Homeostasis 2 Flashcards
Receptor (sensor)
detects change.. which sends a signal to a control centre
Control centre (integrator)
compares with normal level which sends a signal to an Effector
Effector
responds to change
a change in the bodys internal or external environment is detected by….
a recepter
A nerve impulse is sent along a ………… to the brain (control centre) then along a …….to the ……….
sensory neuron….. motor neuron … effector
…… are often glands which will respond by sending ……….. ….. called hormones into the blood
Effectors…. chemical messengers….
What are hormones?
Chemical messengers (signals) released by cells into the blood stream that are transported via the blood stream to act on distant target cells
60 + hormones identified by chemical structure
hormones are specific: (how/why)
only activate cells with tissues that posess the target receptor
What do target cells possess?
receptors that recognize the hormones, others do not possess this
Which two systems work together to control organs and tissues
Nervous system and Endocrine
Nervous system
responds quickly to environment changes
Endocrine system
takes longer but maintains control over long period of time
What is the endocrine system composed of (4)
-A system of ductless sensory organs
-endocrine glands secrete hormones directly into the blood
=blood transports hormones to target tissues
- hormones help the cells in the tissues to elicit a response to maintain homeostasis
Exocrine Glands
do notsecrete hormones into blood or extracellular fluid, into specific ducts that lead outside or into body cavities
ex. salivary glands sweat glands, mammary glands
protein hormones
are polar and water soluble range between 3-200 amino acids long
-cannot cross lipid bilayer, can combine with surface receptors
-causes a series of events and changes in cell
- insulin, growth hormone
Protein Hormone Pathway
-Protein hormones bind to cell membrane receptor molecules.
Receptor molecule changes shape.
-Signal activates and is sent inside the cell (through membrane)
-Signal calls for changes to occur (ie. enzyme release or activation, etc)
Glucagon
Hormone GLUCAGON binds to liver receptor cells → phosphate groups are added → enzyme activated → glycogen broken down to glucose
Steroid Hormones
Steroid hormones are made from a nonpolar cholesterol (lipid) precursor. They are not soluble in water, but are lipid soluble.
Can diffuse through phospholipid bilayer into target cells where they combine with receptor molecules in the cytosol
Then ‘hormone-receptor complex’ moves into nucleus and activates a gene to produce a specific protein
Ex. Testosterone and Estradiol
Steroid Hormone Pathway
-Steroid hormones cross membrane
-Bind to cell receptors (in cytosol or nucleus)
-Hormone-receptor complex binds to a gene control sequence
-Turns gene on/off
-Protein production is activated/deactivated and cell activity changes
Cells can only respond if they have…
receptors for hormones to bind to (in/out)
Hormone receptor complexes respond by…
turning them on and off
amplification
occurs when hormones bind to receptors. Proteins activated, activate other proteins
are hormone responses the same across species
- hormone response different among species
Peptide synthesis
synthesized as prohormones- require further processing (e.g. cleavage ) to activate
Peptide storage
Stored in vesicles (regulatory secretion)
peptide solubility
most are polar and soluble, can travel freely in blood
Peptide receptors
-bind receptors on cell membrane and transduce signal via the use of second messanger systems
effects peptide
often fast onset transient changes in protein activity, though gene expresssion changes can occur
Steroid synthesis
synthesized in a series of reactions from cholesterol
steroid storage
released immediately (constitutive secretion)
Steroid solubility
general non-polar and require carrier proteins to travel blood
Steroid receptors
bind to intracellular receptors to change gene expression directly
Effects Steroids
alterations in gene expression, slower onset, longer duration than peptide hormones
what are many hormones used as signals for
Negative feedback loops
The Hypothalamus
The hypothalamus is the section of the brain that links the nervous and endocrine systems in order to maintain homeostasis
Hypothalamus function
-Receives information from nerves throughout the body and other parts of the brain and initiates endocrine responses
-Secretes certain neurochemicals (called releasing factors) into a portal system which stimulate or inhibit the pituitary gland
-Secretes certain hormones directly into the bloodstream via neurosecretory cells that extend into the pituitary gland
The Pituitary Gland
The “Master Gland”
Secretes hormones which affect most other endocrine glands and interacts with the nervous system (the hypothalamus)
Two parts: Anterior and Posterior Lobes
Pituitary Gland - Posterior Lobe
Stores and secretes hormones produced by the hypothalamus
ADH – acts on kidneys to reabsorb more water back into blood and causes vasoconstriction to increase blood pressure (aka vasopressin)
Oxytocin - causes uterine contractions during labour and milk production in Mammary glands (also associated with bonding)
Pituitary Gland - Anterior Lobe
Produces its own hormones however release is still regulated by the hypothalamus
Thyroid Stimulating Hormone
Reproductive Stimulating Hormones (LH and FSH)
Growth Hormones
Prolactin
Adrenocorticotropic Hormone (ACTH)
Growth Hormone (GH)
promotes protein synthesis by increasing the uptake of amino acids by cells
Too little GH – dwarfism
Too much GH - gigantism
Blood Sugar - The Pancreas
Alpha and beta cells are found in the Islets of Langerhans in the pancreas
They produce glucagon or insulin depending on blood sugar level of the body
Metabolism: The Thyroid
The Thyroid Gland produces mainly Thyroxine (T4) and Calcitonin
calcitonin
bones, lowers calcium conc. in blood
Thyroxine (T4)
most cells, increase metabolic rate essential for body growth
thyroxine importance
Thyroxine contains 4 iodine atoms in its structure.
