Homeostasis and Excretion Flashcards
(129 cards)
1
Q
Why do we need communication systems for survival and activity
A
-cell metabolism relies on enzymes and enzymes need specific set of conditions in which to work efficiently
-all living things need to maintain: suitable temperature, suitable pH, aqueous environment keeping substrate and products in solutions, freedom from toxins and excess inhibitors
-without these conditions, cells become inactive and die
-in multicellular organisms, cells specialised to rely on one another therefore must be able to coordinate activities via communication
2
Q
How do immediate changes in external environments act as a threat
A
-when the external environment including air, water, or soil changes, this puts stress on organism
-for instance, cooler environment will cause greater heat loss - organism must change behaviour or physiology to reduce stress
-the environment change is a stimulus and way which organism changes behaviour or physiology is response
-the animal may have to escape a predator or move from burrow to sunlight for heat
3
Q
How do seasonal changes elicit response
A
-as seasons change, the environment will change eliciting a gradual response
-for example, the Arctic fox has a much thicker and whiter coat in winter and in summer its thinner and grey/brown
in winter it provides camouflage and insulation and in summer it allows the fox to not overheat
4
Q
What is the internal environment
A
-most multicellular organisms have a range of tissues and organs
-many of the cells and tissues are not exposed to the external environment-protected by epithelial tissues and organs such as skin or bark
-in many animals, the internal cells and tissues are bathed in tissue fluid - this is the environment
5
Q
How can internal environments change
A
-as cells undergo various metabolic activities, they use up substrates and create new products
-some of these compounds may be unwanted or toxic
-these substances move out of cells into tissue fluid therefore activities of cells alter own environment
6
Q
Describe the change of CO2 in internal environments
A
-carbon dioxide is a waste product that if allowed to build up in tissue fluid outside cells, it will alter pH of tissue fluid and could disrupt action of enzymes and other proteins
-accumulation of excess waste or toxins in this internal environment must act as stimulus to cause removal of these waste products to ensure cells survive
-in this case, reduced pH of blood stimulates greater breathing activity that expels CO2 from body
7
Q
How is internal environment maintained
A
-the composition of tissue fluid is maintained by blood
-blood flows throughout body and transports substances to and from cells
-any wastes or toxins accumulating in tissue fluid are likely to enter blood and be carried away
-to prevent accumulation in the blood, must be removed from body via excretion
8
Q
What is the importance of monitoring
A
-it is important concentrations of wastes products and other substances in blood are monitored closely
-this ensures body does not excrete too much of any useful substances but removes enough waste products to maintain good health
-it also ensures that cells in the body are supplied with substrates they need
9
Q
Why is the activity of organs required to be coordinated
A
-multicellular organism more efficient than single celled because its cells are differentiated
-this means that its cells are specialised to perform particular functions - groups of cells specialised to perform particular functions form tissues and organs
-the cells that monitor the blood may be in a different part of body well away from source of waste product
-they may also become distance from tissue or organ specialised to remove waste from the body
-therefore a good communication system required to ensure these different parts of body work together effectively
10
Q
Describe a good communication system
A
-cover whole body
-enable cells to communicate with each other
-enable specific communication
-enable rapid communication
-enable both short term and long term responses
11
Q
Describe cell signalling
A
-cells communicate with each other by process of cell signalling
-this is process in which one cell will release a chemical that is detected by another cell
-the second cell will respond to the signal released by first
-signals are specific by involving molecules with specific, complementary shape to cell surface receptor
12
Q
Describe the neuronal system
A
-interconnected network of neurones that signal to each other across synapse junctions
-the neurones can conduct a signal very quickly and enable rapid responses to stimuli that may be changing quickly
-elicit rapid responses, uses action potentials, across synapses and neurone transmitters
13
Q
Describe the hormonal system
A
-system that uses blood to transport its signals
-cells in an endocrine organ release the signal (a hormone) directly into the blood
-the hormone is transported throughout the body, but is only recognised by specific target cells
-the hormonal system enables longer term responses to be coordinated
14
Q
Define effector
A
a cell, tissue or organ that brings about a response
15
Q
Define homeostasis
A
Maintaining constant internal environment despite changes in internal and external factors
16
Q
Define negative feedback
A
mechanism that reverses a change, bringing system back to optimum
17
Q
Define positive feedback
A
mechanism that increases a change, taking system further away from optimum
18
Q
Describe homeostasis
A
-homeostasis used in many living organisms to maintain conditions inside the body, despite external and internal factor changes
aspects maintained by homeostasis include: body temperature, blood glucose concentration, blood salt concentration, water potential of blood, blood pressure and carbon dioxide concentration
19
Q
Define sensory receptors
A
sensory nerve endings that respond to a stimulus in the internal or external environment of an organism and can create action potentials
20
Q
Describe the mechanism of homeostasis
A
-any response to changes in the environment requires complex mechanism which may involve series of tissues and organs that are coordinated through cell signalling
-stimulus - receptor -communication pathway - effector - response
21
Q
Describe sensory receptors
A
-these receptors may be on surface of body such as temperature receptors on skin
