Endocrine system

Endocrine system

• composed of ductless glands that synthesize and sec

• target cells have the specific receptors for a hormone

Two control systems of the body

• Endocrine and nervous system

Both endocrine and nervous system

release ligands - chemical messengers

Comparison of the two control systems - communication

• nervous → a nerve signal causes neurotransmitter releases from a neuron into a synaptic cleft

• endocrine → secretes hormones into blood; hormones transported within the blood are distributed to target cells thoughout body

Target of stimulation

• nervous → other neurons, muscle cells, and gland cells

• endocrine → any cell in the body with a receptor for the hormone

response time

• nervous → rapid reaction time; typically milliseconds or seconds

• endocrine → relatively slow reaction; time seconds to minutes to hours

Range of effect

• nervous → typically has localized specific effect in the body

• endocrine → typically has widespread effects throughout the body

duration of response

• nervous → short-term: milliseconds terminates with removal of stimulus

• endocrine → long lasting; minutes to days to weeks, may continue after stimulus is removed

General functions of the endocrine system

1. regulating development, growth, metabolism

2. maintaining homeostasis of blood composition and volume

3. controlling digestive processes

4. controlling reproductive activities

location of endocrine glands

Glands contain epithelial tissue that makes and release hormones

• some glands are endocrine organs with solely endocrine function

• some glands are cluster of cells in organs with another function

Hormonal stimulation

Release of a hormone in response to another hormone

1. anterior pituitary releases thyroid-stimulating hormone (TSH)

2. TSH stimulates thyroid gland to release thyroid hormone (TH)

Humoral stimulation

Release of a hormone in response to changes in level of nutrients or ion in the blood

1. blood glucose levels increase

2. increased blood glucose stimulates pancreas to release insulin

Nervous system stimulations

Release of a hormone in response to stimulation by the nervous system

1. sympathetic division is activated

2. sympathetic preganglionic axons stimulate adrenal medulla to release epinephrine and norepinephrine

What did you learn?

• The two main control systems are endocrine and nervous

• endocrine has slower longer lasting effects

• changes in level of nutrient or ion in the blood, stimulates pancreas to release insulin

• no, the entire pancreas is not an endocrine organ

3 categories of circulating hormones

• steroids, lipid soluble formed from cholesterol → estrogen, progesterone

• biogenic amines, water-soluble (except thyroid hormone), derived from amino avid that is modiste ( e.g. tyrosine) → norepinephrine, melatonin

• proteins, water-soluble, consists of amino acids chains, three subgroups (small peptides, large polypeptides, glycopeptides) → antidiuretic hormone, insulin, glucagon

Lipid - soluble hormones use carrier proteins

• do not dissolve readily in blood

• carriers are water-soluble portents made by the liver

• carriers protect hormones from early destruction

• binding between hormone and carrier is temporary

  • hormone must be unbound from carrier to bind to target

  • attach -detach - reattach

  • 90+ is typically bound to a carrier at all time

Water-soluble

Most water-soluble hormones travel freely through blood

• a few use carrier proteins to prolong their life

Levels of circulating hormone

a hormones blood concentration depends on how fast it is synthesized and eliminated

• hormone synthesis is done by the gland

• hormone elevation occurs in multiple ways

  • enzymatic degradation in liver

  • removal from blood via kidney exertion or target cell uptake

Half-life

Time necessary to reduce a hormone’s concentration to half of its original level

• water-soluble hormones generally have short half-life

• steroid hormones generally have a long half-life

What did you learn pt 2

• steroids are lipid soluble (estrogen, progesterone, testosterone, cortisol, aldosterone)

• insulin is made up of protein hormone

• insulin is water soluble

• the type of hormone that generally has protein carriers in the blood are water soluble

Lipid soluble hormones

lipid soluble hormones can diffuse across target cell membranes

• such hormones are small, non polar, and lipophilic

Process of lipid-soluble hormones diffusing

1. hormones enters cell and binds to a receptor which can be found in the cytosol (or nucleus) → forms a hormone-receptor complex

