Homeostasis Flashcards
homeostasis definition
the maintenance of a stable equilibrium in the conditions inside the body
(the body maintains a dynamic equilibrium with small fluctuations over a narrow range of conditions)
Role of receptors and effectors
Sensory receptors detect changes in the internal and external environment of an organism
Info from sensory receptors is transmitted to the brain
Impulses are sent along motor neurones to effectors to bring about changes to restore equilibrium in the body
negative feedback
- a small change in 1 direction is detected by sensory receptors
- effectors work to reverse the change and restore conditions to their base levels
- work to reverse the initial stimulus
examples - control of blood sugar levels, temperature control and water balance
Positive feedback
- a change in internal environment is detected by sensory receptors and effectors are stimulated to reinforce the change and increase the response
- EXAMPLE - in the blood clotting cascade - when a blood vessel its damaged, platelets stick to the damaged region and release factors that initiate clotting and attract more platelets - this continues until the clot is formed
Thermoregulation
maintenance of a relatively constant core body temp
(important to maintain optimum enzyme activity)
Processes that affect temperature
- exothermic chemical reactions
- Latent heat of evaporation (objects cool down as water evaporates from a surface
- Radiation - the transmission of electromagnetic waves to and from the air/water/ground
- Convection - heating/cooling by currents of air/water - warm air/water rises and cooler air/water sinks setting up convection currents around an organism
- Conduction (heating as a result of the collision of molecules)
Ectotherms
use their surroundings to warm their bodies
core temperature is dependent on their environment
include all invertebrates, fish, amphibians and reptiles
- their activity levels depend on the temperature - most active at higher temps and less active at lower temps
- ectotherms living in water don’t need to thermoregulate as the high heat capacity of water means the temp of their environment doesn’t change much
temperature regulation in ectotherms
Behavioural responses:
- may need to warm up to reach a temp at which their metabolic rate happens fast enough to be active
- bask in the sun/ orientate their bodies so the max surface area is exposed to the sun
- Can increase their body temp through conduction by pressing their bodies against the ground
- can get warmer through exothermic metabolic reactions - e.g contracting their muscles to increase metabolism to increase their body temp
may need to cool down to prevent core body temp becoming too high and enzymes denaturing
- seek shade
- hiding in cracks in rocks
- pressing their bodies against cool ground
- orientate their bodies to min surface ares is exposed to the sun
- minimise movement to reduce metabolic heat
Physiological responses:
- Dark colours absorb more radiation than light colours - lizards living in colder climates are darker coloured than those in hot countries
- alter heart rate to increase/decrease metabolic rate
Endotherms
- rely on metabolic processes to warm up
- usually maintain a stable core body temp regardless of temp of environment
detecting temp changes - endotherms
temperature regulation in endotherms - cooling down
VASODILATION:
- arterioles near the surface of the skin dilate when temp rises
- arteriovenous shunt vessels constrict
- More blood flows through capillary networks close to the surface of the skin
- more heat is lost from the skin by radiation
- temperature decreases
CONDUCTION
- skin is pressed against cool surfaces and temp decreases
INCREASED SWEATING:
- more sweat is secreted from sweat glands
- water in sweat evaporates from the surface of the skin and heat is lost
- skin and blood below the surface cools down - temp decreases
HAIRS LIE FLAT:
- erector pili muscles in the skin relax - hairs lie flat
- this avoids trapping an insulating layer of air
- skin is less insulates - heat can be lost more easily
temperature regulation in endotherms - warming up
VASOCONSTRICTION:
- arterioles near the surface of skin constrict
- arteriovenous shunt dilate so little blood flows through the capillary networks near the surface of skin
- this reduces heat loss via radiation
DECREASED SWEATING:
- sweat production eventually stops
- reduces cooling by evaporation of water from the surface of the skin
RAISING BODY HAIRS
- erector pili muscle contracts
- hairs stand up,
- traps an insulating layer of air - reduces cooling through the skin + prevents heat loss
SHIVERING:
- the rapid, involuntary contracting and relaxing of voluntary muscles in the body
- the metabolic heat from the exothermic reaction warms up the body
Body releases adrenaline + thyroxine - increase metabolism - more heat is produced
Minimise SA:V ratio to reduce cooling
Thick layer of insulating fat under the skin
hibernate to build up fat stores and lower their metabolic rate so they pass the cold weather in a deep sleep-like state.
