Endocrine System

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Endocrine System
• 2nd great controlling system in the body
• Ductless glands, and produce hormones in the blood or lymph system
• Endocrine hormones are released by glands or specialized cells into
the circulating blood and influence the function of target cells at
another location in the body
• The multiple hormone systems play a key role in regulating almost all
body functions, including metabolism, growth and development,
water and electrolyte balance, reproduction, and behavior
Three general classes of hormones
• Proteins and polypeptides
• Steroids
• Derivatives of the amino acid tyrosine
• Proteins and polypeptides, including hormones secreted by the
anterior and posterior pituitary gland, the pancreas (insulin and
glucagon), the parathyroid gland (parathyroid hormone), and many
others
• Steroids secreted by the adrenal cortex (cortisol and aldosterone),
the ovaries (estrogen and progesterone), the testes (testosterone),
and the placenta (estrogen and progesterone)
• Derivatives of the amino acid tyrosine, secreted by the thyroid
(thyroxine and triiodothyronine) and the adrenal medullae
(epinephrine and norepinephrine)
Hypothalamus
• major part of limbic system
• responsible for neuronal circuitry for emotional and motivational
drive
Hypothalamus

• Functions: temperature regulation, control the body weight, drive to

eat and drink, emotions.
Hypothalamus
• Hormones
a. Thyrotropin-releasing hormone: Stimulates secretion of thyroid-
stimulating hormone and prolactin
b. Corticotropin-releasing hormone: Causes release of
adrenocorticotropic hormone
c. Growth hormone–releasing hormone: Causes release of growth
hormone
d. Growth hormone inhibitory hormone (somatostatin): Inhibits
release of growth hormone
e. Gonadotropin-releasing hormone: Causes release of luteinizing
hormone and follicle-stimulating hormone
f. prolactin inhibiting factor: Inhibits release of prolactin
Pituitary Gland/ Hypophysis
• Small gland, 1cm in diameter
• 0.5 – 1g in weight
• Lies in the Sella Turcica (Bony cavitation at the base of the brain and it
is connected to hypothalamus by Pituitary (hypophysial) stalk)
Pituitary Gland/ Hypophysis
• Anterior Pituitary (Adenohypophysis)
• Posterior Pituitary (Neurohypophysis)
Anterior Pituitary Gland
• arises from the Ratchke's Pouch- embryonic invagination of the
pharyngeal epithelium
• Has five cell types
• These five cell types are:
1. Somatotropes—human growth hormone (hGH)
2. Corticotropes—adrenocorticotropin (ACTH)
3. Thyrotropes—thyroid-stimulating hormone (TSH)
4. Gonadotropes—gonadotropic hormones, which include both
luteinizing hormone (LH) and follicle stimulating hormone (FSH)
5. Lactotropes—prolactin (PRL)
• Hormones
a. Growth hormone (Somatotropin): Stimulates protein synthesis and
overall growth of most cells and tissues
b. Thyroid-stimulating hormone: Stimulates synthesis and secretion of
thyroid hormones (thyroxine and triiodothyronine)
c. Adrenocorticotropic hormone: Stimulates synthesis and secretion
ofadrenocortical hormones (cortisol, androgens,and aldosterone)
d. Prolactin: Promotes development of the female breasts and
secretion of milk
e. Follicle-stimulating hormone: Causes growth of follicles in the
ovaries and sperm maturation in Sertoli cells of testes
Male: stimulates release of sperm
Female: initiates development of oocytes and induces ovarian release
of estrogen
f. Luteinizing hormone:
Males: Stimulates testosterone synthesis in Leydig cells of testes;
Females: stimulates ovulation, formation of corpus luteum, and
estrogen and progesterone synthesis in ovaries
g. MSH – Melanocyte stimulating hormone: Increases skin
pigmentation
h. ACTH- Adrenocorticotropic Hormone : Stimulate the release of
aldosterone and cortisol
Posterior Pituitary Gland
• Neurohypophysis
• Orginates from the neural tissue outgrowth of the hypothalamus
• hormones of the posterior pituitary are synthesized by the cell bodies
in the hypothalamus- magnocellular neurons (located in the
supraoptic and paraventricular nuclei)
• Hormones
a. Antidiuretic hormone (also called vasopressin): Increases water
reabsorption by the kidneys and causes vasoconstriction and increased
blood pressure
b. Oxytocin: Stimulates milk ejection from breasts and uterine
contractions; milk ejection via sucking reflex
Thyroid Gland
• located immediately below the larynx on each side and anterior to
the trachea
• one of the largest of the endocrine glands, normally weighing 15 to
20 grams in adults
• Hormones
a. Thyroxine (T4) and triiodothyronine (T3): Increases the rates of
chemical reactions in most cells, thus increasing body metabolic rate;
produced by follicular cells of the thyroid gland
b. Calcitonin: produced by the parafollicular cells of the thyroid gland,
Promotes deposition of calcium in the bones and decreases
extracellular fluid calcium ion concentration; inhibits bone resorption,
bone building
Parathyroid Gland
• embedded in the posterior surface of the lateral lobe of the thyroid
gland
• Hormone
a. Parathyroid hormone: Controls serum calcium ion concentration
byincreasing calcium absorption by the gut and kidneys and releasing
calcium from bones; bone resorption (increase osteoclastic acitivity
Adrenal Gland
• The two adrenal glands, each of which weighs about 4 grams, lie at
the superior poles of the two kidneys
Adrenal Medulla
• each gland is composed of two major parts, the adrenal medulla and
the adrenal cortex
• adrenal medulla, the central 20 percent of the gland, is functionally
related to the sympathetic nervous system; it secretes the hormones
epinephrine and norepinephrine
• adrenal cortex secretes an entirely different group of hormones,
called corticosteroids
• Hormones of the Adrenal Cortex
Zona Glomerulosa
a. mineralocorticoids (Aldosterone): Increases renal sodium
reabsorption, potassium secretion, and hydrogen ion secretion;
increase water and electrolyte reabsorption
• Zona Fasciculata
a. Glucocorticoids (Cortisol): Has multiple metabolic functions for
controlling metabolism of proteins, carbohydrates, and fats; also has
anti-inflammatory effects; resistance to stress
• Zona Reticularis
a. Androgen, secondary sex characteristics of males
- Stimulate growth of axillary and pubic hair
- If more in females they develop male characteristics, clitoris develops
similar to penis
• Hormones of the Adrenal Medulla
a. Norepinephrine, epinephrine: Same effects as sympathetic
stimulation
Pineal Gland
• small endocrine gland attached to the roof of the third ventricle of
the brain at the midline
• Part of the epithalamus, it is positioned between the two superior
colliculi, has a mass of 0.1–0.2 g
• Hormone
a. Melatonin: controls the body's biological clock
Thymus Gland
• located behind the sternum between the lungs
• Hormones
a. thymosin, thymic humoral factor (THF), thymic factor (TF), and
thymopoietin—promote the maturation of T cells (a type of white
blood cell that destroys microbes and foreign substances) and may
retard the aging process
Pancreas
• both an endocrine gland and an exocrine gland
• A flattened organ that measures about 12.5–15 cm (5–6 in.) in
length, the pancreas is located in the curve of the duodenum, the first
part of the small intestine, and consists of a head, a body, and a tail
• 1–2 million tiny clusters of endocrine tissue called pancreatic islets
or islets of Langerhans
• Hormones by cell types in the pancreatic islet
Alpha Cells
a. Glucagon: increases blood sugar levels
• Beta Cells
a. Insulin, Decreases blood glucose levels
• Delta Cells
a. Somatostatin, balance/ controls the number of insulin and glucagon
- inhibit both insulin and glucagon release from neighboring beta and
alpha cells
• F cells
a. pancreatic polypeptide: inhibits somatostatin secretion, gallbladder
contraction, and secretion of digestive enzymes by the pancreas
Gonads
• Ovaries
Hormones
a. Estrogens: Promotes growth and development of female
reproductive system, female breasts, and female secondary sexual
characteristics
b. Progesterone: Stimulates secretion of “uterine milk” by the uterine
endometrial glands and promotes development of secretory apparatus
of breasts
c. Relaxin: Increases flexibility of pubic symphysis during pregnancy;
helps dilate uterine cervix during labor and delivery

