The term, "menstrual cycle" refers to the hormonal and reproductive tissue changes that occur in adult females during their reproductive years. The cycle is on average 28 days, and is divided into three parts.
Follicular Phase - The first part of the cycle is menstruation and preparation for ovulation.
A woman is born with all the eggs she will ever have - around 450,000. They are stored in the ovaries, inside individual sacks called follicles.
Each month, the hypothalamus, (a gland in the brain which regulates hunger, thirst, sleep, libido and the endocrine system) releases Follicle Stimulating Hormone Releasing Factor (FSH-RF) causing the Pituitary, another gland in the brain, to release Follicle Stimulating Hormone (FSH) and a little Leutenizing Hormone (LH).
The FSH and LH cause follicles to mature. The follicles ripen over a period of 7 days, during which they release increasing amounts of estrogen.
Ovulatory Phase - Preparing the uterus
Estrogen causes the lining of the uterus to thicken. It also causes the cervical mucous to change consistency, which allows sperm to travel more easily into the uterus through the cervix. The body temperature also rises slightly. When estrogen reaches a certain level, the hypothalamus is caused to release Leutenizing Hormone Releasing Factor (LH-RF) causing the pituitary to release a large amount of Leutenizing Hormone (LH). This surge of LH causes the most mature follicle to burst open, releasing an egg. This is called Ovulation.
During the time ovulation is approaching, blood supply to the ovary increases, and ligaments contract, allowing the egg to find its way to the fallopian tube.
Once in the fallopian tube, the egg is carried toward the uterus by cilia - tiny hair-like projections inside the tube.
The Luteal Phase - After ovulation until menses
The burst follicle becomes the "corpus luteum" (meaning Yellow Body). As it heals, it produces estrogen and more progesterone. Progesterone is a hormone which would allow a pregnancy to progress healthily. It causes the uterine lining (endometrium) to become covered with mucous secreted from the glands within the lining itself.
Fertilization occurs if sperm is already in the uterus.
If the woman does not become pregnant, the follicle will turn white, and is called the "Corpus Albicans" (or white body).
If fertilization and implantation do not occur, the spiral arteries of the lining close off, stopping blood flow to the surface of the lining. The blood pools into "venous lakes" which, once full, burst and, with the endometrial lining, form the menstrual flow. Most periods last 4 to 8 days but this length varies over the course of a lifetime.


This tutorial is a review of the Heart and its parts.  The four Heart valves are:
- The tricuspid valve is located between the right atrium and right ventricle. 
- The pulmonary or pulmonic valve, is between the right ventricle and the pulmonary artery.
- The mitral valve is between the left atrium and left ventricle.
- The aortic valve is between the left ventricle and the aorta. Each valve has a set of flaps (also called leaflets or cusps). 
The mitral valve has two flaps; the others have three. Normally, the valves permit blood to flow in just one direction.

Blood Pressure is pressure of blood cells against the walls of the main arteries. Pressure is highest when the ventricles in the heart contract (systole) and lowest when they relax (diastole). The two pressures are measured in millimeters of mercury and shown as follows such as a desirable blood pressure of 120 over 80.

The lungs are a complex organ, consisting of many individual parts that work together.
The bronchus is a branch of the trachea that transports Oxygen (O2) to the lung.
The Bronchioles are numerous small tubes that branch from each Bronchus into the lungs. They get smaller and smaller.
The Alveoli are tiny, thin-walled air sacs at the end of the Bronchiole branches where gas exchange (CO2 to O2) occurs.
Oxygen is drawn into the lungs when the surrounding muscles; called the diaphragm, move away from the lungs.  Oxygen enters the trachea, a tube leading into the lungs, then is dispersed into the bronchus tubes, and is further spread out into the bronchioles. This process acts as a filter to purify the raw air into pure oxygen.
From there, Oxygen enters the Alveioles.
The Alveoli is the final destination of the inhaled air. The Alveoli causes an exchange of Oxygen and Carbon Dioxide.  The Lungs replace Carbon Dioxide (CO2), a waste product made by your red blood cells, with Oxygen (O2), which is necessary for your organs to live. The blue paths represent the bloodstream after Oxygen has been used up, when the blood cells are saturated with Carbon Dioxide. The red paths represent the bloodstream after the blood cells have been infused with freshly inhaled Oxygen.
COPD-Chronic Obstructive Pulmonary Disease includes emphysema and chronic bronchitis and is caused by smoking particles, pollution, dust and other substances blocking the Alveoli.