Controlling thermoregulation - heat loss centre and heat gain centre
The hypothalamus has 2 control centres:
HEAT LOSS CENTRE:
- activated when the temp of the blood flowing through the hypothalamus increases
- sends impulses through autonomic motor neurones to effectors in the skin + muscles
- triggers responses that act to lower core temp
HEAT GAIN CENTRE:
- activated when the temp of the blood flowing through the hypothalamus decreases
- sends impulses through the autonomic nervous system to effects in the skin + muscles triggering responses that raise core body temp
How does the hypothalamus control body temp
- received info about temp from thermoreceptors
- thermoreceptors in the hypothalamus detect internal temperature of the blood
- thermoreceptors in the skin (peripheral temp receptors) detect external temp
- thermoreceptors send impulses along sensory neurones to the hypothalamus, which sends impulses along motor neurones to effectors
Effectors work to restore body temp back to normal
Excretion definition
the removal of waste products of metabolism from the body
Excretion in mammals example
CO2:
- Waste product of respiration
- excreted from the lungs
Bile pigments:
- formed from the breakdown of haemoglobin from old red blood cells in the liver
- excreted in the bile from the liver into the small intestine via the gall bladder + bile duct
Nitrogenous waste products (urea)
- formed from the breakdown of excess amino acids from the liver
- excreted by the kidneys into urine
The structure of the liver
- cells are simple + uniform in appearance
HEPATOCYTES:
- large nuclei
- prominent Golgi apparatus
- lots of mitochondria (indicates they are metabolically active cells)
HEPATIC ARTERY:
- supplies oxygenated blood to the liver (from the heart)
HEPATIC VEIN:
- takes deoxygenated blood away from the liver
HEPATIC PORTAL VEIN:
- brings blood from the duodenum to and ileum (parts of the small intestine) which contains the products of digestion. Starting point of many metabolic activities of the liver.
- Any ingested harmful substances are also filtered out and broken down straight away
BILE DUCT:
- contains bile to the gall bladder to be stored
SINUSOIDS:
- spaces where blood from the hepatic artery and hepatic portal vein are mixed - this increases the O2 content of the blood from the hepatic portal vein, supplying hepatocytes with enough O2
- surrounded by hepatocytes
- contain Kupffer cells
KUPFFER CELLS:
- attached to the walls of the sinusoids
- remove bacteria
- break down old red blood cells
- ingest foreign particles
- help to protect against disease
- ACT AS MACROPHAGES?
liver lobules
liver lobules - cylindrical structures made of hepatocytes arranges in rows, radiating out from the centre
- each lobule has a central vein in the middle that connects to the hepatic vein
- Many branches of the hepatic artery, hepatic portal vein and bile duct are found connected to each lobule
- the hepatic artery and hepatic portal vein and found connected to the central vein by sinusoids (capillaries)
- Blood runs through the sinusoids, past the hepatocytes that remove harmful substances and O2 from the blood
- harmful substances are broken down by hepatocytes into less harmful substances that re-enter the blood
-blood runs to the central vein
- central veins from all the lobules connect to form the hepatic vein
- hepatocytes produce bile and secrete into bile canaliculi which drain into the bile ducts. bile ducts from all the lobules connect and leave the liver
bile function
emulsifies fats
Functions of the liver
carbohydrate metabolism
deamination of excess amino acids
detoxification
- hepatocytes synthesise plasma proteins.
