Laboratory Content

Question 1

Differences between Rat and Human Digestive System.

Answer 1

Dental: Rat teeth are not covered with enamel on the inside, so they are easily chiselled into sharp shapes for gnawing.
Mandibular: Mandible is split horizontally and allowed the distance between incisors and the width of bite to be varied.
Gall Bladders: Not present in rats.
Uterus: Y-shaped in rats with large SA for implantation, as opposed to barrel shaped human uterus.
Pericardium is fibrous and strong in humans but thin in rats.
Shape of spleen is leaf shaped in rats but fist shaped in humans.

Question 2

Structure and function of serous membranes and related serous structures

Answer 2

Consists of a double layer of mesothelial cells forming a sac. Organs ‘sink’ into invaginations formed in the ‘sac’.
The side facing the organs is the visceral side, while the side facing the cavity wall is the parietal side.
Mesothelial cells produce the serous fluids which fill the sac. This provides mechanical shock protection and reduces friction.
Mesentry is a thin tube made of mesothelium, and it contains all vasculature supplying the organ and attaches it to the dorsal abdominal wall.

Question 3

Structure and Function: Stomach

Answer 3

Sits on the left side of the abdominal cavity. In rats, the anterior part is lighter, lined with stratified squamous epithelium and responsible for food storage. The medial/posterior parts(pyloric region) is darker and is secretory (dark colour due to tubular glands lining the stomach). The food enters the stomach in the pyloric region.
No visual division in humans- entirely dark.
Unvascularised appearance. Release of chyme controlled involuntarily by the pyloric sphincter.

Question 4

Structure and Function: Pancreas

Answer 4

Exocrine and endocrine gland. Secretes insulin and glucagon (peptides) into the blood stream. Secretes digestive enzymes in an alkaline pancreatic juice into the duodenum.
Positioned along the greater curvature of the stomach and is suspended by mesentery, Vascularised appearance.

Question 5

Structure and Function: Liver

Answer 5

4-lobed exocrine and endocrine gland. Secretes bile directly into duodenum via cystic duct in humans, or the hepatic duct in rats which joins up with the pancreatic duct.
Liver is highly vascularised by the hepatic/coeliac artery, thus it appears red.
Very soft and susceptible to damage due to thin CT coat.

Question 6

Structure and Function: Spleen

Answer 6

Leaf shaped (in rats) lymphatic organ found dorsal to the stomach. Highly vascularised and lack protective capsule.

Question 7

Structure and Function: Small Intestine

Answer 7

Duodenum->Jejunum->Ileum
Vascularised by the coeliac and the sup. mesentery arteries, and drains into the hepatic portal vein.
Irregularly coiled to fit in the body as it is 4x the body length.
Substances aiding digestion enters via a communal duct that the pancreatic and the hepatic duct joins up into. In humans, the hepatic and cystic ducts join , and then the common duct joins with the pancreatic duct

Question 8

Structure and Function: Large Intestine

Answer 8

In rats: caecum-> colon->rectum->anus.
Caecum: Thin walled bag found in rats. Contains bacteria to act on slow moving gut content.
Colon: Forms an arch shape in both rats and humans, but in humans the ascending and descending limbs are a lot more defined. Distinguishable by the presence of watery faeces in the ascending limb, and dry faeces in the descending limb.
Rectum: Short straight passage leading to anus. Not visible.
Anus: Allows voiding of faeces.

Question 9

Structure and Function: Renal structure (Not digestive)

Answer 9

Kidney: Retroperitoneal organs, with the ventral face in contact with parietal peritoneum. Highly vascularised organs, vascularisation (renal arteries and vein) entering/leaving the organ via the hilus.
Adrenal gland: Found at the anterior pole of the kidneys. Small brown bodies embedded in fat.

Question 10

Structure and Function: Bladder

Answer 10

Cream coloured structure at the midline. Varies from the size of a match head to a grape.

Question 11

Structure and Function: Reproductive Organs (in rats)

Answer 11

Male: Penis is usually hidden in the body. Large curved lumpy structures found dorsal to the bladder are seminal vesicles.
Soft pale structure found around the base is the prostate.
Female: Two long uterine horns positioned dorsally to the bladder, with ovaries at the end.
Uterine horns have large surface areas to allow more room for implantation.

Question 12

Structure and Function: Mouth

Answer 12

In rats, there are 4 incisors in total, and a set of molars for grinding.
Anterior roof of mouth is hard palate, which is grooved to allow arrangement of food by size.
Soft palate is the posterior roof which is sans bone. Palates divide the nasal and oral cavities.

Question 13

Structure and Function: Oesophagus and trachea

Answer 13

Oesophagus is dorsal while trachea is ventral. Crossover occurs at the glottis. During swallowing, the food presses against the epiglottis, which closes up the trachea and creates a ramp that the food can travel up.

