Male reproductive system Flashcards
(18 cards)
male reproductive system :functional anatomy
The testes are the primary sex organs that correspond to the ovary in the female.
The outer layer of the testes is called tunica albuginea, which radiates into the testis
dividing it into many pyramidal lobules with the bases directed towards the periphery.
Each lobule contains coiled tubes called seminiferous tubules, 30-70 cm long and 150
300μm in diameter. Each testis contains about 900 seminiferous tubules, consisting of
three layers, the outermost connective tissue, basement membrane and a complex
stratified epithelium (germinal epithelium). The complex stratified epithelium contains two types of cells, 4 to 8 layers of sperm
forming cells at various degrees of maturation and single sustentacular cells of Sertoli,
which extend from the basement membrane to the lumen, providing support for the
sperm-forming cells. At the periphery of the basement membrane lie the interstitial cells
of Leydig. The Sertoli cells are joined to one another at about the mid-portion of their
lateral walls by tight junctions. The seminiferous tubules converge towards the apex of
the lobules to form straight tubules, which pass into the mediastinum testes to join a
network of rete testes. From the rete testes, efferens ductuli emerge to form the head of
the epididymis, which continues to the body, and tail
and finally creates the vas deferens. The vas is joined by the ducts of the prostate and
seminal vesicle to form the ejaculatory duct, emptying into the prostatic urethra.
Accessory sex organs ;
Including the prostate, seminal vesicles, urethra, and penis. These organs produce their
secretions which add to that of the testis to form semen. The penis is used in the physical
process of sexual intercourse.
Describe the three stages of spermatogenesis: spermatocytogenesis, meiosis, and spermiogenesis.
Spermatogenesis is the process of developing spermatozoa from a primitive germ
cell, and it is inhibited in the fetus by the meiosis-inhibiting factor.
It begins at puberty and continues throughout life, although it decreases markedly
during old age. About 100-200 million spermatozoa can be produced daily. It occurs in
the seminiferous tubules and can be divided into three phases.
Mitosis: The primordial germ cells divide mitotically to produce spermatogonia (A or
B) next to the seminiferous tubule’s basal lamina. The A cell group is like the original
cell and acts as a reservoir for spermatogonia. The B group undergoes further mitotic
division leading to primary spermatocytes; a process also called spermatocytogenesis.
Meiosis: Each primary spermatocyte undergoes the first meiotic division (after pairing
homologous chromosomes and exchanging chromatid segments) to produce two diploid
secondary spermatocytes. Each diploid (23 double-stranded) secondary spermatocytes
further divide meiotically to create two haploid spermatids. Thus, each primary
spermatocyte provides four spermatids. Several primary spermatocytes are produced
from one primitive germ cell. It is therefore estimated that one spermatogonium gives
rise to 64 spermatids.
Spermiogenesis; The spermatids now get embedded into the substance of the Sertoli
cells for differentiation to mature spermatozoa. This involves nuclear condensation,
shrinkage of cytoplasm, and development of the head, acrosome, middle piece, and tail.
Thus, one primary spermatocyte gives rise to 4 haploid mature spermatozoa. The mature
spermatozoa now enter the lumen of the seminiferous tubules from where they are
propelled to the vas. Spermatogenesis takes approximately 60-70 days to accomplish.
How do Sertoli cells support spermatogenesis? Discuss their role in forming the blood-testis barrier and providing nutritional support to developing sperm cells.
Sertoli cells;
Are large pyramidal-shaped cells that can withstand adverse temperature,
ionising radiation, chemical assault, malnutrition, and infections. Their functions include
Endocrine functions: The Sertoli cells produce Mullerian inhibitory factor (MIF),
inhibin and oestrogen.
Exocrine functions; Secretes seminal fluids rich in K+, HCO3- but low in Na+ and Cl-.
Synthesises androgen binding protein and the histocompatibility antigen Y (H-Y
antigen).
Maintenance of spermatids; Provides mechanical support and nutrition for the sperm.
Phagocytosis of a cytoplasmic fragment detached from transforming spermatozoa and
aids in the release of sperm.
Blood testis barrier: The tight junction of the Sertoli cells prevent harmful chemicals in
the blood from getting to the lumen of the tubules to cause damage. This barrier also
prevents the entry of mature sperms into the bloodstream to induce an immune reaction,
and it ensures a high local concentration of testosterone.
What structural and functional modifications occur in spermatozoa during epididymal maturation?
