Friday, 25 March 2016

Eye

See below for the drawings.


Layers in the Eye
Each eyeball is surrounded by three distinct layers.

Sclera
The outer layer in the eye is the sclera, an opaque layer of dense connective tissue. The inner sclera
is located adjacent to the choroid. It contains different types of connective tissue fibers and connective
tissue cells, including macrophages and melanocytes. Anteriorly, the sclera is modified
into a transparent cornea, through which light rays enter the eye.

Vascular Layer (uvea)
Internal to the sclera is the middle or vascular layer (uvea). This layer consists of three parts: a
densely pigmented layer called the choroid, a ciliary body, and an iris. Located in the choroid are
numerous blood vessels that nourish the photoreceptor cells in the retina and structures of the
eyeball.

Retina
The innermost lining of the most posterior chamber of the eye is the retina. The posterior three
quarters of the retina is a photosensitive region. It consists of rods, cones, and various interneurons,
cells that are stimulated by and respond to light. The retina terminates in the anterior region
of the eye called the ora serrata, which is the nonphotosensitive part of the retina. This region continues
forward in the eye to line the inner part of the ciliary body and the posterior region of the iris.

Chambers in the Eye
The eye also contains three chambers.
The anterior chamber is a space located between the cornea, iris, and lens.
The posterior chamber is a small space situated between the iris, ciliary process, zonular
fibers, and lens.
The vitreous chamber is a larger, posterior space that is situated behind the lens and zonular
fibers, and surrounded by the retina.
The anterior and posterior chambers are filled with a watery fluid called the aqueous
humor. This fluid is continually produced by the ciliary process located behind the iris.Aqueous
humor circulates from the posterior chamber to the anterior chamber, where it is drained by
veins. The vitreous chamber is filled with the gelatinous substance called the vitreous body.

Photosensitive Parts of the Eye
The photosensitive retina contains numerous cell types organized into numerous and distinct cell
layers. The layer that is sensitive to light contains cells called rods and cones. These cells are stimulated
by light rays that pass through the lens. Leaving the retina are afferent (sensory) axons
(nerve fibers) that conduct light impulses from the retina via the optic nerve to the brain for
visual interpretation.
The posterior region of the eye also contains a yellowish pigmented spot called the macula
lutea. In the center of the macula lutea is a depression called the fovea. The fovea is devoid of
photoreceptive rods and blood vessels. Instead, the fovea contains a dense concentration of photosensitive
cones.



Retina and Choroid(Hematoxylin-Eosin)











Cornea(Hematoxylin-Eosin)


Cornea (Hematoxylin-Eosin)


Layers of choroid and retina (Hematoxylin-Eosin)



Whole eye-sagittal section (Hematoxylin-Eosin)




Ciliary body, iris, lens (Hematoxylin-Eosin)

Ear


See below for the drawings.



The auditory system consists of three major parts: the external ear, the middle ear, and the inner ear.
The ear is a specialized organ that contains structures responsible for hearing, balance, and
maintenance of equilibrium.

External Ear
The auricle or pinna of the external ear gathers sound waves and directs them through the external
auditory canal interiorly to the eardrum or tympanic membrane.

Middle Ear
The middle ear is a small, air-filled cavity called the tympanic cavity. It is located in and protected
by the temporal bone of the skull. The tympanic membrane separates the external auditory canal
from the middle ear. Located in the middle ear are three very small bones, the auditory ossicles
consisting of the stapes, incus, and malleus; also in the middle ear is the auditory (eustachian)
tube. The cavity of the middle ear communicates with the nasopharynx region of the head via the
auditory tube. The auditory tube allows for equalization of air pressure on both sides of the tympanic
membrane during swallowing or blowing the nose.

Inner Ear
The inner ear lies deep in the temporal bone of the skull. It consists of small, communicating cavities
and canals of different shapes. These cavities, the semicircular canals, vestibule, and
cochlea, are collectively called the osseous or bony labyrinth. Located within the bony labyrinth
is the membranous labyrinth that consists of a series of interconnected, thin-walled compartments
filled with fluid.

