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CIRCULATION AND GAS EXCHANGE Between two lungs it was released, a breath that passed from you to me

42.1: CIRCULATORY SYSTEMS LINK EXCHANGE SURFACES WITH CELLS

THROUGHOUT THE BODY • Gaining O2 and nutrients while shedding CO2 and other waste products

GASTROVASCULAR CAVITIES • Single opening maintains continuity between the fluid inside the cavity and the water outside. • Both inner and outer tissue layers are bathed by fluid • Optimizes diffusional exchange by increasing surface area and minimizing diffusion distances

OPEN AND CLOSED CIRCULATORY SYSTEMS • Circulatory system minimizes the distances substances must diffuse to enter/leave a cell

o Transporting fluid throughout the body, connects the aqueous environment of the body cells to the organs that exchange gases, absorb nutrients and dispose of wastes

• Based on 3 components o Circulatory fluid o Interconnecting tubes o Muscular pump (heart)

Hydrostatic pressure of circulation powers the flow of blood • Open circulatory system

o Circulatory fluids, hemolymph, bathes the organs directly o Also the interstitial fluid o Contractions of the heart pump hemolymph into the sinuses, sinuses squeeze the hemolymph

back into the heart eventually o Advantages:

Lower hydrostatic pressure, less costly • Closed circulatory system

o Blood confined to vessels and is distinct from interstitial fluid o Advantages

Additional functions Relatively high blood pressure—effective delivery of O2 and nutrients to cells or

larger animals Regulating the distribution of blood to different organs

Daniel Oh 2014 Monday, December 17, 2012 5:46:47 PM Central Standard Time

ORGANIZATION OF VERTEBRATE CIRCULATORY SYSTEMS • Cardiovascular system: closed circulatory system of humand another vertebrates • Blood circulate to and from the heart through an extensive network of vessels • The vessel system

o Arteries: carry blood away from the heart to organs o Arterioles: small vessels that convey blood to capillaries o Capillaries: very small vessels with thin, porous walls o Capillary beds: networks of capillaries that allow the diffusion of chemicals o Venules: capillaries converge into these which converge into o Veins: the vessels that carry blood back to the heart o Arteries and veins are not distinguished by the amount of O2 in the blood, but by the direction

Arteries carry blood to the capillaries, veins carry them from capillaries o Atria: chambers that receive blood entering the heart o Ventricles: responsible for carrying blood out of the heart

SINGULAR CIRCULATION • Singular circulation: blood passes through the heart in once in each complete circuit

o Found in bony fish, sharks, rays o Blood entering the heart collects in the atrium before transfer to the ventricle blood to the

gills diffusion capillaries converge into a vessel that carries O2 rich blood to capillary beds through the body blood returns ot the hart

o Blood that leaves the heart passes two capillary beds before entering the heart


DOUBLE CIRCULATION • Double circulation: two distinct circuits—

pumps for two circuits serve different tissues but are combined into a single heart

• Pulmonary circuit: the right side of the heart – delivers oxygen-‐poor blood to the capillary beds of the gas exchange tissues (if involving the lungs)

• Pulmocutaneous circuit: involving the lungs and skin (amphibians)

• Systemic circuit: the oxygen-‐rich blood travels from the lungs, to the left side of the heart, and to the rest of the body. Then the oxygen-‐poor blood moves back to the heart

• Provides vigorous flow of blood to organs

ADAPTIONS OF DOUBLE CIRCULATORY SYSTEMS

AMPHIBIANS • Have a heart with three chambers—two atria and one ventricle

o Ridge within the ventricle diverts 90% of the oxygen-‐poor blood from the right atrium to the pumocutaneous circuit and most of the oxygen-‐rich blood from the left atrium into the systemic circuit

Single circulation in fish


REPTILES (EXCEPT BIRDS) • Three-‐chambered heart with a septum partially dividing the ventricle into separate right/left chambers

MAMMALS AND BIRDS • The ventricle is completely divided: four chambered heart • Left side receives and pumps only O2-‐rich blood, right side receives and pumps only O2-‐poor blood • Supports endothermic way of life, allows circulatory systems to deliver more O2 and remove more

CO2.

