Module 8 - Endocrine System Flashcards
What are the main functions of the endocrine system?
Regulating organic metabolism and water and electrolyte balance, which are important to maintaining homeostasis
Inducing adaptive changes to help body cope with stressful situations
Promoting smooth, sequential growth and development
Controlling reproduction
Regulating red blood cell production
Working with the ANS to control circulation, digestion, and absorption
What is a tropic hormone?
o Hormone that targets another gland and cause another hormone to be released
Describe negative feedback loops
- Maintains homeostasis
- Glands keep producing hormones until feedback is given that there is enough hormone present
- Negative feedback exists when the output of a system counteracts a change in input
Describe positive feedback loops
- Actions of a hormone cause the further release of a hormone
- Takes levels further away from the set point
- Rare as it is opposite homeostasis
What is a neuroendocrine reflex?
- Involve neural and hormonal components
- Produces sudden increase in hormonal secretion in response to a stimulus (generally external)
- Some involve neural input to the endocrine glad as the only way to stimulate hormone secretion
- Some systems have both feedback control controlling the basal level and neuroendocrine reflex when needed
Describe the circadian rhythm and its hormone fluctuations
- Repetitive fluctuations in hormone levels that cycle every 24 hours
- Controlled by endogenous oscillators that pay attention to external cues, such as light/dark cycles
- Negative feedback control maintains whatever levels is set for that time of day
What is another term for the pituitary gland?
Hypophysis
What is another term used for the posterior pituitary due to it being composed of nervous tissue?
Neurohypophysis
What is another term used for the anterior pituitary due to it being composed of glandular epithelial tissue?
Adenohypophysis
In some lower vertebrates, there is a third, well defined lobe. What is it called, what does it secrete, and what is this for?
Intermediate lobe
Secretes several melanocyte-stimulating hormones (MSH)
Regulates skin colour by controlling dispersion of melanin playing a vital role in camouflage
Although humans do secrete a small amount of MSH, it does not control skin pigmentation as it does in lower vertebrates. What does it appear to do for humans?
Helps control food intake
Influence excitability of nervous system and may improve memory and learning
Suppresses immune system
What are the bone cells that produce the organic matrix?
Osteoblasts
What is bone primarily made of?
Calcium phosphate
What gives bone its high degree of elasticity?
Collagen
What is the cylindrical shaft of a long bone called?
Diaphysis
What are the flared articulating knobs at either end of a long bone called?
Epiphysis
What is the growth plate called?
Epiphyseal plate
What is the central cavity of the bone filled with and what does this do?
Bone marrow, site of blood cell production
How does bone grow in thickness?
Osteoblasts within the periosteum add new bone on top of the outer surface of already existing bone
How is the bone marrow cavity developed as the bone grows in thickness?
Osteoclasts within the bone dissolve the boney tissue on the inner surface next to the marrow cavity so that it enlarges to keep pace with the increased circumference of the bone shaft
How does a bone grow in length?
Chondrocytes in the epiphyseal plates next to the epiphysis divide and multiply temporarily widening the plate
Older chondrocytes next to the diaphysis enlarge
The matrix surrounding the hypertrophied chondrocytes becomes calcified and the old chondrocytes die
Osteoclasts clear the dead chondrocytes and calcium matrix away
Osteoblasts come up and begin to lay down new bone
Results in a longer diaphysis and the plate goes back to the original thickness
What is the term for bone formation
Ossification
What are osteoblasts called once they are sealed into their new space by ossification and thus retire from active bone formation activity?
Osteocytes
What is the main role of osteocytes?
Hormonally regulated exchange of calcium between bone and blood
Why do individuals not grow taller at the end of adolescence even though growth hormone is still present?
The epiphyseal plate completely ossifies (closes) under the influence of sex hormones so it can no longer expand
How does GH affect growing bone?
Promotes growth in bone thickness and length
Stimulates osteoblast activity
Simulates proliferation of epiphyseal cartilage promoting lengthening of long bones
Is the GH affect direct on the chondrocytes?
no
• Research shows GH does not directly affect chondrocytes
• Effects are indirect using peptide mediators called somatomedins
What causes GH deficiency?
Pituitary defect (lack of GH) Secondary to hypothalamic dysfunction (lack of GHRH)
What is the master biological clock for the day/night cycle and where is it located?
Suprachiasmatic nucleus (SCN) which is a cluster of cell bodies in the hypothalamus above the optic chiasm
What proteins is the circadian rhythm linked to? How do these proteins work to adjust the bodies internal clock?
Clock proteins
Genes in nuclei of neurons in the suprachiasmatic nucleus begin to send out instructions for clock proteins
Synthesized in the cytosol of neurons in the SCN
As the day goes on, they reach a critical amount, and are then transported into the nucleus
Clock proteins in the nucleus inhibit further synthesis
As the night goes on, they degrade slowly, reducing the inhibition, and they are produced once again, repeating the cycle
What is a protein found in special retinal cells that acts as the receptor for light that keeps the body in tune with external cues?
Melanopsin
How do the melanopsin-containing ganglion cells send their information to the brain? Where do they go and what do they detect?
Basic light detection
Hypothalamic tract to the suprachiasmatic nucleus (SCN)
The SCN sends it to the pineal gland
What are hormones?
What are hormones?
- Chemical messengers that travel in the blood
- Have specific target cells
- Released by glands
- Some chemicals act as both hormones and neurotransmitters
What are tropic hormones?
o Hormone that targets another gland and cause another hormone to be released
What are hydrophilic hormones?
Describe the 2 hydrophilic hormones
• Highly water soluble and low lipid solubility
• Peptides
o Constitutes the majority of hormones
o Amino acids arranged in a chain of varying length
Peptides are short chains
Proteins are long chains
o Often all referred to as simply peptides
• Catecholamines
o Derived from amino acid tyrosine
o Secreted only by the adrenal medulla
o Sometimes referred to as amine hormones with the thyroid hormones
What are lipophilic hormones?
Describe the 2 lipophilic hormones
• High lipid solubility and poor water solubility
• Thyroid hormones
o All of these are from the thyroid follicular cells
o Derived from iodinated tyrosine
• Steroid hormones
o Includes hormones from the adrenal cortex and gonads
o Derived from cholesterol
• Unable to be broken down in the digestive tract so can be taken orally
How are hydrophilic peptide hormones synthesized, stored, and released?
• Preprohormones, or precursor proteins, are synthesized by ribosomes on the rough ER, pinched off into vesicles, and migrates to the Golgi body
o Processed into active hormones
• Golgi body packages finished hormones into secretory vesicles which are stored in the cytoplasm
• When signaled, vesicles fuse with the membrane and are released via exocytosis into the blood stream
• Rate of secretion regulated by release of pre-synthesized stored hormones
How are hydrophilic catecholamine hormones synthesized, stored, and released?
