Topic 6 Flashcards
What is homeostasis
involves using physiological systems to maintain a constant internal environment within fixed limits
Why is maintaining a stable internal temperature and PH important
To ensure that the enzymes involved in metabolic reactions are operating at the optimal temperatures
What is negative feedback
Used in homeostasis
If the stimulus is above the limits ,then the body will work to reduce it and vice versa
When does blood glucose levels rise
After a carbohydrate containing meal
What are the two hormone involved in maintaining blood glucose
Insulin
Glucagon
What is the main organ involved in maintaining blood glucose levels
Pancreas
What is the area of the pancreas where cells secrete insulin
Islets of langerhan
What are the two types of cells which secrete hormones
Beta cells secrete insulin
Alpha cells secrete glucagon
What happens when blood glucose levels are too high
- Pancreas detects the rise in blood glucose
- a cells stop secreting glucagon and b cells start secreting insulin
- Insulin binds to receptors on liver and muscle cells
- Muscle cells are stimulated to take up more glucose
- Liver cells are stimulated to take up glucose and initiate glycogenosis
- Blood glucose levels drop down
What happmes when blood glucose is too low
- The pancreas detects a drop in blood glucose
- a cells start secreting glucagon and b cells stop secreting insulin
3.Glucagon binds to receptors on liver cells - This activates glycogenolysis
- Liver cells release glucose into the blood
- Blood glucose levels return to normal
Define glycogenesis
The process of excess glucose being converted to glycogen when blood glucose is too high
Define glycogenolysis
1.The hydrolysis of glycogen back into glucose in the liver
- Occurs when blood glucose levels are lower than usual
Gluconeogenesis
- Process of creating glucose from noncarbohydrate stores in the liver
- This occurs if all glycogen has been hydrolysed into glucose and your body still needs more glucose
What organ regulates water potential
The kidneys
How does the kidneys regulate water potential
In the kidneys, water is filtered out of the blood and then reabsorbed so that the water potential of blood can be controlled
Where in the kidneys is water filtered
In the nephron
Where is the nephron located
Found in the cortex and medulla layers of the kidney
What is the hormone for the regulation of blood glucose
The hormone ADH is used in the regulation of blood glucose
Where is ADH secreted
It is secreted by the posterior pituitary gland in the brain
What is the role of ADH
It controls how permeable the distal convoluted tubule (DCT) and collecting duct is to water which changes the amount of water that is reabsorbed
What happens if blood water potential is too high
1.Osmoreceptors in the hypothalamus detect the rise in water potential
2.The posterior pituitary gland releases less ADH into the blood
3.Less ADH results in the DCT and collecting duct becoming less permeable to water so less water is reabsorbed
4.This results in a larger amount of more dilute urine being produced
What happens if blood water potential is too low
1.Osmoreceptors in the hypothalamus detect the drop in water potential
2.The posterior pituitary gland releases more ADH into the blood
3.More ADH results in the DCT and collecting duct becoming more permeable to water so more water is reabsorbed
4.This results in a smaller amount of more concentrated urine being produced
How are nerve impulses transmitted
Via neurons
What are three types of neurons
Motor
Sensory
Relay
What is the role of sensory neurone
Sensory neurons transmit impulses from receptors to the CNS
Give two ways person with type 1 diabetes controls blood glucose
Treat with insulin
Control diet
Role of all three neurons
Sensory : transmits information from receptors(pacinian corpuscle )to CNS
relay: transmits signals from sensory to motor
Motor : transmits impulses from CNS to an effector
When a neurone is at rest is the inside of cell membrane negative or positive
Negative
What is the resting potential
-70 mv
How is resting potential maintained
By sodium -potassium pumps
Describe the process in how resting potential is maintained
Higher concentration of potassium ions inside and higher concentration of sodium ions outside
Membrane more permeable to potassium ions
Sodium ions actively transported out and potassium ions in
How does depolarisation occur
When a neuron is stimulated, Na+ voltage-gated channels open so Na+ ions move into the membrane, depolarizing it
