B3.2 Transport

Question 1

Describe how the structures of capillaries are adapted to capillary function (lumen diameter, branching, wall thickness, fenestrations)

Answer 1

1. capillaries have a very narrow lumen diameter which allows passage of a single RBC at a time (optimal exchange such that RBC is forced to travel slowly –> more time for diffusion)
2. wall is made of a single layer of endothelial cells (one cell thick) to minimise diffusion distance for permeable materials
3. walls may be fenestrated (contain pores) to aid in rapid transport of materials between tissue fluid and blood (esp in tissues specialised for absorption like intestines, kidneys)
4. capillary vessels branch out from arterioles to form capillary networks –> increases amount of exposed surface area available for the exchange of products through diffusion
5. narrow diameter increases rate of oxygen diffusion from RBC

less impt:
5. some capillaries are sinusoidal and have open spaces between cells to be permeable to large molecules (eg in liver)
6. wall may be continuous with endothelial cells held tgt tightly by tight junctions to limit permeability of large molecules
7. surrounded by basement membrane which is permeable to necessary materials and prevents large proteins and cells from leaking out of capillaries

*pressure in capillaries are low

Question 2

Compare the diameter, relative wall thickness, lumen size, number of wall layers, abundance of muscle and elastic fibres, and presence of valves in arteries and veins

Answer 2

Artery VS Vein:
1. Diameter: larger than 10 um VS variable but much larger than 10um
2. Relative thickness of wall & lumen size: thick wall & narrow lumen VS thin wall with variable but often wide lumen
3. Number of layers in wall: 3 layers (tunica externa, media and initima) which may be subdivide to form more layers VS 3 layers (tunica externa, media, initima)
4. Muscle and elastic fibres in wall: Large amount VS small amount
5. Valves: None VS present in many veins

Function & Pressure: send blood from heart, high pressure VS send blood to heart, low

Question 3

Given a micrograph, identify a blood vessel as an artery or vein

Answer 3

Artery - thick walls, narrow lumen
Capillary - significantly smaller hence is shown at higher magnification
Vein - thin walls, big lumen, irregular shape

Question 4

State the function of arteries

Answer 4

Arteries are adapted to transport high pressure blood away from the heart which branch into smaller vessels, arterioles. Arterioles distribute blood to capillaries, the sites of exchange of materials between blood and the internal/ external environment.

Question 5

Describe the structures and functions of the three layers in the artery wall

Answer 5

Three layers of arterial wall:
1. tunica externa: tough outer layer of connective tissue, collagen fibres and elastic tissue
- when blood pumped into artery, elastin & collagen fibres are stretched and allow blood vessel to accommodate increased pressure
- once blood surge has passed, the elastic fibres recoil and provide further pressure –> propel blood forward within artery
2. tunica media: thick layer containing smooth muscle & elastic fibres made of protein elastin
- smooth muscle is controlled by autonomic nervous system (ANS) which controls functions in the body that are necessary but not controlled consciously –> it changes the lumen diameter of arteries to help regulate blood pressure
- muscular & elastic tissues permit arteries to withstand high pressure of each blood surge and keep blood moving continuously
3. tunica intima: smooth endothelium forming lining of artery
- smooth surface for blood to flow with low resistance

HENCE, blood can maintain high pressure between pump cycles of heart

Question 6

Discuss how the wall thickness, lumen size, and muscle and elastic allow arteries to withstand and maintain high blood pressures

Answer 6

1. overall wall thickness/ muscle layer withstands blood pressure and prevents rupture of artery wall
2. thick layer of elastic tissue to even out and maintain blood pressure
3. walls stretch to accommodate huge surge of blood when ventricles contract
4. elastic tissue and collagen fibres of tunica externa prevent rupture as blood surges from heart
5. high proportion of elastic fibres first strecthed, then recoil, keeping blood flowing and propelling it forwards after each pulse passes
6. w increasing distance from heart, tunica media progressively contains more smooth muscle fibres and less elastic tissue as less stretching and recoiling occurs due to smaller differences in blood pressure
   - by varying constriction & dilation of arteries, blood flow is maintained
   - muscle fibres stretch and recoil, tending to even out the pressure, but a “pulse” can still be detected
7. lumen is small to keep pressure high
8. smooth muscle contracts to help maintain pressure between heartbeats (blood movement)
9. smooth endothelium for reduced friction and maintain high pressure

• ARTERY WALLS are THICK, not artery

Question 7

State the unit of measurement of the pulse rate

Answer 7

Beats per minute

The pulse rate/ heart rate is a measurement of the number of times you heart beats in a minute
- each time heart contracts & sends blood into arteries, the “pulse” of pressure can be felt in an artery

