ENDOCRINOLOGY Flashcards by V S

Network of ductless glands that secrete hormones directly into the blood
Considered to be the regulatory system of the body
Regulated by means of control of hormone synthesis rather than by degradation

Endocrine System

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Chemical signals produced by specilized cells, secreted into the blood stream and carried to a target tissues

Hormones

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An increased in the product results to elevation of the activity of the system and the production rate
Ex: Gonadal, Thyroidal and Adrenocortical hormone

Positive Feedback System

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An increased in the product results to decreased activity of the system and the production rate
Ex: Leutenizing Hormone

Negative Feedback system

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Secreted in one location and release into blood circulation; binds to specific receptor to elicit physiological response

Endocrine

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Secreted in endocrine cells and released into interstitial space; binds to specific receptor in adjacent cell and affects its dunction

Paracrine

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Secreted in endocrine cells and released into interstitial space; binds to specific receptor in adjacent cell and affects its function

Paracrine Hormones

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Secreted in edocrine cells and sometimes released into interstitial space; binds to specific receptor on cell of origin resulting to self-regulation of its function

Autocrine

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Secreted in endocrine cells and remains in relation to plasma membrane; acts on immediately adjacent cell by direct cell-to-cell contact

Juxtacrine Hormone

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Secreted in endocrine cells and remained as well as function inside the synthesis of origin

Intracrine hormone

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Secreted in endocrine cells and released into lumen of gut; affects their function

Exocrine Hormone

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Secreted in neurons and released into extracellular space; binds to receptor in nearby cell and affects its funciton

Neurocrine Hormone

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Synthesized and stored within the cell in the form of secretory granules and are cleaved as needed
Cannot cross the cell membrane due to their large molecular size and thus; produce their effects on the outer surface of the cell

Peptides and Proteins

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Follicle-Stimulating Hormone
HCG
Thyroid Stimulating Hormone
Erythropoietin

Glycoprotein

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ACTH
ADH
GH
Angiotensin
Calcitonin
Cholecystokinin
Gastrin
Glucagon
Insulin
Melanocyte-Stimulating Hormone
Oxytocin
PTH
Prolactin
Somatostatin

Polypeptide

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Lipid molecules that have cholesterol as a common precurosi
Produced by adrenal glands, ovaries, testes and placenta
Water insoluble (hydrophobic) and circulate bound to a carrier protein

Steroids

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Derived from an amino acid & they are intermediary between steroid and protein hormones
Ex: Epinephrine, Norepinephrine, Triiodothyronine, Thyroxine

Amines

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Portion of the brain located in the walls and floor of the third ventricle
Link between the nervous system and the endocrine system

Hypothalamus

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Hormone
TRH
Gn-RH
GH-IH
GH-RH
PIF

Hormones produced in the Hypothalamus

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Attached to the midbrain
Secretes melatonin that decreases the pigmentation of the skin
Secretions are controlled by nerve stimuli

Pineal Gland

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“Master Gland”
Located in a small cavity in the sphenoid bone of the skull called the sella turcica or Turkish saddle
Connected by the infundibular stalk to the median eminence of the hypothalamus
All pituitary hormones have circadian rhythms

Pituitary Gland
Hypophysis

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“True Endocrine Gland”
Regulates the released and production of hormones
Hormones are either peptides or glycoproteins

Adenohypophysis
Anterior Pituitary Gland

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Secrete growth hormone

Immunochemical Test

Somatotrophs

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Secrete prolactin

Immunochemical Test

Lactotrophs
Mammotrophs

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Secrete TSH | Immunochemical Test

Thyrotrophs

Secrete Proopiomelandcortin produce ACTH, B-endorphin, & B-lipotropin | Immunochemical Test

Corticotrophs

Secrete LH & FSH | Immunochemical Test

Gonadotrophs

Most abundant of all pituitary hormones Major stimulus: Deep sleep Secretion is erratic and occurts in short burst

Growth Hormone (GH) Somatotropin

Reference Value:

(< 7 ng/mL)

