Thyroid, Endocrine pancreas and Parathyroid glands

Question 1

What are the endocrine cells of the pancreas?

Answer 1

Islets of langerhans, which include: Alpha cells, beta cells, delta cells and PP cells

Question 2

What do the endocrine cells of the pancreas do?

Answer 2

Alpha cells: produce glucagon

Beta cells: produce insulin

Delta cells: produce somatostatin

PP cells: produce pancreatic peptide

Question 3

What regulates blood glucose?

Answer 3

Insulin and glucagon help keep blood glucose within a set range (4-7.8 mmol/L)

Question 4

What is the tyrosine kinase second messenger?

Answer 4

An enzyme located within the cytosol, when activated phosphorylates intracellular proteins to produce anabolic reactions

Question 5

What are GLUT 4 transporters?

Answer 5

• When there is no insulin present, glucose cannot enter the cell
• When insulin is present it signals the cell to insert GLUT 4 transports into the membrane for glucose to pass through

Question 6

What are the effects of insulin on carbohydrates?

Answer 6

• (+) Cellular uptake of glucose
• (+) Glycolysis (ATP production)
• Liver: (+) Storage of glucose as glycogen

Question 7

What are the effects of insulin on proteins?

Answer 7

• (-) Gluconeogenesis
• Glucose used over AAs as a source of ATP
• (+) Cellular uptake of AAs
• (+) Protein synthesis
• Lack of insulin: AAs used as fuel source

Question 8

What are the effects of insulin on proteins?

Answer 8

• (-) Gluconeogenesis
• Glucose used over fat as a source of ATP
• Adipose tissue: (+) Conversion of glucose to fat (storage)
• Lack of insulin: fatty acids used as fuel source

Question 9

What are the effects of glucagon primarily on the liver?

Answer 9

• Glycogenolysis: Breakdown of glycogen to glucose
• Gluconeogenesis: Synthesis of glucose from non-carbohydrate molecules e.g. fatty acids, AAs
• Release of glucose by hepatocytes

Question 10

What are the effects of glucagon secondarily on the liver?

Answer 10

• Lowers blood levels of AAs (glucagon release is stimulated by a protein-rich meal)
• Sequestration of AAs triggers gluconeogenesis

Question 11

How does glucagon act?

Answer 11

Via the cyclic AMP second messenger system

Question 12

Vascular supply of the thyroid?

Answer 12

It is very vascular:

• Superior & inferior thyroid arteries
• Superior, middle & inferior thyroid veins

Question 13

External structure of the thyroid?

Answer 13

-Two lobes and an isthmus on the anterior neck

Question 14

Internal structure of the thyroid?

Answer 14

• Composed of hollow spherical follicles

- A ring of follicular ells form the walls of each follicle supported by a basement membrane

Question 15

What do thyroid follicular cells secrete?

Answer 15

Thyroglobulin

Question 16

What is thyroglobulin?

Answer 16

A glycoprotein that is the precursor of the thyroid hormones (T4 & T3)  (Essential role in regulating metabolism)

Question 17

Where is thyroglobulin stored?

Answer 17

In the follicular lumen, suspended in a viscous gel called colloid

Question 18

What do parafollicular (C cells) cells secrete?

Answer 18

Calcitonin

Question 19

What is calcitonin?

Answer 19

Has minor effects of storing calcium in the bone

Question 20

What are the thyroid hormones?

Answer 20

T3- Triiodothyronine

T4- Thyroxin or Tetraoidothyronine

Question 21

How are the thyroid hormones synthesised?

Answer 21

1. Thyroglobulin acts as a precursor
2. Iodide is actively transported into follicular lumen
3. It is oxidised to iodine and attached to tyrosine molecule (requiring thyroid peroxidase enzyme)
4. Monoiodothyronine (T1) and diiodothyronine (T2) are linked together to form T3 and T4

Question 22

How are thyroid hormones released?

Answer 22

1. Hypothalamus (TRH)
2. Anterior pituitary (TSH)
3. TSH binds to receptors on follicular cells (Which release stored thyroid hormone and synthesis of more thyroglobulin to restock colloid)
4. T4 and T3 circulate bound to thyroxine-binding globulins and albumin (small circulate in free form)

Question 23

Which thyroid hormone is released more and which is more biologically active?

Answer 23

T4 and T3

Question 24

What do thyroid hormones perform for gene transcription associated with glucose oxidation?

Answer 24

• Basal metabolic rate

* (+) Body heat production

Question 25

What do thyroid hormones perform that are catecholamine-like?

Answer 25

• (+) Normal cardiac function

* Maintenance of blood pressure (adrenergic receptors in blood vessels)

Question 26

What do thyroid hormones perform that regulates normal development and functioning?

Answer 26

• Nervous system, musculoskeletal system

* Digestive system, reproductive system, integumentary system

Question 27

Structure, function location of parathyroid glands?

Answer 27

STRUCTURE
• Small, ovoid endocrine glands, yellow-brown in colour
• Most individuals have 4 glands, ~5% have more

LOCATION
• Posterior aspect of the thyroid gland

FUNCTION
• Parathyroid cells secrete parathyroid hormone (PTH)
• Increases plasma levels of Ca2+

Question 28

What are the actions of the parathyroid gland?

Answer 28

Respond to low blood calcium by:

• Increasing osteoclast activity in bone to release Ca2+ and PO43- in the blood
• Increase calcium reabsorption in the kidney tubule
• Increase activation of vitamin D by the kidney

Question 29

What is the role of calcium?

Answer 29

1. Provides strength and rigidity to the skeleton
2. Also acts as a dynamic reservoir (Ionised calcium can be released into the ECF)
3. Most important effect: neuromuscular excitability
4. Other effects: Intracellular signalling, blood clotting, secretory activity