1-50 Connective tissues

Question 1

Connective tissues (histology)

Answer 1

• supportive framework for all other tissue types in the body
• found in every organ system, keeps epithelium “in line”
• derived from the mesodermal layer during development
• 4 types:
  
  • loose
  • dense
  • reticular
  • adipose tissue
  • specialized: cartilage, bone, blood
• FXN: structural support, medium for exchange, fat storage, defense protection, healing and remodeling
• Cell types: fibroblasts, macrophages, adipocytes, pericytes, mast cells, WBCs

Defining features:

1. cells separated from one another and surrounded by an ECM that is produced by the cells
2. serving fxnl roles of support, medium, fat storage, defsense, healing, remodeling

Question 2

Answer 2

Fibroblasts/myofibroblasts

structural support

healing/remodeling

make collagen

Question 3

Answer 3

macrophages

structural support

healing/remodeling

Question 4

Answer 4

adipocytes

fat storage

Question 5

Answer 5

pericytes

structural support

Question 6

Answer 6

mast cells

defense, relases cytokines

healing/remodeling

Question 7

connective tissue skin cross section

Answer 7

Question 8

dense irregular connective tissue

Answer 8

• densely packed fibers with waven collagen fibers in a amtrix with some elastic
• ex. reticular dermis
• impact resistant against multidirectional forces

Question 9

dense regular connective tissue

Answer 9

• densely packed fivers with parallel collagen fibers
• ex tendon
• resistant to tension forces

Question 10

loose connective tissue

Answer 10

• many different cell types with fewer fibers
• high fat content (ex: superficial fascia under the skin)
• “packing material” throught the body
• High amount of ground substance (looks like empty space under microscope)
• ex: colonic submucosa

Question 11

H&E stain

Answer 11

pink: acidic
purple: basic

Question 12

Extracellular matrix

Answer 12

• The extracellular matrix provides both structural and biochemical/nutritional support for the other tissues of the body
• Made of fibers (collagen and elastin) and ground substance (glycosaminoglycans)
• FIBERS: Collagen and elastin form the structural framework of the ECM and provide both resistability (collagen) and elasticity (elastin)

Lots of types of collagen (I-IX) but about 90% is Type I and forms the skin, bones, cartilage, ligaments, tendons, etc

• Ground Substance: Made up of glycosaminoglycans like hyaluronan and other glycoproteins that helps with structure. Also hydrates the tissue and is involved in cell migration and cell sensing/reaction to the microenvironment

Question 13

Elastic fibers

Answer 13

• made of elastin and microfibrils
• provide elasticity to tissues
• difficult to see with H&E
• random coiling of elastin molecules provides the elasticity, they can b stretched and will return to the original size and shape
• elastin is an amorphous protein secreted from fibroblasts and is crosslinked extracellularly and assembled as a scaffold of microfibrils to form elastic fibers
• fibrillin is part of microfibrils and is required for assemly of elastin into elastic fibers
  
  • without fibrillin, elastin assembles into sheets rather than fibers
• ex: aorta

Question 14

Reticular Connective Tissue

Answer 14

• supportive tissues found as branched, interconnecting meshwork in the loose connective tissue stroma of lymphatic tissues
  
  • except thymus
• reticular fibers: fine collagen type 3, stain positive with silver

Question 15

Collagen

Answer 15

• most common fibrous protein in the ECM, resists forces, most abundant protein in humans
  
  • glycine and proline with sugar groups
  • acidophilic: stains pink in H&E stains
  • Vitamin C is required for proper formation of collagen fibers, cross linked, tensile strength
  • collagen released from fibroblasts as procollagen and final processing occurs outside the cell

Question 16

Ground substance

Answer 16

• gel-like suspends the ECM
• rich in glycosaminoglycans (GAGs), whose negative charges bind water
• prodices mechanical support, hydrates tissue, binds GAGs to cell membranes and to growth factors to play dynamic roles in regulating cell migration/sensing

Major groups of ground substance molecules

1. GAGs: repeating unvranched disaccharides with negative charges
   
   • hyaluronan, gel like
2. Proteoglycans: have GAGs attached to linear core protein like bristles radiating from a test tube brush
3. Multiadhesive glycoproteins: small prtoeins variety of confibuations have binding sites for most compoenents of connective tissues and basal cell membranes of epithelia, help stabilize the connective tissues