energy transfer y13

What is homeostasis?

The maintenance of constant internal conditions to prevent damage to cells e.g temperature, pH, glucose conc

What organs are involved in homeostasis and how?

• muscles - maintain body temp

• Liver + pancreas - adjust glucose levels

• Kidneys - remove urea, adjust conc of inorganic ions + water potential of blood

• Pottery gland - produces hormone controlling water balance by targeting kidneys

• Lungs - remove co2, water lost when exhale

• Skin - adjusts body temp, water + ions lost when we sweat

What are the components of the blood?

• plasma

• Rbcs

• WBCs

• Platelets

What is the collision theory?

• Metabolic rate being increased by temp

• increased temp=increased rate of reaction=increased kinetic energy of molecules= more successful collisions + reactions

• Temp too high= reaction stops due to hydrogen bonds holding enzyme together breaking, causing denaturation

What is meant by core body temperature?

Maintenance of constant temperature of the brain and other internal organs of the chest and abdomen

(Allows mammals to be independent of changes to external temperatures)

Why is pH important in homeostasis?

• fluctuation in blood pH causes denaturation of enzymes and proteins= lower rate of reaction

• Optimum pH= faster metabolic reactions

How do you calculate pH?

pH=-log10[H+]

H+ means conc of hydrogen ions

Why is blood glucose conc important in homeostasis?

• too high=reduced water potential of blood= water moves out of blood by osmosis= cells die

• Too low= cells have lack of energy from respiration= normal cell activities unable to be carried out

• Unavailable glucose= brain cells can’t function= mammal loses consciousness

What is the purpose of negative feedback?

To restore the system back to its original level e.g regulating blood conc of co2

What does positive feedback do?

Makes changes in the same way the deviation in the norm had, amplifying change e.g release of hormones

Is usually harmful, but useful when body needs to react quickly

What is hypothermia?

The fall in body temp due to prolonged exposure to cold weather, this change is too large to counteract

What is glucagon?

• a hormone

• A protein

• Synthesised by ribosomes

• Travels to target organ/ cell in blood where it binds to receptor due to being complementary

What is glucose?

• a carbohydrate (disaccharide/ monosaccharide)

• Used in respiration for the release of energy

• Present in the blood

• Contains 38 mols of ATP

• Stored in muscles and liver as glycogen

What is glycogen?

• Made up of glucose

• Stores carbohydrates

• Is compact, insoluble and easily hydrolysed

What does insulin do?

Decreases blood glucose levels by binding to hepatocytes (receptors on cell membranes of muscle and liver cells) which increases permeability of membrane to glucose so more glucose taken up by cell

This involved increasing number of channel proteins in cell membrane

Also activates enzymes in muscle and lice cells for glycogenesis

Increases rate of respiration of glucose

What is the normal blood glucose concentration in humans?

90mg of glucose in 100cm³ of blood

How would a fall in glucose effect body cells?

• water potential becomes less negative

• Water moves out of blood into cells

• Rate of respiration slows down

How would a rise in glucose effect body cells?

• water potential becomes more negative

• Water moves out of cells into blood

• Rate of respiration increases

What hormones are involved in homeostasis?

Insulin and glucagon

Where is glucagon and insulin stored?

In the pancreas

How does glucagon increase blood glucose levels?

Causes glycogen to turn into glucose by glycogenolysis

How does the liver regulate blood glucose conc?

• Liver receives all glucose absorbed in blood from intestines via hepatic portal vein

• hepatic vein transports deoxygenated blood to vena cava

• Gall bladder stores bile

• Hepatic artery transports oxygenated blood to liver

• Hepatic and cystic ducts provided bile to intestines

• Hepatic portal vein carries glucose rich blood from intestines (why we don’t go into diabetic coma after meals)

• Small intestine turns proteins to amino acids, carbs into monosaccharides, fibre into digestive transit, fat into fatty acid and glycerol

How can glucose be added to the blood?