Question 8

Outline 2 methods for determining heart rate

Answer 8

1. Take own pulse by feeling for the pulse using your index and middle fingers at 2 possible locations
   - carotid artery: either side of trachea (windpipe) in your neck
   - radial artery: on your wrist with the palm of your hand facing upwards (pulse shd be felt 2cm from base of thumb)
2. Use digital meters to calculate pulse rate
   - pulse oximeters clipped to a finger: they have LEDs that shine red & infrared light through finger and the detector measures how much of the light passes through the tissues of the finger
   - enables detection of variation in amount of blood in tissues each time heart beats and from this heart rate is calculated
   - percentage saturation of blood with oxygen can also be deduced bc deoxygenated blood absorbs red light whereas oxygenated blood absorbs infrared light

Question 9

State the function of veins

Answer 9

Veins are blood vessels that return blood back to the heart after the blood has passed through a capillary bed

Question 10

Discuss how pocket valves, thin walls and skeletal muscles maintain the flow of blood through a vein

Answer 10

1. Veins have thin walls and a large internal diameter bc blood loses a great deal of pressure and velocity in capillary beds –> less resistance to blood flow
2. the unidirectional flow of relatively slow blood in veins is aided by internal valves that help prevent back flow of blood
3. thin walls of veins are easily compressed by surrounding skeletal muscles –> exert pressure on veins
4. thin outer layer of muscle fibres provide structural support

Question 11

State the function of coronary arteries

Answer 11

They are arteries that supply blood to the cardiac muscle

Question 12

Outline the cause and consequence of an coronary occlusion

Answer 12

Overtime, a person may develop a build up of cholesterol and other substances in lumen of arteries
- this build up is called plague and the restriction in blood flow it causes is called an occlusion

Plague build-up is progressive and can severely decrease artery’s blood flow
- if occluded artery is coronary artery –> result in heart attack bc cardiac muscle in one or more areas of heart is deprived of oxygen

Question 13

Evaluate correlations between diet and lifestyle variables and risk of coronary heart disease

Answer 13

Correlation coefficients quantify correlations between variables and allow the strength of relationship to be assessed
- low correlation coefficient/ lack of coefficient = evidence against hypothesis
- strong correlations eg between saturated fat intake & coronary heart disease DONT provide causal link

Question 14

List factors correlated with an increased risk of coronary occlusion and heart attack

Answer 14

Sex, age, family history, diet, diabetes, hypertension, high cholesterol, weight, smoking, chronic stress, sedentary lifestyle, genetic predisposition

Question 15

Epidemiology

Answer 15

Epidemiology is the study and analysis of patterns, causes and effects of health and disease conditions in defined populations

Coronary Heart Disease (CHD) refers to the damage to the heart as a consequence of reduced blood supply to the heart tissues
- often caused by narrowing & hardening of coronary artery, by build-up of plaque within coronary arteries
- ethnic groups can differ in predisposition of CHD bc of differing diets & lifestyles
- gender groups, age groups, groups that differ in physical activity, diff genotypes, differing medical histories –> all have diff probabilities of experiencing CHD

Question 16

What is transpiration & capillary action

Answer 16

Transpiration is the evaporation of water from leaves through open stomata
- a plant relies on the tension force generated by transpiration to bring dissolved minerals up from the roots

Capillary action is the loss of water by transpiration in air space by spongy mesophyll which causes water to be pulled through the cell walls of nearby xylem tissue
- creates tension at upper end of each xylem tube –> results in movement of water up xylem and the entire column of water moves up bc of cohesion [COHESION-TENSION THEORY}
- it is the combination of cohesive and adhesive force

Question 17

Explain the process of transpiration

Answer 17

1. Water moves down concentration gradients (diffusion)
   - space within a leaf have high concentration of water vapour –> water moves from this location to atmosphere which has lower conc of water
2. water leaving through stomata by transpiration is replaced by water from xylem
   - replacing water from the vessels maintains a high water vapour concentration in the air spaces of the leaf
3. water in xylem climbs the stem through the pull of transpiration combined with the forces of adhesion and cohesion
   - cohesion involves the HB forming between water molecules due to dipolarity
   - adhesion involves the hydrogen bonds forming between water molecules and sides of xylem vessels bc of polar bonds which counteracts gravity
4. tension occurs in columns of water in xylem
   - bc of the loss of water in the leaves and the replacement of that lost water by xylem water –> water columns remain continuous bc of cohesion and adhesion
5. water is pulled from root cortex into xylem cells
   - cohesion and adhesion maintain the column of water under the tension created by transpiration
6. water is pulled from soil into roots
   - bc of tension created by transpiration and maintenance of continuous column of water
   - water moves from soil into roots by osmosis due to active transport of minerals into roots
   - once water is in root it travels to xylem through cell walls (apoplaast pathway) & through cytoplasm (symplast pathway)

