Systems Physiology - AP Biology

The primitive streak is an arrangement of cells that forms during gastrula development. The location of the primitive streak establishes the left/right axes, cranial/caudal axes, and bilateral symmetry of the developing embryo.

In gastrulation, the process of ingression forms the mesoderm. In this process, the epiblast ingresses at the primary streak into the area between the epiblast and hypoblast cell layers.

Invagination is the infolding of the epiblast cell layer to form the endoderm germ layer. This process takes place during gastrulation.

The “blastocoel” is a fluid-filled cavity in the blastocyst. It is enclosed by trophoblast cells.

Germ layers are primary layers of cells that form during embryogenesis. In mammals, they are the endoderm, ectoderm, and mesoderm. In embryo development, the germ layers differentiate during gastrulation.

The mesoderm is a primary germ layer that forms during gastrulation. The mesoderm develops into most of the organ systems of the human body, including the muscular system, circulatory system, and excretory system.

A woman is said to be “full term” when she is at 39 to 41 weeks of pregnancy. Medical intervention to induce labor during this time is not ideal.

The duodenum, in the small intestine, is a site of protein, carbohydrate, and fat digestion.

The jejunum is a site of protein and fat absorption. The ileum is a site of salt, vitamin, and excess molecule absorbtion. The colon is a segment of the large intestine for water and ion absortion. Each of these work to absorb different molecules, but do not significantly contribute to their digestion.

Major histocompatibility complex (MHC) class I molecules are found on virtually all cells in the body. They function in routine immune monitoring through presentation of short peptide fragments derived from degradation of intracellular proteins contained within the cell. The T-cell receptor on cytotoxic T-cells interacts with MHC class I, and if a foreign pathogen or peptide is presented, the cytotoxic T-cell becomes activated to kill infected cells. The same system also functions for detection of potential cancer cells.

The immune system is very adaptive. The body has many antibodies that will each recognize different antigens. If an antibody binds to an antigen, the antibody will be copied so that the body can quickly recognize the threat if it is exposed to the antigen a second time. This process is known as the adaptive immune response.

When an antigen is presented for a second time, antibodies to the antigen are released. These antibodies bind to the antigen, labelling it for attack by immune cells and preventing it from interacting the membrane proteins on the host cells.

Antibodies are proteins created by the immune system in order to neutralize foreign objects. An antibody would not be classified as an enzyme because it does not catalyze chemical reactions. When a foreign pathogen enters the body, it will have foreign receptors on its surface. These foreign receptors are known as antigens. When a pathogen is destroyed, immune cells can carry a sample of the antigen to the T-cells for identification. The T-cells help activate B-cells that will synthesize an antibody against the particular antigen. The selected B-cells differentiate into plasma cells and secrete antibody proteins into the blood, which bind the antigens and label the pathogen as foreign. This label attracts other immune cells to attack and destroy the pathogen.

Antibodies are continuously made in the body in different shapes and forms. They are then sent into the blood stream to test for the presence of compatible antigens. Each antibody can only bind to one antigen, and each antigen can only bind to one antibody. Think of them like a codon-anticodon pair; there is only one possibility for them to form a perfectly complementary pair. Once the correct antibody binds to an antigen, they are tagged and used to stimulate production of more antibodies. The antibodies are only capable of binding and tagging the antigens. Cytotoxic T-cells are then able to recognize antibody binding patterns and actually destroy the infected cell.

From the passage, the MHC I molecule's blueprint is on chromosome 6. Therefore, the DNA must have been transcribed in the nucleus then translated in the ribosome. These ribosomes are on the endoplasmic reticulum. While in the endoplasmic reticulum, some of these proteins are degraded and react with a particular MHC I molecule.

According to the passage, after the MHC II molecules are fully synthesized in the endoplasmic reticulum, they are transported to the endosome. Foreign molecules are transported into the cell where they are degraded in the endosome as well. From there, the degraded pathogen interact with the MHC II molecule.

According to the passage, MHC I and cytotoxic t-cells are responsible for identifying the body's own protein. During organ transplant, foreign MHC I molecules are presented into the body. The host's cytotoxic T-cells will recognize these as foreign and will attack.

White blood cells is the correct answer here. After pathogen has entered the body, the antibodies to combat it are created by B cells that are a part of the white blood cells in the human body.

The ability to form any of the three germ layers is known as pluripotency. Totipotent cells, such as the zygote, are able to form an entire organism, multipotent cells are able to form any cell within the same germ layer lineage, and progenitor cells are cells closer to differentiation, often found in adult organisms.

Humoral, or B-cell, immunity is associated with the formation of antibodies. Plasma cells are B-lymphocytes that have been differentiated with the help of a helper T-cell. They release antibodies, which are created to respond to a specific pathogen in the body.

Cytotoxic T-cells are also activates by help T-cells, but are involved in cell-mediated immunity rather than humoral immunity. They target infected cells based on antibody tagging. Monocytes are a part of the innate immune response and are not involved in antibody interactions. They primarily differentiate into macrophages, which engage in phagocytosis of pathogens.

Basophils are the least common leukocyte found in the body, but play a key role in the inflammatory response. They contain histamine, which is a potent vasodilator. Upon release, histamine will increase blood flow to infected areas. Mast cells are another immune cell that is involved in histamine release, but are generally localized to various regions of the body rather than found in circulation.

Basophils, mast cells, eosinophils, and neutrophils are all considered granulocytes and are essential cells in the innate immune response. Plasma cells are differentiated B-lymphocytes that are responsible for mass-producing antibodies to a specific antigen.