- Synthesized in the cytosol
- Store in chromaffin granules
- Secreted via exocytosis of granules
How are lipophilic thyroid hormones synthesized, stored, and released?
- Synthesized and stored in colloid, an inland extracellular site
- Secreted via endocytosis of colloid
How are lipophilic steroid hormones synthesized, stored, and released?
• Cholesterol is common precursor and stored in steroidogenic cells
• Produced through a series of enzymatic reactions
o Appropriate enzymes located only in tissues where the specific steroid is created
• Once produced, immediately diffuse across the membrane and into the blood stream
• Only cholesterol is stored inside the cell
• Rate of secretion regulated by rate of synthesis
How are hydrophilic peptide hormones transported through the body?
• Simply dissolved in plasma
How are hydrophilic catecholamine hormones transported through the body?
- About 50% circulate as free hormones
* About 50% are loosely bound to the plasma protein albumin
How are lipophilic steroid and thyroid hormones transported through the body?
• Only a small amount is biologically active
o Freely dissolved in the plasma and not bound to a plasma protein
o Free to cross the capillary wall and bind to a target cell receptor
• Majority bound to plasma proteins
o Some proteins are specific and other indiscriminatory to the hormones they transport
o Provides a reserve of hormones to replenish the active pool
Where are the receptors located for hydrophilic peptide and catecholamine hormones located?
• Bind with specific receptors on the outer plasma membrane of the target cell
Where are the receptors located for lipophilic steroid and thyroid hormones located?
• Pass easily through surface membrane to bind with specific receptors located inside the target cell
How are hormones metabolized?
• Enzymes metabolize hormones
• Most of the time inactivates the hormone
o Rate is not regulated
• Some cases it activates the hormone (such as thyroid hormone metabolized to a more powerful hormone)
o Usually, rate is under hormone control
Where are common sites throughout the body for metabolism of hormones?
o Liver – most common
o Blood
o Kidneys
o Target cells
How are hydrophilic hormones bound to plasma metabolized?
o Less vulnerable to enzyme inactivation
o Removed slowly and can remain in the blood for hours up to a week
o A series of reactions make it more water soluble so they break away from the plasma protein and then eliminated
How are some peptides such as insulin metabolized?
o Endocytosed into the target cell
o Metabolized inside the cell
What are the 3 major means of action of hormones?
Change cells permeability
• Done by a few hydrophilic hormones
• Alters conformation of adjacent channel-forming proteins already in the membrane
Activate second-messenger system
• Done by most surface-binding hydrophilic hormones
• Alters activity of intracellular target proteins, usually enzymes, for desired effect
Activating specific genes • Done by all lipophilic hormones • Cause formation of new intracellular proteins o May be enzymatic or structural o Produce desired effect
How are most hormones excreted?
- Typically, through urinary system
* Rate is not regulated
What is primary hyposecretion and what are some causes?
• Endocrine gland is secreting too little due to an abnormality within the gland • Causes include o Genetic o Dietary Lack of nutrients needed to synthesize hormone o Chemical or toxic damage o Immunological Autoimmune disease may cause damage to gland o Other disease processes I.e., cancer, tuberculosis o Iatrogenic Surgical removal of gland o Idiopathic
What is secondary hyposecretion?
- Endocrine gland function is normal
* Hyposecretion due to deficiency of tropic hormone
What is the most common treatment for hormone hyposecretion?
• Administer the same or similar hormone
• Sources include
o Endocrine tissues from livestock
o Placental tissue/urine from pregnant women
o Laboratory synthesis
o Bacteria with genes for producing hormones
Describe primary and secondary hypersecretion
Primary hypersecretion
o Defect lies within the gland
Secondary hypersecretion
o Overstimulation from the outside
What are causes of hypersecretion?
o Tumors
o Immunological factors
One causes an antibody to appear like a tropic hormone for the thyroid resulting in overproduction of thyroid hormones
o Substance abuse such as steroids
What are treatments for hormone hypersecretion?
o Removing/destroying tumor
o Medication to block synthesis or secretion of hormone
o Medications that inhibit the action of hormones
What is abnormal target cell responsiveness and what are some causes?
• Plasma concentration is normal
• Target function not responding adequately
• Causes may include
o Inborn lack of receptors
Seen with testicular feminization syndrome
o Target cells lack enzyme required to carry out the desired response
What are target cell receptor alterations?
- Target cells can deliberately alter their receptors as part of a control mechanism
- Allows target cell to fine-tune response to the available hormone
- Receptors are constantly being created and destroyed so number is not constant
What is down regulation?
- Number of target cell receptors reduced
- Important negative-feedback system that acts locally
- As a response to chronically high levels of a hormone
- Results in desensitization to the elevated hormone and blunts effects of hypersecretion
What is permissiveness?
- First hormone enhances target cells responsiveness to a second hormone
- Allows the second hormone to work at its full effect
- Without the first hormone, second hormone may be only marginally effective
What is synergism?
• Combined effect is better than the sum of their parts
What is antagonism?
• Hormones having opposing effects
How does the cAMP second messenger system work?
Cyclic Adenosine Monophosphate (Cyclic AMP or cAMP)
• Hormone (first messenger) binds to a surface membrane receptor of a G protein
• Unactivated G proteins consist of alpha, beta, and gamma subunits and when activated it releases the alpha subunit
• The released alpha subunit breaks away and moves along the inner surface of the membrane until it reaches an effector protein, adenylyl cyclase
• Adenylyl cyclase induces the conversion of ATP to cAMP by cleaving off 2 phosphates
• cAMP activates the protein kinase A enzyme
• Phosphorylates target protein changing its shape and function to either activating or inhibiting it bringing about the desired response
How does the calcium second messenger system work?
• Hormone (first messenger) binds to a surface membrane receptor of a G protein
• Unactivated G proteins consist of alpha, beta, and gamma subunits and when activated it releases the alpha subunit
• The released alpha subunit breaks away and moves along the inner surface of the membrane until it reaches an effector protein, enzyme phospholipase C
• Breaks down phosphatidylinositol (PIP2)
o A component of the tails of the phospholipid molecules of the membrane
o Breaks down to 2 molecules that follow 2 paths
Inositol Triphosphate (IP3)
• Responsible for mobilizing intracellular Ca2+ stores to increase cytosolic Ca2+
• Calcium becomes second messenger and usually activates calmodulin
• Activates Ca2+ – calmodulin – dependent protein kinase (CaM kinase)
• Phosphorylates target protein changing its shape and function to either activating or inhibiting it bringing about the desired response
Diacylglycerol (DAG)
• Activates protein kinase C (PKC)
• Phosphorylates target protein changing its shape and function to either activating or inhibiting it bringing about the desired response
How is the second messenger system terminated once the response is accomplished?
o First messenger is removed
o Alpha subunit rejoins bets and gamma subunits to restore G protein complex
o cAMP and other participating chemicals inactivated
How do cAMP and calcium second messenger system pathways interact?
