Gametes - Male Reproduction Flashcards
The testes are an ______ septa
Incomplete
How many lobules do the testes have
250
How many seminiferous tubules are there
1-4
Name the type of cells associated with the loose connective tissue of the testes
Interstitial cells of leydig
How are the testes gametogenic
Name the processes that take place in the testes
Produce mature spermatozoa
- Spermatogenesis
- Spermiogenesis
- Spermiation - seminiferous tubules
What is the endocrine function of the testes and what is it associated with
Testosterone - leydig cells
What cells start the process of spermatogenesis
Germ cells (at puberty)
What is produced by spermatogenesis
What are the 2 types
Increase in number by mitosis to form SPERMATOGONIA (type A and B)
What is unique about type B spermatogonia
Replicate DNA to have 46 double structured chromosomes to begin meiosis-1 and are called primary spermatocytes
Visual depiction of spermatogenesis
Define spermiogenesis
Spermatid to spermatozoa
What is present in the golgi phase of spermiogenesis
Explain the cap phase of spermiogenesis
- The golgi migrates towards the caudal part of the cell
- The distal centriole (DC) forms the axoneme (AX) or flagellum that projects away from the nucleus toward the lumen of the seminiferous tubule
- The acrosomic vesicle flattens and begins to form a distinct cap consisting of an outer acrosomal membrane (OAM), an inner acrosomal membrane (IAM) and the acrosomal contents (enzymes)
Explain the acrosomal phase of spermiogenesis
- The spermatid nucleus begins to elongate and the acrosome eventually covers the majority of the anterior nucleus
- The manchette forms in the region of the caudal half of the nucleus and extends down toward the developing flagellum
- The neck and the annulus are formed
- The annulus will become the juncture between the middle piece and the principal piece
- All components of the developing spermatid are completely surrounded by a plasma membrane
Explain the maturation phase of spermiogenesis
- Mitochondria form a spiral assembly around the flagellum that defines the middle piece
- the post nuclear cap is formed from the manchette microtubules
- The annulus forms the juncture between the middle piece and the principal piece
What is spermiation
Process by which mature spermatids are released from Sertoli cells into the seminiferous tubule lumen prior to their passage to the epididymis
How long does it take to get from spermatogonia to spermatozoa
64 days
Where are spermatozoa present
In some tubules and predominantly spermatids or primary spermatocytes in other
Temperature required for normal sperm production
2-3 degrees below core body temp
Structure of spermatozoa
Function of the nucleus of sperm
How is DNA stabilised
Active or inactive
- Haploid
- Condensed DNA stabilised by S-S bonds till fertilisation
- Inactive - no synthetic activity occurs
Function of the acrosome of the sperm
Enzymes facilitate sperm penetration
Function of plasma membrane of sperm
Very little cytoplasm in sperm - surrounds the entire tail
What does the mid peice of the sperm do
What is its structure
- Mitochondrial helix
- Gives energy for motility - ATP production
What is the arrangement of the flagellum
Microtubular arrangement
- 9 course outer fibres - structural support (rigidity to tail) do not contract
- 9 inner double tubules - involved in tail movement, contract via beta and alpha tubulin
Visual depiction of spermiogenesis
Explain the 3 functions of sertoli cells
- Nourishment of seminiferous tubule cells
- Inner tubule is avascular
- Transport nutrients to lumen region
- Phagocytosis
- Cytoplasmic droplets from spermatids
- Damaged germ cells
- Add to seminal fluid
- Synthesize luminal proteins
- Maintain tubular fluid
What are the hormonal functions of sertoli cells (4)
- Androgen binding protein - maintains testosterone levels in ST
- Inhibin - inhibits FSH
- Activin - stimulates FSH (modulates spermatogenesis via FSH)
- Converts androgens to oestrogens - hormonal modulation of tubular function
5 functions of the blood-testes barrier
- Prevents autoimmune destruction of sperm
- Produces FAS ligand which binds to the T-cell FAS receptor
- Triggering apoptosis of T lymphocytes
- Prevents immune function
- Barrier to blood toxins
What is the function of leydig cells
Synthesise androgens
- Testosterone
- Dihydrotestosterone
- Dehydroepiandrosterone
Male sex steroid synthesis
Average testosterone levels over a lifetime
What are the effects of androgens on the body
- Increase in spermatogenesis
- Increase in bone matrix and Ca2+ deposition
- Promotes epiphyseal closure
- Increase in muscle mass
- Increase in larynx size
