Chemical Structure and Synthesis of Hormones

Grow Taller 4 Idiots

How to Grow Taller

Get Instant Access

There are three general classes of hormones:

1. 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 (see Table 74-1).

2. Steroids secreted by the adrenal cortex (cortisol and aldosterone), the ovaries (estrogen and progesterone), the testes (testosterone), and the placenta (estrogen and progesterone).

3. Derivatives of the amino acid tyrosine, secreted by the thyroid (thyroxine and triiodothyronine) and the adrenal medullae (epinephrine and norepinephrine). There are no known polysaccharides or nucleic acid hormones.

Polypeptide and Protein Hormones Are Stored in Secretory Vesicles Until Needed. Most of the hormones in the body are polypeptides and proteins. These hormones range in size from small peptides with as few as 3 amino acids (thyrotropin-releasing hormone) to proteins with almost 200 amino acids (growth hormone and prolactin). In general, polypeptides with 100 or more amino acids are called proteins, and those with fewer than 100 amino acids are referred to as peptides.

Protein and peptide hormones are synthesized on the rough end of the endoplasmic reticulum of the different endocrine cells, in the same fashion as most other proteins (Figure 74-2). They are usually synthesized first as larger proteins that are not biologically active (preprohormones) and are cleaved to form smaller prohormones in the endoplasmic reticulum. These are then transferred to the Golgi apparatus for packaging into secretory vesicles. In this process, enzymes in the vesicles cleave the prohormones to produce smaller, biologically active hormones and inactive fragments. The vesicles are stored within the cytoplasm, and many are bound to the cell membrane until their secretion is needed. Secretion of the hormones (as well as the inactive fragments) occurs when the secretory vesicles fuse with the cell membrane and the granular contents are extruded into the interstitial fluid or directly into the blood stream by exocytosis.

In many cases, the stimulus for exocytosis is an increase in cytosolic calcium concentration caused by depolarization of the plasma membrane. In other instances, stimulation of an endocrine cell surface receptor causes increased cyclic adenosine monophosphate (cAMP) and subsequently activation of protein kinases that initiate secretion of the hormone. The peptide hormones are water soluble, allowing them to enter the circulatory system easily, where they are carried to their target tissues.

Steroid Hormones Are Usually Synthesized from Cholesterol and Are Not Stored. The chemical structure of steroid hormones is similar to that of cholesterol, and in most instances they are synthesized from cholesterol itself.

Table 74-1

Endocrine Glands, Hormones, and Their Functions and Structure

Gland/Tissue

Hypothalamus (Chapter 75)

Anterior pituitary (Chapter 75)

Posterior pituitary (Chapter 75)

Thyroid

(Chapter 76)

Adrenal cortex (Chapter 77)

Adrenal medulla

(Chapter 60) Pancreas (Chapter 78)

Parathyroid (Chapter 79)

Testes

(Chapter 80) Ovaries

(Chapter 81)

Placenta

(Chapter 82)

Kidney (Chapter 26)

Heart

(Chapter 22) Stomach

(Chapter 64) Small intestine (Chapter 64)

Adipocytes (Chapter 71)

Hormones

Thyrotropin-releasing hormone (TRH) Corticotropin-releasing hormone (CRH) Growth hormone-releasing hormone (GHRH) Growth hormone inhibitory hormone (GHIH)

(somatostatin) Gonadotropin-releasing hormone (GnRH) Dopamine or prolactin-inhibiting factor (PIF) Growth hormone

Thyroid-stimulating hormone (TSH) Adrenocorticotropic hormone (ACTH) Prolactin

Follicle-stimulating hormone (FSH) Luteinizing hormone (LH)

Antidiuretic hormone (ADH) (also called vasopressin)

Oxytocin

Thyroxine (T4) and triiodothyronine (T3) Calcitonin

Cortisol

Aldosterone

Norepinephrine, epinephrine Insulin (b cells) Glucagon (a cells) Parathyroid hormone (PTH)

Testosterone Estrogens

Progesterone

Human chorionic gonadotropin (HCG)

Human somatomammotropin

Estrogens

Progesterone

Renin

1,25-Dihydroxycholecalciferol Erythropoietin

Atrial natriuretic peptide (ANP)

Gastrin

Secretin

Cholecystokinin (CCK) Leptin

Chemical

Major Functions Structure

Stimulates secretion of TSH and prolactin Peptide

Causes release of ACTH Peptide

Causes release of growth hormone Peptide

Inhibits release of growth hormone Peptide

Causes release of LH and FSH

Inhibits release of prolactin Amine

Stimulates protein synthesis and overall growth Peptide of most cells and tissues Stimulates synthesis and secretion of thyroid Peptide hormones (thyroxine and triiodothyronine) Stimulates synthesis and secretion of adrenocortical Peptide hormones (cortisol, androgens, and aldosterone) Promotes development of the female breasts and Peptide secretion of milk Causes growth of follicles in the ovaries and sperm Peptide maturation in Sertoli cells of testes Stimulates testosterone synthesis in Leydig cells of Peptide testes;stimulates ovulation, formation of corpus luteum, and estrogen and progesterone synthesis in ovaries

Increases water reabsorption by the kidneys and Peptide causes vasoconstriction and increased blood pressure

Stimulates milk ejection from breasts and uterine Peptide contractions

Increases the rates of chemical reactions in most Amine cells, thus increasing body metabolic rate Promotes deposition of calcium in the bones and Peptide decreases extracellular fluid calcium ion concentration

Has multiple metabolic functions for controlling Steroid metabolism of proteins, carbohydrates, and fats; also has anti-inflammatory effects Increases renal sodium reabsorption, potassium Steroid secretion, and hydrogen ion secretion Same effects as sympathetic stimulation Amine

Promotes glucose entry in many cells, and in Peptide this way controls carbohydrate metabolism Increases synthesis and release of glucose from Peptide the liver into the body fluids Controls serum calcium ion concentration by Peptide increasing calcium absorption by the gut and kidneys and releasing calcium from bones Promotes development of male reproductive Steroid system and male secondary sexual characteristics Promotes growth and development of female Steroid reproductive system, female breasts, and female secondary sexual characteristics Stimulates secretion of "uterine milk" by the uterine Steroid endometrial glands and promotes development of secretory apparatus of breasts Promotes growth of corpus luteum and secretion of Peptide estrogens and progesterone by corpus luteum Probably helps promote development of some Peptide fetal tissues as well as the mother's breasts See actions of estrogens from ovaries Steroid

See actions of progesterone from ovaries Steroid

Catalyzes conversion of angiotensinogen to Peptide angiotensin I (acts as an enzyme) Increases intestinal absorption of calcium and bone Steroid mineralization

Increases erythrocyte production Peptide

Increases sodium excretion by kidneys, reduces Peptide blood pressure

Stimulates HCl secretion by parietal cells Peptide

Stimulates pancreatic acinar cells to release Peptide bicarbonate and water Stimulates gallbladder contraction and release of Peptide pancreatic enzymes Inhibits appetite, stimulates thermogenesis Peptide

Nucleus

Was this article helpful?

0 0
Diabetes 2

Diabetes 2

Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...

Get My Free Ebook


Responses

  • ermias simon
    What are synthesis and chemical structure of hormone?
    3 years ago
  • ralph
    What cell structure synthesises steroid hormones?
    11 months ago
  • Mauro Palerma
    Why hormone chemistry synthesis?
    10 months ago
  • massimo
    How the steroid hormones are synthesis from the cholesterol as chemical structure modification?
    1 month ago
  • cassandra
    Why is chemical structure of hormones important?
    14 days ago

Post a comment