B3.2 - transport systems

Adaptions of capillary for exchange of materials

• • Pores (fenestrations) to increase permeability for rapid exchange 

  • Large surface area due to branching and narrow diameters

  • Tissues w/ high oxygen/nutrient requirements (muscles) have high density capillary networks

  • Single layer of flattened endothelial cells to reduce diffusion distance 

• Tissue fluid (fluid coming out of capillaries into tissues → water, oxygen, glucose, ions) 

  • Capillaries near arterioles release tissue fluid more readily, capillaries near veins uptake more readily (differences in external vessel pressures)

Structure of artery

• Thick, muscular wall

• Narrow lumen (hollow inside the artery)

• Circular in shape → maintain shape well

• ‘Ridges’ on inside → ‘inner surface corrugation’

• Visible wall fibers

structure of veins

• Thin wall (rely on skeletal muscle surrounding veins to contract blood back to the heart) 

• Wide lumen

• Somewhat flattened

• No inner surface corrugation → little muscle

• No wall fibers

easy way to remember arteries, veins, capillary comparisons

transport systems and their directions

Adaptations of Arteries for Transport of Blood From Heart

• Narrow lumen → small area maintains high pressure to pump blood 

• Thick muscular wall (with collagen/elastic fibres)

  • Contracts to narrow the lumen (vasoconstriction)
    Relaxes to widen the lumen (vasodilation) 

• Collagen → maintain elasticity, make sure arteries can withstand high pressure

• Elastic fibers → Acts like a pressure reservoir, helping to even out blood flow

  • Stretches during systole (when heart pumps)

Recoils during diastole (heart relaxation) → less energy for a full contraction

Pulses

• Can be taken on wrist or neck/with digital pulse reader 

  • Not the same as heartbeat (heart muscle contractions) but the arteries contracting → same timing, can be used interchangeably

Adaptations of Veins for Return of Blood to Heart

• Thin flexible walls → allows external skeletal muscle to contract/squeeze vein so blood can be pumped back to the heart

• Valves → one-way flaps, close to prevent backflow

Wide lumen → creates low pressure → easier for skeletal muscles to squeeze

Coronary Heart Diseases (occlusion of coronary arteries)

• Coronary Arteries: arteries branching out from the aorta that supply oxygenated blood to the heart tissue

  • Coronary Heart Disease (CHD): coronary arteries become narrowed/blocked with plaque (cholesterol/other lipids)

  • Myocardial infarction (heart attack): coronary artery is totally blocked

    • Risk factors: Smoking, obesity, lack of exercise/genetics, Hypertension, poor diet, age

Transporting Water from Roots to Leaves during Transpiration (entire process)

• Xylem: carries water from roots to shoots (1 upward direction)

  • relies on cohesion and adhesion  

• Transpiration: water evaporates through stomata → causes tension pulling water up from the roots → water drawn out pores of xylem vessels and through cell walls 

  • Capillary action: water moving through/along a material against the force of gravity

COHESION: creates a transpirational pull upwards as water evaporates through stomata (no energy used) → ensures a continuous column of water

Adaptations of Xylem Vessels for Water Transport

• Made of dead, hollow cells → maintains continuous water column + water contact (i.e. allows cohesion to exist) 

  • Lack of cell contents 

• Lignin (polysaccharide) → structural support i.e. prevents xylem collapse and withstands tensions

• Pits in the xylem → water can pass between xylem and phloem

Absence of end walls  → for unimpeded flow

Features of Dicot Stems and their locations

• Vascular bundles: bundles of xylem + phloem → region closer to the inside is the xylem, phloem is closer to the outside

• Pith: core of the stem → ‘bulks out’ the stem

• Cortex: layer under the epidermis → storage/structural support/photosynthesis

Epidermis: outer layer of stem → waterproofing/protection

Features of dicot roots and their functions

• Phloem in between the xylem star

• Endodermis → inner skin of cells that water passes through to access the xylem

• Cortex → unspecialized cells ‘bulk out’ root → strength/higher surface area

• Epidermis → absorbs water/minerals from soil using root hairs (long, narrow outgrowths)

• Pith: core of the stem → ‘bulks out’ the root 

Release and reuptake of tissue fluid in capillaries —> their structure that allows them

• Plasma: fluid consisting of substances (e.g., glucose, amino acids, mineral ions, vitamins, hormones, and plasma proteins) dissolved in water 

• Capillary walls are adapted to allow plasma to leak out into spaces between tissue cells 

  • Plasma proteins (too large) → remain in the blood / small molecules pass out of blood and form tissue fluid 

• Tissue fluid is formed by pressure filtration of plasma in capillaries close to arterioles 

  • promoted by the higher pressure of blood from arterioles → allows release and reuptake of tissue fluid 

  • Lower pressure in venules allows tissue fluid to drain back into capillaries 

Exchanging Substances Between Tissue Fluid and Tissue Cells

• Oxygen passively diffuses into cells (concentration gradient) 

• Glucose moves into cells using sodium-glucose cotransporters (against the concentration gradient) → secondary active transport

  • Energy from sodium / glucose (PASSIVE)   

• CO2 + waste moves into capillaries passively (concentration gradient)

