Lecture Tuesday September 25: head and neck embryology I

A. Pharyngeal Arches
Be able to identify the pharyngeal arches in a picture or drawing of an embryo and what things are derived from them.



Arch 1: muscles of mastication. malleus and incus of the ear. Innervation by V3

Arch 2: muscles of facial expression. stapes, styloid process and upper part of hyoid bone. Innervation by VII.

Arch 3: stylopharyngeus muscle. lower part of hyoid bone. Innervation by IX.

Arches 4 and 6: muscles of pharynx, larynx and upper esophagus. thyroid and cricoid cartilage. Innervation by X.

B. Pharyngeal Pouches
Be able to identify the pharyngeal pouches in a picture or drawing of an embryo and what things are derived from them.

1st pharyngeal pouch: the tympanic cavity and auditory tube. The endoderm of this pouch will fuse to the ectoderm of the 1st pharyngeal cleft to form the tympanic membrane.

2nd pharyngeal pouch: palatine tonsil.

3rd pharyngeal pouch: inferior parathyroid gland and thymus.

4th pharyngeal pouch: superior parathyroid and the parafollicular (C) cells of the thyroid.



C. Tongue

Develops from swellings on the inner surface of the pharyngeal arches. The pharyngeal arch of origin predicts the sensory innervation of the tongue
- anterior 2/3 from arch 1 = Cn V3
- posterior 1/3 from arch 3 = Cn IX
- root of tongue and epiglottis from arch 4 = Cn X





D. Thyroid
The thyroid gland develops in the ventral midline between the 1st and 2nd pharyngeal arches at the foramen cecum. It is connected to the developing surface of the tongue by the thyroglossal duct.

The thyroid migrates caudally while maintaining its thyroglossal duct connection to the tongue. Over time, the thyroglossal duct degenerates. Remnants of the duct might persist as thyroglossal cysts. These cysts are always in the ventral midline in the neck. In addition, ectopic thyroid tissue might be found anywhere along the developmental migratory path of the thyroid.






E. Ear
- Otic pit > otic vesicle > membranous labyrinth of inner ear.
- pharyngeal arches 1 and 2 > middle ear ossicles
- endodermal pouch 1 > auditory tube




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Lecture Monday September 24: Anatomy of the Neck, Pharynx and Larynx

Cervical Spine
- Rotation occurs at C1 and C2
- Vertebral artery runs superiorly through the transverse processes to enter the foremen magnum.

Posterior Triangle of the Neck
SCM is anterior border and trapezius is the posterior border.
Anterior, middle and posterior scalene muscles in the floor. Brachial plexus present between anterior and middle.
Clinical problems:
1. Compression of brachial plexus with resulting nerve problems of the upper limb
2. Torticollis from tight/contracted SCM on one side

Cervical plexus (anterior rami of C1-C4)
Sensory nerves:
- transverse cervical (C2-C3)
- lesser occipital (C2)
- great auricular (C2-C3)
- supraclavicular (C3-C4)
Motor nerves:
- Ansa cervicalis (C1-C3)
- phrenic (C3-C5)



Muscles of the Anterior Triangle
2 Groups above and below the hyoid bone:
Suprahyoid - innervated by either Cranial nerve V or VII
Infrahyoid - innervated by nerves of the cervical plexus C1 or ansa cervicalis

External Carotid artery branches
1. Superior thyroid
2. Ascending pharyngeal
3. Lingual
4. Facial
5. Occipital
6. Maxillary
7. Superficial temporal


Hypoglossal Nerve
Motor to the muscles of the tongue

Vagus Nerve in the Neck (remember pharynx, larynx and palate)
1. Recurrent laryngeal nerve
Motor to muscles of the larynx and sensory to the mucosa of the larynx below the vocal folds

2. Superior laryngeal nerve
- internal laryngeal branch is sensory to the mucosa of the larynx above the vocal folds
- external laryngeal branch is motor to the cricothyroid muscle



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Lecture Wednesday September 19: histology of the ear

Basic Ear Anatomy



- Relationship of middle ear ossicles to the inner ear
Sound waves vibrate the tympanic membrane > vibrates the oval window > fluid wave through the cochlea > wave exits (dampened) at the round window



