Homeostasis and response Flashcards
During puberty, reproductive hormones cause
secondary sex characteristics to develop
follicle stimulating hormone (FSH) causes
the maturation of an egg in the ovary
Luteinising hormone (LH) stimulates
the release of an egg
oestrogen and progesterone are involved in
maintaining the uterus lining with oestrogen being made in the ovaries and progesterone by an empty egg called the corpus luteum.
What two hormones in the menstrual cycle are produced by the pituatry gland in the brain?
FSH and LH
FSH stimulates the
development of a follicle in the ovary
Describe the main male reproductive hormone.
Testosterone which is produced in the testes; testosterone stimulates sperm production.
Describe the main female reproductive hormone.
Oestrogen which is produced by the ovaries. Oestrogen plays an important role in the menstrual cycle which begins at puberty, as well as causing physical changes to occur in the body (such as breast development).
During the menstrual cycle,
eggs in the ovaries begin to mature and one is released approximately every 28 days in a process called ovulation.
Describe the stages of the menstrual cycle.
1, During the menstrual cycle, the lining of the uterus builds up and ovulation occurs. The average menstrual cycle is 28 days long and there are four overall stages:
- menstruation: loss of lining from the uterus, occurs at the start of the cycle if no fertilisation has occurred
- The lining starts to thicken
- ovulation occurs around the middle of the cycle (about day 14) , the egg travels down the oviduct towards the uterus
- The lining is maintained ready to accept a fertilized egg.
What four hormones control the events that occur during the menstrual cycle?
Two of these hormones are produced by the pituatry gland in the brain:
- Follicle stimulating hormone (FSH) causes maturation of an egg in the ovary.
- Luteinising hormone (LH) stimulates the release of the egg
- The other two hormones, oestrogen and progesterone, are involved in maintaining the uterus lining with oestrogen being made by the ovaries and progesterone specifically by an empty egg follicle called the corpus luteum.
Interactions of the hormones in the menstrual cycle (if pregnant and not pregnant)
- The pituatry gland produces FSH which stimulates the development of a follicle in the ovary.
- an egg matures inside the follicle and the follicle produces the hormone oestrogen- so FSH stimulates the production of oestrogen
- Oestrogen causes growth and repair of the lining of the uterus wall and inhibits the production of FSH
- When oestrogen rises to a high enough level, it stimulates the release of LH from the pituatry gland which causes ovulation (usually around day 14 of the cycle)
- The follicle becomes a corpus luteum and starts producing progesterone
- Progesterone maintains the uterus lining (the thickness of the uterus wall)
- If the egg is not fertilised, the corpus luteum breaks down and progesterone levels drop
- This causes menstruation (period)
- If fertilisation does occur the corpus luteum continues to produce progesterone, preventing the uterus lining from breaking down (the breakdown of the lining would prevent a pregnancy).
- Once the placenta has developed, it starts secreting progesterone and continues to do so throughout the pregnancy to maintain the lining.
Hormone level graphs explanation
- FSH is released by the pituatry gland and causes an egg to start maturing in the ovary and it also strimulates the ovaries to start releasing oestrogen.
- The pituatry gland is strimulated to release luteinising hormone when oestrogen levels have reached their peak.
- LH causes ovulation to occur and also stimulates the ovary to produce progesterone.
- Oestrogen levels rise from day 1 to peak just before day 14.
- This causes the uterine wall to start thickening and the egg to mature.
- The peak in oestrogen occurs just before the egg is released.
- Progesterone stays low from day 1-14 and starts to rise after ovulation.
- The increasing levels cause the uterus lining to thicken further;a fall in progesterone levels causes the uterus lining to break down (menstruation).
FSH role in the menstrual cycle
- strimulates egg maturation in the follicles of the ovary.
- stimulates follicles in the ovaries to secrete oestrogen.
LH role in the menstrual cycle
- At its peak stimulates ovulation (release of egg into oviduct)
- results in the formation of a corpus luteum.
Oestrogen role in the menstrual cycle
- strimulates the uterus to develop a lining (to replace the lining lost during menstruation).
- Post-ovulation, inhibits FSH and LH production in the pituatry gland.
Progesterone role in the menstrual cycle.
- maintains and thickens lining of the uterus.
- inhibits FSH and LH production.
- If fertilisation doesn’t occur, levels drop and menstruation occurs,
Contraceptive methods aim to
prevent fertilisation and and pregnancy, and include the use of hormones (oestrogen and progesterone) as well as non-hormonal methods (such as the use of barriers or surgery).
Hormones can also be used to
increase the chance of pregnancy occurring when it previously might not have done.
Benefits of contraception
- preventing unwanted pregnancies or pregnancies that may lead to risks to the mother’s health of pregnancies that have occurred as a result of rape.
counter-arguments to contraception
Ethical and religious concerns about making decisions that may or may not lesd to life.
