Lumen a. vessel that empties into the right atrium
O b. fibrous sac around the heart
O c. structure that keeps fluid moving forward
O d. central opening of a vessel
O e. lower, pointed region of the heart

Lumen corresponds to the central opening of a vessel (option d).

Explanation:

From the biological point of view, lumen is the internal space of any structure or tubular organ, whose purpose is the conduction of substances through it.

In the case of blood vessels, the lumen is a central space covered by a simple epithelium, called the endothelium, which ensures the passage of blood in a fluid form.

The other options do not correspond to the

    a. Vessel that empties into the right atrium is the vena cava

    b. Fibrous sac around the heart is the pericardium.

    c. Structure that keeps fluid moving forward, it is a blood vessel.

    e. Lower, pointed region of the heart, corresponds to the cardiac apex.

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explanation:

these are common warning signs of overtraining syndrome:

washed-out feeling, tired, drained, lack of energy

mild leg soreness, general aches, and pains

pain in muscles and joints

sudden drop in performance

insomnia

headaches

decreased immunity (increased number of colds, and sore throats)

decrease in training capacity/intensity

moodiness and irritability

depression

loss of enthusiasm for the sport

decreased appetite

increased incidence of injuries.

a compulsive need to exercise