Essential Human Physiology: Systems and Functions

Homeostasis and Fluid Regulation

What is Homeostasis?

Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition.

Examples of Homeostatic Regulation:

• Body temperature
• Blood glucose levels
• Lactates in muscles

Physiological Response to Fluid Balance Changes

Fluid flows collectively through the nephrons in the kidney into the collecting duct system. Ultimately, waste is excreted as urine.

Consequences of Imbalance:

• Dehydration
• Kidney stones

The Circulatory System: Blood Components

• Red Blood Cells (RBCs): Carry oxygenated blood from the lungs to the body's organs and muscles.
• White Blood Cells (WBCs): Defend the body's immune system against infection by germs.
• Platelets: Help the blood clot in case of a cut, etc.
• Blood Plasma: Regulates the blood's pH level at approximately 7.4.

Heart Chambers and Valves

The heart contains four chambers and four main valves:

Chambers:

• Ventricles (Left and Right)
• Atria (Left and Right)

Valves:

• Tricuspid valve
• Pulmonic valve
• Mitral valve
• Aortic valve

Blood Vessel Roles and Functions

• Arteries: Generally carry oxygenated blood from the heart to the body.
• Veins: Carry deoxygenated blood back to the heart.

Specific Vessel Functions:

• Coronary Arteries: Supply oxygenated and nutrient-filled blood directly to the heart muscle.
• Pulmonary Vein: Carries oxygenated blood from the lungs to the left atrium.
• Aorta: Distributes oxygen-rich blood to all systemic arteries.
• Hepatic Vein: Drains deoxygenated blood from the liver into the inferior vena cava.
• Carotid Arteries: Supply blood to the head, neck, and brain.

Cardiovascular Physiology: Resting Values

Typical resting values for healthy adults:

• Cardiac Output: 4–6 Liters per minute (L/min)
• Heart Rate (HR): 60–100 beats per minute (bpm)
• Blood Pressure (BP): 120/80 mmHg (Normal) – 140/90 mmHg (Upper limit)

Key Cardiovascular Pathologies

• Thrombosis: A blood clot inside a blood vessel, stopping blood flow through the circulatory system.
• Embolism: Blood flow in an artery is blocked by a foreign body, such as a clot or an air bubble.
• Aneurysm: A balloon-like bulge in an artery wall.
• Angina: Pain originating from the heart, caused by the narrowing of coronary arteries.
• Heart Attack (Myocardial Infarction): Blood supply to the heart muscle is suddenly stopped, usually by a blood clot.

Electrocardiogram (ECG) Wave Components

• P-wave: Deflection wave representing atrial depolarization.
• R-wave: Represents atrial repolarization.
• T-wave: Represents the returning of the muscle to its resting state (ventricular repolarization).

The Digestive System: Processes and Enzymes

The Alveolar-Capillary Membrane

This membrane is thin and extremely strong. In the lungs, it prevents air bubbles from forming in the blood and prevents blood from entering the alveoli.

Digestive Enzymes and Bile

• Amylases: Break down carbohydrates.
• Proteases: Break down proteins.
• Lipases: Break down lipids (fats).
• Bile: Digests fatty food by emulsifying the fat.

Key Digestive Processes

Peristalsis: The contraction and relaxation of muscles in the digestive system which moves food along the tract.

Digestive Organs and Blood Flow

• Stomach: Smooth muscles help move food along. It breaks down food using various chemicals (acids and enzymes).
• Small Intestine: Contains digestive enzymes bound to the membranes of the epithelial cells, facilitating nutrient absorption.
• Hepatic Portal Vein: Carries blood containing digested food, such as glucose, from the small intestine directly to the liver for processing.