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Tissues of the Body > Lecture 3.1: Connective Tissues > Flashcards

Lecture 3.1: Connective Tissues Flashcards

1
Q

What are connective tissues?

A

They are tissues that provide structure, support, strength and space filling

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2
Q

Connective Tissue Components (4)

A

1) Cells
2) Extracellular Matrix (ECM)
3) Ground Substance
4) Fibrillar proteins: Collagen Fibres, Elastin, Fibronectin, Fibrillin

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3
Q

Ground Substance Properties

A

Highly Hydrated
Inflexible
Highly polar, hence attract water (90% of ECM is water)
Resistant to compression (useful in cartilage)

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4
Q

Ground Substance Structure

A

Comprised of highly-glycosylated proteins called Proteoglycans

Attached to a high molecular weight hyaluronic acid (HA) backbone.

HA and the sugar chains of proteoglycans are long, unbranched polysaccharides called glycosaminoglycans (GAGs).

Together, these form hyaluronate proteoglycan aggregates.

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5
Q

Where does connective tissue come from?

A

Cells of the middle embryonic germ layer (mesoderm), proliferate and
migrate to form mesenchyme in the early embryo

Mesenchyme gives rise to the various connective tissues, as well as serous
membranes, the vascular and urogenital systems and muscle

Mesenchyme persists in adults as stromal stem cells.

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6
Q

Mesenchymal Tissue in Developing Foetus’

A

Mesenchymal cells are morphologically similar BUT will give rise to cells that differentiate into a variety of different cell types

Mesenchymal cells persist in the adult and facilitate healing and renewal

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7
Q

Connective Tissue Classification

A

1) Embryonic connective tissue
2) Connective tissue proper
3) Specialised connective tissue

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8
Q

Embryonic Connective Tissue (2)

A

Mesenchyme (mesoderm of early embryo)

Mucous connective tissue (foetal umbilical cord)

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9
Q

Connective Tissue Proper (2)

A

Areolar (loose) Connective Tissue

Dense connective tissue (‘irregular’ or ‘regular’)

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10
Q

Types of Specialised Connective Tissue (4)

A

Adipose Tissue

Blood (haemopoietic) and Lymphatic Tissue

Cartilage (type II collagen)

Bone (type I collagen)

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11
Q

Collagen

A

Collagen is the most abundant human protein, making up ~30% of our whole-body protein content (90% of this is type I)

Collagens forms fibrils and fibres, sheets (e.g. Type IV) or anchors.

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12
Q

Collagen Synthesis

A

RER: Synthesis of pre-procollagen α-chains, Vitamin C-dependent hydroxylation of prolyl and lysyl residues – stabilises and strengthens collagen cross-links, Assembly of triple helix to form procollagen

Golgi: Packing into secretory vesicles

Cell membrane: Constitutive exocytosis

Extracellular environment: Non-helical terminal peptides cleaved, Collagen molecules assemble into fibrils

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13
Q

Type I Collagen Assembly

A

Each fibril is composed of staggered collagen molecules with a periodic banding

Fibrils assemble into fibres (visible under light microscopy), and fibres can assemble into larger bundles

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14
Q

Types of Collagen

A

Type I
Type II
Type III
Type IV
Type VII

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15
Q

Type I Collagen

A

90% of all collagen
Fibrils aggregate into fibres and fibre bundles
Found in tendons, capsules of organs and dermis
Organic component of bone

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16
Q

Type II Collagen

A

Fibrils do not form fibres
Instead forming a very fine mesh
Present in hyaline and elastic cartilage

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17
Q

Type III Collagen

A

Fibrils form branching fibres (not bundles)

Found around muscle and nerve cells, within lymphatic tissues and organs, where they are called reticulin.

Also found in skin (particularly papillary dermis)

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18
Q

Type IV Collagen

A

Unique (sheet) form present in basal lamina of basement membrane

19
Q

Type VII Collagen

A

Anchors basal lamina to underlying reticular lamina

20
Q

Disorders of Collagen Synthesis: Ehlers-Danlos

A

Can result in failures in various stages of collagen biosynthesis

In type IV ED (vascular type)

A failure in type III collagen production can lead to aortic rupture

21
Q

Disorders of Collagen Synthesis: Scurvy

A

A lack of vitamin C reduces prolyl hydroxylase activity

This leads to gum ulceration and haemorrhage

22
Q

Disorders of Collagen Synthesis: Osteogenesis imperfecta

A

Aka brittle bone disease

In type I OI, loss of function of COL1A1 (collagen 1A gene) can result in
spontaneous bone fractures

23
Q

What are elastic fibres? Where are they found? What is their purpose?

