Introduction to Endocrine System Flashcards
What are hormones?
Regulatory substances produced in a gland that stimulate specific cells into action
The term ‘hormone’ is derived from the Greek verb ‘hormao’, meaning ‘to set in motion’.
What are the major physiologic processes controlled by hormones?
- Growth and maturation
- Metabolism
- Reproduction
What distinguishes endocrine glands from exocrine glands?
Endocrine glands secrete hormones into the blood, while exocrine glands secrete through ducts onto surfaces.
Name two types of communication used by hormones.
- Communication between different endocrine glands
- Communication between an endocrine gland and a target organ
What is the role of hormone receptors?
Proteins located inside the cell or on the cell membrane that bind to hormones and initiate cellular responses.
What are the two main types of hormones?
- Peptide-derived hormones
- Steroid hormones
What is the function of second messengers in hormone signaling?
Activate intracellular enzymes and amplify hormonal signals.
True or False: Steroid hormones can be stored in secretory vesicles.
False
Fill in the blank: The term __________ was coined by Starling in 1905 to describe hormones secreted internally.
[endocrine]
List examples of hydrophilic hormones.
- Insulin
- Epinephrine
- Glucagon
What is a bound hormone?
A hormone that is attached to a transport protein.
What is the difference between free hormones and bound hormones?
Free hormones are unbound and biologically active; bound hormones are attached to transport proteins and inactive.
What are the effects of hormones on the body?
- Control growth
- Change sexual function
- Regulate metabolism
- Balance water and electrolytes
- Breastmilk production
- Uterine contraction
- Temperature regulation
- Sleep-wake cycle
What type of hormones are derived from cholesterol?
[steroid hormones]
What is the significance of the ‘free fraction’ of a hormone?
It refers to the percent of hormone that is unbound and biologically active.
Describe the structure of peptide hormones.
Made from chains of amino acids, and can be large proteins such as growth hormone.
What is the role of transport proteins in hormone circulation?
Protect hormones from degradation and increase their half-life in the bloodstream.
Name two examples of amino acid-derived hormones.
- Epinephrine
- Thyroxine
Fill in the blank: The interaction of a single hormone molecule with a receptor can lead to __________ signal-generating events within a cell.
[multiple]
What are the two types of feedback loops in hormone signaling?
- Positive feedback loops
- Negative feedback loops
True or False: Hydrophobic hormones can easily cross the cell’s plasma membrane.
True
What is the effect of increased blood binding protein during pregnancy on hormone concentration?
It can change the total amount of hormone but will not affect the concentration of free hormone.
What is the laboratory result for TSH in the presented clinical case?
0.6 (0.4 - 4.0 mU/L)
TSH stands for Thyroid-Stimulating Hormone.
What is the Total T4 level in the clinical case?
15 (5-12 ug/dl)
Total T4 refers to the total amount of thyroxine in the bloodstream.
What is the Free T4 level in the clinical case?
1.2 (0.9 - 1.8 ng/dL)
Free T4 is the fraction of thyroxine that is not bound to proteins.
What could explain the lab findings in the clinical case despite the absence of hyperthyroid symptoms?
Possible lab error, medication effects, or physiological variations
Hyperthyroidism symptoms may be absent despite lab findings indicating elevated thyroid hormones.
What are the solubility characteristics of steroid hormones?
Hydrophobic
Steroid hormones include cortisol, aldosterone, and sex hormones.
What type of receptors do steroid hormones bind to?
Intracellular receptors
These receptors are typically found in the cytoplasm or nucleus.
What is the plasma half-life of peptide hormones?
Short (minutes)
Peptide hormones include insulin and glucagon.
What is the main mechanism of hormone regulation?
Negative feedback
Negative feedback inhibits secretion of hormones based on their levels in the bloodstream.
What is an example of positive feedback in the endocrine system?
Oxytocin release during childbirth
Oxytocin enhances uterine contractions, leading to more release until delivery.
What can cause hormone overproduction?
Increase in hormone-producing cells
An example is hyperthyroidism associated with Graves’ disease.
What is a common cause of hormone underproduction?
Autoimmunity, as seen in Hashimoto’s hypothyroidism
Other causes include surgical removal of glands or infections.
What is the most common disorder seen by endocrinologists?
Diabetes mellitus
This includes both Type I and Type II diabetes.
What are the methods of testing endocrine function?
- Plasma
- 24 Hour urine collection
- Saliva testing
These methods help in assessing hormone levels.
What is the role of cortisol in the endocrine system?
