Transport - B3.2

adaptations of capillaries for exchange of materials

• large surface area

• thin walls

• fenestrations

how does a large surface area make capillaries adapted for exchange of materials

• narrowest blood vessels

• capillaries branch and re-join to form a capillary network. → ensures sufficient blood supply to all tissues

• → large total surface area

how do thin walls with pores make capillaries adapted for exchange of materials

• one layer of endothelium cells (thin + permeable) → short distance for diffusion (fast + efficient exchange)

• basement membrane : supports endothelium cells + allows small/medium sized particles to pass through. Fluid leaks out because blood pressure is higher than surrounding pressure → allows cells to absorb useful substances + excrete waste products.

how do Fenestrations make capillaries adapted for exchange of materials

• = large pores in capillary walls

• allow larger volumes of tissue fluid to be produced → speeds up exchange between tissue cells and blood

Arteries structure

• carry blood away from the heart to organs

• high pressure

• thick walls + narrow lumen

• corrugated inner surface - due to more muscle fibers + collagen + elastin → allow arteries to stretch

Veins structure

• carry blood from the organs to the heart

• low-pressure

• thin walls + wide lumen

• valves

• smooth inner surface

Adaptations of arteries

• tunica externa - tough outer coat of connective tissues with collagen fibers → prevent swelling/bursting of artery

• tunica media - thick layer containing smooth muscle (elastin) to help pump blood by transmitting the pulse

• tunica intima - smooth endothelium to line artery + reduce resistance to flow (+layer of elastic fibre in some arteries)

• thick wall for strength

• lumen - narrow space → helps maintain high blood pressure + velocity

Collagen fibers role in arteries

• tough rope-like proteins with high tensile strength

• → prevent bursting of artery + aneurysm

• present in tunica externa

what happens in the artery after every systole (ventricles of the heart pump)

wall of the artery expands due to high blood pressure → elastic fibers (in tunica media) stretch + store potential energy.

what happens when the ventricles in the heart stop pumping (diastole)

• blood pressure declines

• elastic fibers (in tunica media) recoil → apply pressure on the lumen → helps pump blood along the artery + makes flow even.

role of smooth muscle cells in arteries

• circular → make the lumen narrower when they contract (vasoconstriction) and wider when they relax (vasodilation)

• high density of smooth muscle cells is found in arterioles (branches of arteries) → flow rate of blood to tissues in each organ can be adjusted depending on availability + need.

adaptations of veins

• tunica externa - tough outer coat of connective tissue to prevent leaks

• tunica media - thin layer + few elastic/collagen fibres (due to low blood pressure + no pulse)

• tunica intima - smooth endothelium → reduce resistance to flow

• thin wall → vein is flexible + can flatten when surrounding tissues apply pressure

• wide lumen which accommodates the slow flow of blood

valves in veins

• pressure in veins can drop so low that blood flow stops and there is a risk of backflow towards capillaries

• valves in main veins prevent this

role of skeletal muscles in venous blood flow

skeletal muscles become wider when they contract pressing the vein flatter raising blood pressure.

traditional way of measuring heart rate

• pulse can be felt with the middle + index finger being placed on the carotid artery or radial artery

• when you can reliably feel a pulse you can use a timer to count the beats per minute

digital methods of finding heart rates

• e.g pulse oximeter

• clipped to a finger tip

• has LEDs that shine into the finger + detectors to measure how much light is absorbed by the finger (depends on amount of blood in the tissues)

epidemiology definition

• research into the nature and spread of diseases in the human population.

• can identify risk factors

how does coronary heart disease occur

• Lipids (e.g fats + cholesterol) are deposited in the walls of arteries → atheroma (plaque)

• atheroma make the lumen of the artery narrower restricting blood flow

• if atheroma continues to build up it can cause occlusion (total blockage of artery)

risk factors for coronary heart disease

• high blood pressure (hypertension)

• smoking

• obesity (BMI≥30)

• inactive lifestyle

• family history of heart disease

• old age

• high blood cholesterol concentration

• diabetes

• alcohol

• diet with many saturated fats

• → all lead to atheroma

consequences of coronary heart disease

• Angina (chest pain)

• heart attack - heart muscle is deprived of oxygen + nutrients → damage/death of heart tissue.

• heart failure - heart attack damages a significant portion of the heart muscle → heart failure (heart is unable to pump blood to meet the body's needs.)

• Arrhythmias (irregular heart rhythms)

• stroke

transpiration

water evaporates from the walls of spongy mesophyll cells and diffuses out through stomata

how is water replenished after water loss due to transpiration in plants

• cell walls contain a mesh of cellulose molecules which form hydrogen bonds with water

• water is drawn from the pores between cellulose molecules due to adhesion between the cellulose + water and cohesion between water molecules (capillary action)

creation of tension in the xylem

• when water evaporates out of the leaf through the stomata it creates negative pressure (tension) in the plant due to the cohesion of water molecules

• negative pressure/transpiration pull pulls water from xylem vessels up to the leaves

adaptations of xylem vessels for transport of water

• lack of cell contents

• incomplete/absent end walls

• lignified walls

• pits

how does a lack of cell contents + incomplete cell walls make xylem vessels adapted for transport of water

• during development xylem cells die → end walls are removed + plasma membrane + contents of the cells breakdown

• → long continuous tubes → flow of xylem sap is uninterrupted

how does a lignification + thick walls make xylem vessels adapted for transport of water

the polymer lignin in the side walls of xylem vessels prevent the vessels from collapsing when pressure inside is low due to the plant transpiring

how do pits make xylem vessels adapted for transport of water

• lignified walls are impermeable to water

• gaps in wall = pits → water can enter + exit → allows horizontal transport of water

• provide flexibility in the water transport system → ensure efficient flow even when some vessels are compromised.

dicot plants definition

plants with 2 embryo leaves in their seeds

dicot stem - epidermis

• single layer of cells with waxy cuticle on the outside

• helps reduce water loss, prevents plant from physical damage, barrier to pathogens

dicot stem - pith

• large thin-walled cells

• fill the center of the stem

• stores nutrients + water

dicot stem - cortex

• medium-sized thin-walled cells

• strengthen the stem when turgid

• stores of starch + nutrients

dicot stem + root - xylem

• wide tubular structures with thick walls

• transport water + minerals

dicot stem + root - phloem

• small thin-walled cells

• transport sugars + other foods (e.g amino acids)

dicot cell - cambium

• small cells with thin walls that divide by mitosis

• responsible for plants secondary growth

dicot root - epidermis

• single-layered thin-walled cells with no cuticle (allows water absorption)

• absorbs water + mineral ions from the soil using root hair cells

dicot root - cortex

• makes up most of root → strengthens + increases surface area

• stores starch for energy