Session 3: Connective and Supporting Tissues Flashcards by Nevan Senaratne

Which organelle is responsible for packaging pro collagen into secretory vesicles which can undergo exocytosis?

Golgi apparatus

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Connective tissue is derived from which stem cell line?

Mesenchymal stem cells

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What is the most abundant protein in the body?

Type 1 Collagen

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Which layer contains most elastic fibres in the walls of blood vessels?

Tunica media

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What are the general properties of connective/supporting tissues?

Tissues that provide general…
- Strength = structural proteins like collagens
- Space filling/volume = glycoproteins + complex carbohydrates
- Elasticity = elastin fibrils

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What are the constituent elements of connective tissue?

Cells: fibroblasts, mast cells, macrophages
Extracellular matrix (ECM): ground substance [hyaluronate & proteoglycan aggregates], fibrillar proteins [collagen fibres, elastin, fibronectin, fibrillin]

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What types of cells can be found in connective tissue?

Fibroblasts, mast cells, macrophages

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From where are the ECM components derived?

The fibroblasts - production of rich ECM of connective tissues. Produce and secrete all the components of the ECM, including the structural proteins, adhesive proteins, and space-filling ground substance composed of glycosaminoglycans and proteoglycans.

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What is the structure of ground substance in the ECM of connective tissues?

Composition: large molecules called glycosaminoglycans (GAGs) which link together to form even larger molecules called proteoglycans.
- Proteoglycan core with covalently-bound glycosaminoglycan (GAG) bristles. These bind to hyaluronate (HA) molecules to form = hyaluronate proteoglycan aggregates.

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Why is ground substance highly hydrated?

Ground substance is highly polar - therefore it attracts water to it (90% of ECM is water)

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What are some properties of ground substance that make it useful in cartilage?

Gel-like, inflexible and resistant to compression

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What type of stem cell is embryonic mesenchymal cells?

Multi potent

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What does mesenchyme persist as in adults?

Stromal stem cells

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What makes up connective tissue ‘proper’?

Loose (areolar) connective tissue
Dense connective tissue (irregular or regular)

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Which organelle produces pre-pro collagen alpha-chains?

The rough endoplasmic reticulum (RER)

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What process in the RER stabilises and strengthens collagen cross-links ?

Vitamin C-dependent hydroxylation of prolyl and lysyl residues - this stabilises and strengthens collagen cross-links

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What is the structure of procollagen?

A triple helix structure

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How wide and long (approximately) is each type 1 collagen subunit?

Each collagen subunit is ~300nm long and ~1.5nm wide

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What do collagen fibrils assemble into (which are visible under light microscopy)?

Fibrils assemble into fibres (which are visible under light microscopy). These in turn can assemble into ‘larger fibre bundles’.

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How much do Type 1 collagen fibres constitute out of all collagen?

Type 1 collagen makes up 90% of all collagen

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Give some examples of disorders of collagen synthesis

Ehlers-Danlos syndrome (ED): failure of collagen biosynthesis
Scurvy (lack of vit. C)
Osteogenesis Imperfecta (IO): loss of function of COL1A1 (collagen 1A gene)

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What is the structure of elastic fibres?

Elastic fibres are made up of an elastin protein core and a fibrillin microfibril scaffold

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What property do elastic fibres provide to arteries?

Elastic fibres allow for recoil

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What structural property do elastic fibres have that allow them to provide elasticity?

The random coils and cross-links in their structure allow for distension and recoil of fibres

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Give some examples of disorders of elastic fibres

- **Marfan syndrome**: autosomal dominant disorder due to ** mutation in fibrillin-1** - **Williams syndrome**: spontaneous deletion of region of chromosome 7

What is the importance of the tunica media in the aorta?

The tunica media is a thick region with many elastic lamellae between layers of smooth muscle. When the heart contracts during ventricular contraction - blood is injected into these arteries and the elastic fibres (walls) stretch to accommodate blood flow. Between heart contractions (during ventricular relaxation) - the elastic walls recoil to maintain blood pressure and continue to move the blood even when the ventricles are relaxed.

What colour are different components stained in the tunica media of the aorta in TRICHROME staining?

- Elastic fibre lamellae: deep purple - (Connective tissue) Collagen and ECM: turquoise - Smooth muscle: red

Give an example of somewhere you can find loose connective tissue in the human body?

The **lamina propria** between the **crypts of Lieberkuhn** consists of loose connective tissue. The submucosa of the colon consists of these loose connective tissues.

What structural quality does the bundles of collagen in the dermis possess that allow for protection/strength and prevention against shearing of the skin?

The bundles of collagen are densely packed but orientated in multiple planes - the skin can thus resist forces in multiple directions to prevent shearing.

What structure in muscle tendons produce the mechanical force from muscles to tendons?

Myotendinous junction

Give an example of a structure in the human body which contains both loose and dense connective tissue

The dermis of the skin has layers of loose and dense irregular connective tissue - Papillary dermis: loose irregular connective tissue - Reticular dermis: dense irregular connective tissue (deepest layer)

What are the function of fibroblasts?

Fibroblasts secrete all ECM components in most regions

____ elastic fibres can be found in the papillary dermis and ____ elastic fibres can be found in the reticular dermis.

**Fine** elastic fibres can be found in the papillary dermis and **thick** elastic fibres can be found in the reticular dermis.

What type of collagen do reticular fibres (reticulin) contain in the lymph nodes?

Reticular fibres (reticulin) consist of type III collagen.

