anatomic and physiologic features

1. In the name of God

2. The Laboratory Rat

4. • Rats are thought to have originated in the area of Asia currently occupied by southern
Russia and northern China.
• Rattus rattus (black or ship rat, 2n = 38) was well established in Europe by 1100 A.D.
• Today, the black rat is restricted to areas near water.
• Rattus norvegicus (brown rat, 2n = 42) commonly found in Europe in the 1700s.
• The brown rat has conquered the planet because of its climatic adaptability and ability to
parasitize human refuse.
• Today’s laboratory rats are the domesticated descendants of Rattus norvegicus.
•
Introduction

5. Differences between wild and laboratory rodents :
Laboratory rats have
• smaller adrenals
• preputial glands
• earlier sexual maturity
• no reproductive cycle seasonability
• better fecundity
• and a shorter life span
Introduction

6. Introduction
Taxonomy of the Rattus norvegicus:
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Genus: Rattus
Species: norvegicus

7. Rats fall into two basic groups depending on whether they are inbred or outbred
• One generally refers to inbred animals as strains, and outbred animals as stocks
• Inbred strains : inbred- brother/sister matings for 20 generations.
• Outbred stocks : outbred in a closed colony for at least four generations.
• Different stocks and strains show variability in many biological parameters including
hematology, clinical chemistry, and anesthesia response.
Nomenclature

8. • Rats are nocturnal animals with most activity occurring at night and in the early morning.
• rats are typically non-aggressive, inquisitive, and easily trainable.
• Frequent handling encourages their non-aggressive nature as they adapt to new
surroundings or experimental situations.
• Improper handling, nutritional deficiencies, and vocalizations from other rats can result in
undesired behavior.
• Rats feel most comfortable in small, dark, confined spaces; a behavior investigators may use
as a reward.
• When designing experiments, it is important to understand the rat’s coprophagic behavior
and its potential impact on metabolic, drug, and other studies.
• Male rats, unlike mice, are unlikely to fight when housed together
Behavior

9. Oropharynx
• Dental formula: 2 (incisors 1/1 canines 0/0 premolars0/0 molars 3/3) = 16.
• The incisors grow continuously.
• Lack water taste receptors found in other animals.
• Lack tonsils.
anatomic and physiologic
features

10. Salivary glands
Three pair of salivary glands:
• Parotid : The parotid salivary gland secretes a serous product, and consists of 3–4 lobesThe
parotid duct opens opposite the molar teeth.
• Submaxillary : The submaxillary (submandibular) glands are mixed glands secreting a serousand
mucous product. There are two types of secretory granules found in the submaxillary glands, one in
the acinar cellsand the other in the granulated portion of thesecretory ducts.
• Sublingual :The sublingual glands are the smallest of the salivary glands and secrete a mucous
product.
anatomic and physiologic
features

11. Esophagus
• The esophagus enters the lesser curvature of the stomach through a fold in the limiting
ridge of the stomach. The fold prevents rats from vomiting.
• The esophageal lining is entirely keratinized epithelium.
Stomach
• The rat’s stomach has nonglandular and glandular portions separated by the “limiting
ridge.
anatomic and physiologic
features

12. Small Intestine
Small intestine lengths and transit times vary with the age of the rat.
• duodenum: 10 cm in length
• jejunum: 100 cm in length
• ileum: 3 cm in length
anatomic and physiologic
features

13. Large Intestine
• Cecum : The cecum is a thin-walled, comma-shaped pouch with a prominent lymphoid
area found on the lateral aspect of the apex.
The lymphoid tissue is thought to be analogous to the vermiform appendix
found in human beings.
• Colon : The colon has three divisions: ascending, transverse, and descending. The
ascending portion has oblique mucosal ridges, whereas the mucosal folds of the
transverse and descending regions have longitudinal mucosal folds.
• Rectum : The rectum is that region of the gastrointestinal tract found in the pelvic
canal.
anatomic and physiologic
features

14. Liver
• Consists of four lobes: median, right lateral, left, and
caudate.
• The rat has no gall bladder.
• The bile from each lobe leaves via ducts. which enters the duodenum approximately 25 mm distal
to the pyloric sphincter.
Pancreas
• Consists of a lobulated, diffuse organ, extending from the duodenal loop to the gastrosplenic
omentum. The pancreas has a darker color and firmer texture than the surrounding adipose tissue.
• The diffuse nature of the organ results in a network ofducts which coalesce into 2–8 larger ducts
emptying into the common bile duct.
anatomic and physiologic
features

15. Urinary System
• Rats, like other rodents, possess a unipapillate kidney,which consists of one papilla and
one calyx and enters the ureter directly.
• Long and short nephrons are present.
anatomic and physiologic
features

