K
Karyotype- A photograph of all of the chromosomes displayed in order.L
Labia majora- Two fleshy folds of skin located in the vulva. Comprised of fat and fibrous tissue.Labia minora- Two smaller folds of skin located between and beneath the labia majora. Lack fat and are pinkish in colour. Surround the openings of the urethra, vagina and the clitoris.
Lactase- An enzyme in intestinal juice that breaks lactose down into monosaccharides.
Lacteal- A lymph capillary located in the villi.
Lactogenic hormones- Hormones secreted by the pituitary gland that affect the breasts of women. Important in milk production. Also known as prolactin.
Lacunae (singular: lacuna)- Spaces between the lamellae in compact bone. Contain bone cells.
Lamellae (singular: lamella)- A bony matrix consisting of bone cells as well as non-cellular material, including inorganic salts.
Laryngitis- Swelling of the mucous membrane covering the vocal cords, making it difficult for them to vibrate.
Larynx- An organ that connects the pharynx with the trachea. Also known as the "voice box" as it has a role in producing sounds.
Leucocytes- Blood cells that defend the body against invading microorganisms and remove dead or injured cells. They are white, hence their common name, white blood cells.
Leukaemia- An abnormal number of white blood cells are produced. These white blood cells fill the red bone marrow, inhibiting the production of the red blood cells, which can lead to anaemia.
Lipase- An enzyme in intestinal juice that breaks down lipids.
Lipids- Water-insoluble molecules stored in the body as energy reserves.
Liver- A rather large organ located just below the diaphragm on the right side of the body. It has many known functions, including blood glucose regulation, deamination, fat conversion, plasma protein production, production of blood-clotting factors, storage of various substances, toxin breakdown, hormone inactivation and heat production.
Lobes- Sections of the breast. There are around 15-25 per breast. Surrounded by fatty connective tissue.
Lobules- Sub-sections of the breasts. Surrounded by fatty connective tissue. The walls are made up of lots of glandular alveoli, which secrete milk. Lead into ducts, which open up into milk spaces, which then lead into short, straight ducts to the nipple.
Longitudinal arch- The front to back arch of the foot.
Longitudinal muscle- Muscle in which the muscle fibres are arranged along the length of something else (such as the alimentary canal).
Loose connective tissue- A type of connective tissue that supports and connects other tissues. Made up of fibres and cells in a semi-fluid matrix.
Lung cancer- Involves the development of a tumour, just like other cancers. Normally begins in the walls of the bronchi- excessive production of mucus is caused by irritation of the mucous membrane lining. Trapped mucus causes alveoli to rupture, resulting in emphysema. Eventually a cancerous growth develops in a bronchus and may spread to other parts of the body.
Luteinising hormone (LH)- A gonadotropic hormone secreted by the pituitary gland. In females, LH promotes final maturation of the ovarian follicle, ovulation and the formation of the corpus luteum. Less LH is secreted as progesterone levels rise. In males, LH stimulates ccells in the testes to secrete the hormone testosterone, which is important for sperm production.
Lymph- The fluid inside the lymph capillaries. Composition is essentially the same as tissue fluid.
Lymph capillaries- Small lymph vessels that eventually join up to form lymphatic vessels.
Lymph nodes- Nodes located along the lymphatic vessels that remove bacteria and foreign particles from the lymph.
Lymphatic system- The system that drains fluid from the tissues. Consists of lymph vessels as well as the lymphoid organs.
Lymphomas- Solid tumour masses formed from cells of blood and/or lymphatic origin.
Lymph vessels- Consist of the lymph capillaries, lymphatic vessels and other ducts of the lymph system. They are squeezed when surrounding muscles contract, pushing the lymph along. They have valves to ensure that the lymph only moves in one direction.
Lymphatic vessels- Lymph vessels that eventually join up to become even bigger lymphatic vessels, which then join in to the thoracic duct and the right lymphatic duct.
Lymphoid organs- The tonsils, thymus and spleen. Are involved in specific immune responses.
Lysosomes- Small membrane-bounded spheres formed by the Golgi apparatus. Contain digestive enzymes which break down material transported into the cell via vesicles as well as worn-out organelles.
M
Male pronucleus- The head of the sperm once it has entered the egg and had its tail absorbed.Malignant neoplasm- An abnormal mass of tissue formed from the uncontrolled division of cells. Also known as a malignant tumour.
