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What are the bony landmarks of the thorax and relationship to boundaries of thoracic cavity
- Bony: spine, ribs, sternum, costal arch, thoracic inlet
- cavity: epaxials? Diaphragm separates, some abd organs found within ribs
draw a basic vertebra, label anatomic feature and function
- body, spinous process, transverse process, cranial articular process (superior), caudal articular process (just behind), laminar arch (leading up to spinous from articular), pedicle arch (leading down to body from articular)
where are the epaxials in relation to the bony thorax?
Radiography and tissue characteristics, white vs black
- imaging that uses electromagnetic radiation (X-rays) to produce 2D images
- Differential absorption of xrays
- black is lucent, less opaque. White is opaque
Computed Tomography and tissue characteristic, white vs black
- imaging that uses a computer to process information about the amount of Xrays travelling through an object. Produces tomorgraphic (cross-sectional) images
- Linear attenuation of X-rays (density)
- more black is low attenuating, hypoattenuating, hypodense. Similar is isodense, isoattenuating. More white is high attenuating, hyperattenuating, hyperdense
Fluoroscopy and tissue characteristics
- imaging that uses Xrays, produces real-time 2D image like a video recording
- differential absorption of Xrays
Ultrasonography and tissue characteristic, white vs black
- cross-sectional imaging technique using high-frequency sounds to produce images
- acoustic impedence.
- black is anechoic, hypoechoic, similar is isoechoic, white is hyperechoic
Nuclear Medicine (Scintigraphy) and tissue characteristic, white vs black
imaging technique--adminiter radionuclides (radioisotopes) attached to drugs, travel to specific organs. Emit energy (gamma rays) that can be assembled into 2D image
Radioisiotope activity (uptake)
Magnetic Resonance Imaging and tissue characteristic, white vs black
- cross-sectional imaging technique using strong magnetic fields and radio waves to form images (proton behavior).
- T1, T2, PD (are different characteristics describing how protons act in a strong magnetic field after removal of a radio frequency pulse).
- black = low signal, hypointense. Same = isointense, white = high signal, hyperintense
imaging that shows morphology like size, shape, margin, etc. MOst of imaging is structural
producing images that depict physiologic actiities like blood flow, peristalsis, joint motion
producing images that depict the expression and activity of speciic molecules or biological processes
visible abnormality in imaging. Visiible clue about underlying problem
Five perceivable degrees of opacity
air, fat, soft tissue/fluid, bone, metal
contrast agents in radiography
- something given to increase contrast. can be postive (barium, iodine) or negative (air), or double (both)
- Naturally occurring diseases can similarly change tissue opacity
differential absorption/differential attenuation
- different tissues absorb or transmit different amounts of x-rays
- lower energy rays, higher atomic number, higher density or thickness cause more x-ray absorption, more white.
summation shadows (+ or -)
different parts of the patient in different planes are superimposed, result is addition of ALL the absorptions (summation). Can be positive (gets whiter) or negative (gets darker)
silhouette effect in radiography
when borders cannot be seen and only the outline is visible. Aka border effacement
when borders cannot be seen and only the outline is visible. aka silhouette effect
Magnification in radiography
- Farther from the detector (table/plate) magnifies an object
- this changes size of object, not like distortion
distortion in radiography
misrepresents shape or placement of object due to unequal magnification
depth perception in radiography
- there is none
- Sometimes cross-sectional imaging is used to get 3D concepts from a 2D image
- each pixel in the scan represents a voxel in the slice
slices, voxels vs scans, pixels
- 3D vs 2D
- pieces of the object vs pieces of the image
window level vs window width
- level is midpoint of the grey scale in imaging, optimizes based on tissue type
- width is number of grey shades, optimizes contrast
- use many of both to see all structures
How to name a radiographic projection/position
- point of entrance to point of exit of the beam
- conventionally a "left thoracic" etc is left side down, labeled by the side farthest from beam
plica vena cava
loose fold of pleura surrounding caudal vena cava (from right caudal mediastinum)
mediastinal and pulmonary pleura fold over the hilus of the left lung
position of diaphragm, bony attachments and things that pass through, natural openings.
