14. Human Physiology

22 lessons

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prerequisite

Prior Knowledge Check

Essential concepts you should know before starting

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Before You Start: Do You Know These?

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concept

Introduction to Breathing

Understanding why organisms need respiration

Why Do We Breathe?

Your cells are like tiny factories. They need fuel to work.

The Energy Problem

Cells break down glucose to get energy. This process needs oxygen $(\text{O}_2)$ . But there's a problem - it creates a harmful waste called carbon dioxide $(\text{CO}_2)$ .

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vocabulary

English Vocabulary

Important words to understand this chapter

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terms

Biology Terms

Key respiratory system terminology

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images

Respiratory System Anatomy

Visual guide to respiratory structures

Complete human respiratory system showing nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, lungs, and diaphragm in sectional view

Click to zoom

Notice how the airways branch like a tree. Air travels from the single trachea to millions of alveoli.

Detailed cross-section of human lungs showing branching bronchi, bronchioles, alveolar sacs, pleural membranes and heart position

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See the branching network? The bronchi divide into smaller and smaller tubes. The pleural membranes wrap around each lung.

Magnified view of alveoli cluster with capillary network showing thin walls for gas exchange

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These tiny sacs are wrapped in blood vessels. The walls are so thin that oxygen and CO₂ can pass through easily.

Single alveolus cross-section showing squamous epithelium, basement membrane, capillary endothelium and red blood cells

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Three layers separate air from blood: (1) Alveolar wall (one cell thick), (2) Basement membrane (very thin), (3) Capillary wall (one cell thick). Total thickness: Less than 1 millimeter!

Larynx structure showing epiglottis in open position during breathing and closed position during swallowing

Click to zoom

During breathing: Epiglottis is open, air flows to trachea. During swallowing: Epiglottis closes, food goes to esophagus.

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anatomy

Human Respiratory System

Structure and organization of respiratory organs

The Human Respiratory System

The Journey of Air

Let's follow the path air takes through your body:

1. Entry Point: Nostrils

Air enters through your nose. The nostrils lead to the nasal chamber.

What happens here:

Hair filters out dust
Mucus traps germs
Air gets warmed
Air becomes moist

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physiology

Mechanism of Breathing

How inspiration and expiration work

How Do We Breathe?

The Basic Principle

Breathing works on a simple rule:

Air moves from HIGH pressure to LOW pressure

Your body creates pressure differences to move air in and out.

Two Stages of Breathing

Stage 1: Inspiration (Breathing IN)

Goal: Make pressure inside lungs LESS than outside air

Stage 2: Expiration (Breathing OUT)

Goal: Make pressure inside lungs MORE than outside air

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concept

Introduction to Breathing

Understanding why organisms need respiration

Why Do We Breathe?

Your cells are like tiny factories. They need fuel to work.

The Energy Problem

Cells break down glucose to get energy. This process needs oxygen $(\text{O}_2)$ . But there's a problem - it creates a harmful waste called carbon dioxide $(\text{CO}_2)$ .

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