Rabbit Anatomy: Respiratory System

Digestive, Respiratory, and Urogenital System of the Rabbit

• Covers the respiratory, digestive, and urogenital systems of rabbits

Respiratory System

• Functions for the exchange of gases
• Includes the external nares, nasal cavity, epiglottis, glottis, larynx, trachea, bronchi, lungs, bronchioles, and alveoli

External Nare

• Nose/nostrils

Epiglottis

• Controls the movement of air and food
• Acts as a flap
• Remains open for air and closes for food
• Located dorsally to the soft palate
• Rabbits are nose breathers because the epiglottis closes when the mouth opens

Glottis

• Functions as the voice box
• Located in the center in front of the larynx

Larynx

• The voice box

Trachea

• Windpipe
• Functions as the passageway of air from the larynx to the bronchi

Bronchi

• Two branches leading to the lungs

Lungs

• Divided into 4 lobes
• The right lung is larger than the left lung due to the presence of the heart in the left pleural cavity
• The air flow volume of the left lung is higher than that of the right lung because of the lower resistance of the proximal airways per unit volume

Bronchioles

• Found in the lungs
• Smaller branches
• The bronchial artery extends to the third division of the bronchi

Alveoli

• End of bronchioles
• Small sacs filled with capillaries
• Site where the exchange of gases happens

Thymus

• Part of the respiratory system

Digestive System

• Includes the oral cavity, tongue, salivary glands, esophagus, gastrointestinal tract, stomach, small intestine, cecum, vermiform appendix, ileocecocolic complex, large intestine, rectum, anus, and accessory organs

Oral Cavity

• Permanent teeth grow in 3-5 weeks
• Peg teeth (pair of small incisors)
• Upper and lower incisors grow 10-13 cm a year
• Incisors 2/1, C 0/0, PreMolar 3/2, Molar 2-3/3x2 = 26 or 28
• Diastema is space between the incisors and premolars and helps to cut off small pieces of vegetation
• Tactile Vibrissae allows rabbits to locate and eat their food
• Rabbits chew quickly and thoroughly with jaw movements of up to 120 per minute

Tongue

• Large relative to the rabbit
• The dorsal surface is covered with small elevations called papillae which gives the tongue its roughened surface

Salivary Glands

• There are 4 pairs
• Parotid gland extends below and in front of the ear base, between the skin and masseter muscle
• Submaxillary or Mandibular is an oval-shaped gland located at the angle of the mandible
• Sublingual is a small gland, under the tongue
• Zygomatic gland lies just below the lacrimal gland in the anteroventral angle of the orbit and is not present in other animals such as humans
• There is a continuous secretion of saliva from the mandibular gland
• In ruminants, saliva is produced from the parotid glands
• In cats and dogs, saliva is produced from the sublingual glands
• Amylase is present in rabbit saliva
• Lipase and urea are only present in trace amounts

Esophagus

• Has three layers of semi-involuntary striated muscles that extend all the way down to the cardia of the stomach
• No mucus glands

Gastrointestinal Tract

• Takes 9 days to be completely empty

Stomach

• Very acidic, pH 1-2
• For young rabbits, the pH is 5-6.5, which allows bacteria to pass through the GI tracts and colonize the hindgut.

Small Intestine

• Short in comparison to other species
• Accounts for 12% of the GI tract
• The bile duct and pancreatic duct enter the duodenum separately
• Duodenum is the first part of the small intestine
• The jejunum is less vascularized, and its walls are thinner than those of the duodenum
• Ileum is the third and final part of the small intestine

Cecum

• The most prominent organ in the abdominal cavity containing 40% of the ingesta

Vermiform Appendix

• It is a thick-walled, narrow, blind tube containing a large number of lymphoid aggregates

Ileocecocolic Complex

• Junction between the end of the ileum, the cecum, and the proximal colon
• The Sacculus Rotundus appears to have immunological properties
• The Ampulla Coli is the beginning of the colon

Large Intestine

• Consists of Ascending Colon (proximal colon), Transverse Colon, and Descending Colon (distal colon)

Rectum

• Part of the large intestine

Anus

• Function is for storage of feces and the exit of waste

Accessory Organs

• Includes the Liver, Gallbladder, and Pancreas

Liver

• Four lobed
• Responsible for making bile

Gallbladder

• Color is green
• Function is storage of bile

Bile

• Emulsifies fat

Hepatic Ducts

• Join to form the common bile duct which receives the cystic duct from the gallbladder
• Enters the dorsal surface of the duodenum immediately caudal to the pylorus

Pancreas

• Hidden in the surrounding mesentery
• Diffuse organ

Urogenital System

• Has distinct openings for males (circular hole) and females (slit)

Urinary System

• Includes the Inguinal Canal, Kidney, Ureter, Uterus, Urinary Bladder, and Urethra

Inguinal Canal

• The penis is hidden there
• Covers the penis

Kidney

• Contains 200,000 nephrons (functional unit of kidney)
• Filters blood
• Number of glomeruli increases after birth

Ureter

• Leads to the uterus

Urinary Bladder

• Stores the urine

Male Genital Organs

• Include the Scrotal Sac and Testis

Scrotal Sac

• Two hairless sacs cranial to the penis

Testis

• Elongated oval shape with blunt cranial pole and a pointed caudal pole
• Descend at 12 weeks and inguinal rings do not close
• Have open inguinal canals and can retract their testicles abdominally, which they do during sexual inactivity or periods of inadequate food

Male Accessory Organs

• Includes the Prostate Gland, Seminal Vesicles, Bulbourethral Gland, and Vesicular Gland

Prostate Gland

• Overlaps the caudal part of the vesicular glands
• Can be distinguished anatomically by its lighter color

Seminal Vesicles

• Most cranial gland
• Located at the neck of the bladder

Bulbourethral Gland

• Located caudal to the prostate
• Separated from it by a distinct groove

Vesicular Gland

• Located caudal to seminal vesicles, cranial to the prostate
• Separated by a very thin connective tissue septum

Female Genital Organs

• Includes the kidney, ureter, urinary bladder, urethra, urogenital orifice, urogenital sinus, ovary, ostium tubae, oviduct of fallopian tube, uterus, and vagina

Urogenital Orifice

• End
• Includes feces from the rectum

Urogenital Sinus

• Combination of urine and secretions from the vagina

Ovary

• Produces eggs

Ostium Tubae

• Entrance of the tube

Uterus

• Has a bicornuate uterus with two cervices that open independently into the vagina

Female Accessory Organs

• Bulbourethral Gland slides on the dorsal wall of the vestibulum
• Clitoris is located along the ventral surface of the urogenital sinus with the glands clitoris projecting into the urogenital aperture