Informative Articles About "Human Circulatory System"
The process by which T cells and B cells interact with antigens is summarized in the diagram below. The pancreas secretes digestive enzymes into the small intestine to complete the chemical digestion of foods. This site is for information only. Like our housework, it's a dirty and a thankless job, but it's also important. It is located just inferior to the stomach and takes up most of the space in the abdominal cavity. As the blood and the surrounding cells continually add and remove substances from the interstitial fluid, its composition continually changes.
Female Reproductive System Anatomy
Water and solutes can pass between the interstitial fluid and blood via diffusion across gaps in capillary walls called intercellular clefts ; thus, the blood and interstitial fluid are in dynamic equilibrium with each other. However, as it flows through the lymph nodes it comes in contact with blood, and tends to accumulate more cells particularly, lymphocytes and proteins. Lymph may pick up bacteria and bring them to lymph nodes, where they are destroyed.
Tubular vessels transport lymph back to the blood, ultimately replacing the volume lost during the formation of the interstitial fluid. These channels are the lymphatic channels, or simply lymphatics. Unlike the cardiovascular system, the lymphatic system is not closed and has no central pump, or lymph hearts which are found in some animals.
Lymph transport, therefore, is slow and sporadic. Despite low pressure, lymph movement occurs due to peristalsis propulsion of the lymph due to alternate contraction and relaxation of smooth muscle tissue , valves, and compression during contraction of adjacent skeletal muscle and arterial pulsation. Lymph that enters the lymph vessels from the interstitial spaces usually does not flow backwards along the vessels because of the presence of valves.
If excessive hydrostatic pressure develops within the lymph vessels, though, some fluid can leak back into the interstitial spaces and contribute to formation of oedema. Flow of the lymph in the thoracic duct in an average resting person usually approximates ml per hour.
This can be elevated several folds while exercising. Thus it can be estimated that without lymphatic flow, an average resting person would die within 24 hours.
In the zoologist Ross Granville Harrison demonstrated the growth of frog nerve cell processes in a medium of clotted lymph. It is made up of lymph nodes and vessels. Lambert grew vaccinia virus in fragments of tissue culture from guinea pig corneal grown in lymph. From Wikipedia, the free encyclopedia.
Lymph Diagram showing the formation of lymph from interstitial fluid labeled here as "Tissue fluid". Note how the tissue fluid is entering the blind ends of lymph capillaries shown as deep green arrows. This section needs expansion. You can help by adding to it. Human Anatomy Gray's Anatomy. Journal of Lipid Research.
Webster's New World Medical Dictionary. Lymph capillary Lymphatic vessel. Lymph trunk Lymph Lymphangion. Nutrient artery Arteriole Metarteriole Elastic artery. In the center of each breast is a highly pigmented nipple that releases milk when stimulated. The areola, a thickened, highly pigmented band of skin that surrounds the nipple, protects the underlying tissues during breastfeeding.
The mammary glands are a special type of sudoriferous glands that have been modified to produce milk to feed infants. Within each breast, 15 to 20 clusters of mammary glands become active during pregnancy and remain active until milk is no longer needed. The milk passes through milk ducts on its way to the nipple, where it exits the body. The female reproductive cycle is the process of producing an ovum and readying the uterus to receive a fertilized ovum to begin pregnancy.
If an ovum is produced but not fertilized and implanted in the uterine wall, the reproductive cycle resets itself through menstruation. The entire reproductive cycle takes about 28 days on average, but may be as short as 24 days or as long as 36 days for some women.
Under the influence of follicle stimulating hormone FSH , and luteinizing hormone LH , the ovaries produce a mature ovum in a process known as ovulation. By about 14 days into the reproductive cycle, an oocyte reaches maturity and is released as an ovum. Although the ovaries begin to mature many oocytes each month, usually only one ovum per cycle is released. Once the mature ovum is released from the ovary, the fimbriae catch the egg and direct it down the fallopian tube to the uterus.
It takes about a week for the ovum to travel to the uterus. If sperm are able to reach and penetrate the ovum, the ovum becomes a fertilized zygote containing a full complement of DNA. After a two-week period of rapid cell division known as the germinal period of development, the zygote forms an embryo. The embryo will then implant itself into the uterine wall and develop there during pregnancy.
While the ovum matures and travels through the fallopian tube, the endometrium grows and develops in preparation for the embryo. If the ovum is not fertilized in time or if it fails to implant into the endometrium, the arteries of the uterus constrict to cut off blood flow to the endometrium. The lack of blood flow causes cell death in the endometrium and the eventual shedding of tissue in a process known as menstruation.
In a normal menstrual cycle, this shedding begins around day 28 and continues into the first few days of the new reproductive cycle. If the ovum is fertilized by a sperm cell, the fertilized embryo will implant itself into the endometrium and begin to form an amniotic cavity, umbilical cord, and placenta. For the first 8 weeks, the embryo will develop almost all of the tissues and organs present in the adult before entering the fetal period of development during weeks 9 through During the fetal period, the fetus grows larger and more complex until it is ready to be born.
Lactation is the production and release of milk to feed an infant. The production of milk begins prior to birth under the control of the hormone prolactin. Prolactin is produced in response to the suckling of an infant on the nipple, so milk is produced as long as active breastfeeding occurs. As soon as an infant is weaned, prolactin and milk production end soon after. Oxytocin is also produced in response to infant suckling so that milk is only released when an infant is actively feeding.
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