Outline: Circulation and Gas Exchange. Chapter 42

I. Function: Intra-organism trafficking.

II. Types of Circulatory Systems

III. Vertebrate Circulatory System


A. Multiple tasks, including:
B. Gross Anatomy: Cardiovascular system
C. Heart: Dynamics
D. Vascular system: Dynamics.
E. Blood: Plasma, RBCs, White Cells
F. Lymphatic System

IV. Respiration: Gas Exchange

A. Diversity
B. Human Respiratory System
C. Gas exchange: O₂ IN / CO₂ OUT

LECTURE NOTES: Circulation and Gas Exchange. Chapter 42

I. Function: Intra-organism trafficking.

A. Cells need access to nutrients, O₂ (release of CO₂ - pH problems).
B. As organisms gets larger (e.g. evolution) distance increases between

cells in need and cells involved in ingestion/digestion or gas exchange.

C. Vascular system required for increase evolution of size increase.
D. Vascular system permits distant cell-cell communication: hormones.

II. Types of Circulatory Systems

A. All: 3 major parts:

1. fluid (blood)
2. channels (vessels)
3. pump (heart)

B. Open (insect hemocoel) vs. closed circulatory systems (fig. 42.2)

III. Vertebrate Circulatory System

A. Multiple tasks, including:

O₂, nutrients, waste, hormones, regulation of body temp
Problems: Prevention of leaks, Prevention of invasion.

B. Gross Anatomy: Cardiovascular system

1. Heart: chambers & valves (fig. 42.3)

- 2 chambers (Fish), 3 chambers (Frogs), 4 chambers (Mammals)
- 4 Chambered Mammalian Heart (e.g. human)

a. Atria: Left and Right (Fill)
b. Ventricles: Left and Right (Pump out - Pressure)
c. Valves: situated at "in" and "out" sides of each ventricle

- atrioventricular valves

-- tricuspid valve (TCV)
-- bicuspid valve (BCV)

- semilunar valves (SLV)

2. Vascular System

a. Away from heart: arteries - arterioles - capillaries
b. Back towards heart: capillaries - veinules - veins

3. Circulation Paths

a. Three Circulatory Loops (fig. 42.4)

- Systemic (body),
- Pulmonary (lung),
- Coronary (heart) - subject of bypass surgery

b. Cardiac Circulation (fig. 42.6)

C. Heart: Dynamics

1. Heart tissue is muscle

a. contracts and relaxes (Cardiac Cycle)
b. actin and myosin (similar to skeletal muscle)

2. Cardiac Cycle: Self sustaining / atrial-ventricular coordination

a. systole - ventricles contract (empty), atria relax
b. diastole - ventricles relax (fill), atria contract

3. cardiac cells are contractile and electrically excitable

- cardiac muscle: autonomous contractions (actin & myosin)

-- electrically excitable cells (can produce action potentials)
-- each cell self stimulating
-- one cell can excite the next

4. coordination: Pacemaker centers (fig. 42.7)

a. Sinoatrial Node (SA Node) self-stimulating
b. Atrioventricular Node (AV Node)
c. conducting fibers: Purkinje fibers

- like nerve cells but really modified muscle cells
- ensures synchronous stimulation of all muscle cells within

respective zones (i.e. atria, vs. ventricles, right and left)

5. neural control: modulation ONLY

a. Vegus nerve comes to SA node
b. releases inhibitory neurotransmitter (acetylcholine)
c. SA activity decreases, heart frequency slows

6. hormonal control: modulation ONLY

- adrenaline (epinephrine) excites SA node

D. Vascular system: Dynamics.

1. Structure of Blood Vessels (fig. 42.8)

Arteries (thick walled):

endothelium, smooth muscle, connective tissue

Veins (thick walled):

endothelium, smooth muscle, connective tissue, valves

Capillaries (thin walled):

endothelium, thin connective tissue
holes: spaces between cells, "leaky"

2. Velocity of blood flow (fig. 42.10)

Arteries	Capillaries	Veins
SMALL X-sectional area	LARGE X-sectional area	SMALL X-sectional area
"canyon" high speed	"flood" low speed	"canyon" high speed
HIGH PRESSURE	LOW PRESSURE	LOW PRESSURE

3. Blood pressure: local resistance, peripheral resistance (fig. 42.10)

a. If pipes are closed, and pump is working, high pressure at pump
b. pressure high in arteries (canyon), low in capillaries (flood)
c. pressure in veins: low

nothing from heart,
"pumps" are skeletal muscle and valves.