Most common cause of GH deficiency in children Children with pituitary dwarfism, normal proportions are retained and show no intellectual abnormalities

Idiopathic Growth Hormone Deficiency

Most common etiology in adult-onset GH deficiency

Pituitary Adenoma

Due to Overproduction of GH

Acromegaly

Patient preparation for Growth Hormone measurement

Rest 30 minutes before blood collection

Screening Test for measurement of GH Result: Elevated Serum GH

Physical Activity Test Exercise test

Confirmatory test: GOLD STANDARD for measurement of GH

Insulin Tolerance Test

2nd Confirmatory Test for GH It is a 24-hour or nighttime monitoring of GH Confirmed GH deficiency: Failure of GH to rise >5ng/mL in adults & >10ng/mL in children

Arginine Stimulation Test

Screening test for detection of Acromegaly

Insulin-like Growth Factor 1 (IGF-1)

Confirmatory test for the detection of Acromegaly Blood is collected every after 30 minutes for 2 hours Fasting sample is required

Glucose Suppression Test

Important markers in diagnosing fertility and menstrual cycle disorders Present in the blood of both male and female at all ages

Gonadotropins FSH & LH

Aids in spermatogenesis in male (Sertoli cells) Aids in follicular growth in female

Follicle-Stimulating Hormone

Helps Leydig cells to produce testosterone and is necessary for ovulation and final follicular growth in female

Luteinizing Hormone

Acts on Thecal cells to cause the synthesis of androgens, estrogens and progesterone

Luteinizing Hormone

Elevation of FSH is a clue in the diagnosis of

Premature menopause

Also known as Thyrotropin Main stimulus for the uptake of iodide by the thyroid gland Acts to increase the number & size of follicular cells; stimulates thyroid hormone synthesis

Thyroid Stimulating Hormone (TSH)

Single-chain peptide without disulfide bonds Produced in response to low serum cortisol, regulator of adrenal androgen synthesis

Adrenocorticotrophic Hormone (ACTH)

Deficiency of ACTH will lead to atrophy of the _____

Zona Glomerulosa Zona Reticularis

Highest levels of ACTH is between

6:00 - 8:00

Lowest level of ACTH is between

6:00 pm - 11:00 pm

ACTH is increased in:

Addison's Disease Ectopic Tumors Protein-rich meals

Best time to collect specimen for ACTH

8:00 am - 10:00 am

Pituitary lactogenic hormone; Stress hormone; Direct effector hormone Functions in the initiation and maintenance of lactation Acts in conjunction with estrogen & progesterone to promote breast tissue development

Prolactin

Major inhibitor of Prolactin:

Dopamine

Highest levels of prolactin during:

4:00 am - 8:00 am 8:00 pm - 10:00 pm

Reference Value of Prolactin

Male: 1-20 ng/mL Female: 1-25 ng/mL

Capable of releasing the hormones: Oxytocin & Vasopressin but not capable of producing it Release is in response to serum osmolality and by suckling

Neurohypophysis Posterior Pituitary Gland

Secreted in association with a carrier protein Stimulates contractions of the gravid uterus at term "Fergusson Reflex" Released in response to neural stimulation of receptors in birth canal & uterus, and of touch receptors in breast

Oxytocin

Nonapeptide that acts on the distal convoluted and collecting tubules of the kidneys Maintains Osmotic homeostatis by regulating Water balance Decreases production of Urine by promoting reabsorption of water by the renal tubules Increases blood pressure Promotes Factor VII release from hepatocytes & factor VIII

Anti-Diuretic Hormone Arginine Vasopressin (AVP)

Reference Value of Vasopressin/ ADH

0.5 - 2 pg/uL

Principal regulator of ADH secretion

Increased plasma osmolality

Deficiency of ADH; Results in severe Polyuria (>3L of urine/day)

Diabetes insipidus

Clinical picture of Diabetes insipidus

1. Normoglycemia 2. Polyuria with low specific gravity 3. Polydipsia 4. Polyphagia

Deficiency of ADH with normal ADH receptor Due to failure of the pituitary gland to secrete ADH Large volume of urine excreted (3-20L/day)

