homeostasis and neurones
- Created by: Andrei stephen
- Created on: 18-02-15 16:36
the endocrine system
the endocrine system is made up of a series of glands that secrete chemicals known as hormones
hormones are transported in the blood and taken to a target organ
this can activate a response by activating enzymes others do this by affecting genes for example steroids
the endocrine system plays a major role in homeostasis which is maintaining a constant internal environment
endocrine glands I need to know and functions
- pancreas = controls blood sugar levels by releasing insulin wich lowers blood sugar levels and glucagon which raises blood sugar levels.
- adrenal gland = responsible for the release of adrenalin
- pituitary gland = connection between the nervous and endocrine systems releases Anti-diuretic hormone which allows control of water potential of the blood.
- finally the hypothalamus of the brain stimulates the releases of many of these hormones
how hormones work
hormones take far longer to take effect than a nervous system response
however the effects of hormones are often long lasting
hormone mechanism for adrenalin
the hormone gets to the target organ through the blood vessels
the hormone then binds to a receptor on the surface of the cell
this causes an enzyme connected to the receptor adrenal cyclase, to change shape and become active
the adrenal cyclase turns ATP into cyclic AMP
the cyclic AMP goes on to activate a second enzyme this is the enzyme that will cause an response
how hormones work
hormones take far longer to take effect than a nervous system response
however the effects of hormones are often long lasting
hormone mechanism for adrenalin
the hormone gets to the target organ through the blood vessels
the hormone then binds to a receptor on the surface of the cell
this causes an enzyme connected to the receptor adrenal cyclase, to change shape and become active
the adrenal cyclase turns ATP into cyclic AMP
the cyclic AMP goes on to activate a second enzyme this is the enzyme that will cause an response
how hormones work diagram
controlling temperature in mammals
Theirs are two different types of animal when it comes to controlling body temperature
endotherms = warm blooded animals they control their body temperature at a set level this allows internal processes to carry on unimpeded their levels of activity fluctuate less
ectotherms = cold blooded their body temperature fluctuates with environmental temperature. as such their enzyme action is dependent on the environment
how temperature is regulated in mammals
the hypothalamus is the thermoregulatory center in the brain detects a cahnge in the core blody tempture by the blood that flows through the brain
it causes a response
such as vasoconstriction(too cold) or vasodiolation(too hot), shivering or sweating
regulating blood sugar levels
- the level of glucose needs to be carefuly controled as a low glucose blood level means their is not enough ennergy for metabolic processes
- to much glucose will lower the water potntail of the blood causeing water to move from the organs to the blood stream causeing majour damage
- blood glucose levels are reguated by a negtive feedback loop allwoing a constant enviorment to be maintained
if their is a rise in blood glucose
- cells in islets of landerhands in the pancreus detect the high glucose blood levels
- insulin is secreted by beta cells
- the insulin causes muscel and liver cells to uptake glucose and convert it into glycogen via glycogensis
if glucose blood levels are too low
- cells in the iselts of landerhans
- glucogon is screted by alpha cells
- this causes cells to convert glcogen into glucose which is then relased via glycogenolysis
regulating blood sugar levels
- the level of glucose needs to be carefuly controled as a low glucose blood level means their is not enough ennergy for metabolic processes
- to much glucose will lower the water potntail of the blood causeing water to move from the organs to the blood stream causeing majour damage
- blood glucose levels are reguated by a negtive feedback loop allwoing a constant enviorment to be maintained
if their is a rise in blood glucose
- cells in islets of landerhands in the pancreus detect the high glucose blood levels
- insulin is secreted by beta cells
- the insulin causes muscel and liver cells to uptake glucose and convert it into glycogen via glycogensis
if glucose blood levels are too low
- cells in the iselts of landerhans
- glucogon is screted by alpha cells
- this causes cells to convert glcogen into glucose which is then relased via glycogenolysis
diabetes and liver functions and structure
type one
- pancreas cannot produce enough insulin or receptors to insulin not working/damaged
- this means after a meal their blood glucose concentration remains high
- kidneys are healthy, but there is so much glucose in the blood it is in the urine
- symptoms include dehydration, weight loss and lethargy
- this can be controlled with insulin injections and a carefully controlled diet
type two
- this occurs in later life
- insulin still works, but receptors cannot respond properly
- glucose uptake is limited
- this can only relay be controlled by a careful diet
structure of the liver diagram
Liver and excretion
the liver plays a vital function to do with excretion it provides one of the main waste products of excretion users
deamination occurs in the live this is where excess amino acids are broken down from proteins.
they are broken down like so
2NH2CH(R)COOH + O2=======>2 R-C=OCOOH + 2NH3
the ammonia produced by this reaction is very toxic
so it is converted into urea by the ornithine cycle
two ammonia and carbon dioxide react to make water and urea
ornithine cycle diagram
the structure of the kidney
the kidney is split into three sections
- the outermost section is called the renal cortex
- the middle section is called the renal medulla
- the innermost section is called the renal pelvis
the renal artery takes blood into the kidney where all metabolic waste products are filtered out of the kidney.
any useful substances filtered out in the kidneys are completely reabsorbed
the thing that actually filters the blood in the kidney is its functional unit the nephron their are hundereds of thousand of nephrons in the kidnay that all filter the blood.