Can issues around contraception be answered by science alone?
No.
Methods of birth control in humans
chemical - contraceptive implant - iud or ius - contraceptive pill Barrier - condom - femidom - diaphragm Natural - abstinence - monitoring body temperature - monitoring changes in cervical mucus Surgical -vasectomy - female sterilisation
Some birth control methods also give protection from
secually transmitted infections
Chemical
- oral contraceptives that contain hormones to inhibit FSH production so that no eggs mature; there are two types;
- the combined pill contains oestrogen and progesterone which is over 99% effective at preventing pregnancy
- High levels of oestrogen inhibit FSH production preventing the maturation and release of eggs
- Progesterone also plays a role in inhibiting the release of mature eggs and stimulates the production of a thick mucus which prevents sperm from reaching any eggs that are released.
- There is also a progesterone-only pill which has fewer side effects.
- Injection, implant or skin patch of slow-release progesterone to inhibit the maturation and release of eggs for a number of months of years.
- Benefits of implants reduce the chance of someone forgetting to take the pill (which should be taken at the same time every day to be most effective)>
- Intrauterine devices (IUD) which prevent implantation of an embryo or release a hormone; there are two types.
- a plastic IUD produces progesterone which stimulates the production of a thick mucus lining preventing sperm from reaching any eggs.
- A copper IUD works by releasing low levels of copper ions which disable sperm cells.
Barrier
- Barrier methods such as condoms and diaphragms prevent the sperm from reaching an egg
- Condoms are the only barrier method that can prevent the spread of sexually transmitted infections.
- Spermicidal agents which kill or disable sperm - only 70-80% effective.
Natural
- abstaining from intercourse when an egg may be in the oviduct
- complete abstinence is the only 100% effective method at preventing pregnancy
- Natural methods involve avoiding intercourse during the most fertile part of the menstrual cycle but they are not as highly effective as fertility cannot be accurately predicted.
Surgical
- Surgical methods of male and female sterilisation
- In a female, the oviducts which connect the ovaries to the uterus (also called the fallopian tubes) can be cut and tied.
- In a male, the sperm ducts (the tube connecting the testes to the penis) can also be cut and tied in a procedure called a vasectomy.
- Both methods are highly effective but there have been a small number of cases where tubes have rejoined.
Infertility
- infertility occurs when a couple find it difficult or are unable to conceive naturally
- This can be a result of insufficient or too low levels of reproductive hormones affecting the development of egg and sperm cells, or as a result of issues with the reproductive system of the female.
Use of hormones to treat infertility
- Artificial hormones are used as part of modern reproductive technologies to treat infertility, particularly when the female is not producing enough eggs, usually as a result of the pituatry gland not producing sufficient FSH to cause egg maturation.
- The hormones FSH and LH are given as a ‘fertility drug’ to stimulate egg production
- An important social issue to consider with this is that several eggs can be released at once so this increases the chance of multiple births (twins, triplets etc)
- It also doesn’t have a particularly high success rate and can be expensive.
IVF treatment
- an alternative treatment is for eggs to be fertilised by sperm outside the body (‘in vitro’ means ‘in glass’) - this is used particularly where there are issues with both male and female fertility.
- The process involves:
. Giving a mother FSH and LH to stimulate the maturation of several eggs
. The eggs are collected from the mother and fertilised by sperm from the father in a laboratory. - The fertilised eggs develop into embryos
- At the stage when they are tiny balls of cells, one or two embryos are inserted into the mother’s uterus (womb).
- The success rate of IVF is low (approximately 30%) but there have been many improvements and advancements in medical technologies which are helping to increase the success rate.
- These advancements include improvements in microscopic techniques and micro-tools that enable single cells to be removed from an embryo for genetic testing to identify if the embryo is healthy or has genetic defaults the couple might want to consider.
Planta produce plant hormones called auxins to
coordinate and control growth
Plants need to be able to grow in response to
light (phototropism) and gravity (gravitropism or geotropism)
How must the shoots grow?
The shoots must grow upwards, away from gravity and towards light, so that leaves are able to absorb sunlight – shoots show a positive phototropic response and a negative gravitropic response.
How must the shoots grow?
Roots need to grow downwards into the soil, away from light and towards gravity, in order to anchor the plant and absorb water and minerals from the soil particles so roots show a negative phototropic response and a positive gravitropic response
Gravitropism and phototropism table
- stimulus- gravity, name of response: gravitropism (sometimes called geotropism), positive response: growth towards gravity (eg: roots) and negative response: growth away from gravity (eg: shoots),
- stimulus- light, name of response: phototropism, positive response- growth towards light (eg: shoots). negative response- growth away from light (eg: roots).
