homeostasis, puberty, plant hormones Flashcards
2 types of nervous systems in the human nervous system
Central nervous system (CNS)
peripheral nervous system (PNS)
Central nervous system (CNS)
Central nervous system (CNS) – the brain and spinal cord - coordinator for rest of the nervous system - contains relay neurones
peripheral nervous system (PNS)
peripheral nervous system (PNS) – all of the nerves in the body - each nerve is made up of lots of specialised cells called neurones - contains sensory and motor neurones
neurone structure - cell body
contains most cellular structures e.g. nucleus, mitochondria
neurone structure - dendrites
highly branched to form connections with other neurones at synapses
neurone structure - axon
long fibre of neurone
neurone structure - axon terminal
highly branched to form connections with other neurones at the nerve ending
reflex response
- doesnt involve brain as coordinator - uses spinal cord
- involuntary/ automatic meaning that they happen without you consciously deciding to carry out the response
- Very rapid & automatic to protect the body from potential damage such as touching a hot surface
sensory neurone
long
cell body containing nucleus at center of axon
relay neurone
short + highly branched
Has an unmyelinated axon -important for role in CNS
motor neurone
cell body at top of cell
reflex arc example - stepping on sharp pin
- Pressure of pin = stimulus & is detected by receptor on the sole of the foot
- Triggers the electrical nerve impulse to start and travel up the sensory neuron to the spinal cord which acts as the coordinator
- The impulse passes across the synapse to a relay neurone in the CNS
- The spinal cord sends the impulse to the motor neurone via another synapse
- Another impulse is simultaneously sent to the brain to ensure there is a conscious awareness of the stimulus but the brain isn’t involved in the response.
- the motor neurone sends the impulse to the effector which contracts and brings about the response of moving the foot away from the pin
K
Some reflexes are not coordinated by the spinal cord such as the eyes.
Some reflex talks don’t have really new ones so the impulse is able to very quickly be transmitted straight from the sensory neurone to the motor neurone
synapses
Neurones never touch each other, they are separated by junctions (gaps) called synapses
In a reflex arc, there are synapses between the sensory and relay neurones, and the relay and motor neurones
Chemicals called neurotransmitters (such as dopamine and serotonin) are released into the synaptic cleft and diffuse across it (down a concentration gradient)
synapse process
brain - cerebral cortex
this is the outer layer of the brain which is highly folded and is responsible for higher-order processes such as intelligence, memory, consciousness and personality
brain - cerebellum
this is underneath the cerebral cortex and is responsible for balance, muscle coordination and movement
brain - medulla
this region controls unconscious activities such as heart rate and breathing
brain - pituitary gland
responsible for regulating many body functions such as controlling the activity of other glands
Mapping regions of the brain - 3 methods
Neuroscientists have been able to map the regions of the brain to particular functions by…
studying patients with brain damage
electrically stimulating different parts of the brain
using MRI scanning techniques
Mapping regions of the brain - studying patients with brain damage
Patients with brain damage can be studied to see what effect it has on them physically or on their personality or capabilities
Mapping regions of the brain - electrically stimulating different parts of the brain
Tiny electrodes can be pushed into different parts of the brain, tiny jolts of electricity stimulate these regions and the effects can be observed
For example, if a region in the medulla responsible for movement is stimulated, the movement caused can be observed
Mapping regions of the brain - MRI scans
- MRI scanners are very important diagnostic tools used to study the brain and other regions of the body using magnetic fields and the effect these have on protons in the water molecules of the body
- Functional MRIs can produce images of different regions of the brain that are active during different activities like listening to music or recalling a memory (the scanners can detect changes in blood flow – more active regions of the brain have increased blood flow)
retina
Contains receptor cells called rods and cones, which are sensitive to light
fovea
the maximum density of cone cells is found here, as most of the light from the lens is refracted to this point.
sclera
tough outer coating to protect the eye.
cornea
where 70% of the light is refracted into the eye
optic nerve
Where the information from the receptor cells collects and the nerve impulses from the Retina are carried to the brain
iris
Controls the amount of light entering the eye.
ciliary muscles and suspensory ligaments
changes the shape of the lens.
pupil
Hole which lets light into the eye
lens
Reflects light onto the retina.
pupil dialation
Stimulus - not enough light
Receptor - rod and cone cells
Coordinator – brain
Effector - radial muscles contract & circular muscles relax.
