Testis (The Male Gonad)

The testis is the primary male reproductive organ. It performs two important functions at the same time, so it acts both as a sex organ and as an endocrine gland.

Location

In human males, a pair of testes is present in the scrotal sac, situated outside the main abdominal cavity to maintain a lower temperature necessary for sperm production.

Dual Function

The testis is a remarkable organ that performs two major roles simultaneously: it acts as a primary sex organ (producing sperm) and as an endocrine gland (producing hormones).

Internal Structure

Microscopically, the testis is composed of highly coiled seminiferous tubules (where sperm is made) and stromal or interstitial tissue (the spaces between the tubules).

The Hormone Source

Located in these inter-tubular spaces are specialized cells called Leydig cells (or Interstitial cells). These cells synthesize and secrete a group of powerful steroid hormones called Androgens, the most important of which is Testosterone.

Functions of Androgens (Testosterone)

Androgens, especially testosterone, are responsible for many important male functions.

Development and Maturation

They regulate the development, maturation, and daily functions of the male accessory sex organs (such as the epididymis, vas deferens, seminal vesicles, prostate gland, and urethra).

Secondary Sex Characters

They trigger the dramatic physical changes during puberty, stimulating heavy muscular growth, the growth of facial and axillary (underarm) hair, aggressiveness, and the characteristic low pitch of voice.

Spermatogenesis

They play a crucial stimulatory role in the ongoing process of sperm formation.

CNS Effect

Androgens act directly on the central neural system to influence and drive male sexual behaviour, scientifically known as Libido.

Metabolism

They are strictly building hormones, producing anabolic (synthetic) effects on protein and carbohydrate metabolism, which is why they are strongly associated with muscle mass increase.

Ovary (The Female Gonad)

The ovary is the primary female reproductive organ. Like the testis, it also has a dual role:

  • acts as a sex organ
  • acts as an endocrine gland

Location

Females have a paired set of ovaries located within the lower abdomen (pelvic cavity).

Dual Function

Just like the testis, the ovary is the primary female sex organ (it produces one ovum, or egg, during each menstrual cycle) and simultaneously acts as an incredibly dynamic endocrine gland.

The Hormone Sources

The ovary primarily produces two distinct groups of steroid hormones, originating from different structures at different times of the cycle:

  1. Estrogen: This is synthesized and secreted mainly by the growing ovarian follicles as they mature around the egg.
  2. Progesterone: After the egg is released (ovulation), the ruptured follicle collapses and transforms into a yellow glandular structure called the Corpus Luteum, which takes over the main job of secreting progesterone.

Functions of Estrogen (The 'Feminizing' Hormone)

  • Growth and Stimulation: Drives the growth and continuous activities of female secondary sex organs.
  • Follicle Maturation: Helps in the ongoing development of growing ovarian follicles.
  • Secondary Sex Characters: Responsible for the appearance of female secondary sexual characteristics during puberty, such as the development of the mammary glands and a high pitch of voice.
  • CNS Effect: Plays a key role in regulating female sexual behaviour.

Functions of Progesterone (The 'Pregnancy' Hormone)

  • Pregnancy Support: Its absolute primary role is to prepare the uterus for, and subsequently support, pregnancy.
  • Mammary Glands: It acts on the mammary glands to stimulate the formation of alveoli (the tiny sac-like structures which actually store the milk) and gets them ready for milk secretion.

Testis and Ovary

1. The Male "L-A-T" Rule:

  • Leydig cells secrete Androgens (mainly Testosterone).

2. The Female Hormone Map:

  • Follicle = Estrogen (Think "FE" -> Female Elegance/Estrogen).
  • Corpus Luteum = Progesterone (Think "CLP" -> Corpus Luteum Protects Pregnancy).

3. Anabolic vs. Catabolic:

  • Androgens are Anabolic (they build muscle/protein). (Don't confuse this with Cortisol, which is catabolic!).

💡 Questions and Answers

Q1. Which cells in the testis secrete androgens?

A1: The Leydig cells or interstitial cells present between the seminiferous tubules of the testis secrete androgens, mainly testosterone.

Key points:

  • Leydig cells = androgen secretion
  • Main androgen = Testosterone

Q2. What is the main function of progesterone?

A2: The main function of progesterone is to support pregnancy. It also helps in the development of alveoli in mammary glands.

Key points:

  • Progesterone supports pregnancy
  • Stimulates alveoli formation

Q3. Which structure secretes progesterone in the ovary?

A3: The corpus luteum of the ovary secretes progesterone.

Key points:

  • Corpus luteum → Progesterone

Q4. List two secondary sex characters regulated by androgens.

A4: Two secondary sex characters controlled by androgens are:

  • growth of facial / axillary hair
  • low pitch of voice

Key points:

  • Facial hair
  • Low pitch voice

Q5. What is the source of estrogen in a non-pregnant female?

A5: In a non-pregnant female, estrogen is mainly secreted by the growing ovarian follicles.

Key points:

  • Growing ovarian follicles → Estrogen