Midterms_Mesodermal Derivatives Flashcards
What are the four major lineages of the mesoderm
Lateral, Intermediate, Paraxial, and Chorda-mesoderm
Intermediate mesoderm gives rise to?
Kidney and Gonads
Axial mesoderm gives rise to?
Notochord
Paraxial mesoderm gives rise to?
Head and Somite
Somites give rise to 3?
Sclerotome, Myotome, Dermotome
Lateral Mesoderm gives rise to?
Splanchnic, somatic, extraembryonic tissues
Give the derivatives:
Sclerotome
Myotome
Dermatome
Splanchnic
Somatic
Sclerotome: Cartilage
Myotome: Skeletal Muscle
Dermatome: dermis
Splanchnic: Circulatory System
Somatic: Body cavity
a transient support structure that is eventually replaced by the
vertebral column.
Notochord
Function of axial mesoderm
include inducing neural tube formation and establishing an anteroposterior axis.
The remnant of the notochord is the?
Nucleus pulposus
Nucleus pulposus location?
invertebral disks
Thick bands of mesodermal cells that are located on each side of the neural tube are called?
paraxial mesoderm
what region of the paraxial mesoderm become the head?
anterior
Head mesoderm gives rise to?
craniofacial musculature
The rest of the paraxial mesoderm soon separates into blocks of cells called?
somites
Somites give rise to cells that form the vertebrae and ribs, the dermis of the dorsal skin, skeletal muscles of the back, skeletal muscles of the body wall, and limbs. They are referred to as what in birds and mammals?
Birds: Segmental plate
Mammals: Unsegmental mesoderm
The formation of somites is referred to as?
somitogenesis
What are the five developmental characteristics?
Periodicity
Separation
Epithelialization
Specification
Differentiation
Process of periodicity
The paraxial mesoderm cells become organized into whorls of cells called somitomeres. They first
appear in the cephalic region of the embryo then develop in a cephalocaudal direction. At the head
region, somitomeres form most of the head mesenchyme. At the occipital region, the somitomeres become compacted and bound together by an
epithelium.
Process of Separation
This is the transition from somitomeres to somite. It involves gene expression of the receptor tyrosine kinase Eph4 and their ligand EphrinB2, both of which cause cell-to-cell repulsion leading to the separation of cells. So, somitomeres are separated from each other
at the boundaries where Eph4 is expressed anteriorly and EphrinB2 is expressed posteriorly. In succeeding somitomeres, EphrinB2 occurs sequentially from anterior
to posterior. Different species have different numbers of somites (ex: 50 in chicks and 500 in snakes).
Process of epithelialization
When the mesenchyme cells express the paraxis gene, they synthesize fibronectin and N-cadherin. These molecules are responsible for linking them together, forming tight junctions, and generating their own basal membrane, converting it into an epithelium.
Process of specification
Initially, the somites look identical. However, they will soon be differentiated into various structures depending on the position along the anteroposterior axis.
Process of differentiation
As the somite matures, its various regions become committed to forming only certain cell types. Two major regions differentiate from each somite: the sclerotome and the dermomyotome. From these two, various mesodermal derivatives are formed.
What are the two mesodermal derivatives formed in the differentiation of somites?
Sclerotome and Dermomyotome
Explain the formation of cartilage via sclerotomes
The mesenchyme from each sclerotome accumulates around the notochord and separates into two different clusters of cells: one becoming the cranial sclerotome, the other becoming the caudal sclerotome. These clusters differentiate into cartilage cells of the embryonic vertebrae and part of the ribs.
Explain the formation of Epaxial and Hypaxial Myotomes
Dermomyotome is the remaining epithelial portion of the
somite which soon divides into a dermatome and a
myotome. The dermatome gives rise to the dermis of
the back skin. The myotome differentiates into
myoblasts, the muscle-forming cells, and gives rise to:
* Epaxial Myotome
- forms the deep muscles of the back
- contributes to the development of the ribs
* Hypaxial Myotome
- forms the muscles of the body wall and
muscles between the ribs (intercostal)
- contributes to the development of the ribs
Also known as the stalk of the somite
Intermediate Mesoderm
DEVELOPMENT OF THE URINARY SYSTEM
Rounding off of the somite encloses a cavity called the _________.
Splitting of the lateral plate mesoderm forms the ________.
The nephrotome (mesomere) likewise splits forming a cavity called _______.
