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Flashcards in Homeostasis Deck (78)
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What is homeostasis?

the maintenance of a stable internal environment


Why is it important to maintain the right core body temp?

-optimum temp for enzyme activity is about 37°C in humans
-if body temp is too high, enzymes may become denatured. enzyme's molecules vibrate too much, which breaks hydrogen bonds holding them in their 3D shape. shape of active site changes and it no longer works as a catalyst, so metabolic reactions are less efficient
-if body temp is too low, enzyme activity is reduced, slowing rate of metabolic reactions


Why is it important to maintain the right blood pH?

-optimum pH for enzyme activity is around pH 7, but some enzymes work best at other pHs, e.g. enzymes in stomach work best at a low pH
-if blood pH is too high or too low, enzymes become denatured. hydrogen bonds that hold them in their 3D shape are broken, so shape of active site is changed an dit no longer works as a catalyst, so metabolic reactions are less efficient


Why is it important to maintain the right blood glucose concentration?
-too high
-too low

cells need glucose for energy and blood glucose conc also affects WP of blood
-too high = WP of blood is reduced to a point where water molecules diffuse out of cells into blood by osmosis, can cause cells to shrivel up and die
-too low = cells are unable to carry out normal activities because there isn't enough glucose for respiration to provide energy


How do homeostatic systems work?

homeostatic systems detect a change and respond by negative feedback

1. receptors detect when a level is too high or too low
2. info is communicated via the nervous system or hormonal system to effectors
2. effectors respond to counteract the change - bringing the level back to normal


What is negative feedback?

the mechanism that restores the level to normal
-body temp


When might negative feedback not work?

if a change is too big, then effectors may not be able to counteract it, e.g. a huge drop in body temp


Why does the body require multiple negative feedback mechanisms?

having more than one mechanism gives more control over changes in the internal environment - means you can actively increase OR decrease a levels it returns to normal


What is positive feedback?

positive feedback mechanisms amplify a change from the normal level
-blood clot after an injury


Explain the positive feedback mechanism that involves blood clotting after an injury.

-platelets become activated and release an chemical - this triggered more platelets to be activated, and so on
-platelets very quickly form a blood clot at the injury site
-process ends with negative feedback, when the body detect the blood clot has been formed


Explain the positive feedback mechanism that is involved in hypothermia.

-hypothermia is low body temp, below 35°C
-it happens when heat is lost from the body quicker than it can be produced
-as body temp falls, the brain doesn't work properly and. shivering stops - making body temp fall even more
-positive feedback takes body temp further away from the normal level, and it continues to decrease unless action is taken


Why is positive feedback not involved in homeostasis?

it doesn't keep the internal environment stable


Why must blood glucose concentration be carefully controlled?

all cells need a constant energy supply to work


What is the normal blood glucose concentration?

around 90 mg per 100cm3 of blood


How is blood glucose concentration monitored?

by cells in pancreas


What causes concentration of glucose in the blood to change?

-blood glucose concentration rises after eating food containing carbohydrate
-blood glucose concentration falls after exercise, as more glucose is used in respiration to release energy


How does the hormonal system control blood glucose concentration?

uses two hormones - insulin and glucagon


How do hormones travel?

in the blood to their target cells (effectors)


Where are insulin and glucagon produced?

they're secreted by clusters of cells in the pancreas called islets of Langerhans:
-beta cells secrete insulin
-alpha cells secrete glucagon


Explain how insulin lowers blood glucose conc when its too high.

-insulin binds to specific receptors on cell membranes of liver cells and muscle cells
-it increases permeability of muscle-cell membranes to glucose, so cells take up more glucose. this involves increasing the number of channel proteins in cell membrane
-insulin also activates enzymes in liver and muscle cells that convert glucose into glycogen (glycogenesis)
-cells store glycogen in cytoplasm, as an energy store
-insulin also increases rate of respiration of glucose, especially in muscle cells


What are liver cells also called?



What is glycogenesis?

formation of glycogen from glucose


Explain how glucagon raises blood glucose conc when its too low.

-glucagon binds to specific receptors on cell membranes of liver cells
-glucagon activates enzymes in liver cells that break down glycogen into glucose (glycogenolysis)
-glucagon activates enzymes involved in the formation of glucose from glycerol and amino acids (gluconeogenesis)
-glucagon decreases rate of respiration of glucose in cells


Compare the responses produced by the hormonal system and the nervous system.

