ICSE Class 10 Biology Chapter 11 The Reproductive System

The Reproductive System

Syllabus: The Reproductive System: Organs, fertilisation and a general outline of nutrition and respiration of the embryo. Menstrual cycle: outline of menstrual cycle

Scope of Syllabus: Functions of organs and accessory glands must be discussed. An idea of secondary sexual characters, structure and functions of the various parts of the sperm and an egg. Fertilization, implantation, placenta, foetal membranes, gestation and parturition, identical and fraternal twins to be explained briefly.

Reproduction is the key point of the continuance of life on earth. In a way, all other systems and processes in the body are for supporting the reproduction process. This chapter on the human reproductive system covers a wide range of information useful for even a common man. For our students, one or two long answer type questions and quite a few small ones always find a place in the question paper. For examination purpose, try to understand and memorise, in particular, the structures in the reproductive system, fertilisation and the functions of the placenta.

The Reproductive Organs

Reproduction In General

Reproduction is the formation of new individuals by sexual or asexual means, which can repeat the process in their own turn.

Many simpler organisms like bacteria and yeast reproduce by fission or budding, etc. Many plants reproduce vegetatively non-sexually by various methods. But in humans, reproduction is only sexual.

Patterns Of Reproduction

Asexual reproduction: The reproductive units may under asexual type of reproduction consist of any portion of the parent body. The size of the units may range from the whole to a small fragment of the parent body.

Example: A bud grows out of the body of hydra, gets separated and grows into a full hydra.

Sexual reproduction: The gametes (sex cells - egg and sperm) are very small (microscopic in human beings). The gametes must normally unite (fertilisation) to produce a zygote which, through a process of development, finally becomes the offspring.

The gametes are usually produced in different sexes (male and female). These sexes often show outwardly differentiated features called secondary sexual characters. At least two features are apparent in a cartoonist's partial drawing of a man and a woman standing in a relaxed pose (next page).

Male Or Female (Some Secondary Sexual Characters)

Think of sexual distinction in certain animals: Lion and Lioness, Cow and Bull, Cock and Hen, Peacock and Peahen. Secondary sexual characters throughout the animal world serve to identify and attract sex partners. Odours (body smells), calling sounds, skin colouration, body contour, behavioural patterns, etc. are some such sex clues. In humans, the secondary sexual characteristics include:

Distribution of hair on body and face (beard and moustaches in males), Breasts in females, Muscularity-stronger built in males, Skeletal structure, Psyche and behaviour, Deeper voice in males

Reproduction In Humans

The organs of the reproductive system are divided into the primary and accessory parts:

(i) The primary reproductive parts include the gonads (testes in males and ovaries in females) which produce the sex cells (or gametes) - the sperms and eggs.

(ii) The accessory reproductive parts include all those structures which help in the transfer and meeting of the two kinds of sex cells leading to fertilisation and in the growth and development of the egg up to the birth of the baby.

So, according to the above criteria, would you consider secondary sexual characters as given in the box above, as reproductive parts? No. These do not participate in reproduction.

Male Reproductive System

The male reproductive system (Fig. 11.1 A-C) consists of the following organs:

(1) Testes (one pair) to produce sperms,

(2) Sperm duct (vas deferens) from each testis to carry the sperms,

(3) Accessory glands (seminal vesicles, prostate and bulbo-urethral glands) to contribute to the seminal fluid, and

(4) A penis for transferring the sperms into the female.

(5) Urethra contained inside the penis, conveys the sperms received from sperm ducts.

Testes (Sing.: Testis)

A. Location Of Testes

The two testes (popularly called testicles) are oval organs which are contained in a thin-walled sac enclosed from scrotum (or scrotal sacs) (Fig. 11.1 A, B & C).

In the embryonic stage, the testes are contained within the abdomen. They descend into the scrotum shortly before birth. An abnormal condition results when they do not descend and it leads to sterility, i.e., incapability to produce sperms.

The high temperature of the body does not permit maturation of sperms. But in the normal condition, being in a separate sac suspended from the body, the testes escape too much body heat.

Temperature regulation in the testes: Sperms are produced in the testes at a temperature 2 to 3 degrees C lower than that of the body. This temperature is regulated in a strange manner through the movements of the scrotum wall. When it is too hot, the skin of the scrotum loosens so that the testes hang down away from the body. When it is cold, the skin contracts in a folded manner and draws the testes closer to the body for warmth.