- hepatocytes carry out transamination - the conversion of one amino acid into another (helpful as the diet doesn’t always contain the required balance of amino acids)
Carbohydrate metabolism
When blood glucose levels rise:
- insulin levels rise and stimulate hepatocytes to convert glucose to glycogen
When blood glucose levels fall:
- glucagon simulates the hepatocytes convert glycogen back into glucose
- the liver stores glycogen as granules in its cell
deamination definition
the removal of an amine group from a molecule
Deamination of excess amino acids
the body can’t store proteins/amino acids as they contain nitrogen
STEP 1 - DEAMINATION :
- Amino groups (NH2) are removed from any excess amino acids forming ammonia (NH3) and organic acids
- the organic acids can be respired to ATP or converted to carbohydrates and stored as glycogen
STEP 2 - AMMONIA IS CONVERTED TO UREA:
- Ammonia is too toxic for animals to excrete directly
- ammonia is combined with CO2 in the ornithine cycle forming urea
STEP 3
- urea is released from the liver into the blood
- the kidneys filter the blood and remove urea as urine
Ornithine cycle
- a set of enzyme controlled reactions in which ammonia is converted to urea
PROCESS:
1) ammonia combines with CO2 and ornithine forming citruline. H2O is released as a product
2) NH3 is added convert argeninosuccinate into argenine. H2O is released
3) Argenine is re-converted to ornithine as a result of the addition of water and the elimination of urea
ORNITHINE CYCLE SUMARY
NH3+ CO2 + ornithine –> citruline + H2O
citruline + ATP + NH3 –> Argeninosuccinate + H2O
Argeninosuccinate –> Argentine
Argenine + H2O –> ornithine + urea
OVERALL EQUATION:
2NH3 + CO2 –> CO(NH2)2 H2O
Detoxification definition
the liver breaks down harmful substances (e.g alcohol, unwanted hormones etc) into less harmful compounds that can then be excreted from the body
Detoxification of Hydrogen peroxide
- H2O2 - a by-product of various metabolic pathways
- hepatocytes contain catalase (an enzyme) that splits the H2O2 into O2 and H2O
Detoxification of ethanol
- excess alcohol over a long period of time can lead to cirrhosis ( when cells of the liver die and scar tissue blocks blood flow)
- the enzyme ethanol dehydrogenase converts ethanol to ethanal
- ethanal is converted to ethanoate (acetate) by the enzyme ethanal dehydrogenase
- ethanoate (acetate) binds to CoA forming Acetyl CoA
ethanoate can be used to build up fatty acids or in respiration
Cirrhosis of the liver
normal liver tissue is replaced by fibrous scar tissue
causes include genetic conditions, hepatitis c and drinking excessive amounts of alcohol
there are 3 stages of alcoholic liver disease - alcoholic fatty liver disease, alcoholic hepatitis and liver cirrhosis
fatty liver - fat filled vesicles displace the nuclei of the hepatocytes and the liver gets larger
alcoholic hepatitis - fatty liver + damaged hepatocytes. the sinusoids and hepatic veins become narrowed
alcoholic cirrhosis - liver tissue is irreversibly damaged, many hepatocytes die and are replaced with fibrous tissue. hepatocytes can no longer divide and replace themselves so the liver shrinks and its ability to deal with toxins in the body decreases
kidney structure
- found attached to the back of the abdominal cavity
- surrounded by a thick, protective layer of fat and a layer of fibrous connective tissue
CORTEX:
- dark outer layer
- this is where blood is filtered
- it has a dense capillary network carrying blood from the renal artery to the nephrons
MEDULLA:
- lighter in colour
- contains the tubules of the nephrons that form the pyramids of the kidney and the collecting ducts
PELVIS:
- central chamber where the urine collects before passing down the ureter
RENAL ARTERY
- supply the kidneys with blood (at arterial pressure)
RENAL VEIN:
- removed blood that has circulated through the kidneys
- drains the blood into the inferior vena cava
- the kidneys are made up of millions of nephrons (act as filtering units)
URETER:
- tubes through which urine passes out of the body
urine - sterile liquid produced by the kidney tubules
role of the bladder
bladder - a muscular sac that can store urine
when the bladder is getting full, the sphincter at the exit of the bladder opens and urine passes out of the body down the urethra
kidney function
They play 2 important homeostatic roles in the body:
- involved in osmoregulation - they help to maintain the water balance and pH of the blood and therefore the tissue fluid
- involved in excretion - they filter nitrogenous waste products out of the blood
Nephron function
Blood is filtered here
the majority of the filtered material is returned to the blood, removing nitrogenous waste and balancing the mineral ions and water
Structure of the nephron
BOWMANS CAPSULE
- contains the glomerulus
- hollow ball
GLOMERULUS:
- a bundle of capillaries
- where ultrafiltration takes place
PROXIMAL CONVOLUTED TUBULE:
- found in the cortex of the kidney
- where substances are reabsorbed into the blood
LOOP OF HENLE:
- creates a region with a very high solute concentration in the tissue fluid in the medulla
- made up of the ascending limb and descending limb- they help to set up the countercurrent multiplier mechanism which helps to reabsorb water back into the blood.
