Oct 6th: Hypothalamus, Pituitary & Thyroid

What does the hypothalamus affect?

the pituitary gland

What is the purpose of the The hypothalamic-hypophyseal tract?

To physically connect to the posterior pituitary

What is the purpose of the The Hypothalamic-Hypophyseal Portal System?

To physically connect to the hypothalamus to the anterior pituitary

What does the anterior pituitary gland target?

Breast

Thyroid

Adrenal

Gonads

Various Tissues

What does the posterior pituitary gland target?

Kidney

Breast

Uterus

Behaviour

What are the 2 neurohormones stored and released in the hypothalamic-hypophyseal tract?

Oxytocin

Antidiuretic Hormone

What does oxytocin do?

• promotes uterine contractions and milk ejections

• supports bonding and feelings of comfort (the “hug” hormone).

What does ADH do?

• promotes water reabsorption in the kidneys, which conserves body water.

What is the condition caused by not having enough ADH called?

Diabetes Insipidus

What do hypothalamic hormones travel through?

travel through the hypothalamic-hypophyseal portal system to the endocrine cells of the anterior pituitary

What are the hormones released by the hypothalamus? Where do the hypothalamic releasing hormones do?

• GnRH

• TRH

• CRH

• GHRH

• Dopamine/PRH

> each one drives an anterior pituitary hormone

What hormones do the Anterior Pituitary release?

• LH & FSH

• TSH

• ACTH

• GH (growth hormone)

• Prolactin

What tissue does GnRH and LH & FSH target

Gonads (testes, ovaries)

What tissue does TRH and TSH target?

Thyroid gland

What tissue does the CRH and ACTH target?

Adrenal glands

What tissue does the GHRH and GH target?

Bone, muscle, liver, adipose

What tissue does the Dopamine/PRH and prolactin target?

Mammary glands

What are the parts the Thyroid

What cells do the thyroid hormone affect in the body?

almost every nucleated cell

What does the thyroid hormone affect? (8)

1. Heart

• increases cardiac output and resting heart rate

2. Circulation

• Dilates blood vessels in the skin and to muscles

3. Bone

• Involved in bone remodelling

4. Reproduction

• Needed for a normal reproductive cycle

5. Metabolism

• increase metabolism → more heat, O2, and glucose use

6. Respiration

• increase hemoglobin production and resting respiratory rate

7. Brain

• supports wakefulness and alertness

8. Kidney

• Affects clearance of medication and drugs

What are the parts that form a follicle and the location of the capillaries?

What two thyroid hormones are made in the follicles

Thyroxine (Tetraiodothyronine) (T4)

Triiodothyronine(T3)

What is the basic building block for T3 and T4

• both use the amino acid tyrosine to which iodine is added

How many iodides are in T3 and T4

T3 = 3 iodides

T4 = 4 iodides

How do we get iodine into our body?

We cannot produce iodine so we get it through our diet

ex. salt

Label the chemical structures as thyroxine, tyrosine, triiodothyronine

What is the stableness and activity of T3 and T4

How is the thyroid hormone made?

1. Trap iodide

• Follicular cells pull iodide out of the blood and into the colloid

2. Provide tyrosine

• Tyrosine is already stored in the colloid

3. Combine

• Iodine attaches to T3 and T4

4. Store and release

• T3/T4 are stored in the colloid until TSH signals their release

How does the Thyroid hormone regulation feedback loop work?

How is thyroid hormone secreted?

1. TSH (from the anterior pit. gland) SIGNAL the follicular cells

2. Follicular cells engulf colloid (colloid is thyroglobulin, a gel like material)

3. Thyroglobulin breaks down, releasing T3 and T4

4. Tissues convert T4 into the active hormone T3

5. T3 acts on tissues

What are T3 and T4 built from, and which is the active hormone?

They are built from tyrosine + iodine. T4 is converted to the active T3 in tissues.

How are thyroid hormone levels held steady?

By TRH/TSH negative feedback.

What occurs in the capillary outside the follicle?

The stimulus, TSH, arrives at thyroid through the capillary

What are follicular cells the site of

Site of T3 and T4 synthesis

What is the colloid the site of

Site of T3 and T4 storage