6 Responding to Change- Homeostasis

Question 1

What is homeostasis?

Answer 1

The maintenance of the internal environment within an optimum range

Question 2

Why does homeostasis need to control high temperature?

Answer 2

-Maintains optimum core body temp (approx 37c)
-If body temp rises above optimum range, enzymes denature
-Higher temp causes hydrogen bonds maintaining enzyme structure to break
-alters enzyme active site so enzyme can no longer catalyse reactions

Question 3

Why does homeostasis need to control low temperature?

Answer 3

-If temp falls ↓ optimum range, enzyme activity declines
-decreased enzyme activity causes rate of important reactions like respiration to slow down

Question 4

Why does homeostasis need to control blood pH?

Answer 4

-If blood pH rises ↑ or falls ↓ optimum range, enzymes denature
-Denatured enzymes can no longer catalyse important reactions
-optimum pH range = around 7 but some enzymes have very different optimum ranges

Question 5

Why does homeostasis need to control high blood glucose?

Answer 5

-If blood glucose levels rise ↑ optimum range, water potential of blood ↓
-Low water potential in blood → water diffuses out of cells by osmosis, into blood
-cells become flaccid/dehydrated & die
-blood pressure also increases

Question 6

Why does homeostasis need to control low blood glucose?

Answer 6

-If blood glucose levels fall ↓ optimum range, there isn’t enough glucose for respiration
-respiration rate ↓, energy levels ↓

Question 7

What is negative feedback?

Answer 7

The mechanism that restores systems to the original level

Question 8

What are the steps involved in negative feedback?

Answer 8

-Detect change; stimulus detected by receptors
-receptors (eg thermoreceptors) stimulated when level = too high/low (eg temp)
-receptors send signal to effectors though nervous system
-effectors counteract change
-negative feedback can only maintain internal environment within specific range. If change = too dramatic it may not be able to prevent it

Question 9

How are multiple negative feedback mechanisms more effective? + examples

Answer 9

-more control; body can respond to multiple changes away from optimum (eg body temp can be reduced/increased by multiple mechanisms)
-Faster response; body can respond in more ways to change away from optimum (eg both shivering & vasoconstriction for low body temp)

Question 10

What are the factors influencing blood glucose levels?

Answer 10

-eating carbohydrates; increase in blood glucose concentration. This is monitored by the pancreas
-exercise; decrease in blood glucose concentration as glucose used in respiration to power muscle contraction. Also monitored by the pancreas

Question 11

Where do glycogenesis, glycogenolysis and gluconeogenesis take place?

Answer 11

The liver

Question 12

What occurs in glycogenesis?

Answer 12

When blood glucose concentration = too↑, liver cells produce enzymes which concert glucose into glycogen, then stored in liver cells

Question 13

What occurs in glycogenolysis?

Answer 13

When blood glucose concentration = too ↓, liver cells make enzymes which break down glycogen stared in cells to glucose

Question 14

What occurs in gluconeogenesis?

Answer 14

When blood glucose concentration = too ↓, liver cells form glucose from glycerol and amino acids

Question 15

What is the process of insulin returning high blood glucose concentration back to optimum levels?

Answer 15

-high blood glucose concentration detected by beta (β) cells (in islets of langerhans) in pancreas
-beta cells secrete insulin into blood, which travels → liver & muscle cells
-insulin binds to receptors on muscle cell membranes. Muscle cells insert more glucose channel proteins in cell membranes, causes;
-rate of uptake of glucose by muscle cells↑, rate of respiration in muscle cells↑
- glycogenesis; insulin binds to receptors on liver cell membranes
-liver cells make enzymes that convert glucose to glycogen (stored in liver cell cytoplasm)

Question 16

What is the importance of insulin?

Answer 16

-Important for maintaining an optimum blood water potential
-if blood glucose levels weren’t ↓ by insulin, blood water potential would ↓
-Water in body cells would diffuse out, causing cells to shrink & die

Question 17

What is the process of glucagon returning low blood glucose concentration back to optimum levels?

Answer 17

-Detected by alpha (a) cells (in islets of langerhans) in pancreas
-alpha cells secrete glucagon into the blood, travels to liver cells
-glycogenolysis; glucagon binds to receptors on liver cell membranes. Liver cells make enzymes converting glycogen to glucose
-gluconeogenesis; binding of glucagon to liver cell membranes also causes release of enzymes forming glucose from glycerol & amino acids
-glucagon also slows cell respiration rate; slows rate at which glucose is used up

Question 18

What is the importance of glucagon?

Answer 18

-If blood glucose levels weren’t ↑ by glucagon there wouldn’t be enough glucose available for respiration
-if there isn’t enough glucose for respiration, there’ll be no energy available for survival

Question 19

What is adrenaline and when is it released?