Originally, the ________ is in communication with the myocoel and the coelom .
Soon, the myocoel is separated from the nephrocoel,leaving the nephrocoel in communication with the coelom via a ciliated funnel called the _________ .
From this simple structure, three distinct excretory organs develop in vertebrates, the _______, ________, and ___________.
Myocoel
Embryonic coelom
nephrocoel
nephrostome
This is the first excretory organ that develops in all vertebrates but is functional only in primitive hagfishes. In other vertebrates,
this excretory organ degenerates and becomes replaced by the ________.
Located cephalically beginning at the junction of the future neck and thoracic region, developing from an anteroposterior direction.
Pronephros
Derivatives of the pronephros
Pronephric Tubules
Pronephric Duct
Glomus
Explain the formation of Pronephric Tubules
The dorsolateral wall of the nephrotome evaginates and elongates forming the pronephric tubule. The cavity of the nephric tubule is an extension of the nephrocoel.
Explain the formation of the pronephric ducts
As the pronephric tubules elongate, their distal ends fuse forming a common duct called pronephric duct. The pronephric ducts (on each side of the body) grow caudally towards the cloaca using cell division and morphogenetic movements of the cells at the terminal ends. The ducts formed enter the cloaca from each side.
Expain the formation of Glomus
The visceral wall of the nephrotome becomes supplied with blood vessels, called glomus , by the dorsal aorta. The glomus covered only with thin epithelium filters wastes from the blood into the coelomic fluid. This mixture of waste and coelomic fluid is carried to the pronephric tubules by the ciliary currents of the nephrostome.
Development of the Mesonephros
The mesonephros replaces the pronephros of vertebrates (except in __________).
It is the functional kidney of adult bony fishes and amphibians.
In reptiles, birds, and mammals, the mesonephros will eventually degenerate and become replaced with the ____________.
Development starts at the level where the ___________ ends at the area of the pelvic region.
Like the pronephros, development proceeds in an _________________ direction.
hagfish
Mesonephros
metanephros
pronephros
Explain the development of the Nephrogenic Cord
The mesodermal cells of the nephrotome form a mass of mesenchyme that extends caudally, running the length of the pronephric duct. This elongated mass, called nephrogenic cord or nephrogenic tissue, will serve as the precursor of the mesonephric
tubules.
Explain formation of Mesonephric Tubules
As one and of the mesonephric vesicle establishes contact with the pronephric duct, the other end continues to elongate in the opposite direction forming as S-shaped mesonephric tubules. These tubules continue to elongate, forming convoluted tubules.
Explain the formation of Glomerulus and Bowman’s Capsule
The free end of the mesonephric tubule enlarges and becomes thin. Afferent blood vessels of the aorta break into glomerular capillaries and push against one side of the wall of the mesonephric tubules. A cup-shaped Bowman’s capsule forms as the glomerulus pushes against this end. Since the tubules do not connect with the nephrocoel (no nephrostome), blood in the glomerular capillaries is filtered into the Bowman’s capsule. Efferent blood vessels leave the glomeruli going toward the elongated and coiled tubule as they, once again, break into capillaries. Resorption of
Explain the formation of Glomerulus and Bowman’s Capsule
The free end of the mesonephric tubule enlarges and becomes thin. Afferent blood vessels of the aorta break into glomerular capillaries and push against one side of the wall of the mesonephric tubules. A cup-shaped Bowman’s capsule forms as the glomerulus pushes against this end. Since the tubules do not connect with the nephrocoel (no nephrostome), blood in the glomerular capillaries is filtered into the Bowman’s capsule. Efferent blood vessels leave the glomeruli going toward the elongated and coiled tubule as they, once again, break into capillaries. Resorption of water and other materials that are still needed by the body is done by these capillaries before the final waste products are transported to the mesonephric ducts.
Development of the Metanephros
The metanephros replaces the mesonephros and becomes the functional kidney of what animals?
It is the most advanced type of excretory organ.
reptiles, birds, and mammals.
Metanephros
Explain the formation of Metanephric Diverticulum
Near the point where the mesonephric duct opens into the cloaca, a tiny bud-like outgrowth develops, called metanephric diverticulum or ureteric bud. The slender end, connected to the mesonephric duct, will become the ureter. The distal end is dilated and will develop into the pelvis of the kidney. The pelvis of the kidney forms branches called the major calyx, which will also re-branch to form minor calyces. Minor calyces also undergo branching and form the straight collecting tubules. Branching out from the straight collecting tubules are smaller arched collecting tubules.
