ENDOCRINOLOGY PART 2 Flashcards
positioned in the lower anterior neck and shaped like
a butterfly. It is made up of two lobes resting on each side of the
trachea, bridged by the
thyroid | isthmus
critical in regulating
metabolism and other body functions.
All are organized into
thyroid - follicles
Spheres of thyrocytes or thyroid cells surrounding a viscous substance
called
colloid
structural unit of thyroid cells composed of follicular cells.
follicle
in the center there’s a colloid incharge of production of T3 & T4
follicular cells
viscous substance is the central core of the follicle.
○ It is a fluid or liquid that is mainly a glycoprotein iodine complex also known
as
colloid - thyroglobulin
Mainly composed of thyroglobulin or thyroid glycoprotein.
colloid
incharge of secreting calcitonin
regulation of calcium
parafollicular cells
These hormones influence nearly every organ system, impacting processes ranging
from heart rate and body temperature to digestion and energy expenditure.
thyroid hormone
in the colloid. It’s the protein precursor of thyroid hormone.
○ Undergoes a process through adding iodine to become T3, T4, rT3 which are
produced only by thyroid follicular cells.
○ Rich in an amino acid called
thyroglobulin - tyrosine
to regulate metabolism
Increased heat production
enhances mitochondria and use of oxygen
in the process
Increased oxygen consumption
upregulate; increased sensitivity to
catecholamines; influences the heartrate and metabolism
Increased adrenergic receptors -
regulates (calcium levels ) electrolytes by inhibiting the bone resorption of calcium
calcitonin
signals the follicular cells to ingest a microscopic droplet of colloid by
endocytosis.
TSH
then secreted by the thyroid cell into the circulation.
T4 and T3
tropic hormone that
acts on the thyroid gland.
TSH
Precursor of T3 and T4
tyrosine
with 4 iodine attached to tyrosine
It is the precursor of T3 and rT3
T4
○ with 3 iodine left because of the iodination of one iodine in the outer ring. Nawala isang iodine
(iodinized).
○ Metabolically active form of metabolism therefore
functional
T3 - outer, active
when inner iodine is lost, still 3 iodine.
An inactive metabolite of T4, which can also
compete with the receptors of T3, but it is inactive,
therefore it gives no help
rT3
Thyroid hormone synthesis is dependent on iodine because it is primarily made of trace element iodine.
TRUE
Can be found in seafood, dairy products, iodine-rich bread, and vitamins.
iodine
Recommended minimum daily intake of iodine:
150 ug
The enzyme needed and responsible for adding iodine to the tyrosine (iodination
of tyrosine).
Conjugation of iodine to form T3 & T4.
thyroid peroxidase
produced from the rough endoplasmic reticulum of the follicular cell. It leaves the cell via exocytosis to enter the colloid
______ is rich in tyrosine, which are the rings you see in the structure
thyroglobulin
Iodination of thyroglobulin will form
Monoiodothyronine (MIT) and
Diiodothyronine (DIT)
Conjugation of 1 DIT and 1 MIT residue forms
triiodothyronine
conjugation of 2 DIT
tetraiodothyronine
is done by THYROID PEROXIDASE
conjugation
Principal secretory product
Prehormone for T3 production
tetraiodothyronine
If the question is what is the prohormone, the answer is ______ because it is
the source of tyrosine for the production of our thyroid hormones
thyroglobulin
T4
3,5,3,5 tetraiodothyronine
T3
3,3’,5 triiodothyronine
Metabolically active thyroid hormone
Major product of the tissue deiodination of T4
triiodothyronine
responsible for the deiodination of T4
to form T3 or rT3
monodeiodinase
If it removes an iodine in the inner ring of T4, it is now
rT3 (3,3,5 triiodothyronine)
Most abundant is
T4
undergo deiodination to form T2
rT3 - 3,3’triiodothyronine
a. Found in liver and kidney
b. Most abundant
TYPE 1 iodothyronine 5- deiodinase
a. Found in brain and pituitary gland
b. Maintain constant levels of T3 in the CNS
TYPE 2 idiodothyronine 5- deiodinase
These are carrier molecules in the bloodstream that transport thyroid hormones,
ensuring their stability and distribution throughout the body. They play a crucial
role in regulating the availability of thyroid hormones to target tissues by controlling
their circulation and release
MAJOR BASIC PROTEIN
most significant MBP
TBG thyronine binding globulin
MBPS
TBG thyroxine binding globulin
TBPA thyroxine binding pre albumin
ALBUMIN
condition characterized by excessive production of thyroid
hormones, typically resulting from an overactive thyroid gland. Symptoms may
include weight loss, rapid heart rate, anxiety, tremors, and heat intolerance.
