Lecture 9

What is an erection?

An erection is a complex physiological process involving a series of neural and vasomotor reactions that result in the rigidity of the penis, essential for copulation.

What occurs during erection 

1. External stimuli acting on sensory nerves

2. Sensory nerves activate the hypothalamus

3. Stimulation of parasympahtetic nerves

4. Terminals of parasympathetic nerves release nitric oxide

5. NO acts on GTP → increases cGMP → vasodilation = cascade of events leading to erection

What are the cavernous sinuses and their function during an erection?

The cavernous sinuses are specialized spongy spaces within the penis. During an erection, these sinuses fill with blood due to vasodilation and increased blood flow, and then trap this blood. This engorgement is what causes the penis to become rigid.

Describe a fibroelastic penis erection and in which animals it is found.

In a fibroelastic penis - only some increases in rigidity and straightening of the sigmoid flexure + relaxation of the retractor penis muscle.

This type of penis is found in bulls, rams, and boars.

Describe a musculocavernous penis and in which animals it is found.

In a musculocavernous penis - see an increase in width, length and rgidity

This type of penis is in horses, cats, and dogs.

What is ejaculation?

The reflex expulsion of spermatozoa and seminal plasma from the male reproductive tract via coordinated muscular contractions

Describe the Rapid Phase of Sperm Transport.

The Rapid Phase of Sperm Transport occurs within minutes after copulation. During this initial phase, spermatozoa quickly reach the oviduct. However, these sperm are generally not yet functional or viable for fertilisation

Describe the Sustained Phase of Sperm Transport.

Spermatozoa are transported to the oviducts in a trickle like effect from the cervix and uterotubule junction

Sperm move into the isthmus and attach to the oviductal epithelium

How does the immune system act as a barrier to sperm transport

Spermatozoa are lost from the female tract by:

• phagocytosis by neutrophils

• retrograde transport

Neutrophils actively phagocytose spermatozoa and can not discriminate between live and dead sperm

How dos the vagina act as a barrier to sperm transport

It is a barrier to spermatozoal transport as it creates two different types of environments:

1. That is highly viscous

   • Sperm here gets flushed out

2. That is not as viscous

   • Sperm that reaches these deep crypts can pass the tract

How does the uterus impact sperm transport

There is usually an inflammatory response and some spermatozoa gets phagocytosed

What is capacitation in spermatozoa? Where is it completed

During the time in the female reproductive tract, some spermatozoa will undergo changes (loss of seminal plasma and surface proteins) that allow them to become fertile

It gets completed in the oviduct

How does motility change in the oviduct

Then the motility patterns of spermatozoa change to a hyperactive motility which facilitates sperm to oocyte contact

Sperm moves along the female reproductive tract and attach to the epithelium (docking) but mainly in the lower isthmus as this is the first region they see after all the challenges they face

How long before undocked sperm die

6-10 hours

What are the 8 stages in fertilisation

1. Hyperactive motility

2. Binding to zona pellucida

3. Acrosomal reaction

4. Penetration/lysis of zona pellucida

5. Sperm oocyte membrane fusion

6. Sperm engulf

7. Decondensation of sperm nucleus 

8. Formation of pronuclei

What zona pellucida proteins do spermatozoa bind to

Region 3

What occurs during the acrosomal reaction

the plasma membrane of the sperm fuses with the outer acrosomal membrane → forms a pore where enzymes can be released

After this reaction, the inner acrosomal membrane will be exposed and the equatorial membrane will be formed

What occurs during penetration of the zona pellucida

Acrosin → Enzyme that helps the spermatozoon to penetrate and make its way through the zona pellucida.

What occurs during sperm oocyte fusion

When the spermatozoon completely penetrates the zona and reaches the perivitelline space it settles into a bed of microvilli formed from the oocyte

What occurs during decondensation of the sperm nucleus

Sperm nuclear membrane disappears and the nucleus decondenses

Signals are sent so that other sperm cannot penetrate the zona pellucida and the zona pellucida starts to harden

How are the male and female pronuclei form

The male genetic material spreads out and there is a membrane that surrounds this male material to form the pronucleus

Female genetic material awakens and forms the female pronucleus

How does the final zygote forme

Syngamy = the two pronuclei get together via microtubules which pull each pronucleus to eachother → chromosomes fuse and form one nuclei