Physiology on emsenn.net

Fri, 06 Mar 2026 00:00:00 +0000

¶What you will be able to do

Describe the six major organ systems covered in this module (nervous, cardiovascular, respiratory, musculoskeletal, digestive, immune) in terms of their primary functions and their contributions to homeostasis.
Explain how the body is organized hierarchically (cell → tissue → organ → organ system) and why each level of organization produces emergent properties that the level below cannot accomplish alone.
Define homeostasis as the body’s self-organizing principle and identify how specific organ systems maintain it (e.g., respiratory system maintaining blood pH through CO2 regulation, cardiovascular system maintaining tissue oxygenation through cardiac output).
Trace how dysfunction in one organ system propagates to others — given a primary disruption (chronic stress, respiratory failure, gut dysfunction), identify secondary effects across at least two other systems.
Connect biomedical organ-system descriptions to alternative frameworks: TCM’s Zang-Fu functional systems, somatic awareness of the musculoskeletal-nervous system interface, and the biopsychosocial model’s integration of biological processes with psychological and social factors.
Explain why “the body is a machine” is misleading and why “self-organizing system” is a more accurate frame for understanding health, disease, and treatment.

¶Prerequisites

No formal prerequisites. The introductory curriculum provides the conceptual foundation.
Familiarity with the foundational terms (cell, tissue, organ, neuron, receptor, homeostasis, inflammation) is helpful and can be acquired through the human body module’s term files.

¶Reference documents

Introduction to the Human Body — the introductory lesson
The Nervous System — neural integration and autonomic regulation
The Cardiovascular System — transport and circulation
The Respiratory System — gas exchange
The Musculoskeletal System — structure and movement
The Digestive System — nutrition, immunity, and the gut-brain axis
The Immune System — defense and inflammation
Zang-Fu (Organ-Function Systems) — TCM’s functional alternative to anatomical organ systems

¶Scope

This skill covers conceptual understanding of organ system integration. It does not cover:

Cell

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The cell is the basic structural and functional unit of all living organisms. Every process in the human body — movement, sensation, thought, digestion, immunity, reproduction — is performed by cells or depends on what cells produce.

¶Structure

A human cell has three essential components:

The cell membrane — a thin, flexible barrier made of a phospholipid bilayer (two layers of fat molecules) with embedded proteins. The membrane separates the cell’s interior from its environment and controls what enters and exits. It is selectively permeable: small, uncharged molecules (oxygen, carbon dioxide) pass through freely; larger or charged molecules (glucose, sodium ions, drugs) require transport proteins to cross. This membrane is why lipophilic drugs (which dissolve in fat) cross cell membranes easily while hydrophilic drugs (which dissolve in water) do not — a distinction that drives much of pharmacokinetics.

Homeostasis

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Homeostasis is the maintenance of stable internal conditions in a living organism despite changes in the external environment. Body temperature stays near 37°C whether the air is 0°C or 40°C. Blood pH stays between 7.35 and 7.45 regardless of what you eat. Blood glucose stays within a narrow range between meals. These are not passive equilibria — they are actively maintained by physiological control systems that detect deviations and correct them.

Inflammation

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Inflammation is the body’s response to tissue damage or infection — a coordinated cascade of vascular, immune, and chemical events that clears damaged cells, fights pathogens, and initiates repair. It is not a disease. It is a defense mechanism. But when inflammation persists beyond its protective function or occurs inappropriately, it becomes a driver of disease — including chronic pain.

¶The acute inflammatory response

When tissue is damaged, the injured cells and resident immune cells release chemical signals — inflammatory mediators — that orchestrate the response:

Introduction to the Human Body

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¶A system, not a machine

The human body is routinely compared to a machine — a collection of parts, each with a function, assembled into a working whole. This metaphor is useful for introducing anatomy: the heart pumps, the lungs oxygenate, the kidneys filter. But the metaphor breaks at every point that matters clinically.

A machine does not repair itself. A machine does not adapt to its environment. A machine does not change its structure in response to the demands placed on it. A machine does not produce its own components or regulate its own operating conditions. The human body does all of these things, constantly, without conscious direction. The better frame is not “machine” but self-organizing system — a system that maintains its own conditions of operation through continuous feedback and adjustment.

Organ

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An organ is a structure composed of two or more tissue types working together to perform a specific function. The heart is an organ: cardiac muscle tissue pumps blood, connective tissue provides structural support, epithelial tissue lines the chambers, and nervous tissue regulates the rhythm. No single tissue type could accomplish what the heart does — the organ is the functional unit.

¶Organ systems

Organs are grouped into systems that carry out major physiological functions:

Receptor

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A receptor is a protein — usually embedded in a cell membrane or located inside a cell — that detects a specific chemical signal and initiates a cellular response. Receptors are the molecular targets through which neurotransmitters, hormones, and most drugs produce their effects. They are the locks to which signaling molecules are the keys.

¶How receptors work

A receptor has a binding site — a region whose three-dimensional shape is complementary to the shape of its specific signaling molecule (called its ligand). When the ligand binds, the receptor changes shape (a conformational change), which triggers a cascade of events inside the cell. This might mean opening an ion channel, activating an enzyme, or initiating a gene expression program.

