Snigdha Goswami

Sliding Filament Theory:  The sliding filament theory explains the mechanism of muscle contraction based on muscle proteins that slide past each other to generate movement. According to the sliding filament theory the myosin filaments of muscle fibres slide past the actin thin filaments during muscle contraction while the two groups of filaments remained at relatively constant at length.  1. I bands are composed of actin filaments and the A Bands principally of myosin filaments. 2. during muscle contraction the actin filaments move into the A bands between the myosin filaments. 3. The backbone of a muscle fibre is actin filaments which extend from z line up to one end of H zone, where they are attached to an elastic component which is named as S filament. 4. Myosin filaments extend from one end of the A band through the H zone up to the other end of the A band. 5. Myosin filaments remain in relatively constant length during muscle stretch or contraction. 6. During stretching o...

Molecular basis of sliding filament theory :  The contraction of skeletal muscle generates the force necessary to move the Skeleton. A contraction is triggered by a series of molecular events known as cross Bridge cycle. I n a skeletal muscle fibre the function of unit contraction is called sarcomere.  A sarcomere shortens when myosin head in thick myofilament forms cross bridges with actin molecules. 1. initiation  :  the formation of a cross Bridge is initiated when calcium ions, released from the sarcoplasmic reticulum binds to troponin. This binding causes troponin to change shape. Tropomyosin moves away from the myosin binding site on actin allowing myosin head to bind and form a cross Bridge. 2. activation   of myosin head :  Activation of myosin head occurs when ATP binds to myosin head and is hydrolysed to ADP and inorganic phosphate. The energy liberated activate the myosin head forcing it into the curved position. 3. Cross Bridge formation : ...

Oogenesis that is formation of ovum of female gamete : Oogenesis starts in the ovary of the female foetus when it is in the womb of her mother. if we zoom into the female reproductive system of the foetus we can see in the ovaries of the female foetus the oogenesis has already started.  the germinal epithelial cells inside the ovary wall of the foetus starts dividing by mitotic cell division and forms  oogonium. This oogonium cells goes through growth phase and forms the primary oocyte inside the ovary of the female foetus.  now the primary oocyte goes through meiosis 1 it gets arrested in prophase 1 of meiosis cell division 1 and stops here until the female foetus borns and becomes a mature woman and comes to the puberty. When it reaches the puberty inside the ovary of the matured female, the cell which got arrested in prophase 1, the primary oocyte, starts dividing again and complete the meiosis 1 and forms secondary oocyte and one polar body tha...

Entamoeba histolytica  is a parasitic protozoan responsible for the disease amoebic dysentry. Entamoeba   histolytica life cycle  : There are two forms - 1. cyst  : non-mobile form  2. trophozoit :  Mobile form   A.Cyst entry :  Injection of food or water contaminated with Entamoeba histolytica cyst will move through the mouth down the oesophagus into the stomach. Cysts are resistant to gastric environment and passes through the stomach. B.Excystation : Each cyst can divide and produce 8 trophozoits the mobile form of Entamoeba histolytica in the small intestine.   C.Multiplication : The trophozoites will then move to colon of large intestine then multiply and colonizes. Entamoeba can cause 2 types of infection :  1.  non-invasive:  90% 2.  invasive  : 10%  1. Non-invasive : Trophozoits remain on the surface of mucus layer of colonic epithelium and multiplies by binary fission. This non-virulent form ...

Immunology is all about our body's mechanism of protection from the harmful pathogens present outside our body in the environment. There are different levels of Defence for protection in our body. The first level of protection that the pathogens coming towards our body faces is called first line of Defence. ( Microbes = any micro-organism both harmful and harmless to human  Pathogen = micro-organism that can cause disease) From where pathogens can enter our body : 1. Skin  : skin covers the internal organs of our body .It is the largest organ covering the most area of our body externally. 2. ear  : hole of the ear is an entrance into the body. 3. Eye: eyes are not covered by the skin and exposed to the environment facing direct contact with pathogens 4. nose:  nostril is an entrance to the Airways which leads towards the internal organ lungs 5. Mouth:  mouth hole is the entrance to the body mainly to the gastrointes...

This is the written form of the video on youtube  Ovarian follicles during oogenesis  . Watch the video for better understanding.  click here Development of oocyte inside ovary:  1. on the over wall the germinal epithelial cells develop into oogonium cells by mitotic cell division. It occurs before the birth of the female. 2. In puberty the oogonium develops into oocyte that is primary oocyte which gets surrounded by follicular cells in the ovary at first it gets surrounded by single layer of follicular cells . at this stage it is called primordial follicle  . 3. now more layers of follicular cells develop surrounding the oocyte .These developing follicles are called growing follicle.   4. Now the follicular cells form an antrum or cavity in between the cells and with this antrum the follicle is called the antral follicle. 5. the antral follicle develops into the most ma...