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RESPIRATORY GAS TRANSPORT. Biochemistry Departement Medical Faculty Of Andalas University Padang. Oxygen Transport. Total Body Oxygen Stores . Oxygen in the Lung (~500 ml O 2 ). Oxygen in the Blood (~850 ml O 2 ). Oxygen in the Cells (very little except Mb-bound). At the Lung Level.

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RESPIRATORY GAS TRANSPORT

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RESPIRATORY GAS TRANSPORT

Biochemistry Departement

Medical Faculty Of Andalas University

Padang


Oxygen Transport


Total Body Oxygen Stores

  • Oxygen in the Lung (~500 ml O2).

  • Oxygen in the Blood (~850 ml O2).

  • Oxygen in the Cells (very little except Mb-bound).


At the Lung Level


At the Tissue Level


Oxygen Is Carried in Blood in 2 Forms

  • Bound to hemoglobin in red blood cells.

  • Dissolved in plasma. Normally insignificant.


Hemoglobin

  • Each “heme” molecule is capable of binding with 1 O2 molecule and each “globin” molecule is capable of binding with 1 CO2 molecule.

  • So, each molecule of Hb can bind to either 4 molecules of O2 and 1 molecule of CO2

  • 100 ml of blood has about 15 gm of Hb, at Hct = 0.45


  • Binding of O2 to 4 heme sites given by:

  • Equilibrium constants for different reactions different

    • Binding of first O2 relatively low affinity

    • 2nd, 3rd and 4th - much higher affinity


Oxygen as Oxyhemoglobin

  • Each gram of Hb can store about 1.34 ml of O2:

  • 1 L of blood (150 gm of Hb) can store about 208 ml of O2  Oxygen Capacity of Hb.

  • With normal cardiac output, about 1040 ml of O2 can be carried in blood per minute. (4 times of the metabolic demands).


O2 Saturation.

  • Units: percent.

  • Fraction or percentage of all the hemoglobin binding sites that are currently occupied by oxygen.


Oxygen Saturation of Hb


Four (5-6?) Things Change Oxyhemoglobin Affinity

  • Hydrogen Ion Concentration, [H+]

  • Carbon Dioxide Partial Pressure, PCO2

  • Temperature

  • [2,3-DPG]

  • Special Case: Carbon Monoxide

  • Hemoglobin variants


Factors Affecting Hb-O2 Affinity: Summary

  • Hydrogen Ion:

    • Increased H+ (decreased pH) increases H+ binding to Hb and reduces O2 affinity (HbO2+H+HbH++O2).

  • Carbon Dioxide (Bohr effect):

    • Increased PCO2 increases CO2 binding to Hb and reduces O2 affinity (increased O2 delivery to tissue).

    • Increased PCO2 increases H+ and reduces O2 affinity (fixed acid Bohr effect).

  • Temperature and 2,3-DPG (diphosphoglycerate):

    • Increased temperature and 2,3-DPG reduces O2 affinity.


Effect of CO & Anemia on Hb-O2 Affinity

Normal blood with Hb=15 gm/dl, anemia with Hb=7.5 gm/dl, and normal blood with 50% HbCO (carboxyhemoglobin).


Exercise

  • Increase temperature

  • Increased PCO2 and

  • Decreased pH (acidosis)


2,3-DPG

  • 2,3-DPG is a glycolytic intermediate

    • accumulates to uniquely high levels in RBCs

      -Increased 2,3-DPGright shift

      -Decreased 2,3-DPG left shift

  • Increased 2,3-DPG associated with hypoxia.


Conditions with Increased 2,3-DPG

  • acclimatization to high altitudes.

  • chronic lung disease; emphysema.

  • anemia.

  • hyperthyroidism.

  • right to left shunt.

  • congenital heart disease.

  • pulmonary vascular disease.


Carbon Dioxide Transport


At the Tissue Level


At the Lung Level


Carbon Dioxide Transport

  • CO2 is transported in blood in dissolved form, as bicarbonate ions, and as protein-bound carbamino compound.

  • Protein-bound CO2 (carbamino compounds):

  • Amount of CO2 stored as carbamino compounds is about 21 ml/L (4% of the total art CO2).


Carbon Dioxide Transport

  • A majority amount of CO2 is transported in the form of bicarbonate ions (HCO3-):

  • Amount of CO2 in HCO3- form at PCO2=40 mmHg is about 420 ml/L (90% of the total arterial CO2).


Carbon Dioxide Transport

  • Haldane Effect: Increasing O2-saturation reduces CO2 content and shifts the CO2 dissociation curve to right. This is because, increasing PO2 leads to :

    • Decrease in the formation of carbamino compound.

    • Release of H+ ions from the hemoglobin and resulting in dehydration of HCO3-.


Carbon Dioxide Dissociation Curve

Over the normal physiological range (PCO2 = 30 to 55 mmHg and PO2 = 40 to 100 mmHg), the CO2 equilibrium curve is nearly linear. But, O2 equilibrium curve is highly nonlinear.