True Diabetes Insipidus Neurogenic DI

Characterized by having normal ADH but abnormal ADH receptor Due to failure of the kidneys to respond to normal or elevated ADH levels

Nephrogenic Diabetes Insipidus

Diagnostic Test for Diabetes Insipidus Fasting: 10:00 pm onwards After 8-12 hours without fluid intake, urine osmolality does not rise above 300 mOsm/kg

Overnight Water Deprivation Test Concentration Test

Overnight Water Deprivation Test ADH: LOW Kidneys rapidly acts to conserve water in response to Exogenous ADH administration

Neurogenic DI

Overnight Water Deprivation Test ADH: N/High Administration of additional ADH has little or no effect on renal water reabsorption

Nephrogenic DI

Refers to the sustained production of ADH in the absence of a known stimuli Characterized by decreased urine volume, low plasma osmolality and normal or elevated urine sodium levels

Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)

Also known as the butterfly-shaped gland Consist of two lobes located in the lower part of the neck

Thyroid Gland

Fundamental structural unit of the thyroid gland

Follicles

Two types of cells in Thyroid Gland

Follicular cells (T3 & T4) Parafollicular Cells (Calcitonin)

Glycoprotein that acts as a preformed matrix containing tyrosyl groups Stored in the follicular colloi of the thyroid gland

Thyroglobulin

Most important element in the biosynthesis of thyroid hormone

Iodine

Neuroendocrine system that regulates the production and secretion of thyroid hormones

Hypothalamic-Pituitary-Thyroid Axis (HPTA)

Most active thyroid hormonal activity 75-80% is produced from the tissue deiodination of T4 Better indicator of recovery from hyperthyroidism as well as the recognition of recurrence of hyperthyroidism

Triiodothyronine T3

Reference Value for T3

Adult: 60-160 ug/dL Child: 105-245 ng/dL

Principal Secretory product Major fraction of organic iodine in the circulation Prohormone for T3 production Amount of serum T4 is a good indicator of the thyroid secretory rate

Tetraiodothyronine T4

Transports majority of T3 (affinity for T3 is lower than T4) Transports 70-75% of total T4

Thyroxine-Binding Globulin TBG

Transports 15-20% of total T4 T3 has NO affinity for prealbumin

Thyroxine-Binding Prealbumin (Transthyretin)

Transports T3 and 10% of T4

Thyroxine-Binding Albumin

Thyroid autoantibodies responsible for autoimmune thyroid disorders:

1. Thyroperoxidase (TPO) 2. Thyroglobulin 3. TSH Receptor

Autoantibody involved in Hashimoto's disease

Thyroperoxidase

Autoantibody involved in Grave's disease

TSH Receptor

Excess of circulating thyroid hormone

Hyperthyroidism

Elevated T3 and T4 Decreased TSH

Primary hyperthyroidism

Increased FT4 and TSH

Secondary Hyperthyroidism

Signs and Symptoms: 1. Tachycardia 2. Tremors 3. Weight LOSS 4. HEAT intolerance 5. Emotional ability 6. Menstrual changes

Hyperthyroidism

Group of syndromes caused by high levels of free thyroid hormone in the circulation

Thyrotoxicosis

FT3 increased FT4 Normal TSH Low

T3 Thyrotoxicosis Plummer's Disease

T3 Normal or Low T4 Increased TSH Low

T4 Thyrotoxicosis

Most commonc cause of Thyrotoxicosis Antibodies are produced that activate the TSH receptor Occurs 6x more commonly in women Features: Exophthalmos & pritibial myxedema

Graves' Disease Diffuse Toxic Goiter

Thyroid turns into a wooy or stony hard mass

Riedel's Thyroiditis

Shows no clinical symptoms but TSH Low FT3 FT4 Normal

Subclinical Hyperthyroidism

Associated with neck pain, low-grade fever and swings in thyroid function tests Thyroidal peroxidase (TPO) antibodies are absent

De Quervain's Thyroiditis Subacute Granulomatous Thyroiditis

Insufficient amounts of thyroid hormone are available to tissues Treated with thyroid hormone replacement therapy

