Laboratory Activity 6: Chick Development Flashcards
By 33 hours of incubation, what subdivisions of the brain are recognizable in the chick embryo?
prosencephalon
mesencephalon
rhombencephalon
The prosencephalon, positioned at the front, further differentiates into the telencephalon and diencephalon.
The mesencephalon, located centrally, appears as an oval-shaped structure primarily responsible for processing visual and auditory information. Its dorsal portion will develop into the optic lobes, which function as visual centers connected to the optic nerves.
The rhombencephalon, involved in auditory and balance functions, is subdivided into the anterior metencephalon and the posterior myelencephalon.
What is the notochord, and what are some of its functions in the embryo?
A rod-like structure in the embryo, located ventral to the neural tube, and plays a crucial role in development. It serves as the primary organizer, inducing the formation of surrounding structures and establishing the body’s axial organization. It also provides axial support until the vertebral column emerges and replaces it. Remnants of the notochord persist in adults as the nucleus pulposus of intervertebral discs, which helps cushion the spine.
What changes do you see in the 72-hour chick embryo that make it look different from a 33-hour or 48-hour chick embryo?
By the 72-hour mark, the chick embryo looks more developed than at 33 hours.
The brain regions are more defined, with the telencephalon growing larger and the optic vesicles beginning to form optic cups.
The heart, which started as a simple tube at 33 hours, has now looped and is actively beating, showing the early formation of its chambers.
The number of somites has increased, contributing to future muscle and skeletal structures, and the neural tube is now fully closed.
Tiny limb buds start appearing, signaling the beginning of limb development.
The circulatory system is also more advanced, with vitelline blood vessels spreading across the yolk sac to nourish the growing embryo.
What changes do you see in the 96-hour chick embryo that make it look different from a 72-hour chick embryo?
By 96 hours, the chick embryo looks even more developed than at 72 hours.
The brain has grown significantly, especially the telencephalon and diencephalon, making the head appear much larger.
The optic cups are now well-formed, and the lens vesicles are starting to take shape.
The heart is more defined, showing clearer chamber separation and more twisting to improve circulation.
The leg and wing buds, which were just starting to form at 72 hours, are now more distinct, marking the early stages of wing and leg development. The tail bud is also more noticeable as the body continues to elongate.
Meanwhile, the vitelline blood vessels have expanded even further, improving nutrient flow to support the growing embryo.
At what temperature and what humidity do you incubate chick eggs?
37.5–38°C (99.5°F) with a relative humidity of 57%.
While eggs can tolerate temperatures between 35°C and 40.5°C (95–105°F), lower temperatures slow development, and higher temperatures accelerate it. Maintaining proper humidity of 57% is also ideal to prevent dehydration but eggs can tolerating an acceptable range between 50-60%.
What is the best way to orient eggs when incubating them if you will be opening them later for observation? Why is this orientation advantageous?
Blunt end facing upward.
This positioning ensures that the embryo develops just below the air space at the blunt end, making it easier to access and observe without disrupting its growth. The yolk naturally orients to gravity, keeping the embryo positioned correctly for proper development and easy dissection.
If you crack open an egg, you may observe the chick ovum (the yolk) intact. Only a fragile _________ overlain by a __________ protects it from being punctured.
cell membrane;
vitelline envelope
Most of the bulk in the chick ovum is not cytoplasm, but spheres of _______ suspended in a sea of _________.
yolk lipid;
yolk protein
Flat disc surrounding the embryo; forms the circulatory system of the chick
Area pellucida
____% of eggs miss the opening and fall into the body cavity
5%
Site of fertilization in chicken reproductive tract
Infundibulum
Most albumen is secreted by cells in this part of the female reproductive tract
Magnum
Chalazae and shell membranes are added in this region of the female reproductive tract
Isthmus
Water and salts traverse the shell membranes and are added to the albumen in this part of the female reproductive tract
Uterus (shell gland)
Once in the oviduct, the ovum packed with yolk is moved along by muscular contractions of the oviduct.
Having traveled with its small end first, its orientation is now reversed, and the egg is laid with the large blunt end first.
Embryonic endoderm and mesoderm are ingressing through the ________. The endoderm is migrating down to join the hypoblast, and the mesoderm is migrating outward between the epiblast and hypoblast, forming an intermediate layer. The prospective mesoderm cells are the next to enter the primitive streak and leave the epiblast. However, they do not move down to join the hypoblast but instead make a U-turn and migrate outward between the epiblast and hypoblast to form a separate layer between the two.
The line along which cells are moving inward from the epiblast, or ingressing, is called the ———.
Primitive streak
In the chick embryo at the top of the primitive streak called ________. It is here that the notochordal cells converge, ingress, and migrate forward, rather than laterally, to form a streak of notochordal cells down the midline.
