4-18-05 monday blood gas continued structure of the brain

4-18-05

Monday

Blood Gas Continued

Structure of the Brain

• The low solubility of oxygen in water is a fundamental problem for animals that rely on the circulatory systems for oxygen delivery (gill)– For example, a person exercising consumes almost 2

L of O2 per minute, but at normal body temperature and air pressure, only 4.5 mL of O2 can dissolve in a liter of blood plasma (blood without RBCs) in the lungs.

– If 80% of the dissolved O2 were delivered to the tissues (an unrealistically high percentage), the heart would need to pump 500 L of blood per minute - a ton every 2 minutes (impossible).

Respiratory pigments transport gases and help buffer the blood

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• In fact, most animals transport most of the O2 bound to special proteins called respiratory pigments instead of dissolved in solution.– Respiratory pigments, often contained within

specialized cells, circulate with the blood.– The presence of respiratory pigments increases the

amount of oxygen in the blood to about 200 mL of O2 per liter of blood (normal output= 5.25liter/min.

– Exercising person output is 5 times normal.– For our exercising individual, the cardiac output

would need to be a manageable 20-25 L of blood per minute to meet the oxygen demands of the systemic system.


Oxygen Transport Pigments

• Pigments load oxygen in lung or gill and carry it to the capillaries where it is unloaded for cell

• Hemoglobin--(tetrameric molecule inside cell) Associated 4 iron molecules bind 4 molecular oxygens.

• Hemocyanin--large molecule (106 Daltons) containing many copper atoms colors hemolymph blue found in crustaceans and molluscs.

• Chlorocruorin--large iron containing molecule found in polychaete.

Physiologists Study Oxygen Transport with Oxygen Binding

Curves• Expose deoxygenated blood to increasing

amounts of air and measure the partial pressure of oxygen in the blood with an oxygen electrode. Plot partial pressure of oxygen in mixtures of air versus partial pressure of oxygen in the blood.

• Cooperative oxygen binding and release is evident in the dissociation curve for hemoglobin.

• Where the dissociation curve has a steep slope, even a slight change in PO2 causes hemoglobin to load or unload a substantial amount of O2.

• This steep part corresponds to the range of partial pressures found in body tissues.

• Hemoglobin can release an O2 reserve to tissues with high metabolism.

Fig. 42.28a

• Like all respiratory pigments, hemoglobin must bind oxygen reversibly, loading oxygen at the lungs or gills and unloading it in other parts of the body.– Loading and unloading depends on cooperation

among the subunits of the hemoglobin molecule.

– The binding of O2 to one subunit induces the remaining subunits to change their shape slightly such that their affinity for oxygen increases.

– When one subunit releases O2, the other three quickly follow suit as a conformational change lowers their affinity for oxygen.


• As with all proteins, hemoglobin’s conformation is sensitive to a variety of factors.

• For example, a drop in pHlowers the affinity of hemo-globin for O2, an effectcalled the Bohr shift.

• Because CO2 reacts with water to form carbonic acid, an active tissue will lower the pH of its surroundingsand induce hemoglobinto release more oxygen.


Fig. 42.28b

Figure 42.28 Oxygen dissociation curves for hemoglobin

Partial pressure of oxygen in Air is 160 mm Hg

P50 is partial pressure at which blood pigment is 50% saturated

P50

Bohr Effect

• Lower pH shifts oxygen binding curve to the right. That means that the oxygen is unloaded more easily at the tissues because of the lower pH.

• At the lungs the pH rises because the carbon dioxide is “blown off” and curve shifts to left making it easier to load oxygen.

Overhead of equilibrium curves with myoglobin and cytochrome

Oxygen passed from hemoglobin to myoglobin (in cell) to cytochrome in

mitochrondia

Figure 42.27 Loading and unloading of respiratory gases

Arterial Blood O2 saturation and O2 content

0

20

40

60

Arterial blood

% O2saturation

PO2 (mm Hg)

OContent

(vol. %)(= mL O2

per 100mL blood)

2 80

100

30 60 90

0

10

20

5

15

Overhead of oxygen content curve

Correlation between habitat and amount of oxygen that is carried in

the blood. Can only be observed with an oxygen content curve.

Figure 42.29 Carbon dioxide transport in the blood

Carbonic anhydrase converts CO2 + water to bicarbonate

Most CO2 transportedas bicarbonate in plasma


Fig. 42.29, continued

• In addition to oxygen transport, hemoglobin also helps transport carbon dioxide and assists in buffering blood pH.– About 7% of the CO2 released by respiring cells is

transported in solution.– Another 23% binds to amino groups of hemoglobin.– About 70% is transported as bicarbonate ions.


