The zygote implants into the uterine wall during the blastocyst stage, approximately 5-6 days after fertilization.

The heart begins to beat around 4 weeks of embryonic development.

Neurulation is the stage of development where the neural tube, which will develop into the central nervous system, forms.

The first trimester is when the embryo is most susceptible to teratogens, as major organs are forming.

Implantation occurs when the blastocyst attaches to the uterine wall, typically around 6-10 days after fertilization.

The heart starts to beat around 6 weeks of gestation.

Implantation occurs during the blastocyst stage when the embryo attaches to the uterine wall.

The heart begins to beat during the embryonic stage, typically around the 6th week of gestation.

The first trimester is critical for organogenesis, where most major organs begin to form.

Exercise increases blood flow and heart rate to meet the higher oxygen demands of the body during physical activity.

Smoking increases mucus production in the respiratory system, leading to blockages and respiratory issues.

The diaphragm contracts and relaxes to change the volume of the thoracic cavity, facilitating inhalation and exhalation.

Food typically stays in the stomach for about 2 to 4 hours before moving to the small intestine.

The adult human skeleton consists of 206 bones.

The average human digestive system processes about 2000 calories per day.

A typical mammalian heart has 4 chambers: two atria and two ventricles.

The human heart has 4 chambers: two atria and two ventricles.

A human sperm cell contains 23 chromosomes.

The human digestive system produces approximately 20 different types of enzymes.

An average adult inhales about 4-6 liters of air per minute at rest.

Humans have 23 pairs of chromosomes, totaling 46.

There are approximately 5500 recognized species of mammals.

There are three stages in human labor: dilation, expulsion, and placental.

An average adult human has 32 teeth, including wisdom teeth.

There are 5 main classes of vertebrates: mammals, birds, reptiles, amphibians, and fish.

During normal breathing, approximately 500 mL of air is exhaled in a single breath.

The average adult human heart pumps about 4 to 6 liters of blood per minute at rest.

Typically, about 4% of exhaled air is carbon dioxide.

The human large intestine absorbs about 1.5 liters of water daily.

Cardiac output is calculated as heart rate multiplied by stroke volume: 75 beats/min * 70 mL/beat = 5250 mL/min or 5.25 L/min.