Fertilization Processes in Mammals

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Questions and Answers

Where does fertilization occur in mammals?

In the uterus

In the vagina

In the cervix

In the oviduct (correct)

What physiological change occurs in sperm that enhances their ability to fertilize an egg?

Decreased temperature sensitivity

Reduced velocity

Hyperactivity (correct)

Motility decrease

What is the primary role of hyaluronidase during fertilization?

To inhibit sperm motility

To assists in penetrating the corona radiata (correct)

To bind to the zona pellucida

To trigger the acrosome reaction

Which of the following sperm characteristics is altered during capacitation?

Ability to sense temperature difference Signup and view all the answers

What mechanism leads to the slow block to polyspermy during fertilization?

Release of Ca from SER of the oocyte Signup and view all the answers

What is the viability period of the ova after ovulation in mammals?

12-24 hours Signup and view all the answers

What is one of the first events that occur during the acrosome reaction?

Release of digestive enzymes Signup and view all the answers

Which substance plays a role in helping sperm cross the zona pellucida?

Acrosin Signup and view all the answers

What is the first phase of sperm penetration during fertilization?

Capacitated sperm passing through corona cells Signup and view all the answers

Which substance induces the acrosome reaction during fertilization?

Zona proteins Signup and view all the answers

During the acrosome reaction, what enzymes are released by the sperm?

Acrosin and Trypsin-like substances Signup and view all the answers

What change prevents polyspermy during fertilization?

Cortical granule reactions Signup and view all the answers

What occurs immediately after the sperm successfully penetrates the zona pellucida?

Completion of the second meiotic division Signup and view all the answers

What is the role of calcium ions (Ca2+) in fertilization?

Activation of cleavage stages of the embryo Signup and view all the answers

How does the oocyte membrane become impenetrable after fertilization?

Modification of sperm receptors on the zona pellucida Signup and view all the answers

Which protein plays a critical role in sperm binding to the zona pellucida?

Fertilin Signup and view all the answers

What happens to the sperm mitochondria during fertilization?

They are degraded in the egg cytoplasm Signup and view all the answers

What is the fertilization cone?

The point of fusion between the egg and sperm membranes Signup and view all the answers

What is the result of the oocyte undergoing its second meiotic division?

Formation of the polar body Signup and view all the answers

Which layer around the egg is crucial for binding and inducing the acrosome reaction?

Zona pellucida Signup and view all the answers

What mechanism is primarily responsible for the fast block to polyspermy?

Electrical changes to the egg membrane Signup and view all the answers

What type of change does the zona reaction induce after sperm contact?

Modification of zona sperm receptors Signup and view all the answers

Study Notes

Fertilization

Occurs in the oviduct of mammals
Ova remains viable for 12-24 hours after ovulation
Sperm remains viable for up to 72 hours inside the female reproductive tract

Mechanisms of Fertilization

Sperm undergoes a process called capacitation to become competent to fertilize the egg
Capacitation involves changes to sperm motility and structure occurring in the female reproductive tract
Sperm undergoes a process called the acrosome reaction to penetrate the zona pellucida surrounding the egg

Capacitation

Occurs within the female reproductive tract
Involves interactions between sperm and mucosal surfaces
Removal of glycoprotein coat and seminal plasma proteins from the sperm plasma membrane
Capacitated sperm exhibit increased motility and force
Capacitated sperm possess hyaluronidase enzymes to penetrate the extracellular matrix of cumulus cells
Sperm exhibit the ability to sense temperature differences and preferentially swim towards warmer sites
Capacitated sperm sense a thermal gradient of 2 degrees Celsius
Sperm also sense molecules secreted by the oocyte and cumulus cells, such as progesterone
Progesterone binds to receptors on the sperm tail, activating calcium channels and increasing sperm activity

Acrosome Reaction

Triggered after sperm binds to the zona pellucida (ZP)
Release of enzymes such as acrosin and trypsin-like substances from the acrosome
Occurs in three phases:
- Penetration of the corona radiata
- Penetration of the zona pellucida
- Fusion of the oocyte and sperm membranes

Phases of Fertilization

Phase 1:
- Millions of sperm reach the fertilization site
- Capacitated sperm pass through corona cells
Phase 2:
- The zona pellucida (ZP) is a glycoprotein shell facilitating sperm binding and inducing the acrosome reaction
- Binding and the acrosome reaction involve interaction with ZP3
Phase 3:
- Release of acrosin allows sperm to penetrate the zona pellucida, establishing contact with the oocyte membrane
- Changes in zona pellucida permeability occur when the sperm head contacts the oocyte surface
- Release of lysosomal enzymes from cortical granules lining the oocyte plasma membrane (zona reaction)
- Only one sperm typically penetrates the egg, despite other sperm being embedded in the zona pellucida

Gamete Fusion

Initial adhesion of sperm to the oocyte involves interaction between integrins on the oocyte and their ligands, disintegrins, on the sperm
Fusion of the sperm and oocyte plasma membranes occurs, forming a fertilization cone
The plasma membrane covering the acrosomal head cap disappears during the acrosome reaction
Fusion of the acrosomal head cap and the oocyte plasma membrane leads to the formation of a fertilization cone

Polyspermy Prevention

Polyspermy, the fertilization of an egg by multiple sperm, is prevented by the fast and slow blocks:
- Fast block: Changes in the electric potential of the egg plasma membrane
- Slow block:
  - Cortical granule reaction, where enzymes are released to modify the zona pellucida, preventing further sperm binding
  - Zona reaction involves the inactivation of species-specific receptor sites on the zona pellucida
  - The Juno protein plays a role in slow block by preventing sperm fusion with the oocyte membrane

Fusion of Genetic Material

The male pronucleus enlarges while the oocyte completes its second meiotic division
Both pronuclei lose their nuclear envelopes and become indistinguishable
The centrosome from the male pronucleus produces asters and contacts the female pronucleus
Each pronucleus migrates toward the other, replicating its DNA during the migration
The nuclear envelopes break down
Glutathione in the egg reduces disulfide bonds and uncoils sperm chromatin
The sperm contributes the pronucleus, mitochondria, and centriole
Mitochondria from the sperm are degraded in the egg cytoplasm
Chromatin condenses into chromosomes which orient themselves on a common mitotic spindle

Calcium Role in Embryo Development

Calcium release activates metabolic reactions involved in respiration and protein synthesis
Increased respiration and protein synthesis contribute to embryo development

Summary

The male nucleus enters the egg cytoplasm and becomes the male pronucleus
The fusion of the sperm and egg triggers the oocyte nucleus to complete its second meiotic division, forming a polar body

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Description

Explore the intricate processes of fertilization in mammals, including the viability of ova and sperm, and the crucial mechanisms of capacitation and the acrosome reaction. This quiz delves into how sperm navigates the female reproductive tract to successfully fertilize the egg.