Dorsal diaphragm is divided into left and right crus, both attach to ventral L3 and L4, ribs 8-13 and the xyphoid process. Ventral called cupula, which is the part that bulges into thorax. aortic hiatus is dorsal between crura, has aorta, azygous, and thoracic duct. Esophageal hiatus is central in right crus, has esophagus, vessels, and vagal trunks. Caval foramen is right side, caudal vena cava
Define epaxial muscles, name muscles in the group
dorsal to the transverse processes of thoracic vertebrae. Extend vertebral column and bear weight. Longissimus, iliocostalis, transersospinalis
Define extrinsic forelimb muscles, name muscles in the group
- one attachment on axial skeleton to other attachment on boneof forelimb (scapula or humerus). Move limb in relation to body or body in relation to limb
- Latissimus dorsi, superficial and deep pectorals
Define muscles of respiration, name muscles in the group
Expiration: external abdominal obliques (caudoventral, 5th and 6th ribs to linea alba), internal intercostals (caudoventral), serratus dorsalis caudalis (originates by aponeurosis from thoracolumbar fascia, runs cranioventral to insert on caudal border of the last three ribs, draws caudally during expiration, serratus ventralis (transverse cervical precesses of vertebrae and from lateral ventral first 7-8 ribs, attaches dorsomedial 1/3 of scapula), rectus abdominus Inspiratory: scalenus (transverse process cervical vertebrae and caudally to ribs, caudoventral to pull ribs open), diaphragm (ribs 8-13, lumber 3 and 4), serratus dorsalis cranialis (aponeurosis of thoracolumbar fascia, cranioventral to craniolateral ribs), external intercostals (cranioventral)
Draw in superificial and deep pectoral, latissimus dorsi, scalenus and intercostal.
draw the muscular layers and boundaries that would be encountered during a surgical approach to the thoracic body wall at the fourth left intercostal space
Skin (epidermis, dermis), subcutaneous fascia (includes fat), cutaneous trunci, latissimus dorsi, serratus ventralis (depending) external intercostals, external intercostals, endothoracic fascia, parietal pleura
muscle with serated edge that helps form a sling around the body. Cranial and caudal portions
lobation of right and left lung
- left: a cranial lobe divided into cranial and caudal portions, and a caudal lobe
- right: cranial, middle, caudal and accessory lobes. Also had cardiac notch at forth and fifth intercostal between cranial and caudal
Attachments of the superficial pectoral, deep pectoral, latissimus dorsi, serratus ventralis, and (generally) epaxials
- superficial pectoral: 2 parts, transverse (deep caudal) is first 2-3 sternebrae to humerus, cranial (superficial) is first sternebra to humerus
- deep pectoral: sternum to humerus, aponeurosis to humerus
- latissimus dorsi: "digging" transverse processes of lumbar vertebrae and thoracolumbar fascia to humerus.
- serratus ventralis: transverse process of cervical vertebrae and lateral first 7-8 ribs to dorsomedial scapula
- epaxials: group of muscles in transverse processes of spinal cord, dorsal arches of ribs to vertebral spinous processes.
Demonstrate proximal attachments of external abdominal oblique, rectus abdominus, transversus abdominus
- external abdominal oblique: last 6-7 ribs to linea alba
- rectus abdominus: aponeurosis to the first few ribs and sternum to pelvic brim (prepubic tendon)
- transverse abdominus: medial surface of last few ribs and transverse processes of lumbar vertebrae, then aponeurosis of linea alba.
define and explain landmark relevance of thoracolumbar fascia
sheet of collagen connective tissue, attaches tissue and stores fat. From thoracic and lumbar regions of vertebrae. Aponeurosis of latissimus dorsi.
define and explain landmark relevance of axilla
Underarm. Just under thoracic limb, attachments of muscles
define and explain landmark relevance of brachial plexus
Bundle of nerves and vessels leading to thoracic limbs
define and explain landmark relevance of thoracolumbar fascia
sheet of connective tissue creating a broad sheet of connection. Also of lateral abdominal body wall muscles that meet at linea alba. Most common route to abdominal cavity
define and explain landmark relevance of costal arch
End of the thorax, where the costal cartilages of the ribs come together. Marker for radiographs, learning approximate locations of liver/diaphragm
define and explain landmark relevance of sympathetic trunk
Runs just ventral and to each side of the spine
explain on a skeleton: dorsal, ventral, crainal, caudal, axial, abaxial
axial is proximal to long axis, abaxial is distal to long axis (such as the center of the leg)
compare and contrast serous membranes associated with thoracic body wall and lungs iwth those associated with heart and mediastinum
pericardium is just one pouch, and is inside the mediastinum with organ/vessels. The pleura is continuous with endothoracic fascia and there are 2
on transverse and longitudinal sections through the thorax, diagram all serous membranes of the thoracic cavity, including those found within the mediastinum
visceral pleura, costal parietal pleura, diaphramatic pleura, mediastinal parietal pleura, fibrous pericardium, cardiac parietal pleura, cardiac visceral pleura
Explain significance of serous cavities of the thoracic cavity in Hugo Young
Serous cavities should contain nothing but a small amount of fluid. In Hugo's case the delicacy of the visceral pleura caused the car impact to tear it and damage the alveoli of the lung, allowing air to escape into the pleural cavity and press on the lung, keeping it from inflating fully.
