Physiology

Question 1

What does sunlight exposure do in relation to vitamin D?

Answer 1

Converts 7-dehydrocholesterol to cholecalciferol (vitamin D3) in the skin.

(Vitamin D3 then gets converted to its storage form 25-hydroxyvitamin D in the liver and then to its active form 1,25 hydroxyvitamin D in the kidney

Question 2

What is the function of thyroid peroxidase (TPO)?

Answer 2

TPO catalyzes the following

1. oxidation of iodide to iodine
2. iodination of thyroglobullin (TG) tyrosine residues
3. iodotyrosine coupling reaction that forms T3 and T4

Question 3

Why can exercise cause hypoglycemia in patients with insulin-treated diabetes?

Answer 3

Exercise causes increased translocation of GLUT4 receptors to the cell membrane of skeletal muscle.

Question 4

Which endocrine hormones have a cAMP (g-protein) signalling pathway

Answer 4

“FLAT ChAMP”

• FSH - MSH
• LH - PTH
• ACTH
• TSH
• CRH
• hCG
• ADH (v2 receptor)

Question 5

Which endocrine hormones have a cGMP signalling pathway?

Answer 5

“BAD GraMPa“ –> all cause vasodilation

BNP (natriuretic peptide)

ANP (natriuretic peptide)

EDRF (NO)

Question 6

Which endocrine hormones have an IP3 signalling pathway?

Answer 6

“GOAT HAG”

GnRH Gastrin

Oxytocin

ADH (v1 receptor)

TRH

Histamine

Angiotensin II

Question 7

Which endocrine hormones have an intracellular receptor signalling pathway?

Answer 7

“PET CAT D”

Progesterone

Estrogen

Testosterone

Cortisol

Aldosterone

T3/T4

Vitamin D

Question 8

Which endocrine hormones have a receptor tyrosine kinase pathway? (MAP Kinase Pathway)

Answer 8

think growth factors (GF)

Insulin

IGF-1

FGF

PDGF

EGF

Question 9

Which endocrine hormones have a non receptor tyrosine kinase pathway? (JAK/STAT Pathway)

Answer 9

“PIGGLET”

Prolactin

Immunomodulators (cytokines, IL-2, IL-6)

GH

G-CSF

Erythropoietin

Thrombopoietin

Question 10

5-alpha reductase deficiency

1. what is this enzyme used for?
2. how does it present?

Answer 10

1. Converts testosterone to DHT

2.

Presents in males as an ambiguous external genitalia (individuals often thought to be females) and male internal genitalia.

When testosterone levels increase during puberty, these individuals then develop external male genitalia

Question 11

What are neurophysins?

Answer 11

Carrier proteins for posterior pituitary hormones (oxytocin and ADH)

They carry the hormones from the paraventricular and supraoptical nuclei in the thalamus to the posterior pituitary.

Question 12

What effects would primary hypothyroidism have on :

1. TSH
2. T4
3. T3

Answer 12

1. Increased TSH (to try and increase TH levels)
2. Decreased T4
3. Normal/Decreased T3

Question 13

Calcium Regulation

1. What regulates short-term calcium concentrations?
2. What regulates long-term calcium concentrations?

Answer 13

1. PTH
2. Calcitriol / 1,25-OH D3 / active Vitamin D

Question 14

What are the 3 primary effects of PTH?

Answer 14

1. increase osteoclastic bone resorption which releases calcium and phosphate into circulation
2. increase calcium and decreased phosphate renal reabsorption
3. increased formation of 1,25-OH D3 (active vit. D) which increases intestinal reabsorption of both calcium and phosphate

Question 15

Postoperative hypoparathyroidism

1. when does it usually occur?
2. what is the result?

Answer 15

1. after a thyroidectomy due to inadvertent damage or removal of the parathyroid gland
2. decreased PTH

Question 16

Brown Adipose Tissue

1. What is its function
2. Who has the most and why?

Answer 16

1. Heat production
2. Neonates, since they are more susceptible to hyperthermia

Question 17

Which type of glucose do GLUT transporters prefer to transport, L-Glucose or D-Glucose?