• glycogenolysis - hydrolysing glycogen to glucose by breaking glycosidic bonds

• Gluconeogenesis - converting non carbohydrate substances to glucose

How can glucose be removed from the blood?

• glycogenesis - condensing glucose and storing it as insoluble glycogen

• Converting glucose to fat

• Using glucose as a fuel for cellular respiration

How does the pancreas regulate blood glucose conc?

• pancreas secretes insulin and glucagon

• These hormones have opposite effects on blood glucose levels (negative feedback)

How are hormones created in the pancreas?

By a group of cells called the islets of langerhans

What are the islets of langerhans made up of?

• alpha cells in the centre that secrete glucagon to increase blood glucose conc

• Beta cells in the centre that secrete insulin to reduce blood glucose conc

How does insulin lower blood glucose concentration?

• binds to hepatocytes

• This increased permeability of muscle and liver cell membranes

• Allows more glucose to be taken up by the cells from the increased number of channel proteins

• Insulin also causes glycogenesis (converts glucose into glycogen)

How does glucagon raise blood glucose concentration?

• binds to hepatocytes on liver cells

• This causes glycogenolysis (hydrolysis of glycogen into glucose)

• Glucagon also decreases the rate of respiration in cells so less glucose is needed via gluconeogenesis

What are glucose transporters?

Channel proteins allowing glucose to be transported across a cell membranes by facilitated diffusion

E.g GLUT4 in skeletal and cardiac muscle cells

What does GLUT4 do when insulin is low?

• GLUT4 activates from insulin binding to receptors on cell surface membranes

• This causes GLUT4 to move to membrane to transport more glucose into the cell

• Causes rapid removal of glucose from blood

Why is either storing glucose or using it for respiration important?

To maintain the concentration gradient

What happens due to hyperglycaemia (rising blood glucose conc)?

• beta cells secreted insulin into blood

• Insulin binds to glycoprotein receptors on cell surface membranes, triggering cell response

• Glucose transporters move to cell membrane

• Enzymes increase rate of glycogenesis

What happens due to hypoglycaemia (falling blood glucose conc)?

• alpha cells secrete glucagon into blood

• glucagon binds to hepatocytes on liver cells, triggering cell response

• Enzymes speed up glycogenolysis (breaking glycogen)

• Glucagon increases rate of gluconeogenesis (making new glucose)

Where is adrenaline produced and when is it secreted?

In adrenal glands in kidneys

• when blood glucose conc is low

• Stressed

• Exercising

What does adrenaline do?

• binds to hepatocytes, activating glycogenolysis and inhibiting glycogenesis

• This causes glucose conc to increase

• Also causes fight or flight due to more glucose being able to be used in respiration for muscles

What is cAMP and how is it activated?

Is a second messenger that causes the breakdown of glycogen to glucose

• adrenaline and glucagon binding to specific receptors on cell surface membranes

• This activates enzymes that accelerate the production of cAMP

What is diabetes?

A metabolic disorder caused by either a lack of insulin or a loss of responsiveness to insulin, resulting in an inability to control blood glucose levels

What is type 1 diabetes?

• usually occurs in childhood

• Is an autoimmune response where immune system attacks beta cells in islets of langerhans, resulting in the inability to secrete insulin

What is type 2 diabetes?

• occurs later in life

• Is a loss of responsiveness to insulin and can be due to insulin deficiency

• Caused by poor diet and obesity

How can diabetes be treated?

• insulin injections taken 2-4 times a day

• Automatic blood glucose metres combined with an insulin pump implanted below the skin (is automatic)

What other health issues can type 2 diabetes cause?

• heart attack

• Kidney disease / failure

What should be altered in diets to reduce risk of type 2 diabetes?

• higher intake of fibre

• Reduce intake of carbohydrates, sugars, adults, fats

How have some food companies attempted to make food products healthier?

