Biology Prefixes and Suffixes: peri-

Tree Bark Split
Periderm or bark is a secondary tissue layer that surrounds and protects underlying layers in some plants. Credit: lynn.h.armstrong photography/Moment/Getty Images

The prefix (peri-) means around, near, surrounding, covering, or enclosing. It is derived from the Greek peri for about, near, or around.

Words That Begin With: (peri-)

Perianth (peri-anth): The outer part of a flower that encloses its reproductive parts is called the perianth. The perianth of a flower includes the sepals and petals in angiosperms.

Pericardium (peri-cardium): The pericardium is the membranous sac that surrounds and protects the heart. This three-layered membrane serves to keep the heart in place in the chest cavity and prevents over-expansion of the heart. Pericardial fluid, which is located between the middle pericardial layer (parietal pericardium) and the innermost pericardial layer (visceral pericardium), helps to reduce friction between pericardial layers.

Perichondrium (peri-chondrium): The layer of fibrous connective tissue that surrounds cartilage, excluding cartilage at the end of joints, is called perichondrium. This tissue covers cartilage in structures of the respiratory system (trachea, larynx, nose, and epiglottis), as well as cartilage of the ribs, outer ear, and auditory tubes.

Pericranium (peri-cranium): The pericranium is a membrane that covers the outer surface of the skull. Also called the periosteum, it is the innermost layer of the scalp that covers bone surfaces except at the joints.

Pericycle (peri-cycle): Pericycle is plant tissue that surrounds vascular tissue in roots. It initiates the development of lateral roots and is also involved in secondary root growth.

Periderm (peri-derm): The outer protective plant tissue layer that surrounds roots and stems is the periderm or bark. The periderm replaces the epidermis in plants that undergo secondary growth. Layers composing the periderm include cork, cork cambium, and phelloderm.

Peridium (peri-dium): The outer layer that covers the spore-bearing structure in many fungi is called the peridium. Depending on the fungal species, the peridium may be thin or thick with between one and two layers.

Perigee (peri-gee): The perigee is the point in the orbit of a body (moon or satellite) around the Earth where it is nearest to the center of the Earth. The orbiting body travels faster at perigee than at any other point in its orbit.

Perikaryon (peri-karyon): Also known as cytoplasm, the perikaryon is all of the contents of a cell surrounding but excluding the nucleus. This term also refers to the cell body of a neuron, excluding the axons and dendrites.

Perihelion (peri-helion): The point in the orbit of a body (planet or comet) around the sun where it comes closest to the sun is called the perihelion.

Perilymph (peri-lymph): Perilymph is the fluid between the membranous labyrinth and bony labyrinth of the inner ear.

Perimysium (peri-mysium): The layer of connective tissue that wraps skeletal muscle fibers into bundles is called perimysium.

Perinatal (peri-natal): Perinatal refers to the time period occurring around the time of birth. This period spans from about five months before birth to one month after birth.

Perineum (peri-neum): The perineum is the area of the body located between the anus and genital organs. This region spans from the pubic arch to the tail bone.

Periodontal (peri-odontal): This term literally means around the tooth and is used to denote tissues that surround and support teeth. Periodontal disease, for example, is a disease of the gums that can range from minor gum inflammation to serious tissue damage and tooth loss.

Periosteum (peri-osteum): The periosteum is a dual-layered membrane that covers the outer surface of bones. The outer layer of the periosteum is dense connective tissue formed from collagen. The inner layer contains bone-producing cells called osteoblasts.

Peristalsis (peri-stalsis): Peristalsis is the coordinated contraction of smooth muscle around substances within a tube that moves the contents along the tube. Peristalsis occurs in the digestive tract and in tubular structures such as the ureters.

Peristome (peri-stome): In zoology, the peristome is a membrane or structure that surrounds the mouth in some invertebrates. In botany, peristome refers to small appendages (resembling teeth) that surround the opening of a capsule in mosses.

Peritoneum (peri-toneum): The dual-layered membrane lining of the abdomen that encases abdominal organs is known as the peritoneum. The parietal peritoneum lines the abdominal wall and the visceral peritoneum covers the abdominal organs.

Peritubular (peri-tubular): This term describes a position that is adjacent to or surrounds a tubule. For example, the peritubular capillaries are tiny blood vessels that are positioned around nephrons in the kidneys.