The Endocrine System Flashcards
What type of communication is used in the endocrine system?
Amplitude modulated signals
What determines the strength of the signal in endocrine communication?
The amount of the hormone determines the strength of the signal
What type of communication is used in the nervous system?
Frequency modulated signals
What determines the strength of the signal in the nervous system?
The frequency of action potentials produced by neurons
Why is it that endocrine and nervous systems are thought to be inseparable?
Neurohormones secreted by the nervous system act on endocrine tissues
What is the scope of action for the endocrine system?
Broad
What is the scope of action for the nervous system?
Precise
What is the speed of the endocrine response?
Slow
What is the speed of the nervous system response?
Fast
Where do autocrine signals act?
On the same cells that secrete them
Where do paracrine signals act?
Diffuse locally and act on neighboring cells
What types of chemical messengers never enter the blood and only communicate from the interstitial fluid?
Autocrine and Paracrine
How do endocrine signals function?
Hormones carried between cells by the blood or other body fluids, bind to specialized receptors on the plasma membrane and induce a response with or without entering the target cell
How do neural signals function?
Diffuse a short distance between neurons
How do neuroendocrine signals function?
They are released from neurons but act on distant cells
What are pheromones?
Hormones released into the environment and act on different individuals
What three feedback mechanisms regulate the synthesis and secretion of hormones of the endocrine system?
Neural control
Genetically encoded or acquired biorhythms
Feedback mechanisms
What is the most common feedback system used in the body to maintain homeostasis?
Negative Feedback System
What is the goal of the negative feedback system?
To have a plasma level of the hormone that feeds back to the hypothalamus to ensure proper levels are maintained
What is the mechanism behind a positive feedback system?
The rate of the process increases as the concentration product increases
How do protein/peptide hormone receptors function?
The receptor is located on the cell surface of the target cell which triggers a response by activating an intracellular enzyme system generating a second messenger
What is the process of signal pathway?
Signal molecule binds to Receptor protein that activates Intraceullular signal molecules altering Target proteins which creates RESPONSE
What is an important aspect of endocrine signaling?
Amplification, the end result is large
What are the two most common second messengers?
cAMP & Ca
What is the predominant effect of second messengers?
Activate protein kinases
What is the general rule of thumb for hormones considered to be peptides or proteins?
All hormones are protein based except those that are secured from the adrenal cortex (steroid hormones)
What are considered amine derived hormones?
Tyrosine
Tryptophan
What hormones are tyrosine based?
Thyroid hormone
Dopamine
Epinephrine
Norepinephrine
What is the tryptophan derived hormone?
Serotonin
What is unique about the thyroid hormone storage?
There is no storage in the cell, when ready for release, the molecules move to the edge of the cell for exocytosis into the circulation
How do thyroid hormones act like steroids?
Thyroid hormones must be bound to protein in the thyroid follicles
What are characteristics of steroid hormones?
All are lipid soluble and derived from cholesterol or have a chemical structure similar to cholesterol
What are the steroid hormones?
Cortisol, aldosterone, estrogen, progesterone and testosterone
How are steroid hormones stored?
Not stored in discrete secretory granules but are compartmentalized within the endocrine cell and released into the ECF by simple diffusion through the cell membrane
Why is the half life of steroid hormone greater than other hormones?
Al steroid hormones (and thyroid) are bound to transport proteins which increase the half life significantly
What do steroid hormones take so much more time compared to other hormones?
They travel bound to a protein, once reach the correct cell membrane, diffuse across cytoplasm where is binds with the DNA, induces start of transcription. Many mRNA are produced amplifying the signal
What two factors determine hormone clearance?
Rate of secretion into the blood
Rate of removal from the blood
How are hormones cleared?
Metabolic destruction by tissues/target cells
Binding with tissues
Excretion into the bile
Excretion by kidneys into the urine
How are water soluble hormones broken down?
Degraded by enzymes in the blood
What are the two components of receptor modulation?
Up and Down Regulation
What occurs during up regulation of receptors?