2. complex enters the nucleus and binds to a hormone-response element of DNA

3. results in creation of mRNA → leaves nucleus

4. ribosome in cytosol uses mRNA to create a new protein → protein expression determines the cell’s function

Water soluble hormones

Water soluble hormones use receptors on the cell membrane

• these hormones are hydrophilic and cannot diffuse through the membrane

Water soluble signal transduction cascade

1. first messenger (hormone) binds to receptor on cell surface

2. binding activates a G-protien

3. G-protien activation causes activation of adenylyl cyclase

4. adenylyl cyclase activates the second messenger cyclic adenosine monophosphate (cAMP)

5. cAMP activates protein kinase A (PKA)

6. PKA modulates the activities of existing proteins and other cellular molecules → the cascade does not act in the cell nucleus

Actions of water-soluble hormones

1. enzyme can be activated or inhibited

2. growth can be stimulated (cell division)

3. cellular secretions can be released

4. membranes permeability can be changed

5. muscles can be contracted or relaxed

Intracellular enzyme cascade and response amplification

• signaling pathway advantages

  • signal is amplified at each enzymatic step

  • there are many places to regulate pathways activities

• signaling pathways controls

  • cells possess mechanism to quickly inactivate intermediate

Target Cells : degree of cellular response

A cells response to a hormone varies with

• its number of receptors for the hormone

• its simultaneous response to other hormones

Recptor number fluctuates

• up regulation: increase number in receptors

  • increase sensitivity to hormone

• Down regulation: decrease number of recptors

  • decrease sensitivity to hormone

synergistic interactions

one hormone reinforces activity of another hormone

permissive interactions

one hormone requires activity of another hormone

antagonist interactions

one hormone opposes activity of another hormone

What did you learn

• target cells receptors are located for lipophilic hormones on chormone reactor complex

• the water soluble signaling does modulate activity, by actuation of kinase enzymes and changes to ion permeability, which can result in inaction of muscle contractions/relaxations, cellular growth/secreations, stimulate or inhibit enzyme pathways

• the molecule that is activated directly by a g-protien is either adenylate cyclase or phospholipase C

• if someone were to take a large dose of artificial hormone the target cell response would be to down regulate, which is decreasing the number of receptors

• when a large cell receptors from two hormones that cause opposing effects it is a antagonistic interactions

Hypothalamus

controls pituitary

• pituitary controls thyroid, adrenal, liver, testes, ovaries

pituitary gland (hypophysis)

• interior to hypothalamus

• connected to hypothalamus by infundibulum (stalk)

• partitioned into anterior and posterior pituitary lobes

antihero pituitary (adenohypophysis)

• larger part of pituitary

• partitioned into there areas:

  • pars distills, pars, tuberlias, pars intermedia

• hypothalami-hypophyseal portal system of blood vessels

posterior pituitary (neurohypophysis)

• smaller part of pituitary gland, directly connected to hypothalamus

• cell bodies found in the paraventricular nucleus (oxytocin) and supraoptic nucleus (ADH)

• azon extends though the infundibulum via the hypothalami-hypophyseal tract

• terminals in the pars nervosa of the posterior pituitary

synthesis in the neurosecretory cells

ozytocin and antidiuretic hormone are systhezide in the neurosecretory cells of the hypothalamus and shipped to the posterior pituitary for storage and release

• release signal is sent from hypothalamus

oxytocin

uterine contraction, milk ejection, emotional bonding

antidiuretic hormone

decrease urine production, stimulate thirst, constrict blood vessels

regualtion of hormones

the hypothalamus secretes regulatory hormones

• these travel to the antihero pituitary via the hypothalamo-hypohyseal portal system

• these hormones can be

  • releasing hormones - increase anterior pituitary release of hormones

  • inhibiting hormones - decrease anterior pituitary reales of hormone

• antihero pitutiyy secrets hormones → general circulation

releasing hormones

• thyrotropin-releasing hormone (TRH) → stimulates thyroid gland to release thyroid hormone