42.2: COORDINATED CYCLES OF HEART CONTRACTION DRIVE DOUBLE

CIRCULATION IN MAMMALS

MAMMALIAN CIRCULATION 1. Right ventricle contraction pumps blood to lungs via…

2. …the pulmonary arteries.

3. Capillary beds load O2 and unloads CO2

4. O2-‐rich blood returns from the lungs via the pulmonary veins to the left atrium of the heart

5. Blood flows to the left ventricle, which pumps O2-‐rich blood the body through the systemic circuit

6. Blood leaves the heart through the aorta

7. Capillary beds in the head and arms;

8. Capillary beds of


abdominal organs and legs

9. The O2-‐poor blood is channeled into the superior vena cava

10. The inferior vena cava drains blood from the trunk and legs

11. The two venae cavae empty their blood into the

12. Right atrium and the cycle starts again…

THE MAMMALIAN HEART: A CLOSER LOOK!

• Located beneath the sternum, made up of mostly cardiac muscle

o Atria have relatively thin walls and serve as collection chambers for blood returning to the heart

o Blood flows from the atria to the ventricles when the chambers are relaxed, contraction of the atria pushes the remainder before the ventricles contract

o Ventricles have thicker walls in order to push blood throughout the body • Cardiac cycle: one sequence of pumping and filling of blood • Systole: contraction phase of the cycle


• Diastole: relaxation phase of the cycle • Cardiac output: volume of blood each ventricle pumps/minute

o Heart rate: beats/minute-‐rate of contraction o Stroke volume: amount of blood pumped by the ventricle in a single contraction

• Valves o Atrioventricular (AV) Valve: between each atrium and ventricle o Semilunar valves: located at the two exits of the heart – aorta leaves the left ventricle and

where the pulmonary artery leaves the right ventricle Lub: recoil of blood against the closed AV valves Dup: recoil of blood against the closed semilunar valves

o Heart mumur: the noise you hear when blood squirts backwards through a defective valve

1. Relaxation phase—blood returning from the large veins flows into the atria/ventricle through AV valves

2. Brief atrial systole forces all blood remaining in the atria into the ventricles

3. Ventricular systole pumps blood into the large arteries through the semilunar valves

MAINTAINING THE HEART’S RHYTHMIC BEAT • Sometimes cardiac muscle cells are autorhythmic – contract and relax repeatedly w/o any signal from

the nervous system • Sinoatrial (SA) node: pacemaker, sets the rate and timing at which all cardiac mucles contract

o Impulses from the SA node spread rapidly within the heart tissue – generate currents that are conducted to the skin via body fluids

o Electrocardiogram (ECD/EKG): uses electrode placed on skin to detect and record currents o Atrioventricular node (AV): the relay point where the impulses are delayed before spreading

to the walls of the ventricles Allows the atrial to empty completely before the ventricles contract

• Things that affect the pacemaker o Sympathetic and parasympathetic nerves – function like spurs and reins o Hormones: epinephrine (Fight-‐or-‐flight) causes the heart rate to increase


o Body temp: 1 C raises heart rate

42.3: PATTERNS OF BLOOD PRESSURE AND FLOW REFLECT THE STRUCTURE

AND ARRANGEMENT OF BLOOD VESSELS

BLOOD VESSEL STRUCTURE AND FUNCTION • Endothelium: single layer of flattened epithelial cells-‐ inner most layer—smooth surface minimizes

resistance to the flow of blood o Capillaries are the smallest blood vessels-‐ have very thin walls comprised of solely

endothelium and basal lamina • Arteries and veins

o Connective tissue—allows the vessel to stretch and recoil o Smooth muscle—more elastic fibers

• Arteries o Artery has a wall about three times as thick as that of a vein because they need to handle the

higher blood pressure


BLOOD FLOW VELOCITY • Blood slows as it moves from arteries to arterioles to capillaries because the number of capillaries is

great • Reduced velocity of blood flow in capillaries is critical to the function of the circulatory system –

capillaries only have extremely thin walls


BLOOD PRESSURE

CHANGES IN BLOOD PRESSURE DURING THE CARDIAC CYCLE • Systolic pressure: pressure when the heart contracts during the ventricular systole—highest arterial

blood pressure • Pulse: rhythmic bulging of the artery walls with each heartbeat • Diastolic pressure: pressure when the ventricles are relaxed

