23 - Thyroid & Parathyroid

Question 1

where is the thyroid gland

Answer 1

anterior to proximal trachea, inferior to thyroid cartilage of larynx

lipophilic because of benzene ring

Question 2

What is the thyroid gland composed of

Answer 2

follicles made up of follicular cells
centre is composed of colloid (glycoprotein) containing thyroid hormone

Question 3

TF thyroid is highly vascularized

Answer 3

true
highly vascularized and several important nerves run by

Question 4

What are the functions of the thyroid hormone

Answer 4

1) increases BMR (basal metabolic rate)
- utilize fuel, consumer O2, generate heat
2) stimulates synthesis of the Na+/K+-ATPase
- improves neuroconduction and increases ATP use
- calorigeneic effect = contributes ot thermoregulation
3) Regulates metabolism
- stimulates protein synthesis (growth)
- stimulates breakdown of glycogen (glycogenolysis) and fats (lipolysis) for ATP production
- stimulates hepatic excretion of cholesterol
4) up-regulates b-receptors for catecholamines
5) permissive with most aspects of growth (nervous & skeletal systems) - works with GH and insulin
- essential for mental development and cognitive skills
- necessary for maintaining reproductive health

Question 5

What is the thyroid hormone made of

Answer 5

amino acid - tyrosine (modified)
- tri-idothyronin (T3)
- tetra-iodthyronine/thyroxine (T4)

Question 6

how is the thyroid hormone regulated

Answer 6

hypothalamic-pituitary hormones
under neg feedback control

1) low blood levels of T3 and T4 or low metabolic rate stimulate release of TRH
2) TRH carred by hypophyseal portal veins to Ant pit stiulates release of TSH by thyrotrophs
3) TSH released into blood stimulates thyroid follicular cells
4) T3 and T4 released into blood by follicular cells
- tissue effects via nuclear receptor
5) elevated t3 inhibits release of TRH and TSH (neg feedback)

Question 7

What causes goiter

Answer 7

no idione
- thyroid gland undergoes hypertrophy (increased number and size of thyroid follicles)
- excessive TSH & TRH

Question 8

What is hyperthyroidism
What are the causes

Answer 8

excessive (abnormally high level) of thyroid hormone secretion

1) overstimulation of thyroid gland to produce thyroid hormones
- excessive TRH (from hypothalamus) or TSH (from ant pit) production or release
- production of auto-antibodies that bind to and stimulate the TSH-receptor (graves’ disease)
2) overproduction of thyroid hormones by the thyroid gland (thyroid adenoma or “toxic nodule”)

Question 9

What could happen in hyperthyroidism

Answer 9

1) increased BMR –> weight loss
2) poor tolerance of hot environmental temps and excessive sweating (hyperhidrosis)
3) tendency to fatigue due to muscle wasting as muscle proteins are broken down
4) abnormally elevated heart rate or palpitations
5) heightened level of alertness making the individual irritable, tense, or anxious
- hyperflexia may also be observed
6) exophthalmos (buldging eyes) = edema in the eyes
- eye dryness cause eyelid can’t close
7) goiter

Question 10

What is hypothyroidism
What are the causes

Answer 10

deficiency (abnormally low level) in thyroid hormone secretion

Failure of thyroid gland to produce thyroid hormones
1) deficiency in TRH (from hypothalamus) or TSH (from ant pit) production or release
- thyroid not stimulated sufficiently
2) inadequate intake of iodine - required for thyroid hormone production
3) loss of thyroid follicular cells
- hashimoto’s thyroidits (autoimmune disorder)

Question 11

What could happen in hypothyroidsim

Answer 11

1) reduced BMR –> weight gain
2) poor tolerance of cold temps
3) fatigue –> insufficient muscle stregnth and nutrient metabolism
4) elevated blood cholesterol levels due to reduced hepatic excretion
5) bradycardia – weak pulse and potentially hypotension
6) abnormally slow reflexes (hyporeflexia) and decreased alertness
7) puffiness in the face, hands and feet = myxedema
- caused by the accumulation of mucoproteins (GAGs) and fluid in connective tissues

Question 12

Where is the parathyroid gland located
how many are there

Answer 12

posterior aspect of the two lobes of the thyroid gland
- near the vascular poles of the thyroid gland
~4

Question 13

What cells secrete parathyroid hormone (PTH)

Answer 13

chief cells

Question 14

What do the thyroid and parathyroid do

Answer 14

regulate blood calcium levels (have antagonistic effects)
- support calcium homeostasis to support muscle and nerve function

thyroid –> calcitonin from parafollicular cells
parathyroid –> PTH from chief cells

Question 15

What regulates serum clacium levels

Answer 15

calcitonin and PTH
calcitriol

two neg feedback loops (dont involve pit gland)
1) high level of Ca in blood stimulates thyroid gland parafollicular cells to release more CT
2) CT inhibits osteoclasts –> decrease Ca levels
3) low level of Ca in blood stimulates PTH chief cells to release more PTH
4) PTH promotes release of Ca from bone extracellular matrix into blood and slows loss of Ca in urine –> increases Ca
5) PTH also stimulates the kidneys to release calcitriol
6) calcitriol sitmulates increased absorption of Ca from foods –> increases Ca level

Question 16

Which hormones control bone length

Answer 16

growth hormone
androgens
estrogens

Question 17

why is calcitonin importnat

Answer 17

during early growht to maximize the calcium salts in bone (when osteoblasts are most active)

Question 18

Why is parathyroid hormone important

Answer 18

modulates serum calcium later in life to control amount of calcium salt (increase or decrease osteoclast activity)

Question 19

Why are androgens and estrogens important

Answer 19

increase the protein matrix and cells that create bone ti increase bone strength
- leads to closure of epiphyseal growth plates

Question 20

How to protext ourselves from osteoporosis

Answer 20

must develop a health peak bone density in our twenties

avoid factors that interfere with mineralization of bone
- inactivity
- smoking
- phosphoric acid (soft drinks)

avoid fractures –> decrease bone mineral density