Unit 8

  • Gas exchange - exchange of carbon dioxide and oxygen gases at cells/tissues via diffusion

    • cells doing aerobic respiration require

      • oxygen → into cell

      • carbon dioxide → outside of cell

    • cells doing photosynthesis require

      • carbon dioxide → into cell

      • oxygen → outside of cell

  • specialized gas exchange surfaces

    • unicellular organisms → large surface area:volume ratio

      • exchange gases directly through plasma membrane

    • animals get bigger → SA:V decreases → less SA for gas exchange relative to size

      • cells cannot get sufficient oxygen

    • gases exchanged by diffusion

      • slow process

        • bigger animals → too much time for oxygen to diffuse to all cells

    • large animals → specialized gas exchange/transport systems → sufficient oxygen for cells

  • Adaptations of gas exchange surfaces

    • large SA

      • increases quantity of gas exchanged

    • thin tissue layers

      • reduces distance gases travel

      • exchange tissues → 1 cell thick

    • permeable membranes

      • gases diffuse through them

    • concentration gradient for diffusing gases

      • gases diffuse from high → low concentration

    • exchange surfaces covered in moisture

      • gases dissolve/diffuse rapidly

  • alveoli - where gas exchange occurs in the lungs

    • composed of 2 types of cells facilitating rapid exchange of gases

      • Type I Pneumocytes

        • long/flat

      • Type II Pneumocytes

        • cuboid shaped

        • secrete surfactant → reduces surface tension + provides liquid for rapid diffusion

          • secreted by secretory vesicles (lamellar bodies)

  • Maintaining concentration gradients

    • gas exchange via diffusion

      • diffusion - passive transport of particles from high → low concentration

      • high concentration gradient needed for gases to diffuse rapidly

    • adaptations

      • dense network of capillaries around tissues in gas exchange

      • constant blood flow through capillaries around tissues in gas exchange

    • Lungs for gas exchange ventilate lungs w air → high concentration of oxygen to alveoli → remove carbon dioxide from alveoli

    • Gills move water through gills → high concentration of oxygen → move carbon dioxide away from gills

  • gas exchange through gills

    • gills adapted for rapid exchange of gases

      • large SA

      • constant supply of blood flow

      • water continuously moves through gills

    • “counter-current exchange”

      • water flows over gill filaments in 1 direction → blood flows through capillaries in gill filaments in opposite direction

      • ensures blood is exposed to water w high oxygen concentration → continuous oxygen diffusion

      • very efficient

  • gas exchange, ventilation, and respiration

    • ventilation - movement of air in/out of alveoli in lungs → facilitate gas exchange

      • breathing

      • maintains concentration gradients of oxygen and carbon dioxide

    • respiration - release of ATP from organic compounds within cells

  • Lungs - allow for exchange of oxygen from air → bloodstream and carbon dioxide from bloodstream → air

    • adaptations

      • branching bronchioles connect to alveoli

      • all alveoli have large SA

        • gas exchange

      • alveoli secret surfactant

        • prevents alveoli walls adhering + moist surface for gas exchange

      • alveoli surrounded by extensive capillary bed

        • maintains high concentration gradients for oxygen and carbon dioxide btwn blood and alveoli

        • capillaries give constant supply of blood w low oxygen + high carbon dioxide concentration → alveoli

  • Ventilation of the lungs

    • Inspiration (breathing in)

      • diaphragm contracts + moves down

      • external intercostal muscles contract → ribcage moves up/out

      • volume in thorax increases → decreases pressure in lungs

      • air moves from air (high pressure) → lungs (low pressure)

    • Expiration (breathing out)

      • abdominal muscles contract → push diaphragm up

      • external intercostal muscles relax + internal intercostal muscles contract → ribcage moves down/in

      • volume in thorax decreases → increases pressure in lungs

      • high pressure lungs moves air out of lungs → surrounding air (lower pressure)

  • Lung volumes

    • tidal volume - volume of air moving in/out normally

    • inspiratory reserve - more volume of air inhaled w max effort

    • expiratory reserve - more volume of air exhaled w max effort

    • vital capacity - greatest volume of air expelled from lungs after deepest possible breath

    • vital capacity = tidal + inspiratory + expiratory

    • measured by spirometers

  • Partial Pressures of Gases

    • partial pressure - pressure exerted by a single gas in a mixture of gases

      • dependent on

        • total pressure exerted by all gases in a mixture

        • concentration of the gas in the mixture of gases

      • correlated w concentration of gas in solution

      • used when looking at oxygen + carbon dioxide in blood

  • Oxygen dissociation curve - shows affinity for hemoglobin for oxygen

    • low partial pressures of oxygen → hemoglobin low affinity for oxygen → slow increase in saturation of hemoglobin