• prolactin-releasing hormone (PRH) → prolactin acts on mammary glands to stimulate milk production

• gonadotropin-releasing hormone (GnRH)

• corticotropin-releasing hormone (CRH)

• growth hormone-real sing hormone (GHRH) → goth hormone stimulates release of IGFs from he liver which synergistically act on all body tissues especially bone, muscle, and adipose connective tissue to stimulate growth

Inhibiting hormone

• Prolactin-inhibiging hormone (PIH)

• Growth hormone-inhibiting hormone (GHIH)

follicle-stimualting hormone (FSH) and luteinizing hormone (LH)

act on gonads (testes and ovaries) to stimulate development of gametes (sperm and oocyte) and release hormones

adrenocorticotropic hormone (ACTH)

acts not he adrenal cortex to cause release of corticosteroids

What is the difference in hormone synthesis location between the posterior and anterior pituitary

• anterior pituitary get regulatory hormones hormones from hypothalamus via hyothalamo-hypophyseal portal, hormones can be realizing hormones or inhibits hormones → anterior pit secrets hormones, general circulation → mechanism of control hormonal

• posterior receives systhezided hormones from the hypothalamus, storage and release, realism signal is sent from hypothalamus → mechanism of control nervous

What types of hormones increase the secretion of anterior pituitary hormones? decrease?

Increase

• thyroptopin realsing

• prolactin releasing’

• gonadoropin relasing'

• corticotropin relasing

• growth hormone relasing

inhibiting

• prolactin inhibity

• growth hormone inhibits

What are the two primary hormones of the posterior

• oxytocin: uterine contraction, milk ejections, emotional bonding

• antidiuretic hormone : decrease urine production, stimulate thirst, constrict blood vessels

Growth hormone

HG functions

• stimulation of linear growth a epiphyseal plate

• hypertrophy of muscle

• release of nutrients from storage into blood

release varies

• children and adolecnes have high amounts, youn adolescents have almost double that of young adults

• at any given age there are daily fluctuations in realize of GH, peak correspond to early stages of sleep

GH releases

influenced by age, time of day, nutrient levels, stress, and exercise

• nutrient blood levels → increase in repose to increase in amino acid levels and to a decrease in glucose levels or fatty acid levels

• stress increase GH release, although sever emotional stress can cause a decrease in its release in children

Growth hormone mechanism of action

GH target hepatocytes (liver cells)

• hepatocytes release insulin like growth factors (IFGs) and increase glycogenolysis/gluecogenesis

  • results in increase in blood glucose levels

All body cells have receptors for HG, IG or both

• cause increase in cell division, protein synthesis, cell differentiation

• bone and muscle are particularly responsive

HG and IGF cause adipose cells to release nutrients

• cells increases lipolysis and decrease lipogenesis

negative feedback relation of GHRH

• increased levels of GH or IGF stimulate hypothalamus to release growth hormone inhibiting hormone (GHIH)

• gh realse also inhibits its own release from pituitary

growth hormone pathway

1. variables that influence realize from hypothalamus

2. receptor, hypothalamus réponse to various stimuli

3. control center, hypothalamus realizes GHRH into hypothalamo-hypophyseal portal system

4. in response anterior pituitary releases GH

5. Gh stimulates hepatocytes to release insulin like growth factor into blood

6. both GH and IGF sitimulate target cells

7. increased protient ysthensis, cell divisions, cell differentiation occur

8. increase levels of gh and igf inhibit FHRH from hypothalamus, also inhibit release of GH from antihero pituitary

Thyroid gland

Largest endocrine organ

• left and right lobes connected at midline by isthmus

• two cell types

  • follicular cells - produce and realize thyroid hormone (TH) → increases metabolic rate and body temperature

• parafollicuar cells - cells around follicular cells that make calcitonin → hormone that decrease blood calcium levels

• TH is synthesized in follicular cells from a combination of iodine and thyroglobulin

• TH is stored in the follicular cells until release is stimulated by TSH

Action of thyroid hormone (TH)

