6. SPERMATOGENESIS Flashcards
1
Q
What do the testes do?
A
- The testes is made up of mainly seminiferous tubules (90%)
- Spermatogenesis occurs in these seminiferous tubules
- Seminiferous tubules = Tightly coiled, 600nm long
- –> Lead to epididymis & vas deferens
2
Q
What are the tight junctions between sertoli cells?
A
- Walls of seminiferous tubules have sertoli cells which are tall, columnar endothelial cells
- Tight junctions between sertoli cells = ADLUMINAL COMPARTMENT
- Adluminal compartment forms an enclosed environment for spermatogenesis to occur
- contains secretions rom sertoli cells
3
Q
What is found in the spaces between seminiferous tubules?
A
- Leydig cells
- blood vessels
- lymphatic vessels
- interstitial fluid
4
Q
What are the 4 cell precursors for spermatoazoa?
A
- Spermatogonia ->
- Primary Spermatocyte ->
- Secondary spermatocyte
- Spermatid
- Spermatazoa
5
Q
What are spermatogonia?
A
- SPERMATOGONIA are primary germ cells found in the basement membrane
- DIPLOID CELLS
- Capable of mitosis or meiosis
- Mitosis = produce more spermatogonia
- Meiosis = produce primary spermatocytes
6
Q
What are the two types of spermatogonia cells?
A
- A d (A dark) - Mitosis
- A p (pale) - Meiois
- A pale cells committed to Meiosis, which then become B cells
- These B cells from primary spermatocytes
A p cell –> B cell –> Primary spermatocyte
7
Q
**What are primary spermatocytes?
A
- PRIMARY SPERMATOCYTES move into the adluminal compartment between sertoli cells
- 46 XY DIPLOID
- DNA replication occurs form sister chromatids
- Sister chromatids exchange genetic material before Meiosis I
8
Q
What are secondary spermatocytes?
A
- SECONDARY SPERMATOCYTES are HAPLOID 23X & 23Y
- Meiosis I forms haploid 23x & 23y
- chromosomes are arranged as sister chromatids which don’t separate
9
Q
What are spermatids & spermatozoa?
A
- SPERMATIDS produced from MEIOIS II
- 4 HAPLOID spermatids produced
- Round spermatids differentiate into elongated spermatids
- SPEMATOZOA = mature sperm extruded into lumen
10
Q
What are the three stages of spermatogenesis & how long does a cycle last?
A
- Mitotic proliferation of spermatigonia
- Meiosis & spermatocyte development
- Spermiogenesis - elongation of spermatid, loss of cytoplasm & arrangement of cellular components
- Each cycle lasts 16 days & takes 74 hours
11
Q
What is a synctium in sperm development?
A
- Each division from a spermatogonia to a spermatid is incomplete because the spermatids are still connected by bridges known as SYNCTIA (individual = synctium)
- The synctia allow for synchronous development
- The synctia are at various stages in their development, so there will always be a constant supply of spermatozoa
12
Q
Describe the effect of the HPG axis in males
A
Hypothalamus
I (GnRH)
Pituitary
I (FSH & LH)
Testes
(testosterone, DHT, androgens)
- LH = Leydig cells -> Testosterone
- FSH = Sertoli cells
13
Q
What are the effects of testosterone produced by the Leydig cells?
A
- Circulates in the body to produce secondary effects
- Testosterone binds to Androgen Binding Protein (ABP), which transports it to seminiferous tubules
- Testosterone binds to androgen receptors within Sertoli cells to cause spermatogenesis
14
Q
What’s the importance of FSH for Sertoli cells?
A
- FSH is needed to maintain a normal number of sertoli cells proportions
- Sertoli cells express FSH receptors, they convert androgens into oestrogen
15
Q
How can anabolic steroids interfere with negative feedback of the HPG axis in males?
A
- Anabolic steroids will acta s sex steroids
- So high kevels of anabolic steroids can cause negative feedback, resulting in decreased FSH & LH
- However, FSH is needed to maintain normal numbers of Sertoli cells. A drop in FSH can lead to testicular atrophy as the Sertoli cells are lost
16
Q
What happens to arterial blood supply during erection?
A
- There’s VASODILATION of blood vessels going into the corpus cavernosum
- There’s partial constriction of the bood vessels leaving the corpus cavernosum
- So dilation of blood vessel into & constriction of blood vessels out, leading to penis being engorged with blood
17
Q
What are erection, emission & ejaculation controlled by?
