Embryology- GI/Pelvis/Perineum Flashcards
What is the original structure that forms the GI tract?
Yolk sac
What do the umbilical arteries become in adults?
Medial umbilical ligaments
What does the urachus become in adults?
Median umbilical ligament
What is the urachus?
Fetal structure that drains urine from fetus to the amnionic sac
- It is the distal portion of allantois that forms later on, remains as median umbilical fold in adults
What does the umbilical vein become in adults?
Falciform ligament and round ligament of the liver (left UV)
What is the allantois?
- Vestigal structure in humans, serves as waste storage until bladder forms
- In birds and lower reptiles, it serves as a respiratory/ waste storage structure
Can cause pathologies in humans if it stays open
What is Meckel’s diverticulum?
- Remnant of vitelline duct in some people, presents as outpouching of intestine
can be connected with fibrous cord to umbilicus (from small intestine)
What does the vitelline vein become in adults?
Portal vein
What do the vitelline arteries become in adults? What areas do they supply?
- Celiac trunk (supplies foregut)
- Superior mesenteric artery (supplies midgut)
- Inferior mesenteric artery (supplies hindgut)
What structures are in the umbilical cord?
- Umbilical arteries
- Umbilical veins
- Vitelline arteries
- Vitelline veins
- Vitelline duct
- Allantois/urachus
- STEM CELLS
What are caval veins (specific to GI)?
Veins that take waste products from intestines to Inferior Vena Cava
What is the stomodeum?
(Primitive) oral cavity
- Ectoderm lined with endoderm
What is the proctodeum?
Tubes within the cloaca that later form:
- Anus
- Vagina (when female)
- Urethra
How does the GI tract rotate?
Note: starts around 50 days
- Intestines herniate into umbilical cord (maybe because there is more space there)
- Intestines loops 180 degrees (or so) around the superior mesenteric artery
- As it grows, the arteries stretch also
- Parietal peritoneum stretches over duct and arteries as they change in conformation to become the viseral peritoneum
- As organs stretch into peritoneum, mesentaries form, which do not separate during intestinal looping - Final positioning is ascending, transverse, and descending colon surrounding small intestine
- Intestines then fall back in to abdomen once folded
What is a retroperitoneal organ?
- Immovable and fixed organ, does not have a mesentary
What is an intraperitoneal organ?
- Movable organ, has a mesentary
What structures are in the foregut?
- Esophagus
- Stomach
- Liver
- Gallbladder
- Pancreas
- Spleen
- First half of duodenum (and part of second half per Dr. Solunias)
Supplied by Celiac trunk
What structures are in the midgut?
- Last 1/4-1/2 of duodenum
- Jejunum and Ileum
- Caecum
- Appendix
- Ascending colon
- Proximal 2/3 transverse colon
Supplied by Superior mesenteric artery
What structures are in the hindgut?
- Distal transverse colon (left 1/3)
- Descending colon
- Sigmoid colon
- Rectum
Supplied by inferior mesenteric artery
How do the liver and its blood supply form?
- Liver cells differentiate and migrate underneath heart (part of yolk sac/gut)
- Vitelline vein runs through early heart and liver
- Liver also forms complex network of veins, anastomoses between umbilical veins and vitelline veins
What is the early gallblader-liver connection?
The liver and gall bladder forms a fibrous matrix of the septum transversum and endodermal diverticula from gut
- Veins invade within
How does the pancreas form?
- Dorsal pancreas forms across from gallbladder on gut
- Ventral pancreas forms on opposite side next to gallbladder
- Ventral pancreas then flips and rotates to same side as dorsal pancreas
- Ventral and dorsal pancreases then join together, still retain two separate ducts (that connect at one point)
Accessory pancreatic duct is on original dorsal pancreas
Pancreatic duct is on original ventral pancreas
What GI structures are outside peritoneal cavity?
- Pharynx
- Esophagus
- Rectum
When is the sex of the fetus determined?
At the moment of fertilization
What does the genital tubercle become in adults?
Generally becomes erectile tissues
- Raphé of penis (line), glans of the penis in males
- forms the vaginal opening in females
Where is the urogenital fold?
In the middle of the genital tubercle
- Forms first in an undifferentiated stage of development
Becomes:
- Raphé of penis (line), glans of the penis in males
- forms the vaginal opening in females
What structure is homologous to the scrotal sacs in males?
Labia majora in females
- Both structures are derived from labiosacral swellings
What structures are derivatives of the mesonephric embryonic duct?
- Vas deferens
- Epididymis
- Seminal vesicles
Mesonephric duct dissolves in females due to hormonal signals
What structures are derivatives of the paramesonephric embryonic duct?
- Oviduct
- Uterus
- Upper part of the vagina
- In males, appendix of the testes is the major remnant
What structure in males is homologous to the uterus in females?