The Cardiovascular System

Fri, 06 Mar 2026 00:00:00 +0000

The cardiovascular system circulates blood throughout the body, delivering oxygen and nutrients to tissues and removing carbon dioxide and metabolic waste. It consists of the heart (the pump), the blood vessels (the network), and the blood (the medium). Airway management exists because the cardiovascular system’s capacity to deliver oxygen depends on the respiratory system’s capacity to acquire it — and both fail together when either fails alone.

¶The heart

The heart is a muscular organ roughly the size of a fist, located in the center of the chest. It has four chambers:

The Digestive System

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The digestive system breaks food into molecules small enough to cross cell membranes — and then absorbs those molecules into the blood for distribution to the body’s cells. It is a long tube (approximately 9 meters from mouth to anus) with specialized regions, each performing a distinct function in the sequence of digestion, absorption, and elimination.

¶Anatomy

Mouth — mechanical digestion begins here. Teeth break food into smaller pieces (increasing surface area for enzymes). Salivary glands produce saliva containing amylase, which begins starch digestion. The tongue forms the chewed food into a bolus and pushes it into the pharynx.

The Immune System

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The immune system defends the body against pathogens (bacteria, viruses, fungi, parasites), eliminates damaged or abnormal cells, and monitors the body’s own tissues for signs of malignancy. It is not located in a single organ — it is distributed throughout the body in the blood, lymph, and specialized tissues.

¶Innate immunity

The innate immune system provides immediate, non-specific defense — it responds the same way to any threat, without memory of previous encounters.

The Musculoskeletal System

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The musculoskeletal system provides structural support, enables movement, and protects internal organs. It consists of bones (the skeleton), skeletal muscles (the motors), and the connective tissues that link them (tendons, ligaments, cartilage, fascia). This is the organ system that somatics works with most directly — and the system whose dysfunction produces a significant proportion of chronic pain.

¶Bones

The human skeleton contains 206 bones. Bones provide:

Structural support — the rigid framework that holds the body upright against gravity
Protection — the skull protects the brain, the ribcage protects the heart and lungs, the vertebral column protects the spinal cord
Movement — bones serve as levers that muscles pull on to produce movement
Mineral storage — bones store calcium and phosphorus, releasing them into the blood as needed
Blood cell production — red bone marrow (inside certain bones) produces red blood cells, white blood cells, and platelets

Bones meet at joints — the points of articulation that determine the range and type of movement possible. Joint types include hinge joints (elbow, knee), ball-and-socket joints (hip, shoulder), pivot joints (atlas-axis at the top of the spine), and gliding joints (wrist, ankle). The range of motion at a joint is determined by the bone shapes, the ligaments (connective tissue bands connecting bone to bone), and the tone of the muscles crossing the joint.

The Respiratory System

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The respiratory system moves air between the environment and the lungs, where oxygen is transferred to the blood and carbon dioxide is removed. It is the organ system that the entire airway fundamentals topic describes and manages.

¶Anatomy

The respiratory system is divided into upper and lower airways:

Upper airway — from the nose and mouth to the larynx:

Nasal cavity — filters, warms, and humidifies inspired air. Air passing through the nose is cleaner and warmer than air entering through the mouth.
Pharynx — the shared passage for air and food; divided into nasopharynx (behind the nose), oropharynx (behind the mouth), and hypopharynx (above the larynx). The pharynx is collapsible — loss of muscle tone during unconsciousness or sedation can cause the tongue and soft tissues to obstruct the airway, which is why airway positioning (head tilt, jaw thrust) is the first intervention in airway management.
Larynx — contains the vocal cords. The larynx protects the lower airway from aspiration (food and liquid entering the trachea) by closing the epiglottis during swallowing. The vocal cords are the anatomical landmark that distinguishes upper from lower airway — and the landmark that a supraglottic airway sits above while an endotracheal tube passes through.

Lower airway — from the trachea to the alveoli:

Tissue

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A tissue is a group of similar cells organized to perform a shared function. Tissues are the level of organization between individual cells and organs — cells assemble into tissues, tissues assemble into organs, organs assemble into organ systems.

The human body has four fundamental tissue types:

¶Epithelial tissue

Lines surfaces and forms barriers. The skin’s outer layer (epidermis), the lining of the airways, the lining of the gut, the lining of blood vessels — all are epithelial tissue. Epithelial tissue controls what crosses from one compartment to another: nutrients from the gut lumen into the blood, oxygen from the alveoli into the capillaries, drugs from the intestinal wall into the portal circulation. The epithelial barrier of the intestinal wall is what determines oral bioavailability.

Airway Anatomy and Physiology Basics

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¶Core anatomical map

The airway is commonly divided into upper and lower segments.

Upper airway: nose, oral cavity, pharynx, and larynx.
Lower airway: trachea, bronchi, bronchioles, and alveolar pathways.

Clinically, this split matters because upper-airway processes (for example swelling, soft-tissue collapse, or supraglottic obstruction) often present and respond differently than lower-airway processes (for example bronchospasm).

¶Four bedside functions

Patency: can air move through the airway without critical obstruction?
Oxygenation: can oxygen reach blood across the lungs?
Ventilation: can carbon dioxide be eliminated?
Protection: can the airway limit aspiration and maintain reflex protection?

Loss of any one of these functions can destabilize a patient, even if the others are temporarily preserved.