Hypothalamic-pituitary-thyroid-axis

• cold temperatures, pregnancy, high altitude, hypoglycemia, or low TH cause hypothalamus to release TRH (thyrotropin releasing hormone)

• TRH causes anterior pituitary to realize TSH which travels to the thyroid and causes a release of TH from follicular cells

net effect: increase protein synthesis (especially in neural tissue), rise in temperature, increased glucose uptake, increased metabolic rate, increased oxygen demand to facilitate aerobic cellular respiration

• negative feedback of TH decrease TRH releasae

Thyroid hormone pathway

1. stimualated by derates in thyroid hormone, or cold weather, pregnancy, high altitude, and hypoglycemia

2. receptor, the hypothalamus responds to various timuli

3. control center, hypothalamus relates TRH into hypothalamo-hypophseal portal system

4. in response to TRh the anterior pituitary releases TSH

5. TSH stimulates the typhoid gland to realize TH into the blood

6. TH then acts on target cells

7. net effect - increase metabolic rate occurs, which is supported by increased release of stored nutrients and increased delivery of O2

8. Th levels increase inhibit release of TRH and TSH

Adrenal glands

anatomy of the adrenal glands

• paired, pyramid-shaped endocrine glands

• located on superior surface of each kidney

• adrenal medulla

  • red-brown color due to extensive blood vessel

  • relates epinephrine and norepinephrine with sympathetic stimulation

• adrenal cortex (outside)

  • synthesizes and releases corticosteroids

  • yellow color due to lipids within cells

  • three zones

    • zona glomerulosa

    • zona fasiculata

    • zona reticularis

Hormones of the adrenal cortex: corticosteroids

1. mineralmcoricoids (ZG): hormones that regulate electrolyte levels

   1. aldosterone regulates the Na and K retention in body

2. gonadocorticoids (ZR): sex hormones

   1. androgens are male sex hormones → converted to estrogen in females

   2. amount of androgen produced by adrenals is less than amount of testes

3. glucocorticoids (ZF): hormones that regulate blood sugar

   1. cortisol increases nutrients levels in the blood

   2. resist stress and help to repair tissue

Cortisol releases

regulated by hypothalamic-pituitary-adrenal axis

• CRH stimulates anterior pituitary to releases ACTH

• ACTH stimulated adrenal cortex to realse cortisol and corticosterone’

net effect of adrenal glands and cortisol; negative feedback

Net effects: increase of all nutrient levels in the blood

• liver cells increase glycogenolysis and gluconeogenesis; decarse glycogenesis

• adipose cells increase lipolysis and decrease lipogenesis

• many body cells break down preteens to amino acids

  • liver cells use the amino acids for glucogeogenesis

• most cells decrease their glucose uptake, sparing it for brain

negative feedback: increasing cortisol levels inhibits relapse of CRH from hypothalamus and ACTH from anterior pituitary

Cortisol pathway

1. variables, negative feedback, time of day, stress

2. 2. receptor hypothalamus réponse to various stimuli

3. the hypothalamus realizes corticotropin-releasing hormone (CRH) into the hypothalamo-hypohyseal portal system

4. in réponse to CRH, the anterior pituitary realseas adrenocotioctropic hormone (ACTH)

5. ACTH stimulates the adrenal cortex to releases glucocorticoids (eg cortisol) into the blood

6. cortisol stimulates target cells

7. increase of all nutrients molecular in the blood occurs

8. cordial increase, inhibiting realize of CRH and ACTH

What hypothalamic hormone stimulates the release of growth hormone

growth hormone releasing hormone

why types of cells in the torpid are responsible for the production and release of TH?

follicular cells

what are the primary hormones produced in the adrenal cortex? adrenal medulla?

adrenal cortex: mineralocorticoids, gonadocorticoids, glucocorticoids

adrenal medulla: epinephrine, norepinephrine

Pancreas

located behind stomach, between duodenum and spleen

has endocrine and exocine functions

• acini cells generate exocrine sections for digestion

• pancreatic islets (of langerhans) contain clusters of endocrine cells

  • alpha cells secrete glucagon

  • beta cells secrete isnuline

  • dealt cells secrete somatostatin (GHIH - inhibits insulin/glucagon release)

