specialized connective tissue Flashcards
composition of cartilage
chondrocytes (cartilage cells)
extracellular matrix (ECM)
3 types of cartilage
Hyaline cartilage
Elastic cartilage
Fibrocartilage
What does hyaline cartilage look like in the living state?
Hyaline cartilage appears glassy and smooth.
What are lacunae in hyaline cartilage?
Lacunae are small spaces in the cartilage where chondrocytes are located.
- Chondrocytes are specialized cells that produce and maintain cartilage.
functions of hyaline cartilage
provides low-friction surface
participates in lubricating synovial joints
distributes applied forces to the underlying bone.
What is hyaline cartilage mainly composed of?
aggrecan
proteoglycan that forms aggregates with hyaluronan
chondroitin sulfate
keratan sulfate.
Why does hyaline cartilage have high levels of hydration?
The aggregates of proteoglycans in hyaline cartilage attract water molecules, resulting in high hydration.
why is hyaline cartilage slow to repair?
Hyaline cartilage is avascular, meaning it lacks blood vessels. It relies on diffusion for nutrients and waste removal, making repair slower compared to vascularized tissues.
what are the 3 major classes of molecules in hyaline cartilage
(index card)
collagen molecules
proteoglycans
multiadhesive glycoproteins
What are chondrocytes and what do they do
specialized cells in cartilage that produce and maintain the extracellular matrix (ECM).
What are isogenous groups in hyaline cartilage?
Isogenous groups are clusters of chondrocytes that have recently divided.
What are metalloproteinases (MMPs) and their role in cartilage?
MMPs are enzymes secreted by chondrocytes that break down the cartilage matrix.
Excessive secretion can cause cartilage degradation, leading to conditions like rheumatoid arthritis.
What are the three regions of the hyaline cartilage matrix?
- based on the staining property of matrix
Capsular matrix: Surrounds chondrocytes, stains intensely, contains Type VI and Type IX collagen.
Territorial matrix: Surrounds isogenous groups, contains Type II and Type IX collagen.
Interterritorial matrix: Fills space between chondrocytes, surrounds the territorial matrix.
What role does hyaline cartilage play in fetal development?
provides a model for the developing skeleton of the fetus.
What surrounds hyaline cartilage?
perichondrium
Why is articular cartilage different from other hyaline cartilage?
Articular cartilage, which covers joint surfaces, does not have a perichondrium.
What are the layers of articular cartilage?
Superficial zone: Flat chondrocytes.
Intermediate zone: Round chondrocytes.
Deep zone: Chondrocytes arranged in columns.
Calcified zone: Cartilage that has undergone calcification.
What makes elastic cartilage different from other types of cartilage?
Elastic cartilage contains elastin, which provides flexibility and allows it to bend easily.
What is present in the elastic cartilage matrix?
dense network of branching and anastomosing elastic fibers
along with interconnecting sheets of elastic material.
Where is elastic cartilage found in the body?
Elastic cartilage is found in:
External ear
Walls of the external acoustic meatus
Eustachian tube
Epiglottis
What is fibrocartilage a combination of?
dense regular connective tissue and hyaline cartilage.
How do chondrocytes in fibrocartilage compare to those in hyaline cartilage?
The chondrocytes in fibrocartilage are similar to those in hyaline cartilage but with less cartilage matrix material.
Where can fibrocartilage be found in the body?
Intervertebral discs
Pubic symphysis
Articular discs of sternoclavicular and temporomandibular joints
Menisci of the knee joint
Triangular fibrocartilage complex of the wrist
Certain places where tendons attach to bones
What types of collagen are found in the ECM of fibrocartilage?
Type I
Type II collagen
Versican
How does fibrocartilage compare to hyaline cartilage?
Fibrocartilage appears similar to hyaline cartilage, but it has less cartilage matrix material.
is the process of cartilage development, from mesenchymal cells, and is triggered by the expression of the transcription factor SOX-9 to differentiate to chondroblasts
Chondrogenesis
what are the 2 types of cartilage growth
Appositional growth:
forms new cartilage at the surface of existing cartilage
Interstitial growth:
forms new cartilage within an existing cartilage mass.