Histology of the Cochlea
Components:
A. 3 ducts: scala vestibuli, scala tympani, and cochlear duct
B. 3 membranes: vestibular, basilar and tectorial
C. Hair cells in the organ of corti
D. Spiral ganglion (CN VIII)


Displacement of perilymph in the scala vestibuli will bend the vestibular membrane > displaces the endolymph in the cochlear duct > bends the basilar membrane.
Movement of the basilar membrane to which the hair cells are attached cause bending of the hair cell processes embedded in the tectorial membrane > depolarization of the hair cells > depolarization of CN VIII at spiral ganglion.


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Lecture Wednesday September 19: histology of the eye

Recognize the basic anatomy of the eye



1. Cornea
3 main layers from outside in: corneal epithelium, stroma, corneal endothelium



2. Sclera
Irregular connective tissue

3. Choroid
Vascularized connective tissue
Anteriorly forms:
- Ciliary Body (ciliary process produces aqueous humor, and ciliary muscle that functions to change the shape of the lens).
- Iris contains constrictor papillae muscle (parasympathetic CN III) and dilator pupillae muscle (sympathetic)
- scleral venous sinus (canal of Schlemm) for drainage of aqueous humor produced by the ciliary body



4. Retina and Pigmented Epithelium

Pigment epithelium important for recycling products of the rods and cones

Layers of the retina


1. Outer nuclear layer = Rods and Cones that depolarize in response to light stimulation
2. Outer plexiform layer = processes of rods and cones that synapse on the cells of the inner nuclear layer
3. Inner nuclear layer = several types of neurons that process the information from the rods and cones
4. Inner plexiform layer = processes of neurons from the inner nuclear layer that synapse on the ganglion cells.
5. Ganglion cell layer = neurons whose axons give rise to the optic nerve.
6. Nerve fiber layer = axons of the ganglion cells

Clinical correlations
1. Cataract - clouding of the lens
2. Glaucoma - Increased ocular pressure due to blockage of aqueous humor drainage through the scleral venous sinus (canal of schlemm)
3. Papilledema- bulging of the optic disc due to increased intracranial pressure.


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Lecture Tuesday September 18: cranial cavity and superficial face

Characterizing Types of Hematomas
1. Epidural
-between skull and dura
- arterial bleed (usually middle meningeal)
- shaped like a biconvex lens in a CT scan




2. Subdural
- between the dura and arachnoid
- venous bleed (bridging veins that cross the Subdural space)
- crescent shaped in a CT scan




3. Subarachnoid
- bleeding into subarachnoid space
- usually from a ruptured arterial aneurysm
- diffuse blood in the subarachnoid space within the brain parenchyma. Blood in the CSF




Innervation of the Parotid Gland

1. Parasympathetic
- Preganglionic fibers (lesser petrosal nerve) synapse in the Otic Ganglion
- Postganglionic fibers run with the auriculotemporal branch of V3 to the parotid gland
- cause secretion from the gland

2. Sympathetic
- Preganglionic fibers from T1-T3 spinal cord synapse in the superior cervical ganglion.
- Postganglionic fibers follow blood vessels to parotid.
- regulate blood flow (some controversy about secretion, may contribute at some minor level).



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Lecture Wednesday September 12: Female Reproductive Histology

A. Follicular Development in the Ovary
- Stimulated by FSH (follicle stimulating hormone) from the pituitary.

1. Primordial Follicle: primary oocyte (arrested in prophase of Meiosis I) and a single layer of squamous follicular cells.

2. Unilaminar Primary Follicle: primary oocyte (arrested in prophase of Meiosis I) and a single layer of cuboidal follicular cells.

3. Multilaminar Primary Follicle: primary oocyte (arrested in prophase of Meiosis I) surrounded by multiple layers of cuboidal follicular cells now termed Granulosa cells and a layer of spindle-shaped Thecal cells.

4. Secondary/antral follicle: primary oocyte (arrested in prophase of Meiosis I) surrounded by Granulosa cells that begin to form small antral spaces between the cells through the secretion of follicular fluid. Thecal cells form two layers, theca interna and externa.

