Practical Lab 4: Kingdom Animalia - Vertebrates (Phylum Chordata)

Organisms belonging to Phylum Chordata are defined by the presence of five major features:

• A dorsal, hollow nerve cord

• A notochord (In the lower chordates, the notochord persists throughout life. However, in the vertebrates it is surrounded and later
  persists as the soft centre of the intervertebral discs)

• The presence, during some stage in the life cycle, of paired pharyngeal pouches in the pharynx or throat (In most aquatic chordates, the pharyngeal pouches perforate to form pharyngeal gill slits, but in higher chordates the
  pharyngeal pouches are present only during embryonic development)

• A gland (or tissue) which concentrates iodine.

• A post-anal tail. A tail that extends past the exit of the anus
  

Phylum Chordata

• Phylum Chordata is divided into three subphyla, of which Subphylum Vertebrata is of interest to us.
  

Organisms belonging to Phylum Chordata are defined by the presence of five major features:

• A dorsal, hollow nerve cord

• A notochord (In the lower chordates, the notochord persists throughout life. However, in the vertebrates it is surrounded and later
  persists as the soft centre of the intervertebral discs)

• The presence, during some stage in the life cycle, of paired pharyngeal pouches in the pharynx or throat (In most aquatic chordates, the pharyngeal pouches perforate to form pharyngeal gill slits, but in higher chordates the
  pharyngeal pouches are present only during embryonic development)

• A gland (or tissue) which concentrates iodine.

• A post-anal tail. A tail that extends past the exit of the anus
  

Phylum Chordata

• Phylum Chordata is divided into three subphyla, of which Subphylum Vertebrata is of interest to us.
  

External Anatomy of the Perch (Perca flavenscens)

• Has a fusiform body shape

• It is laterally flattened and streamlined to reduce resistance as the fish moves through water

• The body is covered by small overlapping scales.

• The direction in which the scales overlap is another way to minimize resistance to movement.

• A layer of mucous covers the scales externally to form a protective layer

External Anatomy of the Perch (Perca flavenscens)

• On the ventral surface of the fish, locate two openings.

• The larger more anterior opening is the anus

• The smaller, more posterior opening is the
  urogenital opening.

External Anatomy of the Perch (Perca flavenscens)

• On each lateral surface of the perch is a large crescent-shaped opening to the gill chamber.

• Each gill chamber is covered laterally by a bony operculum.

• Bend the operculum backward and note four gill arches, with gills attached to each one

External Anatomy of the Perch (Perca flavenscens)

• Locate the pigmented line extending from the dorsal border of the operculum posteriorly to the tail.

• This is the lateral line system and is formed of modified scales containing sensory pits.

• The function of the lateral line system is to detect vibrations of low frequency or movements in the water

External Anatomy of the Perch (Perca flavenscens)

• The body of the perch is divided into three parts: head, trunk and tail
  

External Anatomy of the Perch (Perca flavenscens)

• Note the terminal mouth of the perch (i.e., at the anterior, leading tip of the head).

• The position of the mouth reflects the mode of feeding.

• The perch feeds by overtaking prey while swimming.

External Anatomy of the Perch (Perca flavenscens)

• Just above the mouth are four nasal apertures (nares), two on each side.

• Push a fine probe through one of the anterior nasal apertures and note that it emerges through a posterior nasal aperture.

External Anatomy of the Perch (Perca flavenscens): TRUNK

• Trunk: The two sets of paired appendages (fins) located on the trunk of the perch are homologous to the paired appendages of tetrapods.

• Just posterior to the opercula are the two pectoral fins. They are attached to the pectoral girdle, which can be felt just beneath the skin.

• Posterior and ventral to the pectoral fins are the pelvic fins
  

External Anatomy of the Perch (Perca flavenscens): TAIL

• Tail: Tapering from the trunk, the tail ends as a laterally compressed paddle.

• The symmetrical caudal fin surrounds the fleshy end of the tail.

• This type of symmetrical caudal fin is correlated with the presence of a swim bladder

External Anatomy of the Perch (Perca flavenscens): THE MEDIAN FINS

• The Median Fins: There are four median unpaired fins.

• These are: the caudal fin (just seen); the anal fin (located posterior to the anus); the anterior dorsal fin (beginning at the anterior end of the trunk); and the posterior dorsal fin (located posterior to the anterior dorsal fin)

Perch: Muscular System

Vertebrate skeletal muscles are divided into two groups: axial muscles and appendicular muscles.

• Axial muscles are along the body's center (connected to the spine and ribs).

• Appendicular muscles are in the arms, legs, and their attachments (like shoulders and hips).

Perch: Musculature System

• The axial musculature is composed of myomeres.

• Myomeres are separated by myosepta

• Each myomere is zig-zag and looks like a “W” tilted on its side.

• A horizontal septum divides the myomeres into a dorsal and a ventral portion.

Perch: Digestive System

• The gastrointestinal (GI) tract is a tube starting at the mouth and emptying either into a cloaca or to the external environment via an anus.

• GI tract: the ingestion, absorption, and digestion of food and, the removal of wastes

Perch: Digestive System

• The tube of the tract in chordates, subdivided into the oral cavity (mouth), pharynx (throat), esophagus, stomach, small intestine, and large intestine.

• Accessory organs are associated with the tract.

• Examples of accessory organs are teeth, tongue, salivary glands, liver, and gallbladder
  

Perch: Digestive System

• Herbivores rely on bacteria and protozoa to break down cellulose.

• Many have a caecum, a pouch at the meeting point of the small and large intestines