A lack of iodine in the diet means thyroxine cannot be produced so the anterior pituitary continually sends signals (thyroid stimulating hormones) to your thyroid to produce it.
An overstimulation causes the thyroid to enlarge creating a swelling in the neck called a goiter
Parathyroid Hormone and calcium
low conc. of clacium in blood leads torelease of parathyroid hormone, eillux of calcium from bone, decreased loss of calcium in urine, enhanced absorption in intenstine
Stress & Cortisol
Stress hormones provide more blood glucose to cope with the elevated energy requirements brought on by stress.
Epinephrine
aka adrenaline) is produced by the adrenal gland in response to stress.
It mobilizes (breaks down) stored energy which increase blood glucose which increase energy quickly!
Increases alertness/awareness
Accelerates heart rate
Increases activity of resp. system
Prepares body to do something fast like run from a bear, lift a car off your child, etc.
Cortisol
Produced in the adrenal gland and released in response to stress and a low level of blood glucose. Its primary functions are to:
Increase blood glucose through gluconeogenesis
Suppress the immune system
Aid in fat, protein and carbohydrate metabolism
2 Parts of the Nervous System
Central Nervous System (CNS)
Peripheral Nervous System (PNS)
Peripheral Nervous System (PNS)
All the neurons that carry signals between the CNS and the rest of the body
Central Nervous System (CNS)
Brain and spinal cord
The CNS
The central nervous system (CNS) acts as the control centre in many negative feedback loops. The majority of this activity occurs in the brain, but certain responses can be mediated by the spinal cord (reflexes)
The PNS
The peripheral nervous system (PNS) sends information from receptors to the CNS via afferent sensory neurons and activates effectors via efferent motor neurons
What is the PNS divided into
The anatomy of the PNS is divided into the sensory (afferent) pathway and the motor (efferent) pathway
The motor pathway
can be divided according to whether the response is voluntary (somatic) or involuntary (autonomic)
autonomic division (involuntary motor pathway)
can be split into sympathetic (‘fight or flight’) or parasympathetic (‘rest and digest’) responses
Glial Cells
non-conducting cells, used for structural support and metabolism for nerve cells
Neurons
nerve cells that conduct nerve impulses
Three main types: sensory, inter, and motor
what are the 3 main types of neurons:
sensory, inter and motor.
Each neuron has:
???
-a cell body (contains nucleus & organelles)
-dendrites (receive signals from other cells)
-axons (carry impulses away from the cell body)
Sensory (Afferent) Neurons
Sensory Neurons carry impulses from inside and outside the body to brain and spinal cord. One long dendrite carries nerve impulses from sensory receptor cells to the cell body. One short axon carries impulses away from the cell body to the CNS.
Interneurons
Interneurons are found within brain and spinal cord, and process incoming impulses and pass them on to motor neurons. They have many short dendrites and many short axons.
Motor (Efferent) Neurons
Motor neurons carry impulses away from the brain and spinal cord. Many short dendrites carry impulses from the CNS to the cell body. One long axon carries impulses away from the cell body to effector cells (muscles or glands).
Axons
Axons are bundled together to form nerve fibres similar to the way small fibres are bundled together to form a fibre-optic cable
Neuron Support
chwann Cells (a type of Glial Cell) form tightly wrapped layers around axons called Myelin Sheaths (electrical insulation).
Gaps between the Schwann Cells are called Nodes of Ranvier (ECF exposure)
These support cells allow for the rate of electrical impulses to be as high as it is
Neural Circuits
A neural circuit is the pathway from a stimulus through the different neuron types in response to a stimulus
Neural Circuit steps
- Receptors in the skin sense touch or other stimuli.
2.Afferent/Sensory neurons transmit the touch message. - Information is sorted and interpreted in the brain. A response in determined by interneurons.
- Efferent/Motor neurons transmit a response message to the shoulder muscles.
- The shoulder muscles are activated, causing the head to turn.
Membrane Potential
Any animal cell will have a separation (outside is positive, inside is negative) of charges across a membrane. Membrane potential is this potential difference (voltage) across the membrane.
Nerve Impulses
are small changes in electrical charge or potential being passed from cell to cell
What are nerve impulses cause by
This is caused by K+ and Na+ ions moving in and out of the cell through ion channels.
Electrochemical Potential
-electrochemical potential is changed and maintained by sodium-potassium pumps and potassium and sodium ion channels
-The K+-Na+ pumps move 3 sodium out for every 2 potassium in using active transport (net negative charge inside)
-The channels allow specific ions to diffuse through, but only at certain voltages
Resting Potential
At rest (unstimulated) the inside of a neuron is negatively charged relative to the outside. This is called the resting potential and is about -70mV.