Regulates metabolism and stress response
Cortisol levels vary according to circadian rhythms.
Fill in the blank: Hormones are used for their _______ or suppressive effects.
replacement
Hormones can also be used therapeutically to treat various conditions.
What are the challenges in hormone replacement therapy?
Variability in normal ranges and mimicking normal physiology
Hormone replacement may not perfectly replicate natural hormone levels.
What endocrine disorder is associated with adrenal insufficiency?
Addison’s Disease
This condition results from insufficient production of adrenal hormones.
What is a common endocrine disorder related to the thyroid gland?
Hashimoto’s thyroiditis
This is an autoimmune condition leading to hypothyroidism.
What type of hormone testing measures the response to stimulation or suppression?
Stimulation or suppression testing
This testing helps assess the functional capacity of endocrine glands.
What hormone is primarily responsible for regulating blood glucose levels?
Insulin
Insulin is secreted by pancreatic beta cells.
True or False: Peptide hormones are hydrophilic and do not bind to transport proteins.
True
Peptide hormones circulate freely in the blood.
What is the clinical role of endocrinologists?
Consultation, treatment, and management of endocrine disorders
They often work in outpatient settings.
What is the significance of cortisol measurement timing?
Early morning and late evening measurements are most appropriate
Cortisol levels fluctuate throughout the day.
What are the effects of hormone resistance?
Altered tissue response to hormones
Examples include insulin resistance in type 2 diabetes.
What is a characteristic of steroid hormone production?
Regulated at the level of synthesis
Steroid hormones cannot be stored in secretory vesicles.
Fill in the blank: Hormones are regulatory substances produced in an _______ gland.
endocrine
Endocrine glands include the thyroid, adrenal, and pituitary glands.
What are membrane-bound secretory vesicles responsible for?
The release of these vesicles represents a regulated mode of exocytosis.
What is a prehormone?
A prehormone is a hormone that contains a signal peptide guiding the polypeptide into the endoplasmic reticulum.
What are frequently synthesized as preprohormones?
Hormones.
What happens to the signal peptide in the synthesis of hormones?
It is removed to process the prohormone by prohormone convertases.
Do hormones typically cross cell membranes?
No, they typically do not cross cell membranes and act through transmembrane receptors.
How do most hormones circulate in the body?
As free hormones.
What are the primary methods used in endocrinology for hormone measurement?
Antibody-based methods.
Why are small changes in hormone levels important?
They are often more specific and earlier indicators of disease than physical symptoms.
What challenges are associated with measuring hormone levels?
Concentrations of most hormones are much lower than those of general chemistry analytes.
What replaced earlier chromatographic/mass spectrometric methods in hormone measurement?
Antibody methods.
What types of assays were initially utilized for hormone measurement?
Competitive binding assays using polyclonal antibodies.
What assay method is used for measuring antigens with multiple antibody-binding epitopes?
Immunometric assay.
Where are hormone receptors found in cells?
On the surface, in the cytosol, or in the nucleus of the cells.
What characterizes transmembrane receptors?
They span the thickness of the cell membrane with the hormone-binding molecule on the outer surface.
How many receptor molecules are usually present in target cells?
Usually only a few thousand receptor molecules.
How can cells adjust their responsiveness to hormones?
By changing the number of receptors they express based on the signal received.
What can intense stimulation cause in terms of receptor expression?
It may cause a cell to downregulate the number of receptors expressed.
What is the embryonic origin of the pineal body?
Neuroectoderm from the prosencephalon, then diencephalon
Initially a hollow diverticulum that becomes a solid organ of pinealocytes.
What hormone is secreted by pinealocytes?
Melatonin
Secretion is cyclic, lowest during daylight hours.
What influences the secretion of GnRH by the hypothalamus?
Melatonin
Inhibits GnRH secretion until puberty.
What are the main axes associated with the hypothalamus?
- HPG axis
- HPA axis
- HPT axis
What is the embryonic origin of the pituitary gland?
Neural ectoderm (neurohypophysis) and surface ectoderm (adenohypophysis from Rathke’s pouch)
Development involves the elongation and connection to the infundibulum.
At what week is growth hormone detectable in the developing pituitary?
Week 10
What is the primary function of the thyroid gland by week 10 of development?
- Neural development
- Metabolism
- HPT axis
What structures do the parathyroid glands develop from?
- 3rd Pharyngeal Pouch (inferior parathyroid)
- 4th Pharyngeal Pouch (superior parathyroid)
What is the sequence of pancreatic hormone differentiation?
