Basic & Histological Anatomy

In the upper extremity, shoulder and wrists ends of the bones are the growing ends. In the lower extremity, knee ends of femur, tibia, fibula are the growing ends.

Type III collagen produces a network of delicate reticular fibers, which stain very dark with silver stains and are abundant in immune and lymphoid tissues.

Smooth muscle fibers are individual small, fusiform (tapering) cells, linked by numerous gap junctions.Thin and thick filaments in smooth muscle fibers do not form sarcomeres, and no striations are present. Branching is absent.

Trachea is lined by Ciliated pseudostratified columnar epithelium

Explanation-
Post translational modification occurs in-ribosome, RER and Golgi complex.

Zonulae occludens is another name of Gap junctions

-Nucleus is situated at the periphery in case of yellow fat.
-Yellow fat is unilocular. Brown fat is multilocular.

Foetal skeleton is a hyaline cartilage

[Ref. Junqueira 15th, 89]

Ribosome lies outside nucleus in the cytoplasm.

Unique transitional epithelium or urothelium lines much of the urinary tract, extending from the kidneys to the proximal part of the urethra, and is characterized by a superficial layer of large, dome-like cells sometimes called umbrella cells.

Gap junctions (Nexus) permit the exchange between cells of molecules. Signaling molecules such as some hormones, cAMP and cGMP and ions can move through gap junctions, causing the cells in many tissues to act in a coordinated manner. Such as-the heart’s coordinated beats.

Sweat glands: Stratified cuboidal
Mesothelium: Simple squamous
Fallopian tube: Ciliated columnar

Simple cuboidal epithelium is present in: 
1. Lining epithelium of thyroid follicles
2. Smaller ducts of exocrine glands
3. Covering of the ovary (germinal epithelium)
4. Choroid plexus
5. Inner surface of lens of eyeball
6. Pigmented cell layer of retina
7. Duct of Bartholin gland
8. Some part of tubules in kidney (DCT) Covering, secretion

Functions of mitochondria:
1. Production of ATP by aerobic respiration
2. Mitochondrial DNA takes part in RNA & protein synthesis
3. Role in cellular catabolism by apoptosis (programmed cell death)
4. Mitochondria contains enzymes that take part in-
   a. Respiratory chain or electron transport
   b. Oxidative phosphorylation
   c. Krebs/citric acid cycle
   d. β-oxidation of fatty acid
   e. Ketogenesis

Inner mitochondrial membrane shows long infoldings called cristae (for increasing surface area).
The lipid bilayer of the inner membrane contains unusual phospholipids and is highly impermeable to ions.
Inner mitochondrial membrane is a site for oxidative phosphorylation, respiratory (electron transport) chain, and ATP synthesis.

[Ref. Junquiera 15th, 39]

Aortic opening of diaphragm at the level of T12

Osteocytes (Gr. osteon, bone + kytos, cell), which are found in cavities (lacunae) between bone matrix layers (lamellae), with cytoplasmic processes in small canaliculi (L. canalis, canal) that extend into the matrix

Reference: Junqueira’s Basic Histology; 14th Edition; Page-370

Deep to the capsule the lens is covered on its anterior surface by a lens epithelium. The cells of the epithelium are cuboidal. However, towards the periphery of the lens the cells become progressively longer. Ultimately, they are converted into long fibres that form the substance of the lens.

Functions of SER:
1. Synthesis of lipid: SER is the main site for synthesis of lipid
2. Carbohydrate metabolism
3. Synthesis of phospholipids
4. Detoxification of potentially harmful exogenous molecules such as alcohol & barbiturates in liver
5. Synthesis of steroid hormones
6. Synthesis & storage of cholesterol
7. Participate in contraction process in muscle cells (sarcoplasmic reticulum)

Functions of RER:
1. Protein synthesis: Site for translation (mRNA -> protein)
· Membrane associated proteins
· Proteins of membranous organelles
. Proteins to be secreted by exocytosis
2. Initial glycosylation of glycoprotein
3. Post-translational modification of protein
4. Assembly of multichain proteins
5. Checkpoint: RER destroys defective proteins

The processes of astrocytes are united to those of other astrocytes through gap junctions. Astrocytes communicate with one another through calcium channels. Such communication plays a role in regulation of synaptic activity and in the metabolisms of neurotransmitters and neuromodulators.

Except rich blood supply all are the criteria of white fibers

Smooth ER is the site of Lipid synthesis

Myofibrils are the structural and functional subunits of muscle fiber. Myofibrils are arranged longitudinally in the muscle fiber and runs in the entire length of muscle fiber.

Sarcomere is the structural & functional unit of myofibrils. 

Transitional epithelium prevents urine from leaking of the bladder due to Tight junction

Nestin is found in some stem and embryonic cells. Rests of them are true.

Microtubule, microfilament & intermediate tubule are cytoskeleton of cell

The centromeres also move away from the centre, pulling along the remainder of the chromosome during Anaphase.

* The basic structural unit of chromatin is the nucleosome.
Nucleosomes are composed of  DNA wrapped around a set of eight histone proteins. 

* Gene, the functional unit of DNA, is the unit of inheritance.

* The nucleotides are the basic structural units of the DNA.
• Nitrogen base + sugar = Nucleoside
• Nucleoside + phosphate group = Nucleotide
• Nucleotide polymer = Nucleic acid (DNA/RNA)

Ovarian cortex is covered by the germinal epithelium which is made up of a single layer of cuboidal cells in younger age. 

Chromatid is formed during Prophase

Cytoplasmic organelles Involved in Protein Synthesis (Translation):
1. Ribosome
2. RER
3. Mitochondria

Post-translational Modification of Protein Occurs in:
1. Golgi apparatus
2. Ribosome
3. RER

Osteoclast helps in bone remodelling by bone resorption activity.