What is Action Potential
An action potential is a temporary change in the membrane potential. This occurs when a neuron conducts an impulse.
Neuron at Rest
At rest the K+-Na+ pump is working, and the sodium ions cannot diffuse back into the cell, so there are more positive ions outside the cell than in. This means the inside of the cell is negatively charged at -70 mV. The cell is polarized.
Stimulation & Depolarization
When first stimulated, the membrane potential becomes less negative. Once it reaches its threshold potential (-55mV) the sodium channels open allowing some Na+ ions to diffuse into the cell.
Depolarization
At -55 mV, more sodium channels open and Na+ ions flood into the cell making it positive. We can imagine this as the cell ‘firing’.
Repolarization
At +30 mV, sodium channels close and potassium channels open. The K+ ions that were locked in the neuron the whole time diffuse out, bringing the potential back towards its resting level.
Hyperpolarization
The potassium channels are slow to close, so the charge goes lower than the cell is at rest (below -70 mV)
Back to Rest
The ion channels are closed and reset, and the sodium-potassium pump returns the membrane to its resting potential (-70 mV).
The time from when the sodium channels close to this stage is called the refractory period, after which the cell can be made to fire again.
Action Potentials- what kind of signal and why, how does it change depending on strength of stimulus
Because there is a refractory period after a cell fires, each action potential travels as a separate signal
All action potentials are the same size (+30 mV) no matter how strong the stimulus is (it is an ‘all or nothing’ response), but a stronger stimulus will cause neurons to fire more frequently
How does action potential travel
The action potential travels down the axon as a wave of depolarisation as the sodium ion channels open/close in sequence like at sporting event when people do ‘The Wave’. The wave moves away from areas in the refractory period as they can’t fire.
The Myelin Sheath is important for two reasons:
- Protects nerves from damage
- Speeds up transmission of an impulse
The Nodes of Ranvier are useful for three reasons:
- Cause impulse to jump from node to node
- Speeds up transmission of impulse
- Sodium Channels for action potential (concentrated at no
Myelin Sheath
The gaps between the Schwann cells are called nodes of Ranvier. The sodium channels are concentrated at these nodes. In a myelinated neuron, depolarisation only happens here, making the signal jump from node to node. This is faster than if it travelled along the whole length.
What do neurons do at rest
Neurons at rest push Na+ ions out and keep K+ ions in giving them a negative charge (polarized)
nerve impulses summary
Neurons at rest push Na+ ions out and keep K+ ions in giving them a negative charge (polarized)
Nerve impulses or action potentials are generated when Na+ ions enter the neuron causing the internal charge to rapidly increase for a millisecond (depolarization)
To repolarize the neuron will let the K+ ions out so the charge drops
There will be a short time (refractory period) where the cell is too negative to fire again, but stimulated neurons fire many times a second
Synapses
Nerve impulses only travel in one direction in the neuron - away from the cell body along the axon. The connection between two neurons or neuron/effector is called a synapse.
What is the neuron before the synapse is called?
presynaptic neuron
What is the neuron being signalled called
Postsynaptic neuron
Electrical Synapses
In electrical synapses the two membranes of the neurons (or effector) are in direct contact. When impulses arrive, a gap junction is made and ions can flow directly.
What does the presynaptic neuron contain/ where/ when are they released
neurotransmitters which are released across a microscopic gap called a synaptic cleft, when there is an action potential.
The neurotransmitters diffuse across the synapse and bind to specific receptors on the postsynaptic membrane
If enough receptors are hit they can trigger a continued action potential in the postsynaptic neuron
When the action potential arrives at the presynaptic membrane, voltage gated calcium ion channels open and Ca2+ ions diffuse into the cell
This causes the vesicles containing neurotransmitters to move to the membrane and release them into the synaptic cleft by exocytosis
Where are neurotransmitters found, how does it move?
Because the neurotransmitters are only in the presynaptic membrane, the signal can only travel in one direction: axon ➞ dendrite
what happens once the neurotransmitters are released
Once released, the neurotransmitters diffuse across the synapse to hit postsynaptic receptors
Neurotransmitters remaining in the cleft are ….. and called
absorbed back into the presynaptic neuron in a process called reuptake
When neurotransmitters bind to specific receptors on the postsynaptic membrane they cause
sodium channels to open
What happens If enough neurotransmitters hit receptors, the post-synaptic cell
reaches the threshold (-55mV), and the action potential will continue (fire) in the next neuron
Neurotransmitters are reabsorbed into the presynaptic membrane (reuptake) shortly after they are released and any remaining Ca2+ and Na+ ions are pumped out of the cell using active transport
Synaptic Divergence
If one neuron’s axon synapses with many neurons’ dendrites, the action potential is weakened but can be dispersed to different pathways
Synaptic Convergence
If many neurons’ axons synapse with one neuron’s dendrite, the action potential is amplified
This summation is called synaptic convergence
Adrenaline
fight or flight nerotransmitter
Noradrenaline
concentration enurtransmitter
Dopamine
pleasure
seratonin
mood
GABA
calming
acetylcholine
learning
Gluamate
Memory
Endorphines
euphoria
