The Cell Cycle and Cell Types

The Cell Cycle

• A vital process by which a single-celled fertilized egg develops into a mature organism
• The cycle also plays a key role in tissue and organ renewal
• The cell cycle consists of two distinct periods: Interphase and Mitosis
• Interphase is when the cell grows, accumulates nutrients needed for mitosis and duplicates its DNA
• Mitosis is when the cell splits into two distinct cells, called daughter cells
• Activation of each phase of the cell cycle is dependent on the completion of the previous phase

Types of Cells

• Stable cells: Multiply only when needed, spend most of their time in the Go phase of the cell cycle, and can be stimulated to enter the cell cycle when needed
• Examples of stable cells include liver cells, proximal tubules of the kidneys, and endocrine glands
• Labile cells: Multiply constantly throughout life
• Examples of labile cells include GI lining, bone marrow, and hair
• Permanent cells: Incapable of reproduction or multiplication
• Examples of permanent cells include brain cells, heart cells, and skeletal muscle cells

Phases of the Cell Cycle

• Gap 0/G0: A resting phase where the cell has left the cycle and has stopped dividing
• Interphase: Consists of three subphases:
  • Gap 1/G1: Cells increase in size, and the G1 checkpoint control mechanism ensures that everything is ready for DNA synthesis
  • Synthesis/S: DNA replication occurs
  • Gap 2/G2: The cell prepares for mitosis

Cancer

• Pain: Can be caused by pressure on nerve endings, distention of organs or vessels, or lack of oxygen to tissues and organs
• Effusion: Occurs when lymphatic flow is obstructed, leading to fluid build-up in serous cavities

Cancer Staging

• Stage I: Cancer is only in the cells where it first started, and the area is small. Considered early stage and often curable.
• Stage II: Cancer is in the organ where it first started, and may be larger than Stage I.
• Stage III: Cancer has spread to nearby lymph nodes or tissues.
• Stage IV: Cancer has spread to distant parts of the body.

Cancer Grading

• Grade I: Cancer cells resemble normal cells.
• Grade II: Cancer cells are somewhat abnormal.
• Grade III: Cancer cells are very abnormal.
• Grade IV: Cancer cells are highly abnormal.

Hormone Therapy

• Used to treat cancers that utilize hormones for growth, like prostate and breast cancers
• Works by slowing or stopping the growth of cancer cells
• Approaches:
  • Suppressing the production of hormones
  • Blocking the action of hormones
  • Removing glands that produce hormones

Side Effects of Hormone Therapy

• Fatigue
• Skin rash
• Loss of appetite or weight gain
• Headaches
• Vaginal dryness, itching, or irritation of the skin around the vagina
• Increased risk of blood clots, stroke, and eye problems
• Increased risk of endometrial cancer and uterine sarcoma

Biopsy Types

• Excisional: For easily accessible tumors, the entire tumor and surrounding marginal tissues are removed
• Incisional: A sample of tissue is removed for examination
• Needle: A small sample of tissue is withdrawn using a needle.

Chemotherapy

• Pre-medication: Given prior to chemotherapy to help prevent side effects.
• Side Effects:
  • Cardiac: Heart muscle damage
  • Respiratory: Pulmonary fibrosis
  • Genitourinary: Hemorrhagic cystitis and loss of libido
  • Kidney: Renal failure
• Neutropenia (Low White Blood Cell Count):
  • Stop medication administration immediately.
  • Ice application (except for vinca alkaloids).
  • Aspiration of infiltrated medication (by the physician).
  • Injection of neutralizing solution (e.g., sodium thiosulfate, sodium bicarbonate).
  • Plastic Surgery Consultation

Causes of Cancer

• Physical Agents:
  • Exposure to radiation
  • Exposure to sunlight
• Other etiologies (causes):
  • Viral infections
  • Genetic predisposition
  • Environmental factors
  • Lifestyle choices

Disseminated Intravascular Coagulation (DIC)

• Can occur with all tumors, but is more likely with cancer of the lung, pancreas, stomach, and colon.
• Characterized by abnormal blood clotting and bleeding throughout the body.

Edema

• Caused by obstructed blood and lymphatic flow
• A result of decreased serum protein from anorexia and malnutrition
• Can contribute to swelling in various parts of the body.

Hypercalcemia

• Occurs due to tumors of the bone, multiple myeloma, squamous lung cancer, and cancer of the breast.
• Results from metastasis to the bone and increased bone breakdown.
• Production of a parathyroid-like hormone enhances the release of calcium from the bones.

Additional Notes

• TNM Staging System: This system uses three main categories to describe the extent of cancer:
  • T (Tumor): Describes the size and location of the primary tumor.
  • N (Nodes): Describes whether the cancer has spread to nearby lymph nodes.
  • M (Metastasis): Describes whether the cancer has spread to distant parts of the body.