Lecture2 HumanBio

Complexity of the Human Body

The human body is regarded as the most complex machine ever evolved, showcasing an intricate design that enables survival and adaptation. Each individual organism builds this complexity from a single fertilized egg cell, which undergoes numerous divisions and differentiations to form the trillions of specialized cells that make up various tissues and organs.

Cell Theory

Fundamental concepts in biology outline that:

• All organisms are composed of one or more cells, which serves as the basic unit of structure and function in living things.

• Cells are not only the building blocks but also functionally autonomous units that can perform necessary life processes.

• Cells arise from pre-existing cells through the process of cell division, which is fundamental to growth and repair.

Prokaryotic vs. Eukaryotic Cells

Prokaryotic Cells:

• Nucleus: Absent, with genetic material in a nucleoid region.

• Diameter: Typically around ≈1μm.

• Cytoskeleton: Absent; simpler structural organization.

• Cytoplasmic Organelles: Absent, yet they still perform all necessary functions of life.

• DNA Content: Ranges from 1 × 10^6 to 5 × 10^6 base pairs, usually contained in a single circular DNA molecule.

Eukaryotic Cells:

• Nucleus: Present, housing the cell's genetic material.

• Diameter: Varies from 10-100 μm, allowing for increased complexity.

• Cytoskeleton: Present, providing structural support and mediating intracellular transport.

• Cytoplasmic Organelles: Numerous, including mitochondria, endoplasmic reticulum, and Golgi apparatus.

• DNA Content: Between 1.5 × 10^7 to 5 × 10^9 base pairs, organized into multiple linear chromosomes.

Tissues and Organs

The human body consists of various tissue types that combine to form organs:

• Tissue Types:

  • Epithelial Tissue: Covers body surfaces and lines cavities; crucial for protection and absorption.

  • Connective Tissue: Provides support and structure; includes bone, blood, and adipose tissues.

  • Muscle Tissue: Facilitates movement; includes skeletal, cardiac, and smooth muscle.

  • Nervous Tissue: Transmits impulses and processes information; consists of neurons and glial cells.

• Organ Formation: Tissues organize to form organs, like the stomach, which comprises muscle, epithelial, and connective tissues.

• Organ Systems: Groups of organs that work together; for example, the stomach is a key component of the digestive system, which includes organs like the intestines and the liver.

Functions of Cells

Cells contribute to organ functions through multiple essential roles:

• Supply energy through metabolic processes.

• Provide structural scaffolding to maintain shape and organization.

• Facilitate movement and propulsion across systems.

• Act as pumps for transportation and ventilation.

• Engage in purification and filtration to maintain homeostasis.

• Employ protection mechanisms to shield against harm.

• Implement control systems for physiological regulation.

• Involve in creation, growth, and repair mechanisms crucial for homeostasis.

Cell Composition

Total Number of Cells:

• An estimated approximately 37 trillion (3.7 × 10^{13}) cells reside in the human body, with various cell types serving distinct functions.

Cell Types by Mass and Count:

• Red Blood Cells: 5.5% total mass (around 26 trillion cells), vital for oxygen transport.

• Fat Cells: 8.7% total cells (~50 billion cells), crucial for energy storage and insulation.

• Muscle Cells: 8.7% total cells (~17 billion cells), essential for movement and stability.

• Skin Cells: Largest organ representation; contributes to 5.5% total cells (approximately 2 trillion cells) for protection and barrier function.

• Endothelial Cells: 6.8% (around 2.5 trillion cells), forming the inner lining of blood vessels.

• Nervous System Cells: Comprising 8.3% total cells, including around 100 billion neurons and 3 trillion glial cells for signaling and support.

Body Mass Composition

Total Body Mass Distribution:

• In Females:

  • Fluids: 45% of total body mass; critical for numerous physiological functions.

  • Solids: 40% of total body mass; includes proteins, bones, and fat.

• In Males:

  • Fluids: 60% of total body mass; reflecting differences in body composition.

  • Solids: 55% of total body mass; generally more muscle mass.