    • partial pressure of oxygen increases → hemoglobin affinity for oxygen increases

      • 1 oxygen binds to hemoglobin → conformational change in hemoglobin shape → greater affinity of hemoglobin for oxygen

      • results in rapid increase in oxygen saturation

        • example of cooperative binding

    • high partial pressures of oxygen → curve flattens

      • most hemoglobin molecules have 4 oxygen molecules already

      • “saturated”

    • sigmoid shape

    • 4 molecules of oxygen can bind to 4 haem groups in hemoglobin

    • in lungs → high partial pressure of oxygen that diffuses into capillaries around alveoli

      • respiring tissues use oxygen → low partial pressure of oxygen around respiring tissues

        • hemoglobin releases oxygen at low partial pressures → diffuses into respiring tissues for aerobic respiration

  • Hemoglobin

    • haem groups bind to oxygen molecules

      • every hemoglobin molecule has 4 haem groups → can bind to 4 oxygen molecules

    • cooperative binding of oxygen - binding of 1 oxygen to hemoglobin facilitates binding of other oxygen molecules

      • no oxygen bound to hemoglobin → low oxygen affinity

        • partial pressure of oxygen must be high for oxygen to bind

      • a single oxygen molecule binds to a haem group → shape of the hemoglobin molecule changes → hemoglobin affinity for oxygen increases

    • adult vs fetal hemoglobin

      • Adult hemoglobin

        • 2 alpha + 2 beta chains of polypeptides

        • high partial pressure of oxygen in maternal blood

          • results in release of oxygen

      • fetal hemoglobin

        • 2 alpha + 2 gamma chains of polypeptides

        • low partial pressure

          • results in binding of oxygen

        • greater affinity for oxygen than adult hemoglobin

          • oxygen more likely to be transferred from adult → fetal hemoglobin

  • Bohr Shift - the shift of the oxygen dissociation curve due to carbon dioxide partial pressures

    • high partial pressure of carbon dioxide → reduces affinity of hemoglobin for oxygen → shifts oxygen dissociation curve right

    • In respiring tissues

      • tissues use oxygen + produce carbon dioxide during aerobic respiration → very low partial pressure of oxygen → reduces affinity of hemoglobin for oxygen

      • high partial pressure of carbon dioxide → bohr shift → reduces affinity of hemoglobin for oxygen

        • hemoglobin releases oxygen at respiring tissues

    • In lungs

      • high concentration of oxygen + low concentration of carbon dioxide in alveoli

      • oxygen diffuses from alveoli to blood → high partial pressure of oxygen → high affinity of hemoglobin for oxygen

      • carbon dioxide diffuses from blood to alveoli → low partial pressure in blood → bohr shift → stronger affinity of hemoglobin for oxygen

      • high oxygen + low carbon dioxide partial pressures → oxygen binds to hemoglobin at high saturation levels

  • Carbon Dioxide

    • most CO2 in blood diffuses into RBCs

      • CO2 + water → carbonic acid

        • CO2 + H2O → H2CO3

      • carbonic acid dissociates → hydrogen carbonate ions + hydrogen ions

        • reaction catalyzed by carbonic anhydrase

      • chloride shift

        • hydrogen carbonate leaves cell + chloride ions enter cell

      • reaction reversible, releasing CO2 when partial pressure of CO2 is low in blood plasma

    • transported 3 ways in blood

      • CO2 dissolved in blood plasma

      • CO2 bound to hemoglobin

      • CO2 reversibly converted → hydrogen carbonate ions + hydrogen ions (H+) in RBCs

        • hydrogen ions bind to hemoglobin → conformational change of protein → affinity for oxygen

          • most CO2 transported this way

  • Muscle Tissue

    • muscles - contract and are involved in movement

      • cardiac muscle

        • located in heart

        • responsible for heart beat

        • myofibrils

        • branched + connected by intercalated discs

          • allows rapid transmission of electrical impulses through heart tissue

          • electrical impulses trigger contraction of cardiac muscle cells

          • intercalated discs - gap junctions allowing ions to flow between cells

      • striated/skeletal muscle

        • attached to skeleton

        • involved in bone movement

        • myofibrils

        • long, multinucleated fibers formed via cell fusion

          • debated if they should be considered cells

      • smooth muscle

  • Capillaries

    • small blood vessels connected arteries → veins

    • exchange materials btwn blood and cells

    • adaptations

      • large SA

        • highly branched w narrow diameter

      • narrow lumen

        • wide enough for 1 RBC at a time

      • thin walls

        • allow rapid diffusion

        • capillaries 1 cell thick

  • Micrograph of arteries vs veins

    • arteries

      • thick wall

      • narrow lumen

    • veins

      • thin wall

      • wide lumen

  • arteries

    • transport blood away from heart

    • adapted to withstand/maintain high blood pressure

      • thick wall

        • withstand high blood pressure

      • collagen in outer wall (tunica extrema)

