Endocrine System Dr. Ivy

What are the major endocrine glands? (7)

1. Hypothalamus

2. Pituitary Gland

3. Thyroid Gland

4. Parathyroid Glands

5. Adrenal Glands

6. Pancreas

7. The gonads

   1. Ovaries

   2. Testes

What do the major endocrine glands do?

Release hormones directly into the bloodstream without needing ducts

Hypothalamus location & function

1. Located in the brain between the cerebral hemispheres

2. Can send direct signals to the brain and to other parts of the body or produce hormones that then travel to various target organs (notably the pituitary gland)

Hormones released by the hypothalamus (8)

1. TRH

2. CRH

3. GnRH

4. GHRH

5. Somatostatin

6. Dopamine

7. ADH

8. Oxytocin

TRH

• Thyrotropin-releasing hormone

• Leads to the production and release of thyroid-stimulating hormone (TSH) from the pituitary > Acts on thyroid > ^ Production of Thyroid Hormones

CRH

• Corticotrophin-releasing hormone

• Causes the pituitary to produce ACTH > Acts on the adrenal gland > Stimulates the secretion of cortisol (steroid hormone that regulates metabolic + immune pathways)

GnRH

• Gonadotrophin-releasing hormone

• Causes the pituitary to secrete gonadotrophins FSH and LH

GHRH

• Growth hormone-releasing hormone

• Acts on the anterior pituitary to stimulate secretion of growth hormone (stimulates the growth of long bones and tissues)

Somatostatin

• Causes the pituitary to decrease growth hormone secretion

Dopamine

• Is involved with the body’s reward system

• Reduces the production of prolactin (produced in the pituitary'; involved in breastfeeding)

ADH

• Antidiuretic Hormone

• Causes water retention and vasoconstriction

• Ultimately increases blood pressure

Oxytocin

• Dilates the cervix

• Stimulates uterine contractions

• Stimulates milk ejection from the alveoli in the mammary glands

Pituitary Gland location & function

• Located @ Base of Brain Attached to the hypothalamus by the pituitary stalk

• Anterior pituitary releases hormones directly into the bloodstream

• Releases Tropic Hormones (Act on other endocrine glands)

• Releases Direct Hormones (Act directly on target tissues)

Hormones released by the Pituitary Gland (FLAT PEG)

Tropic

1. FSH

2. LH

3. ACTH

4. TSH

Direct

1. Prolactin

2. Endorphins

3. GH (Growth Hormone)

ACTH

• Adrenocorticotropic Hormone

• Targets the adrenal cortex > stimulates the production + release of cortisol

• Cortisol

  • Promotes gluconeogenesis

  • Inhibits inflammation and suppressing immune cell activity

  • CNS (mood, cognition, alertness)

TSH

• Thyroid-Stimulating Hormone

• Secreted in response to TRH from hypothalamus

• Regulates the production of thyroid hormones by the thyroid gland

Prolactin

• Stimulates milk production in mammary glands

• Dopamine inhibits prolactin secretion

• During breastfeeding

• Baby suckling signals > hypothalamus > Reduced dopamine secretion > Increased prolactin secretion > ^ Milk Production

Endorphins

• Also produces by the CNS

• Role in pain management and mood enhancement

• Bind to opioid receptors in the brain > Reduced pain perception + ^ Feelings of pleasure

• Enhance immune response

• Stress response (exercise)

Growth Hormone

• Regulates by GHRH from hypothalamus

• Primary actions are carried out indirectly through IGF-1 (secreted by the liver in response to GH stimulation + drives the linear growth of bones during childhood and adolescence)

• Raises blood glucose levels (Decreases glucose uptake + stimulates gluconeogenesis)

• Promotes lipolysis

Thyroid Gland location

• Located in the front of the neck/Lower throat area in front of the windpipe

Hormones Thyroid Releases

• Tri iodothyronine (T3)

• Thyroxine (T4)

• Calcitonin

T3 & T4 Function

• Regulate metabolism (heart rate, body temperature)

• Fetal brain development + growth in children

• Maintain strong bones

Calcitonin

• Lowers blood calcium and phosphorus levels by inhibiting bone breakdown (osteoclast activity)

Parathyroid Glands Location

4 small pea-sized glands located in the neck behind the thyroid gland

Hormone Parathyroid Glands Release

• Parathyroid Hormone (PTH)

PTH

• Calcitonin in an antagonist to PTH

• Primary regulator of calcium levels in blood

• When calcium levels in the blood are low, the glands secrete PTH > Increases calcium levels by:

