Cells of the Immune System

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Questions and Answers

What is the primary role of macrophages in the body?

Formation of elastic fibers

Production of antibodies

Local inflammatory response and tissue repair (correct)

Secretion of glycosaminoglycans

Which type of collagen is most abundant in the human body?

Type II collagen

Type I collagen (correct)

Type III collagen

Type IV collagen

What characteristic distinguishes elastic fibers from other fibers in connective tissue?

Ability to stretch and return to original shape (correct)

High tensile strength

Composition of keratin

Presence of collagen type III

Which of the following is a major component of the ground substance in connective tissue?

Glycosaminoglycans Signup and view all the answers

What is the primary characteristic of reticular fibers?

Stained black by silver salts Signup and view all the answers

Which glycosaminoglycan is involved in the formation of proteoglycans?

Chondroitin sulfate Signup and view all the answers

What is the typical appearance of plasma cells' nuclei?

Eccentrically located with a clock-face appearance Signup and view all the answers

What role do fibroblasts primarily play in connective tissue?

They produce collagen and ground substance. Signup and view all the answers

What is the main function of chondrocytes and chondroblasts in cartilage?

To provide flexibility and support Signup and view all the answers

What structure primarily provides elasticity to elastic cartilage?

Elastic fibers Signup and view all the answers

Which type of collagen is the most abundant in bone tissue?

Collagen Type I Signup and view all the answers

What is the primary role of fibroblasts in the context of fibrocartilage?

To provide cushioning and resistance to deformation Signup and view all the answers

Which component is NOT typically found in the matrix of hyaline cartilage?

Elastic fibers Signup and view all the answers

Which characteristic differentiates cancellous bone from compact bone?

It contains trabeculae and has spaces occupied by bone marrow Signup and view all the answers

During endochondral ossification, what is the initial matrix laid down before bone tissue forms?

Hyaline cartilage Signup and view all the answers

What is the mineralized extracellular matrix in bone primarily composed of?

Calcium hydroxyapatite and collagen Signup and view all the answers

What is the primary function of brown adipose tissue?

Heat production Signup and view all the answers

Which type of cartilage is the most abundant and provides smooth surfaces for joint movement?

Hyaline cartilage Signup and view all the answers

What characteristic is unique to white adipose tissue compared to brown adipose tissue?

Has a single large lipid droplet Signup and view all the answers

Which structure is responsible for absorbing water in cartilage?

Amorphous ground substance Signup and view all the answers

Which type of collagen is predominantly found in cartilage?

Type II collagen Signup and view all the answers

What is a key function of adipose tissue in the body?

Serving as an energy storage depot Signup and view all the answers

What is a unique feature of chondrocytes in cartilage?

They are located inside lacunae Signup and view all the answers

What feature is characteristic of brown adipose tissue cells?

Multiple small lipid droplets Signup and view all the answers

Study Notes

Monocytes and Macrophages

Monocytes and macrophages are the same cells at different stages of maturation.
Macrophage-like cells have different names in different human organs.

Mast Cells

Mast cells are oval or irregular-shaped connective tissue cells.
They are 7-20 µm in diameter.
Cytoplasm is full of basophilic secretory granules.
The nucleus is centrally located.
Mast cells have a role in local inflammatory responses, innate immunity, and tissue repair.

Plasma Cells

Plasma cells originate from B lymphocytes.
Antibody-producing cells.
They are large and ovoid with basophilic cytoplasm due to many ribosomes.
Their nucleus is generally spherical and eccentrically located.
Plasma cells have a 'clock-face' appearance due to the arrangement of their chromatin (DNA).

Collagen

The most abundant protein in the human body.
Collagen fibers are strong and resistant to normal and tearing forces.
There are multiple collagen types:
- Fibrillar collagens: Type I, II, and III.
- Sheet-forming collagens: Type IV.
- Linking/anchoring collagens.

Reticular Fibers

Reticular fibers are mainly composed of collagen type III.
Characteristically stained black by impregnation with silver salts (argyrophilic).
Also stain positive using the periodic acid-Schiff (PAS) method.
Found in the reticular lamina of basement membranes and surrounding adipocytes, smooth muscle, nerve fibers, and small blood vessels.

Elastic Fibers

Elastic fibers form sparse networks interspersed with collagen bundles in many organs.
Possess the physical properties to be stretched or distended and return to their original shape.
Composed of fibrillin microfibrils embedded in a larger mass of cross-linked elastin.

Ground Substance

A highly hydrated, transparent, complex mixture of macromolecules, mainly in three classes:
- Glycosaminoglycans (GAGs)
- Proteoglycans
- Multi-adhesive glycoproteins
Fills the space between cells and fibers in connective tissues.
Viscous and acts as a lubricant and a barrier.