16. Reproductive System
To distinguish males and females, note that males have a greater anogenital distance than females .
Female
• Six pair of mammary glands
• Uterus is bicornuate and duplex consisting of two uterine horns, two cervices, and one vagina.
• Hemochorial discoid placentation.
male
• No nipples.
• Has an os penis.
• Accessory sex glands consist of:
anatomic and physiologic
features

17. Respiratory
• Left lung consists of 1 lobe.
• Right lung consists of 4 lobes: cranial, middle, accessory,and caudal.
• Bronchial constriction is under the control of the vagus nerve, not the adrenergic nerve supply.
• The lung is immature at birth and consequently devoid of alveoli, alveolar ducts, and respiratory bronchioles.
Air exchange occurs through the smooth walled channels and saccules until 4–7 days following birth when
remodeling occurs.
• The epithelial serous cell is thought to be unique to the rat. It secretes a product which has a viscosity less than
mucous cell, and is thought to be responsible for the low-viscosity pericilliary liquid layer found at all levels
of the rat’s respiratory tract.
• Regulation of the respiratory system occurs through tissue CO2 exchange in the medullary respiratory center,
with the carotid bodies playing a role.
• The rat has the thinnest pulmonary artery and the thickest pulmonary vein studied. The thickness of the
pulmonary vein is due to the cardiac striated fibers, which are mainly observed in the intrapulmonary branches
anatomic and physiologic
features

18. Glands
• Lacrimal glands extraorbital lacrimal glands lie ventral and rostral to the ear and
intraorbital lacrimal glands lie in the caudal angle of the orbit.
• Steno’s gland lies in the maxillary sinus and is homologous to the salt gland of marine
birds. The gland regulates mucus viscosity and humidifies inspired air.
• Harderian glands are found behind the eye and produce a porphyrin secretion which
usually goes unseen, except in cases of illness or stress. The porphyrin component
causes crusts or tears to form which will fluoresce red under ultraviolet light
• Zymbal’s gland is found at the base of the ear.
Like other rodents, rats have no sweat glands and are poor regulators of core body The rat’s
tail plays a role in thermoregulation .
anatomic and physiologic
features

19. peripheral nervous system (PNS)
• The rat’s PNS consists of 34 pairs of spinal nerves arising
• The autonomic nervous system forms the greater and lesser splanchnic nerves
along with their plexi and ganglia.
central nervous system (cns)
• Th e brain and spinal cord form the CNS. The brain consists
of the cerebrum and cerebellum.
• The CNS has three coverings or meninges — dura mater, arachnoid, and pia mater..
The brain and spinal cord are bathed in cerebrospinal fluid (CSF).
• The ventricles serve as a conduit for the CSF within the brain..
medulla oblongat
anatomic and physiologic
features

20. special senses
• The senses of hearing and smell are well developed in rats; however, rats have poor eyesight.
Cones are virtually absent from the retina of the rat, leaving the animal color blind. This inability to see
long-wave, red light has some advantages when visual inspection of animals is necessary
after hours; however, their ability to perceive dim light is good.
Circulatory
• The cardiac blood supply originates from both the coronary and extracoronary arteries
• There are two precavae present in the rat vena cava, with the right precava emptying into the right
atrium, and the left precava joining with the azygous vein before
dumping into the right atrium.
anatomic and physiologic
features

21. • In general, hematologic samples should be submitted in tubes containing the anticoagulant EDTA.
Heparin is not a suitable anticoagulant for determining complete blood cell counts (CBC)and
interferes with Wright’s stain for differential counts. Heparin, sodium citrate, and other
anticoagulants should be selected based on the assay being performed.
• Complete blood cell counts should be run the same day as sampling. Holding samples overnight,
even if refrigerated, can cause inaccurate counts.
• Most clinical chemistry assays are performed on serum, but for some, plasma is acceptable.
Hemolysis invalidates many clinical chemistry tests. Even minor hemolysis can falsely elevate such
enzymes as lactate dehydrogenase (LDH).
• Storage of samples (serum or plasma) in a refrigerator or freezer may be possible, but some
enzymes are unstable for longer periods of storage at any temperature.
• If storage of samples is unavoidable, care must be taken to place the samples in tight containers
to avoid evaporation which occurs even in frozen samples.
hematology and clinical
chemistry

22. Estrus:
• a state or period of heightened sexual arousal and activity
• The estrous cycle is light sensitive and The estrous cycle is a 4–5 day cycle with the following
cytologic characteristics of vaginal smears
I. Proestrus
II. Estrus
III. Metestrus
IV. Diestrus
Reproduction

23. Pheromones :
• present in male urine
• effects on reproduction
Lee-Boot effect: Females without males – estrus cycles is suppressed
Whitten effect: Male to a female group – estrus cycle synchronized
Bruce effect: Strange male into female group within 24h from mating – implantation
prevented
Reproduction

24. Thank you for your attention