Reproductive systems Flashcards
Describe the process of gametogenesis in males.
1) First, primordial germ cells undergo mitosis to become spermatogonia.
2) The process of division of spermatogonia forms primary spermatocytes, then secondary spermatocytes, then early spermatids which undergo maturation (all in the seminiferous tubules of the testes).
3) Lastly, the late spermatids mature into spermatozoa in the lumen of the epididymis.
Outline the anatomy and histology of the testes.
The testes are paired organs with a flattened egg shape. They develop in the foetal abdomen and descend at ~7th month of development in the scrotum (in order to be held at optimal temperature, which is 2-3 degrees cooler than core body temperature).
The testes have dual endocrine and exocrine function, and are connected to a duct system. A multilayer tunica covers the testes to facilitate blood supply to the testes (also portions it into lobules). There are three main layers:
1) The tunica vaginalis is the outer serosa, which has visceral and parietal layers with some fluid between them (too much fluid can create a hydrocoele – medical condition requiring drainage).
2) The tunica albuginea is the intermediate layer, and is made of dense connective tissue which subdivides the testes into their lobules.
3) The tunica vasculosa is the innermost layer, and it contains blood vessels and connective tissue (facilitates the blood supply to the testes).
Each testis is divided into around 200 lobules, and each lobule has up to four seminiferous tubules (~500m length of tubules per testis). The ductules converge efferently to feed into the epididymis.
Sertoli cells (AKA nurse cells) are epithelial cells of seminiferous tubules within the testes (tall simple columnar cells which span the basement membrane of the lumen and form tight junctions – the blood-testis barrier). These Sertoli cells surround proliferating germ cells, providing them with nutrients and are involved in phagocytosis of spermatid cytoplasm (cytoplasm not required when maturing into spermatozoa).
.The blood-testes barrier is necessary for protecting developing gametes within a protective environment. This is particularly important for fertility, as it prevents the immune system rejecting the spermatogenic cells.
FSH (released from the anterior pituitary gland) will stimulate Sertoli cells to secrete androgen-binding protein into the lumen of seminiferous tubules (binds to testosterone and is used for the developing spermatozoa), and to produce testicular fluid which includes special proteins to bind and concentrate testosterone.
Leydig cells are located between the tubules – they have a pale cytoplasm, as they are rich in cholesterol which is required for them to produce testosterone. Testosterone is produced in response to luteinising hormone (LH) released from the anterior pituitary from puberty onwards. This testosterone promotes spermatozoa production.
Outline the anatomy and histology of the spermatic cord.
The spermatic cord is a collection of structures which runs to and from the testes through the inguinal canal. It travels through the anterior abdominal wall, through the inguinal canal, then into the scrotum, where testicular vessels cool testes via counter-current exchange. It is surrounded by fascia, and the cremaster muscle makes up the middle layer of fascia around the spermatic cord to pull the testes up on contraction.
Structures of the spermatic cord include the vas deferens (main duct), the blood vessels (testicular artery and vein, pampiniform plexus, cremastic artery and vein, and deferential artery), nerves (autonomic nervous system), and lymphatic supply. The pampiniform plexus drains the testis, epididymis, and vas deferens, and carries the testosterone to the rest of the body – on the right it reduces toa single vein in the inguinal canal to form the testicular vein (contributes to the inferior vena cava); on the left it joins with the left renal vein.
Outline the anatomy and histology of the prostate.
The prostate glands are tubule-alveolar glands in a fibroelastic capsule (with smooth muscle for contraction) – they are donut-shaped and around the size of a walnut. It surrounds the prostatic urethra, and lies inferior to the bladder. Secretions liquify sperm, and contain prostate-specific antigen.
Outline the anatomy and histology of the Cowper’s glands.
Cowper’s glands lie interior to the prostate and empty into the spongy urethra – they secrete an alkaline mucous which neutralises urine in the urethra and lubricates it, also protects sperm during ejaculation
Outline the anatomy and histology of the male urethra.
The male urethra is around 20cm long, and is comprised of three parts – the prostatic urethra, the membranous urethra, and the spongy (penile urethra). The prostatic urethra receives ejaculatory and prostatic ducts. The membranous urethra is the shortest section, and is where the bulbourethral gland empties to neutralise the urine and protect the sperm. The spongy urethra leads from the membranous urethra to where the urine and reproductive fluids exit.
