Anterior: Nose
Posterior: Tail
Ventral: Belly
Dorsal: Back
Medial: Near the centerline
Lateral: away from the center line
Differences between human and rat
Internal anatomy:
➔ Teeth: Rats do not have canines, while humans do
● Rodents incisors have adapted for gnawing by becoming sharpened due to
the lack of enamel on the posterior surface.
➔ Gallbladder: Rats do not have, instead their bile enters into the duodenum from the
pancreas via the hepatic duct.
➔ Penis: Rat flaccid is internal while humans’ is external
➔ Uterus: Y shaped for rats while pear shaped for humans
➔ Pericardium: Rats is transparent and delicate while humans is fibrous
➔ Stomach: Rat have two macroscopic subdivisions of the stomach while humans have
microscopic stomach anatomy differences
➔ Spleen: Leaf shaped in rat, fist shaped in human
➔ Caecum: Large in rats and small in humans
➔ Vermiform appendix: Rats do not have
External anatomy:
➔ Both have 5 digits (pentadactyl)
➔ Tail: Used as a balancing organ for rats while humans lose this feature as a foetus
and instead use their brain as a balancing organ
➔ Vibrissae (long hair): Sensory tactile organs for rats to navigate confined spaces in
darkness.
Dissection procedure
1. Mid-ventral incision using scissors through the layers of the abdominal wall to enter
the abdominal cavity
2. Cut upwards until you encounter resistance - the diaphragm physical separation
between the abdominal and thoracic cavity
3. Then cut laterally around the abdominal cavity
4. Cut anteriorly through the ribcage and sternum past the heart
5. Trim away the ribs and cut along the lateral margins of the thoracic cavity
Body cavities
3 x ventral body cavities
Peritoneal cavity
Parietal peritoneum: Outer membrane lining the abdominal wall
Mesentery: Double layer of peritoneum suspending the intestine
Visceral peritoneum: Inner lining covering the intestine
,Pleural cavities x 2
Parietal pleura: Outer membrane
Visceral pleura: Inner membrane lining the lungs
➔ Rats killed by carbon dioxide poisoning which causes haemorrhage of the small
blood vessels so the lungs are dark red and blood filled while usually they are pink
and spongy
Pericardial cavity
Parietal pericardium: Outer membrane
Visceral pericardium: Inner membrane
Serous membrane is a single layered membrane of mesothelial cells secreting serous fluid
to reduce friction on organs (heart, lungs, abdominal)
Heart
Anterior base of the heart overlapped by the two thymus gland lobes
➔ Thymus gland is the primary lymphoid organ and forms T-lymphocytes and secretes
hormones for other lymphoid tissue development
Spleen
➔ Lymphatic system not digestive system
➔ Located underneath greater curvature of the stomach
➔ Very vascular
Pancreas: Exocrine and endocrine
➔ Made of small scattered pink lobules suspended by mesentery
➔ Sits close to the greater curvature of the stomach, pancreatic duct then extends
towards the duodenum on the lesser curvature
➔ Releases alkaline digestive juices containing enzymes to the duodenum through the
pancreatic duct
➔ Secretes hormones through endocrine cells
Liver: Exocrine and endocrine
➔ Largest gland in the body and has 4 lobes
➔ Very vascular, thin connective tissue capsule making vulnerable to injury and internal
bleeding
➔ Performs metabolic regulation functions excretory products is produced as bile
➔ Bile salts aid digestion and absorption of fats and vitamins
➔ Humans: Stored in the gallbladder and the cystic duct joins the bile duct to the
duodenum, Rats: Pancreatic duct joins hepatic duct to discharge to the duodenum
➔ Receives venous blood from the small intestine and atrial blood from the hepatic
artery
Digestive system: Oesophagus -> rectum
, ➔ 5 times the body length of the rat for increased surface area for absorption and
secretion in all organs after the oesophagus
➔ Liver and pancreas are specialised secretory glands where secretions go to the small
