Lab 7: Introduction to Rat Dissection, Digestion, Gas Exchange & Nutrition
Dissecting - Mean “to expose to view”
Types of tools used during dissecting:
Scalpel or single edge razor blade: Used to make initial cut through epidermis (sometimes to excise an organ).
Scissors: Primary cutting instrument.
Forceps: Manipulation, lifting structures.
Blunt probe: Most used tool; lifting, pushing, freeing, tracing, feeling.
Teasing Needle: Useful for careful punctures pr when a sharp point is necessary
Glossary of Terms: (rat’s six anatomical regions)
Cranial region: Head
Cervical region - Neck
Pectoral region - Area where front legs attach
Thoracic region - Chest area
Abdominal region - Belly
Pelvic region - Area where the back legs attach
Other Terms:
Dorsal: Toward the back
Ventral: Toward the Belly
Lateral: Toward the sides
Median: Near the middle
Anterior: Toward the head
Posterior: Toward the hind end (tail)
Superficial: On or near the surface
Deep: Some distance below the surface
Sagittal: Relating to the mid-plane which bisects the left and right sides
Transverse: Relating to the plane separating dorsal and ventral
Frontal: Relating to the plane separating dorsal and ventral
Proximal: Near to the point of reference
Distal: Far from the point of reference
Caudal: Toward the tail end
Cranial: Toward the head
Pectoral: Relating to the chest and shoulder region
Pelvic: Relating to the hip region
Dermal: Relating to the skin
Longitudinal: Lengthwise
Right and Left: Refers to the specimen’s right and left, not yours
Abdominal Cavity: Related to the area below (posterior) to the diaphragm
Thoracic Cavity: Related to the area above (anterior) to the diaphragm
External Anatomy:
Sensory Structures include:
Vibrissae - Sensory hairs (whiskers). Used for vital processes as rats are nocturnal.
Pinna - External part of ears
Nares - Used to sense chemicals in the air (smell)
Eyes - large pupil
Nictitating membrane - Found in the inside corner of the eye for protection.
Dorsal side of Rat:
Manus - Forefoot.
Pes - Hindfoot.
Sharp claws on rats contain keratinized epithelium
Digitigrades - Walks with the heel of each foot elevated off the ground (rats are classified as this).
Plantigrade - Walks with heel and digits of each foot rest on the ground during each step (humans are classified as this).
The Digestive Tract
When food enters the digestive system, food is pushed out.
Waste products of digestion include:
Bile pigments (such as; breakdown of hemoglobin, roughage and bacteria).
Nitrogenous wastes are removed during digestion.
Epiglottis - The special gate-like structure that prevents food from entering the lungs when particles are ingested. The epiglottis opens when food passes through the pharynx and esophagus. In the rat it is a trough-shaped flap composed of cartilage.
Peristalsis - The wave-like movements throughout the digestive tract.
Organs of the Heal and Neck
Types of Salivary Glands:
Parotid Glands: Large, thin, triangular gland covering area between base of ear, shoulder, and angle of lower jaw.
Mandibular Gland: Large, oval gland that lies central and ventral to the parotid gland, posterior to to the angle of the jaw.
Sublingual Gland: Small, flat, narrow gland overlying the mandibular gland. Tiny duct parallels that of the mandibular. Both open under side of tongue.
Lymph nodes - lie anterior to the salivary glands. They are circular, slightly firm, smooth, and pressed against the jaw muscles.
Extraorbital lacrimal gland - Flat, spleen-shaped gland, slight below ear.
Examine the buccal cavity
Oral cavity and nasal cavity separated by hard palate.
Roof of month divisions:
Posterior self palate
Bony secondary (hard) palate anteriorly
Buccal Cavity contains this:
Long, narrow, bony jaw, with teeth set in socket in the jaw bones.
Types:
Heterodont: Teeth that are not alike (have incisors, canines, premolars, and molars).
Esophagus - Soft, muscular tube on dorsal surface of trachea. Compared to trachea it lacks cartilage rings.