-because they travel in the blood to their target cells, responses produced by hormones are slower than those produced by nervous impulses, which are very quick
-hormones are not broken down as quickly as neurotransmitters though, so there effects last longer


What is gluconeogenesis?

formation of glucose form glycerol and amino acids


What is glycogenolysis?

break down of glycogen into glucose


What is GLUT4?
-where is it found?

channel protein (glucose transporter)
-skeletal and cardiac muscles


How does insulin increase membrane permeability to glucose?

-when insulin levels are low, GLUT4 is stored in vesicles in cytoplasm of cells
-when insulin binds to receptors on the cell-surface membrane, it triggers the movement of GLUT4 to the membrane
-glucose can then be transported into the cell through the GLUT4 protein, by facilitated diffusion

-when insulin binds to receptors on cell surface membrane, it disrupts the membrane, causing glucose channels to widen, allowing more glucose to diffuse into the cells by facilitated diffusion


Where is adrenaline produced?

secreted from adrenal glands (just above kidneys)


When is adrenaline secreted?

when there's a low blood glucose concentration, when you're stressed and when you're exercising


How does adrenaline increase blood glucose concentration?

adrenaline binds to receptors in cell membrane of liver cells:
-activates glycogenolysis
-inhibits glycogenesis
-activates glucagon secretion
-inhibits insulin secretion


What effect does adrenaline have on the body?

adrenaline gets the body ready for action by making more glucose available for muscles to respire


Describe how adrenaline and glucagon act via a second messenger.

-receptors for adrenaline and glucagon have specific tertiary structures that make them complementary in shape to their respective hormones
-adrenaline and glucagon bind to their receptors and activate an enzyme called adenylate cyclase
-activated adenylate cyclase converts ATP into a chemical signal called a 'second messenger'
-second messenger is called cyclic AMP (cAMP)
-cAMP activates an enzyme called protein kinase A, which activates a cascade (chain or reactions) that breaks down glycogen into glucose (glycogenolysis)


What is type I diabetes?

immune system attacks beta cells in the islets of Langerhans, so they can't produce insulin. After eating, blood glucose level rises and stays high - hyperglycaemia (can result in death if left untreated). The kidneys can't reabsorb all this glucose, so some is excreted in urine.


What is thought to cause type I diabetes?

-some people have a genetic predisposition to developing it
-may be triggered by a viral infection


How is type I diabetes treated?

-insulin therapy - regular insulin injections or an insulin pump to deliver insulin continuously
-eating regularly and controlling simple carbohydrate intake helps to avoid a sudden rise in glucose


Why does insulin therapy have to be carefully controlled?

too much insulin can produce a dangerous drop in blood glucose levels - hypoglycaemia


What is type II diabetes?

(usually acquired later in life than type I)
occurs when beta cells don't produce enough insulin or when body's cells don't respond properly to insulin because insulin receptors on their membranes don't work properly, so cells don't take up enough glucose. So blood glucose concentration is higher than normal.


What are the risk factors of type II diabetes?

-more likely in people with a family history of the condition
-lack of exercise
-poor diet


How is type II diabetes treated?

-eating a healthy, balanced diet, losing weight, regular exercise
-glucose-lowering medication if diet and exercise can't control it
-insulin injections may be needed


To reduce risk of developing type II diabetes, what do health advisors recommend?
-other responses?

-diet low in fat, sugar and salt, with plenty of whole grains, fruit and vegetables
-regular exercise
-lose weight is necessary

-NHS's 'Change4life' campaign
-challenged food industry to reduce advertisement of junk food (especially to children), to improve nutritional value of products and use clear labelling on products, allowing customers to make healthier choices


What is the response of food companies?

attempted to make products healthier by:
-using sugar alternatives to sweeten food/drinks
-reducing sugar, fat, salt content of products
(even though there's some evidence to suggest that artificial sweeteners are linked to weight gain)


What is the function of the kidneys?

kidneys excrete waste products, such as urea, and regulate WP of the blood


What is ultrafiltration?

as blood passes through capillaries in the cortex of the kidneys, substances are filtered out of the blood and into long tubules that surround capillaries - ultrafiltration


What is selective reabsorption?

useful substances, such as glucose and the right amount of water, are reabsorbed back into the blood - selective reabsorption
(remaining unwanted substances pass along to bladder and are excreted as urine)


What are nephrons?

long tubules along with the bundle of capillaries where the blood is filtered


How many nephrons are in one kidney?

around one million nephrons in each kidney


What is the renal artery?

carries blood towards kidneys


What is the renal vein?

carries blood away from kidneys


What is a glomerulus?