5. Mature/Graffian follicle: Antral spaces coalesce into a single large antral cavity. Secondary oocyte (arrested in metaphase of Meiosis II) surrounded by a layer of Granulosa cells called Corona Radiata.

Theca interna > secrete androstenedione > taken up by Granulosa cells > aromatase enzyme converts to estradiol > circulates systemically > development of the endometrium of the uterus and other effects.




*BE ABLE TO IDENTIFY THESE DIFFERENT STAGES OF FOLLICLE DEVELOPMENT IN A HISTOLOGICAL SECTION OF THE OVARY*

B. Ovulation
- Stimulated by a surge in LH (leutinizing hormone) by the pituitary gland (due to rising estrogen levels).

1. Primary oocyte completes Meiosis I and begins Meiosis II (arrests in metaphase of Meiosis II). Now referred to as a Secondary Oocyte (haploid).

2. If fertilization occurs, secondary Oocyte completes Meiosis II.

3. Following ovulation the remaining granulosa cells and theca interna of Graffian follicle reorganize to form Corpus Luteum. Two cell types;
- Granulosa Lutein cells secrete estrogen
- Theca Lutein cells secrete androstenedione and progesterone.

4. Corpus Luteum secretes progesterone for 10-12 days. Without further LH or a pregnancy the corpus luteum regresses and forms the corpus albicans and the uterine endometrium is shed.

5. If pregnancy occurs > HCG produced by placenta > maintains corpus Luteum for 4-5 months. Placenta eventually produces progesterone and estrogen to maintain the uterine mucosa.




C. Uterus
- Endometrium: a mucosa lined by simple columnar epithelium (functional layer and basal layer)
- Myometrium: a thick highly vascularized layer of smooth muscle

Structural changes occurring during the Menstrual cycle:
1. Proliferation phase: proliferation of basal layer to replace functional layer lost during menstruation.

2. Secretory phase: progesterone stimulates growth and secretion of the uterine glands, edema of stroma.

3. Menstrual phase: contraction of spiral arteries, tissue ischemia, shedding of functional layer.

D. Cervix
- Transformation zone: location in the ectocervix where the epithelium changes from simple columnar typical of the uterus to stratified squamous typical of the vagina.

* This is the site particularly susceptible to infection by papilloma virus and the development of cervical cancers.












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Lecture Tuesday September 11: Male Reproductive histology

A. Seminiferous tubules

- Spermatogenesis -
Spermatogonia to spermatids
1. Spermatogonia (diploid) > MITOSIS > spermatogonia and a Primary Spermatocyte (diploid)
2. Primary Spermatocyte > MEIOSIS I > Secondary Spermatocyte (haploid) > MEIOSIS II > Spermatids (haploid)

- Spermiogenesis -
Spermatids to spermatozoa (haploid cells). Primarily a change in structure.



*BE ABLE TO IDENTIFY THE DIFFERENT CELL TYPES IN A HISTOLOGICAL SECTION OF THE SEMINIFEROUS TUBULE*

B. Sertoli cells - are support cells that form the Blood-Testis Barrier.
Secretory Products:
1. ABP (androgen binding protein) in response to FSH (follicle stimulating hormone). Concentrates testosterone to a level that promotes spermiogenesis.
2. Inhibin that inhibits FSH secretion by the pituitary gland.

Leydig cells - produce testosterone in response to LH (leutinizing hormone) from the pituitary gland.

B. Prostate Gland
3 zones:
- Transitional zone surrounding the urethra (benign prostatic hypertrophy)
- Central zone adjacent to transitional zone surrounding ejaculatory ducts
- Peripheral zone makes up most of the volume and is the primary site of cancer development.

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Lecture Tuesday September 11: UG embryology II

A. Male and Female Sexual Development

Male:
- SRY gene > differentiation of indifferent gonad to testis > Sertoli cells > Mullerian inhibiting substance > regression of Paramesonephric/Mullerian duct
- Leydig cells differentiate > testosterone > cause persistence of Mesonephric duct and tubules > rete testis and epididymis.