Response - people get bigger and more light enters
pupil contraction
Stimulus – too much light
Receptor - rod and cone cells
Coordinator – brain
Effector - radial muscles relax & circular muscles contract.
Response - people get smaller and less light enters
To focus on a near object:
To focus on a near object:
a lot of focusing is needed so
so ciliary muscles contract
suspensory ligaments loosen
lens is thicker and refract light strongly
rays of light converge on the retina
to focus on a distant object:
to focus on a distant object:
less focusing is needed
so ciliary muscles relax
suspensory ligaments are pulled tight
lenses is thinner & only slightly refract light rays
rays of light converge on the retina
Myopia
Myopia is caused because the lens is too strong, or the eyeball is too long.
one way to correct myopia is to use spectacles or hard or soft contact lenses with concave lenses.
In myopia the image is focused in front of the retina
hyperopia
hyperopia is caused because the lens is too weak, or the eyeball is too short
One way to correct hyperopia is to wear spectacles or hard or soft contact lenses with convex lenses
in hyperopia the image is focused behind the retina
Laser surgery
lasers can be used to change the shape of the cornea (changing how it refracts light onto the retina) although like all surgical procedures there is risk of unexpected damage occurring during the procedure which could lead to worse vision or an infection
For myopia: the cornea is slimmed down, reducing the refractive power
For hyperopia: the cornea shape is changed so the refractive power is increased
accommodation
The ability of the eye to change its focus by adjusting the curvature of the lens
Lens replacement surgery
Lens replacement surgery completely replaces the lens of the eye with a plastic artificial lens (rather than changing the shape of the cornea during laser eye surgery) but this procedure is more invasive than laser surgery and carries a risk of damage occurring to the retina leading to complete sight loss
thermoregulatory centre
Body temperature is monitored and controlled by the thermoregulatory centre in the brain
The thermoregulatory centre contains receptors sensitive to the temperature of the blood
The skin contains temperature receptors and sends nervous impulses to the thermoregulatory centre
Monitoring of Body Temperature
The human body needs to maintain a temperature at which enzymes work best, around 37°C
Processes such as respiration release energy as heat; and the body loses heat energy to its surroundings – the energy gained and lost must be regulated to maintain a constant core body temperature
If the body temperature is too high then
blood vessels dilate (vasodilation) - more blood flow to skin so more heat to be carried by the blood to the skin, where it can be lost to the air increasing heat loss
Sweat glands excrete sweat which cools the skin as it evaporates
Hairs lie flat against the skin allowing air to freely circulate reducing the insulating effect of air against the skin increasing heat loss
If the body temperature is too low then
blood vessels constrict (vasoconstriction) - less blood flow to skin so less heat to be carried by the blood to the skin, where it can be lost to the air reducing heat loss
sweating stops
Hair erector muscles will contract so hair stands upright trapping air around the skin so more insulation and less heat loss
Skeletal muscles contract rapidly and shivering occurs - this is involuntary and requires energy from respiration (which releases energy as heat)
Homeostasis
Homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes
e.g. enzyme action and all cell functions
examples of homeostasis
Blood glucose concentration
Body temperature
Water levels
Control of Homeostasis
Maintaining controlled conditions within the body is involuntary (automatic) control
This means that the brain stem (or non-conscious part of the brain) and the spinal cord are involved in maintaining homeostasis – you don’t consciously maintain your body temperature or blood glucose level
control systems for homeostasis
These automatic control systems may involve nervous responses or chemical responses
All control systems include:
* Cells called receptors, which detect stimuli (changes in the environment)
* Coordination centres (such as the brain, spinal cord and pancreas) that receive and process information from receptors
* Effectors (muscles or glands) which bring about responses which restore optimum levels
Hormones
A hormone is a chemical Messenger. This means that they send signals around the body in order to bring about a response in a target organ.
pituitary gland
The pituitary gland is called the master gland because the hormones it secretes control a lot of the other glands in the endocrine system e.g. ADH. It is position just below the brain.
thyroid gland
The thyroid gland in the throat, secretes many hormones, an example of, which is thyroxine, which helps to control the rate of metabolism in the body.
pancreas
The pancreas has many jobs such as releasing enzymes for digestion. But in addition to this, it can also make hormones. Insulin is an example which helps the lower the amount of glucose in the blood.
