LECTURE 2 (Connective Tissue II) Flashcards
What are the properties of Loose connective tissue/Areolar tissue?
- Contains cells, fibers and ground substance
- Delicate consistency
- Flexible
- Not very resistant to stress
What are the properties of Dense connective tissue?
- Fewer cells than loose connective tissue
- Mostly fibroblasts
- Mostly type I collagen fibers over ground substance
- Abundance protects organs and strengthens them structurally
What are the properties of Dense irregular connective tissue?
- Bundles of collagen fibers appear RANDOMLY interwoven with NO DEFINITE ORIENTATION
- Tough 3D network provides resistance to stress from all directions
- Dense irregular and loose connective tissue are closely associated
(EXAMPLES: deep dermis layer of skin & capsules surrounding most organs)
Describe Dense regular connective tissue
- Consists mostly of type I collagen bundles
- Collagen & fibroblasts aligned in parallel for great resistance to prolonged or repeated stresses from the SAME DIRECTION
(EXAMPLES: Tendons, aponeuroses & ligaments)
Why do dense regular connective tissue appear white in the fresh state?
They consist of densely packed parallel collagen fibers separated by very little ground substance and have very few blood vessels
Describe fibrocytes in relation to nuclei
Fibrocytes with elongated nuclei lie PARALLEL to the collagen fibers of DENSE REGULAR CONNECTIVE TISSUE with cytoplasmic folds enveloping portions of the collagen bundles
Describe Aponeuroses
The parallel bundles of collagen exist as multiple layers alternating at 90 degrees to one another
On their outer surface, tendons and ligaments have a layer of _________ _____________ connective tissue that is continuous with the outermost layers of the adjacent muscles and bones
Dense Irregular
What is the difference between Tendon and Aponeurosis?
TENDON:
- tough, rounded cord like structures (extensions of muscle)
- allow attachment of muscle from its originating bone to bone it ends
- has capacity to stretch & allow contraction of muscle by providing strength and support
APONEUROSIS:
- delicate, thin sheath-like structure attached muscles to bones
- property of recoiling
- muscle expands or contracts -> bears extra pressure and tension
What are the properties of reticular tissue?
- Abundant fibers of type III collagen
- Produced by modified fibroblasts (RETICULAR CELLS) that remain associated with and cover the fibers
- Cell-lined system creates a meshwork for the passage of leukocytes and lymph
- MACROPHAGES and DENDRITIC CELLS are disperse to monitor cells formed there or passing through and remove debris
What are the functions of Mucoid tissue?
- Component of FETAL UMBILICAL CORD
- Abundant ground substance & hyaluronan -> gelatinous with sparse collagen fibers and scattered fibroblasts
- Mesenchymal stem cells found in fibroblastic cells
What are the two types of Adipose tissue?
White adipose tissue & Brown adipose tissue
What are the similarities between the two types of Adipose tissue?
- Rich blood supply
- Adipocytes are individually surrounded by a thin external lamina containing TYPE IV COLLAGEN
What are the differences between the two types of Adipose tissue?
WHITE ADIPOSE TISSUE
- more common type specialised for fat storage
- consists of cells each containing one large cytoplasmic droplet of white-yellow fat
- mitochondrial metabolism releases ATP (energy) instead of heat
BROWN ADIPOSE TISSUE
- cells with multiple lipid droplets interspersed among abundant mitochondria
- darker appearance
- releases heat -> warms up the blood
What are the properties of White adipose tissue?
- Specialised for long-term energy storage
- Spherical when isolated but polyhedral when closely packed in situ
- Contains a single huge droplet of liquid filling the entire cell
- Signet ring appearance with lipid droplet displacing & flattening the nucleus against the cell membrane
Why are fat cells empty when seen under a light microscope?
Since lipid is removed from cells by XYLENE and other solvents used in routine histological techniques
What can unilocular adipocytes generate?
Benign tumours called LIPOMAS and sometimes malignant adipose tumours (LIPOSARCOMAS)
What are Hibernomas?
Foetal lipomas of brown fat
Where are most cytoplasmic organelles in a white adipocyte located?
Near the peripheral nucleus
White adipocytes can store triglycerides derived from which sources?
- Dietary fats as CHYLOMICRONS
- Lipids synthesised in liver and transported in blood with VERY LOW DENSITY LIPOPROTEINS
- Free fatty acids and Glycerol (synthesised by adipocytes)
What happens to chylomicrons and VLDLs in adipose tissue?
Both are hydrolysed at the luminal surfaces of blood capillaries by LIPASE
[Lipase is synthesised by adipocytes and transferred to the capillary cell membrane]
What does Insulin stimulate and inhibit?
Insulin stimulates GLUCOSE UPTAKE by adipocytes and accelerates its conversion into TRIGLYCERIDES and the production of LIPASE
Insulin inhibits LIPASE -> reducing fatty acid release & stimulates enzymes for lipid synthesis
What is the difference between Visceral (abdomen) deposits and Subcutaneous deposits of white fat?
Increased Visceral adipose tissue raises the risk of DIABETES and CARDIOVASCULAR DISEASE whereas increased subcutaneous fat does not
Why is increased visceral fat dangerous?
The visceral fat products are released directly to the portal circulation and liver
Describe the development of Adipocytes
1) Adipocytes develop from mesenchymal stem cells and are first produced as PREADIPOCYTES
2) Initially, the droplets white adipocytes are isolated from one another but then fuse to form the single large droplet
How can brown adipocytes develop from beige adipocytes?
During adaptation to cold temperatures
Describe how adipocytes are formed from mesenchymal stem cells
- PREADIPOCYTES developing within the lateral mesoderm of the embryo produce a large number of WHITE ADIPOCYTES and a smaller number of BEIGE ADIPOCYTES
- BROWN ADIPOCYTES differentiate from another population of preadipocytes in PARAXIAL EMBRYONIC MESODERM
Where does new adipocyte formation in adolescence occur?
Around small blood vessels where undifferentiated mesenchymal cells are most abundant
When does excessive adipose tissue accumulation/obesity occur?
When nutritional intake exceeds energy expenditure
What is the difference between adult obesity and childhood obesity
Adult obesity entails increasing the SIZE of existing adipocytes whereas childhood obesity involves increasing the SIZE and NUMBERS due to the differentiation of more preadipocytes from mesenchymal cells
Why is there a link between Obesity and Diabetes?
White adipose tissue secretes cytokines including pro inflammatory cytokines therefore increased amounts of adipose tissue characterises a state of chronic mild inflammation
What gives brown adipose tissue its colour?
- Very abundant mitochondria
- Large number of blood capillaries
Describe the function of brown adipocytes
TO PRODUCE HEAT BY NONSHIVERING THERMOGENESIS
1) Nerve impulses liberate norepinephrine into brown adipose tissue
2) Liberated fatty acids of multilocular adipocytes are quickly metabolised with a consequent increase in O2 consumption and heat production
3) This raises the temp within the tissue and warms the locally circulating blood which distributes the heat throughout the body
Why is heat production in brown adipocytes greater than that of other cells?
Inner mitochondrial membranes have greatly unregulated levels of UCP1 or THERMOGENIN. In the presence of free fatty acids, UCP1 allows the flow of protons from the inter membrane space to the matrix without passing through ATP synthesise. The energy associated with this proton flow dissipates as heat.
What is Leptin?
A polypeptide hormone with target cells in the hypothalamus that is released from white adipocytes and helps regulate eating behaviour
