FINAL: Endocrine system (15,16,17)

Hormones

are chemical messengers that enter the blood which carries them from their site of secretion to the cells upon which they act

The endocrine system is made up of

cells , tissues, and organs that secrete hromone’s into body fluids

What are the master regulators of homeostasis

nervous system and endocrine system

Name the two types of glands in the body

exocrine and endocrine

Exocrine

secrete their products into a duct from where the secretion either exits the body (like sweat) or enters the lumen of another organ such as the intestines

(SECRETE PRODUCTS INTO DUCTS FOR EXCRETION)

Endocrine

are ductless and release hormones into the blood

hormones are first released into the interstitial fluid , from where thye diffuse into the blood to reach a distant target cell

(SECRETE PRODUCTS INTO BODY FLUIDS TO AFFECT TARGET CELLS/ORGANS)

A type of endocrine gland is the hypothalamus explain what it does

hypothalamus secretes several neurohormones that stimulate or inhibit anterior pituitary gland function. Synthesizes two neurohormones that are stored in and released from the posterior pituitary.

A type of endocrine gland is the adrenal glands (cortex and medulla) explain what id does

Makes epinephrine and norepinephrine, which mediate the fight-or-fight response.

A type of endocrine gland is the cortex explain what it does

Makes aldosterone, which regulates Na+ and K+ balance; makes cortisol, which regulates growth, metabolism, development, immune function,and the response to stress;makes some androgens,which play a role in reproduction.

A type of endocrine gland is the liver explain what it does

Produces insulin-like growth factor-1, which controls growth

of bones; secretes angiotensinogen, a precursor required for production of angiotensin Il.

A type of endocrine gland is kidneys explain what it does

Secrete erythropoietin, which regulates maturation of red

blood cells; produce the active hormone 1,25-dihydroxyvitamin D; secrete the enzyme renin, which begins the synthesis of the hormone angiotensin II (see blood vessels).

A type of endocrine gland is pancreas explain what it does

Makes insulin, which decreases blood glucose, and releasing glucagon, which increases blood glucose.

A type of endocrine gland is blood vessels explain what it does

Cells of many blood vessel walls express enzymes that are required to complete the synthesis of angiotensin Il, which helps maintain normal blood pressure.

A type of endocrine gland is adipose tissue explain what it does

Produces hormones (for example, leptin), which regulate appetite and metabolic rate

A type of endocrine gland is parathyroids (behind the thyroid) explain what it does

Make parathyroid hormone, which increases blood Ca?*, and stimulates the production in the kidneys of the active form of

vitamin D

A type of endocrine gland is ovaries explain what it does

Ovaries (in females):

Produce estrogens—such as estradiol—and progesterone, which control female reproduction

A type of endocrine gland is testes (in males) explain what it does

Produce androgens, such as testosterone, which control male reproduction

What are the three main classes of hormones

1. Amines

2. Peptides and proteins

3. Steroids

Amine hormones

• The amine hormones are iodine-containing thyroid hormones and the catecholamines (Epinephrine, norepinephrine, and dopamine) secreted by the adrenal medulla and hypothalamus

are derived from amino acids and include hormones such as epinephrine and thyroid hormones, playing crucial roles in various physiological processes.

Adrenal medulla secretes two catecholamines (NE,E)

-Dopamine is synthesized by neurons in the hypothalamus

why do you think insulin can be administered so quickly to regulate glucose levels, if insulin were a steroid hormone would you expect it ot have such rapid effects

Insulin is able to be administered quickly and act rapidly to regulate glucose levels because it is a peptide hormone, which is water-soluble and acts through cell surface receptors. This allows insulin to trigger fast signaling pathways within the target cells, especially in tissues like muscle and fat, to facilitate the uptake of glucose, increase glycogen storage in the liver, and lower blood sugar levels quickly. The effects are often observed within minutes to hours, which is why insulin is used as an immediate treatment for regulating blood glucose.

If insulin were a steroid hormone, it would likely not have such rapid effects. Steroid hormones are lipid-soluble and act by passing through the cell membrane to bind with intracellular receptors, usually affecting gene expression and protein synthesis. This process takes longer because it involves transcription and translation of new proteins, and these cellular changes take time to produce noticeable effects, often taking hours to days.

In summary, the rapid action of insulin is due to its peptide structure, which allows for quick signaling at the cell surface, while a steroid-based insulin would require a much slower mechanism involving changes in gene expression, leading to slower metabolic effects

Steroid hormones

are produced by cholesterol by the adrenal cortex and the gonads, and by the placenta during pregancy

-predominant steroid hormones are produced by the adrenal cortex are aldosterone, cortisol, DHEA, and androstenedione

ovaries mainly produce

estradiol and progesterone

Testes mainly produce

testosterone

Adrenal gland hormone synthesis

in the cortex it is organized into distinct structural and functional layers

Adrenal cortex secretes aldosterone, cortisol, and androgens

Adrenal medulla secretes epinephrine and norepinephrine

Explain peptide and catecholamine hormones transport

-Form: free (unbound to protein)

Peptide(i.e insulin) and catecholamines (E,NE, Dopamine), are water soluble so they are transported in dissolved plasma

-there receptors are located on the plasma membranes in which they directly bind to on the surface of the target cells

• They signal a cascade of intracellular events through secondary messengers.

