Apoptosis

Events of apoptosis

• enzymes breaks down the cell cytoskeleton
• cytoplasm becomes dense with organelles tightly packed
• the cell surface membrane changes and small bits called blebs form.
• chromatin condenses and nuclear envelope breaks. DNA breaks into fragments
• the cells breaks into vesicles that are taken up by phagocytosis. the cellular debris is disposed of and does not damage any other cells or tissues

How it's controlled

• Apoptosis is controlled by cell signalling
• some from the inside the cell and some from outside
• these include cytokines made by cells of the immune system, hormones, growth factors and nitric oxide
• nitric oxide works by making the inner mitochondrial membrane more permeable to hydrogen ions
• it would prevent the formation of the proton gradient needed for ATP synthesis
• proteins are released into the cytosol
• these proteins bind to apoptosis inhibitor proteins and allow the process to take place

Apoptosis and development

• apoptosis is an important part of the tissue development. Extensive division and proliferation is followed by pruning through apoptosis. 
• Excess cells undergo apoptosis and their components are reused. Different tissues use different signals to induce it.
• Examples:the removal of ineffective or harmful T lymphocytes during the development of the immune system

How often does apoptosis take place?

• In children between 8-14 years old, 20-30 billion cells per day undergo apoptosis.
• in a year this is equivalent to the total body ass
• in adults the figure is around 50-70 million cells per day
• the rate of cell death should = the rate of mitosis
• however, not enough apoptosis leads to the formation of tumours. 
• too much leads to cell loss and degradation
• cell signalling helps maintain the right balance