< Anatomy and Physiology of Animals < Glossary 
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| Word | Meaning | 
|---|---|
| R | |
| Radius | The shorter bone of the forelimb between the humerus and the “wrist” | 
| Receptor | A specialized cell that responds to specific sensory stimuli such as touch,pressure, light etc. | 
| Red marrow | Bone marrow found in the spaces of spongy bone.Makes red blood cells | 
| Reflex | A fast automatic response to a stimulus | 
| Reflex arc | Consists of receptor, sensory, relay and motor neurons and effector | 
| Refraction | Bending of light as it passes from one medium to another | 
| Relaxin | The hormone secreted by the placenta and ovaries that eases the joint between the right and left pelvis and dilates the cervix for birth | 
| Renal | To do with the kidney | 
| Renal pelvis | The cavity in the centre of the kidney | 
| Renal pyramid | A cone shaped structure in kidney medulla | 
| Renal system | The body system involving the kidneys | 
| Reticulum | The part of the modified stomach of ruminants with honeycomb of raised folds on its inner surface | 
| Retina | The inner coat of the eyeball. Nerve calls here (rods and cones) respond to light ray | 
| Ribosome | The organelle in the cell that makes proteins | 
| Rickets | A bone disorder caused by inadequate vitamin D | 
| Rod | The photoreceptor in the retina, specialized for vision in dim light | 
| Rostral | Towards the muzzle | 
| Rumen | The first and largest compartment of the modified stomach of ruminants.It houses the microorganisms | 
| Ruminant | An animal with a rumen e.g. sheep, cow, camel | 
| Rumination | Chewing the “cud” | 
| S | |
| Sacrum | The triangular bone formed from fused sacral vertebrae.Located between the two hipbones | 
| Sagittal plane | Plane that divides the body into left and right portions | 
| Sagittal section | Lengthwise slice of an animal or organ | 
| Saliva | The secretion from the salivary glands | 
| Salivary amylase | The starch digesting enzyme in saliva | 
| Saturated fat | A fat containing saturated fatty acids | 
| Scapula | The shoulder blade | 
| Sciatic nerve | The large nerve that passes down the hind leg | 
| Sclera | The fibrous outer coat of eyeball | 
| Seasonal breeding | Breeding confined to certain seasons of the year | 
| Sebaceous gland | An exocrine gland in the dermis of the skin associated with a hair follicle | 
| Sebum | The waxy secretion from a sebaceous gland | 
| Secondary sex characteristic | A characteristic that develops at sexual maturity. e.g. large body size of males, manes in lions | 
| Secretion | The production or release of a fluid from a gland | 
| Semen | The fluid discharged at ejaculation of male. Consists of sperm and fluid | 
| Semicircular canals | The membranous fluid filled canals containing receptors for equilibrium | 
| Semilunar valve | The valve guarding the entrance to the aorta or the pulmonary artery | 
| Seminal vesicle | A gland that secretes a component of semen | 
| Seminiferous tubule | The tightly coiled duct in the testis where sperm are produced | 
| Semi-permeable membrane | A membrane that allows some substances to cross more easily than others | 
| Sensory neuron | A neuron that carries a nerve impulse towards the central nervous system | 
| Serum | Plasma minus its clotting proteins | 
| Sesamoid bones | Small bones usually found in tendons | 
| Shock | Reduced cardiac output resulting in failure to deliver adequate oxygen and nutrients to the body | 
| Shoulder | The synovial joint where the humerus joins the scapula | 
| Sinus | An air cavity in a bone especially in the bones of the face or skull | 
| Skeletal muscle | Tissue specialized for contraction with striated fibres. Attached to the bones of the skeleton | 
| Skull | The skeleton of the head | 
| Small intestine | The long tube of the gut that begins at the stomach and ends at the large intestine | 
| Smooth muscle | Tissue specialized for contraction with spindle shaped non striated fibres | 
| Soft palate | The posterior portion of the roof of the mouth | 
| Solution | One or more substances dissolved in a liquid | 
| Specific gravity | A measure of the density of a liquid or solid, as compared with that of water. | 
| Sperm duct | The tube that carries sperm from the epididymis to the urethra. Also called the vas deferens | 
| Spermatic cord | The structure in the male reproductive system attached to the testis that carries the vas deferens, arteries, veins, etc. | 
| Spermatozoon | A mature sperm cell | 
| Sphincter | A ring-like muscle that controls movement along a body passage or orifice | 
| Spinal cord | The mass of nerve tissue in the vertebral column | 
| Spinal nerve | One of the nerves that originate in the spinal cord | 
| Spleen | The large lymphatic organ near the stomach that stores blood and produces lymphocytes | 
| Spongy bone | The inner layer of bone; found at the ends of long bones less dense than compact bone | 
| Squamous | Scale like | 
| Starch | The storage polysaccharide in plants consisting of many glucose molecules | 
| Sterile | Free from any living micro organisms | 
| Sternum | The breastbone | 
| Stifle | The joint between the femur and the tibia on the hind leg | 
| Stimulus | Any change in the environment capable of initiating a nerve impulse | 
| Stomach | The large baglike part of the gut between the oesophagus and the small intestine | 
| Striated muscle | Striped or skeletal muscle | 
| Subcutaneous | Beneath the skin | 
| Submandibular gland | The salivary gland beneath the tongue | 
| Substrate | A substance on which an enzyme acts | 
| Sulcus | A groove or depression between the convolutions of the brain | 
| Superficial | Nearer to the surface of | 
| Suture | An immoveable joint in the skull | 
| Sympathetic division | One of the two subdivisions of the autonomic nervous system concerned with reacting to emergency situations | 
| Synapse | The junction between two neurons | 
| Synovial joint | A fully moveable joint | 
| System | An association of organs that have a common function, e.g. digestive system, respiratory system | 
| Systemic circulation | The blood circulation from the left ventricl through the aorta to all the organs of the body and back to the heart | 
| Systole | The phase of the heartbeat involving contraction of the ventricles | 
| Systolic blood pressure | The blood pressure during passage of the pulse | 
| Synapse | The junction between two neurons | 
| Synovial joint | A fully moveable joint | 
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