Homeostasis Revision for exam PDF

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Notes regarding homeostasis for exam or test revision...

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STAGE 2 Biology (Homeostasis) Tolerance Limits and Stimulus Response: Homeostasis is the ability of a body to maintain a stable internal environment. ->Maintain stable temperature to neglect process of enzyme denaturing. All organisms have tolerance limits and tolerance range. ->Organisms adapt to their environmental conditions with their respective conditions to which they are suited. ->Before an organism cannot survive due to environmental conditions is called tolerance limits. ->When outside the tolerance limits, an organism cannot survive for long periods of time. ->Inside the tolerance range, all organisms can still survive. ->The range between the minimum and maximum tolerance limits is called the tolerance range. ->Organisms have different tolerance ranges depending on their evolution. ->The tolerance range of an organism may change as it ages. This is especially seen in humans through the comparison of a teenager and an elder. Teenagers are more stable and versatile about their internal environment whereas elders do not. There are impacts of falling outside a tolerance

limit. Negative feedback is a process used to maintain homeostasis; it reverses the stimulus. ->If homeostasis is the ability of a body to maintain balance, then negative feedback are the processes which allows the body to maintain stability.

STAGE 2 Biology (Homeostasis) ->In a negative feedback process, the response reverses the stimulus. ->Stimulus response model are step by step models that describe the negative feedback processes, allowing for homeostasis to be maintained. The stimulus response model consists of, ->Stimulus = A detectable change in the internal or external environment (Loud bang in lecture) ->Sensory Receptor = Receptors that detect the change (Sensory receptors in ears) ->Messenger = Messages may be sent to the (CNS) which receives and processes the information, then the signal is then transmitted by nerve impulses of hormones (Nervous message sent to (CNS), in which messages are sent out to muscles in body) ->Effector = Organs which are signalled to respond to the change (Muscles contract) ->Response = Opposes the stimulus; negative feedback occurs (response opposes stimulus) (Reaction such as jumping away)

Nervous and Endocrine System: The detecting and responding to environmental changes are carried out using the nervous and hormonal systems. ->The nervous system transmits messages around the body in the form of nerve impulses. ->The nervous system uses receptors to gather information about the function of the body. ->It then provides fast response to that information, by acting on glands or muscles. Vertebrate nervous systems consist of, ->Central Nervous System (Brain and Spinal cord) ->Peripheral Nervous System (Nerves and Receptors) Structure of nerve cells consist of, ->Dendrites = Branching of the nerve cell body, detecting signals from other cells ->Cell body = Contains nucleus and organelles, like Golgi body ->Axon = Located opposite end of the nerve cell body. Transmit messages detected by the dendrite

STAGE 2 Biology (Homeostasis) ->Axon Terminals = Small branches of the axon that form connections (synapses) with other neurons The 3 types of nerve cells are, ->Sensory neurons (Peripheral) = Receive initial stimuli from sense organs; eyes, nose, ears, skin and transmits to the central nervous system The skin is always in contact with some sort of sensory cell; cells inside the skin, and all the skin cells are in contact with some sort of sensory nerve. ->Interneurons = Conduct nerve impulses within the central nervous system. Relay impulses from sensory neurons to motor neurons. All nerves inside the spine and brain are called internerves. ->Motor neuron = Conduct impulses from central nervous system to the effector organs (muscles) or glands

STAGE 2 Biology (Homeostasis)

Synapses are the site connection between nerve cells or neuron and a gland or muscle cell through electric nerve impulses. ->Neurotransmitters are chemicals which allow transmission of the signal across a synapse. ->Pre-synaptic cell (left side) contains neurotransmitters packages into vesicle. ->Arrival of nerve impulses cause exocytosis of neurotransmitters into the synaptic cleft. ->Neurotransmitters diffuse and bind with receptors of the post-synaptic cell initiating a nervous impulse.

STAGE 2 Biology (Homeostasis) Any sort of medication that affects functionality of the brain, generally affects the neurotransmitters; either increasing or decreasing the ability of neurotransmitters to function. The hormonal system is made up of several glands throughout the body. ->Glands secrete hormones directly into the blood stream. ->The hormonal system is slower than the nervous system, however as a more widespread and longer-lasting action. Especially when there was a loud bang in the lecture, an initial response; nervous response, adrenal glands would have secreted adrenaline into bloodstream throughout the body causing factors such as dilated pupil, increase in heart rate or increase in breathing rate. This causes the body to go through faster respiration, lasting a long period of time; hormonal response. ->Both males and females have sex hormones; testosterone, estrogen and progesterone, found in sex organs such as testis and ovaries. ->Hypothalamus: Controls production of insulin and glucagon. ->Pituitary glands: ->Adrenal glands: ->Thyroid glands:

Hormones are chemical messengers. ->They contain a certain shape, and that shape dictates the function; similar to proteins. ->They are chemicals which go through the blood, which then attaches to target cells, stimulating the cells to do something.

STAGE 2 Biology (Homeostasis) The 3 types of hormones are, ->Steroid hormones; testosterone and estrogen, are not all proteins, they are lipids. Lipids are hydrophobic, which causes them to easily pass through the cell membrane to enter cells. This means that the steroid hormone receptors are located inside cells. ->Peptide/Protein hormones are short and long chain(s) or amino acids respectively. Peptide (e.g. Insulin) and Protein (e.g. Growth Hormone) (Protein hormones just consist of longer polypeptide chains of amino acids) These hormones are hydrophillic, which causes them not to easily pass through the cell membrane to enter cells. This means that peptide/protein hormone receptors are embedded in the cell membrane. Through this, the message from the receptor will be sent to a relay molecule, which then is transferred to the nucleus itself.