Prostatic utricle
Urogenital triangle borders
- Right and left Ischial tuberosities (of the pelvis) are on respective sides
- Transverse perineal muscles are superior border
- Penis/Clitoris and vagina are within this area
What are the two erectile tissues?
- Corpora cavernosa- consists of fibrous collagen
- Corpus spongiosum- thinner than corpora cavernosa
Within fibrous matrix is arterial supply that allows for erection
Where is the corpora cavernosa located?
- Right and left sides of shaft of penis in males (there is no opening)
- On sides of clitoris in females
Where is corpus spongiosum located?
- Bulbus penis
- Glans penis (head)
-As it is, it is not in females, later differentiates to bulb of the vestibule
Note: runs midline along penis, surrounds urethra
What is inside the corpus cavernosum?
- Helicine arteries
- Smooth muscles
- Collagen
How does an erection occur?
- Brain sends messages allowing arteries in penis dilate to twice the diameter, blood enters (blood flow increases 16 fold)
- Blood stays inside because of TUNICA ALBUGINEA (around corpora cavernosa)
- The tunica albuginea is multiple layers of tough fibrous material, during erection these fibers slide past each other
- As a result, venous return pinched off and slows down
- Relaxation in the brain causes tension in TA to break down, and the layers relax and move back
How is semen altered before ejaculation?
- Testes bring small volume of semen with lots of sperm to seminal vesicles
- Fluid produced in seminal vesicles dilutes semen
- Goes to prostate from seminal vesicle, where it is diluted further with fluid produced in prostate
- Semen travels out through the urethra during ejaculation
- *No liquid is produced in penis itself
What are the parts of the urethra and which part is the weakest?
- Prostatic urethra (through prostate)
- Membranous urethra (in between prostatic urethra and penile urethra; THE WEAKEST)
- Penile urethra
Where is the bulbospongiosus muscle located in males and females?
- Located on bulb of penus (corpus spongiosum) in males
- Becomes a sphincter around the vagina in females (around vestibular bulb)
What is the function of the bulbospongiosus muscle in males?
- Spastic movement to aid in ejaculation
- Tightens to help maintain erection
What is the homologous female structure to the corpus spongiosum in males?
Bulbs of the vestibule/Vestibular bulbs
- Per Dr. Solunias, this is up for debate
What membrane supports the genital structures in males and females?
Perineal membrane
What is the difference between metanephros and mesonephros?
Metanephros is the adult kidney
Mesonephros is the embryonic kidney
The prostate is derivative of what structures?
Bladder/allantois, cloaca
What are the differences between female and male pelvises?
In general,
- females have a wider sciatic notch; in males it is narrower
- females have a broad pubic area between the pubic bones (u-shaped); in males it is narrower (v shaped)
What are the borders of the anal triangle?
Anterior: superficial transverse perineal m.m.
Posterior: triangle tip is at coccyx
Lateral borders are from ischial tuberosity to coccyx
Note there is lots of fat in the anal triangle
What nervous system controls an erection? Ejaculation?
Generally
Parasympathetic system controls erection
Sympathetic system controls ejaculation
What tissue is the foreskin of the penis derived from? What is a possible function?
Derivative of abdominal wall tissue
Possibly contains cells that cleanse the glans of the penis
Which two areas in the body consist of ectoderm lined with endoderm?
Oral cavity and the rectum
Which anal sphincter muscles are controlled by autonomic vs. voluntary nervous system ?
External anal sphincter m.m. is under voluntary control
Internal anal sphincter m.m. is under autonomic control
What is the function of levator ani muscles? What are the muscle names?
To hold anus in pelvic area
- pubococcygeus
- puborectalis
- iliococcygeus
What is the epoöphoron?
Remnant of the epididymis precursor, found in females
What does the upper gubernaculum become in adults ?
Ovarian ligament in females (connects ovary and uterus) , entire gubernaculum becomes scrotal ligament in males
What does the lower gubernaculum become in adults
Round ligament of the uterus (connects anal canal with labia Majora) in females
In males, entire gubernaculum becomes scrotal ligament
What is the main blood supply in the perineal area?
Mostly Branches off the common iliac artery, named in relation to where they supply blood
- i.e. Lateral sacral artery, middle rectal artery, internal pudendal artery, vaginal artery, uterine artery,
What is the main nerve supply for the genital/ perineal area?
Sacral plexus nerves, main nerve is the pudendal nerve to the genitalia/perineum
- inferior rectal n., perineal n.n. (Deep and superficial), posterior scrotal n. n., dorsal nerve of the penis are branches of the pudendal n.
Pudendal n. Does NOT supply internal anal sphincter
Which structure is immediately internal to the pubic symphisis?
Bladder
