The human placenta secretes estrogen, progesterone, human chorionic gondotropin (hCG), and human placental lactogen (hPL). Aldosterone is produced by the adrenal gland. 

A zygote is a eukaryotic cell formed by a the joining of two gametes (sperm and egg). The zygote then goes on to divide several times till it forms a small clump of cells termed a morula. The next stage is the formation of a blastocyst, which is the final stage before development into an embryo.  

The zygote has developed into an embryo and reached the uterus by day 5 and will generally implant on day 7-10 after ovulation.

The most common cause of first trimester miscarriage is chromosomal abnormalities. These can occur in as many as 1 in 4 pregnancies, and cause the developing embryo issues that are not compatible with life. 

Lifting heavy objects and exercise are NOT generally responsible for triggering miscarriage (though they could potentially trigger a miscarriage in individuals with underlying conditions or other risk factors). 

Mitochondria are often called "the powerhouse of the cell" because they produce ATP, the body's most basic unit of energy. The nucleus houses the cell's DNA, the rough endoplasmic reticulum is the site of cellular protein manufacturing, and the Golgi apparatus packages protein manufactured in the cell for release and transport to the rest of the body. 

The cell membrane has many purposes. It anchors the cytoskeleton to give the cell shape and structure. It houses proteins that both interact with signaling molecules from outside the cell and communicate with secondary messengers within the cell. It facilitates the absorption and release of electrolytes, water, and vesicles carrying proteins or other molecules. It forms junctions with other cells and connects the cell to the extracellular matrix.

One thing the cell membrane does not do, however, is act as a site of protein synthesis. That occurs primarily in the rough endoplasmic reticulum or on ribosomes in the cytoplasm.

The majority of lipid production within the cell occurs within the smooth endoplasmic reticulum. It is also the site of production of steroids and phospholipids. The Golgi apparatus is responsible for packaging of cell products for transport outside of the cell. The mitochondria produce ATP, and the nucleus houses the DNA.

Aerobic cellular respiration occurs exclusively in the mitochondria. These organelles are present in greater number in cells that require a large supply of ATP, such as striated muscle cells, liver cells, and sperm cells. 

The framework of the cell is make up by the cytoskeleton. The cytoskeleton gives the cell both shape and structure, and allows the cell to attach to extracellular connective tissue in order to form tissue types. There are three major fibers that make up cytoskeleton - microfilaments (actin), intermediate filaments, and microtubules.

Cholesterol is a vital component of the cellular membrane. It maintains both the fluidity and structural integrity of the cell. While cholesterol is an integral component of steroid production, this occurs outside of the cell membrane. Cholesterol does not play a significant role in cellular energy production or cell membrane detoxification.