Menstrual cycle

The menstrual cycle, under the control of the endocrine system, is necessary for reproduction. It is commonly divided into three phases:

(1) the follicular phase,
(2) ovulation, and
(3) the luteal phase;

although some sources use a different set of phases:

(1) menstruation,
(2) proliferative phase, and
(3) secretory phase.

The length of each phase varies from woman to woman and cycle to cycle, though the average menstrual cycle is 28 days. Hormonal contraception interferes with the normal hormonal changes with the aim of preventing reproduction.

Stimulated by gradually increasing amounts of estrogen in the follicular phase, menses slow then stop, and the lining of the uterus thickens. Follicles in the ovary begin developing under the influence of a complex interplay of hormones, and after several days one or occasionally two become dominant (non-dominant follicles atrophy and die).

Approximately mid-cycle, 24–36 hours after the Luteinizing Hormone (LH) surges, the dominant follicle releases an ovum, or egg in an event called ovulation. After ovulation, the egg only lives for 24 hours or less without fertilization while the remains of the dominant follicle in the ovary become a corpus luteum; this body has a primary function of producing large amounts of progesterone.

Under the influence of progesterone, the endometrium (uterine lining) changes to prepare for potential implantation of an embryo to establish a pregnancy. If implantation does not occur within approximately two weeks, the corpus luteum will involute, causing sharp drops in levels of both progesterone and estrogen. These hormone drops cause the uterus to shed its lining in a process termed menstruation.

Histology of uterus

Organized into
(1) Mucosa (endometrium)
(2) Muscula Layer (myometrium)
(3) Serosa (perimetrium)



Mucosa (endometrium)
(1) Epithelium - Simple columnar epithelium (with ciliated & secretory cells)
(2) Lamina propria - very thick endometrial stroma
(3) Endometrial (uterine) glands develop as invaginations of the luminal epithelium and almost to the myometrium 

Endometrium is divided into two layers,
Stratum functionalis (functional layer) - lines the uterine cavity and sloughs off  during menstruation
Stratum basalis (basal layer) - is permanent and gives rise to a new stratum functionalist after menstruation


Muscular Layer( Myometrium)
3 layers of smooth muscle inner longitudinal, middle circular, outer longitudinal.

During labor and childbirth, coordinated contraction of the myometrium in response to oxytocin from posterior pituitary help expel the fetus from uterus


Serosa or ( Perimetrium )
part of visceral  peritoneum;c/o simple squamous epithelium               
  

Ligaments of the uterus

Ligaments that support uterus in normal position

Broad ligaments - double folds of peritoneum attaching the uterus to either side of the pelvic cavity, holds the uterus in its position.

Round ligaments of uterus - from junction of uterine tube and uterus to deep inguinal ring, pass through the inguinal canal and attached to mons pubis.

Uterosacral ligaments - on either side of rectum and connect the uterus to the sacrum.

Cardinal or lateral or transverse cervical ligaments - extend from the pelvic wall to cervix and vagina.

Pubocervical ligaments - from anterior aspect of the cercix to back or cervix.

Group 1 hormone: Hormones have intracellular receptors and affect gene expression.

1. Hormones in this group are lipophilic and derived from cholesterol and amino acid derivative T3 and T4.

2. After secretion from specific glands, these hormones associate with transport proteins.

3. As soon as they bind to the plasma membrane of target cells, they detached from binding protein (carrier protein).

4. The free hormone readily traverses the plasma membrane of target cells, and encounter receptors in either the cytosol or nucleus of the target cells.

5. The ligand receptor complex assumed to be intracellular messenger in this group.
The general feature of these hormones are:
a) The hormone diffuses through the plasma membrane of all cells but only encounter their specific, high affinity receptor in target cells.

b) The hormone receptor complex undergoes a temperature and self dependent activation reaction that results in size, conformation, and surface charge changes that render it able to bind to (DNA) chromatin.

c) The hormone receptor complex binds to a specific region of DNA called the hormone response element (HRE) and activates or inactivates specific genes.

d) By selectively affecting gene expression and the production of the respective messenger RNAs, the amount of specific proteins are changed and metabolic processes are influenced.

Classification of hormone by general mechanism of action

1. Group 1. Hormones that bind to intracellular receptors

2. Group 2. Hormones that bind to cell surface receptors
a) Second messenger is c AMP
Eg. ACTH, ADH, PTH, TSH, glucagon
b) Second messenger is c GMP Eg. ANP, NO
c) Second messenger is calcium or phosphoinocitol or both Eg.Ach, α ADRENERGIC, TRH
d) Second messenger is a kinase or phosphatase cascade Eg. GROWTH FACTORS, INSULIN

General mechanism of hormone Action

1. Group 1 hormone: Hormones have intracellular receptors and affect gene expression.

2. Group 2 hormone: Hormones have membrane receptors and use intracellular messengers

Breakdown of hormones

1. Peptide and protein hormones are broken down into amino acid that enter into the amino acid pool.

2. Steroid hormones are hydroxylated in the endoplasmic recticulum and then conjugated with glucuronic acid, sulfate and phosphate. Thus, the end product of steroid hormones are conjugated compounds.