• using sugar alternatives to sweeten foods and drinks

• Reducing sugar, salt and fat content of foods

What is the normal glucose level in urine?

Between 0-0.8mM

• any higher may indicate diabetes

Why is the main function of the kidneys?

• To filter waste products out of the blood (ULTRAFILTRATION) and reabsorb useful solutes (SELECTIVE REABSORPTION)

• Regulates water and ion content of the blood to keep water potential and pressure of the blood constant

Where are nephron tubules located?

In the kidneys

Fill in the blank boxes showing the parts of the nephron and what they do

What is the first stage of filtration in the kidneys?

ULTRAFILTRATION in the nephron:

• blood enters small arterioles which then splits into a knot of blood vessels called the glomerulus

• This creates higher pressure in the glomerulus, causing liquid and small molecules (e.g glucose) to be forced out of the glomerulus from the high hydrostatic pressure and into the bowman’s capsule

What three layers of tissue does filtrate need to pass through to get into the bowman’s capsule?

• capillary endothelium

• Basement membrane (where filtration takes place)

• Epithelium of the bowman’s capsule

What is the second stage of filtration in the kidneys?

SELECTIVE REABSORPTION

• Only useful substances in the filtrate are absorbed into the blood in the proximal convoluted tubule (PCT)

How are these useful substances transported into the blood?

• ACTIVE TRANSPORT → sodium ions and glucose molecules transported from glomerular filtrate into PCT by symports

• Sodium ions actively transported into the blood by a sodium pump, whilst also transporting potassium ions in the opposite direction

• FACILLITATED DIFFUSION → glucose transported out of the PCT and into the blood

What is the third stage of filtration in the kidneys?

• an ion gradient is produced in the medulla by the loop of henle

• At the ascending limb, sodium ions are active pumped out into the medulla → ascending limb is impermeable to water so water potential in medulla is low due to the limb being highly permeable to sodium ions

• Water moved out of the descending limb by osmosis as water potential is lower in the medulla than the limb as the limb is highly permeable to water → this limb is slightly permeable to sodium ions so they move out by diffusion

• Glomerular filtrate is now more concentrated due to ions being unable to diffuse out because of the descending limb being impermeable to them

• The water moved into the medulla is absorbed into the blood through the capillaries

What is the fourth stage of filtration in the kidneys?

• adjustment of the water and ion content of the blood to keep internal environment constant

• Water moves out of DCT and collecting duct by osmosis, and absorbed into the blood due to the lower water potential in the medulla

• The ascending limb is more permeable to salts and less permeable to water causing sodium and chloride ions to move out actively into surrounding tissue

• Water passes out of the descending limb by osmosis, causing the filtrate to become more concentrated

• This results in the countercurrent multiplier mechanisms where the solute concentration is lower in the ascending limb that the descending limb

What is ADH

A hormone that stops you urinating

How is ADH released?

• when osmoreceptor cells in the hypothalamus detect a decrease in water potential, water moves out of the osmoreceptor cells by osmosis which decreases their volume

• This send a signal to the posterior pituitary gland which releases ADH to the kidneys through the blood

What happens when ADH reaches the kidneys?

• binds to receptors on the plasma membrane of cells in the DCT and collecting duct

• This causes channel proteins callled aquaporins to make the DCT and collecting duct more permeable to water

• Thus results in water being absorbed into the medulla of the kidney and is to the blood by osmosis

• This produces a small amount of concentrate during so less water is lost from the body

What is osmoregulation?

the regulation of water potential in the blood to be kept constant

→ water potential too low causes more water being absorbed into the blood from nephrons = more concentrated urine

→ water potential too high causes less water being absorbed into the blood from nephrons = more dilute urine

• this happens in the Loop of Henle and the collecting duct

What is the function of the loop of henle?

• to create and area of high concentration in the medulla so water can be absorbed by osmosis so concentrated urine can be produced