- the descending limb runs from the cortex through the medulla to a hairpin bend at the bottom of the loop
- Ascending limb : travels from the hairpin bend to the cortex through the medulla
DISTAL CONVOLUTED TUBULE:
- here, water is reabsorbed and the ion balance and pH of the blood is regulated
- the permeability of the walls to water varies in response to levels of ADH
COLLECTING DUCT:
- urine passes down the collecting duct through the medulla to the pelvis
- fine tuning of the water balance takes place
- walls are sensitive to ADH
- the nephron has a network of capillaries around it that leads to a venue then to the renal vein
ultrafiltration
1) blood from the renal artery enters afferent arterioles in the cortex
2) each arteriole splits into a glomerulus where ultrafiltration takes place
3) Afferent arterioles take blood into ear cortex and the efferent arteriole takes filtered blood away from the glomerulus
4) the efferent arteriole is smaller in diameter than the afferent arteriole so the blood is under higher pressure
5) the high pressure forces liquid and small molecules in the blood out of the capillary and into the Bowmans capsule.
6) the liquid and small molecules pass through three layers to get into the Bowmans capsule and enter the nephron tubule (the capillary wall, the basement membrane and the epithelium on the Bowmans capsule) - Larger molecules e.g proteins and blood cells can’t pass through and stay in the blood
- the basement membrane is made up of a network of collagen fibres + other proteins that make up a second ‘sieve’
- The wall of the Bowmans capsule contains podocytes that act as a filter. they have extensions (pedicels) that wrap around the capillaries forming slits that make sure cells/platelets/plasma proteins don’t get through into the tubule
7) The liquid + small molecules (filtrate) pass along the rest of the nephron and useful substances are reabsorbed
8) the filtrate flows through the collecting duct and passes out of the kidney along the ureter
ultrafiltration removes urea from the blood along with water, glucose, salt and other substances present in plasma
glomerular filtration rate
the volume of blood that is filtered through the kidneys in a given time
hypotonic
less concentrated than
the ultra filtrate is less hypotonic to blood plasma
isotonic
same concentration
- the filtrate at the end of the PCT is isotonic with the tissue fluid surrounding the tubule and the blood
Reabsorption
1) selective reabsorption takes place as the filtrate flows along the PCT through the loop of Henle and along the DCT
2) useful substances leave the nephron tubules and enter the capillary network that’s wrapped around them
3) the epithelium of the wall of the PCT has microvilli to provide a large surface area for the reabsorption of useful materials from the filtrate into the blood
4) Useful solutes e.g glucose, amino acids, vitamins and some salts are reabsorbed along the PCT by active transport and facilitated diffusion. Some urea is also reabsorbed by diffusion
5) Water enters the blood by osmosis as the WP of the blood is lower than the filtrate. Water is reabsorbed by the loop of hence, DCT and collecting duct
6) The filtrate that remains (urine) passes along the ureter to the bladder
Reabsoroption - the PCT
In the PCT, all of the glucose, amino acids, vitamins and hormones are moved from the filtrate back into the blood by active transport
~ 85% of NaCl and H2O is reabsorbed. Na+ are moved by active transport while Cl- and H2O move by diffusion
ADAPTATIONS OF CELLS LINING THE PCT:
- covered in microvilli , increasing the surface area over which substances can be reabsorbed
- they have lots of mitochondria to provide the ATP needed for active transport
~ 80% of glomerular filtrate is reabsorbed
Reabsorption - the loop of henle
- different areas of the loop have different permeabilities to water
- acts as a countercurrent multiplier, using energy to produce concentration gradients that result in the movement of substances from one area to another
- the changes that take place in the descending limb depend on the high concentrations of Na+ and Cl- in the tissue fluid of the medulla (a result of events in the ascending limb)
descending limb
where water moves out of the filtrate down a concentration gradient
the upper part is impermeable to water and the lower part is permeable to water and runs down into the medulla
Reabsorption - loop of henle process
1) near the top of the ascending limb, Na+ and Cl- ions are actively pumped out into the medulla. The ascending limb is impermeable to water so the water stays inside the tubule. This creates a lower water potential in the medullas there is a high concentration of ions
2) As there is a lower water potential in the medulla than in the descending limb, water moves out of the descending limb into the medulla by osmosis making the filtrate more concentrated (ions can’t diffuse out as the DL isn’t permeable to them). Water in the medulla is reabsorbed into the blood through the capillary network