Hensen’s node (or primitive node)
is the process of a surface folding in on itself to form a cavity, pouch or tube
Invagination
an embryo incubated for 24 hour—total time of development has been more than 24 hours, since development began prior to egg laying.
Posteriorly, where the endoderm is still flat, is the open midgut, and the transition between the closed foregut and open midgut is the _______.
anterior intestinal portal
One of the most notable features of the 24-hour embryo is the ___________.
invaginating neural ectoderm
Notice that at the anterior tip of the embryo, the neural plate does not close completely but leaves an open channel called the ________. This will be closed by _____ hours.
anterior neuropore;
36 hours
As the embryo develops, additional somites will form from the more _________.
posterior unsegmented somite mesoderm
The 24-hour chick embryo was roughly equivalent to a ______ human embryo; a 33-hour chick embryo is roughly equivalent to a ________ human embryo; what takes hours in a chick embryo takes days in a human embryo.
3-week;
4-week
33 Hours
The neural tube, closed along much of its length, has become specialized anteriorly to form the ______. It has 3 major subdivisions—the forebrain (__________), midbrain (_______), and hindbrain (_________)—which are visible as a series of enlargements.
brain;
prosencephalon;
mesencephalon;
rhombencephalon;
33 Hours
The forebrain is further divided into an anterior ______ and posterior ________.
telencephalon;
diencephalon
33 Hours
The diencephalon is becoming very complex: its walls have evaginated to form ________, which later become the _______; its floor has evaginated to form the _______, which later becomes the posterior part of the ________; its roof, at this point, has no evaginations, but by 48 hours will have evaginated to form the _____, later to become the _______.
optic vesicles;
optic cups;
infundibulum;
pituitary gland;
epiphysis;
pineal gland
33 Hours
The hindbrain is also subdivided, forming a _________ anteriorly and a ________ posteriorly.
metencephalon;
myelencephalon
The circulatory system of a 33-hour chick embryo has advanced so that there is now a heart in the form of a relatively straight tube with 4 chambers. It will not start beating until 48 hours of development. At this point, it looks very much like a fish heart.
Posteriorly, the heart has a sinus venosus. This leads forward into an _________, which opens into an ________, swung slightly to the (left, right), which in turn leads into the _______ (or ________).
undivided atrium;
undivided ventricle;
right;
conus arteriosus;
bulbus cordis
33 Hours
From the _______ sprout, a pair of arteries, the ________. Think about your own 4-chambered heart with its 2 atria and 2 ventricles.
conus arteriosus;
ventral aortae
33 Hours
The atrium and ventricle become subdivided into right and left sides. The sinus venosus becomes reduced to the _______ (or pacemaker), and the conus arteriosus becomes subdivided to form the ______ and _______.
sinoatrial node;
base of the aorta;
pulmonary arteries
The embryonic blood vessels in the chick at 33 hours are still very rudimentary. There are a pair of ________ that will bring nutrient (yolk)-laden blood from the yolk sac back to the embryo. These join the heart at the _______.
vitelline veins;
sinus venosus
33 Hour
A pair of ventral aortae leave the heart and connect to the paired dorsal aortae by way of the first pair of ________.
aortic arches
33 Hours
2 subdivisions of the area opaca: the area vitellina and area vasculosa. Notice that these regions are considerably larger than at 24 hours.
At the outer margin of the area vasculosa, there is now a darker band. This is the _______, a circular blood vessel marking the terminal channel of the vitelline (yolk) circulation.
sinus terminalis
This is huge in relation to the rest of the embryo. The ——- is elongating faster than the tissues around it and is lifting off the blastoderm anteriorly, forming the head fold in the process.
Head
In order to create a tubular-shaped body out of a flat plane, _______ tuck down around the embryonic region.
lateral body folds
This is present at the posterior end of the embryo, where gastrulation is still proceeding
Primitive streak
This is the anterior region of the brain, subdivided into a telencephalon and diencephalon.
Prosencephalon (forebrain)
This is not distinctly separate from the diencephalon, and it will suffice to label the brain region anterior to the optic vesicles as telencephalon. Later, the ——– becomes bilobed and is associated with the olfactory organs and the sense of smell, as well as being the center of intelligence. We more commonly call it the cerebrum.
Telencephalon
This opening at the anterior end of the brain is still present at 33 hours.
Anterior neuropore
__________
This is most easily recognized by its lateral evaginations, the optic vesicles. The rest of the lateral walls become the thalamus, a region of sensory integration. The floor becomes the ________, a region that sends hormones into the posterior pituitary for storage and secretes releasing hormones that control the anterior pituitary. It should come as no surprise, therefore, to find that the posterior pituitary forms from an evagination of the ————- floor, the _________. The roof of the ——— will form the anterior _______, a highly vascularized region that secretes cerebral spinal fluid by squeezing out an ultrafiltrate of the blood. An evagination of the ———- roof (the _________) forms later, becoming the ________. In addition, the ——— secretes melatonin and is a seat of control for circadian and seasonal rhythms. In the early 1600s, the famous French philosopher _______ considered the pineal gland to be the seat of the soul.