How does an action potential occur
this depolarization reaches the threshold potential of about -55mV, it is the beginning of an action potential
Describe repolarisation
Na+ voltage-gated channels then close and K+ voltage-gated channels open, repolarising the membrane
What is the threshold value
-55mV
What is the refractory period
The refractory period ensures that the impulse only travels in one direction as the membrane cannot be stimulated
What is a myelinated nerve
A myelinated nerve is covered by a myelinated sheath which is an electrical insulator
What is saltatory conduction
Depolarisation only occurs at these Nodes of Ranvier so the impulse jumps from one Node to the next, speeding it up
This is called saltatory conduction
What is the gaps between neurons called
the Nodes of Ranvier
What affects the speed of transmission
The bigger the axon diameter, the faster the speed of transmission
Temperature affects the speed of transmission - it is fastest at 40C but decreases at any other temperature
Explain why the speed of transmission of impulses is faster along a myleniated axon than along a non myelinated axon
Myelination provides electrical insulation
In myelinated saltatory conduction
In non-myelinated depolarisation occurs along whole length
Describe the presynaptic neuron
The area of the neuron before the synapse is called the presynaptic knob and it is filled with vesicles containing chemicals called neurotransmitters
Describe the cholinegic synapse
In a cholinergic synapse, the neurotransmitter is acetylcholine
Describe the transmission of acetylcholine
1.An action potential reaches the presynaptic membrane
2.This causes Ca2+ voltage-gated channels to open and calcium ions to enter the presynaptic knob
3.The influx of Ca2+ ions causes synaptic vesicles to fuse with the membrane of the presynaptic knob
4.Acetylcholine diffuses across the synaptic cleft and binds with receptors on the postsynaptic membrane
5.This triggers Na+ ion channels to open which results in Na+ entering the membrane and depolarisation occurring
- The acetylcholine in the synaptic cleft is broken down by the acetylcholinesterase enzyme so that the post-synaptic membrane is not triggered multiple times
Describe the pacinian corpuscle
it is a mechanoreceptor which detects pressure and vibrations and it is found in the skin
Where is the pacinian corpuscle
A Pacinian Corpuscle is made up of the end of a sensory neuron wrapped in layers of connective tissue called lamellae
What does the pacinian corpuscle do when a stimulus is applied
1.When a stimulus is applied, eg a nudge, the lamellae deform and press on the sensory nerve ending
2.This causes sodium ion channels called stretch-mediated sodium ion channels to open and sodium ions to enter the cell
3. Greater pressure more channels open
4. This causes a change in the charge of the cell called a generator potential
How is action potential created in the pacinian corpuscle
If this generator potential reaches above a certain threshold, it will form a nerve impulse known as an action potential
Where are photoreceptors
Another example of a receptor is a photoreceptor (light receptor) in the retina of the eye.
What does photoreceptors do
photoreceptor cells that detect light
What are two types of photoreceptors
rods and cones
Describe Rod cells
Rods are very sensitive to light but they have low visual acuity. They can only detect monochromatic light (black and white)
Why do rod cells only detect monochromatic light
this is because many rods join to one neuron so the signal is amplified
but the light from two close points cannot be told apart
Describe cons cells
Cones are less sensitive to light but they have high visual acuity. They can detect light in colour (red, green, and blue)
Why do cone cells detect light in colour
this is because one cone joins to one neuron so the signal is weaker but the light from two close points can be told apart
How do organisms survive by responding to their internal environment
Internal: ensuring that body temperature and pH are optimal for metabolism
How do organisms survive by responding to their external environment
External: avoiding harmful environments or changing by responding to changes in the environment.
How do plants respond to external stimuli
Plants respond to external stimuli like gravity and light
Plants grow towards the light to maximize photosynthesis
They sense gravity so that shoots and roots grow the correct way
What is tropism
A plant’s growth response to a stimulus is called a tropism.
