Organs and Organ Systems - Biology

There are three kinds of T cells: helper T cells, cytotoxic T cells, and regulatory T cells. All T cells have glycoproteins on their surfaces that act as receptors. CD4 and CD8 are two glycoproteins that can be found on T cells. Helper T cells and regulatory T cells have CD4 glycoproteins, whereas cytotoxic T cells have CD8. These glycoproteins serve as markers to distinguish between T cell types.

The question is asking about CD8, or cytotoxic, T cells. Recall that cytotoxic T cells bind to infected cells and induce their death. Typically, cytotoxic T cells bind to infected cells that have the pathogen inside them (meaning intracellular pathogens). Intracellular pathogens include viruses and intracellular bacteria; therefore, T cells that attack these cells will be CD8 cells. In addition, cytotoxic T cells also attack cancer cells; therefore, these T cells will also be CD8 cells.

Extracellular bacterial cells do not infect host cells; therefore, these bacteria are eliminated via the helper T cells. These T cells bind to the bacteria and activate other immune cells such as B cells, macrophages, and granulocytes that eliminate the bacteria.

Adaptive immunity involves immune cells created due to previously experiencing an infection by a particular pathogen. T-cell lymphocytes mature in the thymus, and recognize a specific antigen. T-cells and B-cells work to produce antibodies against a specific antigen, making them highly specific. This specification is only found in the adaptive immune system

In contrast, the innate immune system can respond to any pathogen, regardless of previous exposure, Neutrophils, monocytes, and macrophages are all part of the innate immune response and help with phagocytosis and inflammation.

Each B-lymphocyte cell is responsible for creating one specific antibody. If the B-lymphocyte's antibody matches to the right antigen, the lymphocyte will differentiate into a plasma cell. Plasma cells release free antibodies into the bloodstream. The transition process from B-cell to plasma cell is mediated by helper T-cells.

Memory B-cells are long-lived descendents of B-cells that "remember" their encounter with an antigen and can rapidly respond to reexposure to the same antigen. Helper T-cells stimulate the immune responses by B-cells and cytotoxic T-cells. B-cells produce antibodies. Macrophages destroy invading microbes via phagocytosis and alert other immune cells to the invasion. Effector molecules include histamine and the cell-destroying proteins of cytotoxic T-cells.

In response to infection, white blood cells multiply so that they can make antibodies against whatever it is your body is fighting off.

B-lymphocytes are the immune system's "memory"—once the body is attacked by a certain virus or bacteria, the body produces B-lymphocytes that can specifically recognize that disease. When the B-lymphocyte comes in contact with the disease (recognized by antibodies) it signals killer T-cells and helper T-cells to attack, and creates more antibodies to signal additional T-cells.

Natural killer cells destroy any cells of the human body that have become infected by an attacker.

Macrophages are a general clean-up cell that sweep up debris, old cells, and sometimes attackers via phagocytosis.

Killer and helper T-cells are both activated by B-lymphocytes

B cells make antibodies that are specific to antigens. Antibodies bind to antigens to tag them for destruction. Cytotoxic T cells recognize and bind antigens and destroy them immediately. Helper T cells recognize antigens presented by antigen-presenting cells such as dendridic cells, and bring them to the attention of B cells, stimulating the B cells to begin making lots of antibodies.

Innate immunity is defined as the general protection mechanisms from pathogens. Innate immunity will be present even when the body has not seen a specific pathogen. Antibodies are highly specific for one particular antigen, and only develop in the body after previous exposure to a pathogen. As a result, it is not considered innate. Instead, antibodies are considered a hallmark of adaptive immunity.

Physical barriers (like the skin), chemical barriers (like stomach acid), and non-specific immune cells (like phagocytes) help to protect against all pathogens, regardless of the type of pathogen or previous exposure.

Innate immunity is non-specific immunity linked to general defenses in the body. These immune defenses include inflammation and phagocytosis, which are not determined by the specific responses of B- or T-lymphocytes. Physical barriers, such as tight junctions in the skin and the acidity of the stomach and vaginal canal, also act as innate immune mechanisms.

