Basic & Histological Anatomy

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

Organelles Involved in Protein Synthesis:
1. Ribosome
2. RER
3. Mitochondria

Microvilli is concerned with absorption.

Gap junctions abundant in Muscular tissue

Mitochondria are membrane enclosed organelles with arrays of enzymes specialized for aerobic respiration and production of ATPs. Hence it is called the power house of cell.

- Size: 0.5-1 um in diameter & up to 10 um in length

- Shape: Elongated/rod shaped

- Number: The number of mitochondria is related to the cell's energy needs: cells with a high- energy metabolism (eg, cardiac muscle, cells of some kidney tubules, hepatocytes etc.) have abundant mitochondria, whereas cells with a low-energy metabolism have few mitochondria.

- Mitochondria are absent in RBCs and terminal keratinocytes of skin.

- Mitochondrial matrix contains a small circular chromosome of DNA, ribosomes, mRNA, and tRNA, all with similarities to the corresponding bacterial components.

- Mitochondrial DNA is a small circular double helix DNA that contains 37 genes.
- Mitochondrial DNA is inherited from mother (ovum), as cytoplasm of sperm do not contribute to zygote.
- Due to mitochondrial DNA, mitochondria are self replicating.

- Mitochondria are highly plastic, rapidly changing shape, fusing with one another and dividing, and are moved through the cytoplasm along microtubules.

Barr body:
- Tightly coiled clump of chromatin mass (heterochromatin), genetically inactive
- It represents inactivated X chromosome.**
- During cell division Barr body disappears
- Number of Barr body is always 1 less than the number of X chromosome
- Female has 1 Barr body, male has no Barr body normally.
- Klinefilter syndrome : 47,XXY ; 1 Barr body

Periosteum is a layer of dense connective tissue on the outer surface of bone, bound to bone matrix by bundles of type I collagen called perforating (or Sharpey) fibers.

The genetic code is a series of codons by which DNA directs transcription of RNA and its translation into proteins

Properties of genetic code:
 Specificity
 Universality
 Redundant (degenerate)
 Non-overlapping
 Comma less

Intramembranous ossification, by which most flat bones begin to form, takes place within condensed sheets (“membranes”) of embryonic mesenchymal tissue. Most bones of the skull and jaws, as well as the scapula and clavicle, are formed embryonically by intramembranous ossification.

Hemophilia- X-linked recessive
Myotonic dystrophy, Osteogenesis imperfecta- Autosomal dominant

Examples of autosomal recessive disorders: 

Metabolic:
1. Homocystinuria/Alpha-1 antitrypsin deficiency
2. Cystic fibrosis
3. Phenylketonuria
4. Alkaptonuria
5. Wilson’s disease
6. Galactosemia
7. Lysosomal storage disease
8. Glycogen storage disease

Haematopoietic:
1. Thalassaemia
2. Sickle cell anaemia

Endocrine:
1. Congenital adrenal hyperplasia

Nervous: 
1. Neurogenic muscular atrophy
2. Friedrich’s ataxia
3. Spinal muscular atrophy

Skeletal: 
1. Some variants of Ehlers-Danlos syndrome

[Ref. Junquira 15th, 62]

1. Euchromatin:
- It is a partially condensed and less coiled 
- It is more active and lightly stained
- It is expressed during interphase
- Prominent in metabolically active cells
 
2. Heterochromatin:
- It is a condensed and more coiled 
- It is inactive and darkly stained (intensely basophilic in light microscope)
- It does not express during interphase
- Example: Sex chromatin (Barr body), chromatin in circulating lymphocyte

Events of cell cycle:
1. Mitosis (M phase)
2. Interphase: The long period between two mitosis division (the G1, S, and G2 phases) is  called interphase.
• G1 phase (pre-synthetic phase)
• S phase
• G­­­2 phase (post-synthetic phase)

G1 Phase:
- The period between mitosis and the beginning of DNA replication.
- The G1 phase, usually the longest and most variable part of the cycle.
- It is a period of active RNA and protein synthesis (RNA & regulatory proteins essential for DNA replication)
- Also in G1, the cell volume, reduced by half during mitosis, returns to its previous size.

S Phase:
- The S phase is characterized by DNA replication, histone synthesis, and the beginning of centrosome duplication.
- The cell now contains twice the normal amount of its DNA, that is - the (2n) amount of DNA is doubled (4n) in preparation for cell division.

G2 Phase:
- In the relatively short G2 phase, RNA and proteins essential for cell division are synthesized.

Other than intervertebral disc all are hyaline cartilage

Lysosomal enzymes:
The most common lysosomal enzymes are acid hydrolases such as
 Proteases
 Nucleases
 Phosphatase
 Lipase
 Phospholipases
 Sulfatases
 ß-glucuronidase

Enzymes of peroxisomes: Catalase, D-and L-amino oxidases, urate oxidase, hydroxyacid oxidase

Most tissues undergo cell turnover with slow cell division and cell death. Nerve tissue and cardiac muscle are exceptions because their differentiated cells cannot undergo mitosis.

