Human physiology

The major site of reabsorption of bicarbonate ions is the proximal tubule.

When hydrogen ions are secreted by the tubules, they can combine with NH₃ to form NH₄⁺ and excreted as NH₄⁺.

Calcium is the major divalent cation in the body. But most of this calcium is present in bone. Sodium is the major cation in extracellular fluid. In extracellular fluid, the concentration of sodium is around 135-145mMol/l whereas the concentration of calcium is around 2.25mM, of which about half is protein bound.

Erythropoietin is a glycoprotein hormone consisting a single polypeptide of 166 amino acids. It binds to receptors on early red blood cell precursors and promotes their progression to form red blood cells.

Voluntary phase, starts with the jaws and lips closed, and the tongue tip on the alveolar ridge. Thus, the tongue participates in this phase of swallowing.

Lipid soluble drugs and other lipid soluble substances are able to diffuse across the lipid plasma membrane of cells without special transporter molecules.

After 24 weeks, the fundal height increases by about 1cm/week.
The head usually engages after 37 weeks in a nulliparous woman but is frequently not engaged before labour in multiparous women. Breech presentation is common before 34 weeks and is only of significance if the woman is in (preterm) labour.

There is no secretion of phosphate and is reabsorbed along the nephron. There is a limit to the amount of phosphate that can be absorbed and if this limit exceeds, the excess phosphate remains in the tubular fluid and is excreted in the urine.

As erythropoietin is a protein, it cannot be given orally as it will be digested in the gut. It is usually given subcutaneously, or less commonly intravenously.

There are osmoreceptors in the hypothalamus, which detect an increase in plasma osmolality. In response to input from these receptors and other stimuli, cells in the posterior pituitary gland release ADH.

Women often experience mood swings during early pregnancy because of the changing levels of hormones in their bodies. Mood swings tend to be most noticeable in the first 12 weeks of pregnancy.

If there is vasoconstriction of the efferent arteriole, the pressure upstream the constriction in the glomerulus is increased and so more filtration occurs.

Non-steroidal anti-inflammatory drugs block prostaglandin synthesis and so remove this tonic dilatation. The result is renal vasoconstriction.
Prostaglandins are powerful vasodilators and there is a normal tonic level of vasodilation in the renal blood vessels, which is caused by prostaglandins.

As the swallowing reflex is initiated, the velopharyngeal closes to prevent reflux of material into the posterior choana.

Proprioceptive loss (Romberg's sign, loss of balance in the dark) could be due to a peripheral neuropathy or a disease of the dorsal columns of the spinal cord. However, the presence of increased tone in the lower limbs suggests that the spinal cord is the site of disease here.