T-cells generally serve to recognize antigens and escort them to B-cells to elicit a response (helper T-cells) or to recognize antibodies bound to infected cells (cytotoxic T-cells). B-cells, in contrast, will directly secrete antibodies against the antigen after binding of the antigen at the membrane.

Both types of cells have receptors that can bind to antigens, allowing for recognition and communication. Other commonalities include the presence of a transmembrane domain and the presence of a variable region, which will allow for specificity in antigen binding.

The similarities are mainly structural, and the receptors have many functional differences. T-cell receptors will only bind fragments of antigens, while B-cell receptors will bind full molecules. Only T-cell receptors will interact with major histocompatibility complexes (MHC). Though the structure of both receptors types is determined by peptide chains, B-cells use heavy and light chains, while T-cells use alpha and beta chains.

The spleen plays a key role in the immune system as one of the blood filtration centers of the body. It is also involved as a lymphatic organ, allowing filtrates from the blood to be distributed to the body via lymph.

Macrophages and neutrophils are the major cells of the immune system responsible for phagocytosis. Phagocytosis means ingestion of material. Therefore these cells work as "garbage collectors" within the body. Cells destined for destruction are tagged for phagocytosis by special molecules.

Sperm cells are stored and mature in the epididymis until they are transported to the urethra through the vas deferens. The testes are the site of sperm production, while the seminal vesicles produce fluids that are later incorporated into semen.

The seminal vesicles secrete seminal fluid to promote and nourish sperm as they are released. The bulbourethral glands secrete a component of seminal fluid, while the prostate gland secretes alkaline fluid.

"Germ cells" is simply another term for gametes, and thus refers to either sperm or ovum.

Ovum are produced in the ovaries. After production, the fallopian tubes propel ovum to the uterus using the movement of cilia. The endometrium is the lining of the uterus, and allows for implantation of a fertilized ovum.

In the majority of cases, fertilization occurs in the fallopian tubes of the female. The egg is released from the ovary and travels into the fallopian tube during ovulation. Sperm travel to the fallopian tube to fertilize the egg, creating a zygote. The zygote begins to divide, forming a blastocyst before it reaches the uterus where it becomes embedded in the endometrium via the process of implantation. Certain pregnancy complications can arise if the blastocyst implants while still in the fallopian tube, resulting in ectopic pregnancy.

Sperm is created in the seminiferous tubules of the testes. It is then transported to the epididymis, where it will mature and be stored prior to ejaculation.

The male reproductive system consists of a series of ducts, which includes the epididymis, vas deferens, and urethra. The epididymis is a coiled tube attached to the testis, which receives sperm from the seminiferous tubules. The vas deferens connects the epididymis with the urethra, which in turn conducts sperm to the tip of the penis. 

In female mammals, the fimbriae are finger-like projections that sweep the ovulated egg from the ovary into the oviduct.

Villi are found in the digestive tract and work to increase surface area for more efficient absorption of nutrients. Flagella are threadlike structures that provide motility for sperm. Microtubules are composed of the protein tubulin, and are used in the construction of cilia and flagella. The endoderm is the innermost embryonic tissue layer, which develops to form the lining of the respiratory and digestive tracts.