Lecture 4 Flashcards
Embryonic Folding
1) Cephalocaudal Folding - cephalic (head) and caudal (tail) regions have rapid differential growth in
relation to yolk sac casing head and tail regions to fold onto themselves
- creates future head and buttocks regions
2) Transverse Folding (lateral) - left and right sides curve and migrate eventually forming a cylindrical
embryo (pinch off yolk sac)
- creates cylindrical torso of embryo
- endoderm - internal germ layer, mesoderm - germ layer, ectoderm - exterior germ layer
NEURULATION
process of nervous system formation from ectoderm
Neurulation starts with signals sent out by NOTOCHORD:
Notochord – extends down the midline from the mesoderm
- short rod of condensed mesoderm cells right underneath PS, induces (process of induction) cells of
the ectoderm to form a hollow nervous system tube - neurulation - releases bone hormones and other hormones that act on cells in the ectoderm which stimulates the
area of the ectoderm above the notochord to become the CNS - during third week ectoderm forms thickened layer called NEURAL PLATE (cells proliferate and
become columnar and taller) - by the end of the third week lateral edges elevate to form NEURAL GROOVE
- the folds neural groove folds approach each other gradually in the middle and fuse to form the
NEURAL TUBE - eventually the NEURAL TUBE runs the length of the embryo
note: Spinabifida is the failure of the tube to close, skin doesn’t grow over the neural tube and it is
exposed to the environment
Mesoderm subdivides into:
- notochord - basis for central body axis and axial skeleton, induction of neural tube
- paraxial mesoderm - one both sides of neural tube forms SOMITES, block-like masses responsible
for formation of most bone, muscle, cartilage, dermis and connective tissues - intermediate mesoderm - forms most of urinary and reproductive systems
- lateral plate mesoderm - cardiovascular system, lining of body cavities and all connective tissue
components of limbs - head mesenchyme - connective tissue and musculature of face
Endoderm
- inner-most tissue after embryonic folding
- forms lining of digestive, respiratory and urinary tracts, thyroid gland, parathyroid gland, thymus, liver,
gallbladder and pancreas
Connective Tissues
Tissues that connect or form structures
Most diverse, abundant, widely distributed and microscopically variable
All derived from mesoderm
Examples: bone, cartilage, blood, connective tissue proper – ligament, tendon, fibrous tissue, loose
connective tissue, dense connective tissue, fat
Functions of Connective Tissue
Physical protection – bones of cranium, sternum, vertebral column, thoracic cavity, fat
surrounding organs
- Support and structural framework of the body – bones provide framework and support soft tissues; cartilage supports body structures such as trachea, bronchi, nose and ears; sheets of
connective tissue form capsules to support such organs as spleen and kidneys
• Transporting fluid and dissolved materials – blood carries nutrients, gases, hormones, wastes and blood cells between different regions of the body
• Connecting other tissues – ligaments bind bone to bone; tendons bind muscle to bone; dense irregular tissue (fascia) binds skin to underlying muscle and bone
• Storing energy – fat is major energy reserve in the body, bones are a large reservoir for calcium
and phosphorus
• Immune protection – much connective tissue contains white blood cells (leukocytes) which
protect the body against disease and mount an immune response against foreign material; the viscous nature of the extracellular matrix interferes with the movement and spread of disease causing organisms
Elements of Connective Tissues
Cells spaced far apart (unlike epithelium)
• Lots of extracellular matrix (ECM) between cells
§ Matrix is the collective term for the extracellular component of any connective
tissue that is made of protein fibers and the ground substance
§ ECM is secreted from cells of connective tissue by proteins in fibrous tissues
called fibroblasts
TERMINOLOGY -
______cyte – a generic cell type (eg. osteocyte in bone, adipocyte in fat)
-_______blast – produces something,lays down some foundation (eg. osteoblast is a cell
that lays down (makes) bone matrix, fibroblasts in connective tissue proper)
-______clast – reabsorbs/breaks down something (eg. osteoclast breaks down bone)
§ ECM composed of:
o Ground substances – sugary water and protein and carbohydrate
molecules (gelatin-like), proteins help to keep water in
o Fibers:
§ COLLAGEN – for tensile strength and stretch resistant
§ ELASTIC –which are flexible and resistant
§ RETICULAR – which form an interwoven network
Classification of Connective Tissues: based on type of extracellular matrix:
Connective tissue proper - has a matrix of fibers (loose and dense) in a syrupy ground
substance (kind of like “jello” with fruit in it
• Different types have different numbers of cell types and different relative proportions of
fibers and ground substance (examples include: adipose (fat), ligaments, tendons)
• Fluid connective tissue - has a matrix of watery liquid than contains dissolved proteins
(examples are: blood and lymph)
• Supporting connective tissue - has a matrix consisting of a gel (densely packed fibers),
cartilage or a solid (matrix is calcified of mineral deposits of predominantly calcium), bone
Connective Tissue Proper
Types with Loose fibers: Areolar tissue, Adipose tissue, Reticular tissue
• Types with Dense fibers: Dense regular, Dense irregular, Elastic
Different Types of Connective Tissue Proper contain various types of _____ and _______ cell
Different Types of Connective Tissue Proper contain various types of FIXED and WANDERING cell
Fixed Cells:
Fibroblasts – produce connective tissue fibers
Fibrocytes – maintain connective tissue fibers and matrix
Fixed macrophages – phagocytize pathogens and damaged cells
Adipocytes – store lipid
reserves
Mesenchymal cells – connective tissue stem cells that can differentiate into other cell types
Melanocytes – synthesize melanin
Wandering Cells:
Free Macrophages – mobile/travelling phagocytic cells (derived from monocytes of the blood)
Mast Cells – stimulate local inflammation
Lymphocytes – participate in immune response – can develop into plasmocytes which produce
antibodies (proteins involved in defending the body against disease)
Neutrophils and Eosinophils (white blood cells) – small phagocytic blood cells that mobilize
during infection or tissue injury
Loose Connective Tissue
Areolar Tissue
• Location - deep to the dermis, covered by epithelial lining, between muscles, around
blood vessels, nerves and around joints
• Function - connects skin to muscle, cushions organs, provides support but with 4
movement
• Matrix – abundant collagen fibers, thin irregularly arranged elastic fibers, small fibroblast
cells, adipocyte (fat) cells and abundant gel-like ground substance
Adipose Tissue
• Location – hypodermis, buttocks, breasts, around eyes, surrounds organs
• Function – provides padding and cushions shocks, insulates and stores energy
• Matrix – predominantly adipocytes, inside each cell is drop of fat surrounded by plasma
membrane, pushed nucleus and organelles to the side, absence of fibers, little ground
substance
Reticular Tissue
• Location - liver, spleen, kidney, lymph nodes, tonsils, appendix, bone marrow
• Function - supporting framework
• Matrix – predominantly reticular fibers and fibrocytes