Due to a lack of stimulation, neural receptors increase in number
What occurs during down regulation of receptors?
Due to continuous stimulation of a receptor, neural receptors decrease in number
What does the pituitary gland regulate?
Energy and water balance
Growth
Response to stress
Reproduction
How many hormones does the pituitary gland secrete?
Eight
Six anterior
Two posterior
What does the term trophic indicate?
Act to modulate other endocrine glands, control the function of other tissues
Where is the hypothalamus located?
Floor and lateral walls of the third ventricle
What is the significance of the hypothalamus?
Area of the brain where the endocrine and ANS work together
How is the hypothalamus connected to the pituitary gland?
Pituitary stalk
What surrounds the pituitary gland?
Encased in the sella tunica bounded above by the optic chasm and laterally by the cavernous sinuses
What regulates the anterior pituitary gland?
Negative feedback via hormones from the target organs in the periphery
Where are the four major feedback loops?
GH
TSH
ACTH
LH & FSH ( count as one)
What term is used to describe all of the hypothalamic neuropeptides?
Trophic, releasing hormones that go to the anterior pituitary to release hormones
What part of the pituitary gland has neural connection?
Posterior pituitary gland has direct neural connection
How does the posterior pituitary form?
Downward growth of neural tissues that begins at the diencephalon
How does the anterior pituitary gland form?
Up growth of ectodermal tissue that begins as an evagination of an area of the roof of the mouth
How do the two glands eventually combine?
As the upgrowth expands, it begins to meet the down growth
How does the anterior pituitary gland communicate with the hypothalamus?
Two capillary beds
What is the only hormone of the pituitary gland that is not a trophic hormone?
Growth hormone
What are tropes?
Cell of the pituitary gland, specifically the anterior, which manufacture and secrete anterior pituitary hormones
What is the function of growth hormone?
Skeletal development and body growth, regulates protein and CHO metabolism
What is the function of ACTH?
Regulates growth of the adrenal cortex and the release of cortisol and androgenic hormones from the adrenal gland
What is the function of TSH?
Controls growth and metabolism of the thyroid gland and the secretion of thyroid hormones
What is the function of FSH?
Stimulates ovarian follicle, development/spermatogenesis
What is the function of LH?
Induces ovulation and corpus luteum development, stimulates testes to produce testosterone
What is the function of prolactin?
Promotes lactogenesis, inhibits synthesis and secretion of LH and FSH
How does the thyroid gland get stimulates to release T3 and T4?
Thyrotropin releasing hormone stimulates thyrotroph cells of AP gland –> Thyroid stimulating hormone produces and acts on target tissues at the thyroid gland
Where is growth hormones target site?
All tissues
What is the most common cause of pituitary pathology?
Adenoma
What are the functions of growth hormone?
Sodium retention Decreased insulin sensitivity Lipolysis Protein synthesis Epiphyseal Growth
What is the effect of growth hormone on the liver?
Insulin like growth factor I released
What are the functions of insulin like growth factor I?
Insulin like activity
Anti lipolytic activity
Protein synthesis
Epiphyseal growth
What is another name for growth hormone inhibiting hormone?
Somatostatin
How is growth hormone secreted?
Pulsatile with circadian rhythms
What pathophysiology occurs with excess of growth hormone before puberty?
Giantism, response at epiphyseal plates
What pathophysiology occurs with excess of growth hormone after puberty?
Acromegaly, the diameter increases
What are symptoms typically seen in acromegaly?
Coarsening of facial features, widened fingers, toes, hands and feet, prominent eyebrow ridge and jaws, all organs increase in size
What pathology is present when there is a normal amount of GH but there is low or absent ICF1
Pygmies
How are GH abnormalities diagnosed?
Random GH elevations (know what point of circadian cycle) High normal GH that fails to suppress with glucose administration
Elevated IGF 1 (this does not undergo daily variation)
What airway abnormalities are seen with acromegaly?
