TEAS Science: The Cardiovascular and Respiratory Systems — A Complete Review

If there are two body systems you absolutely must master before taking the ATI TEAS, they are the cardiovascular and respiratory systems. Together, these topics account for a significant portion of the Human Anatomy and Physiology questions on the Science section — and they are deeply interconnected.

This guide covers everything you need to know: the structure and function of the heart, blood vessel types, the cardiac cycle, the anatomy of the respiratory tract, gas exchange at the alveolar level, and the mechanics of breathing. By the end, you will be ready to tackle any TEAS question on these two systems.

Part 1: The Cardiovascular System

The Heart: Structure and Chambers

The heart is a muscular organ roughly the size of a fist, located in the mediastinum (the central compartment of the thoracic cavity). It is divided into four chambers that work in coordinated pairs.

• Right atrium: Receives deoxygenated blood from the body via the superior and inferior vena cava.
• Right ventricle: Pumps deoxygenated blood to the lungs via the pulmonary arteries.
• Left atrium: Receives oxygenated blood from the lungs via the pulmonary veins.
• Left ventricle: Pumps oxygenated blood to the entire body via the aorta. It has the thickest wall because it must generate the most pressure.

Heart Valves

Valves ensure blood flows in one direction only. There are four valves:

• Tricuspid valve: Between right atrium and right ventricle (3 flaps).
• Pulmonary (semilunar) valve: Between right ventricle and pulmonary artery.
• Bicuspid (mitral) valve: Between left atrium and left ventricle (2 flaps).
• Aortic (semilunar) valve: Between left ventricle and aorta.

The Cardiac Cycle

The cardiac cycle is one complete heartbeat, consisting of two main phases:

• Systole (contraction): The ventricles contract, pushing blood out — to the lungs (right ventricle) and to the body (left ventricle). AV valves close (producing the first heart sound, 'lub').
• Diastole (relaxation): The ventricles relax and fill with blood from the atria. Semilunar valves close (producing the second heart sound, 'dub').

The heart's electrical conduction system controls the cardiac cycle automatically. The sequence is: SA node (pacemaker) → AV node → Bundle of His → Purkinje fibers. The SA node generates electrical impulses that cause the atria to contract first, followed by the ventricles.

Blood Vessels: Arteries, Veins, and Capillaries

• Arteries: Carry blood away from the heart. They have thick, muscular walls to withstand high pressure. The largest artery is the aorta.
• Arterioles: Small arteries that regulate blood flow into capillary beds.
• Capillaries: The smallest blood vessels, only one cell thick. This is where gas exchange, nutrient delivery, and waste removal occur between blood and tissues.
• Venules: Small veins that collect blood from capillary beds.
• Veins: Carry blood toward the heart. They have thinner walls and contain valves to prevent backflow. The largest veins are the superior and inferior vena cava.

Blood Pressure and Circulation

Blood pressure is the force of blood against artery walls. It is measured as systolic (during contraction) over diastolic (during relaxation). Normal adult blood pressure is approximately 120/80 mmHg.

• Systolic pressure: The higher number; measures pressure when the heart contracts.
• Diastolic pressure: The lower number; measures pressure when the heart relaxes.
• Hypertension: Chronically elevated blood pressure (≥130/80 mmHg in current guidelines).
• Hypotension: Abnormally low blood pressure (<90/60 mmHg).

Pulmonary vs. Systemic Circulation

• Pulmonary circulation: Right ventricle → pulmonary arteries → lungs (gas exchange) → pulmonary veins → left atrium. Key point: pulmonary arteries carry deoxygenated blood; pulmonary veins carry oxygenated blood.
• Systemic circulation: Left ventricle → aorta → body tissues (delivers O₂, picks up CO₂) → vena cava → right atrium.

Part 2: The Respiratory System

Anatomy of the Respiratory Tract

The respiratory system is divided into the upper and lower respiratory tracts:

• Upper respiratory tract: Nose/nasal cavity (filters, warms, humidifies air) → pharynx (throat) → larynx (voice box, contains the epiglottis that prevents food from entering the trachea).
• Lower respiratory tract: Trachea (windpipe, supported by C-shaped cartilage rings) → bronchi (two main branches entering each lung) → bronchioles (smaller branches) → alveoli (tiny air sacs where gas exchange occurs).

The Alveoli and Gas Exchange

The alveoli are the functional units of the lungs. There are approximately 300 million alveoli in adult lungs, providing an enormous surface area (about 70 m²) for gas exchange.