REGULATION OF BLOOD PRESSURE • Vasoconstriction: physical/emotion stress that can cause the arteriole walls to contract – arterioles

narrow, increasing blood pressure • Vasodilation: increase in diameter that causes blood pressure in the arteries to fall • Coupled with cardiac output – affect blood pressure

o Heavy exercise: arterioles in working muscles dilate, causing greater flow of O2-‐rich blood to the muscles—drop in blood pressure

• Endothelin: inducer of vasoconstriction


BLOOD PRESSURE AND GRAVITY • Generally measured for an artery in the arm at the same height as the heart • Gravity has a significant effect on blood pressure – challenge of pumping blood against gravity

o Legs? It’s hard to pump blood from the legs back to the heart so we have…

• Rhythmic contractions of smooth muscles in the walls of venules and veins • Contraction of skeletal muscles during exercise squeezes blood through the

veins toward the heart • Change in pressure within the thoracic cavity during inhalation causes the

venae cavae to expand

CAPILLARY FUNCTION • Contraction of smooth muscle in walls of arteriole – reduces vessel’s diameter and decreases blood

flow to adjoining capillary beds—smooth muscle relaxes, arterioles dilate and allow blood flow to enter the capillaries

• Precapillary sphincters—rings of smooth muscle located at the entrance to capillary beds – regulate blood flow (nerve impulses, hormones, chemicals)

• Small molecules diffuse across the endothelial cells/openings within/between adjoining cells • Blood pressure drives fluid out of the capillaries, blood proteins pull fluid back into the capillaries

FLUID RETURN BY THE LYMPHATIC SYSTEM • Lymphatic system: returns lost fluid and proteins to blood, includes network of tiny vessel

intermingled among capillaries of cardiovascular system o Drains into large veins of circulatory system at the base of the neck

• Lymph: fluid after entering the lymphatic system by diffusion – same composition as intestinal fluid. • Movement of lymph to from peripheral tissues to the heart relies on valves and vessel contractions

and skeletal muscle contractions • Lymph nodes swell, which causes edema-‐-‐-‐excessive accumulation of fluid in tissues • Lymph nodes: organs along a lymph vessel – filtering lymph and housing cells that attack viruses and

bacteria


42.4: BLOOD COMPONENTS FUNCTION IN EXCHANGE, TRANSPORT AND

DEFENSE

COMPOSITION AND FUNCTION

PLASMA • Liquid matrix that has cells, ions, proteins – function in osmotic regulation, transport and defense • Inorganic salts in the form of dissolved ions – blood electrolytes – important for maintaining osmotic

balance of the blood, directly affects interstitial fluid • Plasma proteins act as buffers against pH changes, help maintain osmotic balance between blood and

interstitial fluid and contribute to the blood’s viscosity (thickness) o Antibodies help combat viruses o Escorts for lipids o Clotting factors

• Respiratory gases, metabolic wastes, hormones, nutrients

CELLULAR ELEMENTS • Platelets: fragments of cells involved in the clotting process

ERYTHROCYTE • Erythrocyte: red blood cells, most numerous – small discs that are biconcave

o Lack mitochondria, generate ATP exclusively through anaerobic metabolism o Transport oxygen

• Hemoglobin: iron-‐containing protein that transports O2

LEUKOCYTE • Leukocyte: white blood cell—fight infections

o Phagocytic o B-‐Cells and T-‐Cells – mount immune responses against foreign

PLATELETS • Pinched-‐off cytoplasmic fragments of specialized bone marrow cells – blood clotting


BLOOD CLOTTING • Fibrin: active form of fibrinogen, aggregates into threads that form the framework of the clot • Thrombus: clot that forms within a blood vessel, blocking the flow of blood


