Cartilage lecture notes for written and viva examination

 Cartilage lecture notes for written and viva examination

It is a special form of connective tissue composed of chondrocytes and a highly specialized extracellular matrix which designed to support to regions of body that require rigidity and flexibility.

Functions of Cartilages:

• Articular cartilage form smooth surface for movement
• It makes shape of ear, nose
• Act as shock absorber in spine ( intervertebral discs)
• It more flexible than the bone, so it breaks less costal cartilage of thoracic cage, ear , nose
• During development of bone, cartilage forms the initial blueprint of the skeletal system before being replaced by bone (a process called endochondral ossification).
• It form framework for respiratory passage to prevent their collapse.

Components of cartilages:

Cells of cartilage: chondroblasts and chondrocytes

Extracellular matrix:

Fibres : collagen and elastic ( impart tensile strength and elasticity)

Ground substance contain hyaluronic acid , glycosaminoglycans and (chondroitin sulphate, keratan sulphate), glycoproteins (chondronectin).

Types of cartilage: (according to the number of cells and the nature of the matrix)  

1. Hyaline cartilage 2.Elastic cartilage 3. Fibrocartilage

 

Features	Hyaline cartilage	Elastic cartilage	Fibrocartilage
Distribution	Tracheo-bronchial cartilage, costal cartilage of rib and nasal cartilage, most of the laryngeal cartilage	Epiglottis, external ear and ear canal, auditory tube, some laryngeal cartilage( corniculate, cuneiform etc.)	Intervertebral discs and pubic symphysis, articular discs of temporo-mandibular, sternoclavicular joint, menisci of the knee joint
Function	Resistant to compression, provides cushioning and low friction surface for joint , structural support in respiratory system	Provides flexible support	Resist deformation under stress
Presence of perichondrium	Yes (except articular cartilage and epiphyseal plates)	Yes	No
Undergoes  calcification	Yes ( during endochondral bone formation )	No	Yes (during bone repair)
Cell types	Chondroblasts, chondrocytes	Chondroblasts, chondrocytes	Chondrocytes, fibroblasts
Chondrocyte in lacunae	Smaller compare to elastic cartilage arranged in isogenous group (2-8)	Larger compare to hyaline  cartilage and closely packed and arranged in isogenous group (2-4)	Small arrange in row parallel to bundles of collagen fibers
Extracellular matrix	Type II collagen fibrils Homogenous and basophilic	Type II collagen fibrils and elastic fibers	Type II & type I collagen fibers Eosinophilic
Slide identification	*Cartilaginous matrix: is homogeneous *Cells: Lacunae (ovoid space within the matrix) contain chondrocyte singly or isogenous groups *Perichondrium: surround the cartilage (if present within the slide then add this points)	*Cartilage matrix contain elastic fiber so it is not homogenous Lacunae (ovoid space within the matrix) contain chondrocyte singly or isogenous groups *Perichondrium surround the cartilage (if present within the slide then add this points)	Cartilaginous matrix: thick collagen fibres located between parallel rows of condrocytes *Cells: the chondrocytes are smaller than those of hyaline or elastic cartilage and they are arranged in  parallel rows between the bundles of  thick collagen fibers *Perichondrium: absent

 

Peculiarities of the cartilage:

1. Cartilages lack blood vessels, lymphatics and nerves.
2. Cartilage has a limited ability to heal and regenerate, primarily because of its avascular nature.
3. when matrix calcified the chondrocytes are die
4. cartilage cells grow by appositional and interstitial methods
5. Cartilages are supplied by diffusion of oxygen and nutrients through extracellular matrix from blood vessels in perichondrium /surrounding tissues/synovial fluid.
6. Extracellular matrix of cartilages is highly permeable.
7. Cartilages are usually surrounded by perichondrium (except articular cartilage and fibrocartilage)

Perichonrium

 it is a connective tissue membrane  that surrounds the hyaline and elastic cartilages.

         It has

(a)  An outer fibrous layer, is composed mostly of fibroblasts and collagen fibers, &

blood vessels  

(b)  A inner cellular or chondrogenic layer, is composed of chondroblast and   chondrogenic cells.

 This   layer helps in growth and repair of cartilage.

Cartilage which are covered by perichondrium:

1.     Hyaline cartilage (except hyaline cartilage of articular surfaces of a  joint, epiphyseal cartilage)

2.     Elastic cartilage

The characteristic features of Chondroblasts and chondrocytes

Chondrocytes and chondroblasts  are derived from mesenchymal cells.

