Browsing Pathways

Kidneys are regulatory organs involved in removing wastes from the blood, hormone production, nutrient reabsorption, and regulating electrolyte concentrations, acid-base balance, extracellular fluid volume, and blood pressure. The early proximal tubule is where glucose, amino acids, sodium, chlorine, phosphate, bicarbonate, and water are reabsorbed. Only water is reabsorbed in the thin descending loop of Henle, while sodium, chlorine and potassium are reabsorbed in the thick ascending loop of Henle. Sodium and chlorine are also reabsorbed in the early distal convoluted tubule. Finally, sodium and water are reabsorbed in the collecting tubules. Blood pressure is regulated by the hormones angiotensin II and aldosterone, which increases sodium chloride reabsorption. This results in an expansion of the extracellular fluid compartment, thus increasing blood pressure.

The Wiggers diagram is a tool used to teach cardiovascular physiology which typically includes pressure and volume changes during ventricular contractions (cardiac cycle). At the end of diastole (relaxation phase), the mitral valve closes and the left atrium contracts. When the left ventricular pressure exceeds aortic pressure, the aortic valve opens (systole), hits a peak and decreases as the volume in the left ventricle decreases. The aortic valve closes and slightly increases the pressure in the aorta (incisura). When the left ventricular pressure is below the left atrial pressure, the mitral valve opens and the left ventricle can begin filling with blood in order to repeat the process.

The primary function of erythrocytes (red blood cells) is to exchange oxygen and carbon dioxide through tiny blood vessels called capillaries. In the lungs, oxygen diffuses into the blood, hemoglobin molecules release carbon dioxide picked up from body tissues. This allows oxygen to attach to the hemoglobin molecules and it can be carried to the rest of the body. Hemoglobin is a protein that makes blood red and carries oxygen throughout the circulation. The adult form of hemoglobin contains 2 alpha chains and 2 beta chains. When CO2 is removed from tissues, a portion of it is dissolved in the plasma and converted to bicarbonate. A majority of the CO2 is taken up by the RBCs and follows one of three transport pathways. 1. The CO2 is dissolved into the RBC cytoplasm. 2. CO2 is converted, by carbonic anhydrase, into bicarbonate which is exchanged at the cell membrane for a chloride ion (involved in the Chloride shift). This bicarbonate removal increases CO2 uptake into the cell. 3. CO2 is carried by carbaminohemoglobin which can be transported to the lung for removal. After offloading of oxygen into tissues, hemoglobin has an increased affinity for carbon dioxide and hydrogen ions (Haldane effect).