Body Fluid Compartments:

• Intracellular Fluid (ICF): Makes up 2/3 of total body fluid, crucial for cellular functions.

• Extracellular Fluid (ECF): Comprising the remaining 1/3, includes interstitial fluid (80%) and blood plasma (20%).

Regulation of Fluids and Electrolytes

The body maintains strict control over fluid and electrolyte content, allowing for variability in:

• Glucose levels: Related to diabetes mellitus and its physiological implications.

• Albumin levels: Indicators of renal health and overall absorption functions.

• Electrolyte and CO2 levels: Critical for maintaining cardiovascular and neurological health.

Balancing Acid and Base

Regulatory Mechanisms:

• Respiratory Control: Manages CO2 exhalation to regulate blood pH.

• Metabolic Control: Utilizes bicarbonate as a buffer to maintain homeostasis.

• Renal Control: Adjusts electrolyte and water balance through filtration and reabsorption.

Fluid Exchange Mechanisms

Surface Area to Volume:

• An example of efficiency in design is seen in lung alveoli, whose surface area is equivalent to 0.5 tennis courts, promoting gas exchange.

Fluid Exchange in the Gut:

• Structural adaptations like villi and microvilli enhance absorption, ensuring that nutrients are effectively taken up into the body.

Understanding Cell Functionality

Cells develop from a single zygote and duplicate to form approximately 37 trillion cells, exhibiting specialization for various functions while retaining essential structural and operational commonalities.

Cellular Components

• Each cell acts as a factory, containing:

  • Plasma Membrane: Regulates exchange with the external environment.

  • Cytoplasm: Gel-like substance where cellular processes occur.

  • Nucleus: Heart of genetic material management.

  • Organelles: Specialized structures like mitochondria (energy production), lysosomes (waste processing), and endoplasmic reticulum (protein and lipid synthesis).

Molecular Activity in Cells

Molecular Components:

• Genome (DNA/RNA): Serves as the template for all genetic information and coding.

• Transcriptome: Represents the complete set of RNA transcripts; reflects gene activity.

• Proteome: Comprises the full range of proteins produced by the cell, essential for diverse functions.

• Metabolome: Offers insights into metabolic processes through the analysis of small molecules produced by metabolism.

Human Genome Project

Timeline:

• Conducted between 1990 - 2003 at the cost of $5 billion; provided crucial insights into cellular functions through an exploration of approximately 20,000 genes.

The Proteome and Cell Functionality

Each cell type possesses a unique set of proteins (between 60,000 - 80,000) that contribute to its specialized function, illustrating the complexity of cellular operations.

Nucleus: Control Center of the Cell

• Functions:

  • Nucleolus: Acts as the site for RNA transcription and ribosome biogenesis.

  • Rough ER: Involved in protein synthesis and folding processes.

  • Smooth ER: Responsible for the synthesis of lipids and steroid hormones.

  • Golgi Complex: Plays a role in processing and sorting proteins from the ER for proper cellular trafficking.

Mitochondria: The Powerhouse

• Functions:

  • Produce ATP through respiration; replicates independently via fission and contains its own DNA inherited maternally.

Lysosomes: Waste Disposal

• Contain digestive enzymes that assist with waste processing and recycling of cellular components.

Cytoskeleton: Support and Transport

• Comprised of various filaments and tubules that maintain cell shape and facilitate intracellular movement, crucial for cell integrity and functionality.

Learning Objectives

• Describe cells as the basic units of life, encompassing their structural and functional diversity.

• Discuss the specialization of different cell types and how these functions underpin organ systems.

• Explain the pivotal role of water in regulating both intracellular and extracellular environments, understanding its importance in biochemical reactions.

• Identify key functions of cellular components, including the nucleus, endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, and cytoskeleton, to illustrate their relevance in maintaining homeostasis and supporting life.

Yes, the structure of alveoli is somewhat folded or more accurately, highly branched and clustered. This increase in surface area allows for more efficient gas exchange. Each alveolus is surrounded by capillaries, facilitating the transfer of oxygen and carbon dioxide.