Problem is directly on the thyroid gland
Symptoms include pale to yellow skin, dry skin, exophthalmos
HYPERTHYROIDISM
Thyroid-stimulating hormone ↓
Triiodothyronine (T3)↑
Tetraiodothyronine (T4)↑
primary hyperthyroidsim
Thyroid-stimulating hormone ↑
Triiodothyronine (T3)↑
Tetraiodothyronine (T4)↑
secondary hyperthyroidsim
drug used to treat arrythmias
○ This drug blocks to conversion of T4 to T3
amiodarone
also causes an acute inhibition of thyroid hormone production
Wolff-Chaikoff Effect
most common
In women
■ With TPO antibodies
■ Thyroid hormone levels revert to normal after several months
■ 4 years after postpartum, there is still persistent hypothyroidism
■ Have goiter
postpartum thyroiditis
painful thyroiditis:
subacute granulomatous thyroiditis,
subacute nonsuppurative thyroiditis, or
de Quervain’s thyroiditis
characterized by neck pain, low-grade fever, myalgia, a tender diffuse goiter, and swings in thyroid
function tests
■ No TPO antibodies
■ Elevated thyroglobulin levels
subacute granulomatous thyroiditis,
subacute nonsuppurative thyroiditis, or
de Quervain’s thyroiditis
only 5% to 9% of thyroid nodules prove to be thyroid cancer
thyroid nodules
small, pea-sized glands
located near or attached to the thyroid gland in the
neck. They secrete parathyroid hormone (PTH),
which plays a crucial role in regulating calcium levels
in the blood and maintaining proper bone health.
parathyroid gland
Affects the bone, kidneys, and GI tract for calcium
homeostasis
Smallest of the endocrine system
parathyroid gland
Form the majority of the cells in the parathyroid
They are small cells around 5-8 um in diameter with
very dark nuclei and with a very very thin cytoplasm
These are the secretor that secretes the parathyroid
hormone
chief cells
Larger and with dark nuclei and the cytoplasm is
strongly eosinophilic because of the numerous
mitochondria present in the cells
Non-secretory
Appear after the first decade of life
oxyphil cells
Involved gland: parathyroid gland
calcium homeostasis
Range of ionized calcium is
1.24 umol/L
Levels of calcium or the ionized calcium itself is the determinant if there is a
problem with the hormones affecting them which is the PTH and relatively your
vitamin D = not a hormone
activated vitamin D= calcitrol
If there is low calcium we stimulate the PTH and it increases bone resorption,
prevents urinary loss, and 1,25 Vit D production to increase GI absoprtion
TRUE
If calcium is high calcium will go back to the bones, can urinate na and stops the
production of 1,25 Vit D
TRUE
part of the kidney where calcium is reabsorbed
distal convoluted tubule
condition marked by intermittent muscular spasms so this is caused by
a malfunction in the parathyroid gland causing a deficiency in calcium
TETANY
electrolyte that is also needed in the physiological function of
the muscles so without it it causes tetany
calcium
abnormally high PTH because we cannot absorb vit
D and calcium therefore low levels of calcium and will cause high PTH
malabsorption syndrome
no absorption of calcium in GI tract also no trigger to stop
PTH, so PTH is increased
vitamin d deficiency
○ detects biologically active PTH by its ability to induce formation of cAMP
○ Low calcium levels the parathyroid gland releases more PTH
CAP assay: cAMP inducible PTH
This type of PTH activates another enzyme which
adenylate cyclase
can also be estimated in needle biopsy specimens obtained from parathyroid
tumors.
PTH
leads to tetany and altered neuromuscular
activity (Chvostek’s sign and Trousseau’s sign)
Calcium level < 8 mg/dL (2.0 mmol/L)
twitching of the face/ facial muscles
Chvostek’s sign
when a pressure is applied to the arm (ex. cuff of
sphygmomanometer) there is twitching or spasm in the arm
Trousseau’s sign spasm
laryngeal stridor
■ Collapse of larynx
○ seizures: tonic-clonic, focal motor, atypical absence and akinetic seizures
Calcium level < 6 mg/dL (1.5 mmol/L)
Stimulating or suppressing a particular hormonal axis, and observing the appropriate hormonal response
DYNAMIC FUNCTION TEST
If excess is suspected: conduct a
suppression test
If deficiency is suspected: conduct a
stimulation test
Patient Preparation: complete rest 30 minutes before
blood collection
Best specimen: fasting serum
Screening Test: Physical Activity/Exercise test
Confirmatory Test : Insulin Tolerance Test (Gold
Standard)
DIAGNOSTIC TESTS FOR
GH INSUFFICIENCY
insulin is administered to produce hypoglycemic
stress
<2.2 mmol/L