Give an example of where you can find dense REGULAR connective tissue in the human body?

Tendons.

Give some examples of specialised connective tissues in the human body

- Adipose tissue (white and brown) - Lymphatic tissue (haemopoietic tissue) - Cartilage and bone

Why do brown adipose tissue cells contain many mitochondria? How might this be important?

There is **abundant mitochondria in brown adipose tissue cells** due to a **high respiratory capacity for the generation of heat (non-shivering thermogenesis)** which is further promoted by the uncoupling of oxidative phosphorylation. Non-shivering thermogenesis is important for babies and hibernating animals.

What is the typical appearance of white adipose tissue in a typical H&E stain?

Cells look empty and stretched as the chemicals used in tissue preparation have dissolved away the lipid: 'signet ring' appearance.

What is the typical appearance of brown adipose tissue in a H&E stain?

Brown fat cells (multilocular adipose cells) each contain MANY lipid droplets as well as a central nucleus. Brown adipose tissue cells appear 'brown' due to the rich vascular supply & abundant mitochondria.

List two histological differences between brown and white fat

White fat: peripheral nucleus, larger size, UNILOCULAR fat Brown fat: more central nucleus, smaller size, MULTILOCULAR fat Brown is darker in appearance due to MORE mitochondria and a greater blood supply.

In subcutaneous adipose tissue, why do adipocytes have a 'signet ring' appearance?

Cells accumulate lipid and push the nuclei to the periphery

Which type of collagen: anchor forming collagen that attaches basal lamina to underlying reticular lamina

Type VII (7)

Which type of collagen: sheet forming collagen found in the basal lamina

Type IV (4)

Which type of collagen: forms fibrils but NOT fibres to give cartilage a glassy appearance

Type II (2)

Which type of collagen: forms fibrils and branching fibres - but does NOT assemble into bundles. Forms a network that supports, for example - immune cells

Type III (3)

Which type of collagen: The most common type of collagen in the body. Forms fibrils, fibres and bundles

Type I (1)

Identify the four different types of connective tissue shown in the photo micrograph below...

A: Dense irregular B: Adipose C: Loose irregular D: Dense regular

Identify the following features (B, C and A) in the image of connective tissue below

B: Collagen bundle C: Fibroblast cytoplasm A: Fibroblast nucleus

What is the name of the fibre in loose connective tissue that allows for distensibility?

Elastic

What is the main structural fibre providing STRENGTH in loose connective tissue?

Bundle-forming collagen (type I)

What is the name of the fibre that creates a mesh to support immune cells in loose connective tissue?

Reticular collagen fibre (type III)

What is the most unique features of the following connective tissue: - Adipose - Mesenchyme - Cornea of the eye - Bone

- Adipose: Energy storage - Mesenchyme: Pluripotent stem cells - Cornea of the eye: Translucency - Bone: Calcium storage

In which of the following tissues can excess fat accumulation occur in obese states?

- Heart - Pancreas - Liver - All of the above All answers are correct

Identify the type of connective tissue in this image. Choose one answer: A: Dense irregular B: Cartilage C: Adipose D: Loose irregular

A: Dense irregular

What type of connective tissue is found in the reticular dermis (organ capsules)?

Dense irregular

Which type of collagen are reticular fibres comprised?

Type III

What type of connective tissue is found in the tendons, ligaments?

Dense regular

Identify the features (A, B, C) in this section of a lymph node treated with a silver stain

A: Capsule B: Trabecula of connective tissue dividing organ into lobes C: Reticular fibre

What type of connective tissue is found in the submucosa of the colon?

Loose irregular

Identify the following features labelled (A, B, C) in the tunica media of an elastic artery stained with Masson's trichrome presented in this image

A - An elastic lamina (stained dark purple) B - Smooth muscle (stained pink) C - Connective tissue e.g., collagen (stained turquoise)

Identify the white/brown adipose tissue in the images below. How do you distinguish these two forms of adipose tissue from each other?

Brown adipose: - Right panel - Features = central nuclei, smaller cells with multilocular fat droplets White adipose: - Left panel - Features = characteristic peripheral (signet ring) nuclei, large cells with unilocular appearance and stretched cell membranes

Identify the arrowed structure in the following image of adipose tissue

Blood vessel

Why is brown fat particularly important to neonates?

Uncoupling of oxidative phosphorylation allows for rapid heat generation - this is important in non-shivering thermogenesis

Where are brown fat depots located in adults? Give the most appropriate answer...

A) Kidneys B) Mediastinum C) Adrenal glands D) Aorta E) Depots are associated with all of these tissues E) Brown fat depots are associated with ALL of these tissues

Identify the following labelled features (A, B, C, D, E) in the following image of a myotendinous junction

A) Collagen B) Fibroblast nucleus C) Interdigitating myotendinous junction D) Skeletal muscle fibre E) Skeletal muscle nucleus

How could you increase adult brown fat depots?

Move to a colder climate (thermogenesis role)

Of which type of connective tissue are tendons composed?

Dense regular

What type of cell will effect the repair of a tendon?

Fibroblast

What name is given to a tough flattened tendon with a wide area of attachment?

Aponeurosis Examples include: the epicranial aponeurosis, the anterior abdominal aponeurosis

Tendons have LITTLE capacity to stretch.

True

Structure of ground substance

- Toilet-brush structure - Proteoglycan core 'brush' - Covalently-bound glycosaminoglycan (GAG) 'bristles' - Bound to hyaluronate (HA) molecules to form hyaluronate proteoglycan aggregates