NEET MDS Lessons
Anatomy
Muscles of the Tongue
- The tongue is divided into halves by a medial fibrous lingual septum that lies deep to the medial groove.
- In each half of the tongue there are four extrinsic and four intrinsic muscles.
- The lingual muscles are all supplied by the hypoglossal nerve (CN XII).
- The only exception is palatoglossus, which is supplied by the pharyngeal branch of the vagus nerve, via the pharyngeal plexus.
Extrinsic Muscles of the Tongue
The Genioglossus Muscle
- This is a bulky, fan-shaped muscle that contributes to most of the bulk of the tongue.
- It arises from a short tendon from the genial tubercle (mental spine) of the mandible.
- It fans out as it enters the tongue inferiorly and its fibres attach to the entire dorsum of the tongue.
- Its most inferior fibres insert into the body of the hyoid bone.
- The genioglossus muscle depresses the tongue and its posterior part protrudes it.
The Hyoglossus Muscle
- This is a thin, quadrilateral muscle.
- It arises from the body and greater horn of the hyoid bone and passes superoanteriorly to insert into the side and inferior aspect of the tongue.
- It depresses the tongue, pulling its sides inferiorly; it also aids in retrusion of the tongue.
The Styloglossus Muscle
- This small, short muscle arises from the anterior border of the styloid process near its tip and from the stylohyoid ligament.
- It passes inferoanteriorly to insert into the side and inferior aspect of the tongue.
- The styloglossus retrudes the tongue and curls its sides to create a trough during swallowing.
The Palatopharyngeus Muscle
- Superior attachment: hard palate and palatine aponeurosis.
- Inferior attachment: lateral wall of pharynx.
- Innervation: cranial part of accessory nerve (CN XI) through the pharyngeal branch of vagus (CN X) via the pharyngeal plexus.
- This thin, flat muscle is covered with mucous membrane to form the palatopharyngeal arch.
- It passes posteroinferiorly in this arch.
- This muscle tenses the soft palate and pulls the walls of the pharynx superiorly, anteriorly and medially during swallowing.
Intrinsic Muscles of the Tongue
The Superior Longitudinal Muscle of the Tongue
- The muscle forms a thin layer deep to the mucous membrane on the dorsum of the tongue, running from its tip to its root.
- It arises from the submucosal fibrous layer and the lingual septum and inserts mainly into the mucous membrane.
- This muscle curls the tip and sides of the tongue superiorly, making the dorsum of the tongue concave.
The Inferior Longitudinal Muscle of the Tongue
- This muscle consists of a narrow band close to the inferior surface of the tongue.
- It extends from the tip to the root of the tongue.
- Some of its fibres attach to the hyoid bone.
- This muscle curls the tip of the tongue inferiorly, making the dorsum of the tongue convex.
The Transverse Muscle of the Tongue
- This muscle lies deep to the superior longitudinal muscle.
- It arises from the fibrous lingual septum and runs lateral to its right and left margins.
- Its fibres are inserted into the submucosal fibrous tissue.
- The transverse muscle narrows and increases the height of the tongue.
The Vertical Muscle of the Tongue
- This muscle runs inferolaterally from the dorsum of the tongue.
- It flattens and broadens the tongue.
- Acting with the transverse muscle, it increases the length of the tongue.
ENDOCRINE
Endocrine glands have no ducts
They secrete into the blood from where the secretion (hormone) reaches a target cell
The following is a list of endocrine glands:
- Hypophysis
- Thyroid
- Parathyroid
- Adrenals
- Islets of Langerhans
- Pineal
- Gonads
Hypophysis: Develops from oral ectoderm and nerve tissue, The oral part forms an upgrowth with an invagination (Rathke's pouch) The nervous part grows from the floor of the diencephalon - staying intact .The oral part separates from the mouth
Ectoderm – adenohypophysis - pars tuberalis
- pars distalis
- pars intermedia .
Diencephalon – neurohypophysis - pars nervosa .
- infundibulum
- median eminence
Rathke's pouch remains as Rathke's cysts
Pars Distalis: Forms 75% of the gland, The cells form cords, with fenestrated capillaries in-between
2 Cell types:
Chromophobes : 50% of the cells, do not stain lie in groups, they are resting chromophils
granules have been used
Chromophils: Stain
They can be subdivided according to their reaction with different stains
Acidophils (40%) :Cells have acidophilic granules in their cytoplasm. The cells are secretory.
