The $pH$ of blood in an artery and a vein is:

Which of the following figures correctly represents the path of a closed circulatory system?

Differentiate between closed circulatory system and open circulatory system.

Which of the following are the pulse points of the lower limb?
$I$. Brachial $\quad$ $II$. Radial
$III$. Posterior tibial $\quad$ $IV$. Dorsalis pedis
$V$. Femoral $\quad$ $VI$. Popliteal
Select the correct option.

The given figure shows a schematic plan of blood circulation in humans with labels $A$ to $D$. Identify the label and give its functions.

$A$: Elevated levels of $Na^+$ decrease the heart rate and contractility.
$R$: Elevated $Na^+$ levels increase the excitability of the $SA$ node.