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Biology Chapter 6
6A, 6B, 6C, 6D, 6E
| Question | Answer |
|---|---|
| homeostasis | the maintenance of a relatively stable internal environment in the body despite changes in the external environment |
| All homeostatic systems can be described using ... | a stimulus-response model and positive and negative feedback systems |
| The stimulus-response model | a model that describes how a system responds to a stimulus |
| 1 Stimulus | a change in the external or internal environment of an organism. |
| 2 Receptor | a structure that detects a signal or external change, usually a protein |
| Receptor process | the stimulus is detected by a receptor in the body which then transfers this stimulus into a chemical or electrical signal for transmission to the modulator. There are many types of receptors |
| 3 Modulator/s | location where information from receptors is sent to and compared to a set point, and where molecules altering the functioning of an effector are released |
| Modulator/s process | info from the receptors sent to the modulator then compares the info received from the receptors with an ideal condition the body aims to maintain. Depending on the result,releases molecules that go on to alter the functioning of an effector |
| 4 Effector | a molecule, cell, or organ that responds to a signal and produces a response |
| 5 Response | the action of a cell, organ, or organism caused by a stimulus the effector initiates the response to the stimulus. The response is any change in the function of a target cell, organ, or organism after stimulation from an initial signal. |
| positive feedback system | a stimulus–response process in which the response increases the stimulus |
| Negative feedback system | stimulus–response process in which the response counters the stimulus, that is, the response attempts to revert the system back to the state it was in before the stimulus occurred. |
| stimulus-response model at a cellular level | Reception – the detection of a stimulus and the transmitting Transduction – the transmission of a signal during cellular signalling. Response – the change in the function of a target cell, organ, or organism. |
| Methods of heat transfer | Conduction, convection, evaporation, radiation |
| Conduction | the transfer of heat through physical contact with another object eg touching something hot and it being transferred to your fingertips |
| Convection | the transfer of heat via the movement of a liquid or gas between areas of different temperature eg hot air rising in double story buildings taking the heat energy with it |
| Evaporation | the loss of heat via the conversion of water from liquid to gas |
| Evaporation when you sweat | the water on your skin evaporates. Turning a liquid into a gas requires a lot of energy, and when sweat evaporates it takes away heat energy from your skin making you cool down |
| Radiation | The transfer of heat via electromagnetic waves such as light (i.e. doesn’t require physical contact with another object) eg sun warming you via radiation |
| thermoregulation | the homeostatic process of maintaining a constant internal body temperature, |
| overall body temperature of an organism organism | total heat change = heat in + metabolic heat – heat out |
| Endotherms | an animal that produces the majority of its own heat via metabolic processes |
| ectotherm | an animal that obtains heat primarily from the environment, rather than its own metabolic heat |
| stimulus-response model of thermoregulation | stimulus: change in core body temp or enviro temp receptor: thermoreceptors brain or skin (detect temp changes) modulator: hypothalamus effector: variety of effector cells and tissues repsonse: cause change in heat transfer to maintain core temp of 37 |
| hypothalamus | a section of the brain in mammals that controls the maintenance of the body’s internal environment |
| What happens if it’s too hot? | the hypothalamus sends signals to a number of different effectors |
| effectors and responses when its too hot | Sweat glands produce sweat ,Small blood vessels in the skin vasodilate, cerebral cortex causes changes in behaviour Arrector pili muscles relax flattens body hair signals sent to hypothalamus to slow metabolic processes |
| effectors and responses when its too cold | Skeletal muscles are stimulated to cause shivering Small blood vessels in the skin constrict, vasoconstriction, cerebral cortex causes changes in behaviour Arrector pili muscles in the skin contract signals are sent to increase metabolic processes |
| what is the extra effector and response of the cold | Brown fat cells are stimulated to produce heat via the burning of triglycerides. |
| glucose | a six-carbon carbohydrate that comes from the food we eat , the main source of energy for all the cells in our body |
| process of how glucose is broken up | is absorbed by the small intestine and released into the bloodstream can travel around the body where it gets taken up into cells, the process of respiration breaks it up into smaller blocks of energy called ATP that are used to power cell function |
| glycogen | another source of glucose Serves as the main storage of glucose in the body ,a long series of glucose molecules joined together so glucose can be stored for prolonged periods of time in cells. |
| glycogenesis | the process of creating glycogen from glucose |
| how is glycogen produced? | . Glycogen is produced by the process known as glycogenesis that joins glucose absorbed by skeletal muscle and liver cells together into glycogen |
| glycogenolysis | the process of breaking down glycogen into glucose , when you use up all your available blood glucose, glycogen is broekn down back into glucose that re enters the bloodstream where it can go to cells |
| Glucose transport around the body | transported in blood plasma around the body. normal blood glucose level in a human is roughly between 4.0 mmol/L and 7.8 mmol/L Our bodies need to maintain our blood glucose level within this narrow range |
| hyperglycaemia | the state of having blood glucose levels above the normal range (>7.8 mmol/L) |
| hypoglycaemia | the state of having blood glucose levels below the normal range (<4.0 mmol/L) |
| how does homeostasis maintain constant blood glucose levels | by releasing insulin to lower blood glucose levls and glucagon to increase , occurs via a negative feedback according to the stimulus-response model |
| blood glucose stimulus response model | stimulus: change in blood glucose levels above below 5mmol/L receptor: pancreas, specifically specialised cells caled the islets of Langerhans compromised of alpha and beta cells, these cells detect glucose levels |