adrenal gland
The adrenal gland, sit on top of the kidneys and can secrete adrenaline which helps the control our fight or flight response.
reproductive hormones
The testes and males release testosterone. And the ovaries in females release oestrogen. Both of these hormones, controlled a secondary sexual characteristics, that aren’t present in a person from birth
How are hormones transported across the body
gland = yellow cells
hormone = green triangles
The hormones are synthesised in the cells of the gland. Once the hormones have been synthesised, they are secreted into the blood and travelled through the circulatory system until they meet their target cells. The target cells have protein receptors on the outside that can bind to the hormone in a similar way.
when the hormone binds to the receptor on the target cell. It triggers chemical reactions in the target cells that brings about the required response.
It is possible for one hormone to have lots of different target cells. For example, there are lots of different types of target cells that respond to the hormone adrenaline because adrenaline causes lots of reactions in different parts of the body.
Any cell that does not need to respond to the hormone If called a non target cell and does not have any receptors that can bind to the hormone
how is the blood glucose level controlled
step 1 in kideys making urine - filtration
the process starts with filtration which is where some of the liquid part of the blood is forced from the glomerulus which is this tangle of blood vessels into the bowman’s capsule which is the start of the tubule
importantly though only very small substances can be filtered through to the bowman’s capsule e.g., water, amino acids, urea, glucose and ions not anything large like cells or proteins
Overall only about 20 percent of the plasma in the blood is filtered through to the bowman’s capsule as it passes
through the glomerulus. The rest of the blood just carries on
through the blood vessels
overview of kidneys function
blood constantly cycles through the kidneys passing in through the renal arteries and out through the renal veins from this blood the kidneys produce urine which passes down the ureters and is stored in the bladder until we urinate it out through the urethra.
nephron location
step 2 in kideys making urine - selective reabsortion
the fluid passes along the tubules and the kidneys reabsorb all the things that they want back into the blood vessels by selective reabsortion:
* all of glucose & amino acids
* some of water & ions
* no urea
step 3 in kideys making urine - final stage
The collecting duct receives fluid from many nephrons and any fluid that passes out of the collecting duct is classed as urine.
The urine passes down the ureter to the bladder and can then be released as waste
How does a dialysis machine work?
In a dialysis machine the person’s blood flows alongside a partially
permeable membrane, surrounded by dialysis fluid.
The partially permeable membrane allows things like ions and waste substances through, but not big molecules like proteins (just like the membranes in the kidney). The dialysis fluid has the same concentration of dissolved ions and glucose as healthy blood. This means that useful dissolved ions and glucose won’t be lost from the blood during dialysis. Only waste substances (such as urea) and excess ions and water diffuse across the membrane.
The dialysis fluid constantly flows in and out of the machine to make sure the fluid in the machine always has the same concentration as healthy blood.
Kidney transplants cons - rejection
A problem of kidney transplants is that the donor kidney can be rejected by the recipient’s immune system - this happens when antigens on the donor kidney aren’t recognised as being part of the body by the recipient’s white blood cells. The white blood cells produce antibodies to attack the donor cells as a result
female reproductive system
Eggs are kept inside the ovaries and after ovulation they transported along one of the fallopian tubes over to the uterus. If the egg was fertilized during its journey, then it
would implant into the uterus lining, otherwise it would break down and pass out.
menstual cycle
(28 days)
stage one - menstruation: when uterus lining breaks dwon- is a period of bleeding that normally lasts about four days.
Stage two-( when oestrogen levels are rising) : is when the uterus lining starts to build up again and becomes a thick spongy layer with lots of blood vessels in it. It lasts around ten days up to day 14- when egg is released- and its role is to prepare the uterus lining for the zygote (fertilized egg) because if there is a fertilised egg, it implants into the uterus lining.
