The Scalp

• The scalp consists of five layers of soft tissue.
• It extends from the superior nuchal line on the posterior aspect of the skull of the supraorbital margins.
• Laterally, the scalp extends into the temporal fossa to the level of the zygomatic arches.

Layers of the Scalp

• The scalp proper is composed of three fused layers. It is separated from the pericranium by loose connective tissue.
• Because of this potential areolar cleavage plane, the scalp is fairly mobile.
• Each letter of the word "S C A L P" serves as a memory key for one of the layers of the scalp: Skin, Connective Tissue, Aponeurosis Epicranialis, Loose Areolar Tissue and Pericranium.

Layer 1: Skin

• Hair covers the scalp in most people.
• The skin of the scalp is thin, especially in elderly people, except in the occipital region.
• The skin contains many sweat and sebaceous glands and hair follicles.
• The skin of the scalp has an abundant arterial supply and good venous and lymphatic drainage systems.

Layer 2: Connective Tissue

• This is a thick, subcutaneous layer of connective tissue and is richly vascularised and innervated.
• It attaches the skin to the third layer of the scalp.
• Fat is enclosed in lobules between the connective fibres.

Layer 3: Aponeurosis Epicranialis

• This is a strong membranous sheet that covers the superior aspect of the cranium.
• This aponeurosis is the membranous tendon of the fleshy bellies of the epicranius muscle.

• The epicranius muscle consists of four parts: two occipital bellies, occipitalis and two frontal bellies, frontalis that are connected by the epicranial aponeurosis. 

Layer 4: Loose Areolar Tissue

• This is a subaponeurotic layer or areolar or loose connective tissue.
• It is somewhat like a sponge because it contains innumerable potential spaces that are capable of being distended by fluid.
• It is this layer that allows free movement of the scalp proper, composed of layers 1-3.

Layer 5: Pericranium

• This is a dense layer of specialised connective tissue.
• The pericranium is firmly attached to the bones by connective tissue fibres called Sharpey’s fibres, however, they can be fairly easily stripped from the cranial bones of living persons, except where they are continuous with the fibrous tissues of the cranial sutures.

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.

Nerves of the Palate

• The sensory nerves of the palate, which are branches of the pterygopalatine ganglion, are the greater and lesser palatine nerves.
• They accompany the arteries through the greater and lesser palatine foramina, respectively.

• The greater palatine nerve supplies the gingivae, mucous membrane, and glands of the hard palate.

• The lesser palatine nerve supplies the soft palate.

• Another branch of the pterygopalatine ganglion, the nasopalatine nerve, emerges from the incisive foramen and supplies the mucous membrane of the anterior part of the hard palate.

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

Eye 

At week 4, two depressions are evident on each of the forebrain hemispheres.  As the anterior neural fold closes, the optic pits elongate to form the optic vesicles.  The optic vesicles remain connected to the forebrain by optic stalks. 
The invagination of the optic vesicles forms a bilayered optic cup.  The bilayered cup becomes the dual layered retina (neural and pigmented layer)
Surface ectoderm forms the lens placode, which invaginates with the optic cup.
The optic stalk is deficient ventrally to contain choroids fissure to allow blood vessels into the eye (hyaloid artery).  The artery feeds the growing lens, but will its distal portion will eventually degenerate such that the adult lens receives no hyaloid vasculature.
At the 7th week, the choroids fissure closes and walls fuse as the retinal nerve get bigger.
The anterior rim of the optic vesicles forms the retina and iris.  The iris is an outgrowth of the distal edge of the retina.
Optic vesicles induces/maintains the development of the lens vesicle, which forms the definitive lens.  Following separation of the lens vesicle from the surface ectoderm, the cornea develops in the anterior 1/5th of the eye.
The lens and retina are surrounded by mesenchyme which forms a tough connective tissue, the sclera, that is continuous with the dura mater around the optic nerve.  
Iridopupillary membrane forms to separate the anterior and posterior chambers of the eye.  The membrane breaks down to allow for the pupil
Mesenchyme surrounding the forming eye forms musculature (ciliary muscles and pupillary muscles – from somitomeres 1 and 2; innervated by CN III), supportive connective tissue elements and vasculature.

Eyelids

Formed by an outgrowth of ectoderm that is fused at its midline in the 2nd trimester, but later reopen.

The Palate

• The palate forms the arched roof of the mouth and the floor of the nasal cavities.
• The palate consists of two regions: the anterior 2/3 or bony part, called the hard palate, and the mobile posterior 1/3 or fibromuscular part, known as the soft palate.