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Genetically a spermatid is same as a spermatozoa, but the two cells are absolutely different in appearance under microscope. Moreover the spermatozoa is highly motile.


Spermatids are formed at the end of meiosis in male gonad, called testes. Spermatids are normal looking animal cell, with haploid number of chromosomes. To transform into a spermatozoa, spermatid must undergo metamorphosis (=spermiogenesis).

Most of the cytoplasm is discarded from spermatid, golgi bodies give rise to a special vesicle where accumulation of lysosomal enzymes takes place and it is now termed acrosome, mitochondrial cloud and a flagella appear so that the cell can become motile.

  • Spermatid is large roundish, regular cell with cell organelles in it. Spermatozoa is needle like, which has three distinct parts: head, middle piece and tail.
  • Spermatid has golgi body, spermatozoa has acrosomal cap: rest of the golgi is discarded during metamorphosis.
  • Nucleus in spermatid is large, round. In spermatozoa, nucleus is dehydrated and oblong in shape.
  • Centrioles are adjacent to nucleus in spermatid, one of which in spermatozoa acts like a basal body as tail filaments arise from it.
  • Mitochondria remain scattered in spermatid. In spermatozoa, a mitochondrial cloud occupies the middle piece.
  • Spermatid is haploid but nonmotile, but spermatozoa can move by using flagellar tail.

Spermatid cannot be used as gamete. Spermatozoa is functional gamete, designed to successfully fertilise an egg cell.

Please read this answer to know more about structure of spermatozoa.




The URT is from the nose to the larynx; the LRT is from the trachea to the alveoli.


The structures of the Upper Respiratory Tract are (in descending order):
1. Nose (or nostrils)
2. Nasal cavity
3. Mouth
4. Pharynx (throat)
5. Larynx (voice box)


The structures of the Lower Respiratory Tract are (descending from the larynx):
1. Trachea (windpipe)
2. Bronchi (one bronchus into each lung)
3. Secondary and tertiary bronchi
4, Bronchioles
5. Alveoli (air sacs surrounded by capillaries for oxygen and carbon dioxide exchange)



Bones and Teeth.


Calcium is the most important and abundant mineral which is found in the parts of our bones and teeth.

  • Our bones and teeth are made up of calcium, thus bones and teeth are the sites of calcium in our body.
  • 99% of calcium is found in bones and teeth.
  • Calcium also helps the nerves, muscles, heart, and other body systems work properly.
  • It helps the muscles in contractions and blood clotting.



Menstrual cycle remains arrested during pregnancy.


  • Menstrual cycle is generally repeated after every 28 days in women of reproductive age. The cycle has distinct preovulatory and postovulatory stages.

  • Oestrogen hormone is secreted from the surrounding tissue of a growing ovarian follicle in preovulatory stage under the influence of follicle stimulating hormone (FSH) of anterior pituitary. Oestrogen helps in thickening of uterine lining by cell proliferation.

  • Rising oestrogen level in blood provides positive feedback for secretion of anther pituitary hormone, namely luteinising hormone (LH).
  • LH leads to bursting of the largest and mature ovarian follicle, disrupting tissues surrounding the follicle. This will:

I) cause drastic lowering of oestrogen level
II) lead to deposition of egg in fallopian tube
III) give rise to an endocrinal structure from empty follicle

  • The new endocrinal structure is called corpus luteum (CL). As ovulation is over, the cycle has now entered post ovulatory stage and CL now starts secreting progesteron.
  • Progesteron helps in maintaining the already thickened uterine lining for a possible implantation of fertilised egg.
  • Pregnancy is possible when female's egg gets fertilised by male's sperms. If fertilisation takes place then there will be implantation of the embryo in uterine lining (within seven days of fertilisation) and this will be beginning of pregnancy.
  • Once implantation of early embryo takes place surrounding tissue of uterus will start releasing a hormone named Human Chorionic Gonadotropin (HCG).
  • HCG provides a positive feedback for corpus luteum of ovary. Thus progesterone secretion continues and as a result the uterine endometrium remains thickened to nurture the implanted embryo.
  • Progesterone is very important for continuation of pregnancy. It is also providing a negative feedback to endocrine system that blocks secretion of FSH. This will cause--

I) no further development of ovarian follicle
II) hence oestrogen level remains low
II) so release of LH and ovulation prevented



  • Maintenance of uterine lining to safe guard a growing embryo means menstrual bleeding will not take place throughout the pregnancy.


The answer is HYPODERMIS, a subcutaneous layer, made of areolar tissue.


The hypodermis is the deepest layer of the skin, and it consists of loose connective tissue called areolar tissue. As stated in the question, it connects the upper layers of the skin (the epidermis and dermis) to underlying muscle, acting like a glue.


Areolar tissue is made up of fibroblast cells which secrete fibrous elements of the matrix i.e. collagen, elastin and reticulin.

There are different immune system cells in areolar tissue: plasma cells, mast cells, and macrophages .

Most importantly, there are fat cells or adipocytes .



The circulatory system pumps blood aroound the body, as you probably already know. But where does the blood come from? The answer is the bone marrow.

Bone marrow is the the soft tissue inside of your bones, and its main job is to create blood cells. There are two type of bone marrow, red and yellow, but it is onlt the red type which creates blood cells. Red marrow produces stem cells, which will then turn into red blood cells, white blood cells or platelets. Because they don't last long, the average adult's bone marrow will produce 222-242 billion blood cells a day.


These cells then enter the circulatory system via small and large blood vessels and veins in the bone. Since bone marrow is found in bones, and bones are part of the skelatal system, the skelatal system is the system that interacts with the circulatory system to create blood.


I hope I helped!

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