BIO 7:  Lecture 19 Preview

Some hormones control development and reproductive cycles.  In most mammals the Y chromosome carries a gene for a protein that stimulates production of the steroid hormone testosterone, by the testes.

After puberty hormones produced by the hypothalamus (in the brain) and the gonads (ovaries and testes), control the production of eggs and sperm.

Other animals also use hormones to coordinate responses and control development. 

Do plants use nervous systems or hormones?

"It's a jungle out there"--Organisms need to protect themselves from predators and the elements.

• External predators are herbivores and carnivores; internal predators are parasites (small organisms eating and breeding on the inside).
• External defenses include fighting or fleeing well, working in a group, hiding well, having a tough covering, not tasting good, and/or being poisonous.
• All organisms can recognize their own cells from invading cells and have a non-specific internal defense response.
• Vertebrates have a non-specific plus a specific internal defense, recognizing a particular kind of invader and responding against it more quickly if it returns.

There are different lines of defense against pathogens aka infectious agents (virus, bacterium, protist, fungus, or small invertebrate).                      Each line of defense requires energy to maintain.

First line of defense:  coverings and secretions (tears, mucus, etc)

Integumentary system and/or skin and associated glands = major part of first line of defense.  Non-specific responses to attack include plugging any breaks in the covering, marking invading cells with proteins, having white blood cells attack and engulf marked invading cells.

Vertebrates also have a specific defense response, which remembers particular kinds of invaders, by their antigens (molecules on their surfaces with specific shapes).

• B lymphocytes are made in the bone marrow and release antibodies (proteins binding to antigens).

• T lymphocytes are made in the bone marrow, mature in the thymus, and have several roles

            -killer T lymphocytes phagocytose viruses or cells carrying the antigen to which their membrane protein binds

            -helper T lymphocytes stimulate the production of B and T lymphocytes

Lymphocytes are concentrated in the lymph nodes of the immune or lymph system

After the invader has been removed, a few B and T memory cells with the antibody or membrane protein recognizing the invader's antigen remain.  If the same antigen is encountered again, the memory cells can divide rapidly, and there is a quicker response.