Diencephalon;
hypothalamus;
infundibulum;
choroid plexus;
epiphysis;
pineal gland;
Descartes
These are evaginations of the lateral walls of the diencephalon. They grow close to the head epidermis and will induce it to form the lens of the eye. The ——— invaginate to form ________, the inner side of which differentiate into the _______ and the outer layer into the ________. The optic nerve grows back from the neural retina along the connection of the optic cup to the diencephalon. The optic nerves from opposite sides then cross underneath the diencephalon and enter the mesencephalon.
optic vesicles;
optic cups;
neural retina;
pigmented retina
The floor of the diencephalon evaginates, forming the __________. It later differentiates into the posterior ________ (or ________), which stores two hormones from the hypothalamus: _______ (which causes the kidney to resorb water and produce more concentrated urine), and _______ (which causes uterine contractions and milk release in mammals).
infundibulum;
pituitary;
neurohypophysis;
antidiuretic hormone;
oxytocin
This is the middle, oval-shaped region of the brain that will serve primarily for processing data from the eyes and ears. The dorsal region will become the optic lobes, visual centers associated with the optic nerves.
Mesencephalon
This region becomes associated with the system of hearing and balance and is divided into an anterior metencephalon and posterior myelencephalon.
Rhombencephalon
____________
This will form the cerebellum dorsally and the pons ventrally. The ___________ primarily coordinates stimuli concerning body position and movement; the ______ is a bundle of connective pathways shunting information between the cerebrum and cerebellum.
Metencephalon;
cerebellum;
pons
____________
Also called the medulla oblongata, this region is characterized by a series of enlargements called ________, each of which will become associated with a specific set of motor and sensory nerves. The ———– becomes the great linking highway between the brain and spinal cord.
Myelencephalon;
neuromeres
This is the posterior continuation of the neural tube. Notice how far back on your embryo the closed neural tube extends.
Spinal cord
___________
These are epidermal thickenings on the side of the head in the region of the myelencephalon. “_____” stands for ear, and these placodes, seen best in cross section, later invaginate to form the inner ear. This is the organ of both hearing (the _________) and balance (the
__________)
Otic placodes;
Otic;
cochlea;
semicircular canals
These are some of the most phenomenal cells in the embryo. The ________ are an evolutionary invention of the vertebrates. 1st residing on the crest of the neural tube, they later migrate to become a host of structures: ______ (except for the pigmented retina), ________, the _________, and _______ are just some of the structures formed.
neural crest cells;
pigment cells;
membrane bones in the face and skull;
adrenal medulla;
sympathetic ganglia of the autonomic nervous system
endoderm forms only ________
epithelial structures
During the formation of the gut, the endoderm contributes only the epithelial tube that forms the inner epithelial lining of the organs of the gut. It is the mesoderm surrounding this endodermal tube that forms the muscle and connective tissue layers of these organs.
This is the region of anterior gut that has been closed into a tube. This happens when the head fold and lateral body folds undercut the embryo, closing off the gut and bringing the cardiac mesoderm together beneath (ventral to) the gut.
The anterior region of the ——— is called the pharynx and forms the esophagus as well as a number of outpocketings, or evaginations. 2 evaginations will form ventrally. The anterior 1 will become the _____ and the posterior one the ________. A series of lateral evaginations are the pharyngeal pouches that are later transformed into the ________ and ________, and the epithelium of the tonsils, thymus, parathyroid, and ultimobranchial bodies. The posterior region of the foregut forms the _______.
foregut;
thyroid gland;
lungs;
eustachian tube;
cavity of the middle ear;
stomach
This is the opening of the foregut into the open midgut. The opening continues to shift posteriorly as closure of the gut continues. It can be seen more readily by turning your slide over and viewing the embryo from the ventral side.
