lecture 17
TRANSCRIPT
Lecture 17: Circulation/Respiration
Covers Chapters 32 & 33
Evolution of Circulatory System
• Earliest organisms (one-celled) lived in the sea, so nutrients were delivered by the surrounding water and wastes could be washed away
• In more advanced organisms (multicellular) that lived outside water, a system needed to be established to deliver nutrients to all cells and remove wastes
3 parts of circulatory system*
• Pump (HEART)• Liquid (BLOOD)• System of tubes to carry liquid (BLOOD
VESSELS)– Arteries – Veins– Capillaries
Functions of Circulatory System*
• Transport O2 from lungs (or gills) to the tissues• Transport CO2 from tissues back to lungs/gills• Distribution of nutrients from digestive system to all body
cells• Transport of waste products to the liver and kidneys• Distribution of hormones from glands/ducts to tissues• Regulation of body temp by adjustments in blood flow• Protection against disease by circulating white blood cells and
antibodies
How does the heart work?*• 4 chambers: 2 atria, 2 ventricles• Divided into right atria & ventricle (deoxygenated blood) and left atria &
ventricle (oxygenated blood)• Deoxygenated blood enters right atria from the body (Superior & Inferior
VENA CAVA)• After filling, right atria pumps blood to right ventricle• Right ventricle pumps blood through PULMONARY ARTIES to lungs• Blood is oxygenated in lungs, carried back to left atria via PULMONARY
VEINS• Left atria filled, pumps blood to left ventricle• Left ventricle pumps blood out through AORTA to body• Valves prevent backflow
aorta
left atrium
pulmonary artery(to left lung)
semilunar valves
pulmonary veins(from left lung)
atrioventricular valve
left ventricle
thicker muscleof left ventricle
descending aorta(to lower body)
rightventricle
inferiorvena cava
atrioventricular valve
superiorvena cava
pulmonary artery(to right lung)
pulmonary veins(from right lung)
rightatrium
Fig. 32-3
Cardiac Cycle
• Coordinated contractions of atria and ventricles allows heart to pump – Both atria contract, pumping blood into ventricles– Both ventricles contract, pumping blood to lungs/body– All chambers relax briefly before next cycle – Cardiac cycle produces blood pressure
• Systolic pressure: ventricular contraction• Diastolic pressue: heart resting between contractions• High blood pressure results from constriction of arteries, resulting
in resistance to blood flow and more strain on the heart
The Cardiac Cycle
Fig. 32-5
Atria contract, forcingblood into the ventricles
Then the ventriclescontract, forcing bloodthrough the arteries tothe lungs and the restof the body
The cycle ends asthe heart relaxes
Deoxygenated blood ispumped to the lungs
Blood fills theatria and beginsto flow passivelyinto the ventricles
Deoxygenatedblood from thebody enters theright ventricle
Oxygenated blood from thelungs enters the left ventricle
Oxygenated bloodis pumped to thebody
321
What mechanism establishes heart rate?*
• Pacemaker cells: specialized cells in heart wall that sets the pace for heart rate.– Sinoatrial node: right atrium– Electrical signals move from SA node through atria
to Atrioventricular Node in area between right atria and right ventricle
– AV Bundle and Purkinje Fibers carry signals through ventricles
Inexcitable tissueseparates the atria and ventriclesAV node
SA node
AV bundle
AV bundlebranches
An electrical signalfrom the sinoatrial (SA)node starts atrialcontraction
1
The signal entersthe atrioventricular(AV) node, whichtransmits it to theAV bundle with aslight delay
3
The signal travelsthrough the AV bundlebranches to the baseof the ventricles
4
Purkinje fibers transmitthe signal to ventricularcardiac muscle cells,causing contraction fromthe base upwards
5
The electricalsignal spreadsthrough the atria,causing them tocontract
2
Purkinjefibers
Fig. 32-7
Factors that affect heart rate
• Sympathetic nervous system increases heart rate when we are scared, stressed or exercising
• Parasympathetic nervous system slows heart rate when we are eating, sleeping, digesting
• Hormones can affect heart rate: thyroid hormones and epinephrine
What is blood?• 55% plasma: clear, pale yellow fluid that is made of:
– Water– Ions: maintain blood pH – Proteins
• Albumin: helps maintain osmotic pressure of blood (solids that prevent too much blood from leaving vessels)
• Globulins: antibodies, transport proteins• Fibrinogen: blood clotting• About 100 types of molecules
• 45% cells:– Red Blood Cells: carry O2– White Blood Cells: immune system (more in Lecture 19)– Platelets: blood clotting
Red Blood Cells
• Life span of 4 months• Produced in bone marrow*• Broken down in spleen and material returned
to bone marrow to make more RBC’s*• Erythropoetin (hormone in kidneys) regulates
the number of RBC’s produced*– Blood loss or low O2 levels will trigger release of
erythropoetin which stimulates bone marrow to make more RBC’s.
