digestion and absorption + mass transport

Question 1

define digestion

Answer 1

• the hydrolysis of large, insoluble molecules into smaller molecules that can be absorbed across cell membranes . (cells lining the intestine)
• digestive enzymes break bonds in macromolecules into monomers

Question 2

which enzymes are involved in carbohydrates digestion ? where are they found ?

Answer 2

• amylase in mouth
• maltase, sucrase, lactase in membrane of smell intestine.

Question 3

what’s the role of amylase ?

Answer 3

• breaks down starch into maltose by catalysing the hydrolysis of glycosidic bonds
• made in salivary glands and pancreas
• salivary glands secrete amylase into mouth (starch begins hydrolysed )
• pancreas secretes amylase into small intestine - remaining starch digested

Question 4

what’s the role of disaccharides ?

Answer 4

• (maltese) break down disaccharides into monosaccharides in small intestine. —> some attached to epithelial cells lining oleum (membrane-bound disaccharides )

Question 5

what are the substrates and products of carbohydrate digestive enzyme ?

Answer 5

• amylase = starch into smaller polysaccharides
• maltase = hydrolysed maltose to 2 glucose molecules
• sucrase = hydrolyses sucrose into glucose + fructose.
• lactase = hydrolysed lactose into glucose * galactose.

Question 6

where are lipids digested ?

Answer 6

• the small intestine.
• lipase synthesised in pancreas and released into small intestine.

Question 7

what needs to happen before lipids can be digested ?

Answer 7

• must be emulsified by bile salts produced by liver .
• this breaks down large fat molecules into smaller, soluble molecules called micelles (increasing surface area to speed up digestion)

Question 8

how are lipids digested ?

Answer 8

• lipase hydrolyses the ester bond between monoglycerides and fatty acids.

Question 9

what’s the role of micelles ?

Answer 9

• help move digested lipid towards the epithelium .
• dynamic structures - continually breaking apart and reforming (they split out monoglycerides + fatty acids —> pass thru bilayer via simple diffusion)

Question 10

how/where are proteins digested ?

Answer 10

• protease breaks down into amino acids by hydrolysing peptide bonds
• some protease made in pancreas + released into small intestine
• others made in cell lining stomach and released into stomach .

Question 11

what enzymes are involved in protein digestion ? what are their roles?

Answer 11

• endopeptidases = break between specific amino acid in middle of a polypeptide = converts longer poly into shorter ones
• exopeptidases = break between specific amino acids at the end of a polypeptide = releases individual amino acid - transported into ileum epithelial cells
• dipeptidases = break dipeptides into amino acids = exopep that hydrolyse peptide bonds in dipeptide

Question 12

how are certain molecules absorbed into ileum despite a negative concentration gradient ?

Answer 12

• through co-transport.

Question 13

which molecules require co-transport?

Answer 13

• amino acids + monosaccharides.

Question 14

explain how sodium ions are involved in co-transport .

Answer 14

• sodium ions (Na+) are actively transported out of cell into the lumen, creating a diffusion gradient.
• nutrients taken up into cells along with Na+ ions

Question 15

why do fatty acids and monoglycerides not require co-transport ?

Answer 15

• the molecules are nonpolar so can easily diffuse across the membrane of epithelium cells.

Question 16

describe the structure of haemoglobin .

Answer 16

• globular , water soluble. consists of 4 polypeptide chains, each carrying a haem group containing iron ion . (quaternary structure )

Question 17

describe the role of haemoglobin .

Answer 17

• present in RBCs = oxygen molecules bind to the haem groups and are carried around the body to where they needed in respiring tissues

Question 18

name 3 factors affecting oxygen-haemoglobin binding .

Answer 18

1) partial pressure/ concentration of oxygen.

2) partial pressure/ concentration of carbon dioxide .

3) saturation of haemoglobin with oxygen.

Question 19

how does partial pressure of oxygen affect oxygen-haemoglobin binding ?

Answer 19

• as partial pressure of oxygen increases, the affinity between haemoglobin for oxygen also increases, so oxygen binds tightly to haemoglobin
• when partial pressure is low, oxygen is released from haemoglobin .

Question 20

how does partial pressure of carbon dioxide affect oxygen-haemoglobin binding ?

Answer 20

• as partial pressure of CO2 increases, the conditions become acidic causing haemoglobin to change shape
• affinity of haemoglobin for oxygen this decreases , so oxygen released from haemoglobin
• known as Bohr effect

Question 21

what does it mean when the graph has a sigmoid / S-shape ?

Answer 21

• binding of the first oxygen molecule causes oxygen to change shape + u cover other oxygen binding sites

—> easier further O2 molecules bind and known - cooperative binding

Question 22

how does saturation of haemoglobin with oxygen affect oxygen-haemoglobin binding?

Answer 22

• hard for the first oxygen molecule to bind
• once it does , changes the shape to make it easier for second and third molecules to bind. = positive cooperativity
• then slightly harder for fourth oxygen molecule to bind as there’s low chance of finding a binding site .

Question 23

explain the bohr effect

Answer 23

• haem affinity for oxygen changes at diff concentrations of CO2
• higher partial pressures of CO2 = haem has lower affinity for oxygen : causing oxyhaem to dissociate more readily

—> useful : tissues with high rates of respiration will be producing larger amounts CO2 - ensures oxygen unloaded from haem at respiring tissues

• high CO2 conc shifts dissociation curve to right

Question 24

explain why oxygen binds to haemoglobin in lungs.

