Medical Physiology Block 7 Week 4 Flashcards
Describe mitosis.
cell division in somatic cells
five phases: prophase, metaphase, anaphase, and telophase
Sister chromatids (two copies of the same DNA on a chromosome) of each chromosome split, one going to each daughter cell during anaphase of the single mitotic division
Describe meiosis.
N= 23; begins with duplication of DNA, like mitosis (4N)
round 1: homologous chromosomes separate during meiosis I (2N); crossing over prophase I
round 2: sister chromatids separate (1N); like mitosis
One spermatogonium yields how many spermatids? One oogonium yields how many oocytes?
four; one mature oocyte and two polar bodies
What is the chromosome number of a zygote?
2N
Describe the Y chromosome.
small and acrocentric; when a Y chromosome is present, the individual develops as a male
How many pairs of chromosomes are the same size in the female karyotype?
8
Describe differentiation of the indifferent gonad in women. men?
In embryos with an XX sex chromosome complement, the cortex develops into an ovary, and the medulla regresses
In embryos with an XY sex chromosome complex, the medulla differentiates into a testis, and the cortex regresses
Are two X chromosome necessary for normal ovarian development?
Yes
What is the testis-determining gene?
SRY on Y chromosome (short arm)
How can sexual differentiation differ from the expected results driven by the genotype?
If the gonads fail to produce the proper messengers, if other organs (the adrenal glands) produce abnormal levels of sex steroids, or if the mother is exposed to chemical agents (synthetic progestins and testosterone) during pregnancy, sexual development of the fetus may deviate from that programmed by the genotype
Describe migration of primordial germ cells. What is the composition of the gonad?
migrate along the mesentery of the gut (originate from the endodermal epithelium of the yolk sac); Migration of primordial germ cells (controlled by chemokine (CXC motif) receptor and CXCR4 and the chemoattractants stromal-derived factor 1; integrins and RTKs are required (coactivators?))
eventually take up their position embedded in gonadal ridges
The gonad forms from a portion of the coelomic epithelium, the underlying mesenchyme, and the primordial germ cells that migrate from the yolk sac.
What is the rete testis?
The rete testis is a system of thin, interconnected tubules that develop in the dorsal part of the gonad (drain the seminiferous tubules)
What hormones regulate the development of male internal genitalia? external genitalia?
androgens (testosterone) produced by the developing testis cause development of the wolffian duct and degeneration of the Mullerian ducts (AMH)
testosterone and DHT cause masculinization of the external genitalia
What hormones regulate development of the female internal genitalia? external genitalia?
In the female embryo, the mullerian ducts develop, whereas the wolffian ducts degenerate; in the absence of a functioning testis, the left and right mullerian ducts develop as the fallopian tubes (oviducts), the uterus, and the upper third of the vagina (internal genitalia)
Absence of androgens causes the external genitalia development to be female
Describe the mesonephros.
Mesonephros has glomeruli and renal tubules which empty into the mesonephric duct, which, in turn, carries fluid to the urogenital sinus (developing bladder)
What structures develop from the wolffian ducts?
vas deferens, seminal vesicles, and ejaculatory duct (and prostate gland?)
Describe Mullerian ducts.
The paramesonephric or mullerian ducts develop as invagination of the coelomic epithelieum on the lateral aspects of the mesonephros; run cadually and parallel to the mesonephric ducts
In the caudal region, mullerian ducts cross ventral to the mesonephric ducts and fuse to form a cylindrical structure, the uterovaginal canal
Does a mature mesonephros exist in men? women?
Yes; proximal end of the epididymis
No
Does development of Mullerian ducts require the ovaries?
No
What is the result of castration on development of wolffian ducts?
development of Mullerian duct instead (no testosterone or AMH)
external genitalia proceed normally
Describe antimullerian hormone.
member of inhibins and activins family (glycosylated, disulfide-linked subunits; activity in c-domain)
transcription may be initiated by SRY
What is the cloaca? What happens to it during development?
A tubular structure called the cloaca is the common termination of the urogenital and gastrointestinal systems (membrane separates the tube from the amniotic fluid)
Wedge of mesenchymal tissues separates the cloaca into a dorsal and ventral cavity (dorsal cavity is the rectum and the ventral cavity of the urogenital sinus)
Both the wolffian and müllerian ducts empty into the urogenital sinus
How many regions are there in the urogenital sinus?
three
In males, the vesicle becomes the urinary bladder, the pelvic part becomes the prostatic part of the urethra, and the phallic part becomes the initial portion of the penile urethra (remnants of the vagina sometimes persist as a prostatic utricle)
In the female, the vesicle part also develops into the urinary bladder, the pelvic part becomes the entire female urethra, and the phallic portion develops into the vestibule of the vagina (urethra, vagina, and the ducts of the greater vestibular gland of Bartholin empty into this vestibule)
Why does the female have separate openings for the urinary and reproductive systems?
A solid core of tissue called the vaginal plate grows caudally from the posterior wall of the urogenital sinus. The lumen of the vagina forms as the center of this plate resorbs. Thus, the female has separate openings for the urinary and reproductive systems.
During early fetal development, the hymen (a think membrane) separates the lumen of the vagina from the cavity of the urogenital sinus