Cell function

Today's Program

• How to use Zotero

• The Cell: Functions, Communications, Reproduction

• Cellular Injury and Death

The Cell

• History of Cell Study:

  • Detailed studies began in the 1830s.

  • Unified concept in biology supported by:

  • Schleiden and Schwann (1838-1839): All organisms composed of cells.

  • Virchow (1850s): All cells arise from preexisting cells.

  • Cells are the smallest unit of life.

Cell Types

1. Eukaryotes:

   • Higher animals, plants, fungi, protozoa, algae.

   • Larger, complex structures, containing organelles (e.g., nucleus).

2. Prokaryotes:

   • Bacteria and cyanobacteria.

   • Simpler structures, lack organelles and nucleus.

Cellular Functions

• Key Functions of Cells:

  • Movement (e.g. muscle cells)

  • Conductivity (e.g. nerve cells)

  • Metabolic Absorption (e.g., all cells)

  • Secretion (e.g., mucous gland cells)

  • Excretion

  • Respiration: Oxygen intake to produce ATP

  • Reproduction

  • Communication

Cellular Components

Nucleus

• Central part of the cell.

• Contains genetic material (DNA/RNA) and proteins (e.g., histones).

• Functions in cell division, genetic control, DNA repair, and transcription (DNA to RNA).

Cytoplasmic Organelles

• Major Components:

  • Cytosol: Contains enzymes, ribosomes, and proteins.

  • Smooth and Rough Endoplasmic Reticulum

  • Golgi Apparatus

  • Mitochondria: Powerhouse of the cell, produces ATP.

  • Lysosomes and Peroxisomes: Responsible for breakdown and processing of cellular waste.

Plasma Membrane

• Surrounds the cell and organelles.

• Functions include:

  • Regulation of movement of molecules inside/outside the cell.

  • Maintenance of cell polarity and structure.

  • Allows for cell-to-cell recognition.

Cell Communication

• Importance of Communication: Essential for maintaining homeostasis.

• Types of Intercellular Signaling:

  • Direct Contact Between Cells

  • Paracrine Signaling: Signals released to nearby different types of cells.

  • Hormonal Signaling: Hormones secreted into the bloodstream.

  • Neurohormonal Signaling: Signaling via neurosecretory neurons.

  • Neurotransmitter Release: Neuron-to-neuron signaling.

  • Autocrine Stimulation: Cell targets itself.

Maintaining Cellular Functions

• Cellular Metabolism: Provides energy for cellular processes through diet (proteins, fats, carbohydrates).

• Energy Source:

  • Produces ATP (adenosine triphosphate):

  • ATP = ext{Ad-}^R- ext{P}^{ ext{n}} + ext{H}_2 ext{O}

Altered Cellular and Tissue Biology

• Causes of Disease:

  • Combination of factors affecting cells and their environment (e.g., ECM).

• Cellular Injury:

  • Results from anything disrupting structures or depriving oxygen/nutrients.

  • Factors Leading to Injury:

  • Chemicals, lack of oxygen, free radicals, infectious agents, etc.

Cellular Adaptation

• Adaptation Types:

  • Atrophy: Decrease in cell size (e.g., skeletal muscle, heart).

  • Hypertrophy: Increase in cell size, often affecting the heart and kidneys.

  • Hyperplasia: Increased cell numbers due to division (e.g., liver regeneration).

  • Metaplasia and Dysplasia: Changes in cell types and structure.

Cellular Injury and Death

• Occurs when cells fail to maintain homeostasis under stress.

• Cellular Injury Causes:

  • Chemicals, oxidative stress, mechanical factors, etc.

• Oxidative Stress:

  • Excess reactive oxygen species (ROS) causing damage to proteins, lipids, and DNA.

Chemical Injury

• Example: Lead

  • Affects learning and memory by interfering with neurotransmission and increasing oxidative stress.

Summary of Cellular Death

• Types:

  • Necrosis: Uncontrolled cell death with inflammation.

  • Apoptosis: Programmed cell death without inflammation.

Quiz Questions

1. Provide an example of cellular adaptation after injury.

2. Explain why free radicals are unstable.

3. Why are children more vulnerable to toxic chemicals leading to cellular injuries?

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