d. Inhibin: Inhibits secretion of FSH from anterior pituitary

• Testes
Hormones
a. Testosterone: Promotes development of male reproductive system
and male secondary sexual characteristics
b. Inhibin: Inhibits secretion of FSH from anterior pituitary.
Placenta
• Hormone
a. Human chorionic gonadotropin: Promotes growth of corpus luteum
and secretion of estrogens and progesterone by corpus luteum
b. Human somatomammotropin: Probably helps promote
development of some fetal tissues, as well as the mother’s breasts
c. estrogen
d. progesterone
Kidneys
• Hormone
a. Renin: Catalyzes conversion of angiotensinogen to angiotensin I (acts
as an enzyme)
b. 1,25-Dihydroxycholecalciferol: Increases intestinal absorption of
calcium and bone mineralization
c. Erythropoietin: Increases erythrocyte production
Heart
• Hormone
a. Atrial natriuretic peptide: Increases sodium excretion by kidneys,
reduces blood pressure
Stomach
• Gastrin: Stimulates hydrogen chloride secretion by parietal cells;
Promotes secretion of gastric juice; increases movements of the
stomach
• Glucose-dependent insulinotropic peptide (GIP): Stimulates release
of insulin by pancreatic beta cells
• Ghrelin: hunger hormone
Small Intestine
• Secretin: Stimulates pancreatic acinar cells to release bicarbonate and
water, stimulates secretion of pancreatic juice and bile
• Cholecystokinin: Stimulates gallbladder contraction and release of
pancreatic enzymes; Stimulates secretion of pancreatic juice;
regulates release of bile from gallbladder; causes feeling of fullness
after eating
Adipocytes
• Leptin: Inhibits appetite, thermogenesis
• Supplemental videos:
• https://www.youtube.com/watch?v=tQVzZaV9yDY
• https://www.youtube.com/watch?v=-B-RVybvffU
• https://www.youtube.com/watch?v=wyanDtvx8K0
• https://www.youtube.com/watch?v=RuwM6M5ohW4
References
• Guyton's Medical Physiology, Chapter 75 (Introduction to
Endrocrinology); Chapter (76-80)
• Principles of Anatomy and Physiology by Gerad Tortora (Chapter 18)