Question 14

Dura Mater and Associated Features

Answer 14

Outermost layer of meninges.
Split into periosteal layer (near the skull) and meningeal layer (near other meninges).
Extends to form a sheet of CT called the falx cerebri, which cleaves the cerebral cortex and the falx cerebelli, which cleaves the cerebellum. Another sheet of CT cleaves the cerebral cortex from the cerebellum, called the tentorium cerebelli.
The dural venous sinuses are channels formed between the two layers of dura mater. These drain venous blood into the jugular veins.

Question 15

Ventricles of the Brain

Answer 15

Lateral ventricles follow the curvature of the caudate nucleus, and are separated anteriorly by the septum pellucidum.
They empty into the third ventricle, which sits in the curvature, via the interventricular foramen.
The third ventricles empties into the fourth ventricle via the the aqueduct of the midbrain.
Lateral ventricles are filled with CSF produced by choroid plexuses, found medially in the lateral ventricles, third and fourth ventricles.

Question 16

Midbrain Anatomy

Answer 16

Located between the thalamus and the cerebellum.
Aqueduct of the midbrain runs through the middle of the midbrain- matchstick thickness.
Colliculi form a B-shaped structure on the side of the cerebellum. Top bump is the superior (reflex in response to visual stim) and lower bump is the inferior (reflex in response to audio stim) .
Cerebral peduncles are Projectional white matter bundles, connecting the internal capsule to the brainstem. Contains corticospinal/corticopontine nerves. Found on the side of the aqueduct closer to the thalamus.
Contains the substantia nigra.

Question 17

Name three types of White Matter Tracts

Answer 17

Projectional: Superior to inferior- Internal Capsule
Commisural: Left to right- Corpus Callosum
Associational: Forward to back- Arcuate Fasciculus

Question 18

Role and formation of CSF

Answer 18

Mechanical protection- acts as an absorber of shock.
Homeostasis. Provides environment of constant pH and transports hormones. secreted by hypothalamus.
Circulation: Acts as a medium for the exchange of material between the blood and nervous tissue.

Blood plasma is filtered out at the choroid plexuses, before being uptaken by ependymal cells to convert it to CSF.
Flow is bidirectional so metabolites from nervous tissue will flow back.

Question 19

Distinguishing Features: Ventral side of Sheep Heart

Answer 19

Curved profile when viewed laterally. 
Vertical interventricular sulcus. 
Only auricles are visible (and a little of the left atrium). 
Pulmonary trunk is nearest. 
Left anterior vena cava barely visible.

Question 20

Distinguishing Features: Dorsal side of the sheep heart

Answer 20

Flat profile when viewed laterally. 
Only atria are visible. 
Curved interventricular sulcus.  
Fat pads visible on the right atrium denoting the position of three visible vena cavae. 
Left ant.: Below the lower fat pad. 
Post.: between the two fat pads. 
Right ant.: Left of the upper fat pad.

Question 21

Distinguishing Features: Right atrium of sheep heart

Answer 21

BOTH LEFT AND RIGHT
External appearance is dark red, collapsed and wrinkled.
Trabecular pattern in the auricles, due to the criss-crossing of muscle fibres. Allows contractions in different directions by different regions of the chamber to maximise ejection.

Fossa ovalis found just downstream of post. vena cava.
Cardiac veins found within the left anterior v.c just before it enters the R.A.

Question 22

Distinguishing Internal Features: Right Ventricle of sheep heart

Answer 22

Moderator band towards the apex across the ventricle. Made of modified purkinje fibres (modified cardiac muscle fibres).
Two visible valve leaflets and two smaller papillary muscles, but there should be three in an intact heart as chordae tendineae holding the third was cut during dissection.
Ventricle is crescent shaped and lumen is larger than the lumen of left ventricle.
Trabecular pattern due to the criss-crossing of muscle fibres. Allows contractions in different directions by different regions of the chamber to maximise ejection.

Question 23

Distinguishing Internal Features: Left ventricle of sheep heart

Answer 23

Circular, smaller lumen with thicc walls.
Two larger valve flaps and papillary muscles. Papillary muscles positioned more superiorly and more chordae tendineae.
Papillary muscles relax during diastole and contract during systole.
Trabecular pattern due to the criss-crossing of muscle fibres. Allows contractions in different directions by different regions of the chamber to maximise ejection.

Question 24

Distinguishing Internal Features: Aorta

Answer 24

Three deflated cusps which can be inflated to form cup shaped cusps.
Small holes called coronary ostia found downstream of aortic valves.
Brachiocephalic artery provides the second branch of the aorta.

Question 25

Pathway of CSF circulation

Answer 25

Capillaries of choroid plexus→ Lateral ventricles→ Interventricular foramen→ Third ventricle→ Aqueduct of the midbrain→ Fourth ventricle → median and lateral apertures→ Subarachnoid space around the brain and spinal cord→ Dural venous sinuses→ Arachnoid villi→ Venous blood→ Heart