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Functional Organization of the Human Body and Control of the 'Internal Environment'

Learning Objectives

• Compare intracellular and extracellular fluid.

• Define homeostasis.

• Describe the regulation systems in the body.

• Describe the process of negative and positive feedback using simple examples.

Glossary of Terms

• Homeostasis: Maintenance of near-constant conditions in the internal environment.

• Negative feedback: Feedback that reduces system output (e.g., high hormone levels reducing further secretion).

• Positive feedback: Feedback that increases system output (e.g., bleeding causing increased clotting factors).

Idiomatic Overview of Physiology

• Physiology: The science explaining physical and chemical mechanisms of life.

• Human physiology: Explains characteristics of the human body's control systems.

  • Processes like hunger, fear, and temperature regulation contribute to homeostasis.

Cells as the Living Units of the Body

• Basic living unit: Cell, composed of numerous specialized cells.

• Functions: Transport oxygen (e.g., red blood cells), perform unique roles.

• Total cells in the human body: Approximately 100 trillion.

Intracellular vs. Extracellular Fluid

• Intracellular Fluid: Inside cells, primarily composed of water and essential ions.

• Extracellular Fluid: 60% of human body fluid; constituent of blood and surrounds cells.

  • Contains sodium, chloride, glucose, etc., and is vital for cellular life.

Homeostasis: The Internal Environment

• Walter Cannon: Coined homeostasis in 1929.

• Organs contribute to maintaining constant conditions (e.g., lung oxygen supply).

• Disease: Often disrupts homeostasis but mechanisms still work to maintain vital functions.

Extracellular Fluid Transport and Blood Circulation

• Movement phases: Blood circulates via vessels; fluid exchanges at capillaries.

• Capillary permeability allows exchange between plasma and interstitial fluid.

Regulation of Body Functions

Nervous System

• Composed of sensory inputs, CNS processing, motor outputs.

  • Peripheral sensors (skin, eyes, ears) detect stimuli.

• Autonomic system: Operates subconsciously; controls organ functions (e.g., heart, digestion).

Hormonal Systems

• Composed of endocrine glands secreting hormones to regulate functions (e.g., thyroid hormone influences metabolism).

Immune System

• Protects the body from pathogens via white blood cells, antibodies, etc.

Integumentary System

• Includes skin and appendages, serving protective and sensory functions.

Reproductive System's Role

• Reproduction helps replace aging cells, contributing to overall homeostasis.

Body Control Systems

• A vast array of control systems regulates organ functions (e.g., respiratory, renal).

Homeostatic Control Systems

Negative Feedback

• Key mechanisms adjust abnormalities (e.g., increased CO2 leading to increases in breathing rate).

Positive Feedback

• Leads to instability (e.g., blood loss weakening the heart), but can also be beneficial (e.g., blood clotting).

Characteristics of Control Systems

• Gain: Measure of control system effectiveness (e.g., baroreceptor systems).

• Normal ranges for body functions are crucial; abnormalities can be lethal.

The Cell and Its Functions

Learning Objectives

• List cell components and their functions.

• Describe cell membrane structure.

• Describe intercellular connections and communications.

Glossary of Terms

• Cell Membrane: Lipid bilayer with embedded proteins.

• Endoplasmic Reticulum: Network for protein and lipid synthesis.

• Nucleus: Control center containing DNA.

Organization of the Cell

• Composed of a nucleus and cytoplasm, with protoplasm as a major component.

• Water makes up 70-85% of the cell's mass.

Proteins and Lipids

• Proteins: Important for structure and function, including enzymes.

• Lipids: Form cell membranes; include phospholipids and cholesterol.

Intracellular Organelles

• Mitochondria: Energy production via ATP synthesis.

• Golgi Apparatus: Modifies and packages proteins.

• Lysosomes: Responsible for intracellular digestion.

Membrane Transport

Diffusion

• Movement from high to low concentration, influenced by concentration gradient.

Active Transport

• Movement against concentration gradient utilizing energy (e.g., Na-K pump).

Molecular Basis of Skeletal Muscle Contraction

Learning Objectives

• Describe skeletal muscle fiber structure.

• Identify how actin-myosin interactions generate contraction.

Sarcomere Functionality

• Basics: Sarcomeres composed of actin and myosin.

• Contraction occurs via sliding filament mechanism facilitated by calcium ions and ATP.

Mechanism of Contraction

1. Action potential leads to calcium release from the sarcoplasmic reticulum.

2. Calcium ions bind troponin, displacing tropomyosin and permitting actin-myosin interaction.

3. Myosin heads pull actin filaments via power strokes, consuming ATP resources.

4. Continuous ATP hydrolysis supports cycle of attachment-detachment, driving muscle contraction.

Energy Source for Contraction

• ATP broken down to generate energy for muscle contraction.

Summary

• Homeostasis is preserved through complex body systems addressing internal and external stimuli.

• Skeletal muscle organization and biochemical processes are coordinated for efficient contraction.