Endocrine System: M.K.Elkerdany, DDS, MSD, PhD

Pineal Gland

Melatonon: Whose release is regulated by the daily cycle of light and dark.

Secreted primarily during darkness! Influences our daily rhythms of sleep, hunger, and body temperature. Appears to affect mood and behavior.

Hypothalamus

Releasing and Inhibiting Factors/Hormones

1. Controls release of hormones by anterior pituitary gland.

2. Control of diverse and general phenomena, such as:

mental alertness, heart rate, blood pressure, hunger, stomach activity, body temperature, water and mineral balance, emotions, and sexual response.

Posterior Pituitary Gland

Antidiuretic Hormone (ADH)

Regulates water reabsorption by the kidney; causes the kidney to recover water from the urine; opposes production of excessive urine.

Oxytocin

1. Has ADH-like activity, and can cause water retention.

2. Stimulates smooth muscle contraction of:

A. mammary glands causing ejection of milk soon after childbirth.

B. uterus right before and during childbirth, leading to passage of the fetus through the birth canal.

Anterior Pituitary Gland:

Prolactin

a. stimulates mammary gland development.

b. stimulates the synthesis of milk.

Growth Hormone:

Influences metabolism and growth by:

i. stimulating synthesis of proteins and nucleic acids.

ii. regulating growth of the skeleton, connective tissue, muscle, and internal organs.

Melanocyte-Stimulating Hormone (MSH)

Plays a role in causing the development of melanin pigmentation.

Adrenocorticotropic Hormone (ACTH)

Stimulates the adrenal cortex; controls production of corticosteroids hormones.

Thyroid Stimulating Hormone (TSH)

Stimulates and regulates the activity of the thyroid gland

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Gonadotrophins:

A. Follicle Stimulating Hormone ( FSH )

In Females: Stimulates the development and maturation of the ovarian follicles, and production of estrogen hormone by the follicular cells in the ovary.

In Males: Stimulates the development of the sperms in the seminiferous tubules of the testis.

B. Luteinizing Hormone ( LH )

In Females: a. Required for the final stages of maturation of an ovarian follicle.

b. Triggers ovulation.

c. Required for the transformation of the mature ovarian follicle, following ovulation, to develop into a glandular structure known as Corpus Luteum, which secretes both Progesterone and Estrogen.

In Males: Targets the “interstitial cells” in the testis to secrete Testosterone, which is required for the final maturation of the sperms; a developmental process known as “spermiogenesis” or “Cytodifferentiation”.

Gonads:

Ovaries: Secrete both Estrogen and Progesterone; both hormones

Estrogen and progesterone induce the growth of the endometrium.

Estrogen and progesterone; egg development, sex characteristics, and menstrual cycle.

Progesterone causes the endometrial glands to secrete and prepare the endometrium for the “implantation” of the early embryo “blastocyst”.

Human Chorionic Gonadotrpin Hormone ( HCG ) ; secreted by the embryo; preventing degeneration of the corpus luteum to maintain pregnancy.

Testes: Testosterone is secreted by the “interstitial cells of Leydig”.

Sperm production and final maturation, sex characteristics, and maintenance of reproductive organs.

Thymus Gland

Thymosins Hormones

Promote and stimulate T-cell lymphocyte development and maturation.

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Kidney:

Erythropoietin: regulates production of RBC’s by the bone marrow.

Adrenal Glands:

Adrenal Cortex:

  1. Corticosteroids (Cortisol):-

A.promotes synthesis of sugars from amino acids.

  1. promotes storage of glycogen.
  2. Promotes release of fatty acids from adipose tissue, and use of fatty acids as energy source during strenuous activity.
  3. Has anti-inflammatory effects by reducing WBC migration into sites of injury.
  1. Aldosterone (Mineralocoticosteroid):-

Maintains body’s salt balance by:

  1. promoting the reabsorption of Na+ into the blood from the kidney tubules (distal convoluted tubule of the nephron).
  2. Promoting the excretion of K+ through the kidney.

Adrenal Medulla:

  1. Epinephrine (adrenaline) 75-80%
  2. Norepinephrine (noradrenaline) 20-25%

Adrenaline (Epinephrine):-

  1. promotes an increase in the blood sugar by mobilizing sugar that has been stored in the liver as glycogen. Norepinephrine has a similar, but less dramatic effect on glycogen mobilization.
  2. promotes the breakdown of stored fat into fatty acids, and the release of these fatty acids into the blood stream.
  3. increases heart rate and blood pressure.
  4. acts as a vasodilator in skeletal muscle.

Norepinephrine:- is a strong vasoconstrictor and , like epinephrine, raises the blood pressure.

Islets of Langerhans (Pancreas):

  1. Beta cells: 70% of the cells in each islet; secretes insulin.
  2. Alpfa cells: 30% of the islet cells: secretes glucagons.

Glucagon:

Promotes the breakdown of glycogen into glucose, and the release of this sugar into the blood. i.e. glucagons is antagonistic to insulin.

Both Insulin and Glucagon ensure that the blood glucose level is neither too high nor too low.