the nephron and its functions
how blood is filtered
blood arrives at the glomerulus the blood is under high pressure due to the contractions of the heart, the arterioles of the afferent arteriole being wider then the venule leaving and the high resistance of the glomerular capillaries and the inner wall of the bowman capsule
the blood undergoes ultra filtration where all particles under 69,000 mm are filtered into the proximal convoluted tube
this makes the glomerular filtrate made up of urea, glucose, water and amino acids
nephron and its functions continued
selective reabsorption takes place in the proximal convoluted tube thanks to its brush border this is where important substances like water glucose and amino acids are reabsorbed
100% of glucose is reasorbed and up to 80% of water
the filtrate then travels through the loop of Henle where some more water is reabsorbed
then it goes through the distal convoluted tube to the collecting duct this is where anti diuretic hormone acts allowing for further water reabsorption to happen here
this leads to the urethra where it is then excreted
how ultrafiltration works
the glomerulus lies very close to the membrane of the bowman's capsule
the glomerulus has many tiny pores
podocytes support the basement membrane
the basement membrane acts like a sieve to the high-pressure blood only allowing small molecules through it
selective reabsorption in the pct
selective reabsorption happens in the PCT due to its brush border this is made of epithelial cells with many microvilli
- this gives the PCT an increased amount of surface area
- glucose is reabsorbed using carrier proteins which pull it into the cell it is then passed into the blood vessels surrounding the PCT
- by the time the filtrate reaches the end of the PCT 100% of the glucose has been reabsorbed
- ions are reabsorbed by ion channels in the pct
- water is also largely reasoned here via osmosis this is where most of the water is reabsorbed
the loop of henle and conserving water
the amount of water in the urine is carefully controlled by the countercurrent multiplication of the loop of Henle as well as the collecting duct.
the loop of Henle works like so
sodium and chloride ions are actively transported from the ascending limb of the loop of handle to the media surrounding it lowering its water potential
the ascending limb is impermeable to water and only ions can leave from the ascending limb
as the filtrate enters the descending limb water leaves the filtrate going from high water potential to low after potential down the water potential gradient as it passes ions from the medulla enter the filtrate as the filtrate passes through the ascending limb the cycle starts over
loop of henle diagram
kidneys and Anti Diretic Hormone
this is controlled by a negative feedback loop
low water potential in the blood.
osmoreceptors detect a fall in the levels of water in the blood the hypothalamus produces ADH
ADH is then released into the blood by the pituitary glands
it then travels through the blood stream to the collecting ducts
this causes vesicles with aquaporins to move towards the membrane of the collecting duct fusing with it
this allows water to be reabsorbed
neurons
all neurones carry these features
- a cell body this is where the nucleus is
- communicate via processes from the cell body
- processes that carry away from the cell body are called axons
- processes that carry towards the cell body are called dendrons and many of them are called dendrites
myelinated neurons
both sensory neurones and motor neurones are examples of these
they are able to transmit an action potential much quicker using saltatory conduction
characteristics of myelinated neurones
- the axon or dendron is surrounded by an insulating myelin sheath
- this is created by Schwann cells that wrap around the axon
- between the cells theirs are gaps called the nodes for Ranvier
how saltatory conduction works
the action potential can only depolarise at the gaps in the myelin sheath as the local circuits are elongated the sodium ions diffuse from one node to the next as such the action potential appears to jump from one node to the next
passing an action potentail allong a nurone
the impulse that passes down an neurone is called an action potential
the neurone is at rest and is polarised it has a resting potential of -70mv
a stimulus causes an action potential to be generated this causes sodium ion channels to open and potassium ions enter causing the neurone to depolarise
if the stimulus is large enough it will reach the threshold potential and an action potential will be generated this causes the neurone to become positive.
at +50mv the sodium ion channels close and potassium ion channels open allowing potassium to exit the cell
this is called repolarization the cell starts to become more negative again it will hyper polarise this will cause the potassium ion channels to close and the sodium-potassium pumps will pump sodium out and potassium in to return the neurone to its resting potential
Theirs is a short refractory period between action potential being fired as the neurone resets itself
synapses and communications between neurons
synapses are the points at which two neurones communicate
these steps happen and allow the action potential to be passed on
- the action potential reaches the presynaptic knob
- this causes the presynaptic knob to depolarise this makes voltage-gated calcium ion channels open
- calcium ions enter the presynaptic knob these cause vesicles containing neurotransmitters to move towards the membrane of the presynaptic knob
- the vesicle then fuses with the presynaptic membrane releasing neurotransmitters into the synapse via exocytosis
what happen next
- the receptors bind to receptors on the postsynaptic membrane
- this causes sodium ion channels to open
- this causes sodium ions to enter the postsynaptic membrane
- depolarising it carrying on the action potential
controlling heart rate
- the heart rate and respiration are carefully linked
- the heart rate is controlled by a part of the brain called the medulla oblongata
- the heart has its own pacemaker that dictates the heart rate this is the SinoAtrial Node
- this is controlled by the medulla oblongata that has two levels connected to the SAN that dictates the pace these are called the accelerator and vegas nerves
- the accelerator nerve causes and increase in the frequency of the heart's contractions
- the vegas nerve causes a decrease in the frequency of contractions fo the heart
what tells the medulla oblongata whether to increase the heart rate?
- movement of the limbs is detected b the stretch receptors sending a message that more oxygen may be needed causing an increase in heart rate
- when exersizing lots of CO2 is produced this reacts with water causing the blood pH to lower slightly this is detected by chemoreceptors in the coroted atery the aorta and the brain this cuses a acion potnetial to be sent b the medulla oblogata that increses the heart rate
- blood pressure is monitored by stretch receptors in the walls of the carried sinus if blood pressure rises to high tis will be detected then causes the vegas nerve to activate nad lower the blood pressure
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