Gravitropism
Growth towards of away from gravitational pull
Phototropism
Growth towards or away from source of light.
Where are auxins produce and where do they diffuse?
-Auxins are produced in the tips of the shoots and the roots; they diffuse to the cells behind the tips.
Effects of auxin
In the shoots auxins promote cell elongation (growth); more auxin = more cell elongation = more growth
In the roots auxins inhibit cell elongation (growth); less auxin = less cell elongation = less growth
The distribution of auxin in the shoots is affected by
light and gravity
The distribution of auxin in the roots is primarily affected by
gravity alone
What happens if a shoot or root is placed in its side?
If a shoot or root is placed on its side, auxins will accumulate along the lower side as a result of gravity; so the uppermost side has a lower auxin concentration
In the shoots, the lower side grows faster the upper side, so the shoot grows upwards
In the roots, the lower side grows slower than the upper side (as auxin inhibits cell elongation and growth in the roots), so the root grows downwards
Unequal distributions of auxin cause unequal growth rates in plant roots and shoots
How auxins control growth in shoots
Auxin is mostly made in the tips of the growing shoots diffuses to the region behind the tip
Auxin stimulates the cells behind the tip to elongate (get larger); the more auxin there is, the faster they will elongate and grow
This is an important point – only the region behind the tip of a shoot is able to contribute to growth by cell division and cell elongation
If light shines all around the tip, auxin is distributed evenly throughout and the cells in shoot grow at the same rate – this is what normally happens with plants growing outside
When light shines on the shoot predominantly from one side though, the auxin produced in the tip concentrates on the shaded side, making the cells on that side elongate and grow faster than the cells on the sunny side
This unequal growth on either side of the shoot causes the shoot to bend and grow in the direction of the light
Positive phototropism in plant shoots is a result of auxin accumulating on the shaded side of a shoot
More plant hormones
Auxins are just one example of hormones found in plants
Gibberellins are important in initiating seed germination – the process that occurs when a seed starts to grow
Gibberellins also have a role in inducing flowering and the growth of fruit
Ethene is a gas released by plants which controls cell division and ripening of fruits
Both gibberellins and ethene are used commercially
definition of homeostasis
Maintaining the same/constant internal environment (bodily functions are working well) by regulating water content level, temperature, ion content and blood glucose level/sugar.
Describe what happens to your body on a hot day
- The thermoregulatory centre (hypothalamus) in the brain and skin receptors will monitor and detect this change
- The blood vessels supplying the skin capillaries will dilate (vasodilation- diameter increases as it widens)
- More blood will flow to the surface of the skin (this is how it can become pink)
- More thermal energy/ heat will be radiated outwards and the body will cool down.
- Hair follicles on the skin will droop/ lie flat.
- Sweating (evaporation of water) also cools the body.
Any deviation is detected by what?
receptors
Pathway
receptor –> coordinator –> effector (nervous connection and blood)
Describe what happens to the human body on a cold day.
- The thermoregulatory centre (hypothalamus) in the brain and skin receptors will monitor and detect this change.
- The blood vessels supplying the skin capillaries will become narrower/ constrict (vasoconstriction)
- Less blood will flow to the surface of the skin and less thermal energy will be radiated outwards.
- The body will restore homeostatic equilibrium.
- Shivering (muscular contractions) will release energy and hair follicles will stand upright/ erect.
Describe what happens to the human body when the blood glucose level/ sugar level is high.
-When the blood glucose level is high, the pancreas will detect this change. The pancreas will secrete more insulin which will convert the excess glucose into glycogen (insoluble) and this will be stored in the muscles and liver for further use.
livers induce
the conversion of glucose into glycogen
LH stimulates
the release of the egg
FSH
- maturation of the egg and stimulates ovary to produce oestrogen
oestrogen
- causes lining of uterus to develop
- inhibits FSH
- stimulates the release of LH
Progesterone
- maintains the lining of the uterus
- inhibits the release of both FSH and LH
Where is auxin produced?
the shoot tip
photoreceptor cells
rod and cone cells
some sugarcanes have
more gibberellin
gibberellin induces
germination and cell elongation
auxin induces
cell elongation
auxin can be used as
weed killers, rooting powders and tissue culture
ethene
used to control fruit ripening
Gibberellin
increase yield of sugar cane, increase fruit size, end seed dormancy
Glucose level high
osmosis- crenation
Insulin will cause
glucose in liver to convert to glycogen
Glucose level low
osmosis- cytolysis
Glucagon will cause
glycogen in liver to be converted back into soluble glucose which enters the bloodstream
Type 1 diabetes
Your immune system is attacking cells which produce insulin
What is another name for endocrine system?
hormonal system