Features of Chondroblasts

1. Immature and young cells of cartilage
2. Shape : oval shape with few processes
3. Location : Chondroblasts are typically found in the perichondrium, a layer of connective tissue surrounding most types of cartilage (excluding articular cartilage, fibrocartilage)
4. Chondroblasts are responsible for producing the extracellular matrix (ECM) of cartilage, which includes collagen fibers and proteoglycans
5. Chondroblasts are precursor cells that can differentiate into chondrocytes, the mature cells of cartilage
6. Chondroblasts contain a high density of organelles, such as the rough endoplasmic reticulum and Golgi apparatus, which are essential for the synthesis and secretion of proteins and other components of the extracellular matrix.
7. Chondroblasts play a central role in both appositional growth (growth in width) and interstitial growth (growth in length) of cartilage.

 

Features of chondrocytes

1. older and mature cells
2. Shape : rounded or spherical shape in the center part of cartilage and oval at the periphery
3. Location : Chondrocytes are found within small cavities called lacunae in the extracellular matrix (ECM) of cartilage singly or in isogenous groups..
4. Chondrocytes generally have a low rate of cell division and mitotic activity, contributing to the limited regenerative capacity of cartilage tissue.
5. Chondrocytes can sense changes in mechanical stress and respond by altering their production of extracellular matrix components.
6. Chondrocytes typically function in a low-oxygen environment because cartilage is avascular (lacks blood vessels).
7. Chondrocytes have some rough endoplasmic reticulum,golgi Apparatus, Lysosome which are involved in the degradation of cellular waste and  mitochondria, which provide energy for cellular activities, primarily through anaerobic metabolism due to the low oxygen environment of cartilage.

Growth of  cartilage

      Cartilage grows by two methods:

 

Interstitial growth: In this type of growth, newly generated chondrocytes deposit extracellular matrix while existing chondrocytes divide mitotically to produce new cartilage.

Appositional growth: The inner layer of perichondrium cells, also known as chondrogenic cells, divide and develop into chondroblasts during a process known as apogephalic growth. The matrix and freshly produced cells are introduced at the surface and periphery.

 

Appositional growth:  In this type of growth,  the inner layer of perichondrium cells ( chondrogenic cells) divide and differentiate into chondroblasts. The newly formed cells and matrix are added at the periphery/surface

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Confusing terminology trabeculae of bone , trabeculae of gland , trabecular sinuses , trabecular artery or vein

 Confusing terminology trabeculae of bone , trabeculae of gland , trabecular sinuses , trabecular artery or vein 

Trabeculae of glands

glands are surrounded by a strong connective tissue capsule, which has fibrous extensions within the gland which is known as trabeculae

Trabeculae or trabeculae of bone

they are the thin columns and plates of bone that create a spongy structure in a cancellous bone, which is located at the ends of long bones and in the pelvis, ribs, skull, and vertebrae.

Trabecular sinus

The trabecular sinuses are those sinuses that surrounding the trabeculae of the lymph node.

Trabecular arteries or vein

They are the name of the branches of the splenic artery after it passes into the trabeculae of the spleen

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periosteum vs endosteum

 periosteum vs endosteum 

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Periosteum	Endosteum
Location : external surface of bone except articular surface	Location : medullary cavity Compact bone facing marrow cavity Lined the trabeculae of spongy bone Haversian canal Volkmann’s canal
Formation : it is a connective tissue membrane formed by dense irregular connective tissue	Formation : it is formed by only one cell layer thick osteoprogenitor cells and little connective tissue
Histology:  it consists of an outer fibrous layer, and an inner cambium layer (or osteogenic layer). The fibrous layer is of dense irregular connective tissue, containing fibroblasts, while the cambium layer is highly cellular containing progenitor cells that develop into osteoblasts	Histology : Osteoprogenitor cells and bone-lining cells are difficult to distinguish at the microscopic level. They are both flattened in shape with elongated nuclei and indistinguishable cytoplasmic features. Because of their location within the bone cavities they are frequently called endosteal cells.

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Osteon vs osteoid : confusing term in skeletal system

 

Osteon vs  osteoid

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Osteon	Osteoid
An osteon, it is also known as a Haversian system which is a cylindrical structure found in compact bone tissue. It provides strength and support to the bone, and it also helps in the repair and remodeling of bone tissue. It is  typically develop in preexisting compact bone	Osteoid, it’s another meaning is ‘like bone’. it is defined as un-mineralized bone tissue and is a key structure in the development of mature mineralized bone

Summary of thyroid gland Gross anatomy histology embryology and clinical anatomy

 

 Summary of thyroid gland Gross anatomy histology embryology and clinical anatomy 

Thyroid gland, the largest endocrine gland of our body which is located in front of trachea at the lower part of neck.