Hypothyroidism

Signs & Symptoms: 1. Bradycardia 2. Weight GAIN 3. Coarsened skin 4. COLD intolerance 5. Mental Dullness

Hypothyroidism

Primarily due to deficiency of elemental ioding Caused by destruction or ablation of thyroid gland

Primary Hypothyroidism

Most common cause of Primary Hypothyroidism Characterized by a thyroid replaced by a nest of lymphoid tissue causing cell lysis and inflammatory reaction TSH High TPO Antibody POSITIVE

Hashimoto's Disease

Peculial nonpitting swelling of the skin Skin becomes infiltrated by mucopolysaccharides

Myxedema

Severe form of Primary Hypothyroidism

Myxedema Coma

Due to pituitary destruction or pituitary adenoma T3 T4 Low TSH Low

Secondary Hypothyroidism

Due to hypothalamic disease T3 T4 low TSH Low

Tertiary hypothyroidism

Defect in the development or function of the fland Screening: T4 Low Confirmatory: TSH High

Congenital Hypothyroidism Cretinism

TSH Value <10mIU/L

No further test

TSH value 10-12mIU/L

Repeat test in 2-6 weeks

TSH >20mIU/L

For Endocrinologic evaluation to diagnose hypothyroidism

T3 T4 Normal TSH S. High

Subclinical Hypothyroidism

Measures the relationship between TRH & TSH secretions Used to differentiate euthyroid and hyperthyroid patients who had undetectable TSH levels

TRH Stimulation Test

Most important thyroid function test Best method for detecting clinically significvant thyroid dysfunction Most clinically sensitive assay for the detection of primary thyroid disorders Helps in early detection of hypothyroidism Differentiates primary from secondary hypothyroidism

TSH Test

Smallest endocrine gland in the body

Parathyroid Gland

Most common cause of hypercalcemia Due to presence of a functioning parathyroid adenoma Accompanied with phosphaturia Lab: 1. PTH High 2. Ionized Ca High 3. Ca in Urine High 4. Phosphate Low

Primary Hyperparathyroidism

Develops in response to decrease serum calcium Diffuse hyperplasia of all 4 glands Patient develops severe bone disease

Secondary Hyperparathyroidism

Occurs with Secondary hyperparathyroidism Phosphate Normal to High

Tertiary Hyperparathyrodism

Due to accidental injury to the parathyroid gland during surgery

Hypoparathyroidism

Has pyramid-like shape located above the kidneys Composed of distinct but conjoined glands, the outer adrenal cortex and inner adrenal medulla

Adrenal Gland

Outer Region of the Adrenal gland secreting the Steroid hormone Major site of steroid hormone production Yellow

Adrenal Cortext

3 Layers of Adrenal Cortex

1. Zona glomerulosa - Mineralocorticoid 2. Zona fasiculata - Glucocorticoid 3. Zona reticularis - Androstenedione & Dehydroepiandrosterone

Principal Glucocorticoid Synthesis is regulated by ACTH Mostly bound to glycoprotein, transcortin Stimulates Gluconeogenesis

Cortisol

Urinary Metabolite of Cortisol:

1. 17-hydroxycorticosteroid 2. 17-Ketogenic steroids

Method to detect 17-hydroxycorticosteroid

Porter-Silber Method (Yellow) Phenyl hydrazine in H2SO4 + Alcohol

Method used to detect 17-Ketogenic Steroids

Method: Zimmermann Reaction (Reddish Purple) Meta-Dinitrobenzene Norymberski (Oxidation procedure)

Excessive production of CORTISOL & ACTH, but decreased Aldosterone & renin

Hypercortisolism Cushing's Syndrome

Due to decreased Cortisol production - 90% destruction of the adrenal cortex Aldosterone deficiency ACTH release Disorder: **Addison's Disease**

Primary Hypocorticolism Primary Adrenal Insufficiency

due to hypothalamic-pituitary insufficiency with loss of ACTH

Secondary Hypocorticolism

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