1. Origin Of The Sexes

Question 1

What is the embryonic kidney comprised of

What is the role of each component

Answer 1

Mesonephric tubules: primitive renal function

Mesonephric duct:

Question 2

Describe primordial germ cells:
Where do they arise
When do they appear
Where do they migrate to

Answer 2

Special population of cells, separate from somatic cells
Arise in epithelium of yolk sac, near base of allantois

Allocated shortly after epic last folding in 2nd week

Migrate to retro peritoneum, along dorsal mesentery

Question 3

Describe the Mesonephric ducts (Wolffian duct)

Answer 3

Part of embryonic kidney
Develops in both male & female
Runs causally
Makes contact with cloaca

Question 4

Describe the paramesonephric ducts (Mullerian duct)

Answer 4

Develop near Mesonephric ducts
Develop in both males & females
Appear as invaginations of epithelium of urogenital ridge
Causally, make contact with cloaca (urogenital sinus)
Cranially, open into abdominal cavity
Grow into peritoneal cavity, taking gonads & fusing as a fold
Creates uterus & Fallopian tube

Question 5

Describe the development of genetic male

Answer 5

Primordial germ cells carry Y chromosome
Expression of SRY gene
Mesonephric ducts reach urogenital sinus
Ureteric bud sprouts
Urogenital sinus expands as smooth muscle appears
UB & MDs make independent openings in UGS
MD now redundant but androgens retain it; involved in dev of testis
Testis secrete Mullerian Inhibiting Hormone from Sertoli cells
Paramesonephric duct degenerates

Question 6

Describe the development of genetic female

Answer 6

Primordial germ cells do not carry Y gene: absence = female dev
Mesonephric ducts reach urogenital sinus
Ureteric bud sprouts from Mesonephric duct
Urogenital sinus begins to expand, Mesonephric duct begins to regress
As MD regression continues, UB opens into UGS
Ovary develops; no androgens = MD degenerates
No testis = no MIH

Question 7

Describe the 3 basic components of the external genitalia in the indifferent stage

Answer 7

Genital tubercle
Genial folds
Genital swellings

Question 8

Describe the development of the male internal & external genitalia
(What happens to basic components, descent of testis, hormone influence)

Answer 8

Genital tubercle elongates
Genital folds fuse to form spongy urethra
Retroperitoneal Testis descend thru inguinal canal & spermatic cord lies in inguinal canal

Influenced by dihydrotestosterone (metabolised testosterone)

Question 9

Describe the development of the female internal & external genitalia
(Does fusion occur, descent of ovaries)

Answer 9

No fusion of genital folds: urethra opens into vestibule
Descent of ovaries:
gubernaculum attaches ovary inferiorly to labio-scrotal folds
Ovary descends into pelvis
Round ligament of uterus lies in inguinal canal

Question 10

What are the common abnormalities of genital development

Answer 10

Genotype-phenotype mismatches

Structural defects:
Cloacal partitioning defects
Hypospadias (abnormally placed urinary hole)
Uterine structural defects (e.g. Bicornate uterus)

Question 11

What are the reproductive hormones secreted by the hypothalamus

Answer 11

Gonadotropin Releasing Hormone
Prolactin Releasing Hormone
Prolactin Inhibiting Hormone

Question 12

What are the reproductive hormones secreted by the posterior pituitary

Answer 12

Oxytocin

Question 13

What are the reproductive hormones secreted by the anterior pituitary

Answer 13

Gonadotrophins:
Follicle stimulating hormone
Luteinising hormone
Prolactin

Question 14

What are the reproductive hormones secreted by the testis

Answer 14

Gonadal steroids:
Inhibin
Testosterone
Mullerian inhibiting hormone

Question 15

What are the reproductive hormones secreted by the ovaries

Answer 15

Gonadal steroids:
Inhibin
Oestrogen
Progesterone

Question 16

What are the reproductive hormones secreted by the placenta

Answer 16

Human chorionic gonadotrophin
Human placental lactogen
Oestrogen
Progesterone

Question 17

Describe the structural layers of the testis

Answer 17

Tunica vaginalis, which contains:
Parietal layer, adjacent to spermatic fascia
Visceral layer, covering surface
Small amt of fluid in between layers

Tunica albuginea: tough, fibrous outer surface
(thickens into mediastinum of testis which seminiferous tubules extend from)

Question 18

What are the 2 types of cells in the testis
Where are they found
What do they produce

Answer 18

Sertoli cells:
Associated with seminiferous tubules
Produce spermatozoa

Leydig (interstitial) cells:
In the interstitial tissue, adjacent to seminiferous tubules
Secrete testosterone

Question 19

Describe the course of sperm from testis to urethra

Answer 19

Seminiferous tubules
Rate testis
Epididymis
Vas deferens
(Through ampulla & ejaculatory duct)
Urethra

Question 20

Describe the urogenital ridge

What does it give rise to?