• Each alveolus is surrounded by a dense network of capillaries.
• Gas exchange occurs by simple diffusion across the respiratory membrane (alveolar wall + capillary wall).
• Oxygen (O₂) diffuses from alveoli (high concentration) into the blood (low concentration).
• Carbon dioxide (CO₂) diffuses from the blood (high concentration) into alveoli (low concentration) to be exhaled.
• Surfactant, a substance produced by type II alveolar cells, reduces surface tension and prevents alveoli from collapsing.

Mechanics of Breathing: Inhalation and Exhalation

Breathing is a mechanical process controlled by the diaphragm and intercostal muscles. It follows Boyle's Law: as volume increases, pressure decreases (and vice versa).

• Inhalation (inspiration): The diaphragm contracts and flattens; intercostal muscles contract and lift the rib cage outward. This increases the volume of the thoracic cavity, decreasing internal pressure below atmospheric pressure. Air rushes in.
• Exhalation (expiration): The diaphragm relaxes and domes upward; intercostal muscles relax and the rib cage moves inward. This decreases thoracic volume, increasing internal pressure above atmospheric pressure. Air is pushed out.
• Normal exhalation is a passive process (muscles relax). Forced exhalation (e.g., coughing, blowing) is active and uses abdominal muscles.

Oxygen and Carbon Dioxide Transport in the Blood

• Oxygen transport: About 98.5% of O₂ is carried bound to hemoglobin (a protein in red blood cells), forming oxyhemoglobin. The remaining 1.5% is dissolved directly in plasma.
• Carbon dioxide transport: CO₂ is carried in three ways — about 70% as bicarbonate ions (HCO₃⁻) in plasma, about 23% bound to hemoglobin (carbaminohemoglobin), and about 7% dissolved in plasma.
• The enzyme carbonic anhydrase (in red blood cells) catalyzes the conversion of CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃⁻.

How the Cardiovascular and Respiratory Systems Work Together

These two systems are inseparable partners. The respiratory system brings oxygen into the body and removes carbon dioxide; the cardiovascular system transports these gases to and from every cell. Here is the complete cycle:

• 1. Air enters the lungs through inhalation and reaches the alveoli.
• 2. O₂ diffuses from alveoli into pulmonary capillaries and binds to hemoglobin.
• 3. Oxygenated blood travels via pulmonary veins to the left atrium, then left ventricle, then out through the aorta.
• 4. Systemic arteries deliver oxygenated blood to tissues throughout the body.
• 5. At tissue capillaries, O₂ is released to cells, and CO₂ (a metabolic waste product) enters the blood.
• 6. Deoxygenated blood returns via veins to the right atrium, then right ventricle.
• 7. The right ventricle pumps blood to the lungs, where CO₂ is released into alveoli and exhaled.
• 8. The cycle repeats with each heartbeat and breath.

High-Yield TEAS Questions on These Systems

Based on the TEAS exam blueprint, expect questions like these:

• "Which chamber of the heart pumps oxygenated blood to the body?" → Left ventricle.
• "What is the function of the pulmonary veins?" → Carry oxygenated blood from the lungs to the left atrium.
• "Where does gas exchange occur in the respiratory system?" → Alveoli.
• "What muscle is primarily responsible for inhalation?" → Diaphragm.
• "How is the majority of CO₂ transported in the blood?" → As bicarbonate ions (HCO₃⁻).
• "What prevents blood from flowing backward in veins?" → Valves.
• "Which part of the heart's conduction system is the natural pacemaker?" → SA (sinoatrial) node.

Key Takeaways

• The heart has 4 chambers: RA, RV, LA, LV. Blood flows RA → RV → Lungs → LA → LV → Body.
• Arteries carry blood away from the heart; veins carry blood toward the heart. Capillaries are the site of gas exchange.
• Pulmonary arteries carry deoxygenated blood; pulmonary veins carry oxygenated blood.
• The SA node is the heart's natural pacemaker. The conduction pathway is SA node → AV node → Bundle of His → Purkinje fibers.
• The respiratory tract goes: Nose → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli.
• Gas exchange occurs at the alveoli via diffusion: O₂ into blood, CO₂ out of blood.
• Inhalation is active (diaphragm contracts); normal exhalation is passive (diaphragm relaxes).
• Most O₂ is carried by hemoglobin; most CO₂ is transported as bicarbonate ions.

Understanding how the cardiovascular and respiratory systems function individually — and how they work together — is essential for the TEAS Science section. Focus on the flow of blood through the heart, the mechanics of breathing, and the process of gas exchange. These concepts appear repeatedly on the exam and are highly predictable.