- Frequently overlap and influence each other
- Calmodulin influences cAMP
- Protein kinase A may change activity of Ca2+ channels or carriers
What is amplification of the second messenger system?
- Can be accomplished by a cascade of events
* Allows a small concentration of hormones and other chemical messengers to trigger significant cell responses
How are modifications of the second messenger pathways made?
• Accomplished through regulation of the number and affinity of surface proteins
What is a second messenger system analogous to cAMP?
Cyclic Guanosine Monophosphate (cyclic GMP)
How do lipophilic hormones activate proteins?
• Free steroids or thyroid hormones not bound to a carrier diffuse through plasma membrane of target cell
• Binds to specific receptor which may be in the cytoplasm or within nucleus depending on hormone
• Hormone-receptor complex then binds with DNA at an attachment site called the hormone response element (HRE)
o Each receptor type binds with different HREs
• Turns on a specific gene which contains a code for synthesizing protein which is then transcribed into mRNA
• mRNA binds to a ribosome in the cytoplasm and synthesizes a new protein
• New protein, enzymatic or structural, produces the desired response
Some steroid hormones (especially sex hormones) act too quickly to be gene transcription. What may be happening?
Nongenomic Steroid Receptor Actions
• They bind with receptors in the plasma membrane
o Accomplishes something different than gene transcription
o May include changing ionic influx across the protein
• Others still bind in the traditional ways
What is a negative feedback loop?
- Maintains homeostasis
- Glands keep producing hormones until feedback is given that there is enough hormone present
- Negative feedback exists when the output of a system counteracts a change in input
What is a positive feedback loop?
- Actions of a hormone cause the further release of a hormone
- Takes levels further away from the set point
- Rare as it is opposite homeostasis
What are the 2 lengths of loops?
- Short loop is anterior pituitary to hypothalamus
* Long loop is end gland to hypothalamus
Describe neuroendocrine reflexes
- Involve neural and hormonal components
- Produces sudden increase in hormonal secretion in response to a stimulus (generally external)
- Some involve neural input to the endocrine glad as the only way to stimulate hormone secretion
- Some systems have both feedback control controlling the basal level and neuroendocrine reflex when needed
What are diurnal rhythms?
Diurnal (Circadian) Rhythms
• Repetitive fluctuations in hormone levels that cycle every 24 hours
• Controlled by endogenous oscillators that pay attention to external cues, such as light/dark cycles
• Negative feedback control maintains whatever levels is set for that time of day
What are the endocrine glands of the body?
• Pineal • Hypothalamus • Pituitary o Also called the hypophysis o Often referred to as the master gland • Thyroid • Parathyroid • Thymus • Adrenal • Pancreas • Ovary
Describe the hypothalamus
• Directly stimulates the autonomic nervous system
• Sits on top of the brain stem
• Releases releasing and inhibiting hormones into blood vessels
o Direct anterior pituitary hormone release
o Releasing hormones (RH) stimulate the release of a specific pituitary hormone
o Inhibiting hormones (IH) prevent the release of a specific pituitary hormone
What type of hormones are all of the hypophysiotropic hormones?
Peptide hormones
Secreted by the hypothalamus that stimulate or inhibit the anterior pituitary
What are the hypophysiotropic hormones released by the hypothalamus that stimulate the anterior pituitary?
o Thyrotropin-releasing hormone (TRH)
Stimulates release of TSH (thyrotropin) and prolactin
o Corticotropin-releasing hormone (CRH)
Stimulates release of ACTH (corticotropin)
o Gonadotropin-releasing hormone (GNRH)
Stimulates release of FSH and LH (gonadotropins)
o Growth hormone-releasing hormone (GNRH)
Stimulates release of growth hormone
o Prolactin-releasing hormone (PRH)
Stimulates release of prolactin
What are the hypophysiotropic hormones released by the hypothalamus that inhibit the anterior pituitary?
o Growth hormone-inhibiting hormone (GHIH)
Inhibits release of growth hormone and TSH
o Prolactin-inhibiting hormone (PIH)
Inhibits release of prolactin
Describe the 3 hormone hierarchy that most hypophysiotropic hormones are a part of
o Hypothalamic hypophysiotropic hormone (hormone 1), controls output of anterior pituitary tropic hormone (hormone 2)
o Hormone 2 regulates secretion of target endocrine gland (hormone 3)
o Hormone 3 provides the desired effect
o Negative feedback of hormone 3 occurs at the pituitary and/or hypothalamus
What is another name for the posterior pituitary and what is it composed of?
• Posterior pituitary is composed of nervous tissue
o Also called the neurohypophysis
o Terminals from the hypothalamus
o Glial-like support cells
Describe the neural pathway that connects the hypothalamus to the posterior pituitary?
o Cell bodies lie within 2 nuclei in the hypothalamus
Supraoptic nuclei
Paraventricular nuclei
o Axons pass through connecting stalk
o Terminate on capillaries in posterior pituitary
Describe the hormone synthesis and storage of posterior pituitary
• Hormones created by the cell bodies in the hypothalamus
o Both nuclei make both hormones, but individual neurons can only make 1
• Secretory granules are transported down the axon
• Stored in neuronal terminals of the posterior pituitary
o Each terminal can store either hormone, but not both
o Allows independent release
Describe hormone release from the posterior pituitary
- Stimulatory input arrives at the hypothalamus
- Action potential originates in cell body, down the axon and into he neuronal terminal in the posterior pituitary
- Hormone is released via exocytosis
Describe oxytocin
• Also referred to as OCT, sometimes OT
• Synthesized in they hypothalamus and stored in the posterior pituitary
• Hydrophilic peptide
• Stimulated by the nervous system
• Causes uterine contractions
• Stimulates milk ejection by stimulating mammary glands contraction
o Milk let down reflex
• Produces vasoconstriction in arterioles
• May work as a neurotransmitter
o May be involved with trust, empathy, and social bonding
o But may also be involved with anger etc.
