5.1.1 Communication and Homeostasis Flashcards
What is homeostasis?
-maintenance of a constant internal environment in response to changes in external/internal environment
-involves control systems that keep internal environment roughly constant
How do animals respond to the environment?
- respond to changes in their external environment i.e by avoiding harmful environments
-respond to changes in their internal environment to make sure conditions are optimal for metabolic reactions
Changes to internal environment
-internal body temp
-blood glucose levels
-water levels
-pH
Changes to external environment
-external temp
-humidity
-light(plants)
-harmful stimuli i.e sudden sounds/pain
Why is homeostasis important?
-essential for enzyme activity
-allows them to avoid harmful environment / ensure that conditions are optimum for metabolism
Why are receptors and effectors needed?
-restore dynamic equilibrium in response to conditions
-receptors trigger and co-ordinate the correct responses
-info from sensory receptors is transmitted to the brain + impulses are sent along motor neurons to effectors(muscles/glands) that react to bring about change in response to stimulus
Why do multicellular organisms need communication systems?
-organs, cells and tissues have different functions, are found in different parts of the body and may have different roles to one another
-need to communicate
Short paracrine cell signalling
-occurs between cells that are close together i.e neurotransmitters between nerves or muscle cells
Long distance endocrine signalling
-involves signalling over long distances
-signalling molecules are transported in the circulatory system
What is a hormone?
-a chemical messenger, secreted by glands and found in the endocrine system
similarities between the endocrine + nervous system
-both have coordination centres(brain, spinal cord)
-both send signals in the body
-both have receptors to detect stimuli
-both have effectors(muscles/glands) to carry out response
Differences between nervous + endocrine system
-chemical messengers vs nerve impulses
-hormones are longer lasting vs nerves are shorter lasting
-nerves work faster than hormones
-hormones are widespread vs nerve impulses are specific
What do cell surface receptors do?
-allow cells to recognise the chemicals involved in cell signalling
What is negative feedback?
-control mechanism that elicits response to help restore changed value to norm
-receptors detect when a level is too high/low-}info communicated via nervous/hormonal system –} effectors respond to counteract the change
What happens if the change from normal is too big?
-effectors may not be able to counteract it, i.e a huge drop in body temp caused by prolonged exposure to cold
What is positive feedback?
-amplifies the change away from normal
-not involved in homeostasis because internal environment isn’t constant
-rapidly activates processes in the body i.e platelets forming blood clots
Why is it important to maintain core body temp?
- temp affects enzyme activity and enzymes control the rate of metabolic reactions
How does high body temp have an effect?
-rise in temperature makes the enzyme’s molecules vibrate more
-if temp goes above a certain level, vibration breaks some H bonds in the tertiary structure
-active site changes shape and enzyme + substrate no longer fit together
-enzyme denatures
How does low body temp have an effect?
-enzyme activity / RoR
-enzyme-substrate complexes cannot form
Why does body temp fluctuate throughout the day?
-it is dependent on the external environment
-respiration is an exothermic reaction, so the temp it works at changes
How are temp changes in the body detected?
-the peripheral temp receptors are in the skin + detect changes in the skin surface temp
-temp receptors in the hypothalamus detect temp of blood in the body
What is an ectotherm?
-an animal that uses their surroundings in order to maintain a relatively constant core temp
-change their behaviour i.e migration
Sources for ectotherms to regulate temp
-radiation= absorbing thermal energy
-evaporation
-convection= thermal energy transferred with air/liquids
-conduction= transfer of thermal energy through solid surfaces
What are endotherms?
-can control their body temperature internally via homeostasis i.e mammals and birds
Difference in metabolic rate between ectotherms and endotherms
-ectotherms don’t have a constant body temp so their metabolic rate varies
–} more active at higher temps and vice versa
-endotherms can keep internal temp constant so they have a constantly high metabolic rate–} largely independent of external temp
Mechanisms to reduce body temp: vasodilation
-atertioles near the surface of the skin dilate when temp rises
-vessels that provide a direct connection between the arterioles + the venules constrict
-this forces blood through the capillaries in the surface layers of the skin
-more heat is lost from the skin in radiation +temp is lowered
Mechanisms to reduce body temp:
Sweating
-more sweat secreted from sweat glands as core temp increases
-water in sweat evaporates from the surface of the skin(uses heat energy to turn water into vapour)—} cools the skin
Mechanisms to reduce body temp:
Hairs lie flat
-as temp increases, the erector pilli muscles in the skin relax, causing hairs to lie flat
-avoids trapping an insulating layer of air–} skin is less insulated and heat can be lost more easily
Mechanisms to increase body temp:
vasoconstriction
-arterioles near me surface of the skin constrict–} less blood flows through the capillary networks close to the surface of the skin
-very little radiation takes place–} the warm blood is kept well below the surface to reduce heat loss
Mechanisms to reduce body temp:
Decreased sweating
-less sweat is secreted from sweat glands when it’s cold–} reducing the amount of heat loss
-less evaporation of water from the skin’s surface
Mechanisms to reduce body temp:
Hairs stand up
-erector pilli muscles in the skin contract, making the hairs stand up
-traps an insulating layer of air, so reduces cooling through the skin
Mechanisms to reduce body temp:
Shivering
-muscles contract in spasms–} rapid, involuntary contracting + relaxing of muscles
-metabolic heat from the increased exothermic reactions (respiration) warm up the body
Mechanisms to reduce body temp:
Hormones
-body releases adrenaline + thyroxine
-increases metabolism + so more heat is produced
What is the endocrine system?
