Glossary of Key Terms in Functioning Systems

abomasum

final part of the stomach of a ruminant where enzymes are secreted and used in digestion; food then passes to the small intestine.

acinar cells

cells of the pancreas that produce and transport enzymes that are passed into the duodenum where they assist in the digestion of food.

adipocytes

cells with large deposits of stored fat.

adrenal glands

small endocrine glands located on top of the kidneys that produce various hormones.

adhesion

attraction of water molecules to other kinds of charged molecules, such as the walls of xylem tubes.

aldosterone

a steroid hormone produced by the adrenal cortex that regulates levels of salt and water and so controls blood pressure.

alimentary canal

the whole passage from mouth to anus; see gastrointestinal tract.

anterior pituitary

anterior lobe of the pituitary gland; it is made of glandular tissue that synthesises and secretes several releasing hormones that activate other endocrine glands.

areolar

loose, irregularly arranged connective tissue

carnassial teeth

paired upper and lower premolars and molars which do not meet, and hence allow a shearing action to tear food

chemical digestion

the chemical reactions changing food into simpler substances that are absorbed into the bloodstream for use in other parts of the body

chief cells

in the parathyroid gland, secretory cells that produce parathyroid hormone (PTH) (Note: different cells with same name are present in the gastric pits of stomach.)

chyme

slurry of partially digested food produced in the stomach which passes into small intestine

circular folds

permanent macroscopic folds (ridges) in the mucosa of the small intestine

cohesion

tendency of water molecules to stick together through the formation of hydrogen bonds between one another

collenchyma

thick, flexible walled cells in plants; the main supporting tissue of stems

colloid

gel-like material inside follicles that is the source of thyroglobulin, a prohormone of the T3 and T4 thyroid hormones

connective tissue

diverse solid tissues that connect and support other tissues and organs, or store fat deposits, and fluid tissues that transport materials such as nutrients, wastes and hormones

corticoid hormones

steroid hormones, including aldosterone and cortisol, produced by cells of the cortex of adrenal glands

cortisol

a steroid hormone produced by the adrenal cortex that has many roles, including control of blood glucose levels during stress and the body's recovery from the stress response

crypts

tube-like depressions of the mucosa located in the intestine and the site of glandular cells

dermal tissue

tissue that protects the soft tissues of plants and controls water balance

ecdysone

steroid hormone which controls moulting in insects

ectoderm

epithelial tissue that covers the outer surface of the body

endocrine system

network of ductless glands that produce and secrete hormones that are transported by the bloodstream to their distant target organs

endocrine glands

ductless glands that distribute hormones via the bloodstream

epithelial tissue

sheets of cells that cover the external surface of the body and also line internal surfaces that connect to the external environment

excretion

process of removal from the body of various types of waste material arising from its metabolic activities

filtrate

fluid composed of blood plasma minus large proteins that is filtered into Bowman's capsule from the glomerulus

flame cells

excretory cells with flagella present in members of phylum Platyhelminthes

follicles

secretory cells that enclose the thyroid follicles and that synthesise and release the hormones, T3 and T4

follicular cells

secretory cells that enclose the thyroid follicles and that synthesise and release the hormones, T3 and T4

gall bladder

sac shaped organ which stores the bile after it has been secreted by the liver

gastric glands

glands of the stomach that contain various epithelial secretory cells, producing neutral mucus, stomach acid and enzymes

gastric juice

acid fluid secreted by the stomach glands for digestion in the stomach

gastrodermal tissue

epithelial tissue that lines the inner cavity of the body

gastrointestinal tract

the whole passage from mouth to anus; see alimentary canal

gizzard

second part of bird's stomach that grinds food

ground tissue

all plant tissues that are not dermal or vascular

gut microbiota

the population of organisms which live in the gut and play a crucial role in maintaining immune and metabolic homeostasis and protecting against pathogens

hemolymph

the internal fluid of insects, analogous to blood in vertebrates; mostly water; it also contains ions, carbohydrates, lipids, glycerol, amino acids, hormones and some cells.

hormones

chemical messengers, released by endocrine glands, that regulate the function of distant organs, each with a specific receptor for its hormone

hydrophilic

substances that dissolve easily in water; also called polar

hydrophobic

substances that tend to be insoluble in water; also called non-polar

hydroponics

process of growing plants without soil; instead the roots are grown in a solution of mineral nutrients.

juvenile hormone

insect hormone in the nymphal and larval stage of all insects; it is a lipid, derived from a fatty acid.

