Download Homeostasis and Urinary System and Body Defenses

Chapter 27 - Maintaining the Internal Environment
1. Homeostasis – regulating the internal environment: Animals maintain their internal conditions
relatively constant despite changes in the outside environment. Bigger changes in the
environment result only in small changes in the organism. Mostly homeostasis is achieved by
negative feedback mechanism. In a negative feedback the result of a process stops that process.
For example, regulation of body temperature, regulation of fluids and solutes in blood, secretion
of hormones. Ectotherms can absorb heat from sunlight to raise body temperature (lizard) and
Endotherms lose heat by evaporation of water, sweating (mammals). Glucose level in blood is
controlled by Pancreas with the help of liver. When glucose level in blood increases above the
upper limit, pancreas secretes Insulin. Insulin causes greater absorption of glucose by liver and
muscles by opening special gates for glucose absorption. When blood sugar level in blood falls
below the lower limit, pancreas secretes Glucagon. It causes the breakdown of glycogen in liver
and muscles and release of more glucose into blood.
2. Diabetes mellitus causes abnormally high blood levels of glucose. Diabetes mellitus type-1 is
caused if pancreas cannot secrete enough insulin which can be on gaining lot of weight. It can be
cured by taking insulin pills or injections. Diabetes mellitus type-2 is caused if the receptors for
insulin are modified. This is caused even when normal insulin is secreted in the body. It cannot
be cured by taking pills. Diabetes mellitus type-2 is mostly associated with obesity.
3. Osmoregulation: is the homeostasis of water and dissolved substances by animals. In organisms
like Amoeba it can be done by a contractile vacuole but higher animals including man need
urinary system.
4. Urinary system of humans is formed of a pair of Kidneys, a pair of ducts called Ureters, a
Urinary Bladder to store urine and Urethra the duct that carries urine outside the body.
Filtration: Kidneys filter the blood and small molecules enter the renal tubules. Reabsorption:
Useful substances are reabsorbed from the filtrate. Secretion: Some substances not filtered
from blood are actively secreted into filtrate. Excretion: The urine with wastes like urea and
excessive salts or amino acids, leaves body with variable amount of water.
Chapter 28 - How animal Body defends itself
1. Lymphatic System plays major role in body defense system. It consists of organs Spleen,
thymus, lymph nodes, and lymph capillaries, lymphatic vessels, and lymphatic ducts. Tonsils and
appendix are lymphatic tissues.
2. Immunity means resistance to a particular disease. Body achieves immunity by non-specific and
specific responses against invaders. Non-specific action is against all invaders and consists of 2
defense lines 1st and 2nd.
Non-specific Immunity:
An intact skin and mucus membranes form 1st line of defense against all invaders. It includes
tears in eyes, sweat on skin, saliva in mouth, and acid in stomach.
• 2nd defense line is formed by Phagocytes, Natural Killer cells and proteins like Interferon.
• Phagocytes eat bacteria and viruses by phagocytosis.
• Interferon interferes in multiplication of viruses.
• Inflammatory response draws phagocytes to the site of injury, causes swelling and redness.
• Lymph nodes filter interstitial fluid and kill cancer cells.
Specific Immunity serves the 3rd line of defense. It produces special proteins effective against a
specific invader.
Humoral Immunity: It involves making Y-shaped proteins called Antibodies which roam in body
fluids like blood to inactivate the invaders. B-cells are responsible for this immunity.
Cellular Immunity: T-cells are responsible to defend against invaders inside cells.
Active Immunity is achieved by making Antibodies inside the body due to infection or
vaccination.
Passive Immunity is achieved by giving antibodies made in another organism of same or
different species. This is done if the patient’s immune system is weak or cannot make antibodies
fast enough to defend against the attack. For example a newly born baby has a weak immune
system and mother’s milk passes its antibodies to the baby to defend against certain diseases.
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8. Comparison of B-Cells and T-Cells
Cell Type
B-Cells
T-Cells
Mature inside
Bone marrow
Thymus gland
Responsible for
Humoral (body fluid) immunity
Cellular immunity
Act by making
Antibodies
Cytotoxic cells and enzymes
Other types
Change to Plasma cells to form antibodies
Helper T-cells and Memory cells
9. HIV attacks Helper T-cells and compromises the immune system and causes AIDS. Then many
opportunistic diseases like Pneumonia attack and kill the person.
10. Memory T-cells live for long periods and alert the immune system when an invader enters the
body after 1st infection or vaccination.