Cochlea
The organ specialized for receiving and transmitting sound (hearing) is found in the inner ear in
the structure called the cochlea. It is a spiral bony canal that resembles a snail’s shell. The cochlea
makes three turns on itself around a central bony pillar called the modiolus.
Interiorly, the cochlea is partitioned into three channels, the vestibular duct (scala
vestibuli), tympanic duct (scala tympani), and cochlear duct (scala media). Located within the
cochlear duct on the basilar membrane is the hearing organ of Corti. This organ consists of
numerous auditory receptor cells or hair cells and several supporting cells that respond to different
sound frequencies. The auditory stimuli (sounds) are carried away from the receptor cells via
afferent axons of the cochlear nerve to the brain for interpretation.

Vestibular Functions
The organ of vestibular functions that is responsible for balance and equilibrium is found in the
utricle, saccule, and three semicircular canals.



Inner ear: cochlea (Hematoxylin-Eosin)


Inner ear: cochlear duct (Hematoxylin-Eosin)




Organ of Corti(Hematoxylin-Eosin) (Taken from real microscopic slide)

Saturday, 26 April 2014

Female Reproductive System


See below for the drawings.


Ovaries
Each ovary is a flattened, ovoid structure located deep in the pelvic cavity. One section of the
ovary is attached to the broad ligament by a peritoneal fold called the mesovarium and another
section to the uterine wall by an ovarian ligament. The ovarian surface is covered by a single layer
of cells called the germinal epithelium that overlies the dense, irregular connective tissue tunica
albuginea. Located below the tunica albuginea is the cortex of the ovary. Deep to the cortex is the
highly vascularized, connective tissue core of the ovary, the medulla. There is no distinct boundary
line between the cortex and medulla, and these two regions blend together.
During embryonic development, germ cells colonize the gonadal ridges, differentiate into
oogonia, divide by mitosis, and then enter the first phase of meiotic division without completing
it. They become arrested in this state of development and are now called the primary oocytes.
Primordial follicles are also formed during fetal life and consist of a primary oocyte surrounded
by a single layer of squamous follicular cells. Beginning at puberty and under the influence of pituitary hormones, the primordial follicles grow and enlarge to become primary, secondary,
and the large mature follicles, which can span the cortex and extend deep into the medulla of the
ovary. The cortex of an ovary is normally filled with numerous ovarian follicles in various stages
of development.
In addition, the ovary may contain a large corpus luteum of an ovulated follicle and corpus
albicans of a degenerated corpus luteum. Also, ovarian follicles in various stages of development
(primordial, primary, secondary, and maturation) may undergo a process of degeneration called
atresia, and the atretic degenerating cells are then phagocytosed by macrophages. Follicular atresia
occurs before birth and continues throughout the reproductive period of the individual.

Uterine (Fallopian) Tubes
Each uterine tube is about 12 cm long and extends from the ovaries to the uterus. One end of the
uterine tube penetrates and opens into the uterus; the other end opens into the peritoneal cavity
near the ovary. The uterine tubes are normally divided into four continuous regions. The region
closest to the ovary is the funnel-shaped infundibulum. Extending from the infundibulum are
slender, fingerlike processes called fimbriae (singular, fimbria) located close to the ovary.
Continuous with the infundibulum is the second region, the ampulla, the widest and longest portion.
The isthmus is short and narrow, and joins each uterine tube to the uterus. The last portion
of the uterine tube is the interstitial (intramural) region. It passes through the thick uterine wall
to open into the uterine cavity.

