The Structure & Function of Loose and Dense Connective Tissue

Question 1

What is connective tissue?

Answer 1

a diverse and abundant supporting tissue

Question 2

what is the function of connective tissue?

Answer 2

• structural support for body and organs
• tensile strength
• binding tissues together
• immune defence
• metabolism and energy storage (fat cells)
• cushioning
• elasticity

Question 3

give examples of specialised connective tissue

Answer 3

bone, cartilage, blood, adipose, dentine and lymph

Question 4

List the structural and functional characteristics of connective tissue that distinguish it from other basic tissue types (epithelial tissue)

Answer 4

• In connective tissue the cells are separate and not packed like in epithelial tissue
• Connective tissue has vast amounts of extracellular matrix whereas epithelial tissue has very little.
• Connective tissue lies below the basement membrane (lamina propria) whereas epithelial tissue lies above the basement membrane.
• Cells of connective tissue are bound by blood capillaries (to gain nutrients) whereas cells of epithelial tissue are not (gain nutrients via diffusion from the cells below them)

Question 5

what are the 3 fundamental components of all connective tissue?

Answer 5

cells
extracellular matrix - fibres and ground substances

Question 6

what are the 3 fibres in connective tissue?

Answer 6

Collagen
Elastin
Reticular

Question 7

what are ground substances and name the 3 in connective tissue?

Answer 7

• viscous clear substance that occupies the space between the fibres and the cells of connective tissue.
• acts as a barrier for penetration by foreign bodies.
• composed of:
  glycoproteins
  proteoglycans
  glycosaminoglycans (GAG)

Question 8

what are fibroblasts?

Answer 8

‘blast’- means making
fibroblasts- make fibres
- have an elongated cigar shaped nucleus
- deposits all the extracellular matrix components (all fibres and ground substance)
- they secrete the precursors of GAG’s, collagen and elastin.
- its cytoplasm expands during synthesis of extracellular fibres and rER and golgi become more apparent.
- they maintain the continuous slow turnover of ECM components.

Question 9

what is a fibrocyte?

Answer 9

the inactive state of a fibroblast, once it has deposited all ground substances and fibres

Question 10

what is a plasma cell?

Answer 10

clock face nucleus, produces antibodies

Question 11

what is an adipocyte?

Answer 11

Fat globule in centre (usually washed away during slide preparation)
Rim of cytoplasm is seen with the nucleus pushed to one end.
They store energy as fat

Question 12

what is a macrophage?

Answer 12

phagocytic in function. The cells have ingested particles in their cytoplasm

Question 13

what are eosinophils, neutrophils and lymphocytes?

Answer 13

eosinophils- 2 lobe nuclei, eosinophilic granules
neutrophils- multilobed nuclei, phagocytic functions
Lymphocyte- round nuclei with small cytoplasm white blood cells used in the immune response

Question 14

what are mast cells?

Answer 14

contain many basophilic granules which store histamine and proteoglycans. These are released during allergic/inflammatory reactions.

Question 15

what cells are wandering and which ones are fixed?

Answer 15

Fibroblast, fibrocyte, adipocyte and macrophage are fixed cells (or resident cells) in connective tissue
Plasma cells, Eosinophils, Neutrophils, lymphocyte, mast cells these are wandering cells which kills pathogens.

Question 16

how do connective tissues carry out defence mechanism?

Answer 16

1. Monocytes secrete cytokines to attract lots of other immune cells.
2. Mast cells produce histamines making blood vessels leaky allowing white blood cells to enter the vessels easily.
3. Macrophages are fixed cells already present in the connective tissue. They begin engulfing pathogens.
4. Plasma cells, Eosinophils, Neutrophils, lymphocyte cells are extrinsic. They arrive via blood vessels and kill pathogens.

Question 17

what are the cells of connective tissue?

Answer 17

Question 18

what are collagen fibres?

Answer 18

Main and most abundant fibre type in the human body. It is secreted by fibroblasts into the ECM in the form of tropocollagen (monomer), which then polymerises to form collagen

Question 19

what are the properties of collagen fibres?

Answer 19

High tensile strength (however if you stretch them over 3% of original length they will break)
Thick bundled fibres
Do not branch
Flexible
Acidophilic (pink-stained)

Question 20

what are the 4 types of collagen fibres?

Answer 20

Type 1: dermis (skin) ligaments, tendons and bones
Type 2: cartilage
Type 3: make up reticular fibres (see below)
Type 4: forms mesh-like structures important in - basal laminar

Question 21

what are reticular fibres?

Answer 21

Crosslink to form a meshwork which is responsible for supporting the liver, spleen, bone marrow and lymph nodes.
Made up of Type 3 collagen fibres
Thin
Able to absorb metallic silver so are stained black

Question 22

what are elastic fibres?

Answer 22

Fibroblasts secrete tropoelastin (precursor form) which undergoes polymerisation in the extracellular tissues. Microfibrils of the structural glycoprotein fibrillin then become incorporated in an around to form elastin fibres

Question 23

what are the properties of elastic fibres?

