Human Reproductive Biology Overview

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Questions and Answers

What is the role of L-selectin in the initial attachment of the blastocyst to the uterus?

It facilitates interactions with carbohydrate receptors on the uterine epithelium. (correct)

It anchors the blastocyst to the amniotic cavity.

It is responsible for the differentiation of epiblast cells.

It interacts with fibronectin to promote migration.

During the differentiation of the embryoblast, which two layers are formed?

Somatic and visceral mesoderm

Epiblast and hypoblast (correct)

Ectoderm and mesoderm

Trophoblast and mesenchyme

What do the anterior visceral endoderm (AVE) cells secrete to influence epiblast development?

Nodal antagonists (correct)

Cytokines

Fibroblast growth factors

L-selectin receptors

What is the significance of the cranial-caudal axis established during implantation?

It helps define the embryo's dorsal-ventral polarity. Signup and view all the answers

What is the main function of integrins on trophoblast cells during implantation?

To promote interaction with extracellular matrix molecules Signup and view all the answers

What is the primary energy source for spermatozoa found in the fluid of the seminal vesicles?

Fructose Signup and view all the answers

What role does the prostatic fluid play in the process of ejaculation?

It helps to protect sperm from acidity. Signup and view all the answers

What mechanism primarily aids the initial rapid transport of spermatozoa through the cervix?

Muscular movements of the female reproductive tract Signup and view all the answers

How long can spermatozoa bind to the epithelium in the uterine tube during capacitation?

24 hours Signup and view all the answers

What is removed from the sperm surface during the capacitation reaction that prevents premature capacitation?

Cholesterol Signup and view all the answers

What is the usual number of spermatozoa that successfully enter the uterine tubes during ejaculation?

Several hundred Signup and view all the answers

In what part of the female reproductive tract does sperm transport begin?

Upper vagina Signup and view all the answers

What is a significant component removed from spermatozoa during the capacitation process?

Glycoproteins Signup and view all the answers

What is the primary purpose of capacitation in spermatozoa?

To prepare the sperm for the acrosome reaction Signup and view all the answers

Which phase of fertilization involves the fusion of the oocyte and sperm cell membranes?

Phase 3: Fusion of membranes Signup and view all the answers

What role does hyaluronidase play during fertilization?

It assists in penetrating the corona radiata Signup and view all the answers

What does the acrosome reaction involve?

The fusion of the outer acrosomal membrane with the sperm plasma membrane Signup and view all the answers

Which glycoprotein plays a specific role in sperm binding during fertilization?

ZP3 Signup and view all the answers

Where does fertilization of the egg typically occur?

In the ampullary portion of the uterine tube Signup and view all the answers

What initiates the acrosomal reaction in spermatozoa?

Influx of calcium ions (Ca++) into the sperm head Signup and view all the answers

What happens after spermatozoa penetrate the zona pellucida?

They enter the perivitelline space and contact the egg's plasma membrane Signup and view all the answers

What is the first step that occurs after sperm enters the perivitelline space?

Binding of the sperm to the egg's plasma membrane Signup and view all the answers

What triggers the zona reaction after sperm entry into the egg?

Waves of Ca++ spreading through the egg's cytoplasm Signup and view all the answers

What role does the acrosomal reaction play in fertilization?

It allows the sperm to penetrate the egg's zona pellucida. Signup and view all the answers

What happens to the sperm's DNA after penetration into the egg?

Histones detach from the sperm's DNA. Signup and view all the answers

Which of the following occurs during the pronucleus formation?

Histones associate with the sperm chromosomes. Signup and view all the answers

What is the primary function of the cortical granules after sperm entry?

To release enzymes that prevent polyspermy. Signup and view all the answers

What does the term 'slow block to polyspermy' refer to?

The alteration of sperm receptors to prevent multiple fertilizations. Signup and view all the answers

What is the fate of the second polar body after the egg completes its meiotic division?

It is released from the egg. Signup and view all the answers

What is the significance of the maternal and paternal chromosomes organizing around a mitotic spindle?

It indicates the completion of fertilization. Signup and view all the answers

What happens to blastomeres during the cleavage stage of zygote development?

They progressively form a more compact structure. Signup and view all the answers

What is formed after the third cleavage of the blastomeres?

The morula. Signup and view all the answers

In the morula, what distinguishes inner cells from outer cells?

Inner cells communicate extensively through gap junctions. Signup and view all the answers

What occurs as the morula enters the uterine cavity?

Fluid penetrates to form the blastocele. Signup and view all the answers

What marks the transition from a morula to a blastocyst?

Development of the blastocele. Signup and view all the answers

What function does the trophoblast serve in early embryonic development?

It contributes to the formation of the placenta. Signup and view all the answers

What effect does the degeneration of the zona pellucida have on the blastocyst?