Oxygen deficiency
Erythropoietinproduction
by the kidneys
Red bloodcell production
in the bone marrow
Restored oxygen level
inhibits
stimulates
causes
stimulates
Red Blood Cell Regulation
Fig. 32-10
Platelets
• Made in bone marrow• Life span 10 days• Contribute to blood clotting
– Break in blood vessel wall (cut, etc)– Blood comes in contact with tissue– Platelets stick to area and a blood clot forms
Blood Clotting
Fig. 32-12
collagenfibers
prothrombin fibrinogenthrombin
thrombinredbloodcells
bloodvessel
plateletsplateletplug
fibrin
Damaged cells exposecollagen, which activatesplatelets, causing them tostick and form a plug
1 Both damaged cellsand activated plateletsrelease chemicals thatconvert prothrombininto the enzyme thrombin
2 Thrombin catalyzes theconversion of fibrinogeninto protein fibers calledfibrin, which forms ameshwork around theplatelets and traps redblood cells
3
What are the types and functions of blood vessels?
• Arteries: carries blood away from the heart (thick, elastic walls)
• Veins: carries blood toward the heart (thin walls, less muscle). VALVES prevent backflow of blood
• Capillaries: exist between arteries and veins, located in tissues, site of gas/nutrient exchange (each body cell is no more than 100 micrometers from a capillary)
• Arteries and veins are three layers thick:– Endothelial cell layer (in contact with blood)– Smooth muscle cell layer– Connective tissue layer
precapillarysphincter
arteriole
venule
veinartery
capillary
to heartfrom heart
endotheliumvalve
smooth muscleconnective tissue
capillary networkwithin body tissues
Structures and Interconnections of Blood Vessels
Fig. 32-15
Red blood cells mustpass through capillariesin single file
Capillary walls are thinand permeable to gases,nutrients, and cellularwastes
Red Blood Cells Travel Single File Through a Capillary
Fig. 32-16
One more note about capillaries
• Pressure of blood not only allows nutrients and O2 to leave the capillaries and go directly into cells, but fluid escapes also…it is the same basic makeup of plasma, without the large plasma proteins. This EXTRACELLULAR FLUID bathes cells, allowing for even more exchange of nutrients and wastes.
• The lymphatic system has the job of draining this ECF from tissues and returning it to the bloodstream.
Lymphatic System*
• Returns ECF to blood stream: lymphatic capillaries START in tissues, picking up excess ECF, carrying it in gradually larger vessels that empty into veins near the neck.
• Once ECF enters a lymphatic vessel, it is called LYMPH• Functions of Lymphatic System:
– Transports fats from small intestine to blood stream- more in Lecture 18
– Filters old blood cells and debris from blood– Housing for white blood cells (immune system) – more in
Lecture 19
thymus
superiorvena cava
spleen
bonemarrow
thoracicduct
lymph vessels
lymph nodes
The thoracic ductenters a vein thatleads to the superiorvena cava
The Human Lymphatic System
Fig. 32-18
Lymph Capillary Structure
Fig. 32-19
lymphcapillary
extracellularfluid
Pressure forces fluid from the plasmaat the arteriole end of the capillary network
Extracellular fluid enters lymph vessels and the venous endsof capillaries
Lymph is transported into larger lymph vessels and back to the bloodstream
arteriole
capillary venule
1
2
3
Respiration
• The act of breathing-GAS EXCHANGE• Cellular respiration is the creation of ATP from
glucose (and other nutrients). This process requires O2 and creates CO2 as a byproduct.
• Our body’s way of bringing in the O2 and getting rid of CO2 is the respiratory system
• Respiratory system works in harmony with circulatory system which carries the O2/CO2
Gas exchange depends on simple diffusion*
• In the cells, cell respiration creates an environment of low O2 (used up in cell respiration) and high CO2 (the byproduct of cell respiration)
• This creates a concentration gradient where CO2 wants to move OUT of the cells (to an area of lower concentration) and O2 wants to move INTO the cells (to an area of lower concentration)
• Same is true in the lungs (O2 wants to move into capillaries from lungs and CO2 wants to move into lungs from capillaries)
An Overview of Gas Exchange in Mammals
Fig. 33-2
O2
O2
CO2
alveoli(air sacs)
Oxygenated bloodDeoxygenated blood
Gases move in and out of the lungs by breathing
O2 and CO2 areexchanged in thelungs by diffusion
Gases dissolvedin the blood are transported by the circulatory system
2
3
O2
O2
1
CO2
left ventricle
leftatrium
O2 and CO2
are exchangedin the tissuesby diffusion
4
O2
rightatrium
rightventricle
CO2
CO2
CO2
CO2 CO2
O2
Animal respiratory systems have 3 requirements*
• Respiratory surfaces must be moist so that gases can diffuse across cell membranes
• Cells lining respiratory surfaces are very thin to facilitate diffusion
• System has a large area in contact with the environment to allow enough gas exchange to maintain the organism.