Answer 23

Allows stretching and recoil to original shape e.g, cartilage of the ear
Thin fibres
Branched
Arranged in fibres or in discontinuous sheets in ECM
Loss of elastic fibres in the dermis of skin leads to wrinkling
Found: in the skin, lungs, arteries, veins

Question 24

what is the structure of the components of ground substances?

Answer 24

• Each long unbranched GAG has many proteoglycans bound to it (via a link protein)
• Proteoglycans are made up of a core protein with GAGs attached (This makes the sidechains charged)
• Their charged sides chains are hydrophilic thus attracting water (trapping it within the matrix - makes the ground substance feel slippery) and ions, particularly sodium which makes up the extracellular fluid.
• In loose connective tissue the main GAG backbone is hyaluronic acid.
• In cartilage the GAG bound to the proteoglycan is chondroitin sulfate
• In the dermis of the skin the GAG bound to the proteoglycan is dermatan sulfate.

Question 25

how does tissue fluid and ground substances interact?

Answer 25

Tissue fluid is associated with ground substance allowing passage of molecules and exchange of metabolites

Question 26

what are the 2 types of basic connective tissue?

Answer 26

loose dense

Question 27

what is loose connective tissue?

Answer 27

plenty of ground substance with loose fibres (type 1 and 3 collagen and elastin) and scattered cells.

Question 28

where is loose connective tissue found?

Answer 28

Found within the lamina propria (under the basement membrane of epithelia) Found surrounding blood vessels

Question 29

explain lamina propria as an example of loose connective tissue

Answer 29

immediately underlying certain epithelia very thin CT layer Ground substance + loosely arranged fibres Allows blood vessels to serve epithelial tissues above Ad: Good for diffusion Dis: Good breeding ground for microbes Usually has immune cells

Question 30

what is the function of loose connective tissues?

Answer 30

- Attaches epithelia to underlying tissue - Forms passages for blood vessels nerves and lymphatics. - Macrophages, mast cells, lymphocytes and plasma cells act as mobile ‘residents’ in loose connective tissues, and other white blood cells can be rapidly recruited from local blood vessels when required.

Question 31

what is dense connective tissue?

Answer 31

Less ground substance and fibroblasts and plenty of closely packed collagen fibres (dense)

Question 32

what are the 2 types of dense connective tissue?

Answer 32

dense regular dense irregular

Question 33

what is dense regular connective tissue?

Answer 33

Type 1 Collagen fibres run in one direction. Dispersed fibroblast cells. Found in tendons (help anchorage) and ligaments (help in connecting). Resists tensile forces in one axis.

Question 34

what is dense irregular connective tissue?

Answer 34

Collagen fibres run transversely and longitudinally so you can see line and dots because of cut fibres. Found in the dermis of skin or capsule of joints. Resists tensile forces from all directions. This means the skin is resistant to tearing is all directions and in the capsule of joints it stops dislocation due to incoming force from all directions.

Question 35

what type of connective tissue is adipose tissue

Answer 35

loose connective tissue

Question 36

what are the 2 types of adipose tissue?

Answer 36

white brown

Question 37

what is adipose white tissue?

Answer 37

Contains adipocytes which store lipids in a single vesicle (unilocular fat cell). Their nuclei are peripherally located. It forms the subcutaneous tissue White adipose tissue is an important energy store and acts as thermal insulator under the skin. It also acts as a shock absorber in areas, such as around the kidneys. It is a pale staining as it contains mainly lipid The cytoplasm is a thin rim around the periphery, containing mostly mitochondria.

Question 38

what is adipose brown tissue?

Answer 38

Contains adipocytes which store lipids in multiple vesicles (multilocular) Nuclei are centrally located. Responsible for generating heat 🡪 It is key in body temperature regulation. Brown adipose tissue is found in new-born mammals and some hibernating animals. Only a small amount is found in human adults. Brown colour due to lots of mitochondria and capillaries

Question 39

what are genetic mutations connective tissue?

Answer 39

Type I collagen: osteogenesis imperfecta - Brittle bones/ malformation Type II collagen: Chondrodysplasia - Cartilage defects, joint abnormalities Type I, III or V collagen: Ehlers Danlos syndrome Fibrillin: Marfan’s syndrome

Question 40

what is lipomas?

Answer 40

lump under the skin due to swelling of adipocyte cells. It is simply a benign non-malignant harmless swelling

Question 41

what is an edema?

Answer 41

Excess accumulation of fluid within the tissue spaces Pitting edema- leaves a pit when pressed down Causes of edema: CV disease (edema of extremities), Renal disorders (puffiness of face) Hyperthyroidism (generalised edema)

Question 42

what is Marfans syndrome?

Answer 42

Results from mutation in fibrillin gene. Therefore, the tissue is less resistant to stretch as it has less functional elastic fibres Risk of aortic aneurysms as the aorta walls are weak and stretch easily. affects tissues rich in elastic fibres

Question 43

what is Ehler’s-Danlos syndrome?

Answer 43

A congenital abnormality resulting in abnormal production of collagen. Symptoms: effects collagen containing connective tissue Joints may be hypermobile Hyper elasticity of the of skin Bones are more prone to fracture Fragile blood vessels etc. Life span depends on the subtype of collagen fibres that are affected. Type 4 collagen fibres have the worse prognosis as they can lead to aortic rupture => death extra elastic skin