-they monitor changes in external environment
-other receptors are internal to monitor conditions inside the body, for example, temperature receptors in brain
-when one receptor detects change it will be stimulated to send message to effector
22
Q
Describe communication systems
A
-such as neuronal or hormonal system
-this acts by signalling between cells
-it is used to transmit a message from receptor cells to effector cells via coordination centre usually in brain
-the messages from receptor to coordination centre known as input
-messages sent to effectors known as output
23
Q
Describe effector cells
A
-such as liver or muscle cells
-bring about response
24
Q
Describe feedback
A
-when the effectors respond to the output from coordination centre, they bring about response that will change conditions inside body
-such changes will be detected by receptors
-this will have effect upon response pathway
-in effect, the input will change
25
Describe negative feedback
-in order to maintain constant internal environment, any change away from optimum must be reversed
-in this way, conditions inside body will be returned to optimum
-when conditions change, receptors detect this stimulus and send input to coordination system
-the coordination centre sends output to effectors and effectors respond
-they bring about a change that reverses initial change in conditions so the system moves it closer to optimum and stimulus reduced
-receptors detect reduction in stimulus and reduce input to coordination centre
-output from coordination centre to effectors also reduced so effectors reduce activity
-as system get closer to optimum, response it reduced
26
Summarise negative feedback
change away from optimum - receptor detects change -(input)-communication system informs effector -(output)- effectors reacts to reverse change - return to optimum condition - optimum condition
27
What are the requirements for negative feedback to work
1. change to the internal environment must be detected
2. change must be signalled to other cells
3. must be effective response that reverses in change of conditions
28
Describe how internal environments constantly maintained
-negative feedback system can maintain a reasonably constant set of conditions
-however conditions will never remain perfectly constant; there will be some variation around optimum conditions
-when stimulus occurs may take time to respond and response may cause slight overshoot - however as long as this variation not too great, conditions will remain acceptable
-when negative feedback applied to living systems, the condition inside living organisms will remain within narrow range
-the conditions will remain warm enough to allow enzymes to continue functioning efficiently but cool enough to avoid damage to proteins
29
Describe positive feedback
-positive feedback less common than negative feedback
-when positive feedback occurs, the response is to increase original change
-this destabilises the system and is usually harmful
-for example, below certain core body temperature enzymes become less active and exergonic reactions that release heat are slower and therefore release less heat
-this allows body to cool further and slows enzyme controlled reactions more - causes body temperature to spiral downwards (hypothermia)
30
Describe oxytocin positive feedback
-there are some occasions where positive feedback is beneficial
-an example is seen at end of pregnancy to bring about dilation of cervix
-as cervix begins to stretch this causes posterior pituitary gland to secrete hormone oxytocin - this increases uterine contractions which stretch cervix more, which causes more secretion of oxytocin
-once cervix fully dilated baby can be born -t this birth ends production of oxytocin
-the activity of neurones also relies on positive feedback
31
Describe ectotherm
-organism that relies on external sources of heat to maintain body temperature
-they are able to control their body temperature as effectively as endotherms
-however, using various behavioural mechanisms some endotherms are able to control their body temperature in all but most extreme conditions
32
Describe endotherms
-organism that uses heat from metabolic reactions to maintain body temperature
-they control their body temperature within very strict limits and are largely independent of external temperatures
33
Why does body temperature need to be controlled
-changes in body temperature can have dramatic effect upon activity of cell processes
-as temperature rises molecules have more kinetic energy - they move about more quickly and collide more frequently
-this means essential chemical reactions occurs more quickly - however in cooler conditions opposite occurs and chemical reactions slow down
34
Why does body temperature need to be controlled - proteins
-the structure of proteins can also be affected by changes - especially increases
-many proteins have metabolic function; for example enzymes increase rate of biological reactions
-enzymes are globular proteins and have very specific tertiary structure giving them a specific 3D shape
-in case of enzymes, the shape of active site is complementary to shape of substrate and any change in shape will affect ability to function
-if temperature is allowed to increase too much, enzymes change shape and their function is lost
35
Describe how enzymes are very sensitive to temperature change
-some enzymes are very sensitive to temperature change
-if body temperature drops by 10 degrees the rate of enzyme controlled reactions falls by half
-many reactions in cells release heat, which can help maintain temperature but if temperature drops and reactions slow less heat is released
-this allows body to cool further - form of positive feedback
-as body cools, organism less able to function normally
-on the other hand, if temperature rises just a few degrees above optimum, enzymes may denature and cease to function
36
Why is core temperature an important factor
-the core temperature is an important factor as all vital organs found in centre of body
-peripheral parts of body may be allowed to increase or decrease in temperature to some extent without affecting survival of organism
37
Describe temperature control in ectotherms
-ectotherms do not use internal energy sources to maintain their body temperature when cold - however once they are active their muscle contractions will generate some heat from increased respiration