They have a well developed EPR and Golgi apparatus.They have secretory granules.
subdivided into:
- Somatotropin cells: secrete somatotropin (growth hormone)
- Mammotropic cells: secrete prolactin
Basophils (10%) : These cells have basophilic granules in their cytoplasm and can be subdivided into:
Thyrotropin cells: secrete thyroid - stimulating hormone (TSH)
Corticotrophin cells: secrete adrenocorticotropic (ACTH)
Gonadotropic cells: secrete two hormones: Follicle stimulating hormone (FSH):
Stimulate follicle development and spermatogenesis
Luteinizing hormone (LH): Stimulate the formation of the corpus luteum and Leydig cells
Pars Tuberalis: Cells lie around the infundibulum . It is continuous with the pars distalis
Cells are cuboidal with no granules. Their function is unknown
Pars Intermedia: Poorly developed in the human. Follicles lined by cuboidal cells and filled with colloid are found Known as Rathke's cysts .There are also a few big basophilic cells
Their function is unknown
Pars Nervosa: Contains: - myelinated axons pituicytes, blood vessels
Axons:
The cell bodies of the axons lie in the supra-optic and paraventricular nuclei of the hypothalamus .From the cell bodies the axons go through the infundibulum forming the hypothalamohypophyseal tract to end in the pars nervosa
The axons have dilated blind endings filled with hormones (Herring bodies) coming from the cell bodies.
Two hormones are secreted:
Oxytoxin: - Cause contraction of the uterus
- Cause contraction of the myoepithelial cells of the milkgland
- The hormone is secreted by the paraventricular nuclei
Vasopressin :- Cause reabsorption of H2O in the kidney (also known as antidiuretic hormone ADH) The hormone is secreted by the supraoptic nuclei. A hypophyseal portal system exists
A primary capillary plexus of fenestrated capillaries form around the median eminence. Inhibitory hormones are secreted into these capillaries
The capillaries rejoin to form the portal veins that traverse the pituitary stalk
The portal veins break up into a secondary capillary plexus which lies close to the cells of the adenohypophysis
This portal system regulates the functions of the anterior pituitary function.
Pineal
Surrounded by pia which sends septae into the gland Cells are mainly pinealocytes and astroglial cells
Pinealocytes:Irregular shaped cells. with processes ending in flattened dilatations
Have a well developed smooth surfaced endoplasmic reticulum, Also a rough EPR not well developed, Lots of microtubules
Astroglial Cells: Elongated nucleus, Cells have long processes, They perform a supporting function
Hormones:
Melatonin - secreted during the night .suppress the onset of puberty
Serotonin - secreted during the day
In humans the pineal form concretions of calcified material called brain sand
Brain sand vary in size and number with age and is visible on X-rays
Mast cells are also found in the pineal and cause the high histamine contend of the gland
THYROID
Has a CT capsule that sends septae into the gland to divide it up into incomplete lobes and lobules. In the lobules are follicles, Follicles vary in size, They are surrounded by surrounded by reticular CT and capillaries
Cells of the Follicle:
Follicular Cells : Single layer of cuboidal cells, lie around the colloid, Follicular cells can become columnar when very active, Nucleus central, EPR has wide cisternae ,Golgi present
- microvilli on the free surface
Parafollicular Cells: Also known as C-cells, Form part of the epithelium or form clusters between the follicles
- They never come into contact with the colloid
- Larger and stain less intensely than the follicular cells, Form 2% of the cells, Secrete calcitonin
Hormones: Thyroxine and thyriodothyronine - stimulate the metabolic rate, Calcitonin - lower the blood calcium
Parathyroid:
Has a CT capsule which send septae into the gland to divide it up into incomplete lobules, The CT contains fat which increase with age - may eventually be 50% of the gland, Glandular cells are arranged in cords
Glandular Cells:
Chief Cells: Small cells so their nuclei lie close together, Rich in glycogen, Biggest omponent
Secrete parathyroid hormone - essential for life
Oxyphil Cells:Develop at puberty, Bigger than the chief cells, Nuclei are smaller, Acidophilic
Hormones:
Parathyroid hormone - regulate calcium and phosphate ions in the blood
ADRENAL
- Thick CT capsule that do not send septae into the gland
Cortex:
Has 3 layers
Zona glomerulosa: 15% of the cortex, Directly under the capsule, Cells are columnar or pyramidal, Arranged in small groups or clusters, Wide fenestrated capillaries surround the clusters, Cells have an extensive smooth EPR
Zona Fasciculata: 78% of the cortex, Cells are arranged in cords ,1 to 2 cells wide perpendicular to the surface, Sinusoids lie between the cords, Cells are polyhedral with a central nucleus which is bigger than that of the zona glomerulosa, Lots of lipid in the cytoplasm cause the cells to stain lightly, Cells have a well developed smooth and rough EPR
The mitochondria in the cells are round with tubular or vesicular cristae
Zona Reticularis: 7% of the cortex, Cells form a network of cords with wide capillaries in-between The mitochondria in the cells are more ofte6n elongated than that in the zona fasciculate Degenerating cells with pyknotic nuclei are found. Cells contain numerous large lipofuscin granules. Cells of the cortex do not store their secretions but form and secrete on demand.
