NEET MDS Lessons
Anatomy
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
The Layers of the Pharyngeal Wall
- The pharyngeal wall is composed of 5 layers. From internal to external, they are as follows.
- Mucous membrane: this lines the pharynx and is continuous with all chambers with which it communicates.
- Submucosa
- Pharyngobasilar fascia: this is a fibrous layer that is attached to the skull.
- Muscular layer: this is composed of inner longitudinal and outer circular parts.
- Buccopharyngeal fascia: this is a loose connective tissue layer.
- This fascia is continuous with the fascia covering the buccinator and pharyngeal muscle.
- It contains the pharyngeal plexus of nerves and veins.
The Hard Palate
- The anterior bony part of the palate is formed by the palatine process of the maxillae and the horizontal plates of the palatine bones.
- Anteriorly and laterally, the hard palate is bounded by the alveolar processes and the gingivae.
- Posteriorly, the hard palate is continuous with the soft palate.
- The incisive foramen is the mouth of the incisive canal.
- This foramen is located posterior to the maxillary central incisor teeth.
- This foramen is the common opening for the right and left incisive canals.
- The incisive canal and foramen transmit the nasopalatine nerve and the terminal branches of the sphenopalatine artery.
- Medial to the third molar tooth, the greater palatine foramen pierces the lateral border of the bony palate.
- The greater palatine vessels and nerve emerge from this foramen and run anteriorly into two grooves on the palate.
- The lesser palatine foramen transmits the lesser palatine nerve and vessels.
- This runs to the soft palate and adjacent structures.
- Long bones (e.g.. femur and humerus)
- Short bones (e.g.. wrist and ankle bones)
- Flat bones (e.g.. ribs)
- Irregular bones (e.g.. vertebrae)
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Pharyngeal Arch |
Arch Artery |
Cranial Nerve |
Skeletal elements |
Muscles |
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1 |
Terminal Branch of maxillary artery |
Maxillary and mandibular division of trigemenial (V) |
Derived from arch cartilages (originating from neural crest): From maxillary cartilages: Alispenoid, incus From mandibular: Mackel’s cartilage, malleus
Upper portion of external ear (auricle) is derived from dorsal aspect of 1st pharyngeal arch.
Derived by direct ossification from arch dermal mesenchyme: Maxilla, zygomatic, squamous portion of temporal bone, mandible
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Muscles of mastication (temporalis, masseter, and pterygoids), mylohyoid, anterior belly of digastric, tensor tympani, tensor veli palatini (originate from cranial somitomere 4) |
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2 |
Stapedius artery (embryologic) and cortiotympanic artery (adult) |
Facial nerve (VII) |
Stapes, styloid process, stylohyoid ligament, lesser horns and upper rim of hyoid (derived from the second arch cartilage; originate from neural crest).
Lower portion of external ear (auricle) is derived from 2nd pharyngeal arch. |
Muscles of facial expression (orbicularis oculi, orbicularis oris, auricularis, platysma, fronto-ooccipitalis, buccinator), posterior belly of digastric, stylohyoid, stapedius (originate from cranial somitomere 6) |
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3 |
Common carotid artery, most of internal carotid |
Glossopharyngeal (IX) |
Lower rim and greater horn of hyoid (derived from the third arch cartilage; originate from neural crest cells) |
Sytlopharyngeus (originate from cranial somitomere 7) |
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4 |
Left: Arch of aorta; Right: Right subclavian artery; Original sprouts of pulmonary arteries |
Superior laryngeal branch of vagus (X) |
Laryngeal cartilages (Derived from the 4th arch cartilage, originate from lateral plate mesoderm) |
Constrictors of pharynx, cricothyroid, levator veli palatine (originate from occipital somites 2-4) |
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6 |
Ductus arteriosus; roots of definitive pulmonary arteries |
Recurrent laryngeal branch of vagus (X) |
Laryngeal cartilages (derived from the 6th-arch cartilage; originate from lateral plate mesoderm) |
Intrinsic muscles of larynx (originate from occipital somites 1 and 2) |
The Eye and Orbit
- The orbit (eye socket) appears as a bony recess in the skull when it is viewed from anteriorly.
- It almost surrounds the eye and their associated muscles, nerves and vessels, together with the lacrimal apparatus.
- The orbit is shaped somewhat like a four-side pyramid lying on its side, with its apex pointing posteriorly and its base anteriorly.
Mylohyoid Muscle
- Origin: Mylohyoid line of the mandible.
- Insertion: Median raphe and body of the hyoid bone.
- Nerve Supply: Nerve to mylohyoid (branch of the trigeminal nerve, CN V3).
- Arterial Supply: Sublingual branch of the lingual artery and submental branch of the facial artery.
- Action: Elevates the hyoid bone, base of the tongue, and floor of the mouth; depresses the mandible.