Homeostasis BIO SL

Hierarchy of body subsystems

• atom

• molecule

• macro-molecule

• organelle

• cells

• tissue

• organ

• organ system

• organism

Two systems of communication and coordination in organisms

• endocrine system

• nervous system

Features of the Endocrine system

• communicates via chemical signals (hormones) in blood stream

• response is usually slow compared to nerves

• effects are long-lasting and in widespread areas of the body

• response is generalised so regulates processes like metabolism and growth

• control is mainly involuntary

Features of the Nervous system

• Communicates via electrical impulses and neurotransmitters

• response is fast

• effects are short-term and in localised areas (specific muscles/glands)

• control can be voluntary or involuntary

Central Nervous System

Brain

• control centre of the body

• processes info, thoughts, emotions, decision making

Spinal Cord

• long thin bundle of nerves that run down back

• transmit signals between brain and body

Peripheral Nervous System

Broken into 2 main sections with sub sections

• somatic nervous system - sensory + motor

• autonomic nervous system - sympathetic + parasympathetic

Somatic nervous system

• controls voluntary movements by sending signals from CNS to skeletal muscles

• uses sensory nerves to carry info from the body to the CNS

• uses motor nerves to carry commands from CNS to the muscles and glands of body

Autonomic nervous system

regulates involuntary functions like heartbeat, digestion, and breathing

• divided into sympathetic (fight or flight) and parasympathetic (rest and digest)

The Brain

• Neurogenesis continues in the hippocampus throughout adulthood

• Glial cells actively participate in neurotransmission synaptic pruning and brain plasticity

• Cleans itself through the glymphatic system during sleep to flush out waste like beta-amyloid

• both sides of brain work together on tasks

• memory is stored across neural networks and are well distributed

Neurogenesis

the growth and development of nervous tissue

Synaptic pruning

the natural process where the brain eliminates excess or unused synapses connections between neurons to refine neural circuits, increase efficiency, and strengthen important pathways

Brainstem

• controls primative behaviour like fight or flight through interactions with autonomic nervous system which controls involuntary body function during stress or danger

Conscious receptors

• photoreceptors - vision

• chemoreceptors - chemical signals

• thermoreceptors - temperature

• mechanoreceptors - hearing

Subconscious receptors

• osmoreceptors - sense solutes and water content of blood

• baroreceptors - sense blood pressure

• proprioceptors - sense balance + coordination

Osmoreceptors

• Found in carotid arteries and hypothalamus

• sense solutes and water content of blood

Baroreceptors

• Found in carotid arteries and aorta

• sense blood pressure

Proprioceptors

• found in muscles and joints

• sense balance and coordination

Spinal Cord

• has 31 pairs of spinal nerves

• white matter - axons that carry impulses to and from the brain

• grey matter - neurons and synapses involved in spinal cord integration processes, and reflex arc

Reflex Arc

• Stimulus is received by receptors

• sensory neurons travel through root ganglion to interneuron in spinal cord

• interneuron in spinal cord sends motor neurons back through ventral root to required muscles and glands to make a change

Reflex Arc Example

• burning pan is touched so nocireceptors (skin) are activated

• sensory neuron is sent through root ganglion to interneuron in spinal cord

• interneuron sends motor neuron back through ventral root to hand to tell it to remove itself from the burning pan

Sensory/afferent neurons - receptors

• receptor is a modified neuron capable of transduction

• neurons that carry action potential from receptors to CNS are called sensory neurons

• info from receptors can be perceived at conscious or subconscious level

• each receptor perceived at conscious level has a specific pathway to CNS

Transduction

conversion of physical stimulus into an electrical signal called action potential

Sensory Gating

The brain receives so much info that it must focus on the important stuff and distractions are regulated by the prefrontal cortex 

Motor/efferent Neurons

• neurons that carry action potential from CNS to muscles or glands

• form synapses with muscle fibres called motor end plates or neuromuscular junction