Hormones:
3 Groups:
Glucocorticoids (e.g. cortisol) - have an affection on carbohydrate metabolism
Mineralocorticoid (e.g. aldosterone) - control water and electrolyte balans
Androgens (e.g. dehyroepiandrosterone) - not very important
Medulla:
- Cells are big and oval and lie in groups and cords around bloodvessels
- Oxidising agents stain the granules in these cells brown - cells are therefore called chromaffin cells
- Granules contain adrenaline or non-adrernalin
- A few parasympathetic ganglion cells are also present
Hormones:
- Adrenaline - increase oxygen uptake
- increase blood pressure
- Noradrenaline - maintain blood pressure
Blood Supply:
- Blood vessel enter from the capsule to form the wide capillaries
- They flow into venules that form a central vein
- Between the endothelium of the capillaries and the glandular cells there is a subendothelial
- space.
- The glandular cells have microvilli protruding into this space.
ISLES OF LANGERHANS
Endocrine part of pancreas. The isles are round clusters in the exocrine tissue
- 100 - 200 µm
Islands consists of slightly stained polygonal or rounded cells, The cells are separated by fenestrated capillaries
- Autonomic nerve fibres innervate the blood vessels and the island cells
- 4 different cell types have been described
A cells : 20% of the cells, Bigger than B cells, Lie at the periphery, Have secretory granules ,Contain glucagon
B cells : 80%, Lie in the centre of the island, The cells are small with granules which are crystals, Granules are formed by insulin
D cells : Not numerous, Membrane bound granules, Store somatostatin (inhibit somatotropin)
F cells : Have membrane bound granules, Store pancreatic polypeptide, The hormone inhibits pancreatic exocrine secretion
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| Motor Innervation | All muscles by hypoglossal nerve (CN XII) except palatoglossus muscle (by the pharyngeal plexus) | ||
| General Sensory Innervation |
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| Special Sensory Innervation |
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CARTILAGE
There are 3 types:
Hyaline cartilage
Elastic cartilage
Fibrocartilage
Matrix is made up by: Hyaluronic acid
Proteoglycans
- In cartilage the protein core of the proteoglycan molecule binds through a linking protein to hyaluronic acid to form a proteoglycan aggregate which binds to the fibres
- In the matrix there are spaces, lacunae in which one to three of the cells of cartilage, chondrocytes, are found
- The matrix around the lacuna is the territorial matrix
- Type II collagen fibrils are embedded in the matrix
- The type of fiber depends on the type of cartilage
- Cartilage is surrounded by perichondrium which is a dense CT
- Apositional growth takes place in the perichondrium
- The fibroblasts of the perichondrium change to elliptic chondroblasts which later change to round chondrocytes
- Interstitial growth takes place around the lacunae
- Nutrients diffuse through the matrix to get to the chondrocytes this limits the thickness of cartilage
Hyaline cartilage
Found: Rib cartilage, articulating surfaces, nose, larynx, trachea, embryonic skeleton, Articulating cartilage has no perichondrium
Bluish-white and translucent
Contains type II collagen that is not visible
Elastic cartilage
Found: external auditory canal, epiglottis
Similar to hyaline except that it contains many elastic fibres ,Yellow in colour, Can be continuous with hyaline
Fibrocartilage
Found: Intervertebral disk, symphysis pubis
Always associated with dense CT, Many collagen fibres in the matrix, No perichondrium
- Chondrocytes tend to lie in rows, Can withstand strong forces
The Tongue
- The tongue (L. lingua; G. glossa) is a highly mobile muscular organ that can vary greatly in shape.
- It consists of three parts, a root, body, and tip.
- The tongue is concerned with mastication, taste, deglutition (swallowing), articulation (speech), and oral cleansing.
- Its main functions are squeezing food into the pharynx when swallowing, and forming words during speech.
Gross Features of the Tongue
- The dorsum of the tongue is divided by a V-shaped sulcus terminalis into anterior oral (presulcal) and posterior pharyngeal (postsulcal) parts.