The sperm takes several days to pass through the epididymis. The pressure of
Sertoli fluids, peristaltic movements, and ciliary actions of ductular cells aid this
movement. Sperm is stored in the epididymis and vas for at least a month, and during
this period, it acquires motility characteristics but no full potential for fertilisation. The
spermatozoa’s ability to fertilise the ovum is further enhanced when deposited in the
female genital tract. It develops total motility and swims up at 3mm/min, reaching the
tubes within 30-60 minutes. Here two processes occur. They are capacitation and
acrosomal reaction.
Capacitation. This is not well understood, but it is believed that the uterine and fallopian
fluids wash away the various inhibitory factors that can suppress sperm activity.
Acrosomal reaction; Hyaluronidase and proteolytic enzymes necessary for penetration
of corona radiata and zona pellucida are released during this process.
Explain the process of capacitation and its significance in fertilization. How do biochemical changes in the sperm plasma membrane enhance its fertilizing ability?
Capacitation. This is not well understood, but it is believed that the uterine and fallopian
fluids wash away the various inhibitory factors that can suppress sperm activity.
factors that affect spermatogenesis
Hormonal factors: Early in spermatogenesis, FSH stimulates Sertoli cells to
function maximally. LH stimulates the Leydig cells to produce testosterone
(which controls later) and epidermal growth factor. Hormones of the Sertoli cells
include oestradiol, stromal growth factor, insulin-like growth factor, inhibin and
activin. These target hormones (testosterone inclusive) interact actively in an autocrine and paracrine manner among Leydig, peritubular, Sertoli, and germ cells to modify sperm production. GH stimulates while oestrogens negatively inhibit GnRH and the conversion of testosterone to DHT. Androgen binding protein, another product of Sertoli cell, binds avidly to testosterone oestradiol and DHT, a situation of extreme value in concentrating these products in the
testis for all essential autocrine, paracrine action.
2. Body temperature: The scrotal temperature is 2C below body temp. Any condition that encourages high temperature, e.g., Constant wearing of tight nylon pants, long distant lorry drivers, and cryptorchidism, leads to reduced
spermatogenesis. Spermatozoa can survive for years at extremely low temperatures. In the presence of glycerol, it can be stored at -269oc and revived after storage by thawing. This is the basis for the formation of a sperm bank
during artificial reproductive techniques.
3. Congenital absence of the testis or inflammation of the testis (orchitis) reduces
spermatogenesis.
Describe the acrosome reaction and its role in penetrating the zona pellucida of the oocyte.
Hyaluronidase and proteolytic enzymes necessary for penetration
of corona radiata and zona pellucida are released during this process.
semen; definition and composition
Semen. The semen is the product of ejaculation during male sexual acts. It consists of
spermatozoa (10%), secretions from the seminal vesicle (60%), and secretion from the
prostate (30%). Secretions from the bulbourethral and urethral glands constitute </%.
The semen is watery at the time of ejaculation but quickly congeals, but after 30 minutes, it undergoes secondary liquefaction. Spermatozoa obtain nutrition from the
anaerobic metabolism of fructose to pyruvate.
WHO reference values for a healthy semen
a) Volume – 1.5-2.5 ml.
b) Liquefaction time – within 30-60 minutes
c) Concentration – at least 15 x 106 cells/ml (39 million per ejaculate).
(Range- 15-250 x 106 cells/ml.)
d) Motility – more than 32% progressively motile
e) Morphology - 4% normal forms
f) Wbc - <1 x 106/ml.
Other standard semen properties: - -
Specific gravity – 1.028
secretions from seminal vesicle
Secretions from the seminal vesicle; The secretions are viscid, alkaline, and yellow, rich
in vitamin C, fructose high K. Also contain the following substances:
phosphorylcholine, fibrinogen, citric acid, pepsinogen, a prostaglandin. The fluid
provides mucus consistency to the semen.
secretion from prostate
Secretions from the prostate; Secretions are thin, colourless, and confer a peculiar odour.