• Has a positive feedback loop so that labour contractions get more intense rather than dying down
Describe the antidiuretic hormone
• Also referred to as ADH or Vasopressin
• Synthesized in they hypothalamus and stored in the posterior pituitary
• Hydrophilic peptide
• Body is made of about 55-60% water, ADH is released when water levels decrease
• Primary endocrine factor regulating water balance
o Inhibits formation of urine
o Kidney tubules to reabsorb more water
o Specifically targets water, is the direct effect
• Minor role in regulating blood pressure
o Constriction of arteriolar smooth muscle
• Stimulus
o High osmotic pressure
o Concentration of solutes is high
o Blood becomes too hypertonic
o Fall in left atrial volume
• Inhibitor
o Increased blood volume
o Sensed by stretch receptors in left atrium
Describe the anterior pituitary
• Also called the adenohypophysis
• Regulated by the hypothalamus via releasing and inhibiting hormones
• Consists of glandular epithelial tissue
• 6 different cell populations secrete the 6 major peptide hormones
o 4 tropic hormones – TSH, ACTH, FSH, and LH
Regulate the secretion of another endocrine gland
o Gonadotropins – LH and FSH collectively
Control secretion of sex hormones from the gonads
Describe the hypothalamic-hypophyseal portal system
- Unique capillary to capillary vascular link that connects the hypothalamus to the anterior pituitary
- Allows releasing and inhibiting hormones released from hypothalamus to bypass systemic circulation and arrive at anterior pituitary in high concentrations
- Releasing and inhibiting hormones synthesized in the cell bodies in the hypothalamus and stored in the axon terminal until stimulated
- Terminal ends located on the capillaries at the base of the hypothalamus that recombine into small portal vessels
- Passes down through connecting stalk into anterior pituitary capillaries
- These drain into systemic system
Describe prolactin
- Often referred to as PRL
- Synthesized in anterior pituitary
- Chemical class is protein
- Promotes breast development
- Initiates milk production
- Males also make prolactin, but it has different target tissues and function is uncertain
Describe follicle stimulating hormone
- Often referred to as FSH
- Synthesized in anterior pituitary
- Chemical class is glycoprotein
- Targets seminiferous tubules in testes or ovarian follicles
- Stimulates testes and eggs to produce gametes
- Stimulates egg to release estrogen
- May enhance immune system in both sexes
- May support development of new blood vessels at the tissue level in both sexes
Describe the luteinizing hormone
• Also referred to as LH
• Synthesized in anterior pituitary
• Also called interstitial cell-stimulating hormone (ICSH) in males
• Chemical class is glycoprotein
• Targets ovarian follicle and corpus luteum to
o Stimulate ovulation
o Corpus luteum development
o Estrogen and progesterone production
• Targets interstitial cells of Leydig in testes to stimulate testosterone secretion
Describe the thyroid stimulating hormone
- Also called TSH or thyrotropin
- Synthesized in anterior pituitary
- Chemical class is a glycoprotein
- Regulated by thyroxine (T4) levels in the blood
- Tropic hormone that stimulates the thyroid follicular cells to secrete T3 and T4
- Stimulates growth of thyroid gland
Describe the adrenocorticotropic hormone
- Also called ACTH or adrenocorticotropin
- Synthesized in anterior pituitary
- Chemical class is a peptide
- Regulated by glucocorticoids
- Targets zona fasciculata and zona reticularis of adrenal cortex stimulating cortisol secretion
- Promotes growth of adrenal cortex
- Stimulates secretion of glucocorticoids
Describe the T3 and T4 hormones
Tetraiodothyronine (Thyroxine or T4) and Triiodothyronine (T3)
• Synthesized in the thyroid
• Chemical class is an amine
• Regulated by TSH
• T3 is more potent, although less is made than T4
• Increases metabolism (basal metabolic rate)
o Increase rate of protein synthesis
o Increase rate of energy release from sugar
This increases rate of oxygen consumption
o Increases temperature
• Essential for normal growth and nerve development
Describe calcitonin
• Made in the C cells of the thyroid gland
• Chemical class is a peptide
• Released in response to high blood calcium levels
• Works in opposition of parathyroid hormone
• Stimulates calcium deposition into bones
o Decreases osteoclast activity
o Increase osteoblast activity
• Stimulate kidney to decrease calcium uptake
• Involved in neurotransmission in synapses
• Plays a role in muscle contraction, blood clotting, and fundamental component of blood and teeth structure
Describe the parathyroid hormone
• Also called PTH
• Synthesized in the parathyroid
• Chemical class is a peptide
• Released in response to low blood calcium levels
• Works in opposition of calcitonin
• Stimulates calcium release from bones
o Increases osteoclast activity
o Decreases osteoblast activity
• Stimulates kidney to increase calcium uptake
• Increases absorption in the small intestine
o Activation of vitamin D
Where is the adrenal medulla located?
Inside the adrenal gland. Cortex is on the outside
Describe epinephrine and norepinephrine
• Synthesized in the adrenal medulla • Chemical class is amine • Stimulated by neurons in the sympathetic nervous system originating in the hypothalamus • Targets sympathetic receptor sites throughout the body • Raises blood glucose level • Increases metabolic activities • Constricts certain blood vessels • Results in flight or flight reaction o Not as fast as the neuron stimulation o Enhances the neuron stimulation o Results in the following symptoms Heart rate and blood pressure increase Blood flow to heart and muscle increases Breathing rate increases Blood glucose rises Metabolism increases
Describe corticoids
• Synthesized in the adrenal cortex
• Chemical class is steroids
• Stimulated by ACTH from the anterior pituitary
• In response to long term stress
• Reduces inflammation
• Suppresses immune system
• Mineralcorticoids
o Kidneys absorb more salts and water follows
Results in an increase in blood volume and blood pressure increase
o Kidneys excrete more potassium
o Regulated by increased potassium levels
• Glucocorticoids
o Protein and fat metabolism stimulated
o Results in an increase in glucose being released
• Gonadocorticoids
o Affects sex hormones
Describe cortisol
- Type of glucocorticoid
- Synthesized in the zona fasciculata and zona reticularis of the adrenal cortex
- Promotes gluconeogenesis
- Proteins are broken down in the liver
- Amino acids are used to create glucose
- Blood glucose levels are increased
- Also acts as an anti-inflammatory (where cortisone comes from)
- Contribute to stress adaption
Describe the hypothalamic pituitary adrenal axis
• Also referred to as the HPA axis
• Regulates stress response
• Corticotropin releasing hormone (CRH) is released by hypothalamus
• Pituitary makes ACTH
• ACTH goes to the adrenal glands causing release of cortisol
o Helps body deal with stress
o Provides extra glucose