| blood glucose stimulus response model | modulator: islets of Langerhans-insulin or glucagon is released depending on whether glucode levels are high or low they travel through the bloodstream to alter effectors throughout the body response: increase/decrease in blood glucose levels |
| what happens when blood glucose levels increase? | when islets of Langerhans detects blood glucose level above 5 mmol/L, beta cells release insulin, insulin goes on to stimulate two effectors via two pathway |
| first effector pathways: | when insulin binds to skeletal and fat cells, glucose transporters are inserted into the cells membrane via facilitated diffusion, this extra glucose can be used by mitochondria to create energy |
| second effector pathways: | liver cells are stimulated to convert more glucose into glycogen . the liver already has a high uptake of glucose and this is unnafected by insulin, however it activates a number of enzymes for glycogenesis, when cells absorb glucose, levels are lowered |
| What happens when blood glucose levels decrease? | When an islet of Langerhans detects a fall in blood glucose levels below about 5 mmol/L, alpha cells secrete glucagon. Glucagon stimulates liver cells to break down glycogen into glucose and release it into the bloodstream via glycogenolysis. |
| osmolality | the total concentration of solute in a given weight of water |
| how does osmolality work | more water is added to extracellular fluid, osmolality decreases as concentration of solutes will be lower.If water is removed from the extracellular fluid, its osmolality will increase as the overall concentration of solutes will be higher |
| osmoregulation | the homeostatic regulation of osmolality in the body via the alteration of water and solute balance |
| the regulation of water in the body can be explained using a stimulus-response model | stimulus: change in water volume causing change in osmolality, blood preassure and blood volume receptors: osmoreceptors and baroreceptors |
| modulators | For the osmoreceptor pathway two main modulators – the hypothalamus and the pituitary gland baroreceptor pathway, cells in the kidneys= modulators. Baroreceptors also send signals to the hypothalamus, adding to the effects of the osmoreceptor pathway |
| rest of stimulus response model | effectors: are the cells of the distal convoluted tubule and collecting duct in the nephrons of the kidneys, and the hypothalamus responses: alteration in the reabsorption of water which changes the osmalality of blood and blood pressure and volume |
| osmoreceptor | a type of receptor found primarily in the hypothalamus that detects changes in osmolality |
| baroreceptor | a type of receptor found throughout the body that detects changes in blood pressure |
| What happens when water levels decrease? | increase in the osmolality of blood decrease in blood pressure and volume osmolality detected by osmoreceptors- hypothalamus initiates release of ADH blood pressure and volume are detected by baroreceptors stimulate the release of renin. |
| Antidiuretic hormone (ADH) pathway | signals are sent to the posterior pituitary gland, release of ADH increases water reabsorption in the nephrons of the kidney increases the number of aquaporins inserted into the cells of the distal convoluted tubule and collecting duct |
| aquaporin | a family of transmembrane proteins facilitating the transport of water into and out of a cell |
| second function of ADH | ADH travels to the thirst centre in the hypothalamus which generates the feelings of thirst, leading to the person to drink something to increase the water volume in their body |
| secretion of renin | decreases in blood pressure and volume are detected by baroreceptors, which sends signals to the hypothalamus which contributes to the release of ADH from the posterior gland and trigger the release of renin from the kidneys |
| renin continued | causes release of aldosterone from adrenal glands, activates sodium potasim pumps in the cells lining the distal convulated tubule and collecting duct, due to osmosis, water follows the movement of sodium , increasing the blood preassure and volume |
| What happens when water levels increase? | amount of water in the body increases, causes decrease in osmolality of blood, increase in blood pressure and volume. Decreases in osmolality are detected by osmoreceptors, and increases in blood pressure and volume are detected by the baroreceptors. |
| continued | receptors signal the hypothalamus to decrease the release of ADH from the posterior pituitary gland( fewer aquaporins will be inserted) the thirst centre in the hypothalamus is suppressed so more water will be excreted in urine |
| type 1 diabetes | an autoimmune disease in which beta cells of the pancreas are destroyed, resulting in an inability to regulate blood glucose levels, produce little to no insulin, the neighbouring alpha cells are also impaired and can no longer function properly. |
| hyperglycarmia in terms of diabetes | Because glucose can’t be absorbed they are at risk of hyperglycaemia, increased pee and excessive thirst, excessive hunger and lethargy, weight loss, as well as long term conditions like vision loss, stroke, kidney damage, due to damged blood vessels |
| Hypoglycaemia in terms of diabetes | if they inject too much insulin or exercise too much as alpha cells are impaired, don’t produce normal levels of glucagon, do not produce normal amounts of glucose via glycogenolysis |
| The thyroid gland | secretes two hormones – T3 and T4 These hormones go on to have a wide range of effects throughout the body |
| stimulus response model in terms of normal thyroid use | hypothalamus periodically releases TRH, which stimulates the anterior pituitary gland to secrete TSH this stimulates the thyroid gland, which then secretes T3 and T4. T3 and T4 inhibit the secretion of TRH and TSH via negative feedback |
| hyperthyroidism | overactivity of the thyroid gland, resulting in increased production and secretion of thyroid hormones, produces too much T3 and T4 and has reduced levels of TSH |
| causes of hyperthyroidism | Graves’ disease |
| graves disease | The immune system of people with Graves’ disease produces an autoantibody called TSI, recognises and binds to the TSH receptors on the thyroid, stimulates T3 and T4 |
| symptoms of hyperthyroidism | increased metabolism, increased repritory rate, increased blood preassure, diarrhoea, eyes bulge |
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