• action potential at neuromuscular junction releases acetylcholine

• ACh initiates the contraction of sarcomeres

Cerebellum Function

• responsible for coordinating voluntary movement, balance, and posture

• receives info from sensory systems and spinal cord and then sends out info to muscles to control movement

• plays a role in memory, attention, and language

Characteristics of the Nervous system

• fast

• accurate

• reset quickly

Types of neurons

• sensory - bring information from body to the brain

• motor - bring information from brain to the muscles and glands of body

Neuron structure names

• cell body / Soma

• dendrites

• axon

• myelin sheath

• nodes of ranvier

• axon terminals

Cell body / Soma

• contains nucleus and most of cells organelles

• processes incoming signals and generates outgoing signals

Dendrites

• branch-like extensions from the cell body that receive signals from other neurons and relay them to the cell body

axon

• long, thin tunnel that transmits electrical impulses (action potential) away from the cell body to other neurons, muscles, or glands

Myelin Sheath

• fatty insulated layer that covers the axon in segments

• formed by schwann cells (part of PNS) or oligodendrocytes (part of CNS)

• speeds up signal transmission along the axon

Nodes of ranvier

• Gaps in myelin sheath where ion exchange occurs

• enables faster impulse conduction through saltatory conduction

Axon terminal

• ends of the axon that release neurotransmitters to communicate with neighbouring neurons or target cells across the synapse

Synaptic Knob

• Part of the end of the axon terminal

Nerve

• bundle of axons from multiple neurons that transmits signals between different parts of the body

Main structure of nerves

• axons - long, threat like extensions from neurons that carry electrical impulses

• Endoneurium - delicate layer of connective tissue surrounding each individual axon, providing insulation and support

• fascicles - small bundle of axons grouped together within the nerve

• perineurium - sheath for each fascicle that protects them

• epineurium - outermost layer of dense connective tissue that surrounds the entire nerve

• blood vessels - small arteries and veins embedded in the nerve that provide oxygen and nutrients to the nerve fibres

Resting potential

• stable, negative electrical charge under cell membrane 

• maintained by a neuron when it is not actively transmitting a signal

• usually around -70mV

Polarized neuron

• a neuron at resting potential

• has a negative charge inside the cell compared to the outside due to uneven distribution of ions

• more Na+ outside, more K+ inside

Sodium potassium pump

• active transport of 3 Na+ ions out of the cell and 2 K+ ions in

• creates net loss of 1 positive ion from the inside per pump cycle which causes negative charge inside cell

Potassium Leak Channels

• Facilitated diffusion

• neuronal membrane that has leak channels that are highly selective for K+ ions

• channels are always open which allows K+ to move out of cell freely according to concentration gradient

Action potential

• rapid, temporary change in neuron’s membrane potential

• membrane potential shifts from negative to positive and back again

• electrical impulse allows signal to travel along the neuron

Depolarization

• process during action potential where Na+ ions rush into the neuron

• causes membrane potential to become less negative

Repolarization

• phase after depolarization where K+ ions exit the neuron

• returns membrane potential back to its negative resting state

• temporary, recovery phase that occurs immediately after depolariztion

Schwann Cells

• specialised glial cells found in the peripheral nervous system

• produce the myelin sheath that wraps around the axon of neurons multiple times

• enables faster signal transmission

• provide support and nutrients to repair neurons if needed

Saltatory conduction

• rapid method of nerve impulse transmission in myelinated axons

• electrical impulse jumps from one node of ranvier to the next

Impulse jumping

• as the action potential moves down the axon, it jumps between nodes, skipping the myelinated sections 

• speeds up signal

energy efficiency

• saltatory conduction is more efficient because fewer ions move across the membrane to reduce the energy needed for ion pumps to restore resting potential

