Human Embryology Exam 1

What are the six anatomical directional terms used in embryology?

Dorsal, ventral, cranial, caudal, medial, and lateral.

What does cranial mean?

Toward the head.

What does caudal mean?

Toward the tail.

What does ventral mean?

Toward the front of the body.

What does dorsal mean?

Toward the back of the body.

What does medial mean?

Toward the midline of the body.

What does lateral mean?

Away from the midline of the body.

In adult anatomy, ventral is equivalent to what?

Anterior.

In adult anatomy, dorsal is equivalent to what?

Posterior.

Why can anterior and posterior be confusing in embryology?

They can refer to the head/tail axis in embryology and animal anatomy.

What terms are used for the head-tail axis?

Cranial-caudal.

What terms are used for the front-back axis?

Ventral-dorsal.

What is a sagittal section?

A cut along the midline.

What is a transverse section?

A cut from left to right.

What is another name for a transverse section?

Cross section.

What is a frontal section?

A cut from cranial to caudal.

What are the three body planes?

Frontal, sagittal, and transverse.

How long does gestation from fertilization to birth last?

About 38 weeks or 9 months.

What are the two periods of pregnancy?

Embryonic period and fetal period.

What is the embryonic period?

Weeks 1–8.

What happens during the embryonic period?

The body plan is established and precursors of the major organ systems are formed.

By 8 weeks, what has happened to the organ systems?

All organ systems are present, but only the heart is functioning.

What is the fetal period?

Weeks 9–38, ending at birth.

What happens during the fetal period?

Organs mature and the fetus grows.

What is organogenesis?

Organ maturation and growth.

What are the three trimesters?

First, second, and third trimester.

How long is each trimester?

About 3 months.

What weeks are the first trimester?

Weeks 1–12.

What happens during the first trimester?

Organ systems are established.

When is the embryo most sensitive to toxins and developmental insults?

During the first trimester.

What weeks are the second trimester?

Weeks 13–27.

What happens during the second trimester?

The fetus triples in length and weight.

What weeks are the third trimester?

Weeks 28 to birth.

What happens during the third trimester?

The fetus doubles in weight and head-to-body proportions normalize.

What is generally the most physically difficult trimester for the mother?

The third trimester.

What happens to kidney function during the third trimester?

It increases by about 50%.

What happens to maternal blood volume during the third trimester?

It increases by about 30%.

What happens to maternal cardiac output during the third trimester?

It increases by about 30–40%.

What are the two common ways of dating pregnancy?

Gestational age and fertilization age.

What is gestational age?

Pregnancy age based on the start of the last menstrual period (LMP).

Who commonly uses gestational age?

Healthcare providers and the public.

Why is gestational age commonly used?

The start of the menstrual cycle can usually be tracked.

What is fertilization age?

The actual age of the embryo based on the fertilization date.

Who commonly uses fertilization age?

Embryologists and scientists.

Why is fertilization age less commonly used clinically?

The exact fertilization date is usually unknown.

What pregnancy dating method is used in this class?

Fertilization age.

What is the relationship between gestational age and fertilization age?

Gestational age = fertilization age + 2 weeks.

If fertilization age is 6 weeks, what is gestational age?

8 weeks.

If gestational age is 10 weeks, what is fertilization age?

8 weeks.

What does LMP stand for?

Last Menstrual Period.

When does gestational age begin?

At the start of the last menstrual period.

When does fertilization occur in the example timeline?

Day 15 of gestational age and Day 1 of fertilization age.

When does implantation begin in the example timeline?

Day 20 of gestational age and Day 6 of fertilization age.

When does the embryo stage begin in the example timeline?

About 4 weeks gestational age or Day 15 fertilization age.

When can primitive heart function be detected?

About 6 weeks gestational age or Day 26 fertilization age.

When does the first trimester end?

About 13 weeks gestational age or 11 weeks fertilization age.

When does the second trimester end?

About 26 weeks gestational age or 24 weeks fertilization age.

When does childbirth occur in the example timeline?

About 39–40 weeks gestational age or 37–38 weeks fertilization age.

If a person says they are 19 weeks pregnant, which dating method is most likely being used?

Gestational age.

If an embryology textbook says an embryo is Day 6 old, which dating method is most likely being used?

Fertilization age.

If a sonogram says someone is 14 weeks pregnant, which dating method is most likely being used?

Gestational age.

If a research embryo is described as 30–33 days old, which dating method is likely being used?

Fertilization age.

What is gametogenesis?

The formation of gametes (sperm and eggs) in which a diploid cell undergoes meiosis to form haploid gametes.

What are the 4 phases of gametogenesis?

1. Primordial germ cells form and migrate to the gonad; 2. Germ cell number increases by mitosis; 3. Chromosome number is reduced by meiosis; 4. Eggs and sperm mature.

Where are primordial germ cells first seen in humans?

In the wall of the yolk sac around week 4.

Where do primordial germ cells migrate?

From the yolk sac toward the mesonephros and then into the genital ridge.

What does the genital ridge become?

The gonad.

What happens if a primordial germ cell is lost during migration?

It can form a germ cell tumor called a teratoma.

Why can teratomas contain many different types of tissues?

Germ cells are pluripotent.

When do male primordial germ cells become spermatogonia?

At puberty.

What happens to spermatogenesis after it begins?

It continues throughout the male's lifespan.

What hormone does the hypothalamus produce?

GnRH.

What does GnRH stimulate the pituitary to release?

LH and FSH.

What hormone do Leydig cells produce?

Testosterone.

What hormone stimulates Leydig cells?

LH.

What cells respond to FSH and testosterone to initiate spermatogenesis?

Sertoli cells.

What are spermatogonia?

Stem cells that can produce more spermatogonia or differentiate into primary spermatocytes.

What does a primary spermatocyte become after meiosis I?

Two haploid secondary spermatocytes.

What do secondary spermatocytes become after meiosis II?

Four haploid spermatids.

What is spermiogenesis?

The maturation of spermatids into mature sperm.

What happens to sperm DNA during spermiogenesis?

It becomes highly condensed and histones are replaced with protamines.

What is spermiation?

The release of mature spermatozoa into the lumen of the seminiferous tubule.

What are the three main parts of a mature sperm?

Head, midpiece, and tail.

What is found in the sperm head?

Tightly packaged DNA and the acrosome.

What is the function of the acrosome?

It contains hydrolytic enzymes used to penetrate the egg.

Where does the acrosome come from?

The Golgi apparatus.

What is found in the sperm midpiece?

Mitochondria.

What is the function of the sperm tail?

Propulsion.

Where are sperm stored after production?

The epididymis.

What is semen?

Sperm mixed with secretions from the seminal vesicles and prostate glands.

How long can sperm remain viable after ejaculation?

About 3 days.

What is capacitation?

The final step of sperm development that occurs in the female reproductive tract.

What does capacitation prepare the sperm to do?

Release acrosomal enzymes when encountering the egg.

Approximately how many sperm are generated per day?

About 100 million.

Approximately how many sperm are present in one ejaculation?

About 200 million.

How many sperm may reach the egg?

Only a few hundred.

How long does one cycle of spermatogenesis take?

About 74 days, or about 3 months including epididymal maturation.

What factors are used to evaluate sperm quality?

Semen volume, total sperm number, concentration, motility, viability, and morphology.

When does oogenesis begin?

During fetal development.

When does oogenesis resume?

At puberty.