4. Flow...

a. Flow through arteries: pressure driven from heart
b. Flow through capillaries: replacement (very low pressure)
c. Flow through veins: no heart pressure (fig. 42.9)

- valves prevent back flow
- skeletal muscle contractions collapse veins,

squeezing blood forward, back to heart

5. Regulation of blood flow through Capillary Beds

a. only 5-10% of capillaries have blood flow

- flow through capillary beds is regulated

b. arteriole control: neural

- Nerves control smooth muscle in arteriole walls
- muscle contracts, arteriole closes, no blood to capillaries

c. Pre-Capillary Sphincters (fig. 42.11)

- Capillary beds can be opened or closed
- sphincters: smooth muscle, hormonally controlled
- local CO₂ detectors: stimulate hormone, dilate at need

6. Gas, Nutrient exchange in capillary beds. (fig. 42.10)

a. Some: endocytosis through cells
b. Most: Bulk Diffusion, through clefts between cells

- too small for proteins (or blood cells)
-O₂, CO₂, nutrients, hormones

c. hydrostatic pressure moves material out and in

- arteriole end, high blood pressure: OUT
- veinule end, low blood pressure (higher outside): IN

-- 85% that leaves returns to capillaries
-- 15% leaks back via lymph system.

1. Plasma: water w/dissolved proteins, nutrients, waste, hormones
2. Blood Cells (fig. 42.13, 42.14)

a. derive from stem cells in bone marrow
b. Red Blood Cells (RBCs) (erythrocytes)

Hemoglobin (Hb), O₂
live ~ 120 days / recycled in spleen and liver
negative feedback reg. numbers

hormone erythopoietin produced in liver if low [O₂]
erythropoietin stimulates stem cells in marrow

Blood Types: genetic differences:

different membrane proteins
tissue rejection if incompatible

c. White Blood Cells: Immune response
d. Platelets - blood clotting

1. Functions:

a. Remove excess body fluid to blood
b. Transport fats from intestine to blood
c. Defense

2. Anatomy (fig. 43.4)

a. Lymph Nodes scattered through out body / Thymus, Spleen

- sites of lymphocyte differentiation from marrow migrants

b. Vessels

IV. Respiration: Gas Exchange

1. Specialized Respiratory Structures
2. Respiratory Surface

a. Maximize surface between air and blood: Maximize exchange
b. Variety of Respiratory Systems (p. 826-832)

- Body Surface (e.g. earthworm) - Gills (e.g. fish)

-- blood reaches out

- Trachaea (insects) - Lungs (e.g. birds, mammals)

-- air reaches in

3. Passive or active ?

- To some degree, all are active (ventilation behaviors / mechanisms).

1. Anatomy

a. To Lungs:

Nasal cavity, pharynx, epiglottis, larynx, esophagus, trachea

b. In Lungs:

bronchi, bronchioles, alveoli (site of gas exchange with blood)

2. Regulation

a. Active Inhale, passive exhale
b. Breathing rate controlled by brain center (CO₂ receptors)


C. Gas exchange: O₂ IN / CO₂ OUT

1. O₂ and CO₂ are soluble in H₂0 (Plasma)



CLICK FIGURE FOR LARGER IMAGE

2. Hemoglobin (Hb) - in RBCs


a. four subunit protein (2 alpha, 2 beta) - heme groups w/ iron center
b. each heme binds one O₂ molecule (4 O₂/Hb)
c. in alveoli, O₂ enters plasma, RBC, binds to Hb, transported to cells
d. fetal Hb: higher affinity than maternal Hb, O₂ moves to placenta


