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0:06 where you can revise biology topics from
0:10 the Cambridge IGCSE syllabus
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0:22 this video summarizes chapter 10
0:37 a transmissible disease is a disease in
0:40 which a pathogen can be passed from one
0:47 a pathogen is transmitted by direct
0:50 contact including Through Blood and
0:52 other body fluids
0:55 so if a person directly gets in contact
0:57 with the sufferer they might also get
1:01 infected and may spread the disease
1:04 examples include chickenpox that can
1:08 spread just by touching or HIV that
1:12 requires sexual contact for spreading
1:16 a pathogen can also be transmitted
1:19 indirectly including from contaminated
1:24 surfaces food animals and Air
1:27 so indirect contact transmission occurs
1:29 when there is no direct human to human contact
1:30 contact
1:34 examples include getting infected by
1:37 eating contaminated food or through a
1:39 mosquito that may be carrying the
1:42 pathogen or even by inhaling droplets
1:45 that are spreading the air through
1:47 coughs and sneezes from an infected person
1:50 person
1:53 the body defends itself against disease
1:56 in several ways
1:59 kin the skin acts as a physical barrier
2:02 to prevent pathogens from entering our
2:06 body if the skin gets wounded it
2:08 immediately starts healing itself
2:16 s in the nose nose hairs act as a
2:19 natural filter to prevent the entry of
2:30 mucus mucus is a sticky substance so it
2:32 traps pathogens before they can enter
2:36 the lungs the trapped pathogen may be
2:39 removed by blowing the nose swallowing Etc
2:47 stomach acid stomach acid is a chemical
2:51 barrier against infection stomach acid
2:54 contains hydrochloric acid which is
2:57 strong enough to kill pathogens that may
3:07 and finally white blood cells
3:09 white blood cells defend the body
3:12 against infections they fight off
3:16 infections by carrying out phagocytosis
3:19 and antibody production
3:22 in the previous video we learned that
3:24 there are two types of white blood cells
3:28 phagocytes and lymphocytes
3:31 phagocytes engulf and digest pathogens
3:34 this is called phagocytosis
3:38 lymphocytes produce antibodies we will
3:41 learn more about this shortly
3:44 the simplest way to prevent disease is
3:47 to stop pathogens from spreading
3:50 the following measures play an important
3:52 role in controlling the spread of disease
3:54 disease
3:57 a clean water supply
4:00 hygienic food preparation
4:04 good personal hygiene
4:07 waste disposal
4:15 so a clean water supply would control
4:17 the spread of disease because
4:20 contaminated water and poor sanitation
4:23 are linked to the transmission of
4:26 diseases such as cholera diarrhea
4:29 dysentery and typhoid
4:32 so having clean water means being able
4:40 hygienic food preparation
4:43 washing hands before handling food and
4:46 making sure the surfaces and utensils
4:49 are clean before cooking food thoroughly
4:54 at high temperatures help kill pathogens
4:57 covering food ensures that flies can't
4:59 land on it thereby making it difficult
5:02 for them to transfer the germs they carry
5:08 good personal hygiene washing hands with
5:11 soap covering the mouth when sneezing or
5:14 coughing washing hands after going to
5:17 the toilet are good personal hygiene
5:21 practices to follow and helps avoid the
5:29 waste disposal when rubbish is exposed
5:31 it attracts flies which may carry
5:35 disease so rubbish must be covered and
5:42 sewage treatment homes and other
5:44 buildings must have a proper sewage
5:47 disposal method to remove feces from
5:50 toilets safely
5:52 sewage should be treated to kill
5:55 pathogens before being disposed off in
6:03 let's learn about active immunity
6:06 active immunity is a defense against a
6:09 pathogen by antibody production in the body
6:11 body
6:15 active immunity is gained after an
6:17 infection by a pathogen
6:24 so as we know a pathogen is a
6:27 disease-causing organism
6:30 each pathogen has a uniquely shaped
6:33 marker on the surface of their membranes
6:36 called antigens
6:39 it is very important to understand that
6:43 antigens are very specific in shape
6:46 every pathogen is unique because they
6:49 have differently shaped antigens on
6:52 their cell surfaces
6:56 each pathogen has its own antigens which
6:59 have specific shapes
7:02 lymphocytes produce proteins called
7:05 antibodies which are a complementary
7:08 shape to the antigens on the surface of pathogens
7:14 antibodies are proteins that bind to
7:18 antigens leading to direct destruction
7:20 of pathogens
7:24 or marking of pathogens for Destruction
7:33 specific antibodies have complementary
7:37 shapes which fit specific antigens
7:40 so let's look at an example let's say
7:43 there's a pathogen with antigen a
7:46 lymphocyte a has receptors that have a
7:50 complementary shape to antigen a
7:54 lymphocyte a gets activated and produces
7:57 antibodies that have a complementary
8:00 shape to antigen a