 It lobes are extends from the oblique line of thyroid cartilage to the 5th-6th tracheal cartilage ring , isthmus extends from 2^nd to 4^th tracheal ring

Vertebral level : it lies opposite to the C5, C6, C7 and T1 vertebrae

Parts of thyroid gland

Thyroid gland is consists of two  lobes connected by isthmus.

A small pyramidal lobe may present occasionally which  extend upwards from the upper border of the isthmus, slightly to the left of the midline.

Sometimes this  pyramidal lobe is connected to the hyoid bone by a strong fibromuscular band called levator glandulae thyroideae (remnant of thyroglossal duct).

Dimensions of thyroid gland: Thyroid gland weighs approximately 25 gms. Each lobe of thyroid gland is 5 cm long, 3 cm wide and 3cm thick.

Capsule of thyroid gland

Thyroid gland is enclosed by two capsules

The inner capsule is also known as true capsule which is formed  by condensation of fibrous stroma of the gland.

An outer capsule is known as false capsule which is formed by the pre-tracheal layer of the deep cervical fascia. It is thin along the posterior border of the lobes and thick on the medial surface of the lobes.

The pre-tracheal fascia is attached above to the body of the hyoid bone  and oblique line of the thyroid cartilage and  after enclosing the thyroid gland it descends down in front of the trachea and blends with fibrous pericardium.

On the medial surface of thyroid lobe, this capsule thickens to form the suspensory ligament of Berry, which attaches the thyroid lobes to the cricoid cartilage.

Gross features and relation of thyroid gland

Each lobe of thyroid gland has following relations:

Apex/Upper lobe: it  is sandwiched between the sternothyroid  and inferior constrictor muscle of pharynx. Superior thyroid artery, branch of external carotid artery and external laryngeal nerve diverge from each other close to upper pole. The artery is superficial and nerve lies deep to the upper pole.

Base/Lower pole: it is related to inferior thyroid artery and recurrent laryngeal nerve.

Lateral (superficial) surface is related to the following muscles:

Sternohyoid, sternothyroid, superior belly of omohyoid and anterior border of sternocleidomastoid.

Medial surface is related to:

Two tubes– trachea and oesophagus

Two muscles – inferior constrictor and cricothyroid

Two cartilages – cricoid and thyroid

Two nerves – external laryngeal and recurrent laryngeal

Posterolateral surface is related to:

Carotid sheath and its contents (common carotid artery, internal jugular vein and vagus nerve). Ansa cervicalis is embedded in the anterior aspect of carotid sheath.

Anterior border is thin and is related to anterior branch of superior thyroid artery.

Posterior border is thick and rounded and is related to parathyroid glands and anastomosis between superior and inferior thyroid arteries.

Isthmus of thyroid gland has following relations:

Anterior surface  is related to sternothyroid and sternohyoid muscles and anterior jugular veins.

Posterior surface is related to 2nd -4th tracheal rings.

Superior border  is related to anastomosis between anterior branches of superior thyroid arteries.

Inferior border is related to inferior thyroid veins  that leave isthmus along this border.

Blood supply of thyroid gland

Thyroid gland is highly vascular and is supplied by the following arteries.

Superior thyroid artery:

It is a branch of external carotid artery, which descends down to the upper pole of lateral lobe of thyroid gland with external laryngeal nerve (the nerve diverges from the artery near the upper pole).

At the apex of lateral lobe, it divides into anterior and posterior branches.

Anterior branch descends along anterior border and anastomoses with the its fellow of opposite side along the superior border of isthmus.

Posterior branch descends along posterior border and anastomoses with the ascending branch of inferior thyroid artery.

It supplies upper 2/3rd of the lobe and upper ½ of the isthmus.

Inferior thyroid artery:

It is a branch of thyrocervical trunk.

It first runs upwards, then passes behind the carotid sheath and descends to reach the base of thyroid gland (forms a loop with convexity upwards).

Near the base (lower pole) the artery is very close to recurrent laryngeal nerve.

It supplies the lower 1/3rd of the lobe and lower half of the isthmus.

Thyroideaima artery: It is not always present. It is a branch of brachiocephalic trunk or arch of aorta. Ascends in front of trachea to enter the isthmus.

Venous drainage of thyroid gland

It occurs mainly via 3 pairs of veins. All thyroid veins do not accompany arteries. The three pairs of veins arise from the venous plexus present deep to the true capsule of thyroid gland.

Superior thyroid veins emerge at the upper pole of thyroid gland and terminates in internal jugular vein.

Middle thyroid veins are short veins, emerges at the middle of the lobe of thyroid gland and drains in internal jugular vein.

