📖 Physiology
Respiratory System
Physiology1. Automatic control (sensory) of respiration is in - brainstem (midbrain)
2. Behavioral/voluntary control is in - the cortex
3. Alveolar ventilation -the amount of atmospheric air that actually reaches the alveolar per breath and that can participate in the exchange of gasses between alveoli and blood
4. Only way to increase gas exchange in alveolar capillaries - perfusion-limited gas exchange
5. Pulmonary ventiliation not effected by - concentration of bicarbonate ions
6. Central chemoreceptors - medulla - CO2, O2 and H+ concentrations
7. Peripheral chemoreceptors - carotid and aortic bodies- PO2, PCO2 and pH
8. Major stimulus for respiratory centers - arterial PCO2
9. Rhythmic breathing depends on
1. continuous (tonic) inspiratory drive from DRG (dorsal respiratory group)
2. intermittent (phasic) expiratory input from cerebrum, thalamus, cranial nerves and ascending spinal cord sensory tracts
10. Primary site for gas exchange - type I epithelial cells for alveoli
Oxygen Transport
PhysiologyOxygen Transport
In adult humans the hemoglobin (Hb) molecule
- consists of four polypeptides:
- two alpha (α) chains of 141 amino acids and
- two beta (β) chains of 146 amino acids
- Each of these is attached the prosthetic group heme.
- There is one atom of iron at the center of each heme.
- One molecule of oxygen can bind to each heme.
The reaction is reversible.
- Under the conditions of lower temperature, higher pH, and increased oxygen pressure in the capillaries of the lungs, the reaction proceeds to the right. The purple-red deoxygenated hemoglobin of the venous blood becomes the bright-red oxyhemoglobin of the arterial blood.
- Under the conditions of higher temperature, lower pH, and lower oxygen pressure in the tissues, the reverse reaction is promoted and oxyhemoglobin gives up its oxygen.
Serum Proteins
PhysiologySerum Proteins
Proteins make up 6–8% of the blood. They are about equally divided between serum albumin and a great variety of serum globulins.
After blood is withdrawn from a vein and allowed to clot, the clot slowly shrinks. As it does so, a clear fluid called serum is squeezed out. Thus:
Serum is blood plasma without fibrinogen and other clotting factors.
The serum proteins can be separated by electrophoresis.
- The most prominent of these and the one that moves closest to the positive electrode is serum albumin.
- Serum albumin
- is made in the liver
- binds many small molecules for transport through the blood
- helps maintain the osmotic pressure of the blood
- The other proteins are the various serum globulins.
- alpha globulins (e.g., the proteins that transport thyroxine and retinol [vitamin A])
- beta globulins (e.g., the iron-transporting protein transferrin)
- gamma globulins.
- Gamma globulins are the least negatively-charged serum proteins. (They are so weakly charged, in fact, that some are swept in the flow of buffer back toward the negative electrode.)
- Most antibodies are gamma globulins.
- Therefore gamma globulins become more abundant following infections or immunizations.
Blood Transfusions
PhysiologyBlood Transfusions
- Some of these units ("whole blood") were transfused directly into patients (e.g., to replace blood lost by trauma or during surgery).
- Most were further fractionated into components, including:
- RBCs. When refrigerated these can be used for up to 42 days.
- platelets. These must be stored at room temperature and thus can be saved for only 5 days.
- plasma. This can be frozen and stored for up to a year.
safety of donated blood
A variety of infectious agents can be present in blood.
- viruses (e.g., HIV-1, hepatitis B and C, HTLV, West Nile virus
- bacteria like the spirochete of syphilis
- protozoans like the agents of malaria and babesiosis
- prions (e.g., the agent of variant Crueutzfeldt-Jakob disease)
and could be transmitted to recipients. To minimize these risks,
- donors are questioned about their possible exposure to these agents;
- each unit of blood is tested for a variety of infectious agents.
Most of these tests are performed with enzyme immunoassays (EIA) and detect antibodies against the agents. blood is now also checked for the presence of the RNA of these RNA viruses:
- HIV-1
- hepatitis C
- West Nile virus
- by the so-called nucleic acid-amplification test (NAT).