Drainage system of excess tissue into lymph ducts

• Not all (~85%) of tissue fluid returns to capillaries

  • Remaining 15% returns into the lymphatic system → prevents oedema (swelling)

  • Drains back into heart/blood/circulatory system

• All tissues have narrow, blind-ended lymphatic vessels with permeable walls → merge repeatedly into left and right lymph ducts 

  • presence of valves and thin walls with gaps in lymph ducts 

  • Tissue fluid enters lymphatic vessels → lymph 

    • Lymph drains into subclavian veins → vena cava → right side of the heart 

Double Circulation of Mammals

• Double circulation (pulmonary and systemic circulation)

• High-pressure body blood/systemic loop (to reach all organs)

Require separate low-pressure pulmonary blood loop to the lungs → allows oxygen to move from alveoli into capillaries & prevents capillaries from bursting

Single circulation of bony fish

• Single circulation

• Blood is pumped from the heart → gills → body → heart (enough remaining pressure to pump oxygenated blood to body and heart)

• water pumped over gill filaments

• oxygen diffuses from water → gills → blood, CO2 diffuses from blood → gills → water 

Water flow reduces risk of capillaries bursting → high-pressure blood can exist in gills

What do the Atria, ventricules, atrioventricular, and semilunar valves do?

1. Atria → contract simultaneously to squeeze blood into ventricles

2. Ventricles → contract simultaneously to pump blood into arteries

   1. Thicker ventricular walls compared to atria (left is thicker than right → pumps blood at higher pressure for systemic circulation)

3. Atrioventricular (AV valves) → prevent backflow into the atria

4. Semilunar (pulmonary + aortic) valves → prevent backflow into the ventricles

other mamallian heart adaptions (besides atria, ventricular, atrioventricular, and semilunar valves)

1. Cardiac muscle → muscles forming walls of atria and ventricles → coordinated myogenic contractions (electrical signals propagated throughout wall of heart) 

2. Septum → wall separating right/left ventricles AND right/left veins → prevents oxygenated (LEFT) and deoxygenated (RIGHT) blood from mixing 

3. Coronary Vessels (coronary arteries and veins in wall of heart)→ bring oxygenated blood to heart tissue and drain deoxygenated blood away 

4. SA (sinoatrial ‘pacemaker’) node (wall of right atrium)→ initiates heartbeat 

• Interval between SA node signals determine heartbeat rate 

• Generates electrical impulse → atrial contraction 

9. AV node (lower back section of right atrium) → gets electric signal to ventricles (coordinates heartbeats) 

• Receives signal from SA node → delays impulse → atria finish contracting → ventricular contraction

Know structure of heart

Stages in the Cardiac Cycle (Atrial Systole)

1. Atrium contracts → rapid but small increase in pressure 

2. Ventricles relax → AV valves open, semilunar valves close 

3. Ventricles filled with blood → small increase in pressure 

4. Blood pressure in artery decreases to its minimum

Stages in the Cardiac Cycle (Ventricular systole)

1. AV valves close (first heart sound “lub”), semilunar valves open 

2. Blood pushed into arteries

   1. pressure in ventricles > arteries

 

Atria slowly relaxes, filled with blood → pressure increases

Ventricular diastole

1. Ventricle relaxes → pressure < arteries (rapidly decreases) 

2. Semilunar valves close (second heart sound “dub”), AV valves remain closed

3. AV valves open 

   1. Ventricle pressure < atrium

4. blood enters ventricle → slow increase in pressure

Know graph for cardiac cycle

Root pressure in xylem by active transport of mineral ions

• Water only moves upwards when transpiration (pulling force initiated by stomata evaporation) occurs 

  • Sometimes transpiration is not possible e.g., high humidity or spring bfr deciduous plant leaves open (closed stomata at night, loss of leaves) 

• If pulling force is unable, plants rely on root pushing force → positive pressure potential in xylem

Plants establish pressure in rootsbyactively transporting mineral ions into root → triggers osmosis (high solute conc. in xylem) → pressure increase

Phloem Sieve Tubes + Companion Cells for Translocation of Sap (definitions)

• Sap: fluid containing water and nutrients, transported within vascular tissues 

• Phloem: bidirectional transport of carbon compounds (sucrose) from source to sink

  • Source: where carbon compounds are made (leaf) 

  • Sink: where carbon compounds are stored/used (root, shoot, flower, fruit)

• Sieve plates: channels through which transport occurs → have pores for phloem sap to flow through

  • Reduced cytoplasm and organelles, no nucleus for sieve tube elements → cant generate energy → relies on companion cells for active transport

• Sieve tube elements: long, elongated cells forming continuous tubes for nutrient transport (leaves to rest of plant)

• Companion Cells: help transport carbon compounds from sources to phloem cells, from phloem cells into sinks

Many mitochondria + cytoplasmic plasmodesmata which allows ATP/carbon compounds to pass through

Process of translocation of sap

1. Phloem Loading: carbon compounds actively transported into the phloem sieve tubes

   1. Water moves via osmosis from the xylem to the phloem → creates area of high pressure

2. Pressurized Movement: Carbon compounds, water (phloem sap) are forced from areas of high pressure to low pressure

3. Sink Pumping: compounds pumped from phloem into sink

   1. Without high solute concentration, water moves back into xylem through osmosis

*these adaptations ease the flow of sap