Prostatic secretions contain the following Na, Ca, Zn, citrate, cholesterol, phospholipids,
acid phosphatase, spermine, fibrinolysin and other clotting enzymes, and proteolytic
enzymes. Acid phosphatase appears in abnormally high levels in blood with the
malignant condition of the prostate. The secretions confer a milky appearance to the
semen,
Other substances:
These are phosphates, Hco3, hyaluronidase,
ENDOCRINE FUNCTION OF THE TESTIS
The testis produces male sex hormones: testosterone (most important),
dehydroepiandrosterone (DHEA), and androstenedione. The interstitial cells of Leydig,
under the influence of the luteinising hormone, produce testosterone. The zona
reticularis of the adrenal gland also makes these androgens but in small amounts
short note on testosterone
Testosterone is a C19 steroid produced by the Leydig cells under LH stimulation. 98% is
bound to plasma proteins, while 2% is free (Sex hormone-binding globulin binds 65%
while 33% links to albumin). The plasma level is 10.4 – 34.7 nmol/L in adult males and
1.04-2.43nmol/L in adult females. Levels decline towards the late decade of life. The
aromatase activity of Sertoli cells produces about 25% of oestrogens in males, while the
rest of male estrogen is made by extra gonadal aromatisation. It is oxidised in the liver to
produce 17 keto steroids (androsterone, epiandrosterone and etiocholanolone). These are conjugated with sulphates and glucuronides and excreted in urine or bile.
Mechanism of Action
Testosterone binds to an intracellular cytoplasmic receptor. The To – receptor
complex then stimulates protein synthesis. Its action on the prostate, hair distribution,
acne formation, and external genitalia is via dihydrotestosterone (DHT), a product of 5
reductase activity.
effect of testosterone on fetus
(a) Sex differentiation; stimulates differentiation of the Wolffian duct to the male
internal genitalia. Produces MIF that aids degeneration of the female reproductive tract.
(b)Testosterone is responsible for the growth of sex organs, penis, scrotum,
testis, epididymis, vas deferens, seminal vesicles, prostate, and bulbo
urethral glands.
(c)It is also necessary to descend the testis from the abdomen to the scrotum.
effect of testosterone on adults
(a)
At puberty, it causes enlargement of the penis, scrotum, and other sex
organs.
(b)Secondary sexual characteristics -
Enlargement of the larynx and development of vocal Cords
leading to deepening of the voice. Growth of male type of hair, e.g., baldness, hairs on the face, chest, and legs. A particular type of pubic hair with an apex that extends up to the linear alba (diamond-shaped), receding temporal
hairline. Increases muscular development.
Stimulates bone development, leading to broadening of shoulders; specific effects on pelvic bone include narrowing of outlet
forming a tunnel-like shape. increased sebaceous gland secretion and acne formation. stimulates male-type mentation with increased aggressiveness and interest in the opposite sex (libido).
Metabolic effects of testosterone
- Metabolic Effects.
Increases protein synthesis (bone and muscular growth) , Increases total bone matrix and causes Ca2+ retention (protection against osteoporosis), cause moderate Na+, K+, H2o, sulphate and phosphate retention.
Increases basal metabolic rate by 15%,
Increases RBC production by 15 – 20%
Decreases all hormone-binding globulins
Increases LDL and VLDL but lowers HDL (making men more prone to atherosclerosis).
Regulation of testosterone function
Regulation of testosterone secretion.
LH stimulates explicitly Leydig cells to produce To, which will negatively feedback on the hypothalamus and anterior pituitary. On the other hand, FSH stimulates the Sertoli cells explicitly to make a glycoprotein called inhibin which will also feedback on the anterior pituitary to decrease FSH production. The Sertoli cells also produce SHBG.
Testosterone also acts locally on the Sertoli cells to aid spermatogenesis. Gonadotrophin-releasing hormone GnRH is a 10 amino acid peptide secreted in pulses
by the neurons in the arcuate nucleus into the median eminence from where they are
transported to the anterior pituitary via the hypothalamohypophyseal portal system to
cause secretion of L/H and FSH. (Phospholipid’s 2nd messenger). FSH /LH acts on target cells by CAMP 2nd messenger mechanism diagram. (Diagram)
Abnormalities of the Male Reproductive system
Abnormalities of the Male Reproductive system
(a) Castration – This is called orchidectomy. When done before puberty, individuals
are usually taller than average due to late epiphyseal closure (eunuchoid habitus).
It is performed as part of treatment for cancer of the prostate to reduce prostatic
stimulation.
(b) Precocious Puberty occurs when secondary sexual characteristics occur before
the usual age (9 years).
(c) Delayed Puberty – This happens when testicular development fails to occur at 20
years.
(d) Cryptorchidism – Undescended testis.
(e) Hypogonadism – Occurs when the testes of a male fetus are nonfunctional during
fetal life. It is called hypogonadotropic hypogonadism when it is due to testicular
failure and hypogonadotropic hypogonadism when it is due to hypothalamic or
pituitary failure.
(f.) Hypergonadism
Tumours of the testes that produce excessive androgens can lead to
hyperfunction with excessive muscular and hair growth. Tumour may lead to
precocious puberty when it occurs early.