Question 18

Adaptations of xylem vessels for transport of water

Answer 18

1. lack of cell contents
   - xylem cells are dead cells and contain no cytoplasm –> larger lumen making water transport more efficient & water transport is passive
2. incomplete/ absent end walls for unimpeded flow
   - long, continuous tubes are arranged end-to-end allows unobstructed water flow upwards
3. lignified walls to withstand tension
   - lignin provides resistance to collapse of the tubes due to tension from transpiration
4. pits for entry and exit of water
   - microscopic holes in its sidewalls for easy flow of water in and out as needed

Question 19

Function of tissues in a stem

Answer 19

Epidermis: prevents water loss and provides protection from microorganisms
Cortex: Unspecialised cell layer that sometimes stores food reserves
Xylem: transport tubes that bring water up from the roots
Phloem: transport carbohydrates, usually from leaves to other parts of the plant
Vascular bundle: contain multiple vessels of both xylem and phloem

Question 20

Draw transverse section of stem & root of a dicotyledonous plant

Answer 20

Stem: Epidermis, cortex, xylem, phloem, vascular bundle
Root: Epidermis, cortex, xylem, phloem, vascular bundle

Question 21

Function of tissues in a root

Answer 21

Epidermis: grows root hairs that increase surface area for water uptake
Cortex: An unspecialised cell layer that stores food reserves
Xylem: transport tubes for water and minerals, starting in roots
Phloem: transport tubes that receive sugars from leaves
Vascular bundle: area in centre of root containing xylem and phloem

Question 22

Define tissue fluid

Question 23

List components of blood plasma

Answer 23

Blood is a fluid (plasma)

Question 24

Process of release and reuptake of tissue fluid in capillaries

Answer 24

Blood is a fluid (plasma) and cells contain a fluid (cytoplasm) –> in order for cells to chemically exchange substances with blood, there must be fluid between cells and blood [tissue fluid]

Tissue fluid is constantly renewed by being released from the side of a capillary bed closest to the arteriole
- arteriole is the smallest of all arteries and directly branches into a capillary bed
- within capillary bed, blood pressure is highest at this end and the release of tissue fluid is called PRESSURE FILTRATION
- pressure at arteriole end of capillary bed is high enough to open gaps between the cells that made up the wall of the capillary

At other end of capillary is smallest of all veins, a venule
- the pressure at this end of capillary bed is relatively low bc it is further away from direct pulse of heart
- lower pressure of capillary bed nearer the venule allows much of tissue fluid to drain back into capillaries

Question 25

Composition of plasma and tissue fluid

Answer 25

Cells: RBC (erythrocytes), WBC (phagocytes, lymphocytes), platelets VS phagocytes *some WBC can squeeze through capillaries into tissue fluid Proteins: more proteins, incl large plasma proteins and hormones VS fewer proteins (smaller) Glucose: 80-120mg per 100ml VS less (absorbed by cells for respiration) Fats: lipoproteins (for fat transport in plasma) VS none Amino acids: more VS fewer (absorbed by cells) Oxygen: more VS less (absorbed by cells for respiration) Carbon dioxide: less VS more (released by cells as product of respiration)

Question 26

Process of exchange of substances between tissue fluid and cells in tissues

Answer 26

1. body cells are in constant need of oxygen and variety of nutrients 2. in turn, they produce waste products like carbon dioxide and a waste product of amino acid metabolism called urea 3. many molecules have natural concentration gradients, eg oxygen, carbon dioxide and glucose --> diffuse directly through cell's plasma membrane / through protein channels in a process called FACILITATED DIFFUSION 4. unlike very porous membranes of capillaries, plasma membranes of cells often use active transport mechanisms to regulate presence of various ions 5. concentration of potassium ions is typically many times higher in cytoplasm compared to tissue fluid 6. concentration of sodium ions is many times higher in tissue fluid compared to cytoplasm 7. cell must use ATP in active transport mechanisms to keep the high concentrations of these and other ions more concentrated on one side of the plasma membrane

