Spermatogenesis

Question 1

Outline the journey of sperm through the male reproductive anatomy

Answer 1

1.Sperm is produced in the testes and store in the epididymis.
During ejaculation there are contractions in the epidydimis and the vas deferens and these will propel the sperm up and out through the vas deferens.

At this point the sperm will be mixed with epidydimal fluid.

This will make its way to the seminal vesicle where further secretions are added

As this mixture makes its way to the ejaculatory duct further secretions are added
from prostate and the calvus gland are added.

This becomes a complete ejaculate.

Corpus Cavernosum and Spongiosum fill with blood during an erection

Question 2

Outline the role /function of the testes .

Where are the testes found ?

Answer 2

The testes produces sperm and also stores it.

It will also produce hormones which are important for regulating spermatogenesis .

The testes lie in the scrotum which lies outside of the body cavity.

This is the optimum temperature for sperm production (1.5-2.5 oC below the body temp)

Overheating of the testes will reduce the sperm count.

Question 3

How is the testes adapted to its function ?

Answer 3

It is well vascularised , well innervated

The testes lie in the scrotum which lies outside of the body cavity.

This is the optimum temperature for sperm production (1.5-2.5 oC below the body temp)

This is the optimum as following ejaculation there is a spike of temperature which serves to activate the sperm

Overheating of the testes will reduce the sperm count.

Question 4

What is the normal volume of testes ?

Answer 4

15-25ml and this can be measured using orchidometer

Question 5

Describe the testicular structure

Answer 5

The testes contains tubules which lead to an area on one side which is the rete.

The rete will lead to the epididymis and vas deferens

The testis is 90% semineferous tubules and its the site of spermatogenesis.

600m of seminiferous tubule in each testis which are tightly coiled.

The tightly coiled tubules are all kept in a structure known as the rete-testis

Question 6

What does the epidydimis lead into ?

Answer 6

It leads to the vas deferens

Question 7

Describe the cross section of a seminiferous tubule

Answer 7

It has a outer lining known as the basal lamina.

There are different cell divisions of germ cells which take place towards the lumen.

The final products of these are to form spermatozoa.

In between each clusters of germ cells there are Sertoli cells and these provide sustenance to the sperm cells.

Question 7

Describe the cross section of a seminiferous tubule

Answer 7

It has a outer lining known as the basal lamina.

There are different cell divisions of germ cells which take place towards the lumen.

The final products of these are to form spermatozoa.

In between each clusters of germ cells there are Sertoli cells and these provide sustenance to the sperm cells.

Question 8

Describe each layer of division beginning from the germinal cell to form the spermatozoa

Answer 8

This begins with the germ cells which are diploid and these will begin division as the primary spermatocyte(diploid).
This will divide through meiosis 1 to form secondary spermatocytes (haploid).

Following this meiosis 2 will take place giving rise to spermatids (haploid) which will mature into spermatozoa.

Question 9

Describe the seminiferous epithelium

Answer 9

These contain tight junctions which exist between sertoli cells which forms the blood-testis barrier.

It opens to allow the passage of spermatogonia prior to completion of meiosis.

Divides into basal and adluminal compartments

Protects the spermatogonia from immune attack

Allows specific enclosed environment for spermatogenesis which is filled with secretions from Sertoli cells.

Question 10

What is spermatogonia ?

Answer 10

Germ cell on basement membrane ,capable of mitotic or meiotic division to produce primary spermatocytes or more spermatogonia through mitosis .They are diploid.

Question 11

What are the two types of sperms and how do they divide ?

Answer 11

The two types are type a dark and type a pale.

It was found that type a dark was able to undergo mitotic divisions at any time to give rise to type A dark again or it can also differentiate to give rise to type A pale.

Question 12

What is a primary spermatocyte?

Answer 12

Cells which are committed to differentiative pathway, primary spermatocytes are 46XY diploid .
They move into the adluminal compartment and duplicate their DNA to produce sister chromatids which exhange genetic material and enter meiosis 1.

Question 13

What are secondary spermatocytes ?

Answer 13

Secondary spermatocytes have undergone meiosis 1 to give 23X and 23Y haploid number of chromosomes arranged as sister chromatids.

Question 14

What are spermatids ?

