Chapter 121 Thyroid and Parathyroid Glands

Question 1

Describe blood supply to the thyroid

Answer 1

Major blood supply from the cranial and caudal thyroid arteries.

Cranial thyroid artery first major branch of common carotid artery
Caudal thyroid artery arises from brachiocephalic artery
Caudal thyroid artery usually absent in cats

Question 2

Describe thyroid innervation

Answer 2

thyroid nerve branch of cranial laryngeal nerve which is a branch of the vagus nerve

Question 3

Blood supply to the external parathyroid gland

Answer 3

branches of the cranial thyroid artery

Question 4

Blood supply to the internal parathyroid gland

Answer 4

Blood supply from vessels surrounding the thyroid parenchyma

Question 5

Describe the locations of the external and internal parathyroids

Answer 5

external parathyroid gland is usually close to the craniodorsal margin of the thyroid. Sometimes its in contact with the thyroid or embedded

Question 6

Describe the location of the internal parathyroid

Answer 6

Often embedded within the thyroid gland in the caudal pole

Question 7

What percentage of dogs vs cats have accessory parathyroid tissue

Answer 7

3-6% of dogs have accessory parathyroid tissue – typically associated with the thymus
35-50% of cats have accessory parathyroid tissue**

Question 8

PTH synthesis

Answer 8

PTH is synthesized, stored, and secreted by chief cells of the parathyroid gland
increases calcium concentration and decreases phosphorus concentration

Question 9

Effects of PTH

Answer 9

increases calcium concentration and decreases phosphorus concentration

Question 10

How does PTH cause decrease in phosphorus and increase in ca

Answer 10

PTH causes decrease in excretion of calcium and increase in excretion of phosphorus by the kidneys.
PTH also increases formation of calcitriol from vitamin d in the kidneys
Calcitriol increases absorption of calcium and phosphorus from the intestine.