3) Near the bottom of the ascending limb Na+ and Cl- ions diffuse out into the medulla, lowering the water potential in the medulla
4) The ion concentration in the medulla is high and the WP is low causing water to move out of the collecting duct by osmosis. the water from the medulla is reabsorbed into the blood through the capillary network
reabsorption - DCT
- balances the water needs of the body
Cells lining the DCT have many mitochondria so they can carry out active transport
plays a role in balancing the pH of the blood
If the body lacks salt, Na+ ions will be actively pumped out of the DCT with Cl- diffusing in swell
Reabsorption - the collecting duct
water moves out of the collecting duct by diffusion down a concentration gradient as it passes through the renal medulla
osmoregulation
DEFINITION - maintaining the water potential of blood within narrow boundaries
if the water potential of the blood is too low…
more water is reabsorbed by osmosis into the blood from the nephron tubules
urine is more concentrated
less water lost during excretion
if the water potential of the blood is too high…
less water is reabsorbed by osmosis into the blood from the nephron tubules
urine is more dilute
more water lost during excretion
Effect of having a longer loop of henle on water reabsorption
- The longer an animals loop of henle, the more water they can reabsorb in the filtrate
- when there’s a longer ascending limb, more ions are actively pumped out into the medulla, which creates a low water potential in the medulla.
this means more water moved out of the nephron and collecting duct into the capillaries, giving very concentrated urine
animals that live in areas where there is little water usually have longer loops to save as much water as possible
ADH overview
the amount of water lost in urine is controlled by ADH in a negative feedback system
ADH is produced by the hypothalamus and secreted into the posterior pituitary gland where it is stored
ADH increases the permeability of the DCT and collecting duct to water
Mechanism of ADH action
osmoreceptors in the hypothalamus monitor the water potential of blood
If the osmoreceptors (specialised sensory neurones) detect a decrease in the WP of the blood, the hypothalamus sends nerve impulses to the posterior pituitary gland to release ADH
ADH enters the blood and travels throughout the body to the collecting duct
ADH binds to receptors on the cell membrane and triggers the formation of cAMP (a secondary messenger inside the cell)
cAMP causes a cascade of events:
- vesicles lining the collecting duct fuse with cell surface membranes on the side of the cell in contact with the tissue fluid of the medulla
The membranes of these vesicles contain aquaporins - when they are inserted into the cell membrane they make it more permeable to water
this provides a route for water to move out of the tubule cells into the tissue fluid of the medulla and blood capillaries by osmosis
- this makes it easier for more water to leave the tubules by diffusion, resulting in the formation of a small amount of concentrated urine and WP of blood and tissue fluid increases
When ADH levels decrease:
- levels of cAMP fall
- aquaporins are removed from tubule cell membranes and enclosed in vesicles
- the collecting duct becomes impermeable to water
- results in the production of large amounts of dilute urine
secondary messenger definition
a molecule which relays signals received at cell surface receptors to molecules inside the cell
when water is in short supply…
concentration of inorganic ions in the WP of the blood and tissue fluid becomes more negative
WP of blood decreases
this is detected by osmoreceptors in the hypothalamus which sends impulses to the posterior pituitary gland to release ADH into the blood
ADH binds to receptors in the collecting duct and increases the permeability of the tubule to water
More water is reabsorbed into the blood by osmosis
a small amount of highly concentrated urine is produced and less water is lost
when there is an excess of water…
WP of blood rises
This is detected by osmoreceptors in the hypothalamus
nerve impulses to posterior pituitary gland are reduced so release of ADH is inhibited
less ADH is released
collecting duct and DCT are less permeable to water
less water is reabsorbed into the blood by osmosis
large amount of dilute urine produced
more water is lost
kidney failure definition
when the kidneys can’t carry out their normal functions because they don’t work properly
causes of kidney failure
kidney infections - this can cause inflammation of the kidneys which can damage the cells. this interferes with filtering in the Bowmans capsule or reabsorption in other parts of the nephron
the structure of the podocytes and tubules may be damaged