        • strengthens artery to withstand high blood pressure

      • smooth muscle in artery

        • contracts to maintain blood pressure btwn heart beats

      • elastic fibers in artery wall

        • allow stretch/recoil as pressure increases/decreases from heart beats

          • recoil keeps blood moving

      • narrow lumen

        • maintains high blood pressure

      • lumen lined w smooth endothelial cells

        • reduces friction during blood flow

  • measuring pulse rate

    • felt using fingertips

    • radial artery in wrist

    • carotid artery in neck

  • Veins

    • return blood to heart

      • blood returning moves slowly + not under high pressure

    • adaptations

      • thin wall

        • allows vein to be compressed by skeletal muscles

          • compression moves blood back to heart

      • wide lumen

        • allows vein to carry high volume of blood

      • valves

        • prevent backflow

  • Atherosclerosis

    • hardening/narrowing of arteries

    • coronary arteries branch off from main artery (aorta) → supply heart w oxygen/nutrients

      • can be occluded (blocked) by atherosclerosis

    • can lead to death of heart tissue + heart attack

    • inner lining of artery is damaged bc high blood pressure, leading to:

      • macrophages (type of WBC) attracted to sites of damage → release growth factors stimulating fibrous tissue growth

      • macrophages consume cholesterol → plaque

      • plaque grows and blocks artery

      • can break away and cause blood clot

    • risk factors

      • genetics

      • age

        • older ppl arteries more likely damaged

      • gender

        • men more likely

      • obesity

        • higher blood pressure

      • physical inactivity

        • can lead to obesity

      • smoking

        • increases blood pressure

      • diet of fats/cholesterol

  • Correlation coefficients (r)

    • quantifies correlations btwn variables

    • allows strength of relationship to be assessed

      • close to 0 → no relationship btwn variables → disproves hypothesis

    • correlation is not causation

  • The lymphatic system

    • tissue fluid surrounds cells → enables exchange of materials btwn blood and cells

      • fluid formed by liquid part of blood (plasma) leaking from capillaries

      • blood leaves artery (arteriole) at high pressure → enters capillary → high hydrostatic pressure of blood filters plasma through capillary gaps → tissue fluid

      • blood pressure decreases as blood moves along capillary → plasma proteins decrease blood osmotic potential

        • most tissue fluid returns to blood by osmosis via oncotic pressure

          • higher than hydrostatic pressure

          • exerted by protein molecules in a fluid that pulls fluid back into blood vessels

        • hydrostatic pressure pushes fluid out of capillaries

        • oncotic pressure pulls it back in

  • blood plasma and tissue fluid

    • high hydrostatic pressure of blood → filters blood through capillary wall gaps

      • large particles (ex. BCs, proteins) too large to pass through gaps

      • small particles/dissolved solutes leave blood → tissue fluid

    • composition

      • blood

        • plasma

        • cell components

      • tissue fluid

        • plasma w/o plasma proteins

        • erythrocytes

        • platelets

      • lymph

        • plasma w/o plasma proteins

        • erythrocytes

        • platelets

        • more lipid droplets

        • larger number of lymphocytes

          • by lymph nodes

    • Blood plasma and tissue fluid shared components

      • dissolved nutrients

        • glucose

        • amino acids

        • fatty acids

      • dissolved oxygen

      • metabolic wastes

        • carbon dioxide

      • WBCs

        • can move through gaps

    • blood plasma components not in tissue fluid

      • RBCs

      • platelets

      • large plasma proteins

  • tissue fluid and cells

    • tissue fluid surrounds cells

      • exchange of materials

    • fluid has high concentration of nutrients/oxygen + low concentration of carbon dioxide/metabolic wastes

    • metabolism in cells use nutrients/oxygen → produce metabolic waste

      • cells have low concentration of oxygen/nutrients + high concentration of metabolic wastes

    • oxygen/nutrients diffuse tissue fluid → cells

    • metabolic wastes (carbon dioxide) diffuse cells → tissue fluid

  • Draining tissue fluid

    • most tissue fluid returns to blood plasma

    • tissue fluid not re-entering blood → taken up by lymph ducts

      • known as lymph

      • lymph ducts collect excess tissue fluid and return to blood

    • lymph travels through lymphatic system → fluid returned to blood via lymph nodes

