Human Reproduction

Human Reproduction

Human reproduction includes the Male reproductive system and Female reproductive system.

1.Male Reproductive System

The scrotum remains connected with the abdomen or pelvic cavity by the inguinal canals. The scrotum is homologous to the labia majora in females.

Cremaster muscles and dortas muscles of the scrotal sac help in the positioning of testes. They also help in maintaining the temperature of the testis(2-3 degree lower than the normal internal body temperature).

Cryptorchidism is the condition when tests fail to descend and inflammation of testis is called orchitis.

Gubernaculum is a fibrous cord that extends from caudal end of the testis to scrotal wall.

Three protective covering surrounds the testis (known as tunica):

  1. Tunica vaginalis (outer covering)
  2. Tunica Albuginea (white fibrous capsule)
    • It sends partitions through its interior surface to divide the testis into lobules.
  3. Tunical vasculosa 

Sperms are produced in seminiferous tubules.

The stratified epithelium of seminiferous tubule is made of three types of cells:

  1. Sertoli cells (Supporting cells)
    • These cells secrete inhibin (a glycoprotein hormone) which is involved in the negative feedback control of sperm production by checking FSH activity.
  2. Spermatogenic cells
  3. Leydig cells (Interstitial cells)
    • These cells secrete testosterone.

Vasa efferentia has large columnar ciliated cells.

Epididymis stores the sperm temporarily and produce essential chemicals required for the nourishment and maturation of sperms.

Vasa deferenta arises from cauda epididymis.

Penial urethra in males transverse through Corpus spongiosum.

Male Accessory Glands:

  1. Seminal vesicles (paired)
    • They secrete an alkaline nutritive seminal fluid which contains fructose, citrate, inositol, prostaglandins and several proteins.
  2. Prostate gland (Single)
    • It secretes a slightly acidic (pH~6.5) milky fluid.
    • The fluid contains calcium, citrate ion, phosphate ion and proteolytic enzymes (Prefibrinolysin, fibrinolysin, and fibrinogenase) and other enzymes like acid phosphatase, amylase, pepsinogen, etc.
  3. Cowper’s glands (Bulbourethral glands) – paired

Semen (pH – 7.5), Bulk of the semen is seminal fluid

  • 10% – Fluid and sperm from vas deference
  • 60% – Fluid from seminal vesicles
  • 30% – Fluid from the prostate gland and small amount of mucus from the bulbourethral gland.

2.Female Reproductive System

Ovaries are primary sex organs of a woman.

They remain attached to the abdominal wall by a ligament called mesovarium.

The free surface of the ovaries is covered by germinal epithelium, which is composed of cubical cells.

 

Fallopian tubes or Oviducts or Mullerian ducts are differentiated into following parts:

  1. Infundibulum
    • Its edges possess finger-like projections called fimbriae, which helps in the collection of ovum after ovulation.
  2. Ampulla
    • It is wider part of the oviduct.
  3. Isthmus

Uterus consist of the following parts:

  1. Fundus
  2. Corpus body
    • It is the lower narrow portion which protrudes into the vagina.
  3. Cervix

Mons pubis or mons veneris is the fleshy elevation above the labia majora, which has pubic hairs.

Clitoris is homologous to the penis.

The areola is the pigmented area that surrounds the nipple in each mammary gland.

In mammary glands, production of milk is stimulated by the hormone Prolactin and the ejection of milk into the ducts o the mammary gland is stimulated by the hormone Oxytocin. The milk contains casein (milk protein).

Homology between organs: Female – Male reproductive system

  • Labia majora – Scrotum/Scrotal sac
  • Clitoris – Penis
  • Glans clitoris – Gland penis
  • Paraurethral/Skene’s gland – Prostate gland
  • Bartholin’s gland – Cowper’s gland

3.Gametogenesis

Spermatogenesis – Production of male gametes or sperms.

  • One primary spermatocyte (2n) produce two Secondary spermatocytes(n).
  • One Primary spermatocyte(2n) give rise to four spermatozoa or mature sperm.
  • One secondary spermatocyte(n) gives rise to two spermatozoa or mature sperm.

Spermiogenesis is the differentiation of spermatid into a mature spermatozoan.

Spermination is the release of sperm from the seminiferous tubule.

Human sperm is first seen by Antonic van Leeuwenhoek in 1677. It is a tadpole-shaped cell of about 2-5 μm in diameter, and 60 μm long.

The sperm head has an acrosomal part which is formed of Golgi complex and contains hydrolytic enzyme sperm lysins (Hyaluronidase and proteinase).

The neck part of the sperm contains a pair of centrioles lying at the right angle to each other: proximal centriole and Distal centriole.Proximal centriole plays a role in the first cleavage of the zygote.

Mitochondria are present in the middle piece of the sperm. It provides energy to sperm for the movement.

Hormonal control of spermatogenesis :

In hormonal control of spermatogenesis, the LH (Luteinising Hormone) acts on Leydig cells and FSH (Follicular Stimulating Hormone acts on the Sertoli cells.

Oogenesis – production of female gametes or eggs.

