Cell bio week 4

Some terms same as week 3

Germ layers

Germ layers

Ectoderm

Mesoderm

Endoderm

Types of tissue in mesoderm

Embryonic connective tissue:

Mesenchyme

Muscle tissue

2 types of adult connective tissue

Connective tissue proper

Specialised connective tissue

Connective tissue proper

Loose

Dense (irregular + regular)

Reticular

Adipose

Specialized connective tissue

Cartilage (supporting ct)

Bone (supporting ct)

Blood (fluid ct)

2 components of cartilage

Cells

Extracellular matrix

Types of cells in cartilage

Chondroblasts

Chondrocytes

Ground substance

Glycosaminoglycans

Glycoproteins

Proteoglycans

Fibers

Collagen

Reticular

Elastic

Chondroblasts 4 points

Oval/ round shape

Round nuclei

Basophilic cytoplasm

Contributes greatly to fibers and ground substance to ECM after transformed to chondrocytes

Chondrocytes

Round/ oval shape

Continue to synthesise and secrete matrix

Located in lacunae

Hyaline cartilage ( collagen fibers type II) components

Perichondrium

Chondroblasts

Chondrocytes in lacunae

Isogenic group

3 types of cartilage

Hyaline

Elastic

Fibrocartilage

Isogenic group

Group of lacunae with Chondrocytes lying close to each other, all chondrocytes of this group come from one chondrocyte

Each chondrocyte lies in its own lacuna

Hyaline cartilage (collagen fibres type II): functions

Provides support, flexibility, resilience

Reduces friction between bony surfaces

The most abundant skeletal cartilage

Hyaline cartilage (collagen fibres type II): Location

Articular- covers the ends of long bones

Costal- connects the ribs to the sternum

Respiratory- makes up larynx, reinforces air passages

Nasal- supports the nose

Elastic cartilage (elastic and collagen fibres type II) components

Perichondrium

Chondroblasts

Chondrocytes in lacunae

Extracellular matrix

Elastic fibres

Isogenic group

Elastic cartilage ( elastic and collagen fibres type II): functions

Provides support with more flexibility

Can be distorted and return to original shape without damage

Elastic cartilage ( elastic and collagen fibres type II): Location

External ear

Epiglottis

Tip of nose

Fibrocartilage (collagen fibres type I)

No pericardium

Chondrocytes in lacunae

Extracellular matrix

Collagen fibres

Fibrocartilage (collagen fibres): Location

Highly compressed with great tensile strength

Found in menisci of knee and in interverbral discs

Between pubic bones

Growth of cartilage diagram

Appositional growth

Mesenchyme cells surrounding the cartilage in the deep part of the perichondrium differentiate into chondroblasts

Occurs also in mature cartilage

Interstitial growth

Chondrocytes within the existing cartilage divide and form small groups of cells (isogenous groups), which produce matrix to become separated from each other by a thin partition of matrix

Occurs mainly in immature cartilage

Major functions of cartilage

Supporting soft tissues

Providing a surface where 2 bones meet

Providing a model for the formation of most of the bones in the body

4 anatomical bones

Lobg

Short

Flat

Irregular

2 histological bones

Woven

Lamellar ( compact, spongy)

Woven bone

Many osteocytes and the osteoid, less the inorganic substance, a lot of collagenous fibres in thick tufts

In foetal life and just after birth

In an adult individual it appears local to the insertion of tendons to the bone, in the skull only in pathological states

Lamellar bone diagram

Components of bone

Cells

Extracellular matrix

Types of bone cell

Osteogenic cells

Osteoblasts

Osteocytes

Osteoclasts

Osteogenic cells

Stem cells that line bone and divide to produce osteoblasts

Located in inner, cellular layer of periosteum and endosteum

Assist in fracture repair

Osteoblasts

Produce new bone

Immature bone cells that secrete matrix compounds (osteogenesis)

Become surrounded by calcified bone and then they become osteocytes

Osteocytes

Connected by cytoplasmic processes through canaliculi in lamellae (gap junctions)

Mature bone cells that maintain the bone matrix

Live in lacunae

found between layers of matrix

Do not divide

Help repair damaged bone

Osteoclasts

Osteoclasts are related to macrophages

Dissolve bone matrix and release stored minerals (osteolysis)

Involved in bone resorption

Secrete acids and protein- digesting enzymes

Often occur in the endosteum lining the marrow cavity

Components of extracellular matrix

Organic matter - osteoid

Inorganic matter - mineral

Organic matter contains:

Ground substance ( complex polysaccharides and glycoproteins)

Fibers: collagen

Inorganic matter contains:

Hydroxyapitite = calcium - phosphate salts

Magnesium salts

Random ions

Long bone diagram

Osteon

Haversian systems (the basic structural unit of mature compact bone)

Osteon: osteocytes arranged in concentric lamellae around a central canal containing blood vessels and nerves

Lamella: weight- bearing column like matrix tubes composed mainly of collagen

Three lamellae types

Concentric lamellae

Circumferential lamellae

Interstitial lamellae

Bone marrow

In the space between trabeculae

Highly vascular

Red bone marrow

Supplies nutrients to osteocytes in trabeculae

Forms red and white blood cells

Yellow bone marrow

Yellow because it stores fat

Bone development (ossification or osteogenesis)

Inter-membranous ossification

Endochondrial ossification

Inter-membranous ossification

Develop within s fibrous sheet

No cartilage is needed for this process

Produces the flat bones of the skull snd part of the clavicle

Endochondrial ossification

Endochondrial ossification

Begins with a hyaline cartilage model and produces most of the other bones of the skeleton

Primary ossification centre - in the diaphysis

Secondary ossification centre - in the epiphysis

Bone length growth

Bone remodelling

Although adult bone size has been reached, the bone continues to reshape itself throughout an animal's lifetime in a constant process of bone resorption and deposition

Homeostasis

The balance between bone building cells (osteocytes and osteoblasts) and bone recycling cells (osteoclasts)

Effects of hormones

Control and regulate growth patterns in bone by altering the rates of both osteoblast and osteoclast activity.

GROWTH HORMONE: affects bone growth by stimulating the formation of another hormone, SOMATOMEDIN which is produced by the liver.

SOMATOMEDIN: directly stimulates growth of cartilage in the epiphyseal plate

CALCITONIN (thyroid hormone) : stimulates bone growth. It acts to decrease the concentration of calcium in the blood, inhibits osteoclast activity.

PARATHORMONE (parathyroid hormone) acts to increase the concentration of calcium in the blood

GROWTH HORMONE and thyroid hormone regulate and maintain normal activity at the epiphyseal plates until puberty.

Major functions of bones

Support

Storage of minerals and lipids

Blood cell productions

Protection

Leverage