Hormonal Heroes: Understanding Sex Hormones in Humans

 

What Are Sex Hormones?

Definition:

• Sex hormones are chemical messengers that control the development of sexual characteristics and regulate processes like puberty, reproduction, and the menstrual cycle.

 

Key Sex Hormones and Their Roles

 

Hormone	Produced By	Functions
Testosterone	Testes (in males)	- Develops male secondary sexual characteristics (e.g., deeper voice, facial hair). - Stimulates sperm production.
Oestrogen	Ovaries (in females)	- Develops female secondary sexual characteristics (e.g., breasts, wider hips). - Regulates the menstrual cycle and helps thicken the uterine lining.
Progesterone	Ovaries (in females)	- Maintains the uterine lining during the menstrual cycle and pregnancy.
FSH (Follicle Stimulating Hormone)	Pituitary gland	- Stimulates the growth of egg follicles in the ovaries.
LH (Luteinising Hormone)	Pituitary gland	- Triggers ovulation (release of an egg from the ovary).

 

Puberty: A Hormonal Makeover

Definition:

• Puberty is the stage where boys and girls develop secondary sexual characteristics due to increased hormone activity.

 

Changes in Boys (Testosterone)	Changes in Girls (Oestrogen)
Growth of facial and body hair.	Development of breasts.
Deepening of the voice.	Widening of hips.
Growth of testes and penis.	Start of the menstrual cycle.
Increased muscle mass.	Deposition of fat in hips and thighs.

 

The Menstrual Cycle: A Monthly Hormonal Journey

• The menstrual cycle prepares the female body for pregnancy.
• It starts in early adolescent girls at ~ 12 years old and is controlled by the hormones in the female
• It lasts approximately 28 days and involves changes in the ovaries and uterine lining.
• In the middle of the cycle ~day 14 Ovulation occurs and the egg travels from the ovary through the oviduct to the uterus ready for fertilisation.
• When fertilisation doesn't occur as the egg doesn't ecounter a sperm cell, menstruation then occurs. 
• In menstruation the uterus lining which thickened breaks down and is shed

 

Hormonal Control of the Menstrual Cycle - Extended

Hormone	Role
FSH (Follicle-Stimulating Hormone)	Released by the pituitary gland, stimulates the development of the egg in the ovary
LH (Luteinising Hormone)	Causes ovulation and stimulates ovary to release progesterone
Oestrogen	Repairs and thickens the uterine lining; inhibits FSH and stimulates pituitary gland to release LH when oestrogen levels are peak.
Progesterone	Maintains the uterine lining; inhibits LH and FSH production to prevent further ovulation.

 

 

Phases of the Menstrual Cycle

Day Range	Phase	Hormonal Activity
1–5	Menstruation	Uterine lining breaks down and is shed as menstrual blood.
6–13	Follicular Phase	FSH stimulates the growth of follicles; oestrogen thickens the uterine lining.
14	Ovulation	LH surge causes the release of an egg from the ovary and travel down oviduct to uterus.
15–28	Luteal Phase	Progesterone maintains the uterine lining in preparation for a possible pregnancy.

 

 

Pregnancy and Hormones

During pregnancy, oestrogen and progesterone levels remain high to support the developing fetus.

Structure	Hormonal Role
Placenta	Produces progesterone to maintain the uterine lining.
Corpus Luteum	Produces progesterone in early pregnancy before the placenta takes over.