- seminal vesicles buds off distal mesonephric duct
- prostate buds off of urethra inferior to bladder

Female:
- No SRY > No Sertoli or Leydig cells > No MIS paramesonephric duct persists > uterus, cervix and Fallopian tubes.
- No testosterone so Mesonephric duct and tubules degenerate.
- Sinovaginal bulbs on the posterior aspect of the urogenital sinus gives rise to most of the vagina.

B. External Genitalia
Male:
Cells influenced by testosterone (5- alpha reductase converts to dihydrotestosterone)

Genital tubercle: glans of penis
Urogenital/urethral folds: shaft of penis and penile urethra
Genital swellings: scrotum
Hypospadias: ventral opening of the urethra failure of urethral folds to close completely

Female:
Genital tubercle: clitoris
Urogenital/urethral folds: Labia minora
Genital swellings: Labia majora

C. Descent of the testes
Processes vaginalis leads the way. The two layers fuse to form the tunica vaginalis. Failure of fusion can lead to indirect ing urinal hernia, hydrocele or testicular torsion.


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Lecture Monday September 10: UG Embryology I

Urorectal septum (a plate of mesoderm) separates the cloaca into urinary bladder and rectum.



Allantosis connected to the apex of the bladder becomes the urachus (median umbilical ligament). Clinical conditions include; urachal fistula, cyst or sinus when portions of the allantois remain open.

Kidney Development
1. Mesonephros forms mesonephric (Wolffian) duct and a set of tubules


2. Metanephros forms as an outgrowth of the distal portion of the mesonephric duct (ureteric bud) and includes the surrounding mesoderm that forms the metanephric blastema.


Ureteric bud = ureter, pelvis, calyces and collecting ducts
Metanephric blastema = kidney tubules or nephrons

Common Clinical Conditions
1. Metanephric kidneys "ascends" from the pelvis. Clinical condition may occur when the inferior poles of the two kidneys fuse to create a horseshoe kidney.
2. Bifid ureter if the ureteric bud splits as it enters the blastema.
3. Multiple renal arteries

Gonadal/Genital Ridges
Develops next to the Mesonephros. Populated by germ cells that migrate in from the yolk sac.

A second longitudinal duct forms called Paramesonephric (Mullerian) Duct.



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Lecture Monday September 10: anatomy pelvis and perineum

Most of this material will be covered in the laboratory exercise. In terms of high yield information from this lecture I would recommend paying attention to the following:

A. Pelvic Diaphragm
-Coccygeus muscle and
-Levator Ani muscle (iliococcygeus, pubococcygeus, puborectalis)
*Innervation by ventral rami of S2-S4

Puborectalis- an important role in fecal continence.

B. Urogenital Diaphragm
Fascia (perineal membrane) and thin muscles including superficial and deep transverse perineal and external urethral sphincter.
*Innervation by pudendal nerve

C. Perineum
Divided into urogenital triangle and anal triangle
External genitalia attached to the external surface of urogenital diaphragm in the urogenital triangle.

Skeletal muscles cover the erectile tissues of both sexes: bulbospongiosus and ischiocavernosus.
*Innervation by pudendal nerve








D. Pouches/spaces within the Pelvis formed by peritoneal folds.
Females: vesico-uterine pouch and recto-uterine pouch (of Douglas)
Males: recto-vesical pouch

Clinical importance of the recto-uterine pouch is a site where infection and fluids typically accumulate.




E. Facial Supports of the Uterus and Vagina
Levator Ani muscles and three main condensations of fascia that form "ligaments":
- Pubocervical
- Transverse cervical/cardinal ligaments (*most important support structure)
- Uterosacral



Failure of these support structures results in uterine or vaginal prolapse.


F. *Learn the Arteries in the Lab*

Relationship of uterine artery to the ureter is important



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Lecture Wednesday September 5: Histology of the urinary System

*A good video on the basic function of the kidney and nephron appropriate for this block
www.youtube.com/watch?v=cc8sUv2SuaY

A. Basic structure of the nephron.

Vascular components:
- afferent arteriole
- glomerular capillaries
- efferent arterioles
- peritubular capillaries

Tubular components:
- Bowman's capsule
- Proximal tubule (distinguished by the presence of a brush border)
- Loop of Henle
- Distal tubule
- Collecting tubule





B. Structure and Function of the Glomerulus

-Glomerular capillaries, basal lamina and Podocytes (visceral layer of Bowman's capsule)
- Bowman's capsule (parietal layer).