  • Breaking down bone

  • Increasing intestinal calcium absorption

  • Conserving calcium in the kidneys

Adrenal Glands Location

Located in the back of the upper abdomen on top of each kidney

Parts of Adrenal Glands (2)

• Adrenal Cortex (Outer Portion)

  • Cortisol

  • Aldosterone

• Adrenal Medulla (Inner Portion) - First responder during fight-or-flight

  • Epinephrine/adrenaline

  • Nor epinephrine

Medulla - Epinephrine/Adrenaline

• Increases heart rate, blood pressure, and blood sugar to prepare for action

Medulla - Norepinephrine

• Heightens alertness and sustains the stress response

Cortex - Cortisol

• Increases blood pressure and cardiac output

• Triggers gluconeogenesis in liver

• Suppresses inflammation

Cortex - Aldosterone

Regulates blood pressure and fluid balance by promoting sodium retention and potassium excretion

Pancreas location

Deep in the upper abdomen, positioned horizontally behind the stomach and in front of the spine

Hormones Pancreas produces

• Insulin

• Glucagon

• Somatostatin

Insulin

• Allows cells to take up glucose from the bloodstream, lowering blood sugar levels

Glucagon

• Signals the liver to release stored glucose when blood sugar dips

Somatostatin

• Acts as a potent inhibitor of both insulin and glucagon secretion from the pancreatic islets

• Predominantly suppresses glucagon more strongly than insulin

Gonads location and function

• Gonads are the body’s reproductive endocrine organs that produce gametes (sperm in males + eggs in females)

• Secrete sex hormones that drive puberty, maintain reproductive function, and influence other body systems (bone density + mood)

• Ovaries = Women

• Testes = Men

Regulation of gonadal hormones

• Hypothalamus releases gonadotrophin-releasing hormone

• GnRH stimulates the anterior pituitary to release FSH and LH

• FSH and LH act on the gonads

• Sex hormones feed back to inhibit the hypothalamus and pituitary (negative feedback)

FSH in Women

• Follicle-stimulating hormone

• FSH stimulates granulosa cells to convert the androgens from theca cells into estrogen

  1. Estrogen builds the uterine lining

• Binds to G protein-couples receptors on the surface of granulosa cells in the ovaries

  • Surround the developing oocyte within the follicle

  • Stimulate follicular growth + estrogen production

    • As follicles grow under the influence of FSH they begin to secrete increasing amounts of estrogen

FSH in Men

• Also bind to Sertoli cells in the seminiferous tubules of the testes

  • Supports spermatogenesis by promoting the maturation of sperm cells

LH in Women

• Luteinizing Hormone

• LH stimulates theca cells to produce androgens (androstenedione), which are then passed to granulosa cells.

  1. Causes egg-containing follicle to rupture

LH in Men

• LH stimulates Leydig cells to produce testosterone

  • Drives spermatogenesis, libido, and male characteristics (muscle mass + body hair)

What is Addison’s disease + Prevalence

• Chronic condition

• Adrenal glands don’t produce enough of the hormones cortisol and aldosterone

• Most common in ages 30-50

• Rare; in the US it affects 1 in 100,000 people

What causes Addison’s disease

• Immune system attacks the adrenal cortex where cortisol and aldosterone are made (approx. 75% of cases)

• Symptoms don’t usually develop until 90% of the adrenal cortex has been damaged, which can take several months to years.

• Can be caused by repeated infections, tuberculosis, adrenal gland bleeding, cancer, other damage (surgery)

What are the symptoms of Addison’s disease (11)

1. Steadily worsening fatigue (most common symptom).

2. Hyperpigmentation around scars, skin creases, + gums

3. Abdominal pain

4. Vomiting + diar rhea

5. Dehydration

6. Low BP + blood sugar

7. Craving for salty food

8. Changes in mood/behavior

   • Women may:

9. Have abnormal menstruation (periods),

10. lose body hair

11. have a decreased sexual drive

How is Addison’s disease diagnosed?

• Blood tests show low levels of sodium or high levels of potassium

• Hyperpigmentation

• ACTH stimulation test (see if adrenal glands produce low levels of cortisol after the shot)

• CT Scan for infection/damage

How is Addison’s disease treated

• Cortisol is replaced by the drug hydrocortisone

• Aldosterone is replaced by the drug fludrocortisone

What is the prognosis for Addison’s disease

• Patients must take medicine for the rest of their lives

• Up to 50% of people with Addison’s disease develop another autoimmune condition