Effects of pancreatic hormones

Pancreatic hormone help maintain blood glucose

not controlled by the hypothalamus-pituitary system

• humoral stimualtion

insulin lowers blood glucose

• after food intake, beta cells detect rise in blood glucose and respond by secreting insulin

• once blood glucose falls, beta cells stop secreting insulin

glucagon raises blood glucose

• alpha cells detect a dip in blood glucose and respond by secreting glucagon

• once blood glucose raise, alpha cells stop secreting insulin

How insulin lowers blood glucose

1. increase in blood glucose levels

2. beta cells within the pancreas detect an increase in blood glucose levels

3. beta cells within pancreas release insulin

4. insulin stimulates target cells

5. decrease blood glucose levels occur (fatty acids and amino acids are also decreased in the blood)

Hepatocytes remove glucose from blood; store it as glycogen

• glycogenesis stimulated; glyogenolysis and gluconeogensis inhibited

• aidpose cells store fat

  • lipogenesis stimulated and lipolysis inhibited

• most body cells increase nutrient uptake in response to insulin

How glucagon raises blood glucose

1. decrease in blood glucose levels

2. alpha cells within the pancreas detect a decrease in blood glucose levels

3. alpha cells within the pancreas release glucagon

4. glucagon stimuatles target cells

5. increase blood glucose and fatty acid levels occur (no change to amino acids or proteins)

Alpha cells detect drop in blood glucose and release glucagon

glucagon acts though 2nd messengers causing body cells to release stored nutrient into blood

• hepatocytes releases glucose

  • glycogenolysis and gluconeogenesis stimulated; glycogenesis inhibited

• adipose cells release fatty acids and glycerol

  • lipolysis stimulated while lipogenesis inhibited

Pineal gland

Pineal gland is a small unpaired body in the epithalamus of the diencephalon

• pineal secretes melatonin at night

  • causes drowsiness, regulates circadian rhythm

parathyroid glands

parathyroid glands are small structures on the back of the thyroid gland

content chief cells which make parathyroid hormone (parathormone;PTH)

• pTH increases blood calcium

• effects counteract the paragollicualr cells of the thyroid that produce calcitonin (decrease blood calcium)

Thymus

secretes thymosin, helps with maturation of white blood cells

kidney

secretes erythropoietin (EPO), causes increased red blood cell production

Stomach

secretes gastrin, gastrin increases secretions and motility in stomach for digestion

skin

produces vitamin D3, converted to calcitriol (synergistic to PTH)

liver

secretions angiotensinogen, helps raise blood pressure when it starts to fall

small intestine

secretes secretin and cholecystokinin (CCK)

• secretin stimulates secretion of bile and pancreatic juice

• CCK stimulates release of bile from fall bladder

Adipose

connective tissue secretes leptin, leptin controls appetite

heart

heart produces atrial natriuretic peptide

• decrease blood pressure

ovaries secrete

• estrogen and progesterone - stimulates follicle maturation

• inhibitin prevents follicle maturation, stops FSH release

Testes

secrete

• testosterone - maturation and function of male reproductive system/ sperm maturation

• inhibit - prevents sperm cell maturation, stops FSH release

What function is served by the pancreatic islets?

contain clusters of endocrine cells

• alpha cells secrete glucagon

• beta cells secrete insulin

• delta cells secrete somatostatin (GHIH) - inhibits insulin / glucagon release )

What effects would a decrease in insulin levels be expected to have on blood sugar

decrease in insulin would cause a lower blood sugar, body increase nutrients uptake in response to insulin

effectors respond to glucagon in what way

effectors cause the blood sugar to increase by stimulating the target cells, which are the effectors

what gland secretes melatonin and what is it effect

Pineal gland, secretes melatonin at night, causes drowsiness, regulates circadian rhythm

what effect does PTH have on blood calcium levels

PTH increases blood calcium