Inferior thyroid veins emerge at the lower border of isthmus, descend in front of trachea (right and left vein communicate and form plexus in front of trachea) to drain into left brachiocephalic vein.

Vein of Kocher: Sometimes a fourth vein (Vein of Kocher) emerges between the middle and inferior thyroid veins which drains into internal jugular vein.

Lymphatic drainage of thyroid gland

Lymphatics from the upper part of thyroid gland drain into pre-laryngeal and upper deep cervical lymph nodes. From the lower part of thyroid gland, the lymphatics drain into pretracheal, paratracheal and lower deep cervical lymph nodes.

Development of thyroid gland

It  is the first of the body's endocrine glands to develop, on approximately the 24th day of intra uterine life . it is originates from two source : the primitive pharynx and the neural crest.

Stroma and follicular cells are developed from primitive pharynx and parafollicular cell develops from neural crest cells.

 

The thyroid gland forms as a proliferation of endodermal epithelial cells on the median surface of the developing pharyngeal floor. The site of this development lies between 2 structures which developed tongue, the tuberculum impar and the copula, and it is known as the foramen cecum.

This embryonic swelling develops from the first pharyngeal arch and occurs midline on the floor of the developing pharynx, eventually helping form the tongue as the two lateral lingual swellings overgrow it.

 

The foramen cecum begins rostral to the copula, also known as the hypobranchial eminence. This median embryologic swelling consists of mesoderm that arises from the second pharyngeal pouch (although the third and fourth pouches are also involved). The thyroid gland, therefore, originates from between the first and second pouches.

 

The initial thyroid precursor, the thyroid primordium, starts as a simple midline thickening and develops to form the thyroid diverticulum. This structure is initially hollow, although it later solidifies and becomes bilobed. The stem usually has a lumen, the thyroglossal duct, that does not descend into the lateral lobes. The two  lobes are located on either side of the midline and are connected via an isthmus

Histology of Thyroid gland

1.      Thyroid follicle is lined by simple cuboidal epithelium

2.     Thyroid follicles are filled with colloid.

3.     Thyroid follicle is formed by  Follicular cells and parafollicular cells

 

Clinical anatomy of thyroid gland

Why during deglutition or swallowing, thyroid swellings rise and fall.

 Once the thyroid gland is encased, the pretracheal fascia connects to the hyoid bone's body and the thyroid cartilage's oblique lines. It thickens on the thyroid lobe's medial surface to produce the Berry suspensory ligament, which joins the thyroid gland's lobe to the cricoid cartilage. Consequently, during deglutition, when the larynx and pharynx are lifted due to the contraction of the pharynx's longitudinal muscles linked to the posterior border of the thyroid cartilage, the thyroid gland also moves up and down. This aids in separating the enlargement of the thyroid from other neck swellings.

Why thyroid gland is removed along with its true capsule?

The venous plexus is situated deep into the true capsule in the case of the thyroid gland. Thus, during a thyroidectomy, the thyroid gland and true capsule are removed in order to prevent bleeding. However, in the case of the prostate gland, the venous plexus is between the genuine and false capsules; as a result, when the prostate gland is surgically removed (prostatectomy), both capsules are left behind.

Why superior thyroid artery is ligated close to thyroid gland?

The superior thyroid artery is located in close proximity to the proximal portion of the external laryngeal nerve, and it diverges close to the lateral lobe apex (the nerve is deep to the apex, while the artery is superficial). To prevent damage to the external laryngeal nerve, the superior thyroid artery during a thyroidectomy should be clamped near the apex.

Why Inferior thyroid artery is ligated away from the thyroid gland.

Near the base or lower pole of the thyroid gland, the inferior thyroid artery is located extremely close to the recurrent laryngeal nerve. To prevent damage to the recurrent laryngeal nerve, the thyroidectomy site should be ligated away from the thyroid gland's inferior pole.

Goitre

"Goitre" is the term used to describe thyroid gland hypertrophy. Iodine shortage in the diet (lower levels of T3 and T4) causes endemic goiter. These goiters exhibit hypothyroidism symptoms and indicators.Excess T3 and T4 secretion causes toxic goiters, also known as thyrotoxicosis, which manifests clinically as elevated BMR, tremors, and tachycardia. Thyroid enlargement often grows either downward or backward. Individuals with big goitres exhibit the typical signs and symptoms of

Dysphonia, or voice hoarseness

Dysnoea, or trouble breathing

Dysphagia, or trouble swallowing

Retinopathy and Lymphoedema

Thyroid hypofunction in adults is referred to as myxedema, and in newborns and children as cretinism.