Answer 14

Meiosis 2 occurs to give 4 haploid spermatids. Round spermatid to elongated spermatid differentiation.

Question 15

What will take place following all the meitic divisions?

Answer 15

Following formation of spermatids these will not undergo a maturation process to give rise to spermatozoa.

Extra cytoplasm is gotten rid of.

This maturation process is known as spermatogenesis.

Question 16

What is spermatogenesis

Answer 16

New cycle every 16 days ,entire process takes approximately 74 days.

Mitotic proliferation of spermatogonia

Meiosis and development of spermatocytes

Spermiogenesis ,elongation ,loss of cytoplasm ,movement of cellular contents

Movement into lumen controlled by Sertoli cell secretions.

Factors produced by Sertoli cells are required for development

Question 17

Describe the process of androgen production in the testis.

Answer 17

Leydig cells contain LH receptors and primarily convert cholesterol into androgens .

Intra-testicular testosterone levels are 100x those in plasma .

Androgens cross over to and will stimulate the Sertoli cell function and will therefore control spermatogenesis.

Sertoli cells will contain FSH receptors and convert androgens to oestrogen.

Question 18

Describe the effects of the hormones /androgens being produced in the testis

Answer 18

LH being produced by the anterior pituitary will act on the Leydig cells and this will produce testosterone which is take up by sertoli cells which will then regulate spermatogenesis.

FSH will act directly on Sertoli cells allowing it to sustain the spermatocytes.

FSH will also act on sertoli cell making it produce androgen binding protein which will bind to testosterone and binds testosterone and helps maintain a high concentration of testosterone within the testes; this is essential for spermatogenesis to occur.
FSH establishes a quantitivaely normal sertoli cell population , whereas androgen initiates and maintains sperm production

Question 19

Outline the production of inhibin in the testis

Answer 19

Inhibin B is produced primarily by sertoli cells in response to FSH

Inhibin B reduces FSH production by the anterior pituitary.

Germ cells appear to be required for inhibin B production.

FSH and inhibin B in combination have been founf to correlate with testicular volume and spermatogenic activity .

Semen analysis is the gold standard.

This is the better way to assess male fertility.

Question 20

Describe the cytoskeleton structure of a sperm cell

Answer 20

It is divided into two main sections: the head and the tail.

The tail is divided into three distinct sections.

The middle piece the principal piece and the end piece.

The head piece is made up of the acrosome and also contains the nucleus .

The middle piece of the sperm will house the mitochondria which is required for the tail to move .

It will also house ion channels which are important for intercellular calcium signalling which takes place when the sperm is inside the female reproductive tract.

Question 21

Give a brief overview of the ejaculation and seminal components

Answer 21

There are around 300 million sperm being produced per day

Normal ejaculate volume is around 1.5ml -6ml

The initial portion of an ejaculate is the most sperm rich

99.9% of the is will be lost before reaching ampullaof the uterine tube.

Seminal fluid consists of secretions from:
Seminal vesicles ,
prostate ,bulbo-urethral gland (contains the calvus gland )and epidydimal fluid.

Question 22

What is the role of the seminal fluid ?

Answer 22

This will transport sperm through the male reproductive tract

Coagulation (it will later liquify ) of the ejaculate and creating a sperm deposit in the vagina

Creates neutral -slightly alkaline buffered milieu in the vagina to protect spermatozoa from acidic vaginal millieu.(environment)

Activation and augmenting the motility of the sperm cells

Coating the sperm cells with capacitation (the process through which sperm goes through for it to be able to fertilise an egg) inhibitors

Supplying nutrients for the sperm cells

Question 23

What sort of information can be collected through a semen analysis ?

Answer 23

This is a test which is requested when looking at male fertility.

Volume
Appearance/colour
Liquefaction
Sperm concentration
Motility
Progressive motility
Morphology
Vitality
pH
Leucocytes

Question 24

What are some abnormalities that can be identified in sperm?

Answer 24

Normal
Condensed - has a  large nuclear region
Small head
Large head
Double headed 
Double tailed
Abnormal middle piece
(due to cytoplasmic droplets can occur during spermatogenesis)

Question 25

What are some important adaptations of sperm production?

Answer 25

There is no male menopause -Sperm production will be continuous from puberty

Sperm is alsi highly specialised for its function