• When cortisol levels rise, negative feedback loop triggers hypothalamus to stop stimulating
Describe aldosterone
• Acts as a mineralcorticoid
• Stimulated by ACTH
• Synthesized in the zona glomerulosa of the adrenal cortex
• Increases blood pressure
o Stimulates sodium reabsorption in the kidney tubules
o Water follows the sodium
• Increases K+ secretion
• While ADH and Aldosterone have the same result, they have different actions
o Aldosterone act on the sodium reabsorption
o ADH acts on water reabsorption
• Stimulate kidneys to excrete excess potassium
o Indirect action
Describe androgens of the adrenal cortex
- Also called dehydroepiandrosterone
- Synthesized in the adrenal cortex
- Targets the brain and bones of females
- Responsible for pubertal growth spurt and sex drive in females
Describe insulin
• Synthesised in the pancreas
• Chemical class is a protein
• Released in response to high blood glucose levels
• Secreted by beta cells in the islets of Langerhans
• Promotes sugar absorption into the cells
• Stimulates energy storage
o Glycogenesis
Converts glucose to glycogen in the liver
o Formation of fats to adipose tissue
Describe glucagon
• Synthesised in the pancreas
• Chemical class is a protein
• Released in response to low blood glucose levels
• Secreted by alpha cells in the islets of Langerhans
• Stimulates glycogenolysis
o Glycogen is broken down into glucose
• Stimulates fat tissue to be broken down into glucose as well
Describe somatostatin
- Synthesised in the pancreas
- Secreted by D cells in the islets of Langerhans
- Targets the digestive system to inhibit digestion and absorption of nutrients
- Targets the pancreatic islet cells to inhibit secretion of all pancreatic hormones
Describe the androgens secreted by the testes
- Synthesized in the testes
- Chemical class is a steroid
- Regulated by FSH and LH
- Supports sperm formation
- Promote development and maintenance of secondary male sex characteristics
Describe inhibin secreted by the testes and ovaries
• Targets the anterior pituitary to inhibit secretion of FSH
Describe estrogens
- Also called estradiol
- Synthesized in the ovaries
- Chemical class is a steroid
- Regulated by FSH and LH
- Promotes follicular development
- Stimulate uterine lining growth
- Stimulates breast growth
- Promote development and maintenance of secondary female sex characteristics
Describe progesterone
- Synthesized in the ovaries
- Chemical class is a steroid
- Regulated by FSH and LH
- Stimulate uterine lining growth and prepares for pregnancy
Describe the hormones secreted by the placenta
Estrogen and Progesterone
• Synthesized by the placenta
• Targets the female sex organs to help maintain pregnancy
• Prepares breasts for lactation
Chorionic Gonadotropin
• Synthesized by the placenta
• Targets the ovarian corpus luteum to maintain it during pregnancy
Describe renin
• Synthesized by the kidneys
• Activates angiotensin
o Targets the zona glomerulosa of the adrenal cortex
o Stimulates aldosterone secretion
Describe erythropoietin
- Synthesized in the kidneys
* Targets the bone marrow to stimulate erythrocyte production
Describe gastrin
• Synthesized by the stomach • Targets o Exocrine glands of digestive tract o Smooth muscles of GI tract o Pancreas o Liver o Gallbladder • Controls motility and secretion to facilitate digestive and absorptive processes
Describe secretin and cholecystokinin
• Synthesized by the duodenum • Targets o Exocrine glands of digestive tract o Smooth muscles of GI tract o Pancreas o Liver o Gallbladder • Controls motility and secretion to facilitate digestive and absorptive processes
Describe glucose-dependent insulinotropic peptide
- Synthesized by the duodenum
* Targets the endocrine cells of the pancreas to stimulate insulin secretion
Describe vitamin D
- Synthesized in the skin
* Targets the intestine to increase absorption of ingested calcium and phosphate
Describe thymosin
- Synthesized in the thymus
* Targets T lymphocytes to enhance their proliferation and function
Describe atrial natriuretic peptide
- Synthesized in the heart
* Targets the kidney tubules to inhibit sodium reabsorption
Describe leptin
- Synthesized in adipose tissue
- Targets hypothalamus to suppress appetite
- Plays an important role to long-term control of body weight
Describe adipokines
- Synthesized in adipose tissue
* Targets multiple sites and plays a role in metabolism and inflammation
Describe melatonin’s main role in the body
• Synthesized in the pineal gland
• Chemical class is an amine
• Targets
o Brain
o Anterior pituitary
o Reproductive organs
o Immune system
• Entrains body’s biological rhythm with external cues
o Uses melanopsin containing illumination detecting retinal ganglion cells
o Signal travels from hypothalamic tract to the suprachiasmatic nucleus
o Message relayed to pineal gland
• Regulated by light/dark cycles
o Secretion increases 10-fold during the nighttime and falls during the day
Describe other roles that melatonin may play a role in
• Induces sleep • Inhibits gonadotropins o Reduction likely initiates puberty o Currently being looked at for forms of birth control in men and women • Acts as an antioxidant • May slow aging process • Enhances immunity
Describe the growth hormone
• Often referred to as hGH GH, or somatotropin
• Synthesized in the anterior pituitary
• Produced by the somatotroph cells in the anterior pituitary
• Anterior pituitary gland that does not affect another gland
• Most produced anterior pituitary hormone, even in adults
o Production declines in middle age
• Chemical class is protein
• Regulates body growth by encouraging mitosis
• Targets bones and soft tissues
• Functions include
o Essential, but not solely responsible for growth
o Stimulates growth of bones and soft tissues
o Metabolic effects including
Protein anabolism
Fat mobilization
Glucose conservation
• Also stimulates somatomedin secretion from the liver
o Directly mediates effects of GH
o This action results in sometimes being called a tropic hormone
What are some factors that affect growth?
• Genetics
• Adequate diet
• Freedom from chronic disease and stressful environmental conditions
o Cortisol stunts growth
o If sickness or stress is corrected before adult height is reached, they can rapidly catch up
• Normal levels of growth-influencing hormones
o Growth hormone (GH)
No role in fetal development
o Thyroid hormone
o Insulin
o Sex hormones
What are the 2 major growth spurts experienced?
• Postnatal growth spurt o Occurs during first two years of life • Pubertal growth spurt o Occurs during puberty o Likely combination of GH, androgens, and genetics
What are the metabolic actions of GH unrelated to growth?
• Helps maintain body during prolonged fasting or other situations in which metabolic needs exceeds available glucose stores by
o Increasing rate of protein synthesis in all body cells
o Increasing fatty acid mobilization from adipose tissue
o Increasing fatty acid use by body tissues
o Decreasing rate of glucose/glycogen use by body tissues
How does GH play a role in growth of soft tissues?