- Increase in BMR
- Increase in RBC density
- Increase O2 utilisation
- Increase in skin thickness
- Increase in melanin deposition
- Increase in sebum secretion
Ligand specific androgen activity in utero
TESTOSTERONE
- Internal ductal system
- Descent of testes
Cryptorchidism
Testes do not descend into the scrotum
What does dihydrotestosterone do in utero
- Stimulates development of external genitalia
Visual depiction of regulation of spermatogenesis
What is the reflex of ejaculation
- Parasympathetic
- Arterioles dilate
- SM relaxation via NO
- Spinal reflex initiated
- Also sympathetic discharge to the genital organs
- Reproductive ducts/accessory glands contract peristaltically, discharging their contents into the urethra
Blood flow during ejaculation
Penis engorged with blood - expansion compresses the veins & slows blood leaving penis
During ejaculation, what happens to the bulbocarvenous muscle at the base of the penis
- Rapid series of contraction
- Propels semen from the urethra
Signalling pathway for penile erection
- ACh increases NO, which causes an increase in cGMP
- cGMP causes smooth muscle relaxation
- Relaxation of arterioles increases blood flow to penis
What is cGMP degraded by
Phosphodiesterase 5 which terminates its action
What is the MOA of viagra
- Inhibits phosphodiesterase 5 (PDE 5) and therefore decreases cGMP breakdown
- Prolonged arteriolar dilation
- Prolonged erection
What is the evaluation of seminal fluid used for
- Assessment of fertility
- Forensic purposes
- Effectiveness of vasectomy - 2 -ve samples 1 month apart
- Suitability for artificial insemination
What does seminal plasma contain (3) and in what proportion
- Prostatic fluid (30% of vol)
- Epididymal fluid (5% of vol)
- Seminal vesicle fluid (remainder)
What are the 2 types of cells in ejaculate
- Spermatozoa
- Leukocytes of various types - bacteria & epithelial cells
Volume of ejaculate
2-6 ml
pH of ejaculate
7.2-8.4 (inflammatory disorders of the accessory glands can take pH outside of this range)
Sperm count of ejaculate
> 20 million/ml
Total count = > 40 million
Morphology of ejaculate
> 30% normal form
Viability of sperm in ejaculate
> 75%
WBC count in ejaculate
< 1 million/ml
RBC count in ejaculate
None
Describe the seminal vesicle
- Fructose - marker for seminal vesicle function - energy source
- Prostaglandins - sperm motility
- Alkaline - neutralises acidic prostate secretion & female tract
- Proteins-coagulate semen
Describe the epididymis
- Alpha-glucosidase - marker for epididymal function
- CD52 - seminal glycoprotein incorporated into sperm membrane
- Glycogen
What does the prostate secrete
- Calcium
- Zinc - anti-bacterial - marker for prostate function
- Citric acid - very high concentration - levels reduced in prostate cancer (biomarker)
- Acid phosphatase - marker for prostatic function
- Albumin
-
Prostatic Specific Antigen (PSA)
- Protein produced by the epithelial cells of the prostate
- Biomarker for prostate cancer (> ng/ml)
At what pH does sperm die
6.9
Rapid progressive spermatozoa
> 25 um/s
Slow progressive spermatozoa
5-25 um/s
Non-progressive spermatozoa
< 5 um/s
Immotile spermatozoa
No flagellar movement
Sperm kinematics
The way sperm swim affects their motility
How must sperm swim in order to get through the cervix
They have to swim in a straight path
How do sperm get through the outer layer of the egg
They have to generate a lot of power - this is seen as hyperactivated motility
Aspermia
No semen ejaculated
Hematospermia
Blood present in semen
Leucocytospermia
WBCs present in semen
Azospermia
No spermatozoa found in semen
Normospermia
Normal semen parameters
Oligospermia
Low sperm concentration
Asthenospermia
Poor motility and/or forward progression
Teratospermia
Reduced % of morphologically normal sperm
Necrospermia
No live sperm in semen
What is different about sperm produced in seminiferous tubules
Morphologically mature but functionally immature
- Non-motile and not capable of fertilisation
What is the biochemical change to sperm
Removal of glycoprotein covering head of sperm takes place in uterus and oviduct over several hours
- functional maturity
How does the sperm cell membrane change
- Alterations in surface glycoproteins
- Removal of cholesterol - increased fluidity of membrane
- Loss of glycoproteins - expose egg binding protein
- Fluctuations in Ca2+
- Protein phosphorylation via cAMP
- Absolute requirement for capacitation
What are the 3 changes in sperm due to capacitation
- Increased metabolism - fructose for energy
- Flagellum increase rate of beating - increased sperm motility
- Activation of acrosomal enzymes - pro-acrosin changes to acrosin
