How are males and females genetically dimorphic?
The presence of two X chromosomes in females instead of an X and a Y in a male
What disadvantage has the Y chromosome developed through evolution?
The Y chromosome lost much of it’s genetic data since it is far smaller, and the significant change in genetic material means that the X and Y cannot swap genetic material during meiosis. Therefore cannot be repaired.
What is X-Inactivation?
X-Inactivation means that female cells will deactivate one copy of this X chromosome.
The X inactivation is random in each cell and therefore can result in X linked diseases
Why will X-linked conditions affect men more than women?
Because the faulty gene carried on the X has no other X chromosome to correct this mistake and therefore will only display this faulty gene in all cells that use it.
In X-linked recessive conditions the recessive gene has no dominant alternative to override it and therefore the faulty recessive gene is used.
Does sex play a role on medical treatment? If so how?
Yes, it can affect required drug dosage, for example males may require more.
Treatment may affect two sexes differently?
Under-diagnosis due to gender bias, e.g. breast cancer in males.
Certain drugs cannot be given to pregnant females to avoid damaging the foetus. e.g. Thalidomide.
What gene is responsible for determining sex in a foetus?
The SRY Gene.
What is the SRY Gene?
It is a transcription factor that triggers embryonic development as a male.
What are two abnormalities associated with the SRY Gene?
Mutation of the SRY gene or other sex-determining genes downstream of SRY can result in an XY female.
If the SRY gene is copied to the X chromosome, an XX male results.
What week during pregnancy does differentiation occur?
What special cells are formed in male sexual differentiation?
What happens to differentiate males from females?
At 6 weeks differentiation will occur.
A group of special cells called germinal cells will form.
These germinal cells will be attracted towards the two urogenital ridges (which are cells developing near the baby’s developing kidneys)
Testosterone and anti-Mullerian hormone are secreted.
What produces sperm in males?
The testes produce sperm and the ducts transport, store and assist in maturation of the sperm.
What produces the seminal fluid portion of semen?
The seminal vesicles, prostate gland and the bulbourethral glands.
What are the testes and their function?
They produce sperm and steroid hormones.
Divided into lobules by septa of tunica albuginea
What in the testes is responsible for producing sperm?
The sperm is produced by seminiferous tubules, there are roughly 600 per teste.
Describe the structure of the seminiferous tubule.
A basement membrane, lined with smooth muscle to aid movement of sperm through tubule, surrounds a complex of epithelial cells known as sertoli cells, with clusters of spermatogonia around them. The spermatogonia become more differentiated the closer to the centre of the tubule they are until mature spermatozoa in the middle.
Adjacent to these tubules are Leydig cells responsible for production of testosterone and blood capillaries.
What are Sertoli cells?
Epithelial cells which are part of the seminiferous tubules that are connected by tight junctions (small gaps between cells). Assist in progression of germ cells to spermatozoa (sperm cells). Also secretes anti-Mullerian hormone.
What are Leydig cells?
Interstitial cells adjacent to seminiferous tubules that produce testosterone.
What is the Mediastinum Testis?
The fibrous connective tissue that divides the testes into lobules, it is wider near the top of the testes than near the bottom.
What are somatic cells?
Any cell that isn’t a sperm or an egg cell.
What is a spermatogonia cell?
An undifferentiated male germ cell
Describe the sequence of maturation of spermatozoa.
Spermatogonia will differentiate through mitosis to primary spermatocytes.
Primary spermatocytes will undergo further meiosis to become secondary spermatocytes (Meiosis I). Primary spermatocytes are diploid.
Secondary spermatocytes will then undergo Meiosis II to form circular spermatids. Secondary spermatocytes are haploid.
Spermiogenesis is a complex process that will produce spermatozoa or sperm cells.
What is the Vas Deferens?
What are the three components of the vas deferens?
A thick walled tubule that stretches from the tail of the epididymis, where sperm is stored prior to ejaculation, to the ampulla of the vas deferens (a sac like enlargement of the vas deferens near base of prostate.
The three components are:
- Dense adventitia
- Pseudostratified columnar epithelium
What are serosa?
Serous membranes are outer layers of mesothelium that cover and provide protection to organs and are lubricated to allow smooth movement when organ is moving.
Serosa cover organs that should move freely inside a cavity.
What is adventitia?