a positive tropism is a growth towards a stimulus
a negative tropism is growth away from a stimulus
Describe phototropism (negative and positive)
Phototropism is the growth response of plants to lights
shoots have a positive phototropic response: they grow towards the light
roots have a negative phototropic response: they grow away from the light
Describe gravitropism
Gravitropism is the growth response of plants to gravity
shoots are negatively gravitropic: they grow away from the direction of the pull of gravity
roots are positively gravitropic: they grow towards the direction of the pull of gravity
What are growth factors
Growth factors are chemicals that speed up or slow down plant growth
Describe the role of auxins
Auxins are a group of growth factors that stimulate growth by causing cells to elongate
Describe how concentration of auxin effect plant elongation
In shoots, high concentrations of auxin cause cell elongation but in roots, high concentrations of auxin inhibit cell elongation
What is IAA
IAA (Indoleacetic Acid) is a type of auxin that is produced in the shoots of flowering plants
It moves around the plants to control tropisms
How does IAA work in phototropism
Phototropism: IAA accumulates on the more shaded side of shoots and roots
This causes shoots to bend towards the light and roots to bend away from the light
How does IAA work in gravitropism
Gravitropism: IAA accumulates on the underside of shoots and roots
This causes shoots to bend upwards and roots to bend downwards
Describe taxes
Tactic responses (taxes) are when organisms move towards or away from a directional stimulus (eg light)
How do woodlice have a phototaxic response
woodlice have a phototaxic response (taxes response to light): they move away from a light source
this helps them to remain in dark conditions that will keep them safe from predators
What is kineses
Kinetic responses (kineses) are when organisms move in response to a non-directional stimulus.
How do woodlice respond to humidity
woodlice have a kinetic response to humidity: in a humid environment, they move and turn less often so they will stay where they are
but in a dry environment, they move and turn more so that it is more likely they will move into a humid environment
How is the cardiac muscle a myogenic muscle
Cardiac muscle is a myogenic muscle: it will contract on its own without a nerve impulse
Describe the role of a pacemaker
The heart has a pacemaker that regulates these contractions called the SAN (sinoatrial node)
Describe how impulses travel from the atria to the ventricles
1.The SAN sends out a wave of electrical activity over the atria of the heart which causes the left and right atria of the heart to contract at the same time
2.The ventricles of the heart are separated from the atria by a band of non-conducting tissue, so the signal passes through the AVN (atrioventricular node)
3.the AVN has a slight delay which allows the atria to fully empty before the ventricles contract
4.The impulse travels from the AVN down the bundle of His (a bundle of nerves that are found in the septum or middle of the heart) and into the Purkyne tissue
5.The Purkyne tissue causes the ventricles to contract simultaneously from the bottom up
What is the role of the sinoatrial node
The SAN sends out a wave of electrical activity over the atria of the heart which causes the left and right atria of the heart to contract at the same time
What is the advantage of the slight delay of the AVN
the AVN has a slight delay which allows the atria to fully empty before the ventricles contract
What is the flow of impulses from atria to ventricle
Sinoatrial node —> atrioventricular node —> bundle of his-> purkyne tissue
What is the rate of SAN controlled by
The rate that the SAN sends out impulses is unconsciously controlled by the brain and the autonomic nervous system
What is the role of the sympathetic and the parasympathetic
The sympathetic nervous system helps the body get ready for action while the parasympathetic nervous system calms it down
What is the role of the medulla oblongata in controlling SAN
The medulla oblongata receives impulses from baroreceptors (pressure receptors) and chemoreceptors (chemical receptors)
Where are baroreceptors found
Baroreceptors are found in the aorta and carotid arteries (in the neck) and are stimulated by high and low blood pressure
What do baroreceptors do when blood pressure is high
If blood pressure is too high, baroreceptors send impulses to the medulla oblongata which passes them to the parasympathetic nervous system. This causes the SAN to reduce heart rate
What do chemoreceptors do and where do you find them
Chemoreceptors are found in the aorta, the carotid arteries, and the medulla and respond to changes in O2 concentration and blood pH
What do chemoreceptors do if blood CO2 is too low
If blood CO2 is too low (which causes blood pH to be high), chemoreceptors send impulses to the medulla oblongata which passes them to the parasympathetic nervous system. This causes heart rate to decrease
What happens if blood O2 is too low
If blood O2 is too low (which causes blood pH to be low), then impulses are sent along the sympathetic nervous system which increases heart rate.
