Animal Cell Structure, Tissues, Organ Systems, and Immunity

Animal Eukaryotic Cells and Organelles

• Nucleus: Holds genetic material. Protected by a double membrane that separates it from the cytoplasm.

• Vacuoles: Small sacs that store different substances.

• Lysosomes: Made by the Golgi apparatus; digest materials inside the cell.

• SER (Smooth Endoplasmic Reticulum): Produces lipids and helps remove toxic substances.

• Mitochondria: Have two membranes; break down glucose to release energy (cellular respiration).

• Cytoplasm: Jelly-like fluid with the cytoskeleton that supports and gives shape to the cell.

• RER (Rough Endoplasmic Reticulum): Stores and transports proteins made by ribosomes attached to it.

• Ribosomes: Smallest organelles, no membrane; make proteins, free or attached to RER.

• Cell membrane: Made of lipids and proteins; protects the cell and controls what enters and leaves.

• Golgi apparatus: Modifies and sends substances from the RER outside the cell using vesicles.

• Centrosome: Formed by two centrioles; separates chromosomes in cell division and forms cilia and flagella for movement.

• Centriole
• Free ribosome
• 

Types of Tissues

1. Connective Tissue

Made of cells that secrete substances forming the intercellular matrix, which separates them. Supports, protects, and connects tissues.

• Connective tissue proper: Common; surrounds and connects organs; gel-like matrix (e.g., tendons, ligaments).

• Adipose tissue: Stores fat in adipocytes for energy and protection.

• Cartilaginous tissue: Forms cartilage; elastic and solid matrix; cells = chondrocytes.

• Blood tissue: Liquid matrix (plasma) with red and white blood cells and platelets; transports substances and protects the body.

Bone Tissue

Hard matrix with calcium phosphate for support. Osteocytes (bone cells) are found in small spaces (lacunae).

• Compact bone: Dense outer part of bones.

• Spongy bone: Inner part with holes containing red bone marrow.

2. Muscle Tissue

Fibers contract to produce movement.

• Smooth muscle: In walls of hollow organs (intestines, blood vessels); involuntary.

• Cardiac muscle: Only in the heart; involuntary; doesn’t tire.

• Skeletal muscle: Attached to bones; voluntary movement; maintains posture.

3. Epithelial Tissue

Covers and lines body surfaces; forms a barrier.

• Covering/lining epithelium: Covers body and lines organs; structure varies with function.

• Glandular epithelium: Forms exocrine glands (excrete substances) and endocrine glands (release hormones into blood).

4. Nervous Tissue

Transmits nerve impulses.

• Made of neurons (star-shaped) and neuroglia (support and protect neurons).

Organ Systems for Nutrition

• Circulatory System: Transports substances.

  • Organs: Heart, arteries, veins.

• Digestive System: Supplies nutrients.

  • Organs: Mouth, tongue, teeth, stomach, intestines.

• Respiratory System: Takes in oxygen, removes carbon dioxide.

  • Organs: Nostrils, lungs, bronchioles, trachea, larynx, pharynx.

• Excretory System: Removes waste, keeps water and mineral balance.

  • Organs: Kidneys, bladder, urethra, ureters.

Organ Systems for Reproduction and Interaction

• Reproductive System: Creates new life.

  • Female: Ovaries, uterus, vagina, vulva, fallopian tubes.

  • Male: Testicles, penis, urethra.

• Nervous System: Receives and interprets stimuli, sends messages.

  • Organs: Brain, nerves, sense organs.

• Endocrine System: Produces hormones.

  • Organs: Hypothalamus; pituitary, thyroid, parathyroid glands; ovaries, testicles.

• Locomotor System: Allows movement; provides support and protection.

  • Organs: Bones, muscles.

Internal Defenses: The Immune Response

Internal defenses start working when pathogens get past the body’s external barriers. These mechanisms together form the immune response. The immune system can identify foreign materials, such as pathogens, that shouldn’t be inside the body and acts to destroy or remove them.

There are two main types of internal defense:

Innate Immunity

This is a non-specific defense that works against any kind of pathogen that manages to enter the body. It reacts in two main ways:

• Phagocytosis:

  White blood cells called phagocytes surround and absorb unwanted materials such as microbes or dead cells. The waste is then eliminated from the body as pus. Phagocytes use extensions called pseudopods to trap and destroy these materials.

• Inflammation:

  Inflammation prevents pathogens that have entered the body from multiplying and increases blood flow to the area. This causes redness and swelling. Large defensive phagocytes called macrophages are then sent to the affected region to fight the infection.

Acquired Immunity

This type of immunity develops throughout life as the body faces different infections. It gives a specific response to known pathogens (antigens).

Acquired immunity involves two types of special white blood cells:

• Lymphocyte B-cells:

  These cells recognize antigens and turn into plasma cells that produce antibodies — proteins that destroy specific antigens. Some B-cells become memory cells, storing information about the antigens so they can respond faster if the same pathogen appears again.

• Lymphocyte T-cells:

  These cells release enzymes that destroy body cells damaged or infected by pathogens or antigens.

Steps of Acquired Immunity

1. Antigens enter the body.

2. B-cells recognize them and multiply.

3. They turn into plasma cells that make antibodies.

4. Some B-cells become memory cells.

5. Antigen enters again.

6. Memory cells recognize it quickly.

7. B-cells activate faster.

8. More antibodies are made.

9. Antigen is destroyed or blocked.

10. T-cells destroy infected or damaged cells.