How does cartilage repair work?
cartilage has limited repair ability and typically forms dense connective tissue instead of true cartilage.
A process where cartilage turns into bone, especially during development or healing.
endochondral ossification
Hyaline cartilage undergoes calcification under:
- Portion of articular cartilage in contact with bone tissue.
- Endochondral ossification.
- Aging.
it is a type of connective tissue that is strong and hard because it has a mineralized extracellular matrix
bone
- The mineral in bone is mostly calcium phosphate in the form of hydroxyapatite crystals. These crystals give bone its hardness.
- bone matrix contains:
type I collagen (lesser other collagen types V, III, XI, XIII), and other matrix (non collagenous) proteins
what are the 4 main groups of the bone
index card
bone composition
bone tissue
other specialized connective tissues: - cartilage
- hemopoietic tissue
- fat tissue
- associated blood vessels.
bone, according to shape
Long bones:
are longer in one dimension than other bones, and consist of a shaft and two ends.
Short bones:
are nearly equal in length and diameter.
Flat bones:
are thin and plate-like.
Irregular bones:
are bones that do not fit into any one of the three previous categories.
parts of a long bone
Diaphysis (Shaft): This is the long, central part of the bone.
Epiphysis (Ends): These are the two rounded ends of the bone.
Metaphysis: The area between the shaft and the ends of the bone.
Marrow/Medullary Cavity: The hollow space inside the bone that is filled with bone marrow.
Different types of joints connect bones
Articular surfaces are the contact areas between two bones that form a movable joint (called diarthroses). These surfaces are covered with hyaline cartilage (as articular cartilage), which helps reduce friction during movement.
amphiarthroses = Some joints are slightly movable
synarthroses = Other joints are immovable
it is a sheath of dense fibrous connective tissue that covers bones, containing osteoprogenitor cells (and periosteal cells).
periosteum
What are the two layers of the periosteum?
has an outer fibrous layer and an inner cellular layer containing skeletal stem cells.
what do periosteal cells secrete
periostin, a regulatory protein crucial for the periosteal response
Perforating fibers (Sharpey’s fibers):
Some collagen fibers from the periosteum reach to the long axis of the bone, to the actual compact of the bone.
it is lined by endosteum, a layer of connective tissue cells that contains osteoprogenitor cells. (endosteal cells)
Bone cavities
How are endosteal and periosteal cells similar?
Both are bone lining cells derived from osteoprogenitor cells and have the ability to transform into osteoblasts.
what are the 2 classification of the bones
Mature bone tissue is classified as either Compact bone (dense bone) or Spongy bone (trabecular bone)
Compact Bone (Dense Bone):
- made up of osteons (Haversian systems), which are cylindrical structures like tree rings.
- each osteon has concentric lamellae, which are circular layers of bone surrounding a central (Haversian) canal that contains blood vessels and nerves.
- Between osteons, there are interstitial lamellae, which are leftover parts of older osteons.
- The circumferential lamellae wrap around the entire bone to give it strength.
Spongy Bone (Trabecular Bone):
- mesh-like structure called trabeculae which helps reduce bone weight while still being strong.
How do osteocytes communicate with each other?
they send out small extensions through tiny channels called canaliculi to share nutrients and signals.
Where is the newer bone tissue located in an osteon?
Where is the older bone tissue found in an osteon?
newer: Closer to the central canal.
older: Further away from the central canal.
How is the structure of immature bone different from mature bone?
It does not have an organized lamellated (layered) structure.
How are the cells arranged in immature bone andhow does the matrix of immature bone compare to mature bone?
The cells are randomly arranged and more numerous per unit area.
It has more ground substance than mature bone.
what are the 5 main types of cells associated with bone tissue
(index card)
What is the origin of osteoclasts?
Osteoclasts come from granulocyte-monocyte progenitor (GMP) cells.