intestine
➔ 3 tubular portions: Oesophagus, small intestine, large intestine
➔ Two sacs: Stomach and caecum
● Where the gut contents temporarily come to a rest
➔ Order goes tube bag tube bag tube
Salivary glands: Secrete into the mouth
➔ Parotid gland
➔ Sublingual glands
➔ Submandibular gland
Oesophagus
➔ Located dorsal to the trachea heart and lungs
➔ Enters the stomach on the lesser curvature side
Stomach
➔ Mainly on the left side
Distinct types of the rat stomach lining
➔ Transparent
● Anterior and lateral
● No glands, protective stratified squamous epithelium
● Food storage
➔ Opaque
● Pyloric - Medial and posterior
● Glands release acid and enzymes for digestion
● Stomach content (chyme) flow is controlled from the stomach to the
duodenum by the pyloric sphincter a collar of smooth muscle
Small intestine
➔ Irregularly coiled organ functioning for absorption of small molecules resulting from
digestion - 4 body lengths
➔ Regions: Stomach -> Duodenum, jejunum, ileum -> Caecum
➔ Attached to the dorsal body wall via the mesentery which has blood vessels fanning
out to supply and drain the intestinal wall
➔ Two branches of dorsal aorta supply blood and then veins take blood for processing
to the liver through the hepatic portal vein
➔ Duodenum receives bile from the liver and alkaline digestive juices from the pancreas
to aid digestion
Large intestine
Caecum, colon, rectum and anus
, Caecum
➔ Thin walled bag where excreted intestinal contents are passed through slowly for
bacteria to act on it
➔ Terminates at the vermiform appendix
Colon
➔ 3 parts: Ascending, traversing and descending
➔ Each part absorbs water from faeces so starts semi-fluid and then becomes firm
Rectum
➔ Short passage leading to the anal outlet
➔ Temporarily stores faeces
Anus
➔ Two parts
● Internal anal sphinter under involuntary control
● External anal sphincter under voluntary control
Renal system
Kidneys
➔ Retroperitoneal - behind the peritoneum
➔ Ventral surface covered with parietal peritoneum
➔ Dorsal surface attached to the body wall
➔ Rich blood supply
Urinary bladder
➔ Varies in size from a match head to a grape
Adrenal glands - endocrine system
➔ Located at the anterior pole of each kidney
➔ Cortex secretes steroid hormones while inner core secretes adrenalin
Reproductive organs
➔ Male
● Long curved and lumpy textured seminal vesicles
● Prostate gland wrapped around the base of the bladder
➔ Female
● Ovary connects to the Y shaped horns of the uterus via the tightly coiled
oviduct
● Shaped because they have multiple offspring
Mouth and pharyx
➔ Breathing: Air from nasal passages (dorsal) to trachea (ventral)
➔ Swallowing: Food from mouth (ventral) to oesophagus (dorsal)
➔ Food in trachea: Coughing
Posterior: Tail
Ventral: Belly
Dorsal: Back
Medial: Near the centerline
Lateral: away from the center line
Differences between human and rat
Internal anatomy:
➔ Teeth: Rats do not have canines, while humans do
● Rodents incisors have adapted for gnawing by becoming sharpened due to
the lack of enamel on the posterior surface.
➔ Gallbladder: Rats do not have, instead their bile enters into the duodenum from the
pancreas via the hepatic duct.
➔ Penis: Rat flaccid is internal while humans’ is external
➔ Uterus: Y shaped for rats while pear shaped for humans
➔ Pericardium: Rats is transparent and delicate while humans is fibrous
➔ Stomach: Rat have two macroscopic subdivisions of the stomach while humans have
microscopic stomach anatomy differences
➔ Spleen: Leaf shaped in rat, fist shaped in human
➔ Caecum: Large in rats and small in humans
➔ Vermiform appendix: Rats do not have
External anatomy:
➔ Both have 5 digits (pentadactyl)
➔ Tail: Used as a balancing organ for rats while humans lose this feature as a foetus
and instead use their brain as a balancing organ
➔ Vibrissae (long hair): Sensory tactile organs for rats to navigate confined spaces in
darkness.
