Body Parts That Start With Z

The human body is a complicated organism made of ten major body systems, organs, cells, tissues, and bones.

Some major systems are nervous, digestive, skeletal, respiratory, cardiovascular, and muscular.

Each system is composed of bones, muscles, organs, limbs, blood vessels, veins, tissue, nerves, and glands.

Out of all these well-functioning systems that work together to keep your body moving, only a handful begin with the letter Z.

We wish to focus on those parts in this article and explain their functions and amusing facts.

Body Parts That Start with the Letter Z


The first body part we want to explain is probably a novelty for many readers, as it is for various doctors who are not experts.

The zonule or zonules are tiny thread-like fibers behind your eyes that hold your eyes in place as you move them around to focus on various objects.

Zonules, also known as the zonule of Zinn, create a ring of fibrous strands or a little band that connects the crystalline lenses of the eye with the ciliary body.

Crystalline lenses or eye lenses of your eyes are transparent biconvex or double-sided lenses located behind the iris that helps your eyes focus on near and far objects.

These lenses refract or redirect the light through your eyes, along with the cornea, vitreous humor, and aqueous.

And the ciliary body is the middle layer of the wall of the eye found behind the iris.

The ciliary body changes the shape of the crystalline lenses as the eye moves due to ring-shaped muscles inside the eye.

Zonules got their name from the German anatomist and botanist Johann Gottfried Zinn, who provided the first detailed anatomy of the human eye in his book Descriptio anatomica oculi humani.

Zinn fibers often refer to the suspensory ligaments of the lens, as they act like ligaments or connective tissue that connects bones with other bones.

What you see when you look at someone’s eyes is the pupil that contains the cornea (transparent part), the iris (the colored part), and the anterior cavity that has an anterior and posterior chamber.

The posterior chamber is in the back of the pupil, where the suspensory ligaments are, and in front of the vitreous chamber, in the far back of our eye.

The zonule of Zinn divides into two layers.

The first is a thin layer that lines the last layer of the pupil, and the second is a thicker layer that connects the crystalline lenses with the rest of the eye.

Both layers are made of fibrillin or a connective tissue protein.

Mutation in this formation of elastic fibers can lead to the condition called Margan syndrome, which can cause lens dislocation.

Other than this syndrome, zonules can be affected by the friction against the lens, which can lead to the irises slowly fading in color.

This gradual fading sometimes leads to glaucoma pigmentosa or damage to the optic nerve.

Glaucoma causes vision loss, as the pupil stops responding to the light, and the redness of the white part of the eye, also known as the sclera.

Zonules are a tiny part of your eye, responsible for so much movement and mobility of your eye muscles.

Zygapophyseal Joints

Another mystery part on our list is zygapophyseal joints, also known as the facet joints, apophyseal, or Z-joints.

Facet joints represent the joints of the vertebral column or the backbones of your spine.

This column includes the cervical spine (from C1 to C7), thoracic spine (from T1 to T12), lumbar spine (from L1 to L5), sacral spine (from S1 to S5), and the tailbone at the of the spine.

The zygapophyseal joints are between the superior and inferior parts of the adjoining vertebrae or between the first sacral vertebra, known as S1, and the axis known as C2.

Accessory ligaments of the vertebral column stabilize the joints, covered by a thin and loose fibrous capsule.

Their sizes, shapes, and positioning depend on the region of the spine, as we have various bones connecting through the end of the tailbone.

Two facet joints exist between each spinal motion segment, and medial branch nerves run through them for motor musculature as each pair of facet joints has a purpose in your movement and limitation to how your spine can move.

The movements are different, and so are the limitations, depending on the area of the joints.

Facet joints can suffer over time due to age and wear and tear, followed by facet joint arthritis or arthropathy.

If these degenerative changes happen, the facet joints become enlarged and narrow the intervertebral space between two spinal vertebrae.

The treatment for displacement includes physical therapy or osteopathic medicine, with correction of posture and muscle strengthening.

Zygomatic Bone

The zygomatic bones, also known as the cheekbones or malar bones, are a pair of diamond-shaped bones that protrude sideways on your cheeks.

They are irregularly shaped, located at the upper part of the face, forming the prominence of your cheeks.

From the top, we have the nasal, lacrimal, palatine, inferior nasal concha, and vomer bone in the nose cavity, followed by maxilla above our mouth, mandible or the jaw bone under, and two zygomatic bones on the sides – a total of 14 facial bones.

Each zygomatic bone consists of three processes: frontal, temporal, and maxillary bones.

The zygomatic bones shape your face but also keep the function of the face while protecting your eyes.

They play a role in jaw movement while talking, eating, and breathing.

High cheekbones or zygomatic arches are considered physically attractive in many cultures, regardless of gender.

This notion is not a new trend, as sculptures of ancient Chinese goddesses had high cheekbones, broad foreheads, and raised eyebrows.

If you do not have chiseled cheekbones naturally, you may undergo cheek augmentation surgery to achieve this timeless look.


Pregnancies have three stages before a baby is born.

The first begins at conception, called the germinal stage, and lasts up to two weeks.

After that, we have the embryonic stage, when the embryo develops into the shape of a baby and gets a forebrain, midbrain, and hindbrain.

And the last stage, or the fetal period, lasts from the ninth week to birth, where everything else is necessary for the baby to be healthy and well-developed.

We will focus on the first stage that happens right after conceit when the fertilized egg is called a zygote.

Just a few hours after the sperm and egg cells unite, the single-celled zygote travels down the fallopian tube to the uterus for the first stage to commence.

The zygote is a combination of DNA from both parents and contains all of the genetic makeup that the baby will have and show.

After the initial travel, this stage is brief as the zygote splits into smaller cells, and the rest of the development follows.

The zygote carries two sets of chromosomes, but the genes are not yet activated to produce proteins and necessary factors for embryo development. That happens in the next stage.

Cell division of the traveling zygote begins 24 to 36 hours after conception in the process of mitosis where the zygote splits into two cells, then four, then eight, sixteen, and so on.

The divided cells evolve into a blastocyst cluster of three layers that develop first – ectoderm (skin and nervous system), endoderm (digestive and respiratory systems), and mesoderm (muscle and skeletal systems).

After the moment the blastocyst attaches to the uterus, the rest of the development and necessary nourishment begins until the baby passes the third and final stage before birth.

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