Human Biology (BIOL 104)

Talk Thirteen:

Cancer

Chapter 22

What Is Cancer?

– Cancer is caused, in part, by a breakdown in control of the cell cycle

– The cell cycle is controlled by proteins in the cell that give either a “GO”, a “STOP” or a “die” signal

– Cancer cells divide excessively

- they have too many “GO” signals or not enough “STOP” signals- cancer cells can also ignore “die” signals = apoptosis

• Normal plant and animal cells have a cell cycle control system

Cancer Cells: Growing Out of Control

• When the cell cycle control system malfunctions– Cells may reproduce at the wrong

time or place– A benign tumor may form

Cancer Cells: Growing Out of Control

• Proto-oncogenes – • Genes whose products

signal and regulate normal cell division

• The abnornal, mutated form of the proto-oncogene that lead to cell transformation and cancer are called oncogenes.

Cancer Cells: Growing Out of Control

• Oncogenes differ from proto-oncogenes in three basic ways

• 1- Timing and quality of expression

• 2- Structure of protein products

• 3 – Degree to which their protein products are regulated by cellular signals

• Gene expression can be regulated at 5 later steps too.

• 1 – transcription turned on or off

• 2- mRNA modified to allow exit from nucleus

• 3 – Alteration of rate of translation

• 4 – modification of protein folding

• 5 – Effector molecules

Remember Regulation of gene expression?

Cancer Cells: Growing Out of Control

• The mutation of a proto-oncogene to an oncogene can alter the cell division signals at any of the 5 steps and trigger uncontrolled cell division

• One type of oncogene codes for a modified growth factor that continuously 2nd messengers and thus always triggers cell division

• Another causes the cell to secrete growth factors allowing the cell to divide

Cancer Cells: Growing Out of Control

• Another codes for altered 2nd messenger that tells the cell to activate cell division

• Another alters the regulatory system in the nucleus– So the DNA continues

to replicate and this drives continuous cell division

Six Hallmarks of Cancer

1.Self-sufficiency in growth signals or response

2.Insensitivity to grown inhibitor signals (antigrowth signals)

3.Evasion of programmed cell death (apoptosis)

4.Limitless replicative potential (no senescence)

5.Sustained angiogenesis (stimulation of blood vessel growth)

6.Tissue invasion and metastasis

Progression of cancer• There are several mechanisms which prevent mutations

causing cancer

• A mismatch leads to a permanent mutation on one DNA strand if not corrected

Progression of cancer• A mismatch repair protein (spell-checking protein) acts

on a mutated DNA strand

• Cuts out the DNA and allows the correct base to be added

What cancer affects - Tissues

• Tissue: Similarly specialized cells that perform a common function in the body.

• 4 main tissue types in the human body:– 1. Epithelial: covers body surface and lines

body cavities.– 2. Connective: binds and supports body

parts.– 3. Muscular: Moves body parts– 4. Nervous-Receives, interprets and sends

signals.

Three types• A: Adhesion junction

• Cells within tissues and organs must be anchored to one another and attached to components of the extracellular matrix.

• Anchoring proteins extend through the plasma membrane to link cytoskeletal proteins in one cell to cytoskeletal proteins in neighboring cells as well as to proteins in the extracellular matrix

Three types• B: Tight junction

• Found in epithelia, they act as barriers that regulate the movement of water and solutes between epithelial layers.

• There is evidence to suggest that the structures in which solutes pass through are somewhat like pores.

• Prevent the highly acidic gastric fluid in your stomach from leaking out and digesting proteins of your own body instead of those you consume as food.

Three types• C: Communicating

(GAP) junctions

• Allow for direct chemical communication between adjacent cellular cytoplasm through diffusion without contact of the extra cellular fluid.

• Protrudes across the cell membrane, and when 2 adjacent cells interact, they form the gap junction channel.

• Play vital roles in the human body, including their role in the uniform contractile of the heart muscle.

• They are also relevant in signal

transfers in the brain, and their absence shows a decreased cell density in the brain.

• Retinal and skin cells are also dependent on gap junctions in cell differentiation and proliferation.

Connective Tissue

• Binds Organs together• Holds epithelium to the body• Provides Protection and Support• Produces Blood Cells• Stores Fat• CT cells secrete a matrix, this matrix is

composed of fluid and fibers-collagen and elastin.

Organs and Organ Systems

• An organ is a collection of tissues joined in a structural unit to serve a common function

• Organs are composed of main tissue, parenchyma, and "sporadic" tissues, stroma.

• The main tissue is that which is unique for the specific organ, such as the specialized cells of the stomach,

• Sporadic tissues include the nerves, blood vessels, and connective tissues.