- Glucagon (alpha cells)
- Somatostatin (delta cells)
- Insulin (beta cells)
What does the zona fasciculata of the adrenal cortex produce?
Cortisol
Functions include increasing blood sugar and suppressing the immune system.
What role do primordial germ cells (PGCs) play in gonad development?
PGCs migrate into the developing gonads
They are involved in the differentiation of the gonads into testes or ovaries.
What gene is crucial for testis development?
Sry gene
Located on the short arm of the Y chromosome.
What hormone do Leydig cells secrete?
Testosterone
What is the role of the corpus luteum during pregnancy?
Maintains pregnancy in response to endocrine signals from the implanting conceptus
Produces progesterone and other hormones.
What are the key protein hormones produced by the placenta?
- Chorionic gonadotropin (hCG)
- Chorionic somatomammotropin (hCS)
- Chorionic thyrotropin (hCT)
- Chorionic corticotropin (hCACTH)
What is the function of Atrial Natriuretic Peptide (ANP)?
Increase filtration rate and decrease Na+ reabsorption
Levels are higher in fetal circulation than in adults.
True or False: The pancreas primarily plays a role in development.
False
The pancreas has metabolic functions but not a significant role in development.
What are the ducts associated with the male reproductive system?
- Mesonephric duct
- Epididymis
- Vas deferens
- Seminal vesicles
What happens to Müllerian structures in the absence of testosterone?
They form uterine tubes, uterus, and upper portion of the vagina.
What do ductless glands secrete into the blood?
Hormones
Hormones are signaling molecules that bind to receptors on target cells.
What types of actions can hormones have?
Endocrine, paracrine, autocrine
These actions refer to the different ways hormones can affect target cells.
What is the primary role of hormones?
Regulation and homeostasis
What is the origin of most hormones?
Mostly epithelia; some mesenchymal (e.g., adrenal cortex)
What are the different cellular arrangements found in endocrine glands?
- Follicles (thyroid)
- Cords (adrenal)
- Nests (parathyroid)
- Clusters (hypothalamus)
What system consists of individual endocrine cells?
Diffuse Neuroendocrine System (DNES)
What is the largest group of hormones?
Peptides
Examples include insulin, GH, glucagon, LH, ADH.
How do peptide hormones behave in solution?
Polar: dissolve in plasma (no carrier protein)
Where do peptide hormones bind their receptors?
Cell surface
What type of hormones are steroids?
Non-polar (require carrier protein)
Examples include testosterone, progesterone, aldosterone, cortisol.
Where do steroid hormones bind their receptors?
Cytoplasm/nucleus
What is the classification of amino acid-derived hormones?
Polar
Examples include epinephrine, histamine.
Where do amino acid hormones bind their receptors?
Cell surface
What is the pituitary gland morphologically and functionally linked to?
Hypothalamus
What are the two main parts of the pituitary gland?
- Anterior (glandular epithelia)
- Posterior (Neural)
What are the subdivisions of the anterior pituitary?
- Pars distalis
- Pars intermedia
- Pars tuberalis
What is found in the posterior pituitary?
- Infundibular stalk (axons)
- Pars nervosa (axons & endings)
What percentage of the pituitary is basophilic?
10% basophilic
What are the types of tropic hormones in the pituitary?
- ACTH (basophils)
- FSH (basophils)
- LH (basophils)
- TSH (basophils)
What are the non-tropic hormones in the pituitary?
- GH (acidophils)
- Prolactin (acidophils)
What is the role of the neurohypophysis?
Storage
Contains pituicytes (neuroglial) and unmyelinated axons.
What are Herring bodies?
Expanded axon terminals containing oxytocin or ADH
What are the three axes associated with the hypothalamus?
- HPG axis
- HPA axis
- HPT axis
What shape is the pineal gland?
Pine-cone shaped
What are the two types of cells in the pineal gland?
- Pinealocytes
- Interstitial cells (glial)
What are ‘brain sand’ markers in the pineal gland?
Corpora arenacea
What is the primary function of the pineal gland?
Release melatonin
What does melatonin regulate?
- Circadian rhythms
- Menstrual cycle (inhibition of GnRH)
What can destruction of the pineal gland lead to?
Early onset puberty
True or False: Seasonal affective disorder (SAD) is altered by the pineal gland’s response to day length.
True
What are the secretory units of the thyroid organized into?
Follicles
Follicles are spherical structures lined with follicular cells.