a bundle of capillaries looped inside a hollow ball called a Bowman's capsule (where ultrafiltration takes place)


What is the afferent arteriole?

takes blood into each glomerulus (wider)


What is the efferent arteriole?

takes filtered blood away from the glomerulus (narrower)


How does ultrafiltration take place at the Bowman's capsule?

efferent arteriole is smaller in diameter than afferent arteriole, so blood in the glomerulus in under high pressure, the high pressure forces liquid and small molecules in the blood out of the capillary and into the Bowman's capsule


What 3 layers does the liquid and small molecules pass through to get into the Bowman's capsule and enter the nephron tubules?

capillary wall, a membrane (basement membrane) and epithelium of Bowman's capsule


What are the substances that enter the Bowman's capsule called?

glomerular filtrate


Why are there no proteins or blood cells in the glomerular filtrate?

they are too large to pass through so stay in the blood


What happens after ultrafiltration?

-glomerular filtrate passes along the rest of the nephron an useful substances are reabsorbed along the way
-finally, filtrate flows through collecting duct and passes out of kidney along the ureter


How is blood supplied to the kidneys?

blood from the renal artery enters smaller arterioles in the cortex of the kidney (each arteriole splits into a glomerulus)


Where does selective reabsorption occur?

takes place as the glomerular filtrate flows along the proximal convoluted tubule (PCT), through the loop of Henle, and along the distal convoluted tubule (DCT)


How is the proximal convoluted tubule adapted for efficient reabsorption?

epithelium of the wall of the PCT has microvilli to provide a large SA for the reabsorption of useful materials from the glomerular filtrate (in tubules) into the blood (in capillaries)


How are useful solutes (e.g. glucose) reabsorbed along the PCT?

by active transport and facilitated diffusion


How is water reabsorbed from the PCT, loop of Henle, DCT and collecting duct?

water enters blood by osmosis because WP of blood is lower than that of the filtrate


What happens to filtrate that remains in tubules?

filtrate that remains is urine, which passes along the ureter to the bladder


What is urine made up of?

-water and dissolved salts
-excess vitamins


What does urine not contain?

-proteins and blood cells (too large to be filtered out of blood)
-glucose (recuasse its actively reabsorbed back into blood)


How do mammals lose water?

-excrete urea (and other waste products) in solution, so water lost during excretion


What is osmoregulation?

regulation of WP of the blood (and urine), so the body has just the right amount of water (carried out by kidneys)


What type of urine is produced when the body is dehydrated?

if WP of blood is too low (body is dehydrated), more water is reabsorbed by osmosis into the blood from the tubules of the nephrons, so urine is more concentrated, so less water is lost during excretion


What type of urine is produced when the body is too hydrated?

if WP of the blood is too high (body is too hydrated), less water is reabsorbed by osmosis into the blood from the tubules o the nephrons, so urine is more dilute, so more water is lost during excretion


Where is water reabsorbed?

regulation of WP mainly take place in loop of Henle, DCT and collecting duct


What controls the volume of water reabsorbed by the DCT and collecting duct?



Which cells monitor the water potential of the blood?
-where are they located?

-in a part of the brain called the hypothalamus


What is the role of ADH?

ADH (antidiuretic hormone) makes the walls of the DCT and collecting duct more permeable to water


What is dehydration?

what happens when you lose water e.g. buy sweating during exercise (so water content of blood needs to be increased)


How does ADH change the water content of the blood when its too low?

-water content of blood drops, so its WP drops
-detected by osmoreceptors in hypothalamus
-posterior pituitary gland is stimulated to release more ADH into the blood
-more ADH means DCT and collecting duct become more permeable, so more water is reabsorbed into the blood by osmosis
-a small amount of highly concentrated urine is produced and less water is lost


What is hydration?

if you're hydrated, you've taken in lots of water, so water content of blood needs to be reduced


How does ADH change the water content of the blood when its too high?

-water content of blood rises, so its WP rises
-detected by osmoreceptors in hypothalamus
-posterior pituitary gland releases less ADH into the blood
-less ADH means DCT and collecting duct become less permeable, so less water is reabsorbed into the blood by osmosis
-a large amount of dilute urine is produced and more water is lost


Gerbils have longer loops of Henle than mice.
Suggest and explain how this helps gerbils to produce less urine than mice.

-a longer descending limb, means more water can be reabsorbed into the blood from the nephron in the descending limb
-a longer ascending limb, means more ions are actively transported out into medulla,
-which creates a really low WP in the medulla
-so more water moves out of collecting duct into capillaries by osmosis, giving a low volume of urine