• Functionally related organs often cooperate to form whole organ systems.

• A hollow organ is a visceral organ that forms a hollow tube or pouch, such as the stomach or intestine, or that includes a cavity, like the heart or urinary bladder

•Used with permission from imgarcade.com

Organ Systems• Circulatory System: The main function

of this system is to transport nutrients and gasses to cells and tissues throughout body. This is accomplished by the circulation of blood.

• Cardiovascular: comprised of the heart, blood, and blood vessels. The beating of the heart drives the cardiac cycle which pumps blood throughout body.

• Cardiovascular organs: – heart, blood vessels, blood

• Lymphatic: This system is a vascular network of tubules and ducts that collect, filter, and return lymph to blood circulation.

• As a component of the immune system, the lymphatic system produces and circulates immune cells called lymphocytes.

• Lymphatic organs: – lymph vessels, lymph nodes,

thymus, spleen, tonsils

From the wikimedia free licensed media file repository

Progression of cancer• A tumor is said to be benign if it is contained in

one location and has not broken through the basement membrane to which normal cells are attached

• Benign tumors often cause no health problems to an individual

• Can grow big enough to interrupt the functioning of normal tissue

• Removal is generally successful as they are not intermingled with other tissue

The Characteristics of Cancer

• Cancer is a result of a series of mutations in the cell’s genes – Larger cell nucleus and less cytoplasm– Loss of structural specialization– Cytoskeleton shrinks– Plasma membrane proteins could be lost or

altered– New plasma membrane proteins may appear– Changes passed on to cell’s descendants

•A cancer cell’s structure is abnormal.

Figure 12.17 (1)Progression of cancer• Malignant tumors invade normal tissue

• Do not just push healthily cells out of the way

Figure 12.17 (2)Progression of cancer• Tumor cells produce protein-degrading

enzymes that breaks down the connective tissue that holds cells together

Figure 12.17 (3)Progression of cancer• As Malignant tumors invade normal produce

that allow them to invade other tissue, they spread to other locations

• Metastasis – one or more transformed cells spread to the rest of the body via the blood system.

The Characteristics of Cancer

•A Cancer cells break away from their home tissue.

•B The metastasizing cells become attached to the wall of a blood vessel or lymph vessel. They secrete enzymes that break down part of the wall. Then they enter the vessel.

•C Cancer cells creep or tumble along inside blood vessels, then leave the bloodstream the same way they got in. They start new tumors in new tissues.

The Skin: an example of an organ system

• The skin is the largest organ in the human body.

• For the average adult human, the skin has a surface area of between 1.5-2.0 square meters (16.1-21.5 sq ft.), most of it between 2–3 mm (0.10 inch) thick.

• On average it weighs about 9 pound

• The average square inch (6.5 cm²) of skin holds:

• 650 sweat glands• 20 blood vessels • 60,000 melanocytes• more than 1,000 nerve endings

The Skin: an example of an organ system

• Skin performs the following functions:

• Protection: an anatomical barrier from pathogens and damage between the internal and external environment in bodily defense;

• Sensation: contains a variety of nerve endings that react to heat and cold, touch, pressure, vibration, and tissue injury

• Heat regulation: Dilated blood vessels increase perfusion and heat loss, while constricted vessels greatly reduce cutaneous blood flow and conserve heat.

The Skin: an example of an organ system

• Control of evaporation: the skin provides a relatively dry and semi-impermeable barrier to fluid loss.– Loss of this function contributes

to the massive fluid loss in burns.

• Aesthetics and communication: Some trained professionals see our skin and can assess our mood, physical state and attractiveness.

• Storage and synthesis: acts as a storage center for lipids and water, as well as a means of synthesis of vitamin D by action of UV on certain parts of the skin.

The Skin: an example of an organ system

• Excretion: sweat contains urea, however its concentration is 1/130th that of urine, hence excretion by sweating is at most a secondary function to temperature regulation.

• Absorption: the cells comprising the outermost 0.25–0.40 mm of the skin are "almost exclusively supplied by external oxygen", although the "contribution to total respiration is negligible".

• Water resistance: The skin acts as a water resistant barrier so essential nutrients aren't washed out of the body.

Figure 12.19a

Figure 12.19b

• Cancer prevention includes changes in lifestyle

Cancer Prevention and Survival

– Not smoking– Avoiding exposure to the sun– Eating a high-fiber, low-fat diet– Visiting the doctor regularly– Performing regular self-examinations

- Chemoprevention

Issues• So, what do you thing of stems cells now if they

can be used to:– Hopefully grow new organs

– Treat all forms of cancer

– Possibly treat all major diseases

– Stop a lot of pain and suffering

The end!

Any questions?