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 two parietal bones (L. paries, wall) form large parts of the walls of the calvaria.
->On the outside of these smooth convex bones, there are slight elevations near the centre called parietal eminences.
->The middle of the lateral surfaces of the parietal bones is crossed by two curved lines, the superior and inferior temporal lines.
->The superior temporal line indicates an attachment of the temporal fascia; the inferior temporal line marks the superior limit of the temporalis muscle.
->The parietal bones articulate with each other in the median plane at the sagittal suture. The medial plane of the body passes through the sagittal suture.
->The inverted V-shaped suture between the parietal bones and the occipital bones is called the lambdoid suture because of its resemblance to the letter lambda in the Greek alphabet.
->The point where the parietal and occipital bones join is a useful reference point called the lambda. It can be felt as a depression in some people.
->In addition to articulation with each other and the frontal and occipital bones, the parietal bones articulate with the temporal bones and the greater wings of the sphenoid bone.
->In foetal and infant skulls, the bones of the calvaria are separated by dense connective tissue membranes at sutures.
->The large fibrous area where several sutures meet are called fonticuli or fontanelles.
->The softness of these bones and looseness of their connections at these sutures enable the calvaria to undergo changes of shape during birth called molding. Within a day or so after birth, the shape of the infant’s calvaria returns to normal.
->The loose construction of the new-born calvaria also allows the skull to enlarge and undergo remodelling during infancy and childhood.

->Relationships between the various bones are constantly changing during the active growth period.
->The increase in the size of the cranium is greatest during the first 2 years, the period of most rapid postnatal growth of the brain.
->The cranium normally increases in capacity until about 15 or 16 years of age; thereafter the cranium usually increases only slightly in size as its bones thicken for 3 to 4 years.

Tongue 
Appears at 4th week.
Musculature derived from mesoderm of occipital somites.  Precursor muscles cells migrate to region of tongue and are innervated by general sensory efferent fibers of CN XII.
Mucosa derived from anterior endoderm lining arches 1-4; accordingly, innervation depends on arch derivation:
              Mucosa of anterior 2/3 of tongue comes from the first arch -> CN V
              Mucosa of posterior 1/3 of tongue comes from third and forth arch -> CN IX, X
Special taste of anterior 2/3 of tongue comes from CN VII.
Special taste of posterior 1/3 of tongue comes from CN X.
Tongue freed from floor of mouth by extensive degeneration of underlying tissue.  Midline frenulum continues to anchor tongue to floor of mouth.

Thyroid Gland

Develops as in growth of mucosal epithelium located in the midline of the tongue (at foramen cecum).  It descends along front of pharyngeal gut, but remains connected to tongue by thyrooglossal duct, which is obliterated later in development.  Thyroid gland descends to a point just caudal to laryngeal cartilages. 

Facial structures (general)

a) medial nasal prominence forms midline of nose, philtrum and primary palate
b) lateral nasal prominence forms alae of nose
c) maxillary prominence forms cheek region and lateral lip
d) clefts can form at inter-prominence fusion lines

Nose

At the time of anterior neural tube closure, mesenchyme around forebrain, frontonasal prominence (FNP), has smooth rounded extended contour.  Nasal placodes (thickening of surface ectoderm to become peripheral neural tissue) develop on frontolateral aspects of FNP.  Mesenchyme swells around nasal placode producing a medial and lateral nasal prominence (nasomedial and nasolateral processes).  These nasal prominences form the nose.

Mouth 

Stomadeum (primitive oral cavity) forms between frontonasal prominence and first pharyngeal arch.  The first pharyngeal arch forms the dorsal maxillary prominence and ventral mandibular prominence.  The maxillary prominence will merge with medial nasal prominences, pushing them closer to cause fusion.  Fused medial nasal prominences will form midline of nose and midline of upper lip (philtrum) and primary palate (first 4 teeth).

Nasolacrimal structures

Maxillary and lateral nasal prominences are separated by deep furrow, the nasolacrimal groove.  Ectoderm in floor of groove forms epithelial cord, which detaches from overlying ectoderm.  The epithelial cord canalizes to form the nasolacrimal duct.  The upper end of the duct widens to form the lacrimal sac.  After detachment of the cord, the maxillary and lateral nasal prominences merge with each other, resulting in the formation of a nasolacrimal duct that runs from the medial corner of the eye to the inferior meatus of the nasal cavity.  
The maxillary prominences enlarge to form the cheeks and maxillae.
The lateral nasal prominences form the alae of the nose.

Secondary (hard) palate

Main part of definitive palate formed by two palatine shelves derived from intraoral bilateral extensions of the maxillary prominences.  These appear at the 6th week.  They are directed obliquely downward on each side of the tongue; they move down when mandible gets bigger.  
At the seventh week, they ascend to attain a horizontal position, then fuse to form the secondary palate.  At the time the palatine shelves fuse, the nasal septum (an outgrowth of median tissue of the frontonasal prominence) grows down and joins the cephalic aspect of the newly formed palate
Anteriorly, shelves fuse with triangular primary palate.  The incisive foramen marks the midline between the primary and secondary palate.