Malignant tumour- An abnormal mass of tissue formed from the uncontrolled division of cells. Also known as a malignant neoplasm.
Mammalia- A class (taxonomic rank) that includes warm-blooded hairy creatures that produce milk.
Mandible- The bone that makes up the lower jaw. It is the only bone in the jaw with a moveable joint.
Matrix- The name for the intercellular material inside tissues.
Maxilla- The bone that forms the upper jaw, as well as part of the mouth, eye sockets and nasal cavities.
Mediastinum- The space between the two lungs.
Meiosis- A type of cell division that results in four haploid "daughter" cells. Used to form the gametes.
Melanocyte- A pigment cell.
Melanoma- A type of cancer that forms from melanocytes. Grow and spread very quickly.
Menarche- The time at which a woman first begins to menstruate. Normally between 9-16 years of age.
Menisci (singular: meniscus)- Articular discs in the knee joint. Consist of fibrocartilage which extends inwards from the articular capsule.
Menopause- The time at which menstruation no longer occurs. Normally occurs around 35 years after menarche, between the ages of 40 and 50.
Menstruation- The expulsion of blood, mucous secretions and cell debris from the uterine lining through the vagina. Occurs roughly once every month.
Mesenteric artery- An artery that takes blood to the intestines.
Messenger RNA- A type of RNA used to transfer the genetic code from the DNA to the ribosomes.
Metabolism- The chemical reactions that take place within cells.
Metacarpals- Bones in the palm of the hand.
Metaphase- The second stage of mitosis. During this stage, the chromosomes line up on the equator of the spindle. The centromere of each chromosome is attached to a spindle fibre.
Metastasis- The process in which malignant cells spread to other parts of the body, forming secondary tumours.
Metatarsals- Foot bones.
Microfilaments- One of the structures of the cytoskeleton. Moves materials around the cytoplasm or moves the entire cell.
Microtubules- One of the structures of the cytoskeleton. Keeps organelles in place or moves them around the cell.
Microvilli (singular: microvillus)- Small projections located on the villi.
Minerals- Elements such as calcium, ion, iodine, zinc and fluorine that are necessary for the body. Different minerals have different functions within the body.
Mitochondria (singular: mitochondrion)- The energy centres of the cell. They have two membranes, which contain enzymes which are involved in energy-releasing cellular reactions. The inner membrane has a series of folds (which the outer membrane lacks), increasing the surface area for chemical reactions.
Mitosis- A type of cell division which results in two diploid "daughter" cells.
Molars- Teeth used for crushing and grinding (along with the premolars). The cusps on the crowns of the molars fit into the depressions of the crowns of the molars on the opposite site, making crushing and grinding more efficient.
Monosaccharide- Simple sugars (e.g. glucose, fructose, galactose) that only consist of one ring of C, H and O atoms. Can combine to form disaccharides or polysaccharides.
Monounsaturated fat- A fat in which there is only one double bond between carbon atoms.
Morula- A ball of cells formed from the zygote dividing. It is roughly the same size as the original zygote as no new cytoplasm is produced, but has many more nuclei due to the increased number of cells.
Mountain sickness- Higher altitudes contain lower pressure air (i.e. fewer gas molecules in the same amount of space as compared to lower altitudes). People who aren't used to the lower pressures may feel sick as their bodies are unable to absorb enough oxygen. Also known as altitude sickness.
Mucosa- The innermost layer of the alimentary canal. In the oesophagus, it secretes mucus, making it easier for the food to move through. In the stomach, it secretes gastric juice, which contains digestive enzymes, among other things. The stomach mucosa can also secrete mucus to protect itself from the hydrochloric acid in the gastric juice. The small intestine mucosa has many folds as well as finger-like projections called villi, increasing surface area. It also contains glands that secrete intestinal juice.
Mucus method- A method of contraception that relies on observing changes in the mucus of the cervix.
Muscle tone- The partial contraction of skeletal muscles.
Muscular dystrophy- Inherited diseases in which individual muscle cells degenerate. Leads to a progressive reduction in the size of the skeletal muscle, an increase in connective tissue and possibly the replacement of muscle fibres with fatty tissue. There are two forms: the Duchenne form and the fascioscapulohumeral form.
Muscular endurance- The ability of a muscle to contract repeatedly or sustain a contraction for an extended period of time.
Muscular strength- The force that a muscle group can exert against a resistance.
Muscle tone- The maintenance of partial contraction of muscles.