It allows the blastocyst to increase in size. Signup and view all the answers

Study Notes

Introduction

Sperm develop the ability to fertilize an egg in the tail of the epididymis.
Ejaculation releases sperm with fluids from seminal vesicles and the prostate gland.
Prostate fluid is rich in citric acid, acid phosphatase, zinc, and magnesium ions.
Seminal vesicle fluid is rich in fructose (energy source for sperm) and prostaglandins.
Fertility can be achieved with as few as 25 million sperm per ejaculate.

Sperm Transport & Capacitation

Sperm transport through the female reproductive tract begins in the vagina and ends in the uterine tube.
Seminal fluid protects sperm from the acidic environment of the vagina.
Rapid sperm transport (5-20 minutes) is driven by muscular movements of the female reproductive tract.
Slow sperm transport (2-4 days) involves sperm swimming through cervical mucus, storage in cervical crypts, and final passage through the cervical canal.
Only a few hundred sperm enter the uterine tube, typically the one containing the ovulated egg.
In the isthmus of the uterine tube, sperm bind to the epithelium for about 24 hours to undergo capacitation.
Capacitation involves removing cholesterol and glycoproteins from the sperm surface, preparing them for fertilization.
Capacitation is essential for the acrosome reaction to occur.
Hyperactivation after capacitation helps sperm break free from the tubal epithelium, penetrate mucus, corona radiata, and zona pellucida.

Fertilization

Fertilization occurs in the ampullary portion of the uterine tube.
Sperm penetrate the corona radiata, the outer layer surrounding the egg.
Hyaluronidase from sperm and active sperm movement facilitate penetration.
Sperm bind tightly to the zona pellucida via the sperm head's plasma membrane.
Sperm specifically bind to the ZP3 molecule on the zona pellucida.
The acrosome reaction releases enzymes from the acrosome (acrosin & serine proteinases) for penetration of the zona pellucida.
Binding to the egg's plasma membrane occurs via the sperm's equatorial region and microvilli on the egg’s surface.
The acrosome reaction is essential for sperm-egg fusion.

Zona Reaction & Pronucleus Formation

The zona reaction prevents polyspermy by modifying sperm receptors on the egg's plasma membrane and releasing hydrolytic enzymes into the perivitelline space.
Sperm entry triggers Ca++ waves in the egg, completing the second meiotic division and activating maternal RNAs.
The sperm's chromatin loosens within the egg, forming the male pronucleus, which moves toward the egg's nuclear material.
Histones re-associate with the male chromosomes.
The egg completes the second meiotic division, releasing a polar body.
The male and female pronuclei form and persist for about 10-12 hours.

Zygote Formation & Cleavage

The male and female pronuclei organize around a mitotic spindle, derived from the sperm's centrosome.
This marks the completion of fertilization, creating a zygote.
Cleavage begins, leading to mitotic divisions of the zygote, creating blastomeres which become smaller with each division.

Morula & Blastocyst Formation

Blastomeres initially form a loose cluster, then compact tightly to form a morula, held together by tight junctions.
Compaction segregates inner cells (inner cell mass) from outer cells (outer cell mass).
The inner cell mass forms the embryo proper, and the outer cell mass forms the trophoblast, which contributes to the placenta.
Fluid penetrates the zona pellucida, forming the blastocele, signifying the development of a blastocyst.
The inner cell mass becomes the embryoblast, located at one end, and the outer cell mass becomes the trophoblast, forming the blastocyst’s epithelial wall.

Embryo Hatching & Implantation

The zona pellucida surrounding the blastocyst degenerates, allowing the blastocyst to grow.
The blastocyst derives nourishment from uterine gland secretions.
The loss of the zona pellucida allows implantation to begin.
Trophoblastic cells penetrate the uterine mucosa, starting around day 6.
Initial blastocyst attachment is mediated by L-selectin on trophoblast cells and its receptors on uterine epithelium.
Integrins on the trophoblast then interact with laminin and fibronectin, promoting attachment and migration for implantation.
By the end of the first week, the blastocyst is implanted in the uterine mucosa.

Epiblast, Hypoblast, & Axis Formation

Embryoblast cells differentiate into epiblast (dorsal) and hypoblast (ventral) layers, establishing dorsal-ventral polarity.
Hypoblast cells form the anterior visceral endoderm (AVE), which migrates to the future cranial end of the embryo.
AVE cells secrete nodal antagonists like cerberus and lefty1, specifying the cranial end of the embryo.
In the absence of these inhibitors, nodal signaling establishes the primitive streak at the caudal end.
This establishes the cranial-caudal axis of the embryo during implantation (days 5.5-6).

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Description

This quiz covers essential aspects of human sperm development, transport, and fertilization. Explore the roles of seminal fluid, the epididymis, and the female reproductive tract in achieving fertility. Test your understanding of the biological processes involved in reproduction.