Primary follicles contain oocyte and begin producing the sex hormone estrogen.

The antrum is the cavity of the Graafian follicle (Secondary follicle mature) with estrogen rich follicular fluid.

Female have about 2 million follicles before birth, but only about 450 eggs develop into secondary oocytes, which are released from the ovary during the menstrual cycle.

One primordial follicle per month develops into a mature follicle in response to the hormone FSH, Known as the Graafian follicle. Within each developing follicle, a primary oocyte starts to develop into an egg.

The maturing oocytes adhere to the wall of follicle through a stalk, cumulus oophorus formed by granulosa cells. Polar bodies formed during oogenesis, are small cells without any role in oogenesis and they eventually degenerate.

Graafian follicle rupture and release the secondary oocyte. After ovulation, the ruptured follicle is converted into corpus luteum, which secretes progesterone.

The ovum possesses three coverings:

  1. Plasma membrane – inner
  2. Zona pellucida – middle (non-cellular glycoprotein)
    • Zona pellucida is the non-cellular, translucent covering of the egg.
    • Fertilizin is a compatibility receptor proteins found in zona pellucida.
  3. corona radiata – outer (cellular)

There are two poles in the egg:

  1. Animal pole – Uppermost pole of an egg that is the site of maturation division.
  2. Vegetal pole – Lower pole of the ovum that is opposite to the animal pole.

4.Menstrual Cycle

Menstrual cycle occurs in three major phases:

  1. Menstrual phase (1-4 days)
  2. Follicular phase or Proliferative phase (5-14 days)
  3. Secretory phase or Luteal phase (15-28 days)
    • Possibility if fertilization is most at initial luteal phase.
    • It is marked by the presence of corpus luteum (yellow body) which secrete hCG (human Chorionic Gonadotropin) hormone during pregnancy.

Menarche is the first menstrual flow or period.

Menopause is the condition in which menstrual cycle stops naturally in a woman.The woman does not remain reproductively active after menopause.The average age of menopause in the woman is 45-50 yrs.

The hormone LH stimulates the corpus luteum to secrete progesterone.

The estrous cycle consists of cyclic changes in the female reproduction system of non-primate mammals.

5.Fertilization

In human reproduction,Fertilization is the union of ovum and sperm and the formation of diploid zygote.

Steps of fertilization process:

  1. Insemination
    • the deposition of sperm into the vagina during sexual intercourse (coitus or copulation).
  2. Capacitation
  3. Penetration of sperm
    • Hyaluronidase enzyme digests hyaluronic acid.

6.Embryonic development

Embryogenesis includes:

  1. Cleavage
    • zygote divide into smaller cells(also called blastomeres)
  2. Morula
    • A solid ball of cells
  3. Blastulation or blastocyst formation
    • The outer peripheral cell enlarges to form trophoblast or trophectoderm.
    • Cells of trophoblasts in contact with the inner cell mass are called cells of Rauber.
  4. Implantation
    • Implantation occurs on days 7-10 in the uterine wall.
    • The trophoblast cells produce lytic enzymes that allow the blastocyst to penetrate into the thick endometrium.
  5. Gastrulation
    • In this, the cell movements(Morphogenetic movements) establish the three primary germinal layers namely ectoderm, mesoderm, and endoderm.
    • Archenteron is the cavity which occurs inside the gastrula and is the future alimentary canal.It opens to the outside through blastopore which later on closes.

Derivatives of the primary germ layers in mammals:

Ectoderm – Lens of eye, inner ear, Brain, spinal cord

Mesoderm – Notochord, Bone, Kidney, Gonads

Endoderm – Liver, pancreas

Foetal Membrane

These membranes are formed from the trophoblast. The four fetal membranes are:

The four fetal membranes are:

  1. Amnion
    • It is a sac that fully encloses the embryo and filled with amniotic fluid. It protects the embryo fro shocks and adhesion.
  2. Allantois
  3. Chorion
    • It completely encloses the developing embryo and extraembryonic tissues. This part is directly connected with blood.
  4. Yolk sac

Placenta-Human reproduction

Placenta consists of the fetal part, the chorion, and maternal part, the decidua basalis.

The human placenta is Hemochorial (the placenta with only three barriers, the maternal part of placenta eroded), Metadiscoidal (the villi are initially distributed uniformly all over the surface but later on get confined to a disc-like area fitting into corresponding depression on the uterine wall), and referred as chorioallantoic placenta because chorion and allantois take part in its formation.

Pregnancy or Gestation period it the time from conception to the day of parturition. In human (280 days), Panther (93 days).

7.Parturition-Human reproduction

Parturition is the act of giving birth. The signal s for parturition originate from the fully developed fetus and the placenta, which induces mild uterine contractions called fetal ejection reflex.

The simulatory reflex between the uterine contraction and oxytocin secretion continues resulting in stronger and stronger contraction which leads to expulsion of the baby.

4th Week  – Heart is formed

12th Week  – Foetus is 56 mm long from head to bottom.

24th Week  – the Legal limit for abortion.

Sexual Reproduction in Flowering Plants

Anatomy of Flowering Plants