The male urethra is comprised of transitional epithelium, continuous with the bladder (cells slide over each other to expand).
Outline the anatomy and histology of the external male genitalia.
1) The penis is composed of endothelial-lined vascular spaces, and can be divided into 3 parts – the root and bulb, the shaft, and the glans penis. The root and bulb connect the penis to the pelvic bones. The shaft contains columns of erectile tissue, and two blood sinuses – the corpus spongiosum, and the corpus cavernosa. The corpus spongiosum lies ventrally, preventing the collapse of the urethra which runs through it, and the corpus cavernosa (2 paired sinuses) run dorsolaterally. The glans penis contains the prepuse/foreskin, which can be removed in a circumcision.
2) The scrotum consists of skin, connective tissue, and the dartos muscle. It is externally covered by pubic hair, and divided by a raphe (ridge). It internally holds the testes, and is divided by a ridge of connective tissue. It is important in the temperature control of the testes, contracting to bring testes closer to the body when cold, or relaxing to hold them further away when warm. The dartos muscle reduces the scrotum size by firming up the skin, and the cremaster muscle pulls the testes nearer to the body.
Describe the physiological functions of the male endocrine system.
Testosterone (synthesised in the Leydig cells) increases muscle cell size and proliferation, muscle mass and bone density, maturation of secondary facial hair. It is passed into the brain, where it is converted to oestradiol-17-beta by aromatase, which is responsible for male brain differentiation. It can cause acne, hypertension, an enlarged heart, and liver damage (acts as an anabolic steroid, causing changes in cholesterol – increased LDL and decreased HDL). It is converted to dihydrotestosterone by 5-alpha-reductase, which encourages the prostate, scrotum, and penis formation and growth.
Outline the anatomy and histology of the ovaries.
The ovaries are paired female reproductive glands which produce eggs (oocytes) and hormones. They are flattened, ovoid shaped gland (~3cm long), and are suspended in the upper pelvis by a range of ligaments. Suspensory ligaments connect them to the posterior pelvic wall, and utero-ovarian ligaments connect the ovaries to the uterus (both these are embedded in a larger ligament – the broad ligament).
Ovaries are made of simple cuboidal germinal epithelium with stromal connective tissue (forms the outer cortex and inner medulla). The outer cortex (tunica albuginea) is the functional area which contains gametes and the site of hormone production. The inner medulla is the “service area” (blood vessels, nerves, etc).
Outline the anatomy and histology of the fallopian tubes.
The uterine/fallopian tubes are paired ducts which facilitate oocyte transport. They extend from the ovary to the uterus (though the ovaries are not actually connected to the fallopian tubes, but the ovary opens into the peritoneal cavity, where the egg transfers through and then enters the fallopian tube). Fallopian tubes are made of ciliated columnar epithelium with supporting lamina propria (cilia transport oocyte to uterus). However, the ciliated cells are oestrogen dependent (deteriorate at menopause). There is also a muscularis (smooth muscle) layer which helps peristalsis of the oocyte.
There are four main regions of the fallopian tubes:
1) The infundibulum is a funnel shaped expansion at the ovary end with long thin projections known as fimbriae (receives the oocyte, this part has the most microvilli to transport the oocyte to the ampulla). The fimbriae enlarge during the menstrual cycle in order to “catch” the oocyte which has been released from the ovary.
2) The ampulla is the longest and widest part of the tube, and is the site of fertilisation.
3) The isthmus is the medial 1/3 of the tube – it is narrow but thick-walled.
4) The interstitial part is continuous with the wall of the uterus (connects the fallopian tubes with the uterine cavity).
Outline the anatomy and histology of the uterus and pelvic floor muscles.
The uterus (AKA the womb) is about the size and shape of an upside down pear, and lies posterior to the bladder, and anterior to the rectum. It is a hollow, muscular organ located in the female pelvis, which provides mechanical and nutritional support for developing embryo and foetus. It can be divided into three main zones; the fundus (large, rounded portion which lies posterior to the fallopian tubes), the body (central portion), and the cervix (neck of the uterus which opens to the vagina).