Dissection procedure
1. Mid-ventral incision using scissors through the layers of the abdominal wall to enter
the abdominal cavity
2. Cut upwards until you encounter resistance - the diaphragm physical separation
between the abdominal and thoracic cavity
3. Then cut laterally around the abdominal cavity
4. Cut anteriorly through the ribcage and sternum past the heart
5. Trim away the ribs and cut along the lateral margins of the thoracic cavity
Body cavities
3 x ventral body cavities
Peritoneal cavity
Parietal peritoneum: Outer membrane lining the abdominal wall
Mesentery: Double layer of peritoneum suspending the intestine
Visceral peritoneum: Inner lining covering the intestine
,Pleural cavities x 2
Parietal pleura: Outer membrane
Visceral pleura: Inner membrane lining the lungs
➔ Rats killed by carbon dioxide poisoning which causes haemorrhage of the small
blood vessels so the lungs are dark red and blood filled while usually they are pink
and spongy
Pericardial cavity
Parietal pericardium: Outer membrane
Visceral pericardium: Inner membrane
Serous membrane is a single layered membrane of mesothelial cells secreting serous fluid
to reduce friction on organs (heart, lungs, abdominal)
Heart
Anterior base of the heart overlapped by the two thymus gland lobes
➔ Thymus gland is the primary lymphoid organ and forms T-lymphocytes and secretes
hormones for other lymphoid tissue development
Spleen
➔ Lymphatic system not digestive system
➔ Located underneath greater curvature of the stomach
➔ Very vascular
Pancreas: Exocrine and endocrine
➔ Made of small scattered pink lobules suspended by mesentery
➔ Sits close to the greater curvature of the stomach, pancreatic duct then extends
towards the duodenum on the lesser curvature
➔ Releases alkaline digestive juices containing enzymes to the duodenum through the
pancreatic duct
➔ Secretes hormones through endocrine cells
Liver: Exocrine and endocrine
➔ Largest gland in the body and has 4 lobes
➔ Very vascular, thin connective tissue capsule making vulnerable to injury and internal
bleeding
➔ Performs metabolic regulation functions excretory products is produced as bile
➔ Bile salts aid digestion and absorption of fats and vitamins
➔ Humans: Stored in the gallbladder and the cystic duct joins the bile duct to the
duodenum, Rats: Pancreatic duct joins hepatic duct to discharge to the duodenum
➔ Receives venous blood from the small intestine and atrial blood from the hepatic
artery
Digestive system: Oesophagus -> rectum
, ➔ 5 times the body length of the rat for increased surface area for absorption and
secretion in all organs after the oesophagus
➔ Liver and pancreas are specialised secretory glands where secretions go to the small
intestine
➔ 3 tubular portions: Oesophagus, small intestine, large intestine
➔ Two sacs: Stomach and caecum
● Where the gut contents temporarily come to a rest
➔ Order goes tube bag tube bag tube
Salivary glands: Secrete into the mouth
➔ Parotid gland
➔ Sublingual glands
➔ Submandibular gland
Oesophagus
➔ Located dorsal to the trachea heart and lungs
➔ Enters the stomach on the lesser curvature side
Stomach
➔ Mainly on the left side
Distinct types of the rat stomach lining
➔ Transparent
● Anterior and lateral
● No glands, protective stratified squamous epithelium
● Food storage
➔ Opaque
● Pyloric - Medial and posterior
● Glands release acid and enzymes for digestion
● Stomach content (chyme) flow is controlled from the stomach to the
duodenum by the pyloric sphincter a collar of smooth muscle
Small intestine
➔ Irregularly coiled organ functioning for absorption of small molecules resulting from
digestion - 4 body lengths
➔ Regions: Stomach -> Duodenum, jejunum, ileum -> Caecum
➔ Attached to the dorsal body wall via the mesentery which has blood vessels fanning
out to supply and drain the intestinal wall
➔ Two branches of dorsal aorta supply blood and then veins take blood for processing
to the liver through the hepatic portal vein
➔ Duodenum receives bile from the liver and alkaline digestive juices from the pancreas
to aid digestion
Large intestine
Caecum, colon, rectum and anus
, Caecum
➔ Thin walled bag where excreted intestinal contents are passed through slowly for
bacteria to act on it
➔ Terminates at the vermiform appendix
Colon
➔ 3 parts: Ascending, traversing and descending
➔ Each part absorbs water from faeces so starts semi-fluid and then becomes firm
Rectum
➔ Short passage leading to the anal outlet
➔ Temporarily stores faeces
Anus
➔ Two parts
● Internal anal sphinter under involuntary control
● External anal sphincter under voluntary control
Renal system
Kidneys
➔ Retroperitoneal - behind the peritoneum
➔ Ventral surface covered with parietal peritoneum
➔ Dorsal surface attached to the body wall
➔ Rich blood supply
Urinary bladder
➔ Varies in size from a match head to a grape
Adrenal glands - endocrine system
➔ Located at the anterior pole of each kidney
➔ Cortex secretes steroid hormones while inner core secretes adrenalin
Reproductive organs
➔ Male
● Long curved and lumpy textured seminal vesicles
● Prostate gland wrapped around the base of the bladder
➔ Female
● Ovary connects to the Y shaped horns of the uterus via the tightly coiled
oviduct
● Shaped because they have multiple offspring
Mouth and pharyx
➔ Breathing: Air from nasal passages (dorsal) to trachea (ventral)
➔ Swallowing: Food from mouth (ventral) to oesophagus (dorsal)
➔ Food in trachea: Coughing
