B6 HORMONES

B.6.1 OUTLINE THE PRODUCTION AND FUNCTION OF HORMONES IN THE BODY

• What is hormone?– Hormones are chemical messenger that are

produced by the body’s endocrine glands (many of which are controlled by the pituitary gland which in turn, is controlled by the hypothalamus)

– Released directly via bloodstream to target organ– Perform a variety of different function and vary

greatly in their chemical composition – Generally have a negative feedback mechanism

whereby a high level of the hormone inhibits its own production.

• Examples of hormone:– ADH (controls body water content)– Aldosterone (a steroid which regulates the Na and

K balance in the blood)– Adrenalin– Thyroxine– Insulin– Sex hormone (male and female)

ADRENALIN

• Produced in the adrenal gland.• A stimulant, closely related to the

amphetamine drugs.• Released in times of excitement and causes a

rapid dilation of the pupils and airways, increases the rate of heartbeat and the rate of release of sugar into the bloodstream.

• Sometimes known as the ‘flight or fight’ hormone.

Structure of adrenalin

THYROXINE• Produced in the thyroid gland (located in the neck)• Contains iodine. • Lack of iodine can cause the thyroid gland to swell.

(goitre)• Thyroxin regulates the body’s metabolism• Low levels of thyroxin cause hypothyroidism,

characterized by lethargy as well as sensitivity to cold and a dry skin.

• Overactive thyroid gland causes hyperthyroidism with the symptoms of anxiety, weight loss, intolerance to heat, and protruding eyes.

Some pictures of goitre

Thyroxine structure

INSULIN• A protein containing fifty-one amino acid residues• Formed in the pancreas and regulates blood sugar levels• Low level of insulin or absence of it can cause

hyperglycemia (high blood sugar) and results in thirst, weight loss, lethargy and circulation problems.

• Long term sufferers of diabetes can suffer blindness, kidney failure, and need limbs to be amputated due to poor circulation.

• Thus, it is treated by reducing sugar intake and taking daily insulin injections.

• Too much insulin can cause hypoglycemia (low blood sugar), where the blood sugar level falls resulting in dizziness and fainting.

Insulin lispro Insulin glargine

SEX HORMONE

• The sex hormones are all steroids.• Steroids contain a characteristic four-ring

structure• The basic building block for the other steroids

is cholesterol formed in the liver and found in all tissues, the blood, brain, and spinal cord.

MALE SEX HORMONE

• Comprise mainly testosterone and androsterone

• Produced in the testes • They are anabolic – encouraging tissue,

muscle, and bone growth – and androgenic – conferring the male sexual characteristics.

The structure of male sex hormones

Testosterone Androsterone

FEMALE SEX HORMONE• Structurally very similar to male sex hormones,

except for the small changes in the functional groups attached to the steroid framework

• They are produced in the ovaries from puberty until menopause

• The two main female sex hormones are oestradiol and progesterone

• They are responsible for sexual development and the menstrual and reproductive cycles in women.

The structure of female sex hormones

Oestradiol Progesterone

B.6.2 COMPARE THE STRUCTURES OF CHOLESTEROL AND THE SEX HORMONES

Common: Steroid backbone

Cholesterol structure • The basic building block

for the other steroids is cholesterol.

• It has a chain of alkanes on one ring

• and a C-OH group (hydroxyl group) on the last ring

• Consist of four carbon rings :– Three cyclohexane – 1 cyclopentane

• Cholesterol is primarily hydrophobic, with only one hydroxyl group.

Testosterone

• C-OH group (hydroxyl group) on the first, ring C=O (carbonyl group) on the last

• The sex hormones have carbonyl groups and hydroxyl groups which make the molecule partly hydrophilic on both ends.

Progesterone

• Carbonyl group (ring C=O) attached to a methyl group on the first ring, carbonyl group (ring c=O) on the last ring