Human Body Systems: Respiratory and Circulatory Functions

Introduction to Basic Life Functions

Humans perform basic life functions, and nutrition is the most important one. The systems involved are: digestive, excretory, respiratory, and circulatory systems.

1. Respiratory System

The respiratory system exchanges gases between the atmosphere and the blood. It allows O₂ to enter the body and CO₂ to leave. This is vital because it allows the main energy-producing processes in cells to happen (energy: ATP). This system is involuntary and responds to changes in blood gases.

Upper Airways

Air enters through the nostrils into the nasal cavity. The paranasal sinuses are connected to the nasal passages. Then, the air passes through the pharynx and then the larynx. Afterward, the air moves to the trachea, which divides into two main bronchi, one for each lung. These bronchi branch into bronchioles, ending in the alveoli.

Structures of the Respiratory System

• Pleura: The lungs are surrounded by pleura that reduces friction.
• Diaphragm: Located below the lungs, it separates the thoracic and abdominal cavities. When it contracts, air flows in; when it relaxes, air flows out.
• Nasal Cavity: Air flows in through the nostrils. The epithelium with mucus and cilia traps and removes dust and microbes, protecting deeper tissues.
• Paranasal Sinuses: These cavities increase the surface area to moisten and warm incoming air, and serve as resonance chambers for the voice.
• Pharynx: A shared passage for air and food.
• Larynx: Contains vocal folds that vibrate to produce sound.
• Trachea: A tube supported by C-shaped cartilage rings to prevent collapse. Cartilage is a flexible connective tissue that keeps the trachea from collapsing while breathing. It is lined with ciliated epithelium and mucus that move particles upward.
• Bronchi and Bronchioles: The trachea divides into two bronchi, which then branch into bronchioles that carry air into the lungs.
• Alveoli: Sacs of simple squamous epithelium that enable gas exchange, surrounded by capillaries for close air-blood contact.
• Lungs: Elastic organs made of millions of alveoli connected by connective tissue. The right lung has 3 lobes, the left lung has 2 lobes, and both are covered by the pleura.
• Diaphragm: A dome-shaped muscle that contracts to draw air in and relaxes to push air out. It is controlled by the brainstem.

Physiology of Respiration

The function of the respiratory system is gas exchange in the alveoli. Through diffusion, O₂ moves into the blood and CO₂ moves out. Efficiency depends on surface area. Alveolar walls are thin, moist, and closely connected to capillaries. O₂ binds to hemoglobin in red blood cells, and CO₂ is released through exhalation. This ensures a constant oxygen supply.

Pathology of the Respiratory System

The system is constantly exposed to the external environment, so it is vulnerable to infection. The respiratory tract can be infected by viruses. In most diseases, the alveoli fill with fluid, reducing surface area.

• Asthma: A chronic inflammatory disease in which the bronchi narrow temporarily due to allergens or pollutants. Medications used include bronchodilators.
• Pneumothorax: Occurs when air leaks into the pleural cavity, causing the lung to collapse.
• Lung Cancer: Uncontrolled cell division in lung cells.

2. Circulatory System

The cardiovascular system delivers and collects materials throughout the body. It carries O₂, nutrients, and hormones while removing waste products.

Heart

The heart is a muscular organ divided into four chambers: the right atrium and right ventricle handle deoxygenated blood, and the left atrium and left ventricle handle oxygenated blood. The septum is a wall separating both sides. The pacemaker makes the heart pump. The myocardium is a dense muscular tissue responsible for contraction. Connective tissue provides strength and elasticity to the valves. If blood vessels are blocked, O₂ supply to the heart stops, leading to a heart attack.

Blood Vessels

• Arteries: Thick, muscular, and elastic walls due to high pressure.
• Veins: Thin walls with valves that stop blood from flowing backward.
• Capillaries: Extremely thin, ideal for diffusion.

Circulation and Regulation

The circulatory system is a double circulation in which blood passes through the heart twice.

• Pulmonary Circulation (right side): Transports blood to the lungs at low pressure.
• Systemic Circulation: Transports oxygenated blood to the body at high pressure.

Tachycardia refers to a fast heart rate, and bradycardia refers to a slow heart rate.

Components of Blood

Blood is a connective tissue composed of plasma. Red blood cells transport O₂ through hemoglobin. White blood cells defend against infections. Platelets clot wounds. Plasma carries materials throughout the body.

Blood Types

• Group A: Has A antibodies and A antigens.
• Group B: Has B antibodies and B antigens.
• Group AB: Has no antibodies and both A and B antigens.
• Group O: Has both antibodies and no antigens.

If a person has the D antigen, their blood is Rh-positive. Without the D antigen, their blood is Rh-negative.