    • adaptations of lymph vessels/ducts

      • gaps in wall of lymph ducts

        • allows fluid to enter

      • thin walls

        • compressed by skeletal muscles → move lymph fluid

      • valves

        • prevent backflow of lymph fluid

    • thoracic duct - returns lymph to blood

      • drains into subclavian vein

  • circulation systems in fish vs mammals

    • bony fish

      • single circulatory system

        • due to 2 chambered heart

      • heart ventricle pumps blood → gills

      • oxygen/carbon dioxide exchanged as blood passes through capillaries in gills

      • oxygenated blood leaves gills → transported to tissues

      • gas exchange occurs as blood passes through body tissues

      • deoxygenated blood returns to heart

    • mammals

      • double circulatory system

        • due to 4 chambered heart

      • right side pumps blood to lungs

      • oxygen/carbon dioxide exchanged as blood passes through lung capillaries

      • oxygenated blood returns to left side of heart + is pumped to body

      • gas exchange occurs as blood passes through body tissues

      • deoxygenated blood returns to right side of heart

  • The heart

    • pericardium

      • protective membrane

      • secretes a fluid → reduces friction as heart beats

    • has 4 chambers

      • right + left atria

        • collecting reservoirs for blood returning to heart

      • right + left ventricles

        • pumps ejecting blood to body

      • separated by valves

        • prevent backflow

    • 4 heart valves

      • right atrioventricular valve (tricuspid valve)

      • left atrioventricular valve (mitral valve)

      • right semilunar valve (pulmonary valve)

      • left semilunar valve (aortic valve)

    • path of blood

      • deoxygenated blood

        • superior/inferior vena vaca → right atrium → right atrioventricular valve (tricuspid) → right ventricle → right ventricle → right semilunar valve (pulmonary) → lungs (becomes oxygenated)

      • oxygenated blood

        • lungs → pulmonary vein → left atrium → left atrioventricular valve (mitral) → left ventricle → pumps blood to whole body → left semilunar valve (aortic) → aorta (brings blood to tissues → deoxygenated)

    • adaptations

      • atria

        • gets blood from body and lungs

      • ventricles

        • lots of cardiac muscle pumps blood

      • cardiac muscle

        • allows heart to contract to create high pressure

        • thicker on the left ventricle than right

          • left ventricle needs high pressure to move blood to body

      • pacemaker (sinoatrial node)

        • initiates/controls rate of heart beat

      • atrioventricular valves

        • prevents backflow of blood from ventricles to atria

      • semilunar valves

        • prevent backflow of blood from arteries to ventricles

      • septum

        • prevents oxygenated/deoxygenated blood from mixing

      • arteries

        • move blood away from heart at high pressure

      • veins

        • return blood to heart

  • control of the cardiac cycle

    • medulla oblongata

      • has 2 nerves connected to sinoatrial node (pacekamer)

      • nerves control the rate the heart beats

    • cardiac muscle = myogenic

      • contracts w/o stimulation

    • sinoatrial node controls rate of heart beat

      • initiates action potential (electrical signal) → rapidly spreads across atria → atrial systole (contraction)

      • fibrous tissue prevents action potential from traveling to ventricle

        • pause before signal reaches ventricles → 4 chambers do not contract at the same time

      • action potential travels to ventricles via atrioventricular node → then Purkinje fibers at apex of heart

      • action potential travels up walls of ventricle → initiates ventricular systole from apex → pumps blood out of ventricles

    • systole - contraction

    • diastole - relaxation

    • left atrium + ventricle in diastole

      • most blood flow directly through atrium → ventricle

      • action potential from sinoatrial node → left atrium enters systole

      • pressure increases in atrium as it contracts → blood forced to ventricle

      • action potential from atrioventricular node → ventricle enters systole

      • ventricle contracts → pressure in ventricle increases → atrioventricular valve closes

        • pressure higher in ventricle than atrium

      • high blood pressure in ventricle increases until semilunar valve opens + blood moves to aorta

      • ventricle enters diastole → pressure in ventricle decreases

      • pressure greater in aorta than ventricle → semilunar valve closes

      • pressure lower in ventricle than atrium → atrioventricular valves open

    • closing atrioventricular/semilunar valves → sound of heartbeat

  • measuring blood pressure

    • systolic pressure

      • caused by ventricular systole

    • diastolic pressure

      • btwn ventricular contractions