Glycosaminoglycans (GAGs)

Most prominent GAGs found in proteoglycans.
- Dermatan sulfate
- Chondroitin sulfate
- Keratan sulfate
- Heparan sulfate

Interstitial Fluid

Ion composition similar to that of blood plasma.
Contains plasma proteins of low molecular weight that pass through the thin walls of capillaries.

Embryonic Connective Tissue: Mucoid Tissue

Found in the umbilical cord.
A gelatinous tissue with a high percentage of ground substance.
Composed of delicate reticular fibers and fibroblasts.

Adipose Tissue

Located throughout the body and represents 15-20% of body weight.
A storage depot for neutral fats.
Regulators of the body's overall energy metabolism.
Helps thermally insulate the body.
Fills spaces between other tissues and helps cushion and keep some organs in place.

Adipose Tissue Types

Brown Adipose Tissue
- Contains cells with multiple lipid droplets.
- Abundant mitochondria present.
- Appears darker in color.
White Adipose Tissue
- It's a more common type.
- Contains one very large droplet of whitish-yellow fat in the cytoplasm.

White Adipose Tissue

Spherical when isolated, but polyhedral when closely packed.
Very large cell that holds a single huge droplet of lipid that fills almost the entire cell.
Unilocular cells.
Function: Long-term energy storage.

Brown Adipose Tissue

Present in 2–5% of newborn body weight, located mainly in the back, neck, and shoulders.
Scattered areas in adults, like around the kidneys, adrenal glands, aorta, and mediastinum.
Cells are generally smaller than white adipose tissue cells.
Brown fat due to abundant mitochondria.
Multilocular cells due to many small lipid inclusions.
Function: Heat production.

Cartilage

A specialized type of connective tissue.
The extracellular matrix is rich in GAGs and proteoglycans.
Has a firm, gelatinous consistency.
Functions:
- Shock absorber.
- Cushioning and sliding for joints.
- Facilitates bone movement.

Cartilage Components

Chondrocytes: Cartilage cells.
Amorphous ground substance: absorbs water.
Fibers: Type II collagen and elastic fibers.

Cartilage Features

Chondrocytes are housed inside cavities called lacunae.
Contains no blood vessels, lymph vessels, or nerves.
Nutrients are provided by the perichondrium.

Hyaline Cartilage

Most abundant cartilage type.
Grossly: Glistening and pearly white.
Locations:
- Temporary skeleton.
- Costal cartilages.
- Epiphyseal plates of long bones.
- Articular surfaces of movable joints.
- Nose, larynx, trachea, bronchi.
Function:
- Smooth, low-friction surfaces in joints.
- Structural support in the respiratory tract.

Hyaline Cartilage Matrix

Collagen type II (40%).
Water (60–80%).

Hyaline Cartilage Cells

Chondrocytes; Occupy a small amount of hyaline mass.
Appear in groups called isogenous aggregates or groups.

Elastic Cartilage

Grossly: Yellowish color and pliable.
Locations:
- Auricle of the ear.
- External acoustic meatus.
- Eustachian or auditory tube.
- Epiglottis.
- Parts of the larynx.
Function:
- Flexibility and stretchability.

Elastic Cartilage Matrix

Less abundant in the matrix compared to hyaline cartilage.
Contains both collagen and elastic fibers.
Elastic fibers appear darkly stained with Van Gieson stain.

Elastic Cartilage Cells

Comprised of chondrocytes and chondroblasts.

Fibrocartilage

A cross between hyaline cartilage and dense connective tissue.
Locations:
- Intervertebral discs.
- Attachment of certain ligaments.
- Symphysis pubis.
Function:
- Resistance to deformation under stress.
- Cushion between bone surfaces.

Fibrocartilage Matrix

Abundant fibers of collagen type I and II.
No perichondrium present.

Fibrocartilage Cells

Few, single chondrocytes in aligned isogenous groups interspersed with fibroblasts.

Bone Tissue

Hardest connective tissue.
Mineralized extracellular matrix composed primarily of:
- 90% collagen type I and V.
- Matrix
- Inorganic substance (Calcium hydroxyapatite).
Functions:
- Protection and support.
- Movement.
- Mineral storage.
- Hematopoiesis (blood cell formation).

Bone Types

Compact (Cortical/Dense):
- No spaces visible; solid mass.
- Comprises 80% of the bone tissue.
- Not occupied by bone marrow.
Cancellous (Medullary/Spongy):
- Contains numerous interconnecting areas called trabeculae.
- Comprises 20% of the bone tissue.
- Spaces are occupied by bone marrow.

Bone Ossification

The process of bone formation.
Two main types:
- Intramembranous Ossification: Bone cells directly differentiate from mesenchyme and begin to secrete bone substance.
- Endochondral Ossification: A preexisting matrix of hyaline cartilage is initially laid out that will progressively undergo ossification.

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Description

This quiz covers key cells involved in the immune response, including monocytes, macrophages, mast cells, and plasma cells. Understand their functions, characteristics, and importance in immunity and tissue repair. Explore the roles of collagen in the human body as well.