Facial deformities, large nose, macroglossia, enlarged thyroid, prognathism, obstructive teeth, hypertrophy of epiglottis, general soft tissue overgrowth and MP 3,4
What cardiac abnormalities are seen in acromegaly?
Arrhythmias, CAD and HTN
What can be done to a patient with Acromegaly to assess from entrapment neuropathies?
Allen test
How can Octreotide be used in the treatment of Acromegaly?
It is a somastatin analog, inhibits GH secretion by binding to somatostatin 2 and 5 receptors
What drug is a GH receptor antagonist used for treating Acromegaly?
Pegvisomant
What is typically the cause of giantism?
Noncancerous pituitary tumor
What symptoms are typically seen in giantism?
Large tongue, coarse body hair, skin thickness, heart failure, weakness and visual problems
What is considered dwarfism?
An adult hight of 4’10
What are the two main categories of Dwarfism?
Disproportionate and Proportionate
What are common characteristics of Achondroplasia?
Average torso, shorter arms and legs, OR short trunk with longer limbs
Large head, protruding jaw, crowded and misaligned teeth, double jointed, spine curves forward
How is dwarfism acquired?
Autosomal dominant genetic syndrome
What are the characteristics of proportionate dwarfism?
The body parts are in proportion but shortened (GH deficiency after birth)
What is the function of ACTH?
Regulates the growth of the adrenal cortex and the release of cortisol and androgenic hormones from the adrenal gland
What is one of the most potent activators of the HPA axis?
Surgery
When does the largest release of ACTH occur during surgical stimulation?
Reversal of anesthesia, extubation and the immediate post operative period
What hormone is released from the adrenal cortex?
Cortisol
Based on circadian rhythms, when is the most amount of cortisol released?
In the morning and during stress
How can ACTH cause hyper pigmentation?
Possesses mild melanocyte stimulating hormone
What is precursor protein that is cleaved to create ACTH?
Pro Opiomelanocortin (POMC)
what controls the release of aldosterone?
Renin –> Angiotensin I –> Angiotensin II
Where does ACTH act in the body?
Acts on the adrenal cortex to release glucocorticoids (cortisol)
What is the process for ACTH to be released?
Hypothalamus –> CRH –> AP –> ACTH
What pathology occurs with hyper secretion of ACTH?
Cushing’s Syndrome
What is typically the cause of Cushing’s Syndrome?
Pituitary gland adenoma or over secretion of corticotropin from the hypothalamus
Why might ACTH be increased without the presence of Cushing’s syndrome?
Adrenal cortex atrophy, cortisol secretion is reduced and does not close the negative feedback loop
What can occur when there is hypo secretion of ACTH as a primary pituitary disorder?
Results in decreased cortisol secretion from the adrenal cortex (fatal)
What are typically the causes of hypo secretion of ACTH?
Pituitary hyopfunction or failure due to intrapituitary bleed or autoimmune adrenal dysfunction
How could an adrenal adenoma causes hypo secretion of ACTH?
Over secretion of cortisol in the negative feedback loop response
What two hormones are released from the posterior pituitary gland?
Vasopressin and Oxytocin
Where is vasopressin synthesized?
Optic nucleus
What are the functions of the two vasopressin receptors?
V1 in blood vessels (high concentration in splenic areas) causes vasoconstriction and increased arterial pressure
V2 in kidneys that cause renal fluid reabsorption and increase blood volume
What are additional factors that can cause the release of vasopressin?
At the level of the hypothalamus pain, trauma, nausea, vomiting and increased temperature
What pathology can occur when there is an overproduction of ADH?
Syndrome of Inappropriate ADH (SIADH)
What are symptoms of SIADH?
Water retention, increased urine osmolality, headache, nausea, vomiting altered LOC and death
What is a very serious complication of SIADH?
Water intoxication causing dilutional hyponatremia leading to brain edema
What is the treatment for SIADH?
Correct hyponatremia with caution and restrict fluids
If profound hyponatremia occurs with SIADH what can be given to prevent deterioration?
