Mm Histology 2 Connective Tissue

Front 1

Matrix

Back 1

Connective tissue cells are surrounded by an extracellular matrix full of proteins and carbohydrate mixes

Ex. GAGs, proteoglycans, collagens/ elastin (fibers), fibronectin/ laminin (adhesion molecules)

Influences cell survival, development,

shape, and function

Secreted by cells within it

Front 2

Collagens

Back 2

Most abundant protein in animals

Long, stiff, triple-stranded helix (ropelike)

3 peptide α chains, rich in proline (stabilizes helix) and glycine (smallest amino acid, permits tight winding of the helix)

42 distinct α chains encoded by separate genes (thousands of molecules possible, but only ~40 collagens have been found)

Front 3

Types of collagen

types 1, 2, 3, and 4

Back 3

Type I – bONE
Type II – carTWOlage

Type III - Lymph (reticular)
Type IV – FOUR on the FLOOR (basement membrane)

Front 4

Synthesis of collagen

Back 4

Collagen α- chains (3) form collagen molecules, molecules aggregate to form fibrils, and fibrils form fibers

Collagens are synthesized => ER assembly into triple helix=>N- and C-terminal telopeptides which prevent cross linking of the 3 chains=>secretion with procollagen peptidases=> propeptides (also called telopeptides) are removed=>lysyl oxidase crosslinks hydroxylysine making fibrils and fibers outside of the cell.

Front 5

Post-translational modifications of Collagens

Back 5

Post-translational hydroxylation of proline and lysine allows inter-chain H-bonds

One of the enzymes that cause linkages is Lysyl Oxidase, which acts extracellularly to cross-link collagen triple helices.

Hydroxylation events need Vitamin C

Hydroxylysine and hydroxyproline are postranslationally modified amino acids that are common in collagens.

Cross-links occur between certain hydroxylysines and lysines in short non-helical segments at the ends of collagen molecules.

Scurvy results from vitamin C deficiency (causes general weakness, anemia, gum disease, and skin hemorrhages)

Front 6

Ehrlers Danlos

Back 6

Problems with propeptide collagenase (called ADAMTS2) and hence do not generate mature collagen fibrillar formation.

Front 7

Messenchym

Back 7

Meshwork of undifferentiated connective tissue cells

Mostly mesodermal

Give rise to connective tissues, blood, lymphatics, bone, and cartilage

Contact inhibited, so they come together after tissue damage to seal up cuts

Hyaluronic acid is the dominant GAG

Front 8

-blast cells vs -cyte cells

Back 8

-blast cells : make stuff

-cyte cells : fully matured cell, no longer making stuff

-blast refers to the committed, not terminally differentiated precursor cell in a given lineage of cells. -cyte refers to the terminally differentiated cell.

(ex.)

skeletal muscle differentiation - myoblasts fuse together to form multinucleated myocytes that become the individual fibers of the muscles.

epidermis - During wound healing, melanoblasts migrate out under epidermis where they differentiate into the melanocytes that give our skin color.

Front 9

Fibroblasts

Back 9

a cell in connective tissue that produces collagen and other fibers

Most common cells of connective tissue in animals

Euchromatic nuclei and a lot ER

Plays a critical role in wound healing

Front 10

Fibrocytes

Back 10

An inactive mesenchymal cell

not synthesizing / secreting proteins

small amount of cytoplasm and rough ER

fibroblasts embedded in collagen fibers

Front 11

Chondroblasts

Back 11

A cell of growing cartilage tissue

They lie in the space or lacunae present in groups of two or more

Euchromatic nuclei and a lot ER

Front 12

Chondrocytes

Back 12

a cell that has secreted the matrix of cartilage and become embedded in it

Front 13

Osteoblasts

Back 13

a cell that actively synthesizes and secretes the matrix for bone formation

Euchromatic nuclei and a lot ER

Found on the surface of the bone

Front 14

Osteocytes

Back 14

a bone cell, formed when an osteoblast becomes embedded in the matrix it has secreted

Front 15

Osteoclast

Back 15

a large multinucleate bone cell that absorbs bone tissue during growth and healing

Derived from monocytes

Front 16

3 types of Loose Connective Tissue

Back 16

Lots of ECM matrix

Resist compression

Adipose - fat cells (white & brown)

Reticular - filters (spleen, lymph nodes)

Areolar - breasts, skin, gut, trachea

Front 17

3 types of dense connective tissues

Back 17

Lots of fibers

Fibrous - tendons/ligaments (regular), skin (irregular)

Elastic - aorta/arteries

Cartilege/Bone - next lecture

Dense connective tissue isn’t dense with cells but rather has a lot of ECM. Loose connective tissue (blood, lymph, fat) actually is much more cellular.

Front 18

Loose Connective Tissue Chart:

Functions, distribution, tissue types

Back 18

Front 19

Brown fat

Back 19

a dark-colored adipose tissue

On chest, sternum, and vertebral column of newborns

Involved in heat production in hibernating animals and human babies

Uncoupled oxidative phosphorylation

In contrast to white adipocytes (fat cells), which contain a single lipid droplet, brown adipocytes contain numerous smaller droplets and a much higher number of (iron-containing) mitochondria, which make it brown.

Many blood vessels

initiated by sensory afferent nerves in the skin which sense temperature (cold temperature stimulates sympathetic output) Sympathetic neurons stimulate beta oxidation of fatty acids in the brown fat tissue.

Rather than generate ATP, there is a mechanism in brown fat to bypass or short circuit ATPase synthetase. This results in a huge O2 utilization to dispose of the electrons.

Front 20

White Fat

Back 20

used to store energy and acts as thermal insulator that help maintain body temperature.

Its cells have receptors for insulin, growth hormones, norepinephrine and glucocorticoids.

One large fat droplet

Front 21

Adipocytes

Back 21

have a single lipid droplet and a thin surrounding cytoplasmic rim

The droplet consists of a core of neutral lipids (triglycerides or cholesterol esters)

Outer layer is a monolayer of amphipathic molecules (phospholipids, cholesterol and proteins)

The surrounding layer contains enzymes and other proteins needed for lipolysis

Front 22

White fat regulation

Back 22

Lipolysis upregulators: epinephrine, norepinephrine, natriuretic peptide.

Downregulator (fat storage): insulin

ob/ob mice lack leptin (anorexic factor produced by adipose tissue) and overeat.

Db/db mice make normal leptin but have mutant receptor and overeat.

Front 23

Reticular connective tissue

Back 23

a type that is present in lymphoid organs (nodes, spleen etc).

Filled with thin collagen III fibers and associated cells.

Front 24

Elastic Fibers

Marfan syndrome

Back 24

Elastic fibers are made of elastin and fibrillin proteins; are irregularly arranged, distensible, and recoils;

in artery walls Marfan syndrome is due to a mutation in fibrillin-1, leading to elongated face, fingers, etc.

Also affects the heart and vasculature and so has life threatening risks involving heart problems and aortic aneurysm/dissection.

The lens of the eye dislocates and aorta is floppy and does not provide rebound (diastolic BP will be low). Marfan’s patients die of aortic rupture.

Front 25

Wharton’s jelly

Back 25

Mucus jelly surrounding umbilical cord.