Brown adipocyte : special connective tissue

Brown adipocyte :

Brown adipose tissue is present in humans during fetal life but diminishes during the first decade after birth. Brown adipose tissue makes up about 5% of the total body mass.

Microscopic features: Multilocular adipose tissue contains numerous fat droplets. Brown (multilocular) adipocytes are smaller in diameter (10–25 µm) than those of white adipose tissue.

Multilocular, spherical, round eccentric nucleus. The multilocular adipocyte contains numerous mitochondria, a small Golgi apparatus, and only small amounts of rER and sER. The mitochondria contain large amounts of cytochrome oxidase, which imparts the brown color to the cells.

Function: Brown adipose tissue is present in large amounts in the newborn, which  prevent  the extensive heat loss by heat production (thermogenesis) that results from the newborn’s high surface-to-mass ratio and avoid lethal hypothermia (a major risk of death for premature babies).

Distribution : It is located on the back, along the upper half of the spine, and toward the shoulders. In adult it is gradually decreases. At first decade of life it is situated in the cervical, axillary, paravertebral, mediastinal, sternal,and abdominal regions of the body.

It then disappears from most sites except for regions around the kidney, adrenal glands, large vessels (i.e., aorta), and regions of the neck (deep cervical and supraclavicular), regions of the back (interscapular and paravertebral), and thorax (mediastinum).

Metabolism: brown fat contain numerous mitochondria which are capable of uncoupling proton leakage and instead of producing adenosine triphosphate (ATP), they release heat, thus arousing the animal from hibernation.

Beige adipocyte : a new hope for losing weight

Beige adipocytes:  Beige fat” is a new kind of energy-burning cell that prevent obesity and help weight loss for adults.

Distribution :  This  new fat cell is found underneath the skin along the spine and in the proximal area of the collarbone in deposits resembling the size of a pea.

Microscopic features: Like brown fat, beige fat cells also have a plentiful amount of mitochondria and iron, giving them their darker color.

Function:

Prevent obesity

Increase insulin receptor sensitivity

How this cell is formed? : These beige fat cells are converted from white fat cells while exercising when muscles release a hormone called irisin. These beige cells then burn extra calories. It is speculated that these beige fat cells developed from shivering, which is categorized at a neuromuscular activity along with exercise.The embryonic origin of beige adipocytes is less clear. But recent study support that large unilocular white adipocytes transform into beige adipocytes in response to cold. Brown fat cells show high levels of UCP1, (a protein essential to mitochondria to generate heat and burn calories), where beige cells usually show lower levels of this protein. Beige cells are able to increase their level of this UCP1 protein, by releasing irisin or being exposed to the cold, making them just as effective as brown cells to burn calories. Beige fat cells behave like white fat cells until they’re activated through a process called “browning.” After they are browned, they start to behave like brown fat and burn other white fat for energy. Beige fat does a lot more than body weight. To take one example, it may also help improve insulin sensitivity.

Factors stimulate browning:

• Social interaction. By increasing the levels of a protein called Brain-Derived Neurotrophic Factor, social interaction can “brown” white fat tissue.

• Exercise. By releasing the hormone irisin, exercise can make cause fat browning. This is a major difference between beige and brown fat inrisin has no real effect on brown fat 

• Cold exposure. Just like brown fat, beige fat gets “turned on” by cold.
• Mild stress:   browning might be activated by mild stress. Mild stress causes small spikes in cortisol, but in chronic stress cortisol level remain high for most of the time that is not good for health. So occasional spikes in cortisol are good for health.
• cancer is really great at browning white fat cells  which is one reason why people with cancer lose so much weight.

    Food stimulates browning:

1.      Green tea

2.      Garlic

3.      Red pepper

4.      Sea weed extract

5.      Fish/flaxseed oil

6.      Curcumin /tumaric

7.      Melatonin

8.      Resveratrol 

White adipocyte : easy and brief description

White adipocyte :

These types of adipocytes are predominantly found in adult. White adipocytes are spherical, but they may appear polyhedral or oval when crowded together. It contains unilocular fat which store triglyceride, flatten nucleus, rim of cytoplasm. Adipocyte looks like signet ring so it also known as signet ring cell.  Early lipoblasts look like fibroblasts but develop small lipid inclusions and a thin external lamina.