• Hyperplasia
o Increasing number of cells
o GH stimulates mitosis and prevents apoptosis
• Hypertrophy
o Increasing size of cells
o GH promotes synthesis of proteins and inhibits protein degradation
Promotes cell uptake of amino acids
Stimulates cellular machinery required for protein synthesis
What are somatomedins?
- Also called insulin-like growth factors (IGF) due to structure similar to insulin
- Peptide mediators that produce the indirect effect of GH on chondrocytes
Describe IGF-I
• Most important somatomedin
• Recent research suggests it works together and independently with GH
• Synthesis stimulated by GH
o Circulating levels secreted by liver
o Secreted by most other tissues but not into circulation
Paracrine actions
More impactful to growth than circulating levels
• Blood plasma levels similar to GH but it lasts longer
• Production controlled by
o Adequate nutrition
o Age influenced
Dramatic increase during puberty
o Tissue-specific stimulatory factors
Describe IGF-II
- A somatomedin
- Production not influenced by GH
- Primary role during fetal development
- Unclear about role in adults
What are the actions of GH that are accomplished wither directly or via IGF?
- Decreased glycogen synthesis
- Reduced glucose use
- Increased lipolysis (breakdown of stored fat)
- Increased use of fatty acids
- Metabolic sparing of glucose and amino acids
- Increased amino acid transport across cell membrane
- Increased protein synthesis
- Increased collagen synthesis
- Increased cartilage growth
- Promotion of hypertrophy and hyperplasia of tissues
How is GH synthesized
• Regulated by 2 antagonistic hypothalamic hypophysiotropic hormones
o Growth hormone-releasing hormone (GHRH) is stimulatory
o Growth hormone-inhibiting hormone (GHIH) is inhibitory
Also called somatostatin
• Both GH and somatomedins inhibit pituitary production of GH
o Presumably by stimulating GHIH secretion
• Somatomedins may inhibit effects of GHRH on anterior pituitary
What are factors that influence GH secretion?
• Diurnal
o Levels up to 5x higher after going to sleep
o Lowest during the day
• During high energy demands
o E.g. exercise, stress, low blood glucose
o Saves glucose for the brain and uses fatty acids for the body
• Rise in blood amino acids
o GH promotes protein synthesis to use them
What other hormones affect growth and how do they stimulate growth?
Thyroid Hormone
• Actions of GH only fully manifest when enough thyroid hormone is present
• Severely stunted growth in children with hypothyroidism
• Hypersecretion may result in excessive skeletal growth, increasing a child’s height
Insulin
• Promotes protein synthesis
• May interact with IGF-I receptors due to similar structure
• Deficiency blocks growth
• Hypersecretion frequently spurs excessive growth
Androgens
• Stimulate protein synthesis in many organs
• Stimulate linear growth, weight gain, and increase in muscle mass
• Effects dependent on presence of GH and work synergistically for linear growth
• Promote closure of epiphyseal plates
Estrogens
• Role not well understood
• Hypersecretion appears to inhibit chondrocyte proliferation at epiphyseal plate while they are still open
• Promote closure of epiphyseal plates
Describe acromegaly
- Excessive growth hormone after growth plates have fused
- Causes excessive growth not associated with height
- Bone thickening most obvious in extremities and face
- Affects internal organs, bone width, cartilage, and other tissues
- Appearance can include swollen nose, ears, hands, and feet
- Peripheral nerve disorders often occur as nerves are entrapped by overgrown connective tissue or bone
Describe dwarfism
• Short stature caused by retarded skeletal growth
• Symptoms may include
o Poorly developed muscles
o Excess subcutaneous fat
• GH deficiencies in adults do not affect growth but may exhibit
o Reduced muscle mass and strength
o Decreased bone density
o Increased risk of developing heart failure
African Pygmies
• Congenital incapacity to produce a normal amount of IGF-I resulting in short stature
Laron Dwarfism
• Abnormal GH receptors that are unresponsive to GH
• Symptoms resemble severe GH deficiency but with high levels of GH found in the blood
Pituitary Dwarfism
• Reduced growth hormone during adolescence
Describe gigantism
- Excessive growth hormone during childhood
- Most common cause is tumour of GH producing cells of anterior pituitary
- All soft tissues grow correspondingly, so body is well proportioned
Which class of hormones are NOT stored after they are synthesized?
a) catecholamines
b) peptides
c) steroids
d) thyroid hormones
C
Oxytocin is stored in the
a) anterior pituitary
b) hypothalamus
c) pineal gland
d) posterior pituitary
D
Growth in long bone length is due to the activity of which one of the following types of cells?
a) astrocytes
b) chondrocytes
c) osteoblasts
d) osteoclasts
B
Which hormone is important for maintaining the body’s inherent circadian rhythm?
a) thymosin
b) somatostatin
c) melatonin
d) prolactin
C
What is the term for when several hormones are complementary and their combined effect is greater than their individual effects?
a) antagonism
b) down regulation
c) permissiveness
d) synergism
D
List the 6 major functions of the endocrine system
Regulate metabolism and water/electrolyte balance
Stress responses
Promote growth and development
Control reproduction
Regulate red blood cell production
Control and integrate the circulatory system and the digestion and absorption of food with the ANS
Define what is meant by permissiveness
Actions of one hormone are dependent on the actions of another hormone
What is a hormone response element?
Intracellular receptors that, once bound with hormones, can interact with DNA
Where are hormones of the posterior pituitary synthesized?
In the cell bodies of neurons in the hypothalamus and then transported down their axons to the posterior pituitary for release
List the hormones that, in addition to growth hormone, contribute to overall growth
thyroid hormone
androgens and estrogens
insulin
When one hormone regulates the release of another hormone it is called a(n)
a) antagonistic hormone
b) permissive hormone
c) synergistic hormone
d) tropic hormone
D
Which class of hormones is BEST associated with hormones that are hydrophilic?
a) peptides
b) thyroid hormones
c) steroids
d) all hormones are hyrdrophilic
A
In the cyclic AMP second-messenger system, which one of the following is responsible for the final activation of the target protein?
a) adenylyl cyclase
b) cyclic AMP
c) G proteins
d) protein kinase A
D
The hormone that has actions on the nephrons of the kidneys is
a) adrenocorticotropic hormone
b) oxytocin
c) prolactin
d) vasopressin
D
Using your knowledge of the hormones associated with growth, the hypersecretion of which one of the following is most likely to lead to gigantism?
a) androgens and estrogens
b) insulin
c) growth hormone
d) thyroid hormone
C
Compare and contrast solubility properties of hydrophilic and hydrophobic hormones
Hydrophilic are soluble in water and can freely dissolve in the plasma for circulation
Hydrophobic (lipophilic) are not soluble in water and generally require carrier proteins to circulate to their sites of action
In the context of second messengers, explain what is meant by signal amplification
A single receptor activates several intracellular signaling proteins, each releasing even more secondary messengers
Describe the functional role of the hypothalamic-hypophyseal portal system
Creates a vascular connection between the hypothalamus and the anterior pituitary. This allows direction communication and regulates the release of anterior pituitary hormones using very small concentrations of hypothalamic hormones
What is the purpose of having both hormone-releasing and release-inhibiting hormones produced in the hypothalamus?