Bicarbonate in RBCs.

  • Carbonic anhydrase is present in RBCs

  • CO2 forms carbonic acid which dissociates to H+ and HCO3-

  • Released H+ is buffered by histidine residues (imidazole group)

• Percent of the total PaCO2: 70%


Carbamino Compounds in RBCs.

  • Approximately 30% of RBC contents is Hb

  • CO2 forms carbamino hemoglobin

  • Released H+ is buffered by histidine residues (imidazole group)

• Percent of the total PaCO2: 23 %


CO2Formation in Plasma

  • Carbamino compounds

    • CO2 binds the amine groups of plasma proteins to form carbamino compounds.


O2 pickup CO2 release


O2 release CO2 pickup


Chloride Shift (Hamburger Shift)

  • Newly formed HCO3- passes out of RBC

  • Cl- diffuses into RBC to maintain electroneutrality

    • Chloride shift is rapid

    • Complete before the RBCs exit capillary


Tissue-Gas Exchange: Summary

  • Gas exchange processes in the peripheral organs are essentially opposite those in the lungs.

  • O2 is released from the capillary blood to the tissues and diffuses to the mitochondria where O2 is converted to CO2 and energy (ATP) through cellular metabolism.

  • CO2 diffuses from the tissues to the blood stream and is transported to the lungs for elimination.

  • The exchange of O2 and CO2 in the blood-tissue exchange unit depends on PO2, PCO2, and also on O2 and CO2 saturation curves.


Gas Transport in Cell


Pelepasan CO2

  • Dilakukan oleh:

    1. isositrat dehidrogenase

    2. α-ketoglutarat dehidrogenase

  • Pelepasan CO2 tidak mengkonsumsi oksaloasetat.


Siklus ATP/ADP

  • Berperan untuk menghubungkan proses-proses yg menghasilkan P-berenergi-tinggi dgn proses yg menggunakan P-berenergi-tinggi.

  • ATP dikonsumsi & dibentuk kembali secara kontinu.

  • Depot ATP/ADP sangat kecil, sehingga hanya cukup untuk mempertahankan jaringan aktif dlm waktu beberapa detik saja.


Siklus ATP/ADP

ATP

CO2

Pernapasan: Penggunaan energi:

pembentukan energi - biosintesis makro-

dari; - karbohidrat molekul

- lemak - kontraksi otot

- protein - transpor ion aktif

- termogenesis

O2

ADP + Pi


Fosforilasi Oksidatif

  • Adalah sistem dalam mitokondria yang memasangkan respirasi dengan proses pembentukan intermediat berenergi tinggi, ATP.

  • Sistem ini memungkinkan organisme aerob menangkap energi bebas dari substrat respiratorik dalam jumlah lebih besar dibanding organisme anaerob.


Peran Rantai Respirasi

asam lemak

+ b-oksidasi

gliserol ATP

O2

glukosa Asetil KoA SAS 2H H2O

rantai respirasi

Asam amino ADP

mitokondria


Produk ATP pada Fosforilasi Oksidatif

Berdasarkan hipotesis kimiosmotik dari Mitchell

yaitu;

rantai bekerja --> proton dipompa keluar dari membran dlm mitokondria --> pH antar membran turun --> proton balik ke dalam matrik lewat tonjolan ATP-sintase--> fosforilasi ADP menjadi ATP.


Produk ATP pada Fosforilasi Oksidatif

  • Diperkirakan satu ATP disintesis setiap dua proton melewati tonjolan tsb.

  • Hasilnya ialah;

    - 3 mol. ATP utk oksidasi 1 mol. NADH

    - 2 mol. ATP utk oksidasi 1 mol. FADH2

  • Laju fosforilasi oksidatif dikendalikan oleh;

    NADH, oksigen, ADP


Resources

  • BIOEN 589: Integrative Physiology. Download 24 jan 05.

  • Kennelly, PJ., Rodwell, V W. Proteins: Myoglobin & Hemoglobin. In: Harper’s Illustrated Biochemistry. 27th Ed. 41- 8.

  • Miliefsky, M. Respiratory System Ch.23. Download 24 Nov 10.

  • Sheardown, H. Blood Biochemistry. McMaster University. Download 20 Mei 07.

  • Irvin, CG. Respiratory Physiology. Lecture 4A CO2 Transport. In: MEDICAL PHYSIOLOGY 30. Download 22 Jun 09.

  • Marks, DB., Marks, AD., Smith CM. Basic medical biochemistry: a clinical approach. 1996. Dalam: B.U. Pendit, penerjemah. Biokimia Kedokteran Dasar: Sebuah Pendekatan Klinis. Eds. J. Suyono., V. Sadikin., L.I. Mandera. Jakarta: EGC, 2000

  • R.K. Murray, D.K. Granner, P.A. Mayes, V.W. Rodwell Harper’s Biochemistry. 27th ed. McGraw-Hill Companies, New York. 2006.


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