Explain the formation of Metanephric Tissue
As the diverticulum grows, it pushes out mesodermal cells of the nephrogenic cord becoming collected at its expanded end forming the metanephrogenic tissue/mass.
Explain the formation of Metanephric Tubules / Nephrons
Close to the arch collecting tubules, the metanephrogenic tissue forms cluster of cells that become metanephric vesicles, much like the mesonephric vesicles. these vesicles elongate with one end moving towards the arched collecting duct and fusing with it. The other end continues to elongate and becomes convoluted, with the terminal end forming a Bowman’s capsule and encapsulating a glomerulus.
DEVELOPMENT OF THE GENITAL SYSTEM
During the early stages of development, the genital system cannot be distinguished as either male or female, thus called the _________ stage.
The _____________ and_______ are therefore simply referred to as indifferent gonads.
However, together with gonadal development, two types of tubules are formed, one pair persisting while the other pair degenerates depending on which sex finally becomes determined. What are these tubules?
Indifferent Stage
Primordial ovaries and testes
Rete testis
The Indifferent Gonad
Gonads develop from three sources: the _________ (coelomic epithelium) lining the posterior abdominal wall, the ________ (intermediate mesoderm), and the __________.
The mesothelium proliferates forming a pair of longitudinal ridges ventral to the developing kidneys, called?
Then, from the endodermal lining of the yolk sac, _________ cells migrate to the gonadal ridge via the dorsal mesentery of the hindgut.
Cells of the mesothelium become spherical and increase in size, forming a thick _________.
The germinal epithelial cells proliferate and penetrate the intermediate mesoderm forming ________________.
The combination of germ cells and primary / primitive sex cords forms the __________,
This indifferent structure now consists of a ________ (inner region) and a ________ (outer region).
This is the basic pattern for the development of the testis and the ovary.
Mesothelium, mesenchyme, primordial gern cells
germinal ridge
indifferent gonad
medulla, cortex
Explain the Formation of the testis
If the embryo is determined as male (XY in humans), the medulla will develop into a testis while the cortex becomes reduced to a thin capsule called tunica albuginea. The primary sex cords enter the medulla and develop into seminiferous cords, that soon become hollowed out and form seminiferous tubules. 50 to 80 primordial germs cells enter the tubules of both testes and will give rise to spermatogenic cells. Cells of the cords give rise to the sustentacular cells of the tubules called Sertoli cells. The parts of the primary sex cords that extend deepest into the medulla form the rete testes, the first of a series of reproductive ducts for sperm transport.
Explain the Formation of the ovary
If the embryo is determined as female (XX in humans), the ovary will originate from the cortex and the medulla will become vascular. The primary sex cords degenerate then secondary sex cords (cortical cords) extend from the germinal epithelium. The secondary cords increase in size as the primordial germ cells are incorporated into them. Soon, the secondary cords break up into isolated clusters called ovarian follicles. The first and youngest ovarian follicles are primordial follicles which consist of an oogonium and a single layer of flat follicle cells derived from the cords.
The Indifferent Duct System
After the determination of the gonads, they can be seen to be in contact with the ________.
The mesonephric tubules grow into the gonadal ridge and remain connected to the?
In the meantime, a second duct system (independent of the mesonephros) arises as an invagination of the lateral side of the gonadal ridge and eventually fuse to form the?
The presence of these two types of ducts represents the indifferent duct system.
mesonephros
wolffian duct
mullerian
Explain the formation of Male Reproductive Ducts
Some mesonephric tubules and the entire mesonephric ducts are retained while the Mullerian ducts degenerate.
➢ Fishes and Amphibians
- the mesonephric tubules fuse with the rete testis to become the efferent ductules
- the mesonephric duct serves as the ductus (vas) deferens, which transports sperm into the cloaca
➢ Higher Vertebrates
- the efferent ductules become highly coiled to form the epididymis
- the mesonephric duct becomes surrounded by smooth muscles and becomes the ductus deferens
- distal to the vas deferens, is a dilated portion forming the seminal vesicle, a gland that secretes a substance for sperm viability
- the mesonephric duct between the seminal vesicle and the urethra constitutes the ejaculatory duct
- from the urethral epithelium, the prostate and bulbourethral glands develop, the secretions of which convey and activate fluids for the sperm
What degenerates and retained in male reproductive ducts?