Unilocular adipocytes are large cells, sometimes 100 µm or more in diameter. The lipid mass in the adipocyte is not membrane bounded. It thin cytoplasmic rim contain a Golgi complex, few poorly developed mitochondria, poorly developed cisternae of the rough endoplasmic reticulum, and free polyribosomes,  the lipid droplet contains cisternae of smooth endoplasmic reticulum and numerous pinocytotic vesicles. Each adipose cell is surrounded by a basal lamina.

Innervation: Few sympathetic nerve fibers

Secretions:  White adipose tissue produces a variety of hormones, growth factors, and cytokines.

ASP(Acylation-stimulating protein ) Influences the rate of triglyceride synthesis in adipose tissue

Insulinlike growth factor I (IGF-I) : Stimulates proliferation of a wide variety of cells and mediates many of the effects of growth hormone

Leptin Regulates appetite and body energy expenditure

Plasminogen activator inhibitor-1 (PAI-1):  Inhibits the fibrinolytic system

Elevated levels are associated with increased formation of blood clots

Prostaglandins I2 F2_, (PGI2 and PGF2_) Helps regulate inflammation, blood clotting, ovulation, menstruation,and acid secretion

Resistin:  Increases insulin resistance ,Linked to obesity and to type 2 diabetes

Distribution: subcutaneous tissue, breast, greater omentum, mesenteries, visceral pericardium, orbital cavity, retroperitoneal space, bone marrow

Metabolism:

It hydrolyzes the stored lipids into fatty acids and glycerol, which are released from the cell.

 Functions of white adipose tissue include

1.      metabolic energy storage,

2.      insulation,

3.      cushioning of vital organs, and

4.      secretion of hormones,

5.       Source of metabolic water.  

6.       Subcutaneous layers of adipose tissue help to shape the surface of the body, whereas deposits in the form of pads act as shock absorbers, chiefly in the soles and palms.

Gray and white matter : composition , location and difference

Grey (British)  gray (American) matter and white matter are  found within the  central nervous system.

Composition of gray matter :

1.      Neuron cell body,

2.      Initial portion of dendrites and axon

3.      Neuroglia

4.      Blood vessels

Composition of white matter:

1.      White matter contain

2.      numerous dendrites and myelinated axons, 

3.      neuroglia, and

4.      blood vessels.

Colour:

Gray matter:  actually has a very light gray colour with yellowish or pinkish hues, which come

from blood vessels and neuronal cell bodies.

White matter:  the colour of white matter arises mainly from the whiteness of myelin.

Location

location of gray matter ::

In cerebrum and cerebrum gray matter situated in outer layer of these organs.

In spinal cord it is situated in inner layer of this organ .

A small collection of gray matter known as nuclei present within the white matter. Example :  basal nuclei/ nuclei: caudate nucleus, putamen, globus pallidus , substantia nigra, subthalamic nucleus , nucleus accumbens and  brain stem nuclei (red nuclei, cranial nerve nuclei) are spread within the cerebral white matter.

Cerebellar nuclei dentate nuclei, fastigi, emboliform etc are the small collection of gray matter present within the white matter of cerebellum .

Ganglia are small collection of gray matter (neuron cell body ) situated outside the central nervous system .

Location of white matter:

White matter forms the bulk of the deep parts of the cerebrum and cerebellum and the superficial parts of the spinal cord  

Difference between gray matter and white matter

Topics	Gray matter	White matter
Composition	Nerve cell body , Neuroglia, Processes , Blood vessels	Neuroglia, Processes , Blood vessels
Colour	Light grey	White
Percentage	Occupy 40% of brain	Occupy 60% of brain
Maturity	Girl  11 years Boy 12 years	Girl 25 years Boy 20 years
Sex difference	Male 6.5 more gray matter	Female   contain 10 times more  white matter
Proportion of	Men have higher proportion of white matter	women have higher proportion of grey  matter
Function	It is the information processing region  of brain	It makes connection between different information processing region of brain
Oxygen use	It uses almost 95% of oxygen	It uses remaining  5%
Loss of volume	It volume losses constantly throughout the life	its volume losses start after mid age
Other name of	Gray matter also known as substantia grisea	White matter also known as substantia alba

Ear ossicle, malleus: easy description and important points

Ear ossicles : malleus, incus ,stapes : short and easy description

Ear osssicles :

The middle ear cavity contains a chain of three small bones the malleus , the incus and the stapes .

Conduction of sound through the middle ear to internal ear is transmitted by these three ossicles. Each ear ossicles is ossified from one ossification centre in the fourth month of intra-uterine life and they attain adult size at birth .