Question 27

How excess tissue fluid is drained into lymph ducts

Answer 27

1. some tissue fluid don't re-enter venous side of capillary bed but enters small tubes called lymphatic capillaries 2. the small lymphatic capillaries are very thin walled and contain gaps between adjoining cells to facilitate easy movement of water & solutes 3. fluid that enters lymphatic capillaries are called lymph 4. the collection of tissue fluid in lymph vessels prevents fluid build-up around body cells 5. lymph vessels are similar to veins in that they have internal valves to keep fluid moving in one direction 6. like veins, they rely on skeletal muscle contractions to squeeze the vessels and one-way valves to keep the lymph fluid moving 7. fluid entering lymphatic vessels often routed through lymph nodes which filter bacteria, viruses, and sometimes even cancer cells out of lymph fluid 8. also like veins, they join together into larger and larger lymph ducts, eventually taking lymph fluid back to veins so it can be part of blood plasma again

Question 28

Differences between single circulation of bony fish and double circulation of mammals

Answer 28

Need to learn how to draw circuit diagrams Fish: 2-chambered heart, one chamber to receive blood, another to pump blood out - when blood is pumped out it is sent to the gills for oxygen and carbon dioxide exchange - reoxygenated blood is collected from the gill capillaries and sent to capillary beds in body tissues - deoxygenated blood is then retuned to the heart to be pumped to gills again Limitation: loss of blood pressure when blood is within capillaries of gills Mammals: double circulation pattern with 4 chambers - one side of the heart is used to pump blood to capillaries in lungs for reoxygenation [PULMONARY CIRCULATION] - blood is returned to other side of heart to be pumped out to capillaries in body tissues, to supply oxygen to where is needed [SYSTEMIC CIRCULATION] - additional trip allows blood pressure to be restored

Question 29

Label a diagram of the heart

Answer 29

see slides 75&76 - need know how to draw the arrow also

Question 30

Adaptations for efficient blood flow

Answer 30

1. Cardiac muscle - highly vascular tissue making up heart muscle which is especially thick in ventricles of heart - muscle making up the wall of left ventricle is the thickest, as it pumps blood out of locations in the entire body 2. Pacemaker aka sinoatrial node (SA node) - area of specialised cells in right atrium generate a spontaneous electrical impulse to start each heartbeat 3. atria-thin muscular chambers of the heart - designed to receive low pressure blood from the capillaries of the lungs or body tissues by way of large veins entering the heart - atria send blood to ventricles 4. ventricles-thick muscular chambers that pump blood out under pressure to lungs or body tissues 5. atrioventricular valves - located between atria and ventricles that close each heart cycle to prevent any back flow into atria 6. semilunar valves - valves that close after the surge of blood into the pulmonary artery or aorta, to prevent back flow of blood into ventricles 7. septum - wall of muscular and fibrous tissue that separates the right side of the heart from the left side 8. coronary vessels - blood vessels that provide oxygenated blood to the heart muscles *heart valves open and close as a result of differences in blood pressure on either side of valves

Question 31

Summary of blood flow

Answer 31

1. double circulation (pulmonary & systemic) 2. heart is a double pump as left and right sides of heart are separate 3. deoxygenated blood pumped to lungs and oxygenated blood to rest of body 4. each side of heart has atrium and ventricle 5. left ventricle pumps blood to body tissues and right ventricle pumps blood to lungs 6. left atrium receives blood from lungs and right atrium receives blood from body tissues 7. left ventricle pumps blood via aorta & right ventricle pumps blood via pulmonary artery 8. left atrium receives blood via pulmonary vein & right atrium receives blood via vena cava 9. lungs require lower pressure blood as high pressure blood damages lungs 10. high pressure required to pump blood to all body tissues apart from lungs 11. pressure of blood returning from lungs is not high enough to continue to travel to body tissues thus blood has to be pumped again after returning from lungs 12. oxygenated blood and deoxygenated blood kept separate so all tissues receive blood with high oxygen content

Question 32

Cardiac cycle for left side (refer to graph on slide 85)

Answer 32

1. slight increase due to left atrial systole 2. left ventricular systole --> bicuspid valve close ("lub") --> pressure increase 3. pressure in left ventricle continues to rise 4. pressure in left ventricle higher than in aorta --> semilunar valves open 5. left ventricle begins to relax --> semilunar valves close ("dup") 6. ventricular pressure continues to decrease 7. ventricular pressure lower than atrial lower than atrial pressure --> bicuspid valve opens 8. ventricular & atrial pressure gradually increases as both chambers fill by passive filling (both chambers at a diastole) 9. cycle repeats