Answer 19

-Hormone secreted in response to low blood glucose concentration
-also released during exercise & times of stress

Question 20

What are the steps of the adrenaline response?

Answer 20

-Adrenaline is secreted from adrenal gland in response to low blood glucose concentration, exercise & stress
-adrenaline binds to receptors on liver cell membrane, induces 2 reactions in liver cells; glycogenolysis activation (glycogen → glucose) & glycogenesis inhibition (glucose → glycogen)
-adrenaline also promotes secretion of glucagon from pancreas, inhibits secretion of insulin

Question 21

What are primary messengers + example?

Answer 21

-Messengers that don’t enter a cell
-exert action on cell membrane by binding to receptors & triggering a change within the cell
-change can be activation of another molecule (secondary messenger) or may initiate reaction
-examples = hormones, eg glucagon & adrenaline

Question 22

What are secondary messengers + example?

Answer 22

-Initiate & coordinate responses taking place inside cell
-usually activated by binding of primary messenger to cell surface receptor
-example = cyclic AMP (cAMP)

Question 23

What is the role of the secondary messenger cAMP controlling blood glucose concentration?

Answer 23

-Primary messengers adrenaline/glucagon bind → receptors on cell membranes of liver cells
-binding activates adenylate cyclase enzyme, which converts ATP → cAMP
-cAMP activates protein kinase A enzyme, which triggers a cascade of reactions resulting in glycogenolysis
-glycogenolysis breaks down glycogen → glucose

Question 24

What is diabetes mellitus?

Answer 24

A chronic health condition where sufferers can’t properly control their blood glucose concentration

Question 25

What is the cause of type l diabetes?

Answer 25

-When beta cells in pancreas are attacked by immune system
-beta cells become damaged, can no longer produce insulin
-some are more genetically predisposed to type 1 diabetes than others; normally develops in childhood

Question 26

How does hyperglycaemia happen and what can it lead to?

Answer 26

-Eating → blood glucose concentration ↑
-people w/ type 1 diabetes can’t make insulin to counteract increased levels of glucose so blood glucose levels remain↑
-can lead to death if not treated

Question 27

What is the treatment for type I diabetes?

Answer 27

-insulin therapy
-insulin is injected regularly during day/ insulin pump can be used continuously
-too much insulin can = ↓ in glucose levels (hypoglycaemia) so insulin therapy needs to be carefully monitored

Question 28

What is the cause of type ll diabetes?

Answer 28

• Correlated w/ obesity, lack of exercise, age & family history
  -develops when beta cells in pancreas can no longer make insulin/when muscle & liver cells stop responding to insulin

Question 29

What is the treatment for type ll diabetes?

Answer 29

• Eating a healthy diet & exercising
  -some cases; medication used to lower glucose levels
  -rare cases; insulin injections used

Question 30

What are examples of initiatives taken to tackle the rise of obesity & type II diabetes?

Answer 30

-Healthy lifestyle; advisors recommend a balanced diet low in salt/sugar/fat & regular exercise
-NHS ‘Change4life’ campaign; educates how to lead healthy lifestyle
-The WHO recommends food industry combats obesity & diabetes by; ↓ levels of sugars/fats/salt in processed foods, developing healthy alternatives, having clear labels on food items & promoting healthier foods

Question 31

What is osmoregulation and where does it take place?

Answer 31

-The control of water potential in the blood
-takes place in the nephron (functional unit) in the kidneys; absorb more or less water according to water potential

Question 32

What occurs when there is a high water potential to return to normal?

Answer 32

-More water must be lost by excretion to return water potential to normal
-blood reabsorbs less water from kidneys
-urine = more dilute & water potential in blood ↓

Question 33

What occurs when there is a low water potential to return to normal?

Answer 33

-Less water must be lost by excretion to return water potential to normal
-blood reabsorbs more water from kidneys
-urine = more concentrated & water potential in blood ↑

Question 34

Nephron structure; what is the bowman’s capsule and its function?

Answer 34

-The beginning of the tubules that make up the nephron
-surrounds a network of capillaries (the glomerulus)
-first step of filtration of blood to form urine takes place here. This produces the glomerular filtrate.

Question 35

Nephron structure; what are the features and function of the afferent and efferent arterioles?

Answer 35

-Blood flows → glomerulus through afferent arteriole & ← glomerulus through efferent arteriole
-afferent arteriole = much wider than efferent arteriole, so blood pressure in capillaries is very high

Question 36

Nephron structure; what is the proximal convoluted tubule (PCT) and its function?

Answer 36

-The site of selective reabsorption
-after glomerular filtrate has been produced in bowman’s capsule, glucose & water → reabsorbed into bloodstream through PCT.