Define mediastinum and explain relationship to serous cavities of the thorax. Explain relative position of cranial vena cava, caudal vena cava, azygous vein, phrenic nerves, esophagus, heart, trachea, aorta, and relationship to each other
Mediastinum is the meeting place of the two pleura of the lungs, at the center line of the thoracic cavity. It encompasses the heart between the two sacs. The vena cavae exit the heart between it. The azygous vein enters the vena cava just before it enters the heart, near the spine, and enters the mediastinum around the same spot. The nerves are in the pleural space by the lung, the esophagus, aorta and trachea are all inside it.
use appropriate nomenclature to define Pericardium and explain why it is useful to you as a future veterinarian
serous membrane that wraps around the heart, attached to the parietal mediastinal pleura. Creates a sac around the heart that could fill with fluid or be an impediment to surgery or prevent unwanted things like bacteria that have gotten into the thorax from getting into the heart
on cadaver, ID pulmonary ligament, plica vena cavae, hilus. Give anatomical definition and one reason to understand as a vet
- Pulmonary ligament is wrapped around left lung hilus.
- Plica vena cava is a fold of pleura wrapped around the vena cava
- hilus is indented entrance of lung (or kidney)
- Know what you'll encounter in surgery, possibly visible on sensitive imaging
Given an isolated lung, explain how to orient cranial/caudal, dorsal/ventral, medial/lateral and how you know right from left. demonstrate lobes of left and right. Position as if in body
- Left has 2 lobes, right has four. Hilus is medial. Accessory wraps around caudal vena cava.
- Left: Cranial lobe has two parts, cranial cranial and cranial caudal. Caudal lobe.
- Right: cranial, middle, caudal, accessory
Which blood constituents are evaluated on a CBC (hemogram)?
- numbers and measurements of CELLS (EDTA)
- RBC, Platelets, WBC
Which blood constituents are evaluated on a chemistry panel? Broad categories
- non-cellular constituents, plasma or serum, (heparin or red-top).
- salts, metabolites, protein, hormones, wastes
list two main functions of blood, with examples
- Transportation: (O2, CO2, nutrients = glucose, amino acids, hormones = insulin, metabolic waste = ammonia, urea, creatinine)
- Immunity: flushing of wound, WBC
- Maintenance of overall fluid level in body
- Regulation of body temperature
describe the difference between plasma and serum
- Plasma is from blood that has not clotted, clotting factors intact (fibrinogen etc)
- Serum from clotted blood, coag factors are gone
know what albumin and globulins are, give two examples of globulins
- proteins. Albumin is half of plasma protein
- globulins are a collective term for all other plasma proteins. Inc coag proteins (fibrinogen), inflammatory proteins (C-reactive protein), transport proteins (transferrin), etc.
describe the main functions of RBC
- Transport O2 and CO2
- transport waste and nutrients
Explain the difference in appearance of neutrophils, eosinophils and basophils
- neutrophils: granules barely stain so whiteish, dark lobulated nucleus
- eosinophils: granules stain pink
- basophils: granules stain blue/purple
know what circulating and marginating neutrophil pools are and why they are important
- sampling blood gets whichever neutrophils are out in the blood = circulating.