What types of cells line the thyroid follicles?
Follicular cells and parafollicular cells
Follicular cells are slightly basophilic, while parafollicular cells appear pale.
What hormones do follicular cells of the thyroid secrete?
Triiodothyronine (T3) and thyroxine (T4)
These hormones are crucial for regulating metabolism.
What substance do T3 and T4 bind to in the thyroid?
Thyroglobulin (colloid)
Most thyroid follicles are filled with stored thyroglobulin.
What hormone is secreted by parafollicular cells?
Calcitonin
Parafollicular cells are not exposed to the follicular lumen.
What are the principal cells of the parathyroid gland called?
Chief cells
Chief cells secrete parathyroid hormone (PTH).
What type of cells in the parathyroid gland are acidophilic and appear during puberty?
Oxyphil cells
These cells are less understood compared to chief cells.
What is the percentage composition of the adrenal cortex’s zona glomerulosa?
15%
Zona glomerulosa is responsible for secreting mineralocorticoids.
What types of hormones are produced by the zona fasciculata of the adrenal cortex?
Glucocorticoids
Zona fasciculata comprises 80% of the adrenal cortex.
What is the primary function of the adrenal medulla?
Produce epinephrine and Chromogranin A
The adrenal medulla consists of sympathetic neuronal tissue.
What is the primary function of the endocrine pancreas?
Secretes hormones to regulate blood glucose
The endocrine component constitutes 1-2% of the pancreas.
What structure in the pancreas is associated with digestion?
Exocrine pancreas
The exocrine pancreas makes enzymes for food digestion.
What are the main cell types found in the Islets of Langerhans?
Alpha, Beta, Delta, F cells, D1 cells, EC cells, Epsilon cells
Each cell type secretes different hormones such as glucagon, insulin, and somatostatin.
What hormone is secreted by alpha cells in the pancreas?
Glucagon
Alpha cells make up 15-20% of the pancreatic islet cells.
What hormone is secreted by beta cells in the pancreas?
Insulin
Beta cells constitute 60-70% of the pancreatic islet cells.
Fill in the blank: The adrenal cortex’s zona reticularis produces _______.
Gonadocorticoids
Zona reticularis comprises 5-7% of the adrenal cortex.
True or False: Fatty infiltration occurs in the parathyroid gland as aging occurs.
True
This is a common observation in aging parathyroid glands.
What is the histological significance of the thyroid and parathyroid glands?
Functional significance of their hormonal products
Understanding their histological organization is crucial in clinical contexts.
What are the two main functions of the pancreas?
Endocrine and Exocrine
The pancreas plays a dual role in hormone secretion and enzyme production.
Define autocrine cell communication
released by a cell to regulate itself
describe how neurocrine cellular communication works
signaling b/t adjacent cells via gap junctions
How does paracrine signaling typically work
similar to neurocrine signaling but more intended to regulate a large group of cells
what peptide hormone is hydrophobic?
thyroid hormone
compare & contrast the differences b/t Addison’s & Cushing’s diseasee
Addison: underproduction of cortisol hormones
chshing: overproduction of cortisol hormones
what are some examples of hormonal disorders of the pituitary gland
Acromegaly, hyperprolactinemia, pituitary adenoma causing secondary cushing’s disease
what factors determine oral hormone dosage & bioavailability
GI absorption & first-pass kinetics
oral administration is more appropriate for what type of hormone?
steroids & thyroid hormones
Parenteral administration is most appropriate for what type of hormones
peptide analogues
eg: insulin, PTH, GH
Standardized normal ranges for hormone levels is clinically problematic for what reasons?
These ranges are wide and therefore not very reliable measures for determining the presence or absence of an endocrine disease
True or false: maternal melatonin can cross the placenta.
True
Mechanism & function not well-understood
The hypothalamus is derived from what embryonic structures?
derived from the diencephalon (evidence also supports telencephalon origin)
ventro-lateral wall intermediate zone proliferates and forms the primordial hypothalamus
List the components of the HPG axis
H: Hypothalamus-GnRH
P: Pituitary-LH & FSH
G: ovaries-progesterone & estrogen
List the components of the HPA axis.
H: Hypothalamus-CRH
P: Anterior Pituitary-ACTH
A: adrenal gland-cortisol
List the components of the HPT axis
H: hypothalamus-TRH
P: anterior pituitary-TSH
T: thyroid-T3 & T4
The anterior pituitary originates from what embryonic structure and what is the clinical significance of this
originates from the Rathke pouch
this pouch is ectodermal in origin derived from oropharynx-ectopic hormone secreting tumors are derived from endocrine cells in the oro & naso pharnxy
endocrine glands that specifically produce steroid hormones arise from which embryonic layer?
mesoderm
What hormones does the fetus secrete endogenously? List in chronological order from beginning to end of gestation.