Evolutionary adaptaions
• Animals living in moist environments had gas-permeable skin that could do gas exchange
• Gills evolved in aquatic animals so that more gas exchange could occur, supplying larger organisms (larger animals need more O2 to stay alive)
• Gills are branched/folded for larger surface area• Terrestrial animals (land animals) needed an internal
respiratory system that could still be moist (LUNGS!)
Human Respiratory System
• Conducting portion– Pharynx– Larynx (Epiglottis & Vocal Cords here)– Trachea-flexible tube reinforced with cartilage– Bronchi- one for each lung– Bronchioles-repeatedly smaller tubes in each lung
• Gas exchange portion– Alveoli-air sacs where gas exchange occurs
(a) Human respiratory system (b) Alveoli with capillaries
bronchiole
pulmonary venule
alveoli
capillarynetwork
pulmonary veins
pulmonary arterydiaphragm
nasal cavity
pharynx
oral cavityepiglottis
larynx
esophagus
trachea
bronchi
bronchiolesrings ofcartilage
pulmonary arteriole
The Human Respiratory System
Fig. 33-7
Alveoli*
• Alveoli are clustered around the end of each bronchiole• 300 million alveoli supply 1500 square feet of surface area for
diffusion (same as a 2-3 bedroom house!!!)• Actual site of gas exchange• Surrounded by capillaries• Bathed in surfactant: soap-like fluid that facilitates gas
exchange across membranes• O2 crosses from alveoli to capillaries, delivered to tissues• CO2 returned to alveoli, crosses from capillaries back to
alveoli and is exhaled
from thepulmonaryartery
alveolarmembrane
respiratorymembrane
surfactantfluid
to the pulmonary vein
(air) CO2
O2
capillary
Oxygen diffuses intothe red blood cells
Carbon dioxide diffusesinto the alveolus
Gas Exchange Between Alveoli and Capillaries
Fig. 33-9
How is O2 transported to tissues?*• Oxygen enters capillaries from the alveoli and binds to
hemoglobin, a large protein in red blood cells (RBC’s)• Each hemoglobin molecule can carry up to four O2
molecules..one molecule for each of the 4 heme groups in the protein (When O2 binds to hemoglobin, it changes shape and color: red!)
• The uptake of O2 by hemoglobin maintains LOW concentration of oxygen floating freely in blood, therefore maintaining diffusion of oxygen from lung (HIGH CONCENTRATION) to the blood (LOW CONCENTRATION)
• When O2 reaches its destination (capillary bed in the tissues) it moves into the tissues by diffusion.
(air inalveolus)
(extracellularfluid)
alveolarwall
surfactantfluid
redbloodcells
hemoglobin
(a) O2 transport from the lungs to the tissues
O2
O2
O2capillarywalls
(plasma)cells ofbody tissues
respiratorymembrane
Oxygen Transport
Fig. 33-10a
How is CO2 transported back to lungs*
• CO2 (byproduct of cell respiration) is waiting in tissues to be picked up and taken back to lungs.
• CO2 is carried in the bloodstream in three different ways: – Dissolved in blood (10%)– Bound to hemoglobin (20%)– Combined with water as BICARBONATE (70%)
• This action maintains a LOW concentration of CO2 in blood so that gradient will be maintained (CO2 will flow from tissues into bloodstream)
• Back at alveoli, bicarb changed back to CO2 to be exhaled
(b) CO2 transport from the tissues to the lungs
CO2
CO2
CO2
CO2
CO2
CO2CO2
CO2
CO2
CO2
+H2O
H2O
+H+
H+ HCO3–
1
2
3
4
5 HCO3–
HCO3–
Carbon Dioxide Transport
Fig. 33-10b
Breathing requires the diaphragm
• Strong, dome shaped muscle that separates heart/lungs from organs of digestion
• When we inhale, diaphragm CONTRACTS and FLATTENS, making chest cavity bigger and pulling O2 into lungs.
• When we exhale, diaphragm RELAXES, making chest cavity smaller.
What controls our breathing?• We don’t have to even think about breathing..each
contraction of the diaphragm is stimulated by impulses from nerve cells.
• These impulses originate in respiratory center of the brain (medulla)
• Respiratory center adjusts breathing rate and volume (how much air we breathe in/out) to meet the needs of the organism*
• Receptors in medulla monitor CO2 levels in the blood. If CO2 rises, breathing rate will be increased to bring in more O2 and lower CO2 levels.*
• (An increase of 0.3% will cause a doubling of breathing rate!)
Control of Respiration