- Some sit against the endothelium and just hang out, get mobilized as needed. These are marginating. Steriods and epinephrine cause mobilization
4) Foreign Material
5) Tissue necrosis
- neutrophils: bacteria, some fungi
- eosinophils, basophils: parasites, some bacteria
- macrophages: tissue necrosis, foreign material, fungus, some bacteria
Terms for increased/decreased numbers of:
RBC, neturophils, eosinophils, basophils, monocytes, lymphocytes, platelets
- RBC: anemia/polycythemia or erythrocytosis
- Neutrophils: neutrophilia, neutropenia
- eosinophils: eosinophila, eosinopenia
- basophils: basophilia, basopenia
- monocytes: monocytosis, monocytopenia
- lymphocytes: lymphocytosis, lymphocytopenia
- platelets:thrombocytosis, thrombocytopenia
Which leukocyte is most common in blood in dog, cat, horse, cow
- Neutrophils most common in horse, dog, cat
- lymphocyte most common in cow
- otherwise monocyte>eosinophil>basophil
which leukocytes are phagocytic?
- macrophages (not dendritic, so monocytes)
- basophils (a little)
what type of lymphocyte produces antibodies?
which leukocyte is a plasma cell derived from?
B cell, so lymphocyte
main two effects of T lymphocytes in immune response
cytotoxic and regulatory
describe platelets. Which bone marrow cell are they derived from?
Small light purple chunks, granules but no real nucleus, vary in size. megakaryocyte
basic function of platelets in blood
Promote blood clotting
production of blood cells. Mostly within bone marrow
Immature RBC, released as needed
When hemoglobin binds to oxygen, found in RBCs from lungs to tissues
when hemoglobin binds to carbon dioxide, found in RBCs from tissues to lungs
One of 3 RBCs with granules: neutrophils, eosinophils, basophils
immature neutrophils, not lobulated nucleus.
increased number of immature neutrophils (bands, possibly metamyelocytes) in blood
innate immune response
broad targets with no memory, most WBC. Attack whatever comes in and looks different
adaptive immune response
very specific targets with memory. Mostly lymphocytes (B and T cells)
humoral immune response
B lymphocytes, mature to plasma cells which produce antibodies
cell-mediated immune response
Type of adaptative immune response, where T lymphcytes use regulatory effects (stimulating or suppressing immune function) or cytotoxic effects (killing tumor cells or virally infected cells)
What does purple top do and how?
- EDTA, anticoagulant for CBC, preserves morphology
- chelates calcium
- No good for electrolytes due to additives
what does green top do and how?
Heparin, anticoagulant, inhibits thrombin. For chemistry and CBCs, good for exotics or small animals
What does blue top do and how?
Sodium citrate, anticoagulant, reversibly chelates calcium, coag panel.
What does red top do and how?
Nothing, no additives. Allows blood to clot naturally, can spin and get serum. Good for chemistry panel.
Blood collection sites
jugular, cephalic, saphenous (lateral or medial)
describe size and appearance of canine erythrocyte. Contrast with horse erythrocyte
- regular, round, pink, with central pallor. Dog's seem larger than horse, no rouleaux formation
- horse smallor, less central pallor, rouleaux
recognize and diagram five different leukocytes in dog blood
What is different about horse eosinophils and basophils?
- Neutrophils: granules almost invisible, dark lobulated nucleus. Kamikaze phagocytosis for bacteria
- eosinophils: pink granules, lobulated nucleus, hypersensitivity and parasites
- basophils: blue granules, purple cytoplasm, hypersensitivity and parasites
- monocytes: few/no granules, vacuoles, huge. Differentiates to macrophage (tissue necrosis, fungus, foreign material, some bacteria) and dendritic cells (antigen-presenting, stimulates adaptive immune)
- lymphocytes: Small, very little blue cytoplasm, huge nucleus
- horse has raspberry eosinophils and very dark purple basophils
Compare and contrast canine leukocyte cytoplasmic granule contents, relate to function
- Neutrophils: microbial killing compounds, good for kamikaze 1st responders, esp for bacteria.
- Eosinophils: parasite killing and hypersensitivity compounds. Can engulf or release into surroundings
- Basophils: parasite-killing and hypersensitivity compounds, like histamine. Recruit eosinophils for defense against parasites
How might tissue appearances be altered by preparation for microscopy?
