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