-temperature regulation relies upon behavioural responses that can alter amount of heat exchanged with environment
-for example they may try absorb more heat from environment via: lying on warm surface, expose more surface area to sun etc
38
Give behaviour adaptation of snakes and its benefits
-bask in sun - absorb heat directly from sun
39
Give behaviour adaptation of locust and its benefits
-in early morning, sit side on to sun exposing large surface area but at midday sit head on to sun, exposing smaller surface area. Also climb to top of plant at midday to get away from soil surface - cool morning they absorb more heat but at midday when sun hotter, absorb less heat. Also avoid heat radiating from soil at midday
-increase both rate of breathing and depth of breathing movements when its hot - more water evaporates from tracheal system cooling the body
40
Give behaviour adaptations of lizards and their benefits
-many lizards use burrows or crevices between rocks. During hottest part of day and coolest part of night, lizards hide in burrows - underground burrows tend to have more stable temperature than air. In day burrow will be cooler than air but at night, burrow will be warmer than air outside
41
Give behaviour adaptations of the horned lizard and its benefits
-can change shape by expanding or contracting ribcage - expanding ribcage exposes larger surface area to sun so more heat can be absorbed
42
Advantages of ectothermy
-rely on external sources of heat and do not use up energy to keep warm therefore:
-less food used in respiration
-more energy and nutrients gained from food converted to growth
-need to find less food
-can survive for long periods without food
43
Disadvantages of ectothermy
-less active in cooler temperatures
-at risk from predators whilst cold and unable to escape
-cannot take advantage of food available while cold
44
Describe temperature regulation mechanisms in endotherms
-temperature regulation relies on effectors in skin and muscles
-the skin is the organ in contact with external environment
-therefore any physiological adaptations to control body temperature involve the skin
-the changes that take place in skin alter amount of heat being lost to environment
-many chemical reactions in body are exergonic - release energy in form of heat
-endotherms can increase respiration in muscles and liver to release heat
-also have other physiological mechanisms that are useful
45
PHYSIOLOGICAL RESPONSE - skin
HOT
-sweat glands secrete fluid onto skin surface; as this evaporates it uses heat from blood as latent heat of vaporisation
-Hairs and feathers lie flat to reduce insulation and allow greater heat loss
-vasodilation of arterioles and precapillary sphincters directs blood to skin surface so more heat can be radiated away from body
COLD
-if too cold, less sweat is secreted so less heat is lost
-Hairs and feathers stand erect to trap air which insulates body
-vasoconstriction of arterioles and precapillary sphincters leading to skin surface, blood is diverted away from skin surface so less heat is lost
46
PHYSIOLOGICAL RESPONSE - gaseous exchange system
HOT
-some animals pant, increasing evaporation of water from surface of lungs and airways. Evaporation uses heat from blood as latent heat of vaporisation
COLD
-less panting so less heat is lost
47
PHYSIOLOGICAL RESPONSE -liver
HOT
-less respiration takes place so less heat it released
COLD
-increased respiration in liver cells means that more energy from food is converted to heat
48
PHYSIOLOGICAL REPSONSE - skeletal muscles
HOT
-fewer contractions means that less heat is released
COLD
-spontaneous muscle contractions (shivering) release heat
49
PHYSIOLOGICAL RESPONSE - blood vessels
HOT
-dilation to direct blood to extremities so that more heat can be lost
COLD
-constriction to limit blood flow to the extremities so blood is not cooled too much - this can lead to frostbite in extreme conditions
50
BEHAVIOURAL RESPONSES - hot
-hide away from sun in shade or in burrow
-orientate body to reduce surface area exposed to sun
-remain inactive and spread limbs out to enable greater heat loss
-wet skin to use evaporation to help cool body - cats lick themselves and elephants spray water over their bodies
51
BEHAVIOURAL RESPONSES -cold
-lie in sun
-orientate body towards sun to increase surface area exposed
-move about to generate heat in muscles or in extreme conditions roll into ball shape to reduce surface area and heat loss
-remain dry
52
Advantages of endothermy
-maintain fairly constant body temperature whatever the temperature externally
-remain inactive even when external temperatures are low which means they can take advantage of prey that may be available or escape from potential predators
-inhabit colder parts of the planet
53
Disadvantages of endothermy
-use significant part of energy intake to maintain body temperature in cold
-need more food
-use for growth a lower proportion of energy and nutrients from food
-may overheat in hot weather
54
How is temperature regulation controlled
-if core temperature changes this alters the temperature of blood
-temperature receptors in hypothalamus detects this change and send out impulse to cause different responses to reverse change
-some responses need to be quick in order to prevent further change in body temperature - neuronal system transmits output from hypothalamus in order to make these responses rapid
-other response may need to be longer term; the hormonal system transmits the output to cause these responses
-if core temperature too low, hypothalamus brings about response
55
What is the role of peripheral temperature receptors
-thermoregulatory centre in hypothalamus monitors blood temperature and detects changes in core body temperature
-an early warning that the body temperature may change could help the hypothalamus to respond more quickly and reduce variation in core body temperature
-if extremities start to cool down or warm up this may eventually affect core body temperature
-peripheral temperature receptors in skin monitor temperature in extremities - this information is fed to thermoregulatory centre in hypothalamus
-if thermoregulatory centre signals to brain that external environment is very cold or very hot, brain can initiate behavioural mechanisms for maintaining body temperature