Answer 24

• partial pressure of oxygen is high
• low conc of CO2 in the lungs, so affinity is high
• positive cooperativity (after first oxygen molecule binds, binding is subsequent molecules easier)

Question 25

explain why oxygen released from haemoglobin in respiring tissues .

Answer 25

• partial pressure of oxygen is low
• high conc of CO2 in respiring tissues, so affinity decreases

Question 26

what do oxygaemoglobin dissociation curve show.

Answer 26

• saturation of haemoglobin with oxygen (in %), plotted against partial pressure of oxygen (in kPa)
• organisms that live low oxygen environments have dissociation curve lies to left (haem good at binding to O2 when partial pressure low)
• active organisms - dissociation curve lies to right (haem good releasing O2 at higher partial pressures so cells use it to respire )

Question 27

how does CO2 affect position of an oxyhemoglobin dissociation curve ?

Answer 27

• curve shifts to right as haemoglobins affinity for oxygen has decreased.

Question 28

name 3 common features of a mammalian circulatory system.

Answer 28

1) suitable medium for transport, water-based to allow substances to dissolve .

2) means of moving medium and maintaining pressure throughout the body . such as the heart

3) means of controlling flow so remains unidirectional, such as valves .

Question 29

relate the structure of the chambers to their function.

Answer 29

• atria - thin-walled and elastic, so can stretch when filled with blood
• ventricles - thick muscular walls pump blood under high pressure - left ventricle thicker than right as it has to pump
  blood all way around body.

Question 30

what is the role and structure of the arteries ?

Answer 30

• carry blood away from heart to various organs of body
• need to cope with high pressure generated from heart forcing out blood with each heartbeat —> thick muscular wall containing lots elastic tissue
• inner lining arteries called endothelium - folded allowing artery to expand help withstand high pressure
• small lumen ensures high pressure maintained

Question 31

describe the role and structure of veins

Answer 31

• carry blood from organs of body towards heart
• blood flowing much lower pressure so veins have larger lumen and much thinner walls containing little elastic fibres / muscle tissue
• valves prevent slow-moving blood from flowing backwards
• contraction of nearby body muscles helps blood to flow through veins

Question 32

describe what is the role and structure of capillaries

Answer 32

• connect arteries and veins
• substances move out of blood to body tissues =(O2, glucose, mineral ions) -> waste products (CO2 + H2O) move out body tissues and into capillaries
• small holes (pores) enable exchange of substances
• walls one cell thick - reduces diffusion distance for these substances
• large no. capillaries (capillary beds) increases surface area available for exchange

Question 33

why are two pumps (left and right) needed instead of one?

Answer 33

• to maintain blood pressure around whole body.
• when blood passes thru narrow capillaries of lungs, pressure drops sharply so not be flowing strongly enough to continue around body
• it’s returned to heart to increase pressure .

Question 34

what is tissue fluid ?

Answer 34

• watery substance containing glucose, amino acids, oxygen and other nutrients . supplies these to cells whilst removing any waste products .
• doesn’t contain things too big to be forced out of capillary so no RBC / large proteins

Question 35

how is tissue fluid formed ?

Answer 35

• as blood pumped through increasingly small vessels , this creates hydrostatic pressure which forces fluid out of capillaries
• bathes the cells, then returns to capillaries when hydrostatic pressure is low enough.

Question 36

define what’s meant by the cardiac cycle

Answer 36

• coordinated sequence of contractions + relaxations by heart muscle causing blood to move from atria into ventricles and then arteries.
• muscle contraction = systole
• relaxation = diastole

Question 37

describe what happened during cardiac disatole .

Answer 37

• heart relaxes
• blood enters atria, increasing pressure + pushing open atrioventricular valves
• this allows blood to flow into ventricles — pressure in heart lower than in arteries, so semilunar valves remain closed

Question 38

describe what happens during 1. atrial systole

Answer 38

• atria contact while ventricles relax
• decreases volume inside atria which increases pressure —> increased pressure forces atrioventricular valves open and pushes blood into ventricles .

Question 39

describe what happens during ventricular systole

Answer 39

• ventricles contact
• pressure increases, closing atrioventricular valves = prevent back flow, + opening semilunar valves ,
• blood flows into arteries .

Question 40

describe what happens during disastole

Answer 40

• both atria and ventricles relaxes = low pressure in both chambers
• since pressure higher in arteries than heart chambers—> semi lunar valves forced closed : prevents blood flowing backwards into ventricles
• blood returned heart - atria filled blood

Question 41

name the nodes involved in heart contraction and where they situated

Answer 41

• SAN (sinoatrial node) - wall of right atrium
• AVN (atrioventricular node ) = in between 2 atria

Question 42

what does myogenic mean?

Answer 42

• hearts contraction initiated from within muscle itself , rather by nerve impulses

Question 43

explain how heart contracts

Answer 43

• SAN initiates + spreads impulse across atria, so they contract
• AVN receives , delays , and conveys impulse down bundle of His
• impulse travels into Purkinje fibres - branch across ventricles so contract from bottom up

Question 44

why does the impulse need to be delayed ?

Answer 44

• if impulse spread straight from atria into ventricles = not be enough time for all blood to pass thru and for valves to close