Role of endocrine glands in regulation of body functions

Author

ass.prof. N.M. Volkova

• The thyroid gland contains spherical follicles (50–500 μmin diameter).

• Follicle cells synthesize the two iodine-containing thyroid hormones thyroxine (T4, tetraiodothyronine) and triiodothyronine (T3).

• Thyroid hormone activation of target cells

Thyroid hormone activation oftarget cells

• Thyroxine (T4) and triiodothyronine (T3) readily diffuse through the cell membrane.

• Much of the T4 is deiodinated to form T3, which interacts with the thyroid hormone receptor, bound as a heterodimer with a retinoid X receptor, of the thyroid hormone response element of the gene.

• This causes either increases or decreases in transcription of genes that lead to formation of proteins, thus producing the thyroid hormone response of the cell.

Regulation of thyroid secretion

Iodine metabolism

• Iodine circulates in the blood as either (1) inorganic I– (2–10 μg/L), (2) organic non-hormonal iodine (traces) and (3) protein-bound iodine (PBI) within T3 and T4 (35–80 μg iodine/L). The average daily requirement of iodine is ca. 150 μg.

• Iodine excreted from the body must be replaced by the diet.

• Since iodine passes into the breast milk, nursingmothers have a higher daily requirement of iodine (ca. 200 μg/day).

The Menstrual Cycle

• The first day of menses is day 1 of the menstrual cycle, and menses typically lasts 4–5 days.

• Ovulation occurs on about day 14 of a 28-day menstrual cycle, although the timing of ovulation varies.

Factors That Influence the Process of Parturition

Hormonal Control of Lactation

Menopause• When a female is 40–50 years old, menstrual

cycles become less regular, and ovulation often does not occur. Eventually menstrual cycles stop completely.

• The cessation of menstrual cycles is called menopause. The time from the onset of irregular cycles to their complete cessation, which is often 3 to 5 years, is called the female climacteric or perimenopause.

• A variety of symptoms occur in some females during the climacteric, including “hot flashes,” irritability, fatigue, anxiety, and occasionally severe emotional disturbances.