Hypertonic 3% saline and IV lasix to correct sodium levels slowly
What pathology can occur with underproduction of ADH?
Diabetes Insipidous
What are common causes of DI?
Trauma, pituitary tumor, surgery or autoimmune
What are symptoms of DI?
Large volumes of dilute urine, dehydration, thirst increased plasma osmolality
What is the treatment of DI?
DDAVP a vasopressin analogue
What is the function of oxytocin?
Stimulates lactation and is thought to help with social affiliation, infant bonding, trust and love
What is the most common cause of hormone pathology?
Anterior pituitary adenoma
What are the three most common types of pituitary adenomas?
Prolactin secreting Growth hormone (acromegaly) ACTH secreting (cushings)
What is the presentation of hypopituitarism?
Decreased thyroid function, depressed glucocorticoid production and suppressed sexual development and reproductive function
What are the causes of depletion of pituitary function?
Primary pituitary destruction or destruction of the hypothalamus
What can occur if a pituitary adenoma grows upward?
Compresses the optic chasm which leads to visual changes
What type of visual changes are seen with compression of optic chasm?
Outer peripheral visual loss (bi temporal hemianopsia)
When severe the patient can only see what is in front of them
What is the stalk effect?
Compression of the pituitary stalk may cause elevated prolactin levels and irregular menses
What is Sheehan syndrome?
Postpartum pituitary necrosis (enlarged pituitary gland from pregnancy becomes compressed and necrosis occurs)
What is pituitary apoplexy?
Occurs when pituitary adenomas suddenly bleed internally leasing to an abrupt in size
The tumor can also outgrow its blood supply leading to swelling and dead tissue
What is the treatment of pituitary apoplexy?
Rapid Transphenoidal decompression with consideration of replacement of glucocorticoids and ICP resolution
What symptoms are typically seen in Sheehan Syndrome?
Failure to start post part lactation, increased fatigue, cold intolerance and HoTN unresponsive to volume and pressers
What are the three layers of the adrenal cortex?
Zona glomerulosa
Zona fasciculata
Zona Reticularis
What portion forms the bulk of the adrenal gland?
The adrenal cortex
What hormones are secreted from the adrenal cortex?
Secretes Minerocorticoids, Glucocorticoids and Sex hormones
What is the function of the adrenal medulla?
SNS mediation, secretes epi and norepi
What does the Zona Glomerulosa secrete and what controls its release?
Aldosterone which is controlled by Angiotensin II
What is a consequence to the adrenal cortex if there are elevated levels of aldosterone for a prolonged period of time?
Hypertrophy of zona glomerulosa
Why are mineralcorticoids the only hormones released from the zona glomerulosa?
They lack an enzyme required from cortisol synthesis
What is the largest zone of the adrenal cortex and what does it secrete?
Zona Fasciculata which secretes glucocorticoids (cortisol) and a small amount of sex hormones
What is the major controller of cortisol?
ACTH which is released from the anterior pituitary gland
What is secreted from the zona reticularis?
Sex hormones and some glucocorticoids which are stimulated by ACTH
How is cortisol transported in the blood?
Highly bound to corticosterone binding globulin (CBG)
What factors increase CBG production?
Estrogen and pregnancy
What factors decrease circulating CBG?
Liver disease and nephrotic syndrome
What is the most accurate measure of cortisol activity?
Urinary cortisol
What is the plasma half life of cortisol?
80-100 minutes
Why is cortisol essential for life?
CHO and protein metabolism Fatty acid metabolism Electrolyte and water balance Anti inflammatory and immunosuppressive actions Catecholamine synthesis Normal vascular peremeability
How is cortisol released by the adrenal cortex?
Hypothalamus –> CTRH –> Anterior Pituitary –> ACTH –> adrenal cortex –> cortisol
What are the target cells for aldosterone?
Epithelial cells in the distal convoluted tubule in the kidney to regulate absorption and potassium secretion
What can alter the amount of Aldosterone secreted?
Angiotensin II
ACTH
K
Na