raised blood pressure -can damage the structure of epithelial cells and basement membrane of the Bowmans capsule. It can damage the capillaries in the glomeruli meaning larger molecules e.g proteins can get through the capillary wall into the urine
if the basement membrane/ podocytes are damaged they can no longer act as filters and large plasma proteins can pass into the filtrate and are passed out in the urine
genetic conditions - the healthy kidney tissue is replaced by fluid-filled cysts or damaged by pressure from cysts
effects of kidney failure
Loss of electrolyte balance:
- the body can’t excrete excess Na+, K+ and Cl- ions. this causes osmotic imbalances in the tissues and eventual death
Build up of urea in the blood:
- the body can’t get rid of urea
- too much urea causes weight loss and vomiting
High blood pressure:
- the kidneys play a role in controlling blood pressure by maintaining the water balance of the blood
- BP increases which can cause many health problems including heart problems and strokes
Weakened bones:
- as the calcium and phosphorous balance in the blood is lost
Pain and stiffness in joints:
- as abnormal proteins build up in the blood
Anaemia (a lack of haemoglobin in the blood):
- caused by LT kidney failure
- the kidneys are involved in the production of erythropoietin (hormone) which stimulates the formation of red blood cells
- reduction of RBC result in tiredness and lethargy
- fluid starts to accumulate in the tissues as the kidneys can’t remove excess water from the blood. this can lead to swelling
Glomerular filtrate rate
Definition - the rate at which blood is filtered from the glomerulus into the Bowman’s capsule
- used to indicate kidney disease
The rate of filtration isn’t measured directly
- a blood test measures levels of creatinine in the blood
- creatinine is a breakdown product of muscles and used to give an estimated GFR (units cm3/min)
if the levels of creatinine in the blood go up (and GFR decreases) , it is a signal that the kidneys are not working properly
FACTORS TO TAKE INTO ACCOUNT:
- GFR decreases with age
- men usually have more muscle mass and therefore more creatinine than women
GFR < 60 for more than 3 months
moderate to severe chronic kidney disease
GFR < 15
kidney failure
renal dialysis
the function of the kidneys is carried out artificially
a patients blood is filtered
Haemodialysis
OVERVIEW:
- involves the use of a dialysis machine
- usually carried out in hospitals
- takes around 3-5 hrs and has
- needs to be repeated regularly (2-3 times a week)
- patients need to manage their diets carefully eating little protein and salt and monitoring their fluid intake
PROCESS
1) Blood leaves the patients body from an artery and flows into the dialysis machine
2) Here, it flows between partially permeable dialysis membranes (which mimic the basement membranes of the Bowmans capsule)
3) On the other side of the membrane is the dialysis fluid.
- during dialysis it is vital that patients lose excess urea and mineral ions that have built up in the blood
- it is important that they don’t lose useful substances e.g glucose - this is prevented by control of the dialysis fluid
4) Dialysis fluid contains normal plasma levels of glucose to ensure there is no net movement of glucose out of the blood
5) the dialysis fluid contains normal plasma levels of mineral ions so any excess mineral ions in the blood moves out by diffusion into the dialysis fluid and restoring the correct electrolyte balance in the blood
6) the dialysis fluid contains no urea so there is a steep concentration gradient and urea diffuses out of the blood
- the blood and dialysis fluid flow in opposite directions to maintain a countercurrent exchange system
Peritoneal dialysis
- makes use of the natural dialysis membranes formed by the lining of the abdomen (peritoneum)
- there is a risk of infection around the site of the tube
- has to be carried out every day - either several times during the day or during the night
- usually done at home - can carry on with normal life while it takes place
PROCESS:
The dialysis fluid is introduced into the abdomen using a catheter
it is left for several hours for dialysis to take place across the peritoneal membranes
excess mineral ions and urea diffuse out of the blood capillaries into the tissue fluid and across the peritoneal membrane into the dialysis fluid
the fluid is drained out via the tube and discarded
Kidney transplant
a new healthy kidney is implanted into the body to replaced damaged ones
the blood vessels are joined and the ureter of the kidney is inserted into the bladder
- the new kidney has to be from a person with the same blood and tissue type
ADVANTAGES:
- cheaper than dialysis
DISADVANTAGES:
- risk of rejection - the antigens on the donor organ differ from the antigens on the cells of the recipient and the immune system may recognise this - can result in the destruction of the new kidney
- will need to take immunosuppressants