A

They are composites of elastin deposited on a fibrillin microfibril scaffold

Varying amounts of elastic fibres are found in most connective tissues

The random coils and cross-links allow tissues to distend and return to their original shape

24
Q

Disorders of Elastic Fibres: Marfan Syndrome

A

An autosomal dominant disorder resulting from a mutation in fibrillin-1

Symptoms:
- Abnormally tall
- Exhibit arachnodactyly
- Frequent joint dislocation
- Can be at risk of catastrophic aortic rupture

25
Q

Disorders of Elastic Fibres: Williams Syndrome

A

Results from the spontaneous deletion of a region of chromosome 7 (which includes ELN-elastin)

Is associated with learning and cardiovascular problems

26
Q

Elastic Fibres and Ageing: Intrinsic vs Extrinsic

A

Fine wrinkles of intrinsic ageing result from the gradual fragmentation of the elastic fibre network

Coarse wrinkles of extrinsic (photoageing) results from elastic fibre hyperplasia and accumulation of amorphous elastic material (solar elastosis)

27
Q

Tunica Intima

A

Thin layer of connective tissue

Superficial

28
Q

Tunica Media

A

Thick region

Many elastic lamellae between layers of smooth muscle

29
Q

Tunica Media of the Aorta

A

Smooth muscle cells produce the elastin, collagen and matrix (rather than fibroblasts)

Elastic lamellae are stained deep purple with trichrome stains

Collagen and extracellular matrix is stained turquoise

Smooth muscle is stained red

30
Q

Areolar (loose) Connective Tissue: Structure

A
  • Branching elastic fibres
  • Collagen fibres (non-branching)
  • Reticular fibres
  • Ground Substance
  • Small blood vessels
  • Fibroblasts
  • Mast cells (immune system) + Macrophages
  • Mesenchymal cells
  • Adipocyte
31
Q

Dermis of the Skin

A

Contains layers of loose (papillary dermis) and dense (reticular dermis) irregular connective tissue

In reticular dermis the bundles of collagen are densely packed but orientated in multiple planes

The skin can thus resist forces in multiple directions to prevent shearing

32
Q

Connective Tissues of Glands

A

Connective tissue encapsulates glands and divides them into lobules

A capsule of connective tissue (which can be loose or dense) surrounds the gland

Trabeculae of connective tissue divide the gland into lobules

33
Q

Reticular Fibres in a Lymph Node

A

Consist of type III collagen

Lymphocytes are densely packed in the spaces between the fibres

Reticular fibres form an irregular anastomosing (connective, branching) network throughout the node

34
Q

Connective Tissue of Tendon

A

Dense-regular connective tissue

Type I collagen bundles in tendons lie in a parallel, densely-packed formation in line with the tensile force exerted by the muscle on bone

Rows of elongated flattened fibroblasts lie between the collagen bundles

35
Q

Myotendinous Junctions

A

Mechanical force is transmitted from muscle to tendons at myotendinous junctions

Tendinous collagen fibres associate directly with complex infoldings of the sarcoalemma at myotendinous junctions

Epimysium (the connective tissue surrounding muscle fibre bundles [fascicles]), is also continuous with the collagen of tendons

36
Q

Short Ligament (bone to bone)

A

Collagen bundles are densely packed in parallel arrangement

But they undulate and are arranged in fascicles, separated by loose connective tissue

37
Q

White Adipose Tissue

A

Most adipose tissue in the body is white fat

In typical H&E-stains, white adipose cells look empty and stretched as the
chemicals used in preparation dissolve away the lipid

Fat is better preserved in cryosections

Adipose tissue is a fuel reserve (triglyceride), but also has a role in thermal insulation and in shock absorption

38
Q

Brown Adipose Tissue

A

Brown fat cells (multilocular adipose cells) each contain many lipid droplets and a central nucleus

Found close to the scapula, sternum and axillae, especially in newborns, Non-shivering thermogenesis’ is important for babies

Also appear to be present in the upper chest and neck of adults

Brown colour is due to the rich vascular supply and abundant mitochondria, thus high respiratory capacity for heat production

39
Q

Hyaline Cartilage: Structure

A

Perichondrium (dense irregular connective tissue composed mainly of type I collagen containing chondroblasts)- at top

Matrix (type II collagen fibres embedded in ground substance)

Chondrocytes in lacunae (unfilled space)

40
Q

Hyaline Cartilage: Function

A

Support and reinforcement

Cushioning

Resistant to compression

41
Q

Hyaline Cartilage: Locations

A

Comprises most of the embryonic
skeleton

Articular surfaces of joints

Covers ends of long bones

Costal cartilages of ribs

Cartilage of nose, trachea and larynx

42
Q

Decalcified Bone: Structure

A

Haversian canals (surround blood vessels and nerve fibres throughout the bone)

Osteocytes in lacunae

Lamellae

Hard, calcified matrix with many type I collagen fibres

Well vascularised

43
Q

Decalcified Bone: Function

A

Support and protection

Levers for muscle to act on

Site of haematopoiesis

Storage of calcium and other minerals.

Tissues of the Body (18 decks)

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