STEM CELLS AND REPLACEMENT OF CELLULAR ELEMENTS • Stem cells: dedicated to replenishing blood cell populations

o Blood cells located in the red marrow of bones – multipotent stem cells can form multiple types of cells

o Erythrocyte, leukocyte, platelets formed from stem cell divisions, replace worn-‐out cellular elements of blood

• Erythropoietin (EPO): hormone that stimulate RBC creation

CARDIOVASCULAR DISEASE

ATHEROSCLEROSIS • Hardening of the arteries by accumulation of fatty deposits • Roughen the lining and lead to inflammation • Leukocytes are attracted to the damaged lining and begin to take up lipids—fatty deposits (plaque)

grows steadily, incorporating fibrous tissue+cholesterol

HEART ATTACKS AND STROKES • Heart attack: damage or death of cardiac muscle tissue resulting from blockage of one+ coronary

artery – b/c arteries are small in diameter, they’re vulnerable to obstruction • Stroke: death of nervous tissue in the brain due to lack of O2—result from rupture /blockage of

arteries in the head • Result frequently from thrombus that clogs the artery

TREATMENT AND DIAGNOSIS OF CARDIOVASCULAR DISEASE • Low-‐density lipoprotein (LDL) : ‘bad cholesterol; -‐-‐ associated with deposition of cholesterol in arterial

plaques • High-‐density lipoprotein (HDL): ‘good cholesterol’ – recue the deposition of cholesterol • Hypertension: contributor to heart attack and stroke

o High blood pressure damages the endothelium that lines the arteries, promoting plaque formation

42.5: GAS EXCHANGE OCCURS ACROSS SPECIALIZED RESPIRATORY SURFACES • Gas exchange: uptake of molecular O2 from the environment and the discharge to CO2 to the

environment

PARTIAL PRESSURE GRADIENTS IN GAS EXCHANGE • Partial pressure: the pressure exerted by a particular gas in a mixture of gases

o Need to know the pressure that the mixture exerts and the fraction of the mixture represented by the particular gas

o For liquids: partial pressure of the gas in the solution equals the partial pressure of the gas in the air

RESPIRATORY MEDIA • Easier to respire with air than with water duh


RESPIRATORY SURFACES • Specialization for gas exchange is apparent in the structure of the respiratory surface – part of the

body where the gas exchange occurs • Have plasma membrane that must be in contact with an aqueous solution—always moist • Movement of O2/CO2 across moist respiratory systems take place by diffusion

o Rate proportional to SA across which it occurs and inversely proportional to the square of the distance through which the molecules must move

• Structure depends on the size of the animal/whether or not lives in water o Simple animals – every cell in the body can diffuse o Larger animals – respiratory system in the animals is a thin, moist, epithelium that constitutes

a respiratory organ o Skin? Earthworms, amphibians

GILLS IN AQUATIC ANIMALS • Outfoldings of body surface suspended in water • Ventilation: maintains the partial pressure gradients of O2/Co2 across the gill

o Most animals move their gills through the water/move water over the gills • Countercurrent exchange: exchange of substance/heat between two fluids flowing in opposite

directions – maximizes efficiency

TRACHEAL SYSTEMS IN INSECTS • Tracheal system: made up of air tubes that branch throughout the body, one variation on the theme

of an internal respiratory surfacd


o Largest tubes—tracheae—open to the outside, diffusion occurs across the moist epithelium that lines the tips of tracheal branches

o Larger insects: ventilate their tracheal systems with rhythmic body movements that compress and expand the air tubes like bellows

LUNGS • Lungs: localized respiratory organs representing the infolding of the body surface, typically subdivided

into numerous pockets – gap bridged between the lungs by the trachea o Amphibians also rely on skin exchange o Size and complexity of lungs are correlated with an animal’s metabolic rate

MAMMALIAN RESPIRATORY SYSTEMS • Branching ducts convey air to the lungs, located in the thoracic cavity • Air enters through the nostrils, filtered by hairs, warmed, humidified, sampled for odors • Pharynx: intersection of where air and food paths cross • Larynx: upper part of the respiratory tract • Trachea: windpipe • Vocal cords: pair of elastic bands of muscle in the larynx, sounds are produced when muscles in the

voice box are tensed, stretching the cords so they vibrate • Bronchi: one leading to each lung • Bronchioles: finer tubes of the bronchi