-made up of endocrine glands–} group of cells which are specialised to secrete hormones
-glands can be stimulated to release hormones by a change in conc of a substance/electrical impulse
Hormones
-chemical messengers i.e steroids, proteins, glycoproteins, polypeptides, amines etc
-secreted directly into the blood and transported through the body in blood plasma
-then diffuse out of the blood and bind to receptors of membranes on target cells–} stimulate hormone to produce response
action of hormones in cell signalling (non-steroid hormones)
-primary messenger(hormone) with a complimentary shape binds to the specific receptor on the cell surface membrane of the target cell from the endocrine gland
-this activates an enzyme in the cell membrane which catalyses the production of a secondary messenger–} activates a cascade of reactions inside the cell(to do with protein synthesis/activation) i.e adrenaline
action of hormones in cell signalling (steroid hormones)
-because they are non-polar + lipid soluble molecules, they can pass through the lipid component of the cell membrane and bind to complimentary receptors inside the cell to form a hormone-receptor complex–} acts as a transcription factor which facilitates/inhibits the transcription of a specific gene i.e oestrogen
Hormonal vs neuronal communication
-communication via hormones vs nerve impulses
-hormone transmission via bloodstream vs nerve transmission is by neurones
-hormones work slow vs nerves work faster
-widespread response in hormones vs localised response in nerves
-slow vs rapid
-long lasting vs short lived
-permanent and irreversible vs temporary and reversible
Structure of the adrenal glands
-two small endocrine glands located just above the kidney
-produce effects that help prepare the body for the ‘fight or flight’ response
-the cortex= outer region of glands, produce hormones that are vital to life released by the pituitary gland i.e cortisol and aldosterone
-the medulla= inner region of the glands, controlled by the nervous system, produces hormones i.e adrenaline and noradrenaline
-these parts are surrounded by a capsule
Cortex: Cortisol
-helps regulate metabolism by stimulating the breakdown of proteins + fats to glucose which increases the amount of energy available so the brain and muscles can form a response
-works with other hormones to suppress the immune system so the body does not attack itself in the fight or flight response
Cortex: Aldosterone
-helps control blood pressure
-regulates blood vol and pressure by regulating the balance of sodium ions + water in the kidneys
Cortex: Androgens
-small amounts of male + female sex hormones are released–} small impact but important especially for women after menopause
Medulla: Adrenaline and Noradrenaline
work together to:
-increase heart rate
-increase breathing rate
-constrict some blood vessels in non-essential organs so blood is diverted to brain and muscles(high bp)
-widening of air passages in the lungs
-convert glycogen to glucose in the liver–}glycogenolysis= increases respiration because more glucose is supplied to muscles, produce more energy
Main functions of the pancreas
-to secrete hormones into the bloodstream as an endocrine gland
-to secrete enzymes/pancreatic juice and release them via a duct i.e digestive enzymes (amylase, lipase etc) into the digestive system as an exocrine gland
3 important digestive enzymes and how they are secreted
-amylase: breaks down starch into simple sugars i.e maltose(disaccharide broken down further by maltase into alpha glucose)
-protease: breaks down proteins into amino acids
-lipase: breaks down lipids into fatty acids and glycerol
the digestive enzymes alongside pancreatic juice are delivered to the small intestines via a duct
Islets of Langerhans and their role
-small regions of endocrine tissue within the exocrine tissue
-found in clusters around the blood capillaries and they secrete insulin and glucagon directly into the bloodstream
-alpha cells secrete glucagon and beta cells secrete insulin–} help to control blood glucose concentration
Histology of Islets of Langerhans
-lightly stained(differential staining normally used to distinguish alpha cells from beta cells)
-large spherical clusters
Histology of exocrine pancreatic tissue(acinus)
-darker stained
-small, berry-like clusters
Blood glucose concentration
-normal level= 90 mg per 100cm3 of blood
-the body uses glucose to produce ATP during respiration
-high levels after a meal but low levels later
-low levels don’t have enough glucose for respiration
Increasing blood glucose concentration: diet
-after eating food containing carbohydrates
–} hydrolysed in the digestive system to release glucose into the bloodstream i.e starch=(amylase) maltose= glucose(maltase)
Increasing blood glucose concentration: glycogenolysis
-glycogen stored in liver + muscle cells is hydrolysed into glucose which is released into the bloodstream
Increasing blood glucose concentration: gluconeogenesis
-production of glucose from a non-carbohydrate source
-produces glucose from amino acids/ glycerol(from lipids) in the liver
Decreasing blood glucose concentration: respiration
-glucose is needed as a substrate for respiration
-higher levels needed to generate more energy for muscle cells to contract during exercise
Decreasing blood glucose concentration: glycogenesis
-formation of glycogen from excess glucose which is stored in the liver when BGC is too high
Role of insulin
-rise of BGC is detected by the B cells in the islets of Langerhans
-Insulin secreted to lower BGC, which targets liver + most body cells:
-increases the rate of absorption of glucose in liver + muscle cells
-increases rate of respiration in cells(more glucose needed)
-increases rate of glycogenesis(store as glycogen in liver + muscle cells)
-increases rate of glucose to fat conversion
-inhibits release of glucagon from a cells
How does insulin enter cells?
