med phys: cranial nerves and endocrine

thyroid gland has two types of cells

follicular and parafollicular

follicular cells of the thyroid

secrete thyroxine (T4)

parafollicular cells of the thyroid

secrete calcitonin, c-cells from last brachial pouch

T4 (thyroxine)

prohormone, 4 iodine atoms, more common

T3 (triiodothyronine)

active form by removing an iodine, more effective

as an embryo the thyroid had a duct to

the tongue (thyroglossal duct)

parathyroid

glands behind thyroid, secrete PTH

thyroxine-binding globulin (TBG)

transport T3 and T4 in the blood, protein

thyroid peroxidase (TPO)

attaches iodine to benzene rings of tyrosine

iodination

adding iodine

T3/4 raise basal metabolic rate

stimulate catabolism and anabolism (create and use glucose, proteins, and fatty acids)

protein synthesis and proteolysis

net result in muscle breakdown

thermogenesis

heat generation from thyroid stimulated metabolic activity

thyrotropin (TSH)

regulating hormone for thyroid from pituitary

coupling

cross-link iodinated tyrosines into thyroxine

follicular cell structure

ring of epithelial storing thyroxine because iodine is a scarce resource

reverse T3

deactivated T3 due to it being able to freely move into cells

hormone categories

modified amino acids, polypeptides, steroids

modified amino acids

small, usually modified tyrosine, one or two benzene rings

polypeptides

most hormones, oxytocin, ACTH

steroids

lipids, 4 ring structure, end in -one, estrogen/aldosterone

hyperthyroidism

high T3/4

hypothyroidism

low T3/4, high TSH

free vs total thyroxine

free: not attached to carrier proteins, small smount

nuclear medicine scan

functional image tracking radiotracers

isthmus

bridge connecting two thyroid lobes

beta particles

high energy electrons that are harmful to tissue

gamma rays

less harmful, used for diagnostic imaging

I-123

emits gamma rays, used for thyroid imaging

I-131

destroys thyroid as treatment for hyperthyroidism

salivary glands and kidneys show up on iodine scan

both excrete iodine from the bloodstream

ddx of hypothyroidism

iodine deficiency, missing thyroid (high TSH), pituitary failure (low TSH)

hashimoto’s disease, autoimmune thyroiditis

high ant-TPO levels, high TSH, low T3/4

hashimoto’s initially appears hyperthyroid

inflammation from anti-TPO causes thyroid to release all T3/4

thyroid is very faint on nuclear scan

hypothyroidism

ddx of hyperthyroidism

pituitary overstimulation (high TSH) or autonomous thyroid (low TSH)

grave’s disease

autoimmune, anti-TSH-R stimulate thyroid to be enlarged and overactive

bulging eyes

grave’s disease can enlarge the extraocular muscles

thyrotoxicosis

excess T3/4 can damage the heart and case arrhythmias

thyroid is large and dark on nuclear scan

hyperthyroidism

hot nodule

autonomous, unregulated, portion of thyroid when generally hypothyroid

multiple hot nodules

can become hyperthyroid and thyrotoxicosis

goiter

enlarged thyroid

cold nodule

non functioning section of thyroid, cyst or tumor

hypothalamus

drives physiological needs, change behavior (hunger, sleep, sex)

hypothalamus and optic chiasm

next to each other, know day/night cycle

anterior pituitary structure

epithelial tissue from embryotic mouth

posterior pituitary

neurons and glia from hypothalamus

hormones vs neurotransmitters

very similar molecules but cell to cell vs bloodstream communication

posterior pituitary hormones

neurocrine, oxytocin and vasopressin

vasopressin

raises blood pressure and fluid retention

lack of vasopressin

diabetes insipidus, excess watery urine

oxytocin

stimulates uterine contractions and milk letdown

nonapeptides

posterior pituitary hormones, very small, only 9 amino acids

hypothalamus hormones

releasing hormones (TRH, CRH, GnRH), stimulate other hormones

pituitary hormones regulation

pos and neg feedback loops, create axes

anterior pituitary hormones

tropins (TSH, ACTH, FSH, LH, GH), stimulate other endocrine glands

thyrotropin (TSH)

stimulates thyroid

corticotropin (ACTH)

stimulates adrenal cortex

gonadotropins (FSH and LH)

stimulate gonads

hypophyseal portal system

small veins connecting hypothalamus and anterior pituitary

HPT axis

TRH (hypot), TSH (pit), thyroxine (thyroid)

HPA axis

CRH (hypot), ACTH (pit), cortisol (adrenal cortex)

HPG axis

GnRH (hypot), FSH/LH (pit), sex steroids (gonads)

axes steps

hypothalamus energy conservation and amplification

pars intermedia

secretes MSH for melanin production, very similar to ACTH

adrenal gland has two parts

cortex and medulla

phenylalanine

essential amino acids needed for adrenalin production

catecholamines

versions of modified amino acids using tyrosine and has two -OH groups on a benzene ring

catecholamine examples

dopamine, norepinephrine, and adrenalin

epinephrine vs norepinephrine

Epi is methylated NE

adrenal medulla

controlled by the spinal cord, part of sympathetic nervous system

adrenal medulla hormones

secrete catecholamines for fight or flight

corticosteroid regulation of adrenal medulla

veins from cortex to medulla synthesize NE to epi

adrenal cortex hormones

steroids, aldosterone, cortisol, and DHEA

steroid hormones features

carried by proteins in the blood, enter cells freely, receptors in nucleus

aldosterone

regulates blood electrolytes, retains sodium

DHEA

precursor to sex steroids, promotes growth and development

cortisol

glucocorticoid, regulated by ACTH, catabolic steroid

cortisol function

raises blood glucose through muscle breakdown (gluconeogenesis)

cortisol surge

breakdown glycogen when sleeping for brain’s need of glucose

glucocorticoids as immunosuppressants

used to treat asthma, autoimmune diseases, and other

common cause of hypercortisolism

HPT axis regulation

pos feedback if thyroid is not working (high TSH levels)

neg feedback if thyroid is working

symptoms of hyperthyroidism

weight loss, goiter, heat intolerance, high heart rate

symptoms of hypothyroidism

weight gain, goiter, cold intolerance, slow pulse, swelling

symptoms of hypercortisolism

truncal weight gain, muscle weakness, stretch marks, fractures, hypertension

hypercortisolism labs

high cortisol and hyperglycemia

cushing’s syndrome

usually iatrogenic from prescribed corticosteroids

cushing’s disease

pituitary tumor with high ACTH

hypoadrenalism

adrenal failure

hypoaldosterone (Addison’s) symptoms

weight loss, dehydration, low blood pressure, skin pigmentation

Addison’s labs

low cortisol, aldosterone, Na, glucose, blood pressure

high potassium, ACTH

primary endocrine disorders

originate in gland (addison’s, hashimoto’s)

secondary endocrine disorders

originate in the pituitary (cushing’s disease)

secondary vs primary lab levels

high T3/4 with high TSH is not grave’s

low T3/4 with low TSH is not hashimoto’s

pheochromocytoma

tumor of adrenal medulla, secretes excess adrenalin

usually in adrenal, but can be in spinal cord

pheochromocytoma symptoms

heart palpitations, high blood pressure, abdominal pain, vomiting

I-123 MIBG

uptake by sympathetic neurons

bind to NE transport

adrenalin waste product

metanephrines (high levels if pheochromocytoma)

adrenalin constricts and dilates blood vessels

alpha and beta adrenergic receptors