabolism and energy balance Thyroid hormones

regulate metabolic rate
-consists of follicles contianing colloid (thyroglobulin)
-thyrotopin-releasing hormone (TRH - hypothalamus) stimulates thyroid stimulating hormone (TSH - anterior pituitary) which stimulates the thyroid to make thyroid hormones
-thyroxine (T4): 4 iodine molecules
-Triiodothyronine (T3): 3 iodine molecules

Thyroid hormones

-stimulates energy consumption
-also increase heat production
-iodine stored in case of deficiency
-iodine deficient goiters can result from low iodine in the diet


-exocrine portion releases contents into small intestine for digestion
-endocrine portion - islets of langerhans
-5 cell types: greek elterrers
-two are important for glucose homeostatis (alpha and beta)
-alpha cells make glucogen and raises blood glucose
-beta cells make insuline and lowers blood glucose

Adrenal glands

-when blood glucose levels are lower than normal: neurons from the sympathetic nervous system activate the secretion of epinephrine by adrenal medulla (stimulates glycogenolysis and gluconeogenesis)
-produce glucocorticoids like cortisol (which activates gluconeogenesis in the liver)

Type 1 diabetes mellitus (T1DM) and Type 2 Diabetes mellitus (T2DM)

Type 1
-immune system has mistakenly destroyed beta cells
-glucose acculuates to high level in blood
-treated by administration of insulin
Type 2
-cells of the body lose much of their ability to respond to insulin
-obesity associated

Isolating insulin

-had been unable to pruify glucose lowering factor due to digestive enzyme inference
-1921: ligate pancreatic ducts to destroy exocrine pancreas and then purify the factor from the remianing pancreatic tissues
-first successful test on humna patients of purified insulin in 1922

Rest of isolating insulin


regulates appetite
-released by adipose cell in proportion to amount of adipose tissue in the body
-acts on hypothalamus to inhibt appetite
-decreasing adipose tissue decreases leptin incresing appetite

Hormonal control of mineral balance

-regulating Ca2+ balance
-among the most tightly regulated ions
-vitamin D derivative faciliates calcium transport in small intestine

Parathyroid hormone

-made by parathyroid gland acts on bone to stimulate Ca2+ release

-calcitonin produced by throid gland lowers blood Ca2+

Regulation of Na+ and K+

-tightly regulated
-no large reservoirs like Calacium in bone
-key is altering rate of reabsorption of water, Na+, K+ from urine
-ADH increases reabsorption of water in kidney
-atrial natriuretic peptide (ANP): secreted from atria of heart to decrease sodium reabsorption in kidney
-Aldosterone from adrenal glands increases sodium reabsorption in kidney

Hormonal control of growth and differentiation

-in invertebrates, anterior pituitary produces growth hormone (GH)
-GH acts on liver to produce insulin like growth factor 1 (IGF-1)
-IGF-1 stimulates elongation of bones, especially during puberty
-eventually gonadal hormones will seal growth plates preventing further elongation
-in adults GH serves metabolic functions in regulating glucose and fatty acid levels in blood

pituitary giants

result from excessive GH during childhood and acromegaly if high levels continue in adulthood

short stature/pituitary dwarfism

results from insufficient GH during childhood
-can be treated with GH injections as long as treatment begins before puberty ends

Amphibians, thyroid hormones

-play critical role in metamorphosis
-promote resorption of tail and development of legs
-thyroid hormones responsible for change in appearance of flat fish as they mature

Hormonal control of reproduction

-gonatds make gamets and secrete sex steroids
-males - testes secrete androgens (testosterone)
-females - ovaries secrete estrogen (estradiol) and progesterone
-sex steroids responsible for 1) sex specific reproductive behaviors, 2) development of sex specific phenotype 3) required maturation of gametes
-gonadotropins secreted by anterior pituitary 1) luteinizing hormone (LH) 2) follicle stimulating hormone (FSH)

Hormonal responses to stress

-adrenal glands
-inner adrenal medulla secretes amine hormones norepinephrine and epinephrine: fight or glight reactions
-outer adrenal cortext subdivided into 3 zones:
1) glomerulosa: aldosterone maintains mineral balance (mineralcorticoid) 2) fasciculata: glucocorticoids like cortisol 3) reticularis: androgens and estrogens


-catabolic hormones promote tissue breakdown
-break down proteins to provide energy
-promote gluconeogenesis in liver during stress to raise blood glucose
-catabolic effects on immune tissue can depress immune system in prolonged stress

Hormone misuse

-androgens for athletic performance enhancement - roid rage
-blood doping - use erythropoietin (EPO) to stimulate maturation for red blood cells

Endocrine disrupteor

-chemicals derived from industrial waste that resemble estrogen enough to bind to estrogen receptors
-decrease in number of functional germ cells
-feminization of fish

Desmasculinization of frogs by low amounts of atrazine

Chain of causation leading to feminization of male ffrogs and the decline of frog populations in regions where atrazine has been used to control weed populations

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