-most body cells have insulin receptors on cell surface membrane(not RBCs)
-insulin binds to glycoprotein receptor which changes tertiary structure of glucose transport protein channels
-causes channels to open allowing more glucose to enter
-can also activate enzymes(secondary messengers) in some cells to covert glucose to glycogen/fat
Regulating insulin secretion
-broken down by enzymes in liver cells–} has to be constantly secreted to maintain effect
-when BGC falls below a certain level, B cells reduce insulin secretion= negative feedback
Role of glucagon
-produced by alpha cells of the Islets of Langerhans after drop in BGC is detected
-target liver + fat cells(highest store of glycogen + lipids)
-Raises BGC levels:
-gluconeogenesis–} increasing conversion of amino acids + glycerol in the liver
-glycogenolysis–} liver breaks down its glycogen store into glucose and releases it back into bloodstream
-reducing the amount of glucose absorbed the liver cells
How does glucagon enter cells?
-only liver and fat cells have specific glucagon receptors–} only cells that respond to glucagon
Negative feedback in glucagon
-when BGC rises above a certain level, the a cells reduce glucagon secretion
Why is maintaining blood glucose self-regualting?
-the level of glucose determines the quantity of insulin and glucagon secreted
Membrane potential
-generated through an unequal distribution of ions either side of the plasma membrane
-most cells have a resting -70 mv
3 things that generate resting potential
-permeability
-electrical gradient
-concentration gradient
Difference between depolarised and repolarised
-mv of membrane closer to 0= depolarising
-mv of membrane further from 0= repolarising
Control of insulin secretion by B cells
-B cells are at rest with -70 mv(potassium ion channels are open)
-high BGC is detected–} more glucose enters the cell via glucose transporter(facilitated diffusion)
-glucose is metabolised in mitochondria= production of ATP via respiration
-Influx of ATP causes K+ channels to close(binds to ATP sensitive K+ channels)
-K+ conc increases inside of the cell
-potential difference of B cells gets more positive and depolarises(-30mv)
-depolarisation causes voltage gated calcium channels to open–} Ca2+ ions diffuse into the cell
-increase of calcium ions causes insulin vesicles to move to and fuse with the plasma membrane
(cascade of reactions)
-insulin secreted via exocytosis
hyperglycaemia vs hypoglycaemia
-hyper= high BGC
-hypo= low BGC
What is diabetes?
-condition where blood glucose concentration cannot be controlled properly
Type 1 diabetes
-autoimmune disease where the body attacks and destroys B cells in the islets–} no insulin produced
-BGC conc stays high after eating and can result in death if untreated
-normally develops in childhood
-risk slightly increased with family history
Treating type 1
-regular insulin injections throughout the day
-insulin pump–} delivers insulin via a tube beneath the skin
-regular testing of BGC(normally pricking finger to analyse blood to calculate conc of insulin needed)
What happens if a person in injected with too much/little?
-too much= may experience hypo and can result in unconsciousness
-too little= hyper= unconsciousness/ death if untreated
Type 2 diabetes
-when B cells don’t produce enough insulin or body cells don’t respond properly to insulin
-insulin receptors on membranes may not work properly–} cells don’t take up enough glucose
-often linked with obesity
-risk increased from certain ethnic groups + family history
Treating type 2
-regulating carb intake and matching it to exercise level(diet and excercise)
-medication to stimulate insulin production or slows down rate of glucose absorption from intestine
What is synthetic biology?
-using other organisms to produce something man-made
Potential treatments:
transplants
-pancreas transplants–} 80% success rate
-B cell injections–} less than 8% success
-hard to source
-over exhausting immunosuppressants
Where did insulin used to get extracted from?
-from animal pancreases i.e pigs and cows
-expensive
-may cause allergic reactions
Potential treatments: Stem cells
-totipotent cells could differentiated to B cells which would be implanted into patient
:( embryos have to be destroyed
:) no need to wait for donor, less likelihood of rejection
Role of pancreatic acini
-produce and secrete digestive enzymes