There are three layers to the uterine wall:
1) The perimetrium is a serous membrane covering the outside of the uterus.
2) The myometrium is the outermost layer of the uterine wall – it is also the thickest layer, and made of smooth muscle (for contractions) – at around 2 weeks pre-term in labour, myometrial cells become polarised towards the threshold of contraction (Braxton Hicks contractions).
3) The endometrium is the innermost layer – it is a mucous membrane with simple columnar epithelium and lamina propria (the site of implantation of the oocyte).
It can also be considered to have two zones – the functional endometrium zone (undergoes changes during the menstrual cycle) and the basal endometrium zone (stratum basalis).
Uterine glands within the basal endometrium zone contain carbohydrates to nourish the embryo, and spiral arteries rupture during menstruation when the functional zone is shed (from 8mm to 1mm thick).
The uterus is held in place by four main ligaments and pelvic floor muscles – the broad ligament, the round ligament, the cardinal ligaments, and uterosacral ligaments. The pelvic floor is a group of muscles found at the base of the pelvis which are responsible for holding lower abdominal organs in place. The pelvic diaphragm has a raphe where the two sides of the pelvic diaphragm meet, and ligaments such as the cardinal, pubovesical, and uteral ligaments assist this.
These pelvic ligaments can be torn during birth, resulting in damage meaning organs may no longer be supported (prolapse). As well as this, the pelvic organs interlock with one another to form a jigsaw arrangement to allow them to stay in place.
Outline the anatomy and histology of the cervix.
The cervix is the neck of the uterus which connects it to the vagina. The cervix contains cervical mucous glands – superiorly, it is composed of columnar epithelium, interiorly, it is composed of squamous epithelium (in between, there is a transformation zone where columnar cells gradually change to squamous). The cervix is vulnerable to pathogens, as it is the deepest female reproductive section which is open to the environment. Cervical mucous glands “clogg” the cervical canal to provide a physical barrier (however, this can be bad if you are trying to conceive – mid-cycle the secretions are more watery to allow sperm to travel up).
Outline the anatomy and histology of the vagina.
The vagina is a fibromuscular tube which is around 10cm long. It is slightly acidic for protective function, and acts as the passageway for menstrual flow, the birth canal during labour, and the interface between the male and female reproductive organs
There are three main components to the vaginal wall:
1) The inner mucosa is a non-keratinising, stratified squamous epithelium (lubrications from the cervical glands protect the wall during intercourse, and there are folded rugae to held the vagina dilate as well).
2) The muscularis layer has two sections – an inner longitudinal and outer circular layer (allowing the vagina to enlarge during intercourse and childbirth).
3) The adventitia is comprised of loose connective tissue to anchor the vagina in place.
Outline the anatomy and histology of the external female genitalia.
The external part of the female genitalia is the vulva, and it serves to protect the sexual organs, and act as a urinary opening and vestibule to the vagina. The vestibule is a space containing the urethral and vaginal openings, and it contains mucous glands – it is bordered by the labia minor skin folds. It also contains the clitoris (erectile structure) and the corpora cavernosa. The labia major is rounded folds of skin and fat around the external genitalia containing sebaceous and sweat glands.
Describe the process of gametogenesis in females.
Two structures develop in oogenesis – the egg (oocyte) and the follicle (supporting tissue):
1) Pre-natal maturation occurs before birth, and involves the enlargement of oogonia to become primary oocytes (oogonia have primordial follicles made of granulosa cells which encapsulate them, these enlarge to form a primary follicle encapsulating the primary oocyte) – primary oocytes are suspended in prophase, awaiting post-natal development.
2) Post-natal development occurs after puberty, in a monthly fashion until menopause. Here, one primary follicle matures each month, along with one primary oocyte which enlarges at ovulation then completes its suspended meiosis to form a secondary oocyte. The follicle then develops an antrum (fluid-filled space) to become a secondary follicle. After meiosis I, the secondary oocyte dissociates from the mature (secondary) follicle. The oocyte begins its 2nd meiotic division, but not does complete this until fertilised.
3) If fertilised by a spermatozoa, the 2nd meiotic division will resume at metaphase.
