Lipids Flashcards
how many classes there are?
There are two classes of lipid-based reproductive hormones, the steroids and the eicosanoids.
Are lipids less soluble in aqueous fluids of the body than are proteins and monoamines?
Lipids are in general less soluble in the aqueous fluids of the body than are proteins and monoamines.
how are they often?
They are often either modified for transport through the body fluid or carried on transporters.
1) Steroids
title
What do steroid hormones comprise/from what are they all derived?
The steroid hormones comprise a large group of molecules all derived from a common sterol precursor: cholesterol.
From what is cholesterol synthesized and what is cholesterol’s role?
Cholesterol is synthesized from acetate in many tissues of the body, and is an important structural component of cell membranes.
what is the first and common step in the formation of all major steroid hormones?
The conversion of cholesterol to pregnenolone marks the first and common step in the formation of all major steroid hormones.
where does the conversion occur?
The conversion occurs on the inner mitochondrial membrane.
where is Pregnenolone then converted?
Pregnenolone is then converted to the sex steroids in the adjacent smooth endoplasmic reticulum.
How many main families of steroids are there?
There are four main families of steroid: the progestagens, androgens, oestrogens and corticosteroids.
What are the first 3 steroids considered as?
The first three steroids are considered as the sex steroids.
How is the interconversion from one class of steroid to another undertaken?
The interconversion from one class of steroid to another is undertaken by a series of enzymes arranged together as a biosynthetic unit.
What do the structural features shared by members of each steroid class give?
The structural features shared by members of each steroid class are reflected in common functional properties.
Androgens
androgens are associated with the development and maintenance of male characteristics and fertility
Oestrogens
oestrogens with the development and maintenance of female characteristics and fertility
Progestagens
progestagens are associated with the preparation of pregnancy and its maintenance
What is dihydrotestosterone (DHT)?
Dihydrotestosterone (DHT), is a product of the conversion of testosterone by the enzyme 5α-reductase.
What happens without DHT?
Without DHT, regardless of the genetic or gonadal sex, the external genitalia will develop along the female template.
2) Eicosanoids
title
what are eicosanoids?
The eicosanoids are non-steroidal molecules that pass through plasma membranes by means of specific transporters.
What do they comprise?
They comprise two major classes of messenger: the prostaglandins (PGs), which are of principal interest for reproductive processes, and the leukotriens, which play a lesser role.
what is the common precursor for a series of prostaglandins?
The arachidonic acid is the common precursor for a series of prostaglandins.
where are PGs synthesized?
PGs are synthesized in most tissues of the body including the ovary and the uterine myometrium, cervix, ovary, placenta and fetal membranes.
describe eicosanoids
Eicosanoids have very short half-lives, are not transported to distant cells and therefore differ from the classic hormones.
how do they act?
They act as local hormones, either by paracrine or after a short passage through the local bloodstream.