56
Describe excretion
-excretion is the removal of metabolic waste from the body
-metabolic waste is unwanted products/substance produced in excess (inside cells) by metabolic processes and may become toxic
57
What products must be excreted
-almost all products that are formed in excess by chemical processes occurring in the cells must be removed from body so they do not build up and inhibit enzyme activity and become toxic
-carbon dioxide from respiration
-nitrogenous waste such as urea
-other compounds such as bile pigments found in faeces
58
EXCRETORY ORGANS - lungs
-every living cell in body produces carbon dioxide as a result of respiration
carbon dioxide is passed from cells of respiring tissues into bloodstream where is it transported mostly in form of hydrogencarbonate ions to lungs
-in lungs carbon dioxide diffuses into alveoli to be excreted as you breathe out
59
EXCRETORY ORGANS - liver
-the liver is directly involved in excretion
-it has many metabolic roles and some of substances produced will be passed into bile for excretion with faeces; for example pigment bilirubin
-the liver is also involved in converting excess amino acids into urea
-amino acids are broken down by process of deamination
-the nitrogen containing part of molecule is then combined with carbon dioxide to make urea
60
EXCRETORY ORGANS - kidneys
-the urea is passed into bloodstream to be transported to kidneys
-urea is transported in solution - dissolved in the plasma
-in the kidneys the urea is removed from blood to become a part of the urine
-urine is stored in bladder before being excreted from body via urethra
61
EXCRETORY ORGANS - skin
-the skin is also involved in excretion but excretion is not primary function of skin
-sweat contains range of substances including salts, urea, water, uric acid and ammonia
-urea, uric acid and ammonia are all excretory products
-the low of water and salts may be an important part of homeostasis - maintaining body temperature and water potential of blood
62
Describe the importance of excretion
-allowing the products of metabolism to build up could be fatal
-some metabolic products such as carbon dioxide and ammonia are toxic
-they interfere with cell processes by altering pH so normal metabolism is prevented
-other metabolic products may act as inhibitors and reduce activity of essential enzymes
63
Describe how carbon dioxide is excreted
-most carbon dioxide is transported in the blood as hydrogen carbonate ions however this also forms hydrogen ions; carbonic acid dissociates to release H+ ions
CO2+H2O - H2CO3
H2CO3 - H+ + HCO3
-this occurs inside the red blood cells under the influence of the enzyme carbonic anhydrase but can also occur in blood plasma
-the hydrogen ions affect pH of cytoplasm in red blood cells
-the hydrogen ions interact with bonds within haemoglobin, changing 3D shape
-the hydrogen ions can then combine with haemoglobin forming haemoglobinic acid
-the carbon dioxide that is not converted to hydrogen carbonate ions can combine directly with haemoglobin producing carbaminohaemoglobin
-both haemoglobinic acid and and carbaminohaemoglobin are unable to combine with oxygen as normal - reducing oxygen transport further
-
64
How does pH change in blood plasma
-in the blood excess hydrogen ions can reduce pH of plasma
-maintaining pH of blood plasma is essential because changes could alter the structure of many proteins in the blood that help transport a wide range of substances around body
-proteins in blood act as buffers to resist changes in pH
-if change in pH is small then extra hydrogen ions are detected by respiratory centre in medulla oblongata in brain
-this causes increase in breathing rate to help remove excess carbon dioxide
65
How is CO2 transported in the blood
-5% dissolved in plasma
-10% CO2 bind to form haemoglobin to form carbaminohaemoglobin which causes Bohr effect and Hb acts as a buffer
-85% as hydrogen carbonate ions
66
Describe respiratory acidosis
-if blood pH drops below 7.35 may cause headaches, drowsiness, restlessness, tremor and confusion
-there may also be a rapid heart rate and changes in blood pressure
-this is respiratory acidosis - can be caused by disease or conditions that affect lungs themselves such as emphysema, chronic bronchitis, asthma or severe pneumonia
-blockage of airway due to swelling, foreign object or vomit can also induce acute respiratory acidosis
67
Describe the removal of nitrogenous compounds
-body cannot store excess amino acids - however amino acids contain almost as much energy as carbohydrates
-therefore it would be wasteful simply to excrete excess amino acids
-instead they are transported to liver and potentially toxic amino group is removed (deamination) - the amino group initially forms the very soluble and highly toxic substance ammonia (NH3)
-this is converted to less soluble and less toxic compound called urea which can be transported to kidneys for excretions
-the remaining keto acid can be used directly in respiration to release its energy or it may be converted to a carbohydrate or fat for storage
68
Why can uric acid not be stored
-uric acid formed from nucleic acid cannot be stored as too much may lead to Gout and kidney stones
69
Summarise how urea formed
ammonia + carbon dioxide - urea (NH2)2CO2 +H2O
70
Summarise deamination
amino acid+ oxygen - keto acid +ammonia
71
Describe blood supply to the liver
-the liver cells (hepatocytes) carry out many hundreds of metabolic processes so liver has important role in homeostasis
-it is therefore essential that liver cell has good supply of blood
-the internal structure of liver ensures that as much blood as possible flows past as many liver cells as possible
-this enables liver cells to remove excess or unwanted substances from blood and return substances to blood to ensure concentrations are maintained
72
Describe the hepatic artery
-oxygenated blood from heart travels from aorta via hepatic artery into liver
-this supplies the oxygen that is essential for aerobic respiration
-the liver cells are very active because they carry out many metabolic processes
-many of these processes require energy in form of ATP so its important the liver has a good supply of oxygen for aerobic respiration
73
Describe hepatic portal vein
-deoxygenated blood from digestive system enters liver via hepatic portal vein