Synapse parts involved

• synapse

• neurotransmitters

• presynaptic neuron

• postsynaptic neuron

• synaptic cleft

synapse

• junction between two neurons where communication occurs

neurotransmitter

• chemical messenger released from a neuron

• transmits signals across synapse

presynaptic neuron

• neuron that sends the signal and releases neurotransmitters into the synaptic cleft

postsynaptic neurons

• neuron that receives the signal by binding neurotransmitters to its receptors

synaptic cleft

• small gap between the presynaptic and postsynaptic neurons where neurtransmitters travel

Transfer of signal in the synapse

• arrival of action potential

• opening of voltage-gated calcium channels

• calcium influx

• vesicle fusion and release

• binding of receptors

• depolarization of postsynaptic neurons

• termination of signal

Arrival of action potential

action potential travels down the axon to the axon terminal

calcium influx

increase in intracellular calcium concentration triggers synaptic vesicles containing neurotransmitters to move towards the presynaptic membrane

vesicle fusion and release

vesicles fuse with the membrane and release neurotransmitters into the synaptic cleft through exocytosis

binding to receptors

neurotransmitters diffuse across the synaptic cleft and bind to receptors on the postsynatic neuron which opens up sodium channels

depolarization of postsynatic neuron

• opening of sodium channels allows Na+ to enter which causes depolarization

• if depolarization reaches threshold potential then a new action potential is generated in postsynaptic neuron

termination of signal

neurotransmitters are degraded by enzymes or taken back into the presynaptic neuron through re-uptake, ending the signal transmission

Endocrine system

responsible for chemical signalling and integration of organs and organ systems through hormones

Hypothalamus

• link between nervous and endocrine systems

• contains both nervous and Glandular cells

Glandular cells

produce hormones that either stimulate hormone release by the pituitary glands, or inhibit the release

Circadian rhythms

• regulates the 24-hour cycle of physical, mental, and behavioral processes, including sleep-wake patterns, hormone release, body temperature, and metabolism

• can be synchronized by light or darkness

• will stay the same for an organism even if it is placed in a different environmental setting

Suprachiasmatic Nucleus (SCN)

• natural pacemaker of the circadian rhythm

• neurons will produce a circadian rhythm of neuron firing frequencies which will synchronise other cells in the body

• visible light can also synchronise the circadian rhythm to the day-night cycle

• cells in the eyes can sense wavelengths of light and send a neural impulse to the SCN

Light/Dark info to suprachiasmatic nucleus (SCN)

• light or dark info can each SCN from cells in the eyes

• when there is darkness, the SCN stimulates the release of melatonin from the pineal gland

Melatonin

• amine hormone

• plays a role in sleep-wake cycle

pineal gland

• small endocrine gland located in the centre of the brain

Melatonin fluctuations

• amount of melatonin circulating in the blood is low during the day and high during the night

• teenagers have natural shift in the timing of the release of melatonin, about a 2 hour delay compared to adults

• leads to later sleeping and waking times

Melatonin effects

• reduce blood pressure

• reduce kidney production of urine

• drop core body temp when sleeping

Nocturnal & Diurnal

• melatonin is released during the night in both diurnal and nocturnal species

• however the secretion of melatonin at dusk promotes activity in nocturnal animals and sleep in diurnal animals

Adrenaline / epinephrine

• amine hormone produced by adrenal glands in preparation for intense activity

• reaction produced by adrenaline is fight or flight response, a survival mechanism that enables quicker reaction towards danger

Effects of adrenaline - liver

• liver and muscle cells break down glycogen into glucose which can be used for cellular respiration to produce energy

effects of adrenaline - lungs

• bronchi and bronchioles dilate due to relaxation of smooth muscles which widens airway for increased air flow during ventilation

• ventilation rate increases, so a larger total volume of air is moved per minute

effects of adrenaline - heart

• speeds up firing of sinoatrial node, increasing heart rate which moves blood tissue faster

