Homeostasis part 1 Flashcards
what are the best conditions for the human body? (temp, blood sugar level, pH)
Temp of 37 Celsius, 100mg/mL blood sugar level, pH of 7.4
What is homeostasis
When the body maintains a relatively constant internal environment. It requires the interaction of several regulatory systems, including body temp, blood glucose levels and blood oxygen levels. They may rise and fall during the day, but still be considered in balance.
Why is homeostasis necessary
The human body can only survive in a narrow range of conditions
Feedback systems have ___ and they ___
- A sensor, it detects a change in the internal environment and sends a signal to a control centre
- Control centre, sets the range of values within a variable should be maintained, receives signal from sensor and sends a signal to effectors
- An effector receives signals from control centre and responds, resulting in a change to an internal variable
What are negative feedback loops
A feedback system that will set the variable back into the acceptable range. They return to a set point until a new stimulus comes along.
What are positive feedback loops
They’re less common because they are designed to reinforce change, whereas negative feedback loops would resist change. Positive feedback systems push the variable further and further from a steady state. Once the event is accomplished, the system stops. Ex. birthing process
What is thermoregulation?
The ability of an organism to keep its body temperature within certain boundaries, even when external conditions are different.
Endotherms vs ectotherms
- Ectotherms “cold blooded” are reliant on external sources of body heat (ex. turtles and lizards)
- Endotherms “warm blooded” generate their own heat from within (ex. Mammals like humans)
What happens to mammals to manage heat stress?
- Sweating occurs - sweat evaporates, taking heat with it
- Blood vessels dialate -brings blood closer to surface of the skin, allowing heat to escape
Cold stress responses
- Shivering - shivering exercises the muscles, heat is created as a by-product of cellular respiration.
- Blood vessels constrict - This brings blood away from the surface of the skin, in the attempt to retain heat in the body. This is apparent in extremities such as nose, ears, fingers and toes
- Hair stands on end - it creates a ‘web’ that traps heat closer to the body
What is mammalian diving reflex?
When the face is exposed to cold water, in the attempt to conserve oxygen, blood is diverted away from extremities and towards the blood-brain circuit, causing pulse to drop.
Why is ice destructive to cells
Cells can expand a bit, so its mostly unharmed when water expands into ice. Ice outside poses more of a risk as it could puncture cells.
Why some animals can survive freezing
They can have cryoprotectants or other antifreeze chemicals in their blood to prevent freezing ex. painted turtles, wood frogs, red flat beetles, etc
Importance of the nervous system
- nervous systems respond to stimuli (external or internal) by controlling the actions of the body through electrochemical messages
- Allows us to: detect light, odour, temperature or pressure
What is the nervous system?
- An elaborate communication system (around two billion nerve cells in the brain alone)
- 2 main divisions:
1. Central nervous system (CNS) - brain and spinal cord
- coordinating system
2. Peripheral nervous system (PNS) - Nerves that carry info between organs and CNS
- Subdivided into somatic (skeletal muscle, bones, skin –> relays info ab environment) and autonomic (internal organs like the heart, not consiously regulated)
types of nerve cells
- 2 types of cells
1. Gillial: Non-conducting (don’t send messages) cells important for structural support and metabolism
2. Neurons: functional units of the nervous system
What are the types of neurons
- Sensory - sense and relay info from the environment to CNS for processing (photoreceptors for light, chemoreceptors for chemicals, etc) and are located in clusters called ganglia
- Motor - relay information to the effectors (muscles, organs, glands)
- interneurons - link neurons in the body (integrate sensory and motor neurons)
What’s a dendrite
- They are a part of a neuron that receives info from sensory receptors by conducting nerve impulses towards the cell body
What’s a myelin sheath?
Part of neuron, covers many axons, insulates the neuron, prevents the loss of charged ions from the nerve cell. formed by special glial cells called schwann cells.
What’s an axon
Part of neuron, projects nerve impulses from the cell body, chain like
What are nodes of Ranvier
areas between sections of myelin sheath, nerve impulses jump from one node to another (speeding up process) so nerve impulses are quicker in myelinated axons.
What is neurilemma
It surrounds the axon and promotes re-generation of a damaged axon
neural circuits
- simplest nerve pathway us called a reflex arc (like when your doctor hits your knee with a hammer)
- Occurs without brain coordination
- 5 components: 1. receptor, 2. sensory neuron, 3. interneuron, 4. spinal cord, 5. motor neuron and effector
What is a wave of depolarization?