B. Structure Of Testis

Each testis (Fig. 11.1 C) is encased in a capsule which is internally partitioned into 15-20 lobes (segments). Each lobule contains:

(i) Seminiferous tubules (semini: sperm, ferous: bearing) where the sperms are produced. The process is called spermatogenesis.

(ii) Interstitial cells (interstitial: filling in between) which are packing tissues between the coils of the seminiferous tubules. The interstitial cells also called Leydig cells produce the male hormone testosterone.

The sperm producing cells of the seminiferous tubules keep multiplying and produce sperms. The mature sperms pass into a small network of tubes (Fig. 11.1 C). From the network, arise 12-14 ducts (efferent ducts) which join a small tubular knot, the epididymis (epi: above, didymis: testicle) fitting like a cap on the upper pole of the testis. The epididymis is continued by the side of the testis upto its back from where a distinct tube sperm duct (vas deferens) arises. The epididymis internally contains a single coiled tube (actually about 6 metres long) which traverses from the upper part of the testis to its back and then it continues into the sperm duct. The epididymis stores the sperms for some days during which they mature and become motile (capable of moving).

Teacher's Note

Understanding the male reproductive system helps students recognize the importance of temperature regulation and structural specialization in producing healthy sperms, concepts that relate to how our bodies maintain optimal conditions for vital biological processes.

Sperm Ducts

The sperm duct (vas deferens) from each testis travels upward into the abdomen passing through an inguinal canal. The inguinal canal originally is the one which allows the descent of testes along with their ducts, blood vessels, nerves, etc.

Sometimes, due to pressure in the abdomen, the intestine bulges into the scrotum through the inguinal canal and causes the most common type of hernia.

The two sperm ducts loop over the ureters of their side, come together, and join the median duct, or urethra, at the back of the urinary bladder.

Accessory Glands (Fig. 11.1 & B)

Three male accessory glands are as follows:

(i) Seminal vesicles: A pair of lobulated glands located between the posterior surface of the urinary bladder and the rectum. A duct from each seminal vesicle joins the corresponding sperm duct just before it unites with the urethra. Produce a secretion which serves as a medium for the transportation of the sperms. The mixture of this fluid and the sperms produces a milky fluid, the semen. In the sperm duct, the sperms are sluggish, but by the addition of this secretion, they become active.

(ii) Prostate gland: A bilobed structure which surrounds the urethra close to its origin from the bladder. It pours an alkaline secretion into the semen as it passes through the urethra. It neutralises acid in female's vagina.

(iii) Bulbo-urethral glands: These are two small ovoid glands which open into the urethra just before it enters the penis. The secretion serves as a lubricant.

Penis

The penis lies in front of the scrotum, cylindrical in shape, serves for the passing out of both semen and urine (Fig. 11.1 C). It is a highly vascular organ, having erectile tissues and vascular spaces. Under the influence of sexual stimulation, blood flows in large amount into the penis and enters into the vascular spaces or sinuses, which makes it rigid and erect. Expansion of these spaces compresses the veins and thus blood cannot drain out. Such condition of penis is called erection.

Semen is the mixture of sperms and secretions from seminal vesicle, prostate, Cowper's and urethral glands. It is a milky fluid. Its average amount is 2-3 ml in a single ejaculation and contains 200,000,000-400,000,000 sperms.

The Course Of Sperms In Male

Seminiferous tubules (produce sperms) leads to Network of tubules leads to Efferent ducts leads to Upper part (head) of epididymis leads to Middle part (body) of epididymis leads to Hind part (tail) of epididymis leads to Sperm duct (vas deferens) leads to Urethra (in penis)

Teacher's Note

The accessory glands and their secretions demonstrate how the male body provides an optimal environment for sperm survival and transport, much like how various support systems in daily life (transportation, fuel stations) keep essential operations running smoothly.

Progress Check

1. Tick-mark the correct meaning of reproduction

(a) increase in population

(b) increase in the number of parents

(c) production of new individuals

(d) production of identical individuals

2. What is the significance of the testes being located in scrotal sacs?

3. State very briefly the chief function of each of the following:

(i) Seminal vesicles

(ii) Prostate gland

(iii) Cowper's gland

(iv) Sperm duct (vas deferens)

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