What transcription factors help osteoclasts develop?
C-fos and NF-kB help regulate osteoclast formation.
How do osteoclasts break down bone?
By releasing protons (H⁺) and lysosomal hydrolases into the extracellular space.
What are the key enzymes used by osteoclasts?
Cathepsin K (breaks down bone proteins)
MMPs (Matrix Metalloproteinases) (digest collagen and bone matrix)
How do osteoclasts remove calcium from bone?
Carbonic Anhydrase II creates an acidic environment in the resorption bay, helping to dissolve calcium.
what hormone regulates osteoclast activity?
calcitonin, secreted by the thyroid gland, helps control osteoclast function.
how does the bone develops
Intramembranous Ossification:
Osteoblasts form directly from mesenchymal cells and start producing bone.
= flat bones like the skull, face, mandible, and clavicle.
Newly formed bone appears as small, irregular spicules and trabeculae in microscopic views.
Endochondral Ossification
Bone forms indirectly by replacing a cartilage model with bone.
Starts with hyaline cartilage, which is broken down and replaced by osteoblasts that produce osteoid (bone matrix).
This process forms bones of the limbs (extremities) and axial skeleton.
What is responsible for bone length growth in long bones?
The epiphyseal cartilage (growth plate) is responsible for bone length growth.
*it gradually replaced by vascularized bone tissue, a process initiated by VEGF (vascular endothelial growth factor).t is gradually replaced by vascularized bone tissue, a process initiated by VEGF (vascular endothelial growth factor).
*the epiphyseal closure occurs, and cartilage proliferation stops, ending bone length growth.
it is the process where old bone is replaced by new bone tissue, forming new osteons.
bone remodeling
- made up of:
Cutting cone (removes old bone)
Closing cone (fills with new bone) - new osteoclasts - create a resorption cavity (tunnel) through compact bone, where old bone is broken down.
What happens after osteoid is laid down?
The mineralization process begins, where bone minerals (calcium and phosphate) are deposited in the matrix.
How is mineralization triggered?
concentration of calcium and phosphate ions must exceed a threshold, and osteocalcin helps bring calcium to the bone to start the process.
What role does osteocalcin play in bone mineralization?
Osteocalcin binds calcium and circulates it toward the bone, attracting osteoblasts to begin mineralization.
How does high calcium concentration affect mineralization?
stimulates the release of tissue nonspecific alkaline phosphatase (TNAP), which increases local phosphate levels, promoting further mineralization.
What stimulates osteoblasts to release matrix vesicles?
High concentrations of calcium and phosphate ions.
What do matrix vesicles contain?
Annexins (A5)
Na+-phosphate cotransporter 3 (NPT3)
Tissue nonspecific alkaline phosphatase (TNAP)
What happens in the matrix-mediated mineralization phase?
The formation of amorphous calcium phosphate, which later undergoes crystallization.
What happens after the formation of amorphous calcium phosphate?
It crystallizes into osteocalcium phosphate, which further forms hydroxyapatite crystals.
What occurs during the collagen mineralization phase?
Hydroxyapatite crystals form mineralized nodules in the bone matrix.
it is a specialized connective tissue that plays an important role in energy homeostasis.
adipose tissue
- composed of adipocytes
[Energy reserves are stored within lipid droplets of adipocytes in the form of triglycerides.]
Considered as a major endocrine organ as they regulate energy metabolism by secreting autocrine, paracrine, and endocrine substances.
adipose tissue
by secreting autocrine, paracrine, and endocrine substances etc
What stem cells give rise to white adipocytes?
Perivascular stem cells differentiate into white adipocytes.
What transcription factors are involved in white and brown adipocyte differentiation?
white: PPAR gamma (peroxisome proliferator-activated receptor gamma)
RXR (retinoid X receptor)
brown:
Myogenic factor five
PRDM16
PGC-1 (PPAR gamma cofactor 1)
What stem cells give rise to brown adipocytes?
Skeletal myogenic progenitor cells differentiate into brown adipocytes.