Malleus :

It is the largest bone of middle ear.

Shape: like a round-headed club

Parts:

Head: it lies in the epi- tympanic part of middle ear cavity. Head articulate with the incus forming a siddle shaped synovial joint

Neck:  it situated in between head and handle and lies just medial to pars flaccida of tympanic membrane. Its medial side is related with chorda tympani nerve

Handle: it is attached with medial side of tympanic membrane and its upper part receives insertion of tendon of tensor tympani muscles.

Anterior process: situated just below the neck: it receives attachment of anterior ligament which extends up to spine of sphenoid. This ligament derived from perichondrium of 1^st pharyngeal arch cartilage.

Lateral process: mallear folds are attached to the apex of the lateral process.

Incus

Shape : like premolar tooth

Development : 1^st pharyngeal arch

Parts :

Body : articulate with head of malleus

Short process : directed posteriorly

Long process : it is situated parallel to the upper part of handle of malleus and tip of incus forms a knob known as lentiform nodule which articulate with head of stepes . 

Stepes:

Shape : it looks like stirrup

Development :2^nd pharyngeal arch

Parts :

Head : articulate with lentiform nodule of incus

Neck : receive insertion of stepedius muscle

Anterior and posterior limbs

Base or foot- plate : it is attached with fenestra vestibule by annular ligament

What are the structure seen through auroscope

Lateral process of malleus

Long process of incus

Two small muscles are associate with ear ossicles

1.      Stapedius :

Attachement : origin : interior of hollow pyramid

Insertion : neck of stepes

Nerve supply :  facial nerve

Functions: contraction of this muscle draw the stapes laterally thus tilting its foot plate in the oval window.

 it prevent excessive movement of stapes so its paralysis leads  to uninhibited movement of stapes and excessive acuteness of hearing (hyperacusis) 

SN: paralysis of the stapedius causes an abnormally increased power of

2.      Tensor tympani:

Attachment : origin : bony part of auditory tube

Insertion : handle of malleus

Nerve supply : mandibular division of trigeminal nerve

Functions: contraction of this muscle draw the handle of malleus medially (inward) which makes tympanic membrane more concave laterally  and tense. It prevent wide excursions of the ear ossicles and potential damage to the inner ear when exposed to loud sounds

          Functions of both muscles: damp high frequency vibrations 

Histological features of hard palate

Histology of hard palate :
 The hard palate is a thin horizontal bony plate of the skull, located in the roof of the mouth.
Formations:  It is formed by the palatine process of the maxilla and horizontal plate of palatine bone.

It has two surfaces:

1. nasal surface and 
2. oral surface 

functions : it is important for feeding and speech
 

Histology of nasal surface of hard palate:

1. It is lined by pseudo-stratified ciliated columnar epithelium.
2. This epithelium contains intraepithelial gland.
3. Sub-epithelial connective tissue contains glands, blood vessels and lymph vessels.
4.  The epithelium and the sub-epithelial connective tissue are collectively known as the mucoperiosteum, which is firmly attached to the bony shelf of the palate.

Histology of oral surface of hard palate 

Parts of oral surface of hard palate: 

1. Anteriorly fatty part 

2. Posteriorly glandular part   

 

The oral surface of hard palate  is covered by masticatory mucosa,  it is a specialized mucosa of oral cavity 

 

Masticatory mucosa :

It is found in the gingival (gums) and the hard palate. 
From superficial to deep it has three layers

1.      Lining epithelium: Keratinized stratified squamous epithelium and in some place parakeratinized

Keratinized epithelium of hard palate likes skin but stratum lucidum layer is absent.

Criteria of parakeratinized stratified squamous epithelium :

·         Superficial cells have nuclei like keratinized stratified squamous epithelium but nuclei are pyknotic (highly condensed) remain until the cell is exfoliated and

·         cytoplasm is not intensely stain by eosin

  Rete ridges are present in epithelium they are deep invagination of epithelium with

   subepithelial connective tissue  

2.      Lamina propria is formed by connective tissue contain dense collagen fibres, blood vessels and nerves. Hard palate's lamina propria  is also containing large deposits of adipose tissue at its anterior part and mucous gland at its posterior part.
3.  Reticular layer of dense connective tissue : Deep to lamina propria contain reticular fibre rich dense connective tissue which firmly bind the palatine mucosa to the periosteum.