Aquaporins are membrane proteins that span the entire membrane. An aquaporin protein must be able to interact with polar regions that are both extracellular and intracellular as well as polar water molecules moving through it’s core. Additionally, it must be able to interact with the nonpolar phospholipid tails. How is it possible that this protein (a collection of amino acids) can meet all of these requirements?

- Proteins have the ability to change their conformation in order to establish multiple types of interactions  

- Proteins are macromolecules that are large enough to cross the membrane of biological cells regardless of different regional polarities and they may act as pores through which molecules diffuse.

- Proteins have well-defined domains with amino acid residues whose R-groups contain both polar and nonpolar portions and thereby they interact with surrounding molecules according to their requirements.

Explanation:

Porins are a type of protein that cross the cell membrane and thus act as pores through which molecules can diffuse. Aquaporins are porins that form pores across the cell membrane and allow the transport of water molecules between cells. These proteins consist of six transmembrane α-helices embedded in the cell membrane. Aquaporins have five loop regions that enter and exit the cell membrane, and two of these regions are hydrophobic.

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.