- freezing destroys details of structures
- dehydrating causes shrinkage, so spaces enlarge. Also removes lipids (fats, steroids, membrane lipids), leaving small spaces
- staining, uneven staining
What are the steps of tissue prep for microscopy? (10)
- 1. fix/preserve (formaldehyde)
- 2. dehydrate (ethanol)
- 3. make translucent (xylene)
- 4. plastic or paraffin
- 5. cooling (paraffin) or crosslinking (plastic)
- 6. cut thin sections (microtome)
- 7. float in water and mount on slide
- 8. stain
- 9. dissolve paraffin (xylene) or plastic (acetone) and re-hydrate (ethanol)
- 10. mounting medium and cover slip
transmission electron microscope
highest resolution, like light microscopy
scanning electron microscope
for surface of cells, not cut, coated. 3-D image
function of plasma membrane
- control entry and exit
- regulate cell-cell interactions
- transduce extracellular signals
- phospholipid bylayer with proteins forming channels, transport and receptors
carbohydrates coating a cell (glycoproteins and glycolipids) that protect and help with communication
water-based viscous cytosol containing organelles, inclusions, cytoskeleton, dissolved stuff
smooth endoplasmic reticulum
network organelle that stores Ca2+, detoxifies drugs and synthesizes lipids (steroids, membrane phospholipids)
- subunits of rRNA and protein, translate mRNA into polypeptides.
- Free in cytoplasm makes cytoplasmic proteins, rough ER make membrane and transported proteins
a group of ribosomes translating an mRNA molecule in cytoplasm
Rough Endoplasmic Reticulum
ER (network organelle) associated with ribosomes
How proteins get from RER to where they're going
transport vesicles move them to golgi apparatus (glycosylation), packaged for insertion into membrane, incorporation into lysosomes
packaging center. Receives vesicles from RER and modifies (glycosylation), packaged for insertion. Makes glycosaminoglycans
endocytosis and pinocytosis
cell eating and cell drinking
vesicles that break down everything
large complexes of enzymes that degrade abnormal proteins in cytoplasm
- sythesize ATP, sythesize steroid hormones
- Can generate heat from brown fat for hibernation by being inefficient at ATP
- macromolecules in suspension in cytosol
- glycogen, lipid, pigments, crystals
- microfilaments: actin; muscle contraction, pseudopod formation and cell division
- intermediate filaments: maintain 3D structure
- microtubules: cilia, centrioles, tracks for transport
brain. Contains nuclear envelope, double membrane continuous with RER, with nuclear pores for protein movemnt. Nucleoli are where actual transcription of RNA happens
heterochromatin and euchromatin
- hetero is wrapped tight, no translation happening
- eu is loosely wrapped, lots of translation
4 basic tissue types and composition
- connective tissue, eipthelium, nervous tissue, muscle tissue
- all composed of cells and extracellular matrix
- tissue with lots of extracellular matrix in relation to number of cells.
- 2 kinds, proper (general) or specialized
- "proper": architectural support, exchange nutrients/waste, defense and protection
- specialized: blood, cartilage and bone
- large clusters of fat cells in connective tissue
- can be brown or white
- ground substance (viscous soln with glycosaminoglycans, proteoglycans and cell adhesive glycoproteins) + fibers (collagen/reticular and elastic)
- surrounds most connective tissue cells
- part of extracellular matrix, resist tensile forces.
- Ligaments and tendons
- need Vit C
long flexible chains of disaccharides that cushion. in ECM
glycosaminoglycans linked to a protein core, shakped like a bottle brush. in ECM
cell adhesive glycoproteins
bind everything together in ECM to stabilize
part of extracellular matrix, provide elasticity (elastin proteins made of fibrillin)
cells of connective tissue
fixed (adiposite, fibroblast) or transient (leukocytes)
fixed cell in connective tissue, most of macromolecular component of extracellular matrix
fat cell, fixed in connective tissue. Can be brown or white
Classification of connective tissue proper
- loose: fewer fibers, support epithelium of digestive and respiratory tract
- dense irregular: dermis, surround and protect organs (kidney, testes)
- Dense regular: fibers in alignment, tendons and ligaments
- reticular: mesh that support soft, cellular tissues like liver, lymph nodes, thymus and spleen
- covers surfaces, forms glands. Polarized
- protect tissue
- regulate/promote movement of fluids/substances
- secrete watery/oily substances
- sense environment
- only extracellular matrix in epithelial tissue
- anchors base layer of cells
one layer of cells. Can be squamous, cuboidal, or columnar
- multiple layers, named by apical layer (outermost)
- can be squamous, cuboidal, columnar
simple epithelium that appears stratified but is just long, irregular cells, all touch basement membrane.
stretchy. In urinary system.