A
- The AUTONOMIC NERVOUS SYSTEM is responsible for producing the co-ordinated smooth muscle contraction of the vas deferens, glands & urethra
- It’s an involuntary process mainly involving the sympathetic, parasympathetic. But the somatic system is also involved
- Point, Shoot & Score (erection, emission & expulsion)
18
Q
What is erection controlled by?
A
- Erection = PARASYMPATHETIC
19
Q
What is emission controlled by?
A
- Emission = SYMPATHETIC
20
Q
How is the somatic nervous system involved in ejaculation?
A
- Expulsion of glandular secretion sis controlled by the somatic nervous system, particularly the perineal branch of the pudendal nerve
- However, erection & ejaculation are not under conscious control although somatic nerves are involved
21
Q
Describe the properties of ejaculate
A
- 300 million sperm are produced per day on average
- Normal ejaculate volume = 1.5 - 6ml
- The initial portion of ejaculate is the most sperm rich
- Seminal fluid is epidydimal fluid combined with secretions from the seminal vesicles, prostate & bulbo-urethral gland
22
Q
What three structures contribute to seminal fluid?
A
- Epidydimal fluid is combined with secretions from:
1. Seminal vesicles
2. Prostate
3. Bulbo-urethral glands
23
Q
What do seminal vesicles contribute to seminal fluid?
A
- Seminal vesicles contribute to (50 -70%) majority of seminal fluid
- Consists of proteins, enzymes, mucus, Vitamin C, prostaglandins, fructose
- high fructose content = source of energy
- High pH protects against acidic environment of the vagina
24
Q
*What does the prostate contribute to seminal fluid?
A
- Contributes to 30% of seminal fluid
- Secrete milk or white fluid
- Protein content is less than 1%
- Consist of proteolytic enzymes, prostatic acid phosphatase & prostate specific antigen involved in liquefication
- High zinc content makes it antibacterial
25
What do the bulbo-urethral glands contribute to seminal vesicles?
- Bulbo-urethral glands don't form part of the ejaculatory process but they do form pre-ejaculate
- Pre-ejaculate is a clear, viscous fluid high in salt
- Pre-ejaculate helps to lubricate the penile urethra. The sperm is propelled at a high speed, so the pre-ejaculate prevents damage to the sperm
- The pre-ejaculate also neutralizes traces of urine
26
What are the 9 basic parameters in semen analysis?
1. Volume
2. Sperm concentration
3. Liquefaction
4. Motility
5. Progressive motility
6. Vitality
7. Morphology
8. pH
9. leucocytes - > 1 million
27
What should the volume of sperm be?
1.5 - 6ml
28
What should the concentration of sperm in semen be?
> 15 million
< 15 million -= OLIGOSPERMIA
Sperm count of zero = AZOOSPERMIA
29
What is liquefaction?
- Liquefaction refers to the process by which the gel-like consistency of sperm becomes liquid when it's deposited near the cervix
30
What is motility & progressive motility?
- Motility = percentage of sperm swimming, >40%
| - Progressive motility = proportion of sperm moving in a somewhat linear position, >32%
31
What is vitality?
- Vitality refers to the proportion of sperm that are alive, measured with a dye (>58%)
32
What should the pH of sperm be?
>7.2
| - A high pH is needed for sperm to survive in the acidic environment of the vagina
33
What are the 4 parts of the sperm?
1. HEAD
2. MID-PIECE
3. PRINCIPAL PIECE
4. END-PIECE
34
What does the head of the sperm contain?
- The head of the sperm has very little cytoplasm & contains an acrosome & nucleus
- The acrosome contains enzymes that digest the zona pellucida. The acrosome bursts when it comes to contact with the egg. The inner acrosome
also contains adhesion molecules which help it bind to the egg
35
What does the mid-piece of the sperm contain?
- The mid-piece contains the mitochondrial sheath which provides energy for sperm motility
36
What does the principal piece of the sperm contain?
- The principal piece is made up of 9 pairs of fibres which form the AXONEME
- These fibres use energy in the form of ATP from the mitochondria.
- The ATP allows the fibres to slide over each other, propelling the sperm
37
What are the differences between oogonia & spermatogonia production?
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1:
- Oogonia begin Meiosis BEFORE BIRTH
- Spermatogonia begin Meiosis AFTER PUBERTY
2:
- CANNOT make new oogonia by mitosis
- CAN make more spermatozoa by mitotic division of spermatogonia
3:
- Oogonia = LIMITED supply
- Spermatogonia = UNLIMITED supply
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