Lab 5: Endocrinology

Thyroid gland function

• Release T3 and T4 hormones

• Increase basal metabolic rate (BMR): ↑ O2 and energy consumption, ↑ thermogenesis

• Increase sensitivity to adrenergic receptors: ↑ heart rate and cardiac output, ↑ vasodilation

Thyroid gland location

Located on both sides of the trachea below the larynx

Parts of the adrenal gland and what they make

• zona glomerulosa: mineralocorticoids

• zona fasciculata: glucocorticoids

• zona reticularis: androgens

• medulla: epinephrine

Mineralocorticoids purpose

• ↑ water and Na+ reabsorption; K+ excretion

• ↑ blood pressure

Glucocorticoids purpose

• ↑ blood glucose (via gluconeogenesis and inhibiting glucose utilization)

• ↑ sensitivity to adrenergic receptors (BP)

• ↓ immune response (anti-inflammatory response)

• Enhance effects of norepinephrine on blood pressure

Androgens purpose

• Least understood function

• Possible source of sex hormones during menopause

Epinephrine purpose

• Fight or flight response

Endocrine Pancreas composition and function

Beta cells secrete insulin

• ↓ blood glucose

Alpha cells secrete glucagon

• ↑ blood glucose (via glycogenolysis)

• ↑ release of fatty acids from triglycerides

Nuclei

Neurons involved in a specific center that are organized in functional clusters

Hypothalamic nuclei regions and functions:

• Anterior: circadian rhythm, thermoregulation)

• Medial/tuberal: eating habits, satiety, regulation of BP and HR

• Posterior: memory, energy balance, shivering, sleep, learning

Hypothalamus-pituitary connection

Hypothalamus is connected to the anterior pituitary via a portal vascular system

• Hypothalamic hormones travel a short distance through the blood vessels to bind to receptors on cells in the anterior pituitary

Portal Vascular System

Hypothalamic Pituitary Thyroid Axis steps

1. TRH released from hypothalamus and acts on anterior pituitary

2. TSH released from anterior pituitary and acts on thyroid

3. T3/T4 released from thyroid and acts on hypothalamus (feedback) and various tissues

Hypothalamic-pituitary adrenal axis steps

1. CRH released from hypothalamus and acts on anterior pituitary

2. ACTH released from anterior pituitary and acts on adrenal glands

3. Cortisol released from adrenal glands and acts on hypothalamus, anterior pituitary (feedback) and various tissues

Hypothalamic-pituitary gonadal axis

1. GnIH(-) or GnRH(+) released from hypothalamus acts on anterior pituitary

2. LH/FSH released from anterior pituitary acts on gonads

3. Sex hormones released from gonads acts on hypothalamus, anterior pituitary (feedback), and various tissues

Hypothalamic-Pituitary Growth Hormone Axis

1. GHRH(+) or GHIH (-) released from hypothalamus

2. GH released from anterior pituitary acts in liver, various tissues, hypothalamus (feedback)

3. Liver released from IGF-I acts on hypothalamus (feedback) and various tissues

Hypothalamic-Pituitary Prolactin Axis

1. TRH(+) or Dopamine(-) released from hypothalamus acts on anterior pituitary

2. Prolactin released from anterior pituitary acts on breast and other tissues (also responsible for brooding in hens)

Hypothalamus role in integrated axes

integration centre

Posterior pituitary role in integrated axes

• Neural connection to hypothalamus

• Neuroendocrine cells in the hypothalamus release neurotransmitters into capillary network in the posterior pituitary

Anterior pituitary in integrated axes

• Connected to the hypothalamus via portal vascular system

• Neuroendocrine cells in the hypothalamus secrete neuropeptides into the capillaries, stimulate/inhibit endocrine cells in the anterior pituitary to release trophic hormones

How is anterior pituitary regulated

• Very small amount of neuropeptides needed to stimulate the anterior pituitary

• Neuropeptides are only active for a short period

• System allows for multiple levels of regulation

Long loop feedback

endocrine gland hormone has inhibitory (or stimulatory) effects on hypothalamus/pituitary gland