  • 1. Hormone binds receptor on surface on plasma membrane

  • 2. activating a G protein

  • 3. Producing adenylate cyclase

  • 4. producing cAMP

  • 5. cAMP activates PKA allowing for phosphorylation and activates cascade leading to intracellular changes

.Explain steroid and thyroid hormone transport in the blood

-they are not water soluble, instead they are lipid soluble and pass through the cell membranes to bind intracellular receptors

-they are protein bound

-intracellular receptors directly alter gene expression which takes longer, so this process is slow

What are the major organs that remove hormones by metabolizing and/or excreting them

liver and kidneys are the major organs

Explain which hormones are rapidly removed from blood and which are not?

peptide and catecholamine hormones are rapidly removed from blood whereas steroid and thyroid hormones are removed more slowly in part because they are circulating bound to plasma protein

-so peptide and catecholamine hormones can enter the filtrate → since they are protein free allowing them to be excreted as urine

Where are the receptors for steroid and thyroid hormones?

they are located inside their target cells

-they are lipid soluble steroid hormones diffuses through the cell membrane, binding intracellular receptors inside the cell/nucleus and the resulting hormone-receptor complex binds regions of the target cells DNA altering transcription of specific genes involved to the hormones signal

Where are receptors for peptide and catecholamine hormones

on the plasma membrane of their target cells

What are the factors that alter rate of hormone secretion in a endocrine cell?

(Ions/nutrients, neurotransmitter, hormones (tropic)

Explain the flowchart when plasma glucose concentration increases

1. increase in plasma glucose concentration

2. increase in insulin secretion from insulin secreting cells

3. increase in plasma insulin concentration

4. increase in action insulin (which transports glucose from extracellular to intracellular fluid) from insulin targets cells

   • remember insulin is a peptide hormone

Explain what the outcome of the hormone can be once the endocrine cell secretes the hormone? flowchart

1. Endocrine cell: secretes hormone

2. Hormone is now circulating in blood

3. It can either be excreted in urine/feces, OR be inactivated by metabolism,

4. OR, be activated by metabolism

5. if activated by metabolism it can go to target cells and bind to receptor and produce a cellular reponse, (it can also just directly bind to the receptor)

How does the autonomic nervous system control hormone secretion?

by the adrenal medulla and endocrine gland cell

In the autonomic nervous system, the adrenal medulla is modified by what?

sympathetic ganglion cells , and is stimulated by sympathetic pre-ganglionic fibers releasing epinephrine

what are the four types of endocrine disorders

hypo-secretion, hyper-secretion, hypo-responsiveness, and hyper-responsiveness

Hyposecretion is a type of endocrine disorders that

has too little hormone secretion

hypersecretion is a type of endocrine disorder that

has too much hormone secretion

Hyporesponsiveness

is when there is decreased responsiveness of the target cell to the hormone (deficiency/loss of function of target cell receptors or downstream intracellular signaling )

Hyperresponsiveness

is when there is increased responsiveness of the target cell to the hormone (synergistic effects of hormones-permissiveness)

Primary disorder

defect occurs inn the cells/tissue that secretes the hormone

secondary disorders

defect occurs as a result of hypo/hyper secretion of a tropic hormone

where are the hypothalamus and pituitary gland located?

In the brain

The pituitary is dividied into

into an anterior and posterior portions

The anterior pituitary does what?

secretes hormones is response to hypo-physiotropic hormones(which are hormones that are produced by the hypothalamus and regulate release from the pituitary gland )

The posterior pituitary gland is

just an extension of axons from the hypothalamus that terminate there, releasing posterior pituitary hormones

Often hormone secretion sequences/pathways initiate with

initiate with tropic hormones from the hypothalamus and pituitary gland

Explain the general pathway of the 3 pathway sequence flow chart, no need to say a specific hormone

1. stimulis

2. hypothalamus increases hormone 1 secretion

3. increase in plasma 1 secretion in the hypothalamo-hypophyseal portal vessels

4. increase hormone 2 secretion in anterior pituitary

5. increase in plasma hormone 2

6. third endocrine gland: increase in hormone 3 secretion

7. increase in plasma hormone 3

8. target cells of hormone 3 respond to hormone 3

Secretion of anterior pituitary gland is controlled by

the hypo-physiotropic hormones which are secreted into the portal vessels connecting the hypothalamus and pituitary

The hypothalamo-hypophyseal portal vessels connect

the capillary bed of the hypothalamus to the second capillary bed of the anterior pituitary gland and facilitate the transport of hormones.