Acquired and active immunity only result from a prior exposure to an antigen. Antibodies are produced by B-cells. Cell-mediated immunity involves the regulatory and cytotoxic activites of T-cells during the specific immune response. Humoral immunity is the term used to describe the protective activities of antibodies against infection by common microorganisms.

The innate immune system is a general defense against infections. Antibodies are very specific to the type of infection they can fight. Thus antibodies are considered specific defense.

Lymphocytes are part of the adaptive (specific) immune system, which monitors and dispatches in response to specific threats. The adaptive immune response utilizes antibody secretions from B-lymphocytes to target specific pathogens for elimination.

In contrast, the innate immune system is largely designed to prevent entry and propagation of non-specific pathogens. It is composed of barriers (such as skin and mucus linings) as well as non-specific immune cells (such as macrophages and natural killer cells).

The innate immune system is the part of your immune system that responds to threats almost immediately. It contains all the aspects which react to all threats and is generally seen as less complex than the adaptive immune system. The adaptive immune system includes aspects that respond to specific threats and develop memory to fight threats later on.

The urinary bladder is not a part of the female reproductive tract. Rather, it collects urine created by the kidneys. The ovary produces the female gametes. The fallopian tubes transport the eggs from the ovary to the uterus each month. The uterus provides a location and the necessary nutrients to the fertilized egg that develops into the fetus. The vagina receives the penis during sexual intercourse and expels menstrual flow from the uterus.

Ejaculation is the act of ejecting sperm and semen from the male body. Fertilization and implantation are the first steps of pregnancy that occur inside the female body after sexual reproduction has begun. Transpiration is the evaporation of water from plant leaves.

Fertilization occurs when the genetic material from a sperm and egg combine to form a zygote. This is a form of sexual reproduction because it required the genetic information from two sources to combine**,** and then form another individual. The new offspring will have genetic material from both parents, making it genetically different from either individual parent.

Asexual reproduction occurs when the offspring come from a single parent and only have the genes from a single parent. Fission typically occurs in bacterial reproduction when a single organism splits into two; each of these pieces of the original organism forms a separate organism with the same genetic material as the parent. Budding occurs when a new organism is formed from a bud off of the original organism. When the process is completed, two separate organisms can survive on their own. Sporogenesis usually happens in plant and fungal species, and occurs when the parent organism forms spores which later develop into mature organisms. Vegetative propagation occurs when a piece of a "parent" plant is cultivated and develops into a new organism. This can be done by scientists and horticulturalists or it can occur naturally. None of these processes require more than a single organism to create offspring, and each offspring will be genetically identical to the parent.

There are three primary structures that contribute fluids to sperm in order to create semen in the body: the seminal vesicles, the prostate, and the bulbourethral glands. The pituitary gland has an impact on the development and maturation of sperm, but does not directly add fluid to semen.

As estrogen increases in the female body, it can cause a spike of luteinizing hormone (LH) resulting in a temporary positive feedback loop (the luteal surge). This spike in estrogen and LH levels causes the follicle to burst, releasing the egg into the fallopian tube. This event is called ovulation.

Females' ovaries secrete estrogen, testosterone, and progesterone. Estrogen has many functions, including development of female secondary sex characteristics. Such charactersistics include, but are not limited to: development of breast tissue, redistribution of body fat to the hips, thighs, buttocks, and breasts, and initiation of menses. In females, testosterone functions primarily to increase sexual arousal. Progesterone, luteinizing hormone, and follicle-stimulating hormone play roles in the menstrual cycle. The corpus luteum is formed from the follicle and remains in the ovary after the egg has been released. It secretes progesterone for about two weeks, then deteriorates in the absence of a pregnancy.

The male gonads, the testes, are responsible development and maturation of sperm and secretion of testosterone. Ovaries and fallopian tubes can be ruled out because they are found only in females, and thus do not contribute to the development of sperm. The prostate gland does not produce sperm, rather it secretes fluid that nourishes and protects sperm. The bulbourethral gland aids in the process of ejaculation.

Sperm are produced in the testes. They then travel into the epididymis where they mature and are stored. During the time of ejaculation, the sperm are expelled into the right and left vasa deferentia which join and form the urethra, through which they leave the body.