lacteals

the vessels of the lymphatic system which absorb digested fats

lumen

the inside space of a tubular structure

meristematic tissues

plant tissue found in tips of roots and shoots that is made of unspecialised cells that can reproduce by mitosis

mechanical digestion

digestion that uses physical factors such as chewing with the teeth

metamorphosis

process of transformation — in insects (holometabolous) and amphibians — from an immature form to an adult that involves major changes in body structure and physiology

microvilli

sub-microscopic outfoldings of the plasma membrane of enterocytes of the small intestine that form the so-called 'brush border' of these cells

moult

in insects, the periodic event during development of larvae or nymphs which involves growth in epidermal cell numbers, shedding of the noncellular outermost cuticle and production of a new expanded cuticle

mucosa

the innermost lining of the digestive system

muscularis

muscle tissue of the gut

nephron

functional unit of the kidney

neurosecretory cells

cells that receive nerve impulses and respond by a chemical stimulus

omasum

third part of the stomach of a ruminant which acts as a filter and where water is absorbed

parafollicular cells

secretory cells, located in small areas between follicles, that produce the thyroid hormone, calcitonin

parathyroid hormone

a protein hormone synthesised and secreted by the parathyroid glands in response to a falling blood calcium levels

parenchyma

thin-walled living plant cells; in leaves the site of photosynthesis and in roots, tubers and seeds the site of stored starch and oils

peristalsis

involuntary constriction and relaxation of muscles in the alimentary canal to push food to the stomach

permanent tissues

plant cells that can no longer divide and includes dermal tissue, ground tissue (parenchyma, collenchyma and sclerenchyma) and vascular tissue (xylem and phloem)

phloem

complex plant tissue that transports sugars and other organic compounds

posterior pituitary

posterior lobe of the pituitary gland; it is made of neural tissue that stores and releases hormones sent from the hypothalamus.

proenzyme

a precursor of an enzyme that must be activated to form the functional enzyme

prothoracicotropic hormone (PTTH)

hormone released in the brain of insects related to moulting and metamorphosis

proventriculus

first part of bird's stomach where proteins are digested by enzymes

pyloric sphincter

a sphincter at the join of the stomach and the duodenum of the small intestine; it controls the flow of acidic chyme into the alkaline duodenum.

reticulum

second part of the stomach of a ruminant that is the smallest of the four chambers; collects any heavy objects

root hairs

extensions of cells of the epidermal tissue that forms the outer cellular covering of the root; responsible for absorption and uptake of liquid water

root system

the below-ground system of plants which anchors the plant in the soil, is responsible for the absorption and conduction of water and minerals, and the storage of excess sugars (starch)

rumen

first part of the stomach of a ruminant where digestion occurs with the aid of gut microbiota

ruminants

animals that absorb nutrients by fermenting food in a specialised stomach prior to digestion

sclerenchyma

dead cells with thickened walls for strength and rigidity

serosa

outer connective tissue which encloses the gut

shoot system

the above-ground system of plants, the site of photosynthesis, transport of sugars and the site of reproductive organs

sphincters

thickened rings of muscle which control the opening and closing of a tube

stress response

combined physiological reactions to stress, also known as the 'fight or flight' response, that results from release of the hormones, adrenaline and noradrenaline from the adrenal medulla

stomata

pores, each surrounded by two guard cells that regulate the opening and closing of the pores

sub-mucosa

connective tissue forming the second layer of the gut lining

thyroid gland

endocrine gland located in throat that produces and secretes the hormones including T3 and T4

tracheids

major water conducting cells in the xylem of all vascular plants

transitional epithelium

type of stratified epithelium present only in the hollow organs of the excretory system

transpiration

loss of water from the surfaces of a plant

urinary tract

a series of hollow organs comprising ureters, bladder and urethra that transport urine to the outside of the body

vascular plants

plants with xylem and phloem tissue — the majority being flowering plants and conifers

vascular tissue

plant tissue composed of xylem and phloem

vessels

major water conducting cells in the xylem of angiosperms

villi

outfoldings or projections of the mucosa of the small intestine

X-organ

sinus gland complex major neuroendocrine control centre of malacostracans (including crabs, hermit crabs, lobsters, shrimp and isopods)

xylem tissue

the part of vascular tissue that transports water and minerals throughout a plant and provides a plant with support

xylem

the part of vascular tissue that transports water and minerals throughout a plant and provides a plant with support