3. CO₂ and the Carbonic Acid / Bicarbonate System


        a. CO2 + H2O <> H2CO3 <> H+ + HCO3- <> 2H+ + CO32-
             acidic      physiological        basic

b. HCO₃^- neutral pH, buffers blood. Concentration stable
c. CO₂ + H₂O <> H₂CO₃ facilitated by Carbonic Anhydrase (CA) in RBC

H₂CO₃ <> H⁺ + HCO₃^- spontaneous (at physiological pH, ca. 7.0)

d. CO₂ produced in glycolysis > blood > converts to H₂CO₃ > H⁺ + HCO₃^-
e. CO₂ influences pH which influences O₂-Hb binding



CLICK FIGURE FOR LARGER IMAGE
4. IN CELLS: CO₂ produced, moves to blood

a. 10% stays dissolved CO₂, rest converts to HCO₃^-
b. conversion facilitated by carbonic anhydrase in RBC
c. relative high CO₂ means high H₂CO₃ means low pH > O₂ release from Hb


5. IN ALVEOLI (LUNGS): CO₂ moves to air

a. high CO₂ in blood, low CO₂ in air (.003%)

- CO₂ partitions into air, lowering CO₂ conc.

b. lower CO₂ concentration:

- raises pH >> drives O₂-Hb binding
b. drives HCO₃^- > CO₂ via CA acting in reverse



CLICK FIGURE FOR LARGER IMAGE
6. RE-STATEMENT: pH, [CO₂] and O₂-Hb binding

a. in lungs, low CO₂ (pH 7.4) makes higher pH >>> Hb binds O₂
b. in tissue, high CO₂ (pH 7.2) makes lower pH >>> Hb release O₂
c. Some (10%) CO₂ stays in plasma as CO₂.
d. Some (small amount) of CO₂ binds to Hb; but most CO₂ converts to HCO₃^-.


7. Fetal Hb (fHb) / Maternal Hb (mHb), Myoglobin, High Altitude

a. In Fetus: Fetal Hb

a. fHb higher O₂ affinity than mHb
- O₂ moves from maternal blood to fetal blood in placenta

b. In Muscles, Myoglobin (Red Meat)

- Myoglobin higher O₂ affinity than Hb
- Facilitates O₂ movement into muscle cells

c. High Altitude

- native populations: high altitude Hb
- others, high altitude adaptation > erythropoietin > RBC production

V. Revisiting O₂, CO₂, Hemoglobin

A. Hemoglobin:

1. 4 subunites, 4 O₂ molecules, Hb + O₂ <<---->> 4O₂-Hb
2. Experiment:

a. Hb in solution : O₂ loading as function of O₂ concentration
b. observe sigmoidal curve to saturatin

- sigmoid suggests dynamic, non-linear loading
- cooperativity: first O₂ increases ease of 2,3,4 O₂ binding

B. O₂ Transfer

1. Lungs: O₂ air <> O₂ plasma <> Hb + O₂ <> 4O₂-Hb
2. Tissue: 4O₂-Hb <> Hb + O₂ <> O₂ plasma <> O₂ cell
3. QUESTION: O₂ Goes On / Why Does it Come Off? Answer: pH

C. Hemoglobin (Hb) / O₂ Interactions

    Cells                             Lungs
    O2 + Hb <<<<<<<<<------->>>>>>>>> 4O2-Hb
    favored                           favored	
  low pH (7.2)                      high pH (7.4) 

D. CO₂ - Bicarbonate System

           (RBC)
             CA    reversible       reversible
  CO2 + H2O <--> H2CO3 <--> H+ + HCO3- <--> 2H+ + CO32- 
          reversible     Physiological pH
           ACIDIC            pH 7ish           BASIC
           low pH	                      high pH

1. Tissue: CO₂ high - pH shifts left (low): O₂ + Hb favored
2. Lungs: CO₂ low - pH shifts right (high): O₂-Hb favored

Vocabulary, Chapter 38