Anterior intestinal portal
This lies ventral to the foregut. At this point in development, like the brain, it is huge compared to the rest of the body. The —– must shift posteriorly to the thoracic region. This will occur primarily through an elongation of the head and neck regions. Look for the large vitelline veins coming in from the extraembryonic regions and entering the posterior chamber of the heart, the sinus venosus. At this point in development, the sinus venosus cannot be readily distinguished from the next chamber, the atrium. Therefore, you can refer to them both as the _______. The ventricle is the next chamber and is easily distinguishable since it bends to the right. Where the heart narrows again anteriorly mark the ______
heart;
sinoatrial region;
conus arteriosus
_____________
This is visible as a dark line in the midline ventral to the neural tube. The notochordal mesoderm has been called the “_________” because of its many inducing functions that initiate an axial organization of the organism. It also provides axial support for the embryo until the vertebrae engulf it, taking over this function. In the adult, notochordal tissue between the vertebrae expands to form the ______ (________) of the intervertebral disc. When a person suffers from a “_______” or _______, stress on the back has caused the nucleus pulposus to bulge outward. The bulging disc puts pressure on the spinal cord and causes back pain. Often, rest and proper back exercises can remedy this condition without the need of surgery. There is also a core of notochord left in the centrum of each vertebra. Sometimes this remnant of notochord gives rise to tumors called _________. These tumors cause extreme back pain by narrowing the spinal canal and pinching the spinal cord and must be removed surgically.
Notochord;
primary organizer;
gelatinous center;
nucleus pulposus;
slipped disc;
herniated disc;
chordomas;
These blocks of mesoderm are found on either side of the neural tube. Each _______ becomes subdivided into a _______ that forms the vertebrae and ribs, a _______ that forms skeletal muscles for the back and limbs, and a __________ that gives rise to dermis.
somite;
sclerotome;
myotome;
dermatome
This is a streak of mesoderm lying lateral to the somites. It will form the kidneys, the urogenital ducts, and the gonads.
Nephrogenic (intermediate) mesoderm
Lateral to the nephrogenic mesoderm is the _________, which delaminates to form 2 layers: the _______ and _______ layers. The splitting creates a cavity, the body coelom. Somatic lateral plate mesoderm becomes associated with the epidermal ectoderm, and together they form the _______. This later will form the body wall and, in the extraembryonic regions, the amnion and chorion (the extraembryonic membranes that surround and protect the embryo). The splanchnic lateral plate mesoderm associates with the endoderm, which together form the _________. This forms the gut wall and, in the extraembryonic regions, the vascularized yolk sac and allantois. Because of its extensive vascularization, the yolk sac can transport yolk nutrients back to the embryo, and the allantois can receive nitrogenous waste from the embryo for storage as uric acid.
lateral plate mesoderm;
splanchnic;
somatic;
somatopleure;
splanchnopleure;
Description of Embryo:
After laying, cleavage is complete and gastrulation has begun, but the primitive streak has not yet formed.
Stage 1: Prestreak
There is a space between the head and the proamnion called the ________(“below the head”) __________.
Subcephalic pocket
The foregut in this region comes in contact with the epidermal ectoderm to form the oral membrane. Fortunately, this membrane is removed by programmed cell death; the opening produced is the mouth opening. When cell death fails to occur, an anomaly results called ______ (“no mouth”).
astomia
A pair of first _______ connects the ventral aortae with the dorsal aortae.
aortic arches
Just posterior to the region of the sinus venosus, the foregut opens at the anterior intestinal portal to become the _________.
open midgut
The old-fashioned, ___________, still used by many small chicken farmers, consist of a thermostated heating coil with a small fan that circulates air within the box.
cedar box incubators
Humidity is controlled very simply by _____________.
placing pans of water in the incubator
A humid atmosphere is also essential in order to __________ of the egg.
avoid dehydration
It is necessary to dehydrate the embryos because the mounting medium used here will not mix with water.
For proper development, eggs should be turned several times a day—as many as six. It is best to turn them to a 45° angle from their vertical position.
A ______ is no more than a light in a box shining through a hole the diameter of an egg.
candler
Candling is best done in a dark room. Move the egg around, holding it against the lighted hole of the candler. In the living embryo, vascularized regions will be particularly obvious. A dead embryo will look dull and dense.
The eggs you will be using for whole mounts should not be turned while incubating and should have been positioned with their blunt end up.
Chick embryo Ringer’s solution
NaCl
KCl
CaCl
_______ is the first step in any procedure in which tissue is to be preserved for histological study.
Fixation
You will be washing out the fixative using __________.
70% ethanol
This is a general nuclear stain that is excellent for whole mounts.
Mayer’s carmalum stain
Rather than removing the water from your specimens in a single step, which could damage the tissue, you will use a graded series of alcohols to slowly replace the water with alcohol. This avoids severe convection currents that are set up as one fluid replaces the other. Following dehydration, the embryos must be cleared in a clearing agent. You could use xylene or toluene.
Toluene is better
Clearing will make the embryos transparent.
Xylene and toluene are both very toxic and also must be disposed of as hazardous waste.
The mounting medium you use should be a neutral mounting medium, such as _______.
Histoclad
Cheaper mounting media are acidic. They cause the stain to fade and oxidize very quickly, making a cloudy ring around the edge of the slide that gradually works its way to the middle.
Once you start the mounting procedure, work with speed. Do not let your specimen dry out. It will do so very quickly.