Exercise increases heart rate
Describe role of receptors and the nervous system in this process
Chemoreceptors detect rise in CO2
Send impulses to cardiac centre
More impulses in the SAN
By the sympathetic
Explain how the fovea enables an eagle to see its prey
High visual acuity
Each cone is connected to a single neuron
Cone sends separate impulses to the brain
Owls have a high density of rod cells
Explain how this enables an owl to hunt its prey at night
High visual sensitivity
Several rods connected to a single neuron
Enough neurotransmitter to reach threshold
What is the 4 step process by which water is absorbed in the kidneys
Ultrafiltration
Selective re absorption
Loop of henle
Distal consulates tubule and the collecting duct
Outline ultrafiltration
- High blood pressure in the glomerulus
- Water ,glucose pass out
- Through small pores in endothelium
- And through the capillary basement membrane
Outline selective reabsorption
1All the glomerular filtrate must be absorbed however urea doesn’t need to be
2.Glucose is reabsorbed in the process of co transport in the epithelial cells of convoluted tubule to blood capillaries
- Sodium ions move in from the proximal consulates tube bringing glucose and glucose is diffused Into capillaries
Outline the loop of henle
Works to reabsorb water
Sodium ions are actively transported out of the ascending limb using ATP
Therefore creates a low water potential between the two limbs
The ascending limb is impermeable to water ,so water moves out by osmosis by the descending limb
Water meters blood capillaries
What is the role of skeletal muscles
They are stimulated to contract by nerves and act as effectors
What types of pairs do skeletal muscles work in
Antagonistic pairs ;one muscle pulls one way and the other pulls the other way
Describe the structure of skeletal muscle
Made up of long muscle fibres cells
Cell membrane of muscle fibres is known as the sarcolemma and it folds on itself to form a network of T -tubules
What is the endoplasmic reticulum of muscle cells
Sarcoplasmic reticulum
What is the role of the sarcoplasmic reticulum
It stores and releases Ca 2+ ions that are needed for muscle contraction
Where do muscles get energy from
They have loads of mitochondria which release energy needed for muscle contraction
What do muscle fibres contain
Myofibrils
Describe structure of myofibril
Made up of bundles of myosin and actin filaments
Myofibril is made up of short units called sarcomeres
Describe the structure of sarcomeres
End of sarcomeres are called z lines
Actin is also in the sarcomeres
Around the M -line is the H zone that only contains myosin
How do sarcomeres contract
The mysoin and actin fibrils slide over each other instead of contracting themselves
This causes the muscle cell to reduce in length and the muscle to contract
What two things provide energy for muscle contraction
ATP and phosphocreatine
How is ATP produced for muscle contraction
Aerobic respiration in cell’s mitochondria
Anaerobic respiration
ATP -phosphocreatine system
Outline the ATP phosphocreatine system
- ADP + phosphocreatine —> ADP + creatine
- Phosphocreatine is stored inside the cells and can release ATP very quickly
- Creatine is Brocken down into creatinine and removed from the blood via the kidneys
4.The system is anaerobic and alactic
What are the two types of muscle fibres
Slow twitch and fast twitch
What is the difference between slow twitch and fast twitch
Slow twitch
-contracts slowly
-good for endurance
-used for posture
- red because rich in myoglobin
Fast twitch
-contacts fast
- good for short burst of speed
-used for fast movement
- whitish because lack myoglobin
Describe myofibril contraction
1.An action potential arrives at a muscle cell and spreads down the T-tubules into the sarcoplasmic reticulum
2.The sarcoplasmic reticulum releases Ca2+ into the sarcoplasm (cytoplasm)
- Ca2+ binds to a receptor on tropomyosin and this causes it to uncover the binding sites on the actin filament
4.The troponin head binds to the binding site
5.ATP on the troponin head is converted to ADP + Pi, releasing energy and this causes the troponin head to bind, forming an actin-myosin cross bridge
6.This pulls the actin filament across the myosin filament, which shortens the myofibril
7.Another ATP attaches to the troponin head, which causes it to detach from the actin filament and be ready to bind onto another
- This continues as long as the muscle cell is depolarised.
Role of ATP in myofibril contraction
Provides energy to move myosin head
Allows binding of myosin to actin
Role of calcium ions for muscle contraction
Calcium ions bind to tropomyosin
Tropomysoin molecules move away
Binding sites on actin revealed
Cross bridges can form
Myosin head moves