• increases the strength of cardiac contraction

• stops an increased volume of blood to be moved with each heartbeat

effects of adrenaline - bladder

two main muscles involved with bladder control

• detrusor muscle - empties bladder

• internal and external sphincters - control release of urine

during fight or flight 

• detrusor muscle is relaxed which prevents immediate urination

• sphincters contract which keeps urine in the bladder

Vasodilation

• widening of arterioles that carry blood to the skeletal muscles so more blood flows into them

• vasodilation redirects blood flow to the areas of the body that are the most crucial for dealing with the immediate threat

Vasoconstriction

• narrowing of arterioles that carry blood to the gut, kidney and skin so less blood flows to them

• vasoconstriction redirects blood flow away from the areas of the body that are not vital for dealing with the immediate threat

feedback mechanisms

• negative feedback loop - restores balance

• positive feedback loop - reinforces imbalance

Feedback control of heart rate

baroreceptors - detect changes in blood pressure and are located on carotid arteries

Chemoreceptors - detects changes in the content of the blood and are located near the baroreceptors but outside of blood vessels

Feedback control of ventilation rate

chemoreceptors

• in carotid arteries and medulla

• detects levels of CO2 and pH

• normal pH of blood is 7.35-7.45

• changes activate negative feedback mechanism

Control of peristalsis

excitory neurotransmitter - causes contractions in smooth muscles

inhibitory neurotransmitters - causes relaxation in smooth muscles

Peristalsis

involuntary movement of food in alimentary channel

Homeostasis

• process where living organisms regulate their internal environment to maintain stable conditions essential for survival

• unicellular organisms can maintain homeostasis by controlling water balance, expelling waste, and regulating nutrient intake

• multicellular organisms can maintain homeostasis through temperature, pH, and nutrient levels

4 examples of homeostasis levels

• body temp - maintains a stable internal temp (37 in humans)

• blood glucose levels - regulating sugar levels in the blood (70-110 mg/dL in humans)

• Blood pressure - keeping blood pressure within a healthy range (120/80 mmHg in humans)

• pH levels - maintaining a stable pH in bodily fluids (blood pH 7.4)

range of tolerance

• if an environmental variable goes outside of an organisms range of tolerance, the organisms will experience stress and could die if limits are too far excedded

Example of negative feedback loop

if body temp rises, sweating will bring it back down to normal levels

example of positive feedback loop

during childbirth, contractions intensify until delivery

Blood glucose regulation

• chemoreceptors in carotid artery detect changes in blood glucose levels

• hypothalamus processes the info and signals pancreas to respond

• pancreas either releases insulin (beta cells) to lower blood glucose or Glucagon (alpha cells) to increase blood glucose

• liver then processes hormone and either stores more glucose in glycogen or breaks down glycogen into glucose for energy

Role of insulin

• increases glucose uptake by binding to insulin receptors on cell membranes

• triggers GLUT4 transporters to move to the cell surface

• transporters allow glucose to enter cells into muscles and fat tissue where it is used for energy or stored

Why neurons do not need insulin

• use GLUT1 and GLUT3 transporters that facilitate glucose entry independently of insulin

• ensures a constant supply of glucose to the brain and nervous system, even when insulin levels are low

Diabetes

• chronic metabolic disorder that causes elevated blood glucose due to insufficient insulin production, impaired insulin action or both

Type 1 diabetes

• autoimmune condition where the immune system destroys insulin-producing beta cells in the pancreas

• results in little to no insulin production

• diagnosed in childhood or adolescents

Type 2 diabetes

• condition where cells become resistant to insulin or the pancreas cannot produce enough insulin to meet the bodies needs

• associated with obesity, age, and genetic factors

symptoms of type 1 and 2 diabetes

• frequent urination

• fatigue

• extreme thirst

Type 1 diabetes treatment options

• insulin therapy

• blood glucose monitoring

• diet and exercise

Type 2 diabetes treatment options

• diet and exercise

• oral medications like metformin

• insulin therapy

• blood glucose monitoring

Thermoregulation

• process where the body maintains its internal temp within a stable range, despite external temperature changes