A signal that travels along the axon, primarily the movement of two positive ions (K and Na) from one side of the axon’s cell membrane to another
- Resting neuron info
- not coducting signals, but holds poteintial energy caused by the difference between the positive fluid outside the membrane against the negative inside (neuron is polarized)
- the plasma membrane of the neuron keeps large negatively charged molecules in the cell
- K can diffuse out of the cell freely while Na has to go through channels
- (-70) milivolts resting potential
- Action potential
- governed by the all or none principle
- if an axon is stimulated sufficiently, the axon will trigger an impulse down the length of the axon, axon can respond or not
- when an axon is stimulated, a wave of depolarization is triggered
- gates of K channels close and Na open
- input of positively charged ion neutrilizes negative charge (40mV)
- Transfer of action potential
- the depolarization of the one part of the axon causes the gates of neighbouring Na channels to open, and the depolarization continues along the axon
- any region of the axon is only depolarized for a split second
- Hyperpolarization
- almost immediately after Na channels have opened to cause depolarization, the gates if the K channels reopen and K moves out
- the Na channels close at the same time
- this process, combined with the rapid active transport of Na out of the axon by the pump re established the polarity of that area of the axon
- restoring balance
- the Na-K pump actively transports more Na out of the cell than K into the cell, contributing to the buildup of positive charge outside while keeping the concentration of Na low in the cell and the concentration of K high
- axon can send many impulses per second because this happens so fast
What is the refractory period
The refractory period is a state of recovery that occurs after a neuron has fired an action potential. During this period, another action potential cannot be easily produced. lasts approximately 0.001s
What is a synapse
The gap between two neurons
- neuron that carries the wave of depolarization towards the synapse is the presynaptic neuron, the one that receives the stimulus is the postsynaptic neuron
General info action potential
- the signal moves at about 2m/s
- the myelin sheath can increase the speed of the wave of depolarization, and also the ability of the impulse to jump from one node of Ranvier to another (can increase to 120 m/s)
The process (synapse)
- Ca gates open when the wave hits the end, triggering the exocytosis of neurotransmitter molecules which are contained by synaptic vesicles
- neighbouring dendrite has specialized receptor sites and the neurotransmitter attaches to these receptors and excites or inhibits the neuron
- ex acetylcholine neurotransmitter, is then destroyed by cholinesterase so the postsynaptic neuron isn’t in a constant state of depolarization
Neurotransmitters
Acetylcholine –> plays a role in brain functions like memory and muscle contractions
Dopamine –> reward centre
Seratonin –> carries messages from CNS to PNS
GABA –> calming
Norephinephrine –> causes fight or flight in PNS
Oxytocin –> bonds between loved ones
The importance of the endocrine system
- no cell operates in isolation - body function depends on hormonal chemical control
- a small amount of hormone can make a big impact
- nervous system helps an organism to adjust quickly to changes to environment while endocrine system maintains control over a longer duration (can regulate and sustain development for years)
Horomones
- chemicals released by cells that affect cells in other body parts by speeding up or slowing down bodily processes
- endocrine hormones: produced in glands and secreted directly into the blood (some glands make multiples hormones, like the thyroid)
What are the types of hormones
steroid and protein
steroid hormones
- made from cholesterol (sex hormones)
- diffuse from capilleries into intestinal fluid then into target cells
- combine with receptor molecules located in cytoplasm
- hormone receptor complex moves to nucleus and attaches to DNA where there is a complimetry shape
- a gene is activated that makes a specific protein
protein hormones
- chain of amino acids of varying length (insulin and GH)
- combine with specific receptors on the cell membrane
- this complex (hormone-receptor) activates the production of an enzyme called adenylyl cyclase which causes the cell to convert ATP into cAMP (cyclic adenosine monophosphate)
- cAMP functions as a messenger, activating enzymes in the cytoplasm to carry out normal functions
Pituitary gland
- it controls other endocrine glands
- a small, sac-like structure, connected by a stalk to the hypothalamus
- produces and stores hormones
-stimulated through hypothalamus via nerve impulses to release hormones
Lobes of pituitary gland
-Posterior lobe (back), does not make own hormones: stores those made by the hypothalamus such as ADH and oxytocin
Anterior lobe (front)
- produces its own hormones which generally regulate other glands
- such as: thyroid-stimulating hormone, follicle stimulating, etc
- Release of these hormones is related through nerve impulses from the hypothalamus
- hypothalamus also inhibits the secretion of hormones