->Amino acid derived hormones; thyroxin, are similar to amino acids being hydrophilic, generally resulting from the modification to tyrosine or tryptophan into a hormone. The amino acid derived hormone receptors are also embedded in the cell membrane.

STAGE 2 Biology (Homeostasis) Reflex Response and Carbon Dioxide Regulation: The role of reflex response is an automatic response. ->Only involves nerves. ->Often, reflex response does not involve the brain. ->A rapid response that reduces/ avoids damage to tissues; leaving hand on something very hot or assist in escaping from predators. The pathway for reflex response, -

>The central nervous system interneuron will always be the nerves in the spine ->The effector is always the muscles

->In the middle of the spinal cord is where the nerves are protected. Carbon dioxide is produced in the body; end product of aerobic respiration. ->Uses nervous system ->CO2 is removed from the body through exhalation. ->The CO2 concentration in the blood is used to stimulate and control the rate and depth of breathing.

STAGE 2 Biology (Homeostasis) The reason why you exhale is due to the CO2 concentration. When inhaling, the CO2 concentration increases which causes the purpose of exhaling. ->When hyperventilating, you breath into a paper bag as this supports the body to understand the appropriate level of CO2 that it should be at. Carbon dioxide is transported in the blood plasma in 3 forms, ->Dissolved CO2 (Approximately 5%) ->Bicarbonate (Approximately 90%) ->Combine with proteins (Approximately 5%) When CO2 dissolves in water, it produces carbonic acid; H2CO3 ->The blood plasma is predominately made of water. ->When carbonic acid reacts further with water, it creates protons which is the measure of your pH. Therefore, the more protons there are in a solution, the lower the pH is; more acid. The conversion of carbon dioxide and water to carbonic acid and back is catalysed by an enzyme called carbonic anhydrase. -

>The diffusion of oxygen into the blood capillary will allow the process of aerobic respiration. The body regulates CO2 levels in the blood maintain 5-6% dissolved CO2 and blood pH around 7.35 using the nervous system. ->Stimulus = Change in blood pH ->Receptor = Chemoreceptor cells located in the brainstem (medulla oblongata) can detect changes in the pH of the blood in the brain. ->Control centre = Messages send via neurons to the respiratory centre in the brain (CNS). ->Effectors = Nervous messages are then sent to respiratory muscles – diaphragm and intercoastal muscles. ->Response = Negative feedback; reverse of stimulus, and results in an increase or decrease in blood pH back to ‘normal’ (pH 7.35).

STAGE 2 Biology (Homeostasis) When blood pH is too low, the breathing rate increases to increase the amount of CO2 removed from the blood at the lungs. Lower levels of carbon dioxide in the blood leads to an increase in blood pH. When blood pH is too high, the breathing rate decreases to decrease the amount of CO2 removed from the blood at the lungs. Higher levels of carbon dioxide in the blood leads to a decrease in blood pH.

Glucoregulation and Osmoregulation: Regulation of blood glucose levels is critical as glucose is used in cellular respiration. ->Respiration provides the energy to produce ATP from ADP and inorganic phosphate (Pi). ->Blood glucose levels fluctuate during meals. Glucose levels are maintained by the endocrine system, using hormonal messages. ->Glucose can either be stored in the blood stream as glucose or stored in the liver as glycogen. Glycogen is a large molecule (polysaccharide) composed of glucose subunits (monosaccharide). The hormone involved in this process are called glucagon and insulin. ->Glucagon is a hormone that binds to liver cells and stimulate cells to convert glycogen to glucose. Causes the breakdown of glycogen into singular sugars in which releases it back into the blood stream. Therefore, if blood sugar levels were low, you would want to secrete glucagon. ->Insulin is a hormone that binds to liver cells and stimulate cells to convert glucose to glycogen. Liver cells will absorb glucose from the blood and store it as glycogen. The pancreas is the organ that will be making and secreting the hormones. It contains two different types of cells; alpha cells and beta cells. ->Beta cells release insulin (blood sugar decreases). ->Alpha cells release glucagon (blood sugar increase).

STAGE 2 Biology (Homeostasis)

Diabetes is a disorder where the person does not produce enough insulin or that the body does not respond appropriately to the insulin produced. This results in a hormonal imbalance. ->Type 1 diabetes = Antibodies destroy cells in the pancreas that produce insulin; beta cells. An autoimmune disease where the immune system mistakenly attacks the body. The white blood cells in the body accidently recognises that the beta cells are foreign and essentially secretes special types of antibodies in which breakdown and destroy the body’s own beta cells. ->Type 2 diabetes = The body cells become resistant to the effect of insulin. The insulin receptors on the cells are no longer responding to the insulin. Insulin will still be produced by the liver, however the insulin and insulin receptor will not bind together. This causes the glucose in the blood not being able to enter the liver to become glycogen. Therefore, causing high blood sugar, leading to type 2 diabetes. Individuals with diabetes suffer from hyperglycaemia; higher than normal blood glucose due to lack of insulin. ->Hyperglycaemia is a big issue in terms of factors such as nerve damage, retinal damage, damage to blood vessels and renal failure. In some cases, it can even result in a coma or death. Osmoregulation refers to the control of water levels in the blood. ->It is important to control water levels in the blood as imbalance can cause hypotension and hypertension. Hypotension (low water levels) = Low blood pressure (reduced blood flow to organs) Hypertension (high water levels) = high blood pressure (increases risk of heart disease or kidney failure)

STAGE 2 Biology (Homeostasis)...