Why is anterior pituitary hormone secretion more efficient ?

the local route for the hypophysiotropic hormones to travel directly from the hypothalamus to act on the anterior pituitary (bypassing general circulation) which allows for more efficient regulation of anterior pituitary hormone secretion

Why does it take only very small quatities of hypophysiotropic hormones to achieve concentrations that are effective in regulating anterior pituitary gland hormone secretion

this is due to the hypothalamo-hypophyseal portal vessels

-the volume of blood is low

What hormones are secreted by posterior pituitary gland

vasopressin : involved in regulation of water balance

and oxytocin: involved in milk ejection reflex of nursing mothers and emotional bonding

Gonadotropin releasing hormone (GNRH) secretes what from the hypothalamus

stimulates secretion of LH and FSH from the anterior pituitary gland.

Name the major hypophysiotropic hormones

Gonadotropic releasing hormone (GnRH), Growth hormone releasing hormone (GHRH), somatostatin (SST), Thyroid releasing hormone (TRH), Dopamine (DA) , and Corticotropin releasing hormone (CRH)

Growth Hormone releasing hormone is secreted from hypothalamus which stimulates secretion of

growth hormone from the anterior pituitary gland

Somatostatin (SST) is secreted from the hypothalamus which

inhibits secretion of growth hormone

Thyroid releasing hormone is released from the hypothalamus which stimulate secretion of

thyroid-stimulating hormone (TSH) from the anterior pituitary gland.

Dopamine is released from the hypothalamus and does what

it inhibits secretion of prolactin

Corticotropin-releasing hormone (CRH) is released from the hypothalamus and does what

it stimulates secretion of adrenocorticotropic hormone (ACTH) from the anterior pituitary gland.

FSH and LH stimulate the gonads which

which is important for germ cell development and secrete hormones

Growth hormone stimulates livers and other cells to

Livers and other cells :secrete insulin-like growth factors-1 (IGF-1)

Many organs and tissues:protein synthesis, metabolism

thyroid stimulating hormone (TSH) stimulates

stimulates the thyroid to secrete thyroxine (T4) and triiodothyronine (T3)

Prolactin stimulates

the breasts for breast development and milk production

adrenocorticotropic hormone (ACTH) stimulates

adrenal cortex to secrete cortisol

If all the neural connections between the hypothalamus and the pituitary gland were severed , the secretion of which pituitary gland hormones would be affected?

The posterior pituitary hormones would be affected since they are just an extension of axons from the hypothalamus while the anterior is released into the blood (hormonal blood based)

The thyroid gland sits within

the neck straddling the trachea

What produce and secretes thyroid hormones?

follicular epithelial cells of the thyroid gland.

What are the two iodine containing thyroid hormones ?

T3: triiodothyronine

T4: thyroxine

Explain T3 and T4

T4 is the main secretory product of the thyroid gland, but T3 is the active hormone (produced from T4 in target tissues)

What stimulates T3(triiodothyronine) and T4(thyroxine)

thyroid stimulating hormone (TSH)

Aside from TSH stimulating T3/T4 what else does it stimulate?

it stimulates growth (cell division/hypertrophy) of thyroid tissue- where excessive TSH can lead to the formation of a goiter

What feeds back on the anterior pituitary gland? in regards to thyroid gland

T3 and T4

Explain what T3 does

it increases metabolic rate and promotes the consumption of calories→ resulting in increased heat production. It stimulates carbohydrate abosrption and fatty acid release providing energy to maintain high metabolsim

• it has permissive effects on catecholamines (permissive actions). It up regulates beta adrenergic receptors in many tissues (heart and nervous system) , potentiating sympathetic nervous system activity

• it is required for the normal production of growth hormone by the anterior pituitary gland (important for normal growth and development, and nervous system function)

Clinical Issues:Hypothyroidism AKA HASIMOTO’s Disease (explain what is is and effects, and how it is treated)

most commonly results from autoimmune destruction of all or part of the thyroid gland (HASHIMOTOS disease)

• characterized by weight gain, fatigue, cold intolerance, and changes in skin tone and cognition, may result in goiter

• it can result from iodine efficiency

• can be treated with the administration of thyroxine (T4)

Clinal issues: hyperthyroidiism (GRAVES disease) explain what it is, what it causes, how its treated

is typically the result of an autoimmune disorder where antibiodies agonize TSH receptors

• characterized by weight loss, heat intolerance, irritabillity and anxiety, and can lead to a goiter

• can have dangerous affects on the cardiovascular system

treated with drugs that inhibit T3 synthesis/ and or removal of thyroid tissue or even radioactive iodine

How does hashimotos disease lead to a goiter

In Hashimoto's disease, the autoimmune destruction of thyroid tissue leads to an inadequate production of thyroid hormones, stimulating the pituitary gland to produce more TSH. This excess TSH can cause the thyroid gland to enlarge, resulting in a goiter.

