Introduction to Endocrine Physiology

Question 1

What are the methods of controlling body functioning?

Answer 1

Nervous
Hormonal

Question 2

How can hormones be classified according to nature?

Answer 2

Local Hormones
General Hormones
Specific Hormones

Question 3

Characteristics of Local Hormones

Answer 3

Act locally
E.g. acetylcholine

Question 4

Characteristics of General Hormones

Answer 4

Act on all body cells
E.g. thyroid hormone

Question 5

Characteristics of Specific Hormones

Answer 5

Act on specific target tissues
E.g. adrenocorticotropic hormone (ACTH) acts on adrenal cortex

Question 6

How can hormones be classified according to their chemical structure?

Answer 6

Protein and Polypeptide Hormones: E.g. anterior and posterior pituitary hormones
Steroid hormones: Have a steroid nucleus and derived from cholesterol, e.g. cortisol, aldosterone, testosterone, estrogen
Amino acids derivatives: E.g. T₃, T₄, Epinephrine, Norepinephrine

Question 7

How are protein hormones formed and stored?

Answer 7

Preprohormones are formed by the rough ER
Cleaved into smaller protein called prohormone in ER
Cleaved into active hormone in Golgi Apparatus
In golgi apparatus they are packed as secretary vesicle and stored
Specific signal cause the secretion

Question 8

How are steroid hormones formed and stored?

Answer 8

Stored in small quantities on specific signal enzymes
Act on precursor molecules to synthesize hormones

Question 9

How are thyroid hormones formed and stored?

Answer 9

Formed as a part of large protein thyroglobulin
Stored in follicle of thyroid gland

Question 10

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What are cyclical hormonal variations?

Answer 10

Periodic variations in hormone release

Question 11

How are peptide hormones transported?

Answer 11

Dissolved in plasma

Question 12

How are steroid and thyroid hormones transported?

Answer 12

Circulate in blood bound to plasma proteins

Bound proteins are physiologically inactive since they cannot diffuse across the capillaries

Question 13

What factors affect hormone concentrations?

Answer 13

Hormone secretion
Metabolic clearance rate

Question 14

What are the types of hormone receptors?

Answer 14

Membrane receptors: Peptide hormone receptors
Cytoplasmic receptors: Steroid hormone
Nucleus receptors: T3 and T4

Question 15

What are the methods by which hormone binding affects cells?

Answer 15

Activating receptors
Activating intracellular enzymes
Activating genes

Question 16

How does hormone binding cause receptor activation?

Answer 16

Binds to receptors and causes conformational change

Question 17

How does hormone binding cause activation of intracellular enzymes?

Answer 17

Activates adenylyl cyclase forming cAMP from ATP
cAMP acts as a second messenger causing intracellular changes

Question 18

How does hormone binding cause gene activation?

Answer 18

Some steroid and thyroid hormones bind to receptors inside the cells
Activates portion of DNA

Question 19

What are the types of second messengers?

Answer 19

Cyclic AMP (cAMP)
Calcium-Calmodulin
Phospholipid

Question 20

How does cAMP act as a second messenger?

Answer 20

It activates a cascade of enzymes
Initiates biological actions (e.g. secretion + muscle contraction and relaxation)

Question 21

Describe the Calcium-Calmodulin second messenger system

Answer 21

Calcium channels open allowing Ca to bind to calmodulin
Four Ca⁺⁺ ions can bind to calmodulin
Calmodulin activates other enzymes

Question 22

Describe the formation of IP₃ and DAG in phospholipid second messenger systems

Answer 22

Phospholipase C activated by hormone binding
Phospholipase C causes breaks down phosphatidylinositol biphosphate (PIP2) forming inositol triphosphate (IP₃) and diacylglycerol (DAG)

Question 23

How do IP₃ and DAG act as second messengers?

Answer 23

IP₃ causes mobilization of Ca
DAG activates protein kinase C and cause cell division and proliferation
This action is enhanced by Ca that have been released by IP₃
Eg. Angiotensin II, TRH, Oxytocin etc