Question 33

SA (sinoatrial) node

Answer 33

1. it is a complex spindle-shaped structure that lies at the junction between the superior vena cava and right atrium 2. it generates impulses automatically by spontaneous depolarisation of its membrane (due to small influx of Na ions into cell) at a rate quicker than any other cardiac cell type 3. these cells have few of the proteins (actin & myosin) that cause contraction in other muscle cells, but they have extensive membranes 4. SA node initates each heartbeat in each cardiac cycle & hence acts as a pacemaker 5. if it becomes defective, its output may be regulated/ replaced entirely by an artificial pacemaker placed under the skin which electrodes implanted in the wall of heart Impt: 6. SA node initiates a heartbeat by contracting and simultaneously sends out an electrical signal (impulses) that spread rapidly through walls of atria 7. this can happen bc there are interconnections between adjacent fibres across which the electrical signal can be propagated - the fibres are branched so each fibre can passes the signal onto several others - this propagation causes both left & right atria to contract 8. after time delay of 0.1s, the electrical signal passes to AV node, then is conveyed to walls of ventricles - time delay allows atria to pump blood they are holding into ventricles - signal is then propagated throughout walls of ventricles, stimulating them to contract & pump blood out into arteries Idk if in syllabus: 9. nerves from brain transmit messages to SAN to alter (increase/ decrease) rate of SAN 10. medulla oblongata of brain can change the heart rate through nerves 11. the vagus nerve slows the heart rate & sympathetic nerve accelerates it 12. the medulla of brain controls heart rate via production of epinephrine by adrenal gland 13. epinephrine increase heart rate as it prepares body for vigorous activity

Question 34

Whole cardiac cycle

Answer 34

1. both atria collect blood from veins 2. SA node sends impulses to heart muscles to initiate contraction 3. blood is pushed to ventricles from both atria by simultaneous contraction of atria (atrial systole) 4. AV valves are forced to open as atria contract. semilunar valves remain closed so ventricles fill with blood 5. then, both ventricles contract simultaneously (ventricular systole) to push blood to pulmonary artery and aorta 6. AV valves close to prevent back flow to atria ('lub' sound) . semilunar valves pushed open 7. when ventricles relax (diastole), semilunar valves close to prevent back flow of blood back to ventricles ('dup' sound)

Question 35

Interpretation of systolic & diastolic blood pressure measurements

Answer 35

- blood pressure refers to arterial pressure: the pressure that circulating blood puts on the walls of arteries - during each heartbeat, the pressure of blood within arteries varies from a peak during ventricular systole to minimum near the beginning of the cardiac cycle where ventricles are filled with blood & are at diastole - blood pressure measurements are often quoted in the pressure unit "mmHg" eg 120 over 80 --> higher number refers to pressure in artery (systolic pressure) & lower number refers to pressure in artery due to ventricular diastole (diastolic pressure) Blood pressure categories: Normal: less than 120/ less than 80 Hypotension: 90 or less/ 60 or less Pre-hypertension: 120-139/ 80-89 high blood pressure (stage 1 hypertension): 140-159/ 90-99 high blood pressure (stage 2 hypertension): 160 or higher/ 100 or higher hypertension crises: higher than 180/ higher than 110

Question 36

Define myogenic contraction

Answer 36

Heart muscles are myogenic, meaning the control of heartbeat originates within the heart muscle itself rather than from the nervous system

Question 37

Mechanisms for roots to maintain positive pressure potential

Answer 37

3 transport routes for water movement 1. apoplast pathway - mass flow occurs through interconnecting free spaces between cellulose fibres of plant cell walls - free space in cellulose makes up 50% of wall volume - apoplast pathway passes water through non-living parts of cell and inter-cell spaces, avoiding the living contents of cells 2. symplast pathway - diffusion occurs through cytoplasm of cells & via cytoplasmic connections between cells (aka plasmodesmata) - as plant cells are packed with many organelles which resist flow of water, this pathway is v significant 3. vacuolar pathway (transmembrane) - osmosis occurs from vacuole to vacuole, driven by a gradient in osmotic pressure - active uptake of mineral ions in roots causes absorption of water by osmosis - not significant pathway of water transport across plant but it is means by which individual cells absorb water

Question 38

List conditions in which a plant may generate root pressure to transport water

Answer 38

1. in a root, the centrally placed vascular tissue is contained by the endodermis 2. the endodermis is a layer of cells unique to the root 3. at the endodermis, a waxy strip called the Casparian strip blocks the passage of water from entering the central portion of the root by apoplast route 4. this forces water into symplast pathway 5. this endodermis enables the control of water into the xylem, stopping it from flowing back via apoplast route 6. cytoplasm of endodermal cells actively transports ions from cortex to endodermis