• When an air-breathing animal swims underwater, it lacks access to the normal respiratory medium.– Most humans can only hold their breath for 2 to 3

minutes and swim to depths of 20 m or so.– However, a variety of seals,

sea turtles, and whales can stay submerged for much longer times and reach much greater depths.(Weddell

– 700m)

Deep-diving air-breathers stockpile oxygen and deplete it slowly


Fig. 42.30

Figure 42.30 The Weddell seal, Leptonychotes weddelli, a deep-diving mammal

Unnumbered Figure (page 899) Dissociation curves for two hemoglobins

Fetal hemoglobin

Organophosphates displace Oxygen from hemoglobin

• One adaptation of these deep-divers, such as the Weddell seal, is an ability to store large amounts of O2 in the tissues.

– Compared to a human, a seal can store about twice as much O2 per kilogram of body weight, mostly in the blood and muscles.

– About 36% of our total O2 is in our lungs and 51% in our blood.

– In contrast, the Weddell seal holds only about 5% of its O2 in its small lungs (small because they exhale before they dive and their lungs collapse so they can avoid the bends) and stockpiles 70% in the blood.


• Several adaptations create these physiological differences between the seal and other deep-divers in comparison to humans.– First, the seal has about twice the volume of blood

per kilogram of body weight as a human.– Second, the seal can store a large quantity of

oxygenated blood in its huge spleen, releasing this blood after the dive begins.

– Third, diving mammals have a high concentration of an oxygen-storing protein called myoglobin in their muscles (meat is reddish black in color).• This enables a Weddell seal to store about 25% of its O2

in muscle, compared to only 13% in humans.


• Diving vertebrates not only start a dive with a relatively large O2 stockpile, but they also have adaptations that conserve O2.– They swim with little muscular effort and often use

buoyancy changes to glide passively downward.– Their heart rate and O2 consumption rate decreases

during the dive (bradycardia) and most blood is routed to the brain, spinal cord, eyes, adrenal glands, and placenta (in pregnant seals).

– Blood supply is restricted or even shut off to the muscles, and the muscles can continue to derive ATP from fermentation after their internal O2 stores are depleted (none to the kidneys—our kidneys would “die”).


Nervous System

CHAPTER 48NERVOUS SYSTEMS


An Overview Of Nervous Systems

1. Nervous systems perform the three overlapping functions of sensory input,

integration, and motor output

2. Networks of neurons with intricate connections form nervous systems

• Peripheral nervous system (PNS).– Sensory receptors are responsive to external and

internal stimuli.• Such sensory input is conveyed to integration centers.

– Where the input is interpreted an associated with a response.

Nervous systems perform the three overlapping functions of sensory

input, integration, and motor output


Fig. 48.1

• Motor output is the conduction of signals from integration centers to effector cells.– Effector cells carry out the body’s response to a

stimulus.


• The central nervous system (CNS) is responsible for integration.


• The signals of the nervous system are conducted by nerves.


• Neuron Structure and Synapses.– The neuron is the structural and functional unit of the

nervous system.• Nerve impulses are conducted along a neuron.

– Dentrite cell body axon hillock axon

– Some axons are insulated by a myelin sheath.

Networks of neurons with intricate connections form nervous systems


Fig. 48.2

• A Simple Nerve Circuit – the Reflex Arc.– A reflex is an autonomic response.


Fig. 48.3

• A ganglion is a cluster of nerve cell bodies within the PNS.

• A nucleus is a cluster of nerve cell bodies within the CNS.


• Schwann cells are found within the PNS.– Form a myelin sheath by insulating axons.


Fig. 48.5

Degradation of Myelin Sheath=Multiple Sclerosis

The ability of cells to respond to the environment has evolved over

billions of years

• Nerve nets.

Nervous systems show diverse patterns of organization


Fig. 48.15a, b

• With cephalization come more complex nervous systems.


Fig. 48.15c-h


Vertebrate Nervous Systems1. Vertebrate nervous systems have central and peripheral components

2. The divisions of the peripheral nervous system interact in maintaining

homeostasis

3. Embryonic development of the vertebrate brain reflects its evolution from three

anterior bulges of the neural tube

4. Evolutionarily older structures of the vertebrate brain regulate essential

autonomic and integrative functions

1. Vertebrate nervous systems have central and peripheral components


• Central nervous system (CNS).– Brain and spinal cord.

• Both contain fluid-filled spaces which contain cerebrospinal fluid (CSF).

– The central canal of the spinal cord is continuous with the ventricles of the brain.

– White matter is composed of bundles of myelinated axons

– Gray matter consists of unmyelinated axons, nuclei, and dendrites.

• Peripheral nervous system.– Everything outside the CNS.

• Structural composition of the PNS.

– Paired cranial nerves that originate in the brain and innervate the head and upper body.

– Paired spinal nerves that originate in the spinal cord and innervate the entire body.

– Ganglia associated with the cranial and spinal nerves.

The divisions of the peripheral nervous system interact in

maintaining homeostasis


• Functional composition of the PNS.


Fig. 48.17

• A closer look at the (often antagonistic) divisions of the autonomic nervous system (ANS).


Fig. 48.18

4-18-05 monday blood gas continued structure of the brain

Documents

oxygen increases

oxygen electrode

partial pressure of

blood copyright

oxygen binding curves

cooperative oxygen binding

liter of blood plasma

oxygen delivery gill