The cribriform plate of the ethmoid bone has many foramina through which pass olfactory nerves that transmit sensory information from inhaled air to the olfactory bulbs.

The substance of the tongue is made up chiefly of skeletal muscle supported by connective tissue. The muscle is arranged in bundles that run in vertical, transverse and longitudinal directions. This arrangement of muscle permits intricate movements of the tongue associated with the chewing and swallowing of food, and those necessary for speech.

A. Prophase I: It lasts for a long time and is subdivided into the following 5 phases:

1. Leptotene : Individual chromosomes, composed of two chromatids joined at the centromere, are visible as long strands in the nucleus.

2. Zygotene: Homologous chromosomes are arranged in pairs lengthwise. This process is called synapsis or conjugation.

3. Pachytene: The two chromosomes together constitute a bivalent. A bivalent contains four chromatids in it, forming a tetrad. The two central chromatids become coiled over each other, so that they cross at a number of points (chiasmata). This is called crossing over. 

4. Diplotene: Chromosomes continue to condense and then begin to separate, revealing chiasmata.

5. Diakinesis: The homologous centromeres pull apart and the chromosomes are separated. Meanwhile the nucleolus disappears, as does the nuclear membrane, freeing the chromosomes into the cytoplasm.

Stages of Mitosis:

1. Prophase: 
- The nucleolus disappears.
- The chromatins become coiled. They condense, shorten, and thicken into discrete chromosomes.
- The microtubules of the mitotic spindle appear between the two centrosomes.

2. Metaphase:
- Chromosomes migrate to the equatorial plane of the cell due to the activity of microtubules.
- Each chromosome divides longitudinally to form two chromosomes called sister chromatids.
- The chromatids attach to the microtubules of the mitotic spindle at centromere

3. Anaphase:
- The sister chromatids of each chromosome separate from each other and migrate toward the opposite poles of the cell.
- The centromeres also move away from the centre, pulling along the remainder of the chromosome.

4. Telophase:
- Nucleoli reappear in the daughter cells.
- The chromosomes become less distinct and a new nuclear envelope appears around each daughter chromosomes.
- A constriction develops at the equatorial plane of the parent cell and progresses until the cytoplasm and its organelles are divided in two.
- Formation of a new plasma membrane between the two portions of the dividing cell completes the two new cells, termed daughter cells.

1. Intramembranous ossification:
Involves direct conversion of mesenchymal tissue to bone. Bones produced by this process are called membranous (flat) bones. 
Examples: Bones of cranial vault, facial bones.

2. Endochondral (cartilaginous) ossification
Involves conversion of mesenchyme to hyaline cartilage that later gets replaced by bone.
Examples: All long bones (except clavicle), base of skull, vertebrae & ribs are formed by cartilaginous ossification. 

Uniaxial- elbow
Biaxial- wrist
Multiaxial- shoulder/hip

Visceral striated muscles:
These are microscopically identical to the skeletal muscles, but they are confined to the viscera such as tongue, pharynx, peripheral part of the  diaphragm, and upper two third of esophagus.

The first meiotic division reduces the chromosome number (Reductional division), but the DNA amount is unchanged (2n)

The second meiotic division reduces the DNA amount (n), but the chromosome number is unchanged (Equatorial division)

Posttranslational modifications of proteins take place in Golgi complex

RBC has no mitochondria

Plasma Membrane: 

Thickness: 7.5 to 10nm 

Composition: It is composed of 
a.Protein -55% 
b. Lipids: 42% 
  ✓ Phospholipids -25% 
  ✓ Cholesterol - 13% 
  ✓ Other lipids- 4% 
c. Oligosaccharides -3%

Features of epithelium:
- Epithelial tissues are composed of closely aggregated polyhedral cells adhering strongly to one another and to a thin layer of extracellular matrix (ECM).
- The forms and dimensions of epithelial cells range from high columnar to cuboidal to low squamous cells. Epithelial cell nuclei vary in shape corresponding roughly to the cell shape.
- Epithelium is an avascular structure. It receives nutrition by diffusion.
- The epithelia have got nerve supply
- Epithelial cells rest on basement membrane. 
- Epithelial cells show various types of junctions with adjacent cells and basement membrane.
- Epithelial cells isolate deeper structures from surface environment.
- Epithelial cells show surface modifications as per functional need. 
- Epithelial cells undergo mitosis and can regenerate damaged portion.
- Epithelium is derived from all three germ layers.
- Epithelial cells generally show polarity. 

Protein synthesis occurs in-ribosome, RER and mitochondria.

Autophagy is the function of lysosome.

Lysosomes can digest material into the cell from its environment by phagocytosis. Hence they are known as the suicidal bags of the cell.

Uniaxial- elbow
Biaxial- wrist
Multiaxial- shoulder/hip

Functions of centriole/centrosome:
1. Centrosome initiate formation of microtubules.
2. Centrosome forms mitotic spindle.
3. Centrosome provides basal bodies for cilia and flagella.
4. Centrioles self-replicate just before cell division.

About 50% of the dry weight of bone matrix is inorganic materials. Calcium hydroxyapatite is most abundant, but bicarbonate, citrate, magnesium, potassium, and sodium ions are also found. Significant quantities of noncrystalline calcium phosphate are also present. The surface of hydroxyapatite crystals is hydrated, facilitating the exchange of ions between the mineral and body fluids.

Most of the cell contain single nucleus except
– RBCs and platelets do not have nuclei
– Striated muscle cells are multinucleated
– Few hepatocytes and transitional epithelial cells are binucleated