Epithelium directional terms
- apical: top
- basal: basement membrane side
- lateral: sides of each cell
finger-shaped protrusions (can be on the apical part of epithelium with other structures) to increase cell surface area
larger than microvilli, mobile, beat to swim or generate a current. Made of microtubules of cytoskeleton. On apical surface of epithelium
- Barrier. Rings a cell and conncets it to all of its neighbors, prevents anything from passing through.
- most apical junctional complex in epithelium, made at lateral surface.
anchor cell to neighbors with actin filaments. On lateral surface of epithelium, basal to tight junctions and apical surface.
spot welds to anchor cells together, lower than adhering junctions on epithelial lateral surface.
- allow ions and cAMP to pass from epithelial cell to epithelial cell.
- on lateral surface, basal to adhering and tight junctions, near desmosomes.
anchor cell to basement membrane in epithelium
central nervous system
brain and spinal cord
peripheral nervous system
all nerves except brain and spinal cord
- cell body and processes to provide rapid communication, send commands and secrete neurotransmitters
- insulated by myelin
clusters of neuronal cell bodies in connective tissue
- 2 kinds, in CNS and PNS. "helper cells"
- insulate, scavenge waste, store glycogen, phagcytize debris
types of muscle (3)
skeletal, cardiac, smooth
like basement membranes of epithelium in muscles. linked with cytoskeleton of muscle cells, binding cells together
- most voluntary muscle. Striated/striped (parallel alignment).
- Multinucleated, packaged by external lamina and connetive tissue. Connective sheath continues to form tendon and anchor to bone
- striated but single-nucleus. Branched, forming a contractile sheet.
- Inherent rhythmicity.
- involuntary in organs, blood vessels and dermis. Involuntary (hormones, ANS control).
- mesh of contractile so not striated.
- corkscrew nucleus when contracted.
how is embryo segregated from extraembryonic tissue
- Outer layer of Morula (fertilized egg, divided) becomes trophoblast, secretes fluid inside to make blastocoel, cells go to one side to make Inner Cell Mass (ICM)
- inner cell mass sends hypoblast off to form yolk, remaining is called epiblast. This splits, some line amniotic cavity which fills. Remaining epiblast sandwiched between yolk and amniotic cavity
- gastrulation, makes layers (primitive streak). Embryo is all three layers = trilaminar disk.
how was the first body cavity made?
- mesoderm differentiates into notochord, paraxial mesoderm, intermediate mesoderm and lateral mesoderm
- lateral mesoderm splits into splanchnic and somatic mesoderm, with space in between
- embryo and amnion grow, yolk sac doesn't, causing folding. Folds in lateral and cranio-caudal directions at the same time. cranial brings heart from over head into ventrum, caudal brings gut and urinary into ventrum
How was the extraembryonic coelom incorporated into the embryo, forming what?
lateral folding, peritoneal, pericardial, pleural cavities
Trace a molecule of oxygen in the fetus from placenta to left subclavian artery. Compare to adult
- Placenta to umbilical artery(?) to umbilicus, through posterior vena cava into right ventrical through ductus arteriosus to descending aorta, into left subclavian
- An adult would breathe in O2 through the pharynx, trachea, bronchus, bronchi, bronchioles, alveoli, exchange into capillaries to be picked up by hemoglobin, carried through pulmonary vein to left atrium, through tricuspid valve to left ventricle, through semilunar valve into aortic arch, descending aorta to subclavian artery
Diagram transverse view of early embryo at foregut, midgut, showing lateral folding, with all germ layers and including cavities
Distinguish between epithelial and mesenchymal cells
embryonic epithelial tissues fold, mesenchymal cells are connective tissue of embryo. Often change into each other during development
Why do most congenital diaphragmatic hernias occur on left side?
the left hole is larger and closes later. Liver is on the right, so that hole is smaller.
shunt allowing fetus to carry oxygenated blood from placenta directly from right ventricle of fetus into systemic circulatory system (aortic arch)
gastrulation and what it makes
formation of the trilaminar disc (=flat embryo + three germ layers)
- groove in epiblast. Epiblast cells mibrate through into blastocoel, causes gastrulation. This becomes cranial/caudal axis.
- amphibians have a similar "blastopore lip"