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

***Microvilli has core of microfilaments.

Microtubules:
Microtubules are non-branching hollow tubules made up of tubulin proteins (∝ and ß tubulin) with a diameter of 25 nm.

Locations:
· Cilia
· Flagella
· Centrioles
. Mitotic spindle
· Elongating cell processes and
· Growing axons

Functions:
1. Movement of cilia, flagella (tail of sperm)
2. Intracellular transport of vesicles
3. In cell division, formation of mitotic spindle
4. Maintenance of cell shape

Fibroblasts are the most common cells in connective tissue proper, produce and maintain most of the tissue’s extracellular components. Fibroblasts synthesize and secrete collagen (the most abundant protein of the body) and elastin, which both form large fibers, as well as the GAGs, proteoglycans, and multiadhesive glycoproteins that comprise the ground substance.

Peroxisomes are spherical organelles enclosed by a single membrane and named for their enzymes producing and degrading hydrogen peroxide, H₂O₂

Enzymes of peroxisomes: Catalase, D-and L-amino oxidases, urate oxidase, hydroxyacid oxidase

Functions of peroxisome:
1. Peroxisomes contain oxidative enzymes that are required for amino acid oxidation and ß-oxidation of fatty acids.
2. Inracellular hydrogen peroxide H₂O₂ is eliminated by the enzyme catalase which is present in the peroxisomes.
3. Catalase also degrades several toxic molecules and drugs, particularly in liver and kidney peroxisomes

Functions of Golgi apparatus:
1. Post-translational modification of proteins:
Freshly synthesized proteins are transferred from RER to the Golgi apparatus. These proteins are modified by the Golgi apparatus. This is done by glycosylation, sulfation, phosphorylation, and limited proteolysis of proteins.
2. Packaging Enzymes for lysosomes and proteins for secretion
3. Storing of all materials for lysosomes, secretion, and incorporation into the plasma membrane.
4. Lysosome may be produced in the Golgi complex.
5. It is necessary for the synthesis of acrosome in the spermatozoa.

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

*** Normoblasts have nucleus, after this stage, they loss their nuclei to become reticulocytes, and the mature RBCs. 

Intercalated discs join the membrane of one cardiac cell with its neighbour and promote rapid conduction of depolarisation between cells.

Phagocytosis of ECM components and debris done by macrophage

Nucleolus:
Nucleolus is a highly basophilic spherical mass of heterochromatin in cells actively engaged in protein synthesis. The intense basophilia of nucleoli is due not to heterochromatin but to the presence of densely concentrated ribosomal RNA (rRNA).

Function of nucleolus: Ribosomal RNA (rRNA) synthesis

Capillaries have only an endothelium, with no subendothelial layer or other tunics.

Autosomal dominant disorders: 
Skeletal
1. Marfan syndrome
2. Osteogenesis imperfect
3. Achondroplasia
4. Ehlar Danlos Syndrome
Nervous
1. Huntington’s disease
2. Neurofibromatosis
3. Myotonic dystrophy
4. Tuberous sclerosis
Urinary
1. Polycystic kidney disease
Metabolic
1. Familial hypercholesterolemia
2. Acute intermittent porphyria
Gastrointestinal
1. Familial adenomatous polyposis coli
Haematopoeitic
1. Von Willebrand disease
2. Hereditary spherocytosis

Smooth endoplasmic reticulum is abundant in cells involved in lipid synthesis-
• Liver cells
• Cells of adrenal cortex
• Leydig cells of testis
• SER also appears in a specialized form, called sarcoplasmic reticulum, found in the striated muscle cells.

[Ref. Junqueira 15th] 

Lamina propria is a loose connective tissue

Adherent or anchoring junctions, formed by interacting proteins of the cadherin family, are points of strong attachment holding together cells of the epithelium.

Capillaries have only an endothelium, with no subendothelial layer or other tunics.

Microtubule provides structural support to astrocytes

Mitochondria have two membranes: a porous outer membrane encloses the intermembrane space and an inner membrane with many folds (cristae) enclosing a gel-like matrix.

Classification of glands based on nature of secretion:
1. Mucous glands- Secrete thick mucoid secretion called mucin.
Example: Goblet cells, sublingual salivary glands

2. Serous glands- Secrete a protein rich watery secretion.
Example: Exocrine pancreas, parotid glands, lacrimal gland, von Ebnar's gland in tongue.

3. Mixed glands- Which contain both mucous and serous cells and produce sero-mucous
secretion. Example: Submandibular salivary gland.

Microtubules are non branching hollow tubules made up of tubulin proteins (α and b tubulin) with a diameter of 25 nm

Locations:
• Cilia
• Flagella
• Centrioles
• Mitotic spindle
• Elongating cell processes and
• Growing axons

Functions:
1. Movement of cilia, flagella (tail of sperm)
2. Intracellular transport of vesicles
3. In cell division, formation of mitotic spindle
4. Maintenance of cell shape

[Ref. Junquira 15th, 43]