-this blood is rich in products of digestion
-the concentrations of various substances will be uncontrolled as they have just entered the body from the products of digestion in the intestines
-the blood may also contain toxic compounds that have absorbed from the intestine
-it is important that such substances do not continue to circulate around body before their concentrations have been adjusted
74
Describe hepatic vein
-blood leaves the liver via the hepatic vein
-the hepatic vein rejoins the vena cava and blood returns to bodys normal circulation
-when blood reaches end of sinusoid the concentrations of many of its components have been modified and regulated
-at centre of each lobule is branch of hepatic vein known as intralobular vessel
-the sinusoids empty into this vessel
-the branches of hepatic vein from different lobules join together to form hepatic vein which drains blood from liver
75
Describe the bile duct
-bile is a secretion from the liver which has functions in digestion and excretion
-the bile duct carries bile from the liver to the gall bladder where it is stored until is it required to aid digestion of fats in the small intestine
-bile also contains some excretory products such as bile pigments like bilirubin which will leave the body with the faeces
76
Describe structure of the liver (lobules)
-the cells, blood vessels and chambers inside the liver are arranged to ensure the greatest possible contact between blood and liver cells
-the liver is divided into lobes which are further divided into lobules
-the lobules are cylindrical
77
Describe liver structure (sinusoids)
-as the hepatic artery and hepatic portal vein enter the liver they split into smaller and smaller vessels
-these vessels run between and parallel to lobules - interlobular vessels
-at intervals, branches from hepatic artery and hepatic portal vein enter lobules
-blood from two blood vessels is mixed and passes along special chamber called sinusoid which is lined with hepatocytes
-as blood flows along sinusoid its in close contact within liver cells
-these cells are able to remove substances from blood and return other substances to the blood
78
Describe Kupffer cells
-specialised macrophages called Kupffer cells move about within the sinusoids
-their primary function appears to be to breakdown and recycle old red blood cells
79
Describe bile canaliculi
-one of the products of haemoglobin breakdown is bilirubin which is one of bile pigments excreted as part of bile
-bile is made in liver cells and released into bile canaliculi
-the bile canaliculi join together to form bile duct which transports bile to gall bladder
80
Describe liver cells
-liver cells of hepatocytes appear to be relatively unspecialised
-they have simple cuboidal shape with many microvilli on surface
-however, their many metabolic functions include protein synthesis, transformation and storage of carbohydrates, synthesis of cholesterol and bile salts, detoxification and many other processes
-this means that their cytoplasm must be very dense and is specialised in the numbers of certain organelles that it contains
81
Describe metabolic functions of the liver
-controlling blood glucose levels, amino acid levels, lipid levels
-synthesis of bile, plasma proteins, cholesterol
-synthesis of red blood cells in fetus
-storage of vitamins A, D, B12, iron and glycogen
-detoxification of alcohol and drugs
-breakdown of hormones
-destruction of red blood cells
82
Describe the structure of glycogen
-monomer is alpha glucose
-1-4 glycosidic bonds (between)
-1-6 glycosidic bonds (off side)
-branched so can be hydrolysed for quick release of energy to meet high metabolic demands
-compact for storage
-insoluble so doesn't affect the water potential of the cell
83
Describe the storage of glycogen in the liver
-liver stores glucose in the form of glycogen
-carbohydrates are transported as glucose in the blood
-when blood sugars are high - glucose stored as glycogen which requires the enzyme glucose synthase
-this occurs via a condensation reaction and is initiated by the hormone insulin
-when blood sugars are low - glycogen hydrolysed by glycogen phosphorylase to raise them
-initiated by hormone glucagon
-the liver is able to store approximately 100-120g of glycogen
-glycogen forms granules in the cytoplasm of hepatocytes
84
Which enzymes hydrolyse bonds of glycogen
-1-4 glycosidic bonds by amylase
-1-6 glycosidic bonds by glycosidase
85
Why is the liver needed for detoxification
-helps to remove toxins
-for example, hydrogen peroxide, recreational drugs and medicines
-rendered harmless via oxidation, reduction or methylation
86
Describe detoxification of hydrogen peroxide
-the enzyme catalase breaks down hydrogen peroxide
-2H2O - H2O +O2
-catalase has a very high turnover number (number of molecules of hydrogen peroxide that one molecule of catalase can render harmless in one second) of five million
87
Describe detoxification using cytochrome P450
-cytochrome c is involved in electron transport chain in respiration and photosynthesis therefore toxins can affect metabolism
-cytochrome P450 is a protein and due to DNA, individuals have different active site shapes and some are more or less complementary to break down cocaine and other various medicinal drugs
-therefore individuals have varying side effects
88
Describe ethanol
-C2H5OH
-Depresses nerve activity
-small, lipid molecule
-broken down into harmless substances
89
Describe how alcohol is detoxified
-alcohol is broken down in hepatocytes by action of enzyme ethanol dehydrogenase
-ethanol loses 2H therefore oxidised
-the resulting compound is ethanal
-this is further dehydrogenated and oxidised by enzyme ethanal dehydrogenase
-final compound produced is acetate
-this acetate is combined with coenzyme A to form acetyl coenzyme A which enters the process of aerobic respiration in a stage called the Krebs cycle
90
Describe how fatty liver occurs
-NAD is also required to oxidise and breakdown fatty acids for use in respiration
-if liver has to detoxify too much alcohol it uses up its stored of NAD and has insufficient left to deal with fatty acids
-these fatty acids are then converted back to triglycerides and stored as fats in the hepatocytes causing liver to become enlarged
-this is a condition known as fatty liver and can lead to hepatitis or cirrhosis