8:03 these antibodies can lock onto antigen a
8:06 and Destroy them
8:09 the antibodies made by lymphocyte B on
8:12 the other hand will not be able to fit
8:22 so how do the antibodies destroy the pathogen
8:25 pathogen
8:27 they attach themselves to the antigen
8:30 and cause them to Clump or be stuck together
8:32 together
8:35 this makes it difficult for the pathogen
8:42 then they can be killed directly
8:46 or marked for Destruction by phagocytes
8:49 the antibody sends a chemical signal for
8:52 phagocytes to come and engulf the pathogen
8:54 pathogen
8:56 so how do phagocytes destroy the pathogen
8:57 pathogen
9:00 we learned in the previous video that
9:03 phagocytes engulf pathogens by a process
9:06 called phagocytosis
9:08 so basically when a phagocyte comes
9:12 across a germ or pathogen it engulfs or
9:14 surrounds it completely taking it inwards
9:16 inwards
9:19 then it releases digestive enzymes on it
9:22 which digests the pathogen and destroys it
9:30 lymphocytes that have made antibodies
9:33 for a particular pathogen also produce
9:36 memory cells
9:38 these are cells that remain in the blood
9:43 even after the infection is over
9:45 they are able to quickly produce the
9:48 original antibodies if they were to come
9:51 across the same pathogen again
9:54 this is how people can become immune to
9:57 certain diseases after only having them once
9:58 once
10:02 an example is chickenpox most people who
10:05 have had chickenpox will be immune to
10:08 the disease for the rest of their lives
10:11 therefore memory cells give long-term immunity
10:14 immunity
10:17 let's move on to vaccination
10:20 vaccination is a way of protecting the
10:23 body against harmful diseases before we
10:26 come into contact with them
10:30 the process of vaccination is as follows
10:33 weakened pathogens or their antigens are
10:35 put into the body
10:38 since the pathogen is weak it cannot
10:40 cause illness but it can trigger an
10:47 the antigens stimulate an immune
10:50 response by lymphocytes which produce antibodies
10:52 antibodies
10:55 memory cells are produced that give
10:57 long-term immunity
11:00 the memory cells remain in the blood and
11:02 will quickly respond to the antigen if
11:05 it is encountered again in an infection
11:08 by a live pathogen
11:12 so vaccination is done to stimulate the
11:22 so once again weakened pathogens are put
11:24 into the body
11:26 the antigens stimulate the lymphocytes
11:29 to produce antibodies
11:32 and memory cells are produced that give
11:35 long-term immunity
11:38 what is the role of vaccination in
11:41 controlling the spread of diseases
11:44 the effectiveness of a vaccine in a
11:47 population depends on the proportion of
11:53 when the majority of a population is
11:56 vaccinated against a pathogen it breaks
11:59 the pathogens Chain of Infection
12:02 this means that the pathogen will have
12:05 fewer places to breed and therefore it
12:09 is unable to pass from person to person
12:12 hence vaccination prevents the spread of
12:23 now let's learn about passive immunity
12:26 passive immunity is a short-term defense
12:29 against a pathogen by antibodies
12:32 acquired from another individual
12:34 examples of where these antibodies may
12:36 be obtained are
12:39 from across the placenta antibodies from
12:42 mothers are passed to their unborn
12:45 babies through the placenta
12:52 breastfeeding is important for the
12:54 development of passive immunity in infants
12:56 infants
12:58 antibodies pass from the mother to
13:01 infant through breast milk
13:04 this is important because a baby's
13:07 immune system is not well developed and
13:09 so the mother's antibodies can protect
13:13 it against any diseases to which she is
13:15 immune for the first few months of its
13:18 life until their immune system is stronger
13:24 passive immunity is a fast acting
13:27 short-term defense
13:30 memory cells are not produced in passive immunity
13:37 now let's learn about cholera
13:40 cholera is a disease caused by a
13:42 bacterium which is transmitted in
13:45 contaminated water
13:48 cholera causes diarrhea which is the
13:56 how does this happen
13:59 the cholera bacteria attached to the
14:02 wall of the small intestine
14:10 the toxin causes the cells lining the
14:13 intestine to secrete chloride ions into
14:16 the small intestine
14:19 this causes the water potential inside
14:22 the intestine to reduce
14:25 the water potential in the cells lining
14:28 the intestine is higher therefore water
14:30 moves from the cells to inside the small
14:39 large quantities of water are lost from
14:44 the body in watery feces or diarrhea
14:48 this also leads to dehydration and loss
14:50 of ions from the blood
14:54 diarrhea can be effectively treated by
14:57 Oral rehydration therapy
15:00 this is a drink with a small amount of
15:08 so that concludes chapter 10 diseases
15:11 and Immunity hope this video helped you
15:14 thank you for watching and please don't
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