Adventitia is loose connective tissue found primarily covering arteries and veins. Retroperitoneal organs will also be bound in adventitia.
Adventitia covers organs that should be bound to surrounding structures for support.
Describe the structure of pseudostratified columnar epithelium.
The structure consists of long irregular columnar cells that stretch up with small basal cells that fill in the irregular gaps at the base of these cells. Occasional goblet cells line this epithelium to produce mucus as well as other functions.
What is the spermatic cord?
What is it comprised of?
The cord responsible for transporting sperm from the testes to the ejaculatory duct next to the seminal vesicle in the prostate.
It is comprised of the Vas deferens, testicular veins and arteries surrounded by it’s serosal covering, the tunica vaginalis.
What is the prostate and it’s function?
The prostate gland is a gland located by the seminal vesicles at the end of the spermatic cord and the start of the ejaculatory duct.
It secretes fluid which:
- Is slightly acidic, counteracting vaginal acidity (pH 7.2 -7.6)
- Contains citrate, thought to be used as nutrient by sperm
- Contains enzymes: PSA (prostate specific antigen) which helps to liquify
semen that may congeal in female reproductive tract.
PSA levels can be used to screen for prostate cancer.
What is the prostate gland composed of?
Is is composed of 30-50 tubuloalveolar glands that empty into 25 excretory ducts.
The glandular epithelium is cuboidal/columnar.
The ducts are simple columnar epithelium which transforms into transitional epithelium.
Surrounding the lumen of the glands and epithelium is fibromuscular stroma (smooth muscle).
What are the bulbourethral glands?
They are located beneath the prostate gland and secrete an alkaline, mucus-rich lubricating fluid which is released before ejaculation.
(Also known as Copwer’s glands)
What are the seminal vesicles?
Located either side of the prostate gland, they empty sugar rich secretions into ejaculatory duct.
What is the epididymis?
The coiled tubule above each testis that is responsible for retaining sperm until ejaculation. Spermatozoa produced from the seminiferous tubules, coming from the Sertoli cells will further mature and concentrate.
Describe the structure of a spermatozoa
The cell is comprised of 5 main components:
- Tail or flagellum
What is the acrosome of a spermatozoa?
The acrosome is a special secretory vesicle containing hydrolytic enzymes that break down the outer coatings and membrane of the egg cell.
What is the head of a spermatozoa?
The head is the membrane surrounding the nucleus, acrosome and midpiece of the cell.
What is the midpiece of a spermatozoa?
The slender part of the sperm cell before the tail starts, it contains the mitochondria that produce the energy needed for cell motility.
What is the flagellum of a spermatozoa?
The flagellum is the apparatus used for motility. It is comprised of the axoneme, which are a collection of 11 microtubules and a thin membrane. There are two central microtubules surrounded by nine evenly spaced pairs of microtubules with thousands of dynein motor proteins attached.
How do dynein proteins in the axoneme produce movement?
Upon introduction to ATP, the proteins arms will shift position in a walking like manner, and in essence, ‘slide’ down the doublet opposite to the one it is attached to, this will produce the movement seen in cilia and flagella.
Describe the regulation of hormones in the testes starting from the hypothalamus.
- The hypothalamus releases gonadotropin releasing hormone directly to the anterior pituitary gland.
- The gonadotrophs in the anterior pituitary gland will then release luteinising hormone and follicle stimulating hormone into the bloodstream.
- The luteinising hormone will stimulate Leydig cells to produce testosterone.
- In the presence of testosterone and follicle stimulating hormone, Sertoli cells can undergo spermatogenesis, androgen binding protein will also be produced and will bind to testosterone and keep concentration high in seminiferous tubules.
- Inhibin will be produced when Sertoli cells are stimulated by FSH, this hormone inhibits FSH secretion of anterior pituitary gland.
- Testosterone inhibits LH secretion in anterior pituitary and gonadotropin releasing hormone in hypothalamus?
What are androgens?
A group of sex hormones, most predominant of which is testosterone. Mostly present in males and present in small amounts in females.
How is testosterone activated?
Testosterone is activated by 5a-reductase to dihydrotestosterone.
Aromatase converts testosterone into oestradiol, an oestrogen derivative. Aromatase is present in higher amounts in adipose tissue.
What are testosterone and DHT important for?
- Differentiation of the foetus
- Development of male secondary characteristics at puberty
- Acts on brain to promote sex drive
As well as other body processes.