7 weeks: ACTH
8 weeks: GH
12 weeks: TSH, LH, & FSH
What embryologic processes does prolactin participate in and at what week of gestation can fetal prolactin be detected
Can be detected starting at 24 weeks
Inhibition of GnRH secretion from the hypothalamus
stimulates proliferation of oligodendrocyte cells involved in production of lung surfactant
what is the first gland to develop in the fetus?
thyroid gland
GH stimulate follicular growth in the thyroid. True or False.
True
At birth, TSH, T3, T4 are very low but increase after the first 5-7 days of life. True or False?
False
it’s the other way around: levels are high at birth and subside within the first week of life
Later onset of fetal TSH secretion stimulates the production of what
brown fat
The parathyroid is derived from the ectoderm. True or False?
False
PTG is derived from the endoderm
What pancreatic structures are derived from the dorsal primordium?
body, tail, & superior/anterior head
accessory duct
what pancreatic structures are derived from the ventral primordium?
posterior/inferior head
main pancreatic duct
The pancreatic buds arise out of what embryonic structures
outpouchings of the duodenal endoderm
True or false: the fetus starts producing pancreatic hormones at 7-8 weeks gestation.
True
The adrenal gland is derived from the endoderm. True or false.
FALSE
It’s the mesoderm
The renal medulla is derived from what embryonic layer?
ectoderm
The renal medulla, adrenal glands, & gonads all originate from what embryonic structure?
mesonephros
The gonads are derived from the mesoderm. True or false.
True
The absence of TDF (encoded on the SRY gene) will determine what fate in the gonads
development of ovaries
The sertoli cells stimulate the degeneration of what embryonic structure?
the Mullerian duct
What can happen if the sertoli cells fail to degenerate the the mullerian duct?
Partial/Inappropriate development of female genitalia
If testosterone is not present by 10 weeks of gestation, what is the most likely fate of the wolffian and mullerian ducts
The wolffian ducts degenerate and male genitalia will not be formed while the mullerian will continue to develop and form the fallopian tubes, uterine tissues & upper portions of the vagina
Wolffian duct development stimulates the formation of male external genitalia. True or False. If false, explain your reasoning
Not entirely false nor true
Wolffian ducts form the internal male genitalia
DHT stimulation for the development of external male genitalia depends on wolffian duct development
follicles secrete what hormone?
estrogen
The external male genitalia are derived from what embryonic structure in the Wolffian ducts?
the mesonephric ducts
What is the ultimate fate of the mesonephric duct in the male and the female?
Male: mesonephric ducts persists and become the epididymis, Vas Deferens, & seminal vesicles
Female: mesonephric ducts degenerate due to the absence of testosterone
what are important biomarkers of cardiac organogenesis?
ANP & BNP
What role do endothelins play in fetal development
regulation of fetal HR
Induces myocyte differentiate into purkinje fibers
High levels of ANP in adults indicates what?
ventricular hypertrophy
What is the role of hCG?
supports corpus luteum
facilitates adrenal cortex growth
What is the role of hCS?
stimulates maternal metabolic processes and breast growth
what hormone is the primary maintanace hormone for continuation of pregnancy?
progesterone
what fetal hormone supports and maintains the maternal endometrium?
estrogens
what is the definition of a tropic hormone?
hormones that are secreted to stimulate downstream secretion of hormones from another endocrine organ
what is the definition of a non-tropic hormone?
directly stimulate target cells to induce effects
acidophils produce what hormones?
GH & prolactin
basophils secrete what hormones?
ACTH, FSH, LH, TSH
The posterior pituitary glands contain what hormones
oxytocin & ADH
what is the main content in thyroid follicular cells?
stored thyroglobulin (colloid)
T3 & T4 bind to what protein
thyroglobulin
What happens to the parathyroid as it ages?
fatty infiltration
Oxyphil cells facilitate the puberty process. True or false?
True
What is the function of Chromogranin A?
precursor to autocrine neuropeptides
The zona glomerulosa produces what type of corticoids?
mineralocorticoids
the zona fasciculata produces what type of corticoids?
glucocorticoids
the zona reticularis produces what type of corticoids?
gonadocorticoids