-cirrhosis is where the sinusoids are replaced by fibrous tissue: symptoms include infections due to depressed immune system, vitamin deficiencies, nerve damage and eventually coma and death
91
Describe the formation of urea
-everyday we need 40-60g of protein
-however, most people in developed countries eat far more than this
-excess amino acids cannot be stored because amino acids make toxins
-however amino acid molecules contain a lot of energy, so it would be wasteful to excrete whole molecule
-therefore excess amino acids undergo treatment in liver to remove and excrete amino component
-this treatment consists of deamination followed by ornithine cycle
amino acid - (DEAMINATION)- ammonia+ keto acid - (ORNITHINE CYCLE) - urea
92
Describe deamination
-process of deamination removes amino group and produces ammonia
-ammonia is very soluble and highly toxic
-therefore ammonia must not be allowed to accumulate
-deamination also produces organic compound, a keto acid, which can enter respiration directly to release its energy
-deamination: amino acid + oxygen - keto acid + ammonia
93
Describe the ornithine cycle
-because ammonia is so soluble and toxic it must be converted to a less toxic form very quickly
-the ammonia is combined with carbon dioxide to produce urea
-this occurs in the ornithine cycle
-ammonia and carbon dioxide combine with amino acid ornithine to produce citrulline
-this is converted to arginine by addition of further ammonia
-the arginine is then reconverted to ornithine by removal of urea
-urea is both less soluble and less toxic than ammonia
-it can be passed back into blood and transported around body to kidneys
-in kidneys urea filtered out blood and concentrated in urine
-urine can safely be stored in bladder until its release from body
94
Describe the breakdown of steroid hormones in the liver
-steroid hormones include testosterone, oestrogen and thyroxine
-they are altered or broken down by the liver
-they make them more water soluble and therefore easier to remove in the urine
-liver oxidises, reduces or methylates them
95
Describe the breakdown of non polar drugs/medicines
-non polar medicines include antibiotics, barbiturates, paracetamol
-need to be taken to the liver so they stop effecting/working else would be harmful
-taken to liver to be oxidised, reduced, or methylate to make them more water soluble and therefore easier to remove in urine
96
Describe basic structure of kidneys
-most people have two kidneys- these are positioned on each side of spine, just below lowest rib
-each kidney is supplied with blood from renal artery and drained by renal vein
97
What is the role of the kidneys
-role of kidneys is excretion
-they remove waste products from blood and produce urine
-urine passes out of kidney, down ureter to bladder where it can be stored until it is released
98
Describe the fine structure of the kidney
-outer region =cortex
-inner region= medulla
-centre=pelvis
-bulk of each kidney consists of tiny tubules called nephrons
-each kidney contains about one million nephrons - functional part
-each nephron starts in cortex at cup shaped structure called Bowman's capsule
-remainder of nephron is coiled tubule that passes through cortex, forms a lop down into medulla and back to cortex before joining collecting duct that passes back down into medulla
-capsule is made of fibrous material, has a protective function
99
Describe blood supply and filtering of the kidneys
-the renal artery splits to form many different arterioles which each lead to a knot of capillaries called glomerulus
-blood from glomerulus continues into efferent arterial from afferent arteriole under high pressure and carries blood to more capillaries surrounding rest of tubule
-these eventually flow together into renal veiin
-each glomerulus is surrounded by Bowman's capsule
-fluid from blood is pushed into Bowman's capsule by process called ultrafiltration
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How is the kidney adapted for ultrafiltration
-the endothelium of capillary - there are narrow gaps between cells of endothelium of capillary wall. the cells of endothelium also contain pores called fenestrations. the gaps allow blood plasma and substances dissolved in it to pass out of capillary
-the basement membrane - consists of a fine mesh of collagen fibres and glycoproteins. the mesh acts as a filter to prevent passage of molecules with relative molecular mass greater than 69000. this means that most proteins and all blood cells are held in capillaries of glomerulus
-epithelial cells of bowmans capsule - cells called podocytes have specialised shape (they have finger like projections called major processes). on each major process are minor processes or foot processes that hold the cells away from the endothelium of the capillary. these projections ensure there are gaps between the cells. fluid from blood in glomerulus can pass between these cells into lumen of Bowmans capsule
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Describe ultrafiltration
-ultrafiltration is the filtering of blood at molecular level
-blood flows into glomerulus through afferent arteriole which is wider than the efferent arteriole that carries blood away from glomerulus
-the difference in diameters ensures that blood in the capillaries of the glomerulus maintains a higher pressure than the pressure in Bowman's capsule
-this pressure difference tends to push fluid from blood into Bowman's capsule that surrounds the glomerulus
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What is filtered out of the blood
-blood plasma containing dissolved substances is pushed under pressure from capillary into lumen of Bowman's capsule
-blood plasma contains: water, amino acids, glucose, urea, inorganic mineral ions (sodium, chloride, potassium)
-the concentrations of dissolved solutes will depend upon water balance in the organism and therefore variable
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What is left in the capillary
-blood cells and proteins are left in the capillary
-the presence of proteins means that blood has very low water potential
-this ensures that some of fluid is retained in blood and this contains some of water and dissolved substances listed above
-the very low water potential of blood in capillaries is important to help reabsorb water at a later stage
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Describe the functions of nephrons