Answer 20

Region of intermediate mesoderm

Gives rise to:
Gonad (indifferent)
(also derived from primordial germ cells: extra gonadal)

Embryonic kidney (mesonephros)

Question 21

Describe the differentiation of Type B spermatogonia into spermatozoa

Answer 21

Undergoes fixed number if mitotic clone divisions (usually 64)

A chain of primary spermatocytes push their way towards lumen of tubule

Begin meiosis:
1st division produces 2 haploid secondary spermatocytes
Each divides again to form spermatids

Spermatids re-modelled as pass down tubule to form sperm (spermatozoa) by spermiogenesis

Cytoplasmic bridges between them broken down

Released into tubule lumen

Washed down rate testis by fluid secreted by Sertoli cells

Spermatozoa mature during progress thru epididymis

Question 22

Describe the process of spermatogenesis (from foetus to puberty)

Answer 22

Germ cells colonise sex cords in primordial gonad

Before birth: germ cells proliferate by mitosis - from spermatogonia stem cells

At puberty: cords hollow out to from seminiferous tubules

At intervals, A1 spermatogonia emerge from stem cells

Differentiate into either:
more Type A stem cells
Type B cells, committed to differentiation into spermatozoa

Question 23

Define Spermatogenic cycle

Answer 23

Amount of time it takes for reappearance of same stage of cycle within given segment of tubule
Development of A1 spermatogonia through to 256 sperms

Question 24

Define spermatogenic wave

Answer 24

Distance in tube between parts that are in the same stage

Different parts of the tube begin spermatogenic cycle at different times in a ‘wave’, so sperm production is constant

Question 25

Describe the role of rete testis

Answer 25

Network of canals in mediastinum of testis

Seminiferous tubules drain into them

Question 26

Describe the role of the epididymis

Answer 26

Convoluted duct where sperms stored & continue to mature

Question 27

Describe the role of the vas deferens

Answer 27

Continuation of epididymis

Contracts in copulation, forcing sperm along tube to be mixes with other components of ejaculate

Question 28

Describe the role of the seminal vesicles

Answer 28

Secrete thick, alkaline fluid rich in fructose & coagulating agent

Question 29

Describe the role of the prostate

Answer 29

Fluid makes up 20% of semen vol

Role in activating sperms

Question 30

Describe the role of the bulbourethral glands

Answer 30

2 pea-sized glands, largely embedded in external urethral sphincter
Ducts open into proximal part of spongy urethra in bulb of penis
Mucus-like secretion enters urethra during sexual arousal

Question 31

Describe the development of oocytes in the foetus

Answer 31

Primordial germ cells colonise cortex of primordial gonad, becoming oogonia

Proliferate rapidly by mitosis

Most die, leaving approx 2 million

All enter meiosis 1 before birth to become primary oocytes
Stimulated by Mesonephric cells/follicular cells (somatic)

Single layer of somatic granulomas cells surround primary oocytes to form primordial follicles

Meiosis arrested at resting stage of prophase
Influenced by oocytes maturation inhibitor, secreted from follicular cells

Question 32

Describe the 3 stages of ovulation that forma a mature gamete

Answer 32

Pre-antral / primordial follicle

Antral / secondary follicle

Pre-ovulatory follicle

Question 33

Describe the pre-antral/ primordial follicle stage

Answer 33

Independent of hormones: occurs in ovary

Primary oocyte grows dramatically

Flat follicular cells become cuboidal granulosa cells

Granulosa cells secrete glycoprotein to surround oocyte with zona pellucida

Surrounding CT (stroma) cells from theca folliculi

Theca & granulosa cells collaborate to secrete oestrogens

Question 34

Describe the antral / secondary follicle phase

Answer 34

Granulosa cells continue to proliferate
Fluid appears between them = Antrum

As more fluid forma, secondary / Graafian follicle expands

Further development depends on reproductive hormones
Under influence of LH, thecal cells secrete adrogens (oestrogen)

Question 35

Describe the pre-ovulating follicle stage

Answer 35

37hrs before ovulation

Oestrogen cases receptors for LH to appear on outer Granulosa cells

LH stimulates these receptors = rapid changes in follicle

Within 3 hrs of LH surge, follicle starts meiosis

Secondary follicle enters meiosis II & arrests again 3 hrs prior to ovulation

Follicle size increases by increase in antral fluid

Structure begins to weaken

LH stimulates collagenase activity = follicle rupture

Ovum carried out into fluid & gathered up into Fallopian tube by fimbra

Meiosis not completed unless ovum fertilised

Question 36

Describe the formation of the corpus luteum

Answer 36

Remains of follicle re-organise themselves
Secretes progesterone & oestrogen under influence of LH
Lives for 14 days before regressing spontaneously (in absence of fertilised ovum)

Question 37

How long does it take for sperm to mature
How often are new groups of spermatogonia produced
How many haploid spermatids are produced by each spermatocyte
Approx how many spermatids are produced from one A1 spermatogonium

Answer 37

70 days

16 days (4 spermatogenic processes simultaneously)

4

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