Physiology and Homeostasis (03:30)
The human body maintains a stable condition inside while outside conditions change. Systems in the body, such as the nervous system and endocrine system, work to maintain balance.
Nervous System (06:03)
The central nervous system includes the brain and spinal chord; the peripheral nervous system is a network of nerves throughout the body. Somatic nerves control muscles, skin, and joints; autonomic nerves control internal organs. Neurons are cells that carry electric charge.
Endocrine System (02:55)
Seven endocrine glands produce hormones. The pancreas produces digestive juices, insulin, and glucagon, which regulate blood glucose levels through a negative feedback loop. The endocrine system often works with the nervous system to produce responses.
Digestive System (05:07)
Humans obtain chemical energy from food, and digestion converts food to usable products. Learn chemical processes that involve enzymes in the mouth, stomach, liver, pancreas, and intestines.
Excretory System: The Liver (01:37)
When cells metabolize nutrients, they produce waste products, which the blood transfers to the excretory system. The liver detoxifies the blood, and makes blood proteins and urea. It also destroys old red blood cells, makes bile, and stores and releases glucose in response to glucagon.
Excretory System: The Kidneys (01:42)
The kidneys filter blood, collecting waste products which become urine. Capillaries in the kidneys exert pressure so waste products leave through selectively permeable membranes. Some of these molecules are reabsorbed with nephrons.
Musculoskeletal System (02:02)
The skeleton protects organs, facilitates movement, and stores minerals, growth factors, and alkaline salts; marrow produces blood cells. Muscles contract and expand as actin and myosin filaments slide past each other.
Germ Theory (03:56)
Ignaz Semmelweis noticed a high death rate from puerperal fever in women who had given birth in hospitals, and connected this to doctors performing autopsies before assisting with births. He directed doctors to wash their hands between operations and infection rates decreased. Louis Pasteur supported Semmelweis with proof that disease is caused but by exposure to germs.
Types of Germs and Defenses (03:25)
Bacteria are free living prokaryotes, while viruses need a host to survive. The body's main defenses are the skin and white blood cells. Lymphocytes have many receptor sites that react to specific antigens.
When a receptor on a T-cell encounters an antigen from a pathogen, the T-cell divides, becoming a natural killer cell. T-cells influence B-cells to make antibodies; when they bond with specific antigens, B-cells divide and produce more antibodies.
Human immunodeficiency virus destroys T-cells and macrophages, making the body vulnerable to infection. The virus also infects the thymus and interferes with negative selection.
To prevent disease, Pasteur created artificially weakened pathogens. The immune system recognizes foreign antigens and initiates the immune response, which leads to the formation of memory T-cells and memory B-cells, which can last a lifetime.
Credits: Human Physiology and Immune Response (00:17)
Credits: Human Physiology and Immune Response
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