-as fluid from Bowmans capsule passes along nephron tubule its composition is altered by selective absorption - substances are absorbed back into tissue fluid and blood capillaries surrounding the nephron
-in proximal convoluted tubule, the fluid is altered by reabsorption of all sugars, most mineral ions and some water. in total about 85% of fluid is reabsorbed here. the cells of these tubules have a highly folded surface producing a brush border which increase surface area
-in descending limb of loop of Henle, water potential of fluid decreased by addition of mineral ions and removal of water
-in ascending limb of loop of Henle the water potential is increased as mineral ions removed by active transport
-in collecting duct water potential is decreased again by removal of water. the final produce is urine
-this ensures urine has low water potential and therefore higher concentration of solutes than is found in blood and tissue fluid
-urine passes into pelvis and down ureter to bladder
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How are cells lining convoluted tubule specialised to carry out reabsorption
-cell surface membrane in contact with tubule fluid is highly folded to form microvilli - increases surface area for reabsorption
-cell surface membrane also contains special cotransporter proteins that transport glucose or amino acids, in association with sodium ions, from tubule into cell
-opposite membrane of the cell, close to tissue fluid and blood capillaries is also folded to increase its surface area. this membrane contains sodium / potassium pumps that pump sodium ions out of cell and potassium ions into cell
-the cell cytoplasm has many mitochondria. this indicates that an active or energy requiring process is involved because many mitochondria will produce lot of ATP
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Describe the mechanism of reabsorption
1) Na/K+ pump on basal membrane. For each ATP (from mitochondria) Na pumped out of PCT cell into blood. K+ pumped into PCT cell from blood to balance the charge. This lowers the concentration of Na+ in PCT cell
2) Na+/glucose cotransporter on brush border. Facilitated diffusion (passive transport). Na+ diffuses down its concentration gradient from lumen to PCT cell. At same time, brings useful substance (e.g. glucose, amino acids)
3) Facilitated diffusion transport protein on basal membrane. The useful substances e.g. glucose move down concentration from PCT cell into blood
4) Osmosis. Addition of many solutes to blood creates low water potential in blood and high water potential in glomerular filtrate. So water moves by osmosis from lumen to blood. 65% water reabsorbed here.
-larger molecules that may have entered filtrate will be reabsorbed by endocytosis
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What is the glomerular filtrate rate (GFR)
-rate at which fluid enters nephrons
125cm3min-1 or 180dm3day-1
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Describe reabsorption of water
-each minute about 125cm3 fluid is filtered from blood and enters nephrons
-after selective reabsorption in proximal convoluted tubule about 45cm3 left
-by time fluid reaches bladder, volume dropped to about 1.5cm3
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Describe the loop of Henle
-the loop of Henle consists of a descending limb that descends into medulla and an ascending limb that ascends back out to cortex
-the arrangement of the loop of Henle allows mineral ions (sodium and chloride)) to be transferred from ascending to descending limb
-the overall effect is to increase concentration of mineral ions in tubule fluid, which has similar effect upon concentration of mineral ions in tissue fluid
-this gives tissue fluid in medulla a very low water potential
-the loop of Henle system is a Hairpin countercurrent multiplier - arrangement in which fluid in adjacent tubes flows in opposite directions, allowing relatively large differences in concentrations to be built up
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What is the role of the loop of Henle
1) Makes interstitial fluid going down medulla very low water potential and gives filtrate leaving loop of Henle high water potential
2) Water can be reabsorbed by osmosis from collecting duct
111
Describe the loop of Henle mechanism
1) Na+/Cl- pump at top of ascending limb. Na+/Cl- pumped out ascending limb into tissue fluid
2) Na+/Cl- move into descending limb by facilitated diffusion - move down concentration gradient
3) Water leaves descending limb by osmosis. Moves from descending limb high water potential to tissue fluid low water potential and carried away by blood
4) Fluid in descending limb loses water and gains salts so filtrate at apex has very low water potential. Apex freely permeable so tissue fluid in apex also has very low water potential
5) Na+/Cl- move out ascending limb by facilitated diffusion from salty filtrate to tissue fluid. Filtrate in ascending limb loses salts but keeps water due to impermeability so filtrate at top has high water potential
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Compare the PCT, DCT, and collecting duct
PCT
-thick walls
-metabolically active
-brush border
-no visible cell membrane
DCT
-no brush border
-thinner walls
-no visible cell membrane
COLLECTING DUCT
-thin walls
-visible cell membranes
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What happens at the DCT (before collecting duct)
1) Na+/K+ pump uses ATP. Na pumped into blood. K pumped into filtrate then to urine
2) Urea pump uses ATP. Urea pumped into filtrate then into urine
114
Describe ADH
-protein hormone
-travels in blood
-made by neurosecretory cells
-stored in vesicles in posterior pituitary gland
115
Describe the steps of osmoregulation
1) low water potential in blood (below 300mmol kg-1) detected by osmoreceptors
2) water moves by osmosis from osmoreceptor in hypothalamus to blood causing osmoreceptors to shrink
3) osmoreceptors send chemical message to neurosecretory cell
4) neurosecretory cell synthesise and store ADH. ADH stored in vesicles in posterior pituitary gland
5) Neurosecretory cell releases ADH into blood
6) this travels to collecting duct walls
7) ADH binds to complementary receptors on membrane of collecting duct walls
8) this causes series of enzyme controlled reactions
