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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
Disorders of Elastic Fibres: Williams Syndrome
Results from the spontaneous deletion of a region of chromosome 7 (which includes ELN-elastin) Is associated with learning and cardiovascular problems
26
Elastic Fibres and Ageing: Intrinsic vs Extrinsic
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
Tunica Intima
Thin layer of connective tissue Superficial
28
Tunica Media
Thick region Many elastic lamellae between layers of smooth muscle
29
Tunica Media of the Aorta
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
Areolar (loose) Connective Tissue: Structure
- Branching elastic fibres - Collagen fibres (non-branching) - Reticular fibres - Ground Substance - Small blood vessels - Fibroblasts - Mast cells (immune system) + Macrophages - Mesenchymal cells - Adipocyte
31
Dermis of the Skin
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
Connective Tissues of Glands
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
Reticular Fibres in a Lymph Node
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
Connective Tissue of Tendon
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
Myotendinous Junctions
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
Short Ligament (bone to bone)
Collagen bundles are densely packed in parallel arrangement But they undulate and are arranged in fascicles, separated by loose connective tissue
37
White Adipose Tissue
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
Brown Adipose Tissue
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
Hyaline Cartilage: Structure
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
Hyaline Cartilage: Function
Support and reinforcement Cushioning Resistant to compression
41
Hyaline Cartilage: Locations
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
Decalcified Bone: Structure
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
Decalcified Bone: Function
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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