Some mesonephric tubules and the entire mesonephric ducts are retained while the Mullerian ducts degenerate.
What is retained and degenerated in Female reproductive Ducts?
The Mullerian ducts persist while mesonephric tubules and mesonephric ducts degenerate.
The Descent of the Gonads
Gonads descend in what animals?
As the mesonephros grows in bulk, it bulges out into the peritoneal cavity, pushing the ____________ (lining of the body wall).
In this process, the peritoneum is thrown into _______.
The anterior fold becomes the _____________.
The posterior fold becomes the ___________ of the mesonephros.
mammals
peritoneum
folds
diaphragmatic ligament
inguinal ligament
Explain the Descent of the Testis
As the testis grows and the mesonephros degenerates, it takes up the peritoneal coat of the mesonephros, becomes closely related to the inguinal ligament of the mesonephros, and is then referred to as the gubernaculum. At the same time, coelomic evaginations are formed at the posterior end where the gubernaculum is attached, called scrotal pouches. As the surrounding pelvic structures grow, the gubernaculum fails to elongate in proportion to this growth. Due to this differential growth, the testis seems to be pulled by the gubernaculum, shifting its position caudally. Soon, the testis slips down under the peritoneal lining and comes to lie within the scrotal pouch.
Explain the Descent of the Ovary
As the ovaries and their corresponding ducts increase in size, they begin to sag caudally and ventrally. As the ovaries descend slowly, they pull the peritoneum and stretch it into a mesentery-like structure which serves as the supporting membrane and path of blood vessels. Due to this descent, the inguinal ligament is bent into an angular form. The anterior of the bend becomes the round ligament of the ovary. The posterior of the vend becomes the round ligament of the uterus.
The Indifferent External Genitalia
During early mammalian development, a conically shaped protrusion called a _________ appears between the umbilical cord and the tail.
At its posterior area, a shallow groove called the __________ has a thin roof, the _____________ , and an opening called the ___________.
Lateral to the grooves are elevated walls called ____________. Lateral to the folds are rounded ridges that appear on each side forming the ___________.
Rupturing of the genital membrane will provide an __________ for the urogenital sinus.
This is now referred to as the ____________ from which either the male or female external genitalia would differentiate.
genital tubercle
urogenital groove, urogenital membrane, urogenital sinus
urogenital folds, genital swellings
external opening
indifferent genitalia
Explain the development of the male genitalia
The genital tubercle elongates to form a cylindrical structure called phallus. The genital swellings shift their position caudally and are then referred to as scrotal swellings (scrotum). Each becomes half of the scrotum, separated from the other internally by the scrotal septum and externally by the scrotal raphe. The phallus elongates further and becomes the penis. The edges of the urogenital folds unite closing the urogenital sinus from the outside, forming a tube called the cavernous urethra. This tube is continuous with the tip of the phallus, called the glans penis, which has retained a small opening from the primitive urogenital sinus. The fold of the skin below the glans penis begins to grow towards the tip, eventually covering the glans penis and is called the prepuce.
Explain the formation of the female genitalia
The genital tubercle has limited elongation and becomes the glans clitoris. The genital folds become the labia minora. The genital swellings become the labia majora. The opening of the urogenital sinus persists and leads to the opening of the vagina and the urethra.
HYPOMERE / LATERAL PLATE MESODERM
Attached to the intermediate mesoderm is the lateral plate mesoderm and gives rise to the ________, ________, and the __________ (except muscles).
This mesoderm delaminates, forming two layers; the _________ mesoderm and a __________ mesoderm.
The somatic mesoderm underlies the ectoderm and both layers for the __________.
The splanchnic overlies the endoderm and both layers form the ____________.
Between the somatopleure and the splanchnopleure is a cavity called the ___________ that extends from the future neck region to the posterior of the body.
As the coelom of the left and right sides of the body meet and fuse, folds of tissue extending from the somatic mesoderm divide the coelom onto separate cavities.
In mammals, the body coelom is divided into ______, _______, and ______.
Circulatory system, lining of the body cavities and the mesodermal components of limbs
somatic mesoderm and ventral splanchnic mesoderm
somatopleure
splanchnopleure
Body coelom
pleural, pericardial and peritoneal