Question 37

Nephron structure; what is the function of the loop of henle and what does it consist of?

Answer 37

-Produces low water potential in medulla of kidney
-consists of ascending limb (impermeable to water) & descending limb (permeable to water)

Question 38

Nephron structure; what is the collecting duct and its function?

Answer 38

-Water is reabsorbed into blood through collecting duct
-amount of water absorbed depends on water potential of blood; if blood water potential= low, more water absorbed. If blood water=high, less water absorbed
-this → osmoregulation

Question 39

Osmoregulation; what is the process of the glomerular filtrate being formed in the Bowman’s capsule?

Answer 39

-Branch of capillary entering the glomerulus = much wider than branch exiting glomerulus. This creates high blood pressure in glomerulus
-fluid & its solutes (glucose,amino acids) in blood forced out of capillary→ this = pressure filtration
-fluid flows through pores in capillary endothelium
-smaller molecules (most proteins, all blood cells too big) filter through slit pores in basement membrane → mesh of collagen fibres & glycoprotein
-substances pass between epithelial cells (podocytes, have finger-like projections that substances can flow between) of Bowman’s capsule
-fluid that has filtered from capillaries → Bowman’s capsule = glomerular filtrate; contains water, amino acids, urea, glucose and inorganic ions.

Question 40

Osmoregulation; what is the process of globular filtrate substances being selectively reabsorbed into bloodstream in the PCT?

Answer 40

-Na+ ions actively transported out of PCT epithelial cells & → blood by sodium-potassium pumps. K+ ions also transported → epithelium
-active transport of Na+ ions = conc of Na+ inside epithelial cells ↓
-Na+ ions in filtrate diffuse → epithelial cells down conc gradient via co-transporter proteins, which allow glucose & amino acids to be transported into epithelial cells along w/ Na+ ions
-as glucose & amino acids co-transport → PCT epithelial cells, their conc ↑ inside cells. They diffuse down conc gradient → blood
-blood pressure=relatively high so substances in blood carried away quickly, maintains steep conc gradient.
-movement of Na+ ions, glucose & amino acids → bloodstream causes WP to ↓in blood & ↑in PCT.
-water in PCT diffuses → blood via osmosis.
-any substances not reabsorbed= excreted as waste.

Question 41

Osmoregulation; what is the process of the loop of henle allowing water to be reabsorbed in the collecting duct?

Answer 41

-Na+ ions actively transported out of the top of the ascending limb → surrounding tissue fluid in medulla.
-solute conc of medulla ↑, WP ↓
-ascending limb= impermeable to water so water inside tubule can’t diffuse out
-Na+ ions diffuse out of the bottom of the ascending limb → medulla; further ↑solute conc of medulla
-descending limb= permeable to water so water inside tubule can diffuse out as there’s a lower WP in medulla.
-water reabsorbed by bloodstream
-overall effect of descending & ascending limb= create high solute conc & WP in tissue fluid surrounding collecting duct.
-causes water inside collecting duct to diffuse → surrounding tissue fluid by osmosis
-water then reabsorbed → bloodstream
-volume of water reabsorbed → bloodstream depends on permeability of collecting duct.
-permeability of collecting duct varies according to WP of blood; if water potential= high, collecting duct is less permeable & less water absorbed in blood. If water potential= low, collecting duct is more permeable & more water absorbed in blood.

Question 42

What does antidiuretic hormone (ADH) control and influence?

Answer 42

-controls osmoregulation.
-influences permeability of distal convoluted tubule & collecting duct. -controls how much water is reabsorbed from kidney → blood

Question 43

What is the role of osmoreceptors in the hypothalamus?

Answer 43

-monitor blood WP
-if WP ↑, water diffuses into osmoreceptor cells & cells swell.
-if WP ↓, water diffuses out of osmoreceptor cells & cells shrink

Question 44

What does the posterior pituitary gland detect and then release?

Answer 44

-detects osmoreceptors shrinking
-then releases ADH into blood

Question 45

What does ADH bind to and what does this result in?

Answer 45

-binds to receptors on cell membrane of epithelial cells of distal convoluted tubule (DCT) & collecting duct.
-when ADH binds, vesicles containing aquaporins fuse w/ cell membrane.
-aquaporins= protein channels for water, ↑ permeability of DCT & collecting duct.
-so, more water is reabsorbed into blood by osmosis.

Question 46

How does the amount of ADH in the blood influence how concentrated urine is?

Answer 46

-If more ADH= in bloodstream, more water reabsorbed from nephron → blood.
-So urine= more concentrated
-If less ADH= in bloodstream, less water reabsorbed from nephron → blood.
-So the urine= more diluted