HPT & HPA

Question 1

Organismal energy regulation involves two basic elements:

Answer 1

Maintenance and growth
Protection from survival threatening events

Question 2

Thyroid hormone actions (5)

Answer 2

1) Generally permissive modulatory effects on other hormones
2) Consumption if oxygen (lvl of mitochondria)
3) Adequate growth and tissue differentiation
4) Modulation of metabolic enzymes
5) Facilitate thermogenesis

Question 3

Hypothalamic-Pituitary-Thyroid axis:
Hypothalamus (Paraventricular nucleus) -> Adenohypophysis (Thyrotropes) -> Thyroid gland

Answer 3

Thyroid releasing hormone (TRH)
Thyrotropin or Thyroid hormone stimulating hormone (TSH)
T3, T4
- Metabolic rate, o2 consumption, thermogenesis, growth and tissue differentiation

• T3 and T4 negative feedback on all regions to regulate production

Question 4

Thyroid gland:
- Colloid secretion source
- Where T4 is stored
- C-cells secrete what
- Calcitonin regulates what homeostasis
- 4 small glands on thyroid secrete what + what does it regulate

Answer 4

Follicle cells
Colloid
Calcitonin
Calcium homeostasis (decreasing Calcium in blood)
Parathyroid hormone (PTH) + calcium homeostasis (increasing Calcium in blood)

Question 5

TSH from pituitary binds to receptors on follicle cells
GOCR activates Gs (cAMP) and Gq (DAG-IP3) signalling cascades
- What does this up regulate? (3)

Answer 5

Iodine efflux into colloid
Increased thyroglobulin (Tgb) production (used to produce T4)
Increased peroxidase (TPO) activity

Question 6

thyroid hormones are synthesized un the colloid and follicle cells by? (5)

Answer 6

1) iodine collected from blood and transported into colloid
2) enzyme thyroid peroxidase (TPO) iodinates tyrosine residues in the thyroglobulin protein (Tgb-I)
3) TPO couples two iodinated molecules to create T4
4) Tgb-I is endocytosed and sent to lysosome, which releases T4 into cytosol
5) T4 can enter blood stream or convert into T3 by enzyme deiodinase (DIO) which enters blood stream

Question 7

T3 and T4 are transported thru circulation by binding proteins (3)

T3 and T4 enter cell passively or actively to regulate gene expression?
Binds to what thyroid receptors
Enhances expression of mitochondrial proteins (3)

Answer 7

Thyroxine-binding globulin
Thyroid-binding prealbumin
Albumin

Both (like steroids)
TRalpha, TRbeta
Mitochondrial transcription factor A (mtTFA), P43, p28 (involved in metabolism and ATP production)

Question 8

Proteins that help T3 and T4 cross blood brain barrier (3)
What converts T4 to T3 and is released to extracellular space

Answer 8

MCT8, OATP1C1, LAT1/2
Astrocytes

Question 9

Stress response
Components (2)
Primary, secondary, tertiary endocrine responses

Answer 9

Adaptive mechanism to protect animal from environmental stressors
- Shunts energy to where it’s needed and inhibit physiological systems that aren’t required
- Blood flow shunted to from core regions to limbs

General adaptation response (controlled by HPA)
Fight or flight response

Increase in corticosteroids/catecholamine hormones; alterations in neurotransmitter activity
Metabolic changes, cellular changes, osmoregulatory disturbance, changes in hematological features and immune function
Changes in whole-animal performance characteristics, modified behav patterns

Question 10

Adrenocortical vs chromaffin cells

Answer 10

Produces glucocorticoids, mineralocorticoids, weak androgens

Produces epinephrine, norepinephrine
- Under direct control of nervous system

Question 11

Glucocorticoids transported by? (3)
Why isn’t aldosterone found in low levels and not bind to transport protein?

Answer 11

Corticosteroid binding globulin (CBG), transcortin, albumin

Passively transports into cells so only released near target areas - Too much will cause it to be taken up by everything

Question 12

Neurons expressing coricotropin-releasing hormone located in? (2)
Binds to what 2 receptors coupled to what G protein?

Answer 12

Paraventricular nucleus and arcuate nucleus

CRH-R1 - Gs (ACTH eased into circulation leading to arousal)
CRH-R2 - Gs/Gi (Shuts down stress response)

Question 13

Actions of glucocorticoids (4)

Answer 13

1) Gluconeogenesis (glucose production) increased in liver, mobilization of proteins from skeletal muscle, deamination of amino acids released from protein breakdown
2) Glycogen deposited in liver bcuz of increase in glycogen synthase rxn
3) Glycogenolysis is inhibited in peripheral tissues
4) Peripheral utilization of glucose is inhibited

Question 14

Fight or flight response
- Controlled by which nervous system and release of what hormone

Adrenal medulary branch (Adrenal medula) from HPA axis vs Nervous branch (Sympathetic ganglia) from Sympathetic adrenomedullary component
- PNMT

Answer 14

Sympathetic nervous system
Catecholamine hormone

Releases epinephrine (depends on presence of PNMT, regulated by cortisol) and a bit of norepinephrine
Norepinephrine

Question 15

Norepinephrine bind to which type of G protein adrenoreceptors

Answer 15

Alpha- and beta-adrenergic receptors
- Alpha decreases activity of adenyly cyclase
- Beta increases

Question 16

Emotional stress releases epinephrine or norepinephrine
Physical stress?
Physical stress W/ serotonin?

(Rat example)

Answer 16

Epinephrine -> glucose breakdown

Norepinephrine (a bit of epinephrine$ -> Glucose and FFA breakdown

Equal (emotional part activated too) -> Glucose and FFA breakdown

Question 17

(Tadpole metamorphosis)
- CRH is controlled by TSH or TRH in non-mammalian vertebrates vs tadpoles
- When T3 not present (2)
- TR and RXR forming heterodimers peaks when and is increased by what
- Presence of what during pro-metamorphosis exponentially increases what in tissues (2)

Answer 17

TRH
TSH -> Caused by environmental stressors

When T3 not present, thyroid receptor (TR) inhibits gene expression and natural metamorphosis doesn’t occur

Peak in expression during metamorphosis, which is increased by corticosterone activity

Low T3/T4, TR and deiodinase