How do birds develop without a placenta?

Because they do not give birth to young ones directly.

Explanation:

Placenta is required by the animals who give birth to the young one because the developing embryo gets attached to the uterus lining of the mother through the placenta. This placenta helps the embryo to get nutrition from the mother's body.

Birds do not give birth to young rather they lay eggs which do need to be attached to the uterus lining. The eggs of birds contain egg yolk which provide essential nutrients to the developing embryo. Therefore as birds do not produce babies directly therefore they do not develop placenta.

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

jomady. when the body perspires due to the temperature rising, trepidation, exercise, or a disease known as hyperhidrosis, then you would lose the sodium and potassium stored in your body, also known as the na+/k+-atpase enzyme.