A student drew a sketch to show the formation of tissue fluid.
Which label is correct?
▶️ Answer/Explanation
Ans: C
At the venous end of capillaries, tissue fluid has higher water potential (more water, fewer proteins) than blood plasma. This osmotic gradient causes water to move back into capillaries. Red blood cells (B) don’t leave capillaries, and blood pressure decreases (A is wrong) as blood flows through capillaries.
The pumping action of the heart creates hydrostatic pressure in the blood. The table shows the hydrostatic pressure in a blood capillary.
About 90% of the tissue fluid which surrounds a capillary is returned to the blood at the venule end.
How is this achieved?
▶️ Answer/Explanation
Ans: D
At the venule end, lower hydrostatic pressure allows plasma proteins to create osmotic pressure, pulling water back into capillaries. Other options are incorrect: permeability is similar (A), tissue fluid pressure is lower (B), and blood has more solutes (C).
One type of congenital heart defect is where the left and right atria are not completely separated. This is called an atrial septal defect (ASD).
ASD usually results in blood moving from the left atrium into the right atrium. This causes increased blood pressure in the right atrium and decreased blood pressure in the left atrium.
Which row describes other effects caused by ASD?
▶️ Answer/Explanation
Ans: D
In atrial septal defect (ASD), oxygenated blood from the left atrium leaks into the right atrium, causing:
- Increased pulmonary blood flow (right atrium pumps extra blood to the lungs).
- Reduced systemic circulation efficiency (less oxygenated blood reaches the body).
- Right ventricular hypertrophy (due to increased workload).
These effects match row D, where pulmonary circulation increases while systemic circulation decreases.
An irregular heartbeat may be the result of ineffective electrical stimulation of the atria. Which area of the heart could be damaged, causing this irregular heartbeat?
▶️ Answer/Explanation
Ans: D
The sinoatrial (SA) node is the natural pacemaker of the heart, initiating electrical impulses that stimulate atrial contraction. If damaged, it can lead to irregular heartbeats (arrhythmias) due to improper signaling. The atrioventricular (AV) node (A) and Purkyne tissue (C) are involved in later conduction steps, while the septum (B) is structural and unrelated to electrical stimulation. Thus, the correct answer is D.