9) these cause vesicle of aquaporins to move and fuse with the membrane
10) this puts more water channels on the membrane making it more permeable
11) water moves by osmosis from lumen (high water potential) to blood (low water potential)
12) urine will be small volume and very concentrated
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What is the importance of osmoregulation
-osmoregulation is control of water potential in body
-water potential is tendency of water to move from one place to another
-correct water balance between cells and surrounding fluids must be maintained to prevent water entering cells and causing lysis or leaving cells and causing crenation
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How does the body gain and lose water
-gains water from three sources - food, drink and metabolism
-water lost from body in urine, sweat, water vapour in exhaled air and faeces
-these gains and losses need to be balanced
-kidneys act as effector to control water content of body and salt concentration in body fluids
-on cool day or when you drunk lots fluid, kidneys will produce large volume of dilute urine with a less permeable collecting duct
-however on hot day or when drunk very little, kidneys produce smaller volumes of more concentrated urine with more permeable collecting duct
118
What is kidney failure
-if kidneys fail completely they are unable to regulate levels of water and electrolytes in body and remove waste products such as urea from blood
-this will rapidly lead to death
119
How is kidney function assessed
-estimating glomerular filtration rate and by analysis of urine for substances such as proteins
-proteins in urine indicate basement membrane been damaged
-the GFR measure of how much fluid passes into nephrons each minutes
-normal reading =90-120cm3min-1
-below 60cm3min-1= chronic kidney disease
-below 15cm3min-1=kidney failure
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What are possible causes of kidney failure
-diabetes mellitus
-heart diseases
-hypertension
-infection
121
Describe renal dialysis
-most common treatment for kidney failure
-waste products, excess fluids and mineral ions removed from blood by passing it over partially permeable dialysis membrane that allows exchange of substances between blood and dialysis fluid
-the dialysis fluid contains correct concentrations of mineral ions, urea, water and other substances found in blood plasma
-any substances in excess in blood diffuse across membrane into dialysis fluid
-any substances too low in concentration diffuse into blood from dialysis fluid
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Describe haemodialysis
-blood from artery or vein passed into machine that contains artificial dialysis membrane shaped to form many artificial capillaries which increases surface area for exchange
-heparin is added to avoid clotting
-artificial capillaries surrounded by dialysis fluid which flows in opposite direction to blood (countercurrent)
-this improves efficiency of exchange
-usually performed at clinic two or three times a week for several hours at each session
-some patients learn to carry it out at home
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Describe peritoneal dialysis
-dialysis membrane is bodys own abdominal membrane (peritoneum)
-first a surgeon implants a permanent tube in abdomen
-dialysis solution is poured through tube and fills space between abdominal walls and organs
-after several hours, used solution drained from abdomen
-PD can be carried out at home or at work
-because patient can move, method sometimes called ambulatory PD
-must also have a carefully controlled diet
124
Describe a kidney transplant
-a kidney transplant is best life extending treatment for kidney failure
-involves major surgery
-while patient under anaesthesia surgeon implants organ into lower abdomen and attaches it to blood supply and bladder
-patients given immunosuppressant drug to prevent rejection
-many patients feel immediately better afterwards
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Advantages and disadvantages of kidney transplant
ADVANTAGES
-freedom from time consuming renal dialysis
-feeling physically fitter
-improved quality of life - able to travel
-improved self image - no longer chronically ill
DISADVANTAGES
-need to take immunosuppressants and side effects
-need for major surgery under anaesthetics
-need for regular checks for sign of rejection
-side effects of immunosuppressants - fluid retention, high blood pressure, susceptibility to infections
126
What is urine analysis
-molecules with relative molecular mass less than 69000Mr can enter nephron
-any metabolic product or other substance in blood can therefore be passed into urine if its small enough
-if these not reabsorbed further down, they can be detected in urine
-glucose in diagnose of diabetes
-alcohol to determine blood alcohol levels in drivers
-many recreation drugs for safety tests
-human chorionic gonadotropin in pregnancy testing
-anabolic steroids to detect improper use in sporting competitions
127
How is hCG released
-once human embryo implanted in uterine lining it produces a hormone called human chorionic gonadotrophin
-hCG relatively small glycoproteins with molecular mas of 36700 that can be found in urine as earlier 6 das after conception
-pregnancy testing kits use monoclonal antibodies which bind to hCG
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How do pregnancy tests work
1) urine poured onto test stick
2) hCG binds to mobile antibodies attached to blue head
3) Mobile antibodies move down test stick
4) Mobile antibodies with no hCG attached to bind to a fixed site to show test working - control zone
5) if hCG present, binds to fixed antibodies holding bread in place - blue line forms
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Describe the testing for anabolic steroids
-anabolic steroids increase protein synthesis within cells which results in build up of cell tissue, especially in muscle
-non medical uses for anabolic steroids are controversial because they can give advantages in competitive sports and have dangerous side effects
-anabolic steroids have half life about 16hrs and remain in blood for many days
-relatively small molecules and can enter nephron easily
-testing for anabolic steroids involves analysing urine sample in laboratory using gas chromatography