Having both allows the hypothalamus to act as an integratory center for hormone control. Acting through feedback mechanisms, the hypothalamus can increase the secretion of either to fine-tune the levels of circulating hormones
Describe the process of bone growth
At the hypophyseal plate, chondrocytes divide in pillar-like structures to increase the length of long bones. As they age, chondrocytes enlarge and secrete matrix called cartilage. Eventually these chondrocytes die and are cleared away by osteoclasts. Osteoblasts then invade these spaces and deposit bone over the cartilage
If the neurosecretory neuronal cells in the paraventricular nucleus were secreting large amounts of their hormone(s), which one of the following symptoms would you likely observe?
a) inhibition of milk ejection
b) decreased permeability of the distal tubules to water
c) Excessive release of luteinizing hormone
d) vasoconstriction of most arterioles
D
Which one of the following hormones is MOST likely to activate the cAMP second-messenger pathways?
a) epinephrine
b) thyroid hormone
c) cortisol
d) estrogen
A
In response to the stress chain of command, corticotropin releasing hormone is released from the
a) anterior pituitary
b) adrenal gland
c) posterior pituitary
d) hypothalamus
D
If a person’s liver secretes very low levels of IGF-I during childhood, which of the following would be the most likely result?
a) dwarfism
b) gigantism
c) no effect during childhood
d) excessive hair growth
A
Which of the following is the MOST likely outcome for a person who has sustained damage to their suprachiasmatic nucleus?
a) loss of growth hormone secretion
b) gigantism
c) disruption of circadian rhythms
d) decreased release of all anterior pituitary hormones
C
Would you expect the concentration of hypothalamic releasing and inhibiting hormones in a systemic venous blood sample to be higher, lower, or the same as the concentration of these hormones in a sample of hypothalamic-hypophyseal portal blood?
Lower, and in fact would be nearly nonexistant
Thinking about the feedback control loop among TRH, TSH, and thyroid hormone, would you expect the concentration of TSH to be normal, above normal, or below normal in a person whose diet is deficient in iodine (an element essential for synthesizing thyroid hormone)?
Above normal
A patient displays symptoms of excess cortisol secretion. What factors could be measured in a blood sample to determine whether the condition is caused by a defect at the hypothalamic/anterior pituitary level or the adrenal cortex level?
If CRH and/or ACTH is elevated in accompaniment with the excess cortisol secretion, the condition is secondary to a defect at the hypothalamic/anterior pituitary level
If CRH and ACTH levels are below normal in accompaniment with excess cortisol secretion, the condition is due to a primary defect at the adrenal cortex level, with the excess cortisol inhibiting the hypothalamus and anterior pituitary in a negative-feedback fashion
Why would males with testicular feminization syndrome be unusually tall?
Inability of testosterone to promote closure of the epiphyseal plates of the long bones in the absence of testosterone receptors
A black market for growth hormone abuse already exists among weightlifters and other athletes. What actions of growth hormone would induce a full-grown athlete to take supplemental doses of this hormone? What are the potential detrimental side effects?
Promotes increased skeletal muscle mass through its protein anabolic effect
Side effects include diabetes or high blood pressure
At 18 years of age and 2.4 meters tall, Anthony was diagnosed with gigantism caused by a pituitary tumor. The condition was treated surgically removing his pituitary gland. What hormonal replacement therapy would Anthony need?
Thyroid hormone (absence of TSH)
Glucocorticoid (absence of ACTH)
Male sex hormones
Growth hormone and prolactin will not need to be replaced as their absence will have no serious consequences
Vasopressin may need to be replaced if insufficient quantities of this hormone are picked up by the blood at the hypothalamus in the absence of the posterior pituitary
Compare and contrast the synthesis, storage, secretion, and transport in the blood of peptide hormones and steroid hormones
In general, peptide hormones are synthesized and stored within vesicles. Upon appropriate simulation, the vesicles undergo exocytosis to release them into the blood. They are usually hydrophilic so they do not require a transport protein in the blood to reach their target
In contrast, because steroid hormones are lipophilic, once they are synthesized they are not stored, but will leave the cell. In the plasma, they are generally bound to transport proteins to help them reach their targets
Explain how a common second messenger such as cAMP can induce widely differing responses in different cells
Different cells have different proteins available for phosphorylation by protein kinase A. THe particular cellular action of cAMP depends on what these proteins do one they are phosphorylated.
Describe the three general mechanisms of controlling hormone secretion that are common to many different hormones
Negative feedback maintains plasma concentrations of a hormone at a given set level because the output of the hormonal control system counteracts a change in the input
Neuroendocrine reflexes produce a sudden increase in hormone secretion in response to a stimulus
Diurnal (circadian) rhythms are rhythmic fluctuations up and down in the secretion rate of many hormones as a function of the time of day
Explain down regulation, permissiveness, synergism, and antagonism
Down regulation is a reduction in the number of target-cell receptors in the face of a prolonged increase in hormone
Permissiveness refers to the need for one hormone to be present in adequate amounts to permit another hormone to fully exert its effects
Synergism results when the combined effect of two hormones is greater than the sum of their separate effects
Antagonism takes place when one hormone decreases the effectiveness of another hormone
Describe the process by which lipophilic hormones initiate cellular responses
Free lipophilic hormones diffuse through the plasma membrane and bind with their receptor either in the cytoplasm or nucleus
Receptor-hormone complex binds to its specific site of attachment on DNA known as hormone response element (HRE)
Binding results in creation of mRNA. mRNA heads into cytoplasm, finds a ribosome, and protein is created resulting in the desired response
Describe the hierarchic chain of command and negative feedback in the hypothalamic-anterior pituitary-peripheral target endocrine-gland axis
Input to the hypothalamus causes the release of hormone 1 which goes through the portal system and causes the anterior pituitary to release hormone 2. Hormone 2 travels through systemic circulation to the target endocrine gland which secretes hormone 3 to the target cells resulting in the desired effect.