How can graves disease lead to production of goiter

1. T3 and T4 Increase: Since the thyroid is being overstimulated, it produces excessive amounts of T3 (triiodothyronine) and T4 (thyroxine).

2. TRH and TSH Decrease: The hypothalamus and pituitary gland normally regulate thyroid hormone levels through a feedback loop:

   • The hypothalamus produces TRH (thyrotropin-releasing hormone), which stimulates the pituitary to release TSH (thyroid-stimulating hormone).

   • TSH stimulates the thyroid to produce T3 and T4.

However, when the levels of T3 and T4 rise too high (as in Graves' disease), the negative feedback mechanism kicks in:

• High levels of T3 and T4 signal the hypothalamus and pituitary to reduce TRH and TSH production.

• As a result, TSH levels drop significantly, often to very low or undetectable levels, because the thyroid is already being overstimulated by the autoantibodies.
  

Growth (lengthening of the shaft) stops when

the epiphyseal plates close after puberty. / when the growth plates are completely converted to bone

Osteoblasts

secrete collagen to form a matrix to which calcium is deposited -mineralization of bone

osteoclasts

break down bone to release ca+ stored into the blood (resporption)

epiphyseal growth plates

convert cartilage to bone

chondrocytes

cells that produce cartilage and are involved in the growth and maintenance of cartilage tissue.

What are the major hormones influencing growth

GH, insulin, TH, testosterone, estrogen, cortisol

growth hormone (GH)

major stimulus of postnatal growth: it induces precursor cells to differentiate and secrete IGF-1 which stimulates cell division

-stimultes liver to secrete IGF-1

stimulates protein synthesis

Insulin influences growth

stimulates fetal growth, stimulates postnatal growth by stimulating secretion of IGF1

stimulates protein synthesis

thyroid hormone

permissive for growth hormones secretion and actions

permissive for development of the cenrral nervous system

testosterone

stimulates growth at puberty, stimulating secretion of growth hormone, causes epiphyseal closure , stimulates protein synthesis in male

estrogen

stimulates secretion of growth hormone at puberty

causes epiphyseal closure

cortisol

inhibits growth

stimulates protein catabolism

What is a major stimulus for postnatal growth? explain what it does

Growth hormone, it can directly promote growth in target tissues by stimulating protein synthesis, most of its effects are exerted by stimulating the secretion of insulin like growth factor 1 (IGF1) in the liver

GH STIMULATES:

bone and other tissues to differentiate and secrete IGF1

liver to secrete IGF1

-protein synthesis in muscle

IGF-1 acts locally and systemically to promote cell division

Explain how growth hormone can also promote energy availabillity via its anti-insulin effects

release and breakdown of fat stores

stimulates gluconeogenesis

decreases effectiveness of insulin

Explain the pathway controlling the release of growth hormone

1. Stimulus: excercise, stress, low plasma glucose, sleep

2. hypothalamus: increases secretion of GHRH and decreases secretion of SST (somatostatin inhibits secretion of GH)

3. Increase plasma GHRH and decrease plasma SST in the hypothalamo-hypophyseal portal vessels

4. anterior pituitary gland: increases secretion of GH

5. increases plasma GH

6. Liver and other cells: secrete insulin growth factor 1 (IGF1)

7. increasing plasma IGF1

Clinical issues: Short stature

can be caused by hyposecretion of GH and or/ IGF-1 during childhood development

-there is too little Gh → leading to decrease IGF-1

Clinical issue: Gigantism

can be caused by hypersecretion of GH before puberty. (very tall)

Clinical issue:Acromegaly

can be caused by hypersecretion of GH after puberty. Charcaterized by enlarged organs . Growth plates are closed so long bones cant respond instead there is growth of other tissue

Insulin promotes

the uptake of glucose into adipose and skeletal muscle tissue for consumption (growth) and inhibits protein degradation. Very important during fetal growth/development

Cortisol (stress hormone) has what effects on growth

inhibitory effects on growth

-stimulting protein and bone breakdown, inhibiting bone growth and IGF1 secretion

What are three effector sites for regulation of body calcium

1. Bone: 99% of calcium stored in bone as minerals on collagen matrix, and calcium storage/release is regulated

2. Gastrointestinal tract: absoprtion of calcium from the diet is regulated

3. Kidneys: excretion of calcium in the urine is regulated

Resoprtion:

osteoclasts break down bone to release Ca+ stores into the blood