A&P12 - Respiratory System

Nasal Cavity

Warms, moistens, and filters air; lined with cilia and mucus to trap particles.

Pharynx (throat)

Passageway for both air (to the larynx) and food (to the esophagus).

Larynx (voice box)

Contains vocal cords; produces sound and protects the trachea from food entry.

Trachea (windpipe)

Tube supported by cartilage rings; conducts air to bronchi; lined with cilia/mucus.

Bronchi

Two main branches from the trachea to each lung; distribute air to lungs.

Alveoli

Tiny air sacs; site of gas exchange with capillaries. One cell thick for diffusion.

Diaphragm and Ribs

Diaphragm contracts to inhale (pulls air in); ribs expand thoracic cavity.

Pleural Membranes

Surround lungs; reduce friction during breathing; attach lungs to chest wall.

Thoracic Cavity

Chamber of chest that holds lungs and heart; changes volume to allow breathing.

Fetal Circulation

Before birth, a fetus does not use its lungs to breathe. Instead, it receives oxygen and nutrients from the mother’s placenta through the umbilical cord. Because of this, the fetal circulatory system has special adaptations to bypass the lungs and liver.

Foramen Ovale (Oval Opening)

• An opening between the right and left atria of the heart.

• Allows blood to bypass the lungs by flowing directly from the right atrium to the left atrium.

• Closes after birth when lungs become functional.

Ductus Arteriosus (Arterial Duct)

• A blood vessel connecting the pulmonary artery to the aorta.

• Redirects blood away from the lungs and into the body’s main artery (aorta).

• Also closes shortly after birth.

Ductus Venosus (Venous Duct)

• A shunt that connects the umbilical vein to the inferior vena cava.

• Allows oxygenated blood from the placenta to bypass the liver and go directly to the heart.

• This is important because the liver is not fully needed for filtering in the fetus.