Stage three is ovulation (LH produced) - this takes place in a single day and involves the egg being released from one of the ovaries.
stage four (progesterone levels increase)- stretches all the way to day 28 and it involves maintaining the lining of the uterus.
end of cycle- if no fertilized egg has made it to the uterus then the uterus wall would start to breakdown so we’ll be back to stage 1 and cycle repeats. if there was a fertilized egg then it would implant into the uterus lining and slowly develop into a fetus
Oestrogen
Oestrogen is secreted in the ovaries and it stimulates uterus lining to thicken, ready to recieve zygote. stops FSH production. controls progress of maturing follicle, so has a small ‘spike’ just before ovulation. hormone targets- uterus
progesterone
after ovulation, the remainder of the follicle becomes the corpus luteum. The corpus luteum produces progesterone. It maintains the thickness of the uterus lining. If fertilisation occurs progesterone levels remain high, and placenta takes over progesterone production during pregnancy. If no fertilisation- ovum + corpus luteum break down- progesterone levels drop- uterus lining breaks down- menstruation. hormone targets- uterus
luteinizing hormone LH
luteinizing hormone -LH- is secreted from the pituitary gland. Stimulates ovulation (release of ovum from ovary), on day 14. hormone targets- ovaries
follicle stimulating hormone FSH
follicle stimulating hormone FSH is secreted from the pituitary gland. It stimulates one of the eggs to mature/develop in one of the ovaries. Stimulates oestrogen production. hormone targets- the follicles in the ovaries
how hormones interact with each other during menstual cycle
once menstruation over:
FSH is secreted by the pituitary gland which stimulates egg development in one of the ovaries.
FSH also stimulates the ovaries to produce/secrete oestrogen which is why we see higher levels of FSH just before oestrogen starts to increase.
As the oestrogen level starts to increase it inhibits FSH production while stimulating the uterus lining to thicken. when oestrogen levels get high/ spike just before day 14, it stimulates the pituary gland to secrete LH, leading to ovulation.
The empty follicle after ovulation- corpus luteum- produces progesterone which inhibits pituary gland secreting LH and FSH while maintaining the uterus lining.
If fertilisation- progesterone levels remain high+ placenta takes over progesterone production during pregnancy.
if no fertilisation- ovum+ corpus luteum break down, thus progesterone levels drop, so uterus wall breaks down, and menstruation begins again.
In vitro fertilisation (IVF)
IVF involves the following steps: 1. FSH and LH are given to
the woman to stimulate the
maturation of multiple eggs.
2. Eggs are then collected from the woman’s ovaries.
3. The eggs are fertilised in a lab using the man’s sperm.
4. The fertilised eggs then grow into embryos (small balls of cells) in a laboratory incubator.
5. Once the embryos have formed, one or two of them are transferred to the woman’s uterus. Transferring more than one improves the chance of pregnancy
Developments in microscopy - IVF
Advances in microscope techniques have helped to improve the techniques (and therefore the success rate) of IVF.
Specialised micro-tools have been developed to use on the eggs and sperm under the microscope.
More recently, the development of time-lapse imaging (using a microscope and camera built into the incubator) means that the growth of the embryos can be continuously monitored to help identify those that are more likely to result in a successful pregnancy.
tsh and thyroxine negative feedback relationship
When the level of thyroxine in the blood is higher than normal, the
secretion of TSH from the pituitary gland is inhibited (stopped).
This reduces the amount of thyroxine released from the thyroid gland,
so the level in the blood falls back towards normal.
When the level of thyroxine in the blood is lower than normal, the secretion of TSH from the pituitary gland is stimulated (started up) again. This increases the amount of thyroxine released from the thyroid gland, so the level in the blood rises back towards normal.
auxin - shoots - light
Shoots - Positive phototropism
Auxin is produced at the base of the tip of the plant. As light is shining from the side, more diffuses down the shaded side of the shoot
Therefore, there is uneven distribution of auxin on both sides of the shoot, which causes unequal growth and elongation of cells on shaded side of the shoot (the shaded side grows more). Therefore the plant grows towards the light.
auxin - shoots - gravity
Shoots – negative geotropism
When a shoot lays sideways, gravity causes an uneven distribution of auxin in the tip (more auxin on lower surface)
In shoots, auxin promotes growth, so the presence of higher levels of auxin causes the lower side to grow faster, which bends the shoot upwards – away from gravity.
auxin - roots - gravity
Root – positive geotropism
When a root lays sideways, gravity causes an unequal distribution of auxin in the tip (more auxin on lower surface)
In the roots, high auxin levels inhibit cell elongation
Therefore the upper surface of the root grows more quickly than the lower surface; so the root grows downwards – towards gravity
similarites and diffrences between nervous system and endocrine system
Both have the similarities of sending signals around the body to help to regulate the conditions inspired the body that part of homeostasis. both trigger responses in the body from their signals.
