BMICCT 102 Reproduction - MODULE IX.pptx

BMICCT 102 Reproduction - MODULE IX

1. BMICCT 102 - MODULE IX: REPRODUCTIVE SYSTEM Unit 1: Formation of semen & spermatogenesis Unit 2: Brief account of menstrual cycle By Sujoy Tontubay Assistant Professor of Medical Laboratory Technology, iLEAD

2. A  man’s reproductive system  is specifically designed to produce, store, and transport sperm. Unlike the  female genitalia , the male reproductive organs are on both the interior and the exterior of the pelvic cavity. They include: the testes ( testicles ) the duct system: epididymis and vas deferens (sperm duct) the accessory glands: seminal vesicles and prostate gland the  penis

3. Sperm production occurs in the testicles. Upon reaching  puberty , a man will produce millions of sperm cells every day, each measuring about 0.002 inches (0.05 millimeters) long.

4. How is sperm produced? There is a system of tiny tubes in the testicles. These tubes, called the seminiferous tubules, house the germ cells that hormones — including  testosterone , the male sex hormone — cause to turn into sperm. The germ cells divide and change until they resemble tadpoles with a head and short tail. The tails push the sperm into a tube behind the testes called the  epididymis . For about five weeks, the sperm travel through the epididymis, completing their development. Once out of the epididymis, the sperm move to the vas deferens. When a man is stimulated for sexual activity, the sperm are mixed with seminal fluid — a whitish liquid produced by the seminal vesicles and the prostate gland — to form semen. As a result of the stimulation, the semen, which contains up to  500 million sperm , is pushed out of the penis (ejaculated) through the  urethra .

5. How long does it take to produce new sperm? The process of going from a germ cell to a mature sperm cell capable of egg fertilization takes around  2.5 months

6. semen semen , also called  seminal fluid ,  fluid  that is emitted from the male reproductive tract and that contains  sperm  cells, which are capable of fertilizing the female’s eggs. Semen also contains liquids that combine to form  seminal plasma , which helps keep the sperm cells viable. The total volume of semen for each ejaculation of a human male averages between 2 and 5 ml . In human beings each ejaculation contains normally 200 to 300 million sperm. Semen frequently contains degenerated cells sloughed off from the network of tubules and ducts through which the semen has passed.

7. testis testis , plural  testes,  also called  testicle , in animals, the  organ  that produces  sperm , the male reproductive  cell , and  androgens , the male hormones. In humans the testes occur as a pair of oval-shaped organs. They are contained within the scrotal sac, which is located directly behind the  penis  and in front of the  anus . Anatomy of the testes In humans each testis weighs about 25 grams and is 4–5 cm long and 2–3 cm in diameter. Each is covered by a fibrous capsule called the tunica albuginea and is divided by partitions of fibrous tissue from the tunica albuginea into 200 to 400 wedge-shaped sections, or lobes. Within each lobe are 3 to 10 coiled tubules, called  seminiferous tubules , which produce the sperm cells. The partitions between the lobes and the seminiferous tubules both converge in one area near the anal side of each testis to form what is called the mediastinum testis.

8. Spermatogenesis The seminiferous tubules, in which the sperm are produced,  constitute  about 90 percent of the testicular mass. In the young male the tubules are simple and composed of undeveloped sperm-producing cells ( spermatogonia ) and the  Sertoli cells . In the older male the tubules become branched, and spermatogonia are changed into the fertile sperm cells after a series of transformations called  spermatogenesis . The Sertoli cells found in both young and adult males mechanically support and protect the spermatogonia. Each seminiferous tubule of the adult testis has a central lumen, or cavity, which is connected to the  epididymis  and spermatic duct ( ductus deferens ). Sperm cells originate as spermatogonia along the walls of the seminiferous tubules. The spermatogonia mature into spermatocytes, which mature into spermatids that mature into spermatozoa as they move into the central lumen of the seminiferous tubule. The spermatozoa migrate, by short contractions of the tubule, to the mediastinum testis; they are then transported through a complex network of canals (rete testis and efferent ductules ) to the epididymis for temporary storage. The spermatozoa move through the epididymis and the spermatic duct to be stored in the  seminal  vesicles for eventual  ejaculation  with the  seminal fluid . Normal men produce about one million spermatozoa daily. In animals that breed seasonally, such as sheep and goats, the testes regress completely during the nonbreeding season and the spermatogonia return to the state found in the young, sexually immature males. Frequently in these animals the testes are drawn back into the body cavity except in the breeding season, when they again descend and mature; this process is known as recrudescence.