When the desired amount of Hormone 3 is detected by either the hypothalamus or the anterior pituitary, they stop secreting their own hormones so that hormone production shuts down in a negative feedback system
List the posterior pituitary hormones, the anterior pituitary hormones, and they hypophysiotropic hormones
Posterior pituitary - vasopressin (antidiuretic hormone), oxytocin
Anterior pituitary - growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, follicle-stimulating hormone, luteinizing hormone, and prolactin
Hypophysiotropic - thyrotropin-releasing hormone, corticotropin-releasing hormone, gonadotropin-releasing hormone, growth hormone-releasing hormone, somatostatin (growth hormone-inhibiting hormone), prolactin-releasing hormone, and dopamine (prolactin inhibiting-hormone)
Compare the means by which the hypothalamus controls hormonal output from the posterior pituitary and from the anterior pituitary
The hypothalamus controls hormonal output from the posterior pituitary by a neural connection and controls hormonal output from the anterior pituitary by a vascular connection. Posterior pituitary is a neural extension of the hypothalamus. Neuronal cell bodies in the hypothalamus produce vasopressin and oxytocin, which are transported down the axons that pass through the connecting stalk to the posterior pituitary where these hormones are stored in the neuronal terminals. When stimulated by the hypothalamus, these hormones are independently released into the systemic blood. The hypothalamus secretes hypophysiotropic hormones into the hypothalamic-hypophyseal portal system, a capillary-to-capillary vascular link that transports them through the connecting stalk to the anterior pituitary, where they control the secretion of hormones produced by the anterior pituitary into the systemic blood
Describe GH’s metabolic effects
GH directly increases fatty acid levels in the blood by enhancing the breakdown of triglyceride store in the adipose tissue and increases blood glucose levels by decreasing glucose uptake by muscles and increasing glucose output by the liver, thus mobilizing fat stores as a major energy source for muscle, while conserving glucose for the brain.
GH also directly and indirectly (via IGF-I) brings about protein synthesis decreasing blood amino acids in the process
Explain the relationship between GH and IGF-I in promoting growth
GH does not act directly to bring about most of its growth-producing actions (increased cell division, enhanced protein synthesis, and bone growth). Instead, GH stimulates the liver to release IGF-I, which directly mediates these growth-promoting actions. GH’s only direct growth promoting action is to stimulate protein synthesis, which is does in conjunctions with IGF-I
What factors can influence the release of growth hormone
Growth hormone has a well-characterized diurnal rhythm for secretion.
It is primarily under the control of growth hormone-releasing hormone and growth hormone-inhibiting hormone.
Secretion can be increased by exercise, stress, and low blood glucose
Compare the endocrine system to the previously studied nervous system
Compared to the nervous system, the other major regulatory system of the human body, the endocrine system produces a slower but longer-lasting response.
Describe the main functions of the endocrine system
Functions of the endocrine system include regulation of electrolyte and water balance, digestion and absorption of food, reproduction, growth and development, and adaptation to stress.
Where in the hypothalamus is vasopressin produced?
Paraventricular nucleus
Where in the hypothalamus is oxytocin produced?
supraoptic nucleus
What are vasopressin’s main functions?
Vasopressin functions to increase water reabsorption in the kidneys, to cause vasoconstriction of blood vessels, and to induce thirst. All of these actions serve to increase blood volume, which indirectly increases blood pressure.
What are oxytocin’s main functions?
Oxytocin is released during parturition (childbirth) to stimulate contraction of the uterus. Oxytocin is also released reflexively when the baby suckles the breast to stimulate milk ejection (“milk let down”).
Describe the hierarchy for prolactin including the target cells and primary function
Prolactin-releasing hormone (PRH) and prolactin-inhibiting hormone (PIH) released from the hypothalamus to regulate prolactin secretion from the anterior pituitary. The target cell is the uterus to increase contractility and the mammary glands in the breasts to promote milk ejection
Describe the hierarchy for TSH including the target cells and primary function
Thyrotropin-releasing hormone (TRH) and growth hormone-inhibiting hormone (GHIH) (I know that’s weird, it’s not wrong lol) are released by the hypothalamus to stimulate or inhibit release of thyroid stimulating hormone (TSH) from the anterior pituitary.
TSH travels to the thyroid gland for production of they thyroid hormones T3 and T4. They target most cells and function to increase the metabolic rate
Describe the hierarchy for ACTH including the target cells and primary function
Corticotropin-releasing hormone (CRH) from the hypothalamus stimulates release of ACTH from the anterior pituitary. ACTH travels to the adrenal cortex and stimulates the release of cortisol. Cortisol targets most cells in the body and increases blood glucose levels
Describe the hierarchy for GH including the target cells and primary function
Growth hormone-releasing hormone (GHRH) and growth hormone-inhibiting hormone (GHIH) are released by the hypothalamus to regulate the release of growth hormone from the anterior pituitary.
GH travels to the liver to promote the release of somatomedins.
Both GH and somatomedins target bone and soft tissue to promote growth
Describe the hierarchy for LH including the target cells and primary function
Gonadotropin-releasing hormone (GnRH) is released by the hypothalamus to stimulate the anterior pituitary to release luteinizing hormone.
LH directly influences ovulation and corpus luteum development.
LH goes to the ovaries to stimulate release of estrogen, which goes to the female sex organs stimulating the female reproductive system and progesterone which targets the uterus to prepare the body for pregnancy
LH goes to the testes to stimulate release of androgen which targets the male sex organs stimulating the male reproductive system.
Describe the hierarchy for FSH including the target cells and primary function
Gonadotropin-releasing hormone (GnRH) is released by the hypothalamus to stimulate the anterior pituitary to release follicle stimulating hormone.
FSH goes to the ovaries to stimulate release of estrogen, which goes to the female sex organs stimulating the female reproductive system and progesterone which targets the uterus to prepare the body for pregnancy
FSH goes to the testes to stimulate release of androgen which targets the male sex organs stimulating the male reproductive system.
What is the result of GH hyposecretion in childhood and in adulthood?
Dwarfism results from GH hyposecretion during childhood. As an adult, GH hyposecretion leads to decreased skeletal muscle mass and decreased bone density.
What is the result of GH hypersecretion in childhood and in adulthood?
GH hypersecretion results in gigantism if it occurs during childhood, or acromegaly if it occurs during adulthood.
Describe the difference between primary and secondary hyposecretion of GH?
Primary hyposecretion results from the failure of the endocrine gland to secrete adequate amounts of the hormone, which in the case of GH would be a failure of the anterior pituitary to secrete appropriate amounts of GH. Secondary hyposecretion results from the failure of the tropic hormones to adequately stimulate the endocrine gland, which in the case of GH could result from a lack of growth hormone releasing hormone (GHRH) from the hypothalamus.