- A portion of the plasma containing ions, glucose, amino acids and other small molecules is filtered through the fenestrated capillary endothelial cells, basal lamina (charged filter) and Podocytes (filtration slits) into Bowman's Space.



*Be able to recognize the components of the glomerulus in an electron micrograph.


1. Urinary space
2. Glomerular Capillary
3. Podocytes
4. Mesangial cells
5. Basal lamina


C. The 3 basic functions of the nephron: Filtration, Secretion, Reabsorption
*note the directions of flow*


- Proximal convoluted tubule: reabsorption of most of the primary filtrate including glucose, amino acids and some ions

- Descending loop of Henle: reabsorption of water due to hypertonic medullary space

- Ascending loop of Henle: reabsorption of Na and Cl and establishment of a hypertonic medullary space.

- Distal convoluted tubule: further modification/reabsorption of ion concentration in the filtrate

- Collecting duct: reabsorption of water in response to ADH. Concentration of the urine.

*Secretion occurs at multiple sites along the nephron*


D. The Juxtaglomerular Apparatus



- Primary Function: Senses tonicity of tubule fluid and degree of stretch of afferent arteriole – secretes renin.

The three cellular components of the apparatus are
1. Macula Densa cells of the distal convoluted tubule (next to the afferent arteriole)
2. Juxtaglomerular cells (JG cells) specialized smooth muscle cells of the afferent arteriole.
3. Extraglomerular mesangial cells (unknown function).

JG cells sense pressure in afferent arteriole and secret renin to regulate blood pressure. (low blood pressure > renin secretion by JG cells > Angiotensin causes systemic vasoconstriction; release of ADH causes increased water reabsorption in collecting ducts which increases blood volume > increased systemic blood pressure).

Macula Densa cells sense NaCl concentration in distal tubule. If NaCl concentration is high these cells secrete a locally acting molecule to cause constriction of afferent arteriole to decrease glomerular filtration rate and decrease filtrate formation.

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Lecture Tuesday September 4: GI Embryology III

The spleen is NOT a derivative of the GI tract!

Liver Development
Liver grows from the primitive gut tube into the ventral mesentery/septum transversum which becomes the lesser omentum and falciform ligament.

Cranial portion of ventral mesentery/septum transversum contributes to the formation of the diaphragm (central tendon). Muscle of diaphragm from somitic mesoderm (epimeres).

Vitelline veins form hepatic sinusoids, hepatic veins and ductus venosus.

Pancreas Development
- Dorsal pancreatic bud: part of the head, all of body and tail. Accessory pancreatic duct
- Ventral pancreatic bud: outgrowth from the main bile duct. "rotates posteriorly" uncinate process and part of the head. Main pancreatic duct.

Clinical condition:
1. Annular/ring Pancreas (overgrowth of ventral pancreatic bud)

Midgut Development
- The midgut loop extends into the umbilical cord at 6 weeks of development
- The midgut loop rotates and returns to the abdominal cavity at 10 weeks of development producing the normal pattern seen in the adult.

Clinical conditions:
1. Malrotation: positions the whole of the small intestine on right and large intestine on left or puts the duodenum anterior to the transverse colon which may obstruct the duodenum.








2. Failure of recanalization of the gut tube: abnormal lumen partially or completely blocked (stenosis). Imperforate anus (no anal opening)

3. omphalocele: failure of the midgut to return to the abdominal cavity. Portion of gut surrounded by peritoneum within the umbilical cord.

4. Gastroschisis: herniation of gut outside of abdominal wall. Failure of abdominal wall to form correctly. Herniated gut Not covered by peritoneal sac or umbilical cord.

5. Meckel's diverticulum: persistent yolk stalk off of the ilium.



6. Hirschsprung's disease (aganglionic mega colon)
Failure of neural crest to migrate into distal colon to form ganglia of the Myenteric and submucosal plexus. The affected segment of the colon fails to relax causing an obstruction and proximal dilation.



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