Partial Thyroidectomy

In partial thyroidectomy the posterior part of thyroid lobes are left behind to avoid removal of parathyroid glands which otherwise may result in tetany.

Epidermis of skin : microscopic and clinical anatomy

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Epidermis of skin : microscopic and clinical anatomy 

Skin : It has two  layers  

1.      Epidermis

2.     Dermis

Sometimes, hypodermis consider as third layer of skin contain subcutaneous fat.

Epidermis

It  is the superficial layer of skin which is formed by  keratinized stratified squamous epithelium.

Cells of epidermis:  It is composed of four cell types:

1.      Keratinocytes,

2.     Melanocytes,

3.     Langerhans cells, and

4.     Merkel cells.

The keratinocytes are arranged in five layers, and the remaining three cell types are interspersed between them .

 Five layers of the epidermis: deep to superficial

1. Stratum Basale :

A single layer of cuboidal to columnar cells that stand on the basement membrane. This is a region of cell division.

It also contains melanocytes and Merkel cells.

2. Stratum Spinosum: it is composed by many layers of polyhedral prickle cells bearing intercellular bridges. Mitotic activity is also present.

It also contains Langerhans cells and processes of melanocytes.

3. Stratum Granulosum : it is composed by flattened cells which contain keratohyalin granules.

It is absent as a distinct layer in thin skin.

4. Stratum Lucidum A thin, translucent layer that is also absent in thin skin.

5. Stratum Corneum it is composed of squamous cells packed with keratin. Superfi cial squamous cells  are desquamated.

 

        Location of skin cells and functions

Difference between location, functions & development of different skin cells

Cells of skin	Location	Functions	Development
Keratinocytes	New skin cells develop at the bottom layer of your epidermis (stratum basale) and travel up through the other layers as they get older.	It forms barrier against environmental damage by heat, UV radiation, dehydration, pathogenic bacteria, fungi, parasites, and viruses.	Surface ectoderm
Melanocytes	Stratum basale	Melanocytes are well known for their role in skin pigmentation, and their ability to produce and distribute melanin has been studied extensively	Neural crest
Langerhans cells	Stratum spinosum	These cells act as the outermost guard of the cutaneous immune system and are likely to induce the first reactions against pathogens encountered via the skin	Fetal Langerhans cells from Primitive yolk sac in fetal life , in adult Langerhans cells  from fetal monocytes
Merkel cells	Stratum basale	It is also known as tactile epithelial cells, which is an  oval-shaped mechanoreceptors essential for light touch sensation	Surface ectoderm

Keratinocytes, reach the outermost layer of your epidermis after about a month, where the skin cells shed from your body as new cells develop at the bottom layer.

Albinism

 It is a congenital disorder characterized by the complete or partial absence of melanin pigmentation in the skin, hair,  iris of eye, and eyelashes.

 It is an autosomal recessive/X -linked disorder. 

 Although the melanocytes are present, but genetic mutation results in lack of tyrosinase enzyme, which catalyzes the production of melanin from tyrosine.

People with albinism have skin that is very sensitive to light and sun. Sunburn is one of the most serious complications of albinism.

This allows light to shine through the irises and makes the eyes extremely sensitive to bright light.

Vitiligo

 It is s a clinical condition with presence of spots without melanin in the skin, which occurs due to partial or complete absence of melanocytes.

Carotid triangle of neck

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Carotid triangle

Anterior triangle of neck contains four triangles; Carotid triangle is one of the subdivisions of it. It name occurs according to the content of it. It contains all the 3 carotid arteries, viz. common carotid, internal carotid and external carotid.

Boundary:

Posteriorly: Anterior border of sternocleidomastoid (SCM) muscle

Superiorly: Posterior belly of digastric and stylohyoid muscle

Antero-inferiorly: Superior belly of omo-hyoid muscle

Roof is covered  by the investing layer of deep cervical fascia.

Contents of carotid triangle

Arteries: 

1.    Common carotid artery

2.    Internal carotid artery

3.    External carotid arteries: origin of five branches of external carotid artery 

·         Superior thyroid artery

·         Ascending pharyngeal artery

·         Occipital, lingual and

·         Facial arteries.

Veins: 

·         Internal jugular vein and its tributaries : common facial, lingual, pharyngeal, superior thyroid, middle thyroid veins. 

Nerves:  Last three cranial nerves

1.     Vagus nerve

2.    Hypoglossal nerve

3.    spinal accessory,

4.     ansa cervicalis and

5.    cervical part of the sympathetic chain.

·         Lymph nodes: Deep cervical lymph nodes.

·         Others: Carotid sinus and carotid body.