Answer 17

D-Glucose

Question 18

what converts the storage form of Vit. D (25-hydroxvitamin D3) in the liver to its active form (1,25-dihydroxyvitamin D3) in the kidney?

Answer 18

1-alpha hydroxylase

Question 19

What are the effects of Chronic Kidney Disease (CKD) on Vitamin D?

Answer 19

decreased levels of 1,25-dihydroxyvitamin D3

(active form of vitamin D)

Question 20

How does PTH increase bone resorption by osteoclasts?

Answer 20

1. PTH binds receptor on osteoblasts
2. osteoblasts secrete RANK-L
3. RANK-L binds the RANK receptors on osteoclasts and their precursors
4. Activation of NF-KB transcription factor
5. osteoclasts resorp bone which releases calcium and phosphate into blood

Question 21

GnRH stimulates the release of?

Answer 21

FSH and LH

Question 22

What is the function:

1. LH
2. FSH

Answer 22

1.

LH stimulates the release of testosterone from the leydig cells of the testis

2.

FSH stimulates the release of inhibin B from the sertoli cells of the testis (also required for spermatogenesis)

Question 23

What can taking excess vitamin D supplements result in?

Answer 23

Hypercalcemia which results impaired depolarization of neuromuscular membranes

Presents as:

- muscle weakness

- constipation

- confusion

Question 24

Why can patients with granulomatous diseases (TB, Sarcoidosis) have increased levels of 1,25-dihydroxyvitamin D3?

Answer 24

The activated macrophages express 1-alpha-hydroxylase so they are able to convert 25-hydroxyvitamin D (storage form in liver) into its active form independent of PTH

Question 25

Why does **oral glucose** result in a greater insulin release than IV?

Answer 25

Since the GI tract releases **_Incretins (GLP-1 and GIP)_** in response to oral glucose

Question 26

What is the mechanism of insulin release?

Answer 26

1. Glucose enters pancreatic B cell 2. Increase in intracellular ATP 3. K+ channels close 4. Membrane depolarizes 5. Opening of voltage-gated Calcium channels 6. Vesicle release (exocytosis of insulin granules)

Question 27

What are **3 forms of thyroid hormones** and how are they produced?

Answer 27

1. **_T4_**: produced by the thyroid via TSH stimulation 2. **_T3_**: small amount produced by thyroid, majority is produced via peripheral conversion of T4 --\> T3 via **5-deiodinase** 3. **_rT3:_** inactive form of T3 produced via peripheral conversion of T4

Question 28

What affects would T3 supplementation have on: 1. TSH 2. T4 3. rT3

Answer 28

1. **decreased TSH** (via negative feedback) 2. **decreased T4** (due to decreased TSH) 3. **decreased rT3** (due to decreased T4)

Question 29

What is the pathway of **insulin synthesis?**

Answer 29

1. **Preproinsulin** (synthesized in RER) 2. **Proinsulin** (stored in secretory granules) 3. Cleavage of proinsulin into **Insulin** and **C-peptide** 4. Vesicles move towards cell membrane and wait for **exocytosis**

Question 30

What is the pathway of **insulin-dependant glucose uptake**?

Answer 30

1. insulin binds to an i**ntrinsic tyrosine kinase receptor** 2. receptor gets autophosphorylated 3. activation of **PI3K** and **MAP-K** 4a. _PI3K_ (in cytoplasm): increased glycogen, protein and lipid synthesis, increased GLUT-4 expression 4b. _MAP-K_ (in nucleus) -cell growth -DNA sythesis

Question 31

What are the effects of **Cortisol** in the body?

Answer 31

Increased **_A_**petite Increased **_B_**P (upregulates alpha receptors) **_I_**nsulin resitance (diabetogenic) Increased **_G_**luconeogenesis, lipolysis, proteolysis Decreased **_F_**ibroblast Activity (poor wound healing) Decreased **_i_**mmune Response Decreased **_b_**one formation (decreased osteoblasts) "Cortisol is **_A_** **_BIG_** **_FIB_**"