Under diagnostic tests for GH insufficiency
Done when hypopituitarism is suspected
also known as Insulin Tolerance Test
insulin stress test
DIAGNOSTIC TESTS FOR
ACROMEGALY THAT SCREENING TESTS
Somatomedin C or Insulin-like growth factor 1
(IGF-1)
Confirmatory Test of DIAGNOSTIC TESTS FOR
ACROMEGALY
Glucose Suppression Test/OGTT
provide a 75 grams of oral glucose then
monitor the level of growth hormone
OGTT
should suppress GH to <1ug/ L
hyperglycemia
Failure to suppress GH below 2 ug/L can
actually indicate the presence of acromegaly
and it is also associated with higher
prevalence of diabetes mellitus, heart diseases
and hypertension because OGTT is also used
as a confirmatory test for diabetes mellitus
below 2 ug/L
A.k.a. Concentration Test or Dehydration Test (Gold
standard) or indirect water deprivation test
Patient Preparation: No fluid intake for 8-12 hours
(Ideal should start: 10:00 PM
○ Or until 5% of the fluid has been lost
○ Avoid smoking and caffeine intake that might
affect AVP output
overnight water deprivation test
to continue to
excrete dilute urine; UOsm < 300 mOsm/kg
Central or nephrogenic DI <300 mOsm/kg
to concentrate urine; UOsm
300-800 mOsm/kg
prinary polydipsia 300-800 mOsm/kg
if the serum Osm increases to >
305 mOsm/kg, it is highly suggestive of
DI
Reference range Serum Osmolality:
275-295
mOsm/kg
Reference range Urine Osmolality (UOsm):
300-900 mOsm/kg
is a sign of DI
> 295 mOsm/kg
Screening test for adrenal insufficiencies
Differentiates the types of adrenal insufficiencies
cosyntropin
tetracosactide test
injection of TRH and measurement of the output of
TSH
Provide synthetic TRH
TRH is involved in the hypothalamic-pituitary-thyroid
axis
used in the diagnosis of combined pituitary-thyroid
disorders
Differentiates secondary hypothyroidism and
tertiary hypothyroidism
TRH is given as an IV bolus
Blood sampling done at 0, 20, and 60 minutes
THYROTROPIN
RELEASING HORMONE
(TRH) STIMULATION TEST
Confirms borderline response to ACTH stimulation
test
Confirmatory test for Secondary Adrenal
Insufficiency - gold standard test
INSULIN TOLERANCE TEST
Patient prep: fasting (8 hours)
Oral dose: 0.05 U/kg of insulin
Requirement: induced hypoglycemia
INSULIN TOLERANCE TEST
Ideal serum glucose: <40 mg/dL (after insulin dose)
Blood collection: 0, 15, 30, 45, 60, 90, and 120 mins
following oral insulin
INSULIN TOLERANCE
TEST
Assesses hypogonadism
Can be done together with anterior pituitary function
test (IST, TRH, GnRH tests)
GNRH TEST
GnRH causes marked rise in LH
(increments of greater than or equal to 15 U/L)
and smaller rise in FSH (> 2 U/L)
adults
GnRH causes a marked rise in FSH
and smaller rise in LH
children
used for the diagnosis of MTC (Medullary
Carcinoma of the Thyroid)
Also used to assess the result of thyroidectomy
Can also be used to detect residual C-cells
a malignancy of the calcitonin-secreting cells of the,thyroid gland
commonly associated with an elevated calcitonin
level, but an elevated level may not always be
obvious.
Pg dose IV: 0.5 ug/kg body weight
pentagastrin stimulation test
sensitive indicator of
endogenous coritsol
URINE FREE CORTISOL
Best time of collection: 6 am to 8 am (avoid drinking
alcohol before and during the urine collection)
24-hour urine collection (follow usual diet & drink
fluids as you ordinarily would)
cortisol testing
Screening test: plasma aldosterone
concentration/plasma renin activity ratio (PAC/PRA)
Confirmatory test: saline suppression, oral sodium
loading, fludrocortisone suppression, and captopril
challenge test
Saline Suppression Test
Dose:2 L NaCl
Procedure: dose should be infused in 2 hours
hyperaldosteronism test
Primary hyperaldosteronism: > 10 ng/dL plasma
aldosterone
TRUE NORMAL < 5ng/dL
autoimmune disorder where the immune system mistakenly attacks the
thyroid gland, leading to inflammation and eventual destruction of thyroid tissue. This
can result in hypothyroidism, causing symptoms such as fatigue, weight gain, and
depression.
HASHIMOTO’s THYROIDITIS
Also known as Chronic Lymphocytic Thyroiditis
Most common cause of hypothyroidism
Targets thyroid gland
Thyroid gland increases in size
Associated with goiter
TPO antibody is positive
HASHIMOTO’s THYROIDITIS
causes hyperthyroidism due to the production of autoantibodies
called thyroid -stimulating Immunoglobulins (TSIs). These antibodies mimic the
action of thyroid-stimulating hormone (TSH) and bind to the receptors on thyroid
follicular cells.
Most common cause of thyrotoxicosis
graves’ disease