Short Loop Feedback

trophic hormone (from pituitary) has inhibitory (or

stimulatory) effects on hypothalamu

Hormonal axes diagram

What is activated and inhibited when you treat with a hormone

• You activate all the levels below that hormone, all the way to the biological actions

• You inhibit all levels above that hormone, including the producing gland, by means of negative feedback

Adrenal gland location

Paired organs that are located on top of the kidneys

Adrenal gland function

Cortex is composed of the zona glomerulosa, zona fasiculata and zona reticularis and produces mineralcorticoids, glucocorticoids, androgens, respectively

Endocrine pancreas location

Located in the abdominal cavity alongside the duodenum

Endocrine pancreas function

Produces insulin and glucagon

Insulin function

Upregulates glucose transporters and incorporates glucose into storage molecules

Glucagon function

• Increase blood glucose in response to metabolite levels by promoting glycogenolysis to release glucose from glycogen

• Stimulates the release of fatty acids from triglycerides

What does each hormone produced by the hypothalamus produce or inhibit in the pituitary

1. LH/FSH →GnRH/GnIH

2. ACTH → ACTH-RH

3. TSH → TRH

4. GH → GH-RH/GH-IH

5. Prolactin →Dopamine

Which hormones produced by the hypothalamus have an inhibitory effect on hormones produced by the pituitary

• GnIH

• Dopamine

• GH-IH

Using the concept of negative feedback control, what effect would exogenous TRH have on different organs

Stimulated:

• thyroid gland

• pituitary gland

Inhibited:

• body weight

No change:

• testes

• adrenal gland

• seminal vesicles

• prostate

• thymus gland

Using the concept of negative feedback control, what effect would exogenous TSH have on different organs

Stimulated:

• thyroid gland

Inhibited:

• body weight

• pituitary gland

No change:

• thymus gland

• prostate

• adrenal gland

• testes

• seminal vesicles

Using the concept of negative feedback control, what effect would exogenous ACTH have on different organs

Stimulated:

• adrenal gland

Inhibited:

• thymus gland

• pituitary gland

• body weight

No change:

• seminal vesicles

• prostate

• testes

• thyroid gland

Using the concept of negative feedback control, what effect would exogenous cortisol have on the different organs

Inhibited:

• body weight

• thymus gland

• adrenal gland

• pituitary gland

No change:

• seminal vesicles

• prostate

• testes

• thyroid gland

Using the concept of negative feedback control, what effect would exogenous testosterone have on the different organs in an intact male

Stimulated:

• prostate

• body weight

• seminal vesicles

Inhibited:

• pituitary gland

• testes

No change

• thyroid gland

• adrenal gland

• thymus gland

Using the concept of negative feedback control, what effect would exogenous testosterone have on the different organs in a castrated male

Stimulated

• seminal vesicles

• body weight

• prostate

Inhibited

• pituitary gland

No change

• adrenal gland

• thyroid gland

• thymus gland

Using the concept of negative feedback control, what effect would exogenous LH have on the different organs in a castrated male

No change

• body weight

• seminal vesicles

• thymus gland

• prostate

• adrenal gland

• thyroid gland

Almost no change

• pituitary gland

Using the concept of negative feedback control, what effect would exogenous LH have on the different organs in a intact male

Stimulated

• prostate

• testes

• body weight

• seminal vesicles

Inhibited

• pituitary gland

No change

• adrenal gland

• thymus gland

• thyroid gland

Steps of long-loop negative feedback that regulates the production of testosterone starting with the hormone produced in the hypothalamus

1. release of GnRH

2. GnRH binds to receptors on pituitary

3. Release of LH

4. LH binds to receptors on the testes

5. Release of testosterone

6. Testosterone feeds back to pituitary and hypothalamus

7. Once sufficient levels of testosterone are achieved production is stopped at the level of the hypothalamus or pituitary

Short loop negative feedback is when..

hormones produced by the pituitary feedback to the hypothalamus to stop the production of hormones from the hypothalamus.