- The apex of the V is posterior and the two limbs diverge anteriorly.
- The oral part forms about 2/3 of the tongue and the pharyngeal part forms about 1/3.
Oral Part of the Tongue
- This part is freely movable, but it is loosely attached to the floor of the mouth by the lingual frenulum.
- On each side of the frenulum is a deep lingual vein, visible as a blue line.
- It begins at the tip of the tongue and runs posteriorly.
- All the veins on one side of the tongue unite at the posterior border of the hyoglossus muscle to form the lingual vein, which joins the facial vein or the internal jugular vein.
- On the dorsum of the oral part of the tongue is a median groove.
- This groove represents the site of fusion of the distal tongue buds during embryonic development.
The Lingual Papillae and Taste Buds
- The filiform papillae (L. filum, thread) are numerous, rough, and thread-like.
- They are arranged in rows parallel to the sulcus terminalis.
- The fungiform papillae are small and mushroom-shaped.
- They usually appear are pink or red spots.
- The vallate (circumvallate) papillae are surrounded by a deep, circular trench (trough), the walls of which are studded with taste buds.
- The foliate papillae are small lateral folds of lingual mucosa that are poorly formed in humans.
- The vallate, foliate and most of the fungiform papillae contain taste receptors, which are located in the taste buds.
The Pharyngeal Part of the Tongue
- This part lies posterior to the sulcus terminalis and palatoglossal arches.
- Its mucous membrane has no papillae.
- The underlying nodules of lymphoid tissue give this part of the tongue a cobblestone appearance.
- The lymphoid nodules (lingual follicles) are collectively known as the lingual tonsil.
A. Anatomic position-erect body position with the arms at the sides and the palms upward
B. Plane or section
1. Definition-imaginary flat surface formed by an extension through an axis
2. Median plane-a vertical plane. that divides a body into right and left halves
3. Sagittal plane
- Any plane parallel to the median plane
- Divides the body into right and left portions
4. Frontal plane
- Vertical plane that forms at right angles to the sagittal plane
- Divides the body into anterior and posterior sections
- Synonymous with the term coronal plane
5. Transverse plane
- Horizontal plane that forms at right angles to the sagittal and frontal planes
- Divides the body into upper and lower portions
- Synonymous with the term horizontal plane
C. Relative positions
1. Anterior
- Nearest the abdominal surface and the front of the body
- Synonymous with the term ventral
- In referring to hands and forearms, the terms palmar and Volar are used
2. Posterior
- Back of the body
- Synonymous with the term dorsal
3. Superior
- Upper or higher
- Synonymous with the term cranial (head)
4. Inferior
- Below or lower
- Synonymous with the term caudal (tail)
- In referring to the top of the foot and the sole of the foot. the terms dorsal and plantar are used respectively
5. Medial-near to the median plane
6. Lateral-farther away from the median plane
7. Proximal-near the source or attachment
8. Distal-away from the source or. attachment
9. Superficial-near the surface
10. Deep-away from the surface
11. Afferent-conducting toward a structure
12. Efferent-conducting away from a structure
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Cartilage model is covered with perichondrium that is converted to periosteum
- Diaphysis-central shaft
- Epiphysis-located at either end of the diaphysis
- Growth in length of the bone is provided by the emetaphyseal plate located between the epiphyseal cartilage and the diaphysis
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Blood capillaries and the mesenchymal cells infiltrate the spaces left by the destroyed chondrocytes
- Osteoblasts are derived from the undifferentiated cells; form an osseous matrix in the cartilage
- Bone appears at the site where there was cartilage
Microscopic structure
- Compact bone is found on the exterior of all bones; canceIlous bone is found in the interior
- Surface of compact bone is covered by periosteum that is attached by Sharpey's fibers
- Blood vessels enter the periosteum via Volkmann's canals and then enter the haversian canals that are formed by the canaliculi and lacunae
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- Marrow
- FiIls spaces of spongy bone
- Contains blood vessels and blood ceIls in various stages of development
- Types
- Red bone marrow
- Formation of red blood ceIls (RBCs) and some white blood cells (WBCs) in this location
- Predominate type of marrow in newborn
- Found in spongy bone of adults (sternum, ribs, vertebrae, and proximal epiphyses of long bones)
- Yellow bone marrow
- Fatty marrow
- Generally replaces red bone marrow in the adult, except in areas mentioned above
- Ossification is completed as the proximal epiphysis joins with the diaphysis between the twentieth and twenty-fifth year