External Ear

The auricle is derived from 6 auricular hillocks (mesenchymal proliferations) along the dorsal aspect of arches 1 (top of ear) and 2 (bottom of ear).  These fuse to form the definitive auricle.  At the mandible grows, the ear is pushed upward and backward from its initial horizontal position on the neck.
The EAM is derived from the 1st pharyngeal arch.  
The eardrum (tympanic membrane) is composed of 3 layers of cells: 1) ectodermal epithelial lining of bottom of EAM; 2) endodermal epithelium lining of tympanic cavity; 3) intermediate layer of connective tissue.
The eardrum is composed of multiple cell layers because it represents the first pharyngeal membrane, and thus lies at the junction of the first pharyngeal pouch and cleft.

Middle Ear

The middle ear consists of an auditory tube (from the 1st pharyngeal pouch, along with tympanic cavity) and the ossicles (from pharyngeal arches 1 and 2 cartilage).  
The first arch cartilage forms the malleus and incus.  The tensor tympani (muscle of the malleus) is derived from the fourth somitomere (associated with the first arch) and is therefore innervated by CN V.
The second arch cartilage forms the stapes.  The stapedius (muscles of the stapes) is derived from the sixth somitomere (associated with the second arch) and is therefore innervated by CN VII.
The ossicles are initially embedded in mesenchyme, but in the 8th month, the mesenchyme degenerates and an endodermal epithelial lining of the tympanic cavity envelops the ossicles and connects them to the wall of the cavity in a mesentery-like fashion.

Inner Ear

The inner ear is derived thickening of surface ectoderm on both sides of the hindbrain (otic placodes).  The placodes invaginate to form otic vesicles (otocytes).  The vesicles then divide into ventral and dorsal components.
The ventral component forms the saccule and cochlear duct.
The dorsal component forms the utricle and semicircular canals and endolymphatic duct.

Cochlear Duct

Derived from an outgrowth of the saccule during the 6th week.  The outgrowth penetrates the surrounding mesenchyme in a spiral fashion.  The surrounding mesenchyme forms the cartilage and undergoes vacuolization.
The scala vestibule and scale tympani form and surround the cochlear duct.  They are filled with periplymp to receive mechanical vibrations of ossicles. The mechanical stimuli activates sensory (ciliary) cells in the cochlear duct.  

Semicircular canals

The utricle is initially three flattened outpocketings, which lose the central core.  From this three semicircular canals are forms, each at 90 degree angles from one another.  Sensory cells arise in the ampulla at one end of each canal, in the utricle and saccule. 

Muscles Around the Eyelids

• The function of the eyelid (L. palpebrae) is to protect the eye from injury and excessive light. It also keeps the cornea moist.

The Orbicularis Oculi Muscle

• This is the sphincter muscle of the eye.
• Its fibres sweep in concentric circles around the orbital margin and eyelids.
• It narrows the eye and helps the flow of tears from the lacrimal sac.

• This muscle has 3 parts: (1) a thick orbital part for closing the eyes to protect then from light and dust; (2) a thin palpebral part for closing the eyelids lightly to keep the cornea from drying; and (3) a lacrimal part for drawing the eyelids and lacrimal punta medially.

• When all three parts of the orbicularis oculi contract, the eyes are firmly closed and the adjacent skin becomes wrinkled.
• The zygomatic branch of the facial nerve (CN VII) supplies it.

The Levator Palpebrae Superioris Muscle

• This muscle raises the upper eyelid to open the palpebral fissure.
• It is supplied by the oculomotor nerve (CN III).

• Bones begin to form during the eighth week of embryomic life in the fibrous membranes (intramembranous ossification) and hyaline cartilage (endochondral ossification)

Nerves of the Face

Innervation of the Muscles of Facial Expression

The Facial Nerve (CN VII)

• The seventh cranial nerve supplies the superficial muscle of the neck (platysma), the muscles of facial expression, the auricular muscles and the scalp muscles.
• CN VII is the sole motor supply to the muscles of facial expression.

• The facial nerve emerges from the skull though the stylomastoid foramen.
• Almost immediately, it enters the parotid gland. It runs superficially in this gland before giving rise to its five terminal branches: temporal, zygomatic, buccal, marginal mandibular, and cervical.
• These nerve emerge from the superior, anterior and inferior margins of the gland and spread out like the abducted digits of the hand to supply the muscles of facial expression.

• The temporal branches of CN VII cross the zygomatic arch to supply all the superficial facial muscles superior to it, including the orbital and forehead muscles.

• The zygomatic branch of CN VII passes transversely over the zygomatic bone to supply the muscles in the zygomatic, orbital and infraorbital regions.

• The buccal branches of CN VII pass horizontally, external to the masseter muscle, to supply the buccinator and the muscles of the upper lip.

• The marginal mandibular branch of CN VII supplies the muscles of the lower lip and chin.

• The cervical branch of CN VII supplies the platysma and the superficial muscles of the neck.