Uterus
The human uterus is a pear-shaped organ with a thick muscular wall. The body or corpus forms
the major portion of the uterus. The rounded upper portion of the uterus located above the
entrance of uterine tubes is called the fundus. The lower, narrower, and terminal portion of
the uterus located below the body or corpus is the cervix. The cervix protrudes and opens into the
vagina.
The wall of the uterus is composed of three layers: an outer perimetrium lined by serosa or
adventitia; a thick smooth muscle layer called the myometrium; and an inner endometrium. The
endometrium is lined by simple epithelium that descends into a lamina propria to form numerous
uterine glands.
The endometrium is normally subdivided into two functional layers, the luminal stratum
functionalis and the basal stratum basalis. In a nonpregnant female, the superficial functionalis
layer with the uterine glands and blood vessels is sloughed off or shed during menstruation, leaving
intact the deeper basalis layer with the basal remnants of the uterine glands—the source of
cells for regeneration of a new functionalis layer. The arterial supply to the endometrium plays an
important role during the menstrual phase of the menstrual cycle.
Uterine arteries in the broad ligament give rise to the arcuate arteries. These arteries penetrate
and assume a circumferential course in the myometrium of the uterus. Arcuate vessels give
rise to straight and spiral arteries that supply the endometrium. The straight arteries are short
and supply the basalis layer of the endometrium, whereas the spiral arteries are long and coiled
and supply the surface or functionalis layer of endometrium. In contrast to the straight arteries,
spiral arteries are highly sensitive to hormonal changes in the blood. Decreased blood levels of the
ovarian hormones estrogen and progesterone during the menstrual cycle produces degeneration
and shedding of stratum functionalis, resulting in menstruation.

Cervix and Vagina
The cervix is located in the lower part of the uterus that projects into the vaginal canal as the portio
vaginalis. A narrow cervical canal passes through the cervix. The opening of the cervical canal
that directly communicates with the uterus is the internal os and, with the vagina, the external
os. Unlike the functionalis layer of the uterine endometrium, the cervical mucosa undergoes only
minimal changes during the menstrual cycle and is not shed during menstruation. The cervix
contains numerous branched cervical glands that exhibit altered secretory activities during the
different phases of the menstrual cycle. The amount and type of mucus secreted by the cervical
glands change during the menstrual cycle as a result of different levels of ovarian hormones.
The vagina is a fibromuscular structure that extends from the cervix to the vestibule of the
external genitalia. Its wall has numerous folds and consists of an inner mucosa, a middle muscular
layer, and an outer connective tissue adventitia. The vagina does not have any glands in its
wall and its lumen is lined by stratified squamous epithelium. Mucus produced by cells in the
cervical glands lubricates the vaginal lumen. Loose fibroelastic connective tissue and a rich vasculature
constitute the lamina propria that overlies the smooth muscle layers of the organ. Like
the cervical epithelium, the vaginal lining is not shed during the menstrual flow.

Placenta
The placenta is a temporary organ that is formed when the developing embryo, now called a blastocyst,
attaches to and implants in the endometrium of the uterus. The placenta consists of a fetal
portion, formed by the chorionic plate and its branching chorionic villi, and a maternal portion,
formed by the decidua basalis of the endometrium. Fetal and maternal blood come into
close proximity in the villi of the placenta. Exchange of nutrients, electrolytes, hormones, antibodies,
gaseous products, and waste metabolites takes place as the blood passes over the villi. Fetal
blood enters the placenta through a pair of umbilical arteries, passes into the villi, and returns
through a single umbilical vein.

Mammary Glands
The adult mammary gland is a compound tubuloalveolar gland that consists of about 20 lobes.
All lobes are connected to lactiferous ducts that open at the nipple. The lobes are separated by
connective tissue partitions and adipose tissue.
The resting or inactive mammary glands are small, consist primarily of ducts, and do not
exhibit any developed or secretory alveoli. Inactive mammary glands also exhibit slight cyclic
alterations during the course of the menstrual cycle. Under estrogenic stimulation, the secretory
cells increase in height, lumina appear in the ducts, and a small amount of secretory material is
accumulated.



Mammary Gland(Hematoxylin-Eosin)


Ovary(Hematoxylin-Eosin)


Uterine Tube(Hematoxylin-Eosin)


Uterus(Hematoxylin-Eosin)


Vagina(Hematoxylin-Eosin)

Chorionic villi: placenta during early pregnancy (Hematoxylin-Eosin)

 
Chorionic villi: placenta at term (Hematoxylin-Eosin)