• Mucus traps dust/pollen/contaminants • Alveoli: air sacs clustered at the tips of the tiniest bronchioles

o Lack cilia, surrounded by white blood cells • Surfactants: secretions that are required to relieve the surface tension in the fluid that coats their

surface o If they don’t exist, the alveoli collapse


42.6: BREATHING VENTILATES THE LUNGS • Breathing: alternation of inhaling and exhaling of air

HOW AN AMPHIBIAN BREATHES • Positive pressure breathing: inflating the lungs with forced airflow

HOW A MAMMAL BREATHES • Negative pressure breathing: pulling, rather than pushing, air into lungs

o Muscle contraction to expand the thoracic cavity – lower air pressure in lungs relative to the air outside

o Diaphragm: sheet of skeletal muscle that forms the bottom wall of the cavity – contracting rib muscles expand the rib cage

o Double membrane: surrounds the lungs – inner adheres to the outside fo the lungs, outside adheres to the wall of the thoracic cavity

Fluid separates the two layers • Tidal volume: the volume of air inhaled and exhaled with each breath • Vital capacity: tidal volume during max inhalation and exhalation • Residual volume: air that remains after a forced exhalation


HOW A BIRD BREATHES • Ventilation is more efficient and complex in birds

o Pass air over a gas exchange surface in only once direction—fresh air does not mix with used air

o Have 8/9 air sacs—keep air flow through the lungs o Parabronchi exist instead of alveoli

• High maximum lung capacity

CONTROL OF BREATHING IN HUMANS • Breathing control centers: networks of neurons that regulate breathing—located in two brain regions

(medulla oblongata and pons) o Medulla: establish rhythm o Pons tempo o O2 concentration in the blood usually has little effect on breathing control centers o Negative feedback systems


Breathing Control Centers: medulla: set basic rhythm, pons moderates tempo.

Nerves from the control center send impulses to diaphragm and rib muscles contract inhalation

Sensors in the medulla detect change in pH of blood and cerebrospinal fluid

Sensors in major blood vessels detect changes in blood pH and send nerve impulses to the medulla

Aorta sensors as well work for regulation

42.7: ADAPTATIONS FOR GAS EXCHANGE INCLUDE PIGMENTS THAT BIND AND

TRANSPORT GASES

COORDINATION OF CIRCULATION AND GAS EXCHANGE • Partial pressures of O2 and CO2 in blood vary at different points of the system • Gradients exist b/c of cellular respiration


RESPIRATORY PIGMENTS • Circulate with blood/hemolymph and are contained with special cells – greatly increase the amount of

O2 that can be carried in fluid

HEMOGLOBIN • Heme group—iron atom at the center • Iron binds O2 • Bohr shift: low pH decreases the affinity of hemoglobin for O2 – CO2 production is greater and

hemoglobin releases more O2


CARBON DIOXIDE TRANSPORT • Released by respiring cells • Binds to animo ends of hemoglobin polypeptide chains • Transported in the blood in HCO3-‐

1. CO2 diffuses into interstitial fluid/plasma 2. 90%+ diffuses into the red blood cells 3. Some is picked up & transported by

hemoglobin 4. CO2 reacts w/ water in red blood cells,

forming H2CO3 5. Acid dissociates into HCO3-‐ and H+ 6. Hemoglobin binds most of the H+ from

H2Co3, preventing acidification 7. Most HCO3-‐ diffuses into the plasma 8. In the lungs HCO3-‐ diffuses from plasma

into red blood cells 9. Carbonic acid is converted to Co2 and

water 10. CO2 diffuses into the plasma 11. CO2 diffuses into alveolar space, expelled

during exhalation

A SECTION ABOUT ANIMALS WHO HAVE

EXTREMELY EFFICIENT BREATHING SYSTEMS • The pronghorn—endurance! They breathe

very often • Weddell seal – myoglobin: can store

oxygen in the muscles o They can send more blood to the

heart/brain/lungs/spinal cord as pressure builds and O2 consumption rates decrease


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