9. S permatogenesis spermatogenesis , the origin and  development  of the  sperm cells  within the male  reproductive  organs, the  testes . The testes are composed of numerous thin tightly coiled tubules known as the  seminiferous tubules;  the sperm cells are produced within the walls of the tubules. Within the walls of the tubules, also, are many randomly scattered cells, called  Sertoli cells , that function to support and nourish the immature sperm cells by giving them nutrients and blood products. As the young germ cells grow, the Sertoli cells help to transport them from the outer surface of the seminiferous tubule to the central channel of the tubule. Sperm cells are continually being produced by the testes, but not all areas of the seminiferous tubules produce sperm cells at the same time. One immature germ  cell  takes as long as 74 days to reach final maturation, and during this growth process there are  intermittent  resting phases. The immature cells (called  spermatogonia ) are all derived from cells called  stem cells  in the outer wall of the seminiferous tubules. The stem cells are composed almost entirely of nuclear material. (The nucleus of the cell is the portion containing the chromosomes.) The stem cells begin their process by multiplying in the process of cell duplication known as  mitosis . Spermatogonia destined to develop into mature sperm cells are known as primary sperm cells. These move from the outer portion of the seminiferous tubule to a more central location and attach themselves around the Sertoli cells. The primary sperm cells then develop somewhat by increasing the amount of  cytoplasm  (substances outside of the nucleus) and structures called organelles within the cytoplasm. After a resting phase the primary cells  divide into a form  called a secondary sperm cell. During this  cell division  there is a splitting of the nuclear material. In the nucleus of the primary sperm cells there are 46 chromosomes; in each of the secondary sperm cells there are only 23 chromosomes, as there are in the egg. When the egg and sperm  combine  and their chromosomes unite, the characteristics of both individuals blend and the new organism starts to grow. The secondary sperm cell still must mature before it can fertilize an egg; maturation entails certain changes in the shape and form of the sperm cell. The nuclear material becomes more condensed and oval in shape; this area develops as the head of the sperm. The head is covered partially by a cap, called the acrosome, which is important in helping the sperm to gain entry into the egg. Attached to the opposite end of the head is the tail piece. The tail is  derived  from the secondary sperm cell’s cytoplasm. In the mature sperm, it consists of a long, slender bundle of filaments that propel the sperm by their undulating movement. Once the sperm has matured, it is transported through the long seminiferous tubules and stored in the  epididymis  of the testes until it is ready to leave the male body.

10. S perm sperm , also called  spermatozoon , plural  spermatozoa , male reproductive  cell , produced by most animals. With the exception of  nematode  worms, decapods (e.g., crayfish), diplopods (e.g., millipedes), and mites, sperm are flagellated; that is, they have a whiplike tail. In higher vertebrates, especially mammals, sperm are produced in the  testes . The sperm unites with ( fertilizes ) an ovum (egg) of the female to produce a new  offspring . Mature sperm have two distinguishable parts, a head and a tail. The head of the sperm varies in shape for each  animal  species. In humans it is flattened and almond-shaped, four to five micrometres long and two to three micrometres wide (there are about 25,000 micrometres in an inch). The head portion is mainly a cell nucleus; it consists of genetic substances, called  chromosomes , which are responsible for transmitting specific characteristics of an individual, such as the colour of eyes, hair, and skin. In each body cell of healthy humans, there are 46 chromosomes, which are responsible for the individual’s general physical makeup. The sperm cells have only 23 chromosomes, or half of the usual number. When a sperm cell unites with the  ovum , which also has 23 chromosomes, the resulting 46 chromosomes determine the offspring’s  characteristics . The sperm cells also carry the X or Y chromosome that determines the  sex  of the future child. Covering the head of the sperm is a cap known as the  acrosome , which contains enzymes that help sperm to enter an egg. Only one sperm fertilizes each egg, even though 300,000,000 to 400,000,000 sperm are contained in an average  ejaculation . Each egg and sperm produced has slightly different genetic information carried in the chromosomes; this accounts for the differences and similarities between children of the same parents.