The dental formula for the rat is as follows:
1 0 0 3
x2 = 16
1 0 0 3
(Incisors) (Canines) (Premolars) (Molars)
upper row refers to upper jaw while lower row refers to lower jaw
The Abdominal Cavity & Thoracic Organs
The Diaphragm - Separates the chest or thoracic cavity from the abdominal cavity.
Coelom - Body cavity within which the viscera (internal organs) are located.
Mesentery - A sheet of tissue that suspends the organs. It is continuous with the lining (peritoneum) of the abdominal cavity.
Peritoneum - The membrane that covers the inner body cavity. Types include:
Visceral peritoneum - Covers internal organs.
Mesenteries - Attach the internal organs to the dorsal body wall. Blood vessels and nerves pass to the organs through this.
Omentia - Connect organ to organ.
Stomach structure:
Types of sphincters in the stomach:
Cardiac sphincter: Entrance to the stomach.
Pyloric sphincter: Attaches the small intestine to the stomach.
*Inside the stomach contains rugae, and contains glandular epithelial (produces acid and pepsin).
Greater Curvature: Outer margin of the stomach.
Lesser Curvature: The inner margin.
Fungus: Blind sac extension to the left of cardiac region.
Pylorus: Thickened area near junction with small intestine.
Greater omentum: Forms sac that extends caudally from greater curvature and then curves dorsally to attach to the body wall. This is where spleen and excess fat is stored.
The Small Intestine:
Consists of three sections:
Duodenum - First to met with chyme (partially undigested food/enzyme mixture)
Ileum - Water and nutrients are absorbed.
Jejunum - Further digestion/absorption of nutrients and water.
Pancreas - brownish, flattened, diffuse gland. They produce insulin, glucagon and pancreatic enzymes to break down the four major food types:
Proteins
Carbohydrates
Lipids
Nucleic acids.
*The liver functions:
Produces bile (contains: bile salts, pile pigment and cholesterol) - This helps in digestion.
The Large Intestine:
Caecum - Where the small intestine mets with the large intestine. Is the sac for fermentation of fibrous plant material.
Divided into three regions: (Similar functions)
Ascending colon
Transverse colon
Descending colon (ends with the rectum)
Defecation - The process of egestion where waste is excreted from the anus.
The Respiratory System
Trachea - Long tube composed of cartilaginous rings.
Bronchial tubes - Branch from trachea and enter the lungs on either side.
Larynx - Square shaped protrusion toward the cranial end of the trachea (also known as the voice box).
The trachea branches into the left and right bronchi which leads to the left or right lung.
The left lung is one large lobe while the right is divided into:
Cranial Lobe
Middle Lobe
Caudal Lobe
Accessory Lobe
The bronchi is subdivided into alveoli.
Our breathing is called negative breathing.
Parietal Pleura - covers the outer, middle and inner layer of the chest wall.
Rib inclose the thorax
Intercostal muscles between the ribs provide much of the pumping force for lung respiration.
Problems for gas exchange:
Respiratory surface of adequate dimension to sustain the organism’s cellular demands for gas exchange.
Surface area is moist.
Protect the surface from mechanical injury.
Transporting the gasses between the sites for exchange within the environment and internal body cells.
Respiratory Volumes and Lung Capacities – Spirometry
Influnces:
Size
Sex
Age
Physical condition
Terms given to measurable respiratory volumes:
Tidal Volume (TV) - Amount of air inhaled or exhaled with each with each breath resting conditions (500mL).
Inspiratory reserve volume (IRV) - Amount of air that can be forcefully inhaled after a normal tidal volume inhalation (3100mL)
Expiratory reserve volume (ERV) - Amount of air that can be forcefully exhaled after a normal tidal volume exhalation (1200mL).
Vital capacity (VC) - Maximum amount of air that can be exhaled after a maximal inspiration (4800mL).
Equation:
VC = TV + IRV + ERV
Spirometer - Measures respiratory volumes. There are two types:
Handheld dry or wheel spirometer
Wet spirometer