Mutagens- Agents that can increase the rate at which mutations occur (though do not cause mutations). Include mustard gas, sulfur dioxide, X-rays, radiation, and so on.
Myocardial infarction- A complete stop in blood flow to a part of the heart muscle, resulting in death of the muscle in that area. This causes sudden and severe chest pain. Can heal if only a small area is affected; adverse effects and death can also occur. Symptoms include chest pain, pain radiating to the left arm, shoulder, neck or jaw, sweating, breathlessness, faintness and palpitations. Also known as a heart attack.
Myofibrils- Thread-like structures found within the sarcoplasm.
N
Nasal cavity- The part of the nose inside the skull.Neck (part of tooth)- The part of the tooth between the crown and the roots.
Net diffusion- The overall movement of particles along a diffusion gradient.
Neurons- Nerve cells.
Non-specific urethritis (NSU)- An infection of the urethra. Can be caused by the Chlamydia bacteria, though there are many other causes.
Nuclear membrane- The membrane surrounding the nucleus. It is actually a double membrane- two membranes separated by a space.
Nucleic acids- Molecules consisting of chains of nucleotides. RNA (ribonucleic acid) has one chain, while DNA (deoxyribonucleic acid) has two chains.
Nuclear pores- Gaps in the nuclear membrane which allow substances to pass through.
Nucleolus- An area in the nucleus that contains RNA, which plays a role in synthesising proteins.
Nucleoplasm- The fluid inside the nucleus. Suspended in it are chromatin threads and the nucleolus.
Nucleotide- A small molecule consisting of a nitrogen base, a sugar and a phosphate group. RNA (ribonucleic acid) has ribose sugar, while DNA (deoxyribonucleic acid) has deoxyribose sugar.
Nucleus- One of the organelles of the cell. Nearly all cells contain one, though some contain more, and some don't have a nucleus at all. It is the largest organelle, is normally oval or spherical in shape, and is surrounded by a nuclear membrane. The nucleus is often thought of as the "control centre" for the cell as it contains DNA (deoxyribonucleic acid), which determine which proteins and enzymes a cell can make, which then determine which chemical reactions can take place in the cell.
O
Oblique muscle layer- A layer of muscles in the stomach that provide the stomach with more ways in which it can churn the food.Oestrogen- One of the sex hormones in females.
Olfactory receptors- Nerve endings located in the upper part of the nasal cavity. Are sensitive enough to distinguish different smells.
Oogenesis- The process in which ova are produced.
Oogonia (singular: oogonium)- "Egg mother cells." Diploid cells that will eventually divide to form ova. Millions are already present at birth.
Oophorectomy- Removal of ovaries.
Opposability- The ability of the thumb to reach across and touch the tips of the other fingers of the same hand.
Organelles- Small structures within the cell that carry out various functions.
Origin- The end of the muscle attached to the stationary bone.
Osmosis- The diffusion of water across differentially permeable membranes (e.g. the membranes of cells).
Osmotic pressure- The pressure caused by osmosis when solutes that can't pass through a differentially permeable membrane are added.
Osteoarthritis- A much more common, but much less damaging form of arthritis (as opposed to rheumatoid arthritis). It involves deterioration of the articular cartilage, causing bony spurs to develop from the ends of the bone forming the joint. Due to these spurs, the space in the joint is decreased, which in turn restricts the movement of the joint.
Osteoblast- Bone-forming cell that allows bones to repair themselves after a fracture. Stimulated when the bone is used for support and movement.
Osteocyte- Bone cell
Osteoporosis- A gradual reduction in the rate of bone formation while the rate of bone absorption remains normal. This results in the bones becoming porous, fragile and relatively easily broken.
Ova (singular: ovum)- The female gametes.
Ovarian cyst- A fluid-filled tumour in the ovary that is usually not cancerous.
Ovary- The organ in which ova are produced. They are located within the body, on either side of the pelvic cavity, and are supported by ligaments.
Oviduct- A tube that carries the ovum from an ovary to the uterus. Also known as the Fallopian tube or uterine tube.
Ovulation- The expulsion of an ovum from the mature follicle into the uterine tube.
Oxyhaemoglobin- A bright red compound produced when oxygen and haemoglobin combine.
Oxytocin- A hormone secreted by the pituitary gland. Causes the small muscles around the milk-filled lobules in the breast to contract, pushing milk through the openings on the nipple.
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