11. Menstruation – Definition In a life cycle, a woman’s body is vulnerable to a variety of changes. The cycle of these changes occur in women every month, positively for pregnancy is called the menstrual cycle. When an ovum is unfertilized, the uterus lining sheds and leads to a hemorrhage, called menstruation.

12. In a girl, menstruation starts from the age of 10 to 15 when she attains puberty and this beginning is known as menarche. The ending of menstruation is known as menopause which takes place at the age range of 50. The first day of bleeding is marked as the first day of a menstrual cycle and the period from one menstrual cycle to another can vary from 28 to 30 days.

13. Phases of the Menstrual Cycle The menstrual cycle is divided into four phases, namely: Menstrual phase:  Day 1, uterus lining which is prepared for implantation starts to shed which lasts 3 to 5 days. Follicular phase:  In this phase, the primary follicle starts developing into a mature Graafian follicle. The endometrium also starts proliferating. The uterus starts preparation for another pregnancy. Ovulatory phase:  Mid-cycle phase, this is the phase in which ovulation takes place i.e., day 13-17. The end of the follicular phase along with the ovulation period defines the fertilization period. Luteal phase:  It is the post-ovulation phase, where the fate of the corpus luteum is decided. If fertilization occurs, pregnancy starts. If fertilization doesn’t occur, it marks the onset of another cycle.

14. Role of Hormones in Menstrual Cycle The chemical messengers in our body called hormones, released by various endocrine glands are responsible for many changes in a human body. Menstruation is a slave to certain hormones. Every phase of the menstrual cycle is influenced by a  female hormones  namely estrogen, progesterone, FSH and LH. The variation in the level of each of these hormones decides the phase which a girl undergoes. Let’s have a look at the role of hormones in the menstrual cycle with the help of a diagram.

15. Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are secreted by the anterior pituitary. FSH stimulates the growth of ovarian follicles that secrete estrogen. Progesterone is secreted by the corpus luteum.

16. As we can see in the above diagram, the secretion of FSH and LH gradually increases during the follicular phase. They stimulate the development of follicles and the release of estrogen from them. Estrogen stimulates the proliferation of the endometrium. The level of LH and FSH peaks in the middle of the cycle. LH induces ovulation. There is a sudden surge in LH level just before ovulation. After ovulation, the ruptured follicle develops into the corpus luteum, which secretes progesterone, hence the level of progesterone increases in the luteal phase. Progesterone is required for the maintenance of the endometrium for implantation. In the absence of fertilization, corpus luteum regresses and progesterone level decreases. It leads to the disintegration of the endometrium and menstrual flow occurs.

17. Frequently Asked Questions What is the duration of a menstrual cycle? The duration of a menstrual cycle is usually 28 days. But, under different physiological conditions, it may vary anywhere between 20 and 40 days. What is ovulation? Ovulation is a process by which the Graafian follicle ruptures with the consequent discharge of the ovum into abdominal cavity. This phase is primarily influenced by the luteinizing hormone. It occurs on the 14th day of menstrual cycle in a normal cycle of 28 days. During this process, the ovum enters the fallopian tube. What is corpus luteum? Corpus luteum is a glandular yellow body developed from the ruptured Graafian follicle after the release of the ovum.