What is the primary type of adipose tissue in adult humans?
White (unilocular) adipose tissue is the predominant type in adult humans.
functions:
Energy storage
Insulation
Cushioning of vital organs
Secretion of hormones
found in:
Subcutaneous layer
Mammary glands
Greater omentum
Mesenteries
Retroperitoneal space
Visceral pericardium
Orbits
Bone marrow cavity
What do white adipocytes synthesize and secrete?
Adipokines, which are hormones that influence various bodily functions.
They are spherical, polyhedral, or oval, with a flattened nucleus at the periphery, and contain one large lipid droplet.
the shape and structure of white adipocytes
What are specific markers for white adipocytes?
Ob (leptin)
Hoxc8
- required for the fixation of tissues and has its own specific cellular marker.
HOXC9
Through the brain-gut-adipose axis, which regulates
Appetite
Hunger
Satiety
Energy homeostasis
What are the two types of weight regulation?
Short-term weight regulation
Long-term weight regulation
what does ghrelin and Peptide YY (PYY) do in short-term weight regulation?
ghrelin:
Produced by gastric epithelial cells.
Stimulates appetite by signaling the hypothalamus to increase hunger.
Clinical correlation: Overproduction of ghrelin can cause Prader-Willi syndrome.
peptide YY:
Produced by the small intestine.
Increases fullness after eating, reducing appetite.
What role does leptin play in long-term weight regulation?
Reflects the amount of adipose tissue and energy stored.
Inhibits food intake, stimulates metabolic rate, and promotes weight loss.
Encourages fatty acid oxidation and reduces fat accumulation outside adipose tissue.
- insulin play in long-term weight regulation:
Regulates blood glucose levels and promotes the conversion of glucose into triglycerides (lipid droplets) through lipogenesis.
What triggers neural mobilization of lipids?
Fasting or exposure to cold
Norepinephrine activates lipase, which breaks down triglycerides and mobilizes lipids.
What hormones are involved in hormonal mobilization of lipids?
Insulin
Glucagon
Growth hormone
Thyroid hormones
Adrenal steroids
How does insulin regulate fat metabolism?
Stimulates lipogenesis (fat formation)
Inhibits lipolysis (fat breakdown)
primary function of brown adipose tissue (BAT)
Thermogenesis (heat generation).
Brown adipocytes produce batokines and contain UCP-1, which allows protons to bypass ATP synthase, producing heat instead of ATP.
What are the specific markers and the major batokines produced by brown adipocytes?
specific markers:
LHX8
ZIC1
major batokines produced by brown adipocytes:
NGF, FGF21, VEGF-A (promote hypertrophy and hyperplasia of BAT)
FGF21, neuregulin-4, myostatin, BMP-8B, exosomal miRNA (endocrine factors targeting other organs).
It is regulated by the sympathetic nervous system, which releases norepinephrine.
brown adipose tissue
What is the role of UCP-1 in brown adipose tissue?
allows protons to flow back into the mitochondrial matrix without passing through ATP synthase, creating heat instead of ATP.
beige adipose tissue?
Beige adipose tissue is intermediate between white and brown adipose tissue.
It has fewer lipid droplets than brown adipocytes but still shows thermogenic activity.
specific markers for adipcytes:
tBX1
TMEM26
how are beige adipocytes produced:
white-to-brown transdifferentiation or de novo differentiation.
pre-adipocytes expressing TBX1 and TMEM26 become beige adipocytes.
Where do white and brown adipocytes originate from?
white: Perivascular stem cells (cells around blood vessels).
brown: Skeletal myogenic progenitor cells (muscle-related stem cells).
it is the process where adipocytes change from white to brown or brown to white based on the body’s thermogenic needs.
Transdifferentiation
What induces white-to-brown transdifferentiation?
cold exposure
Physical activity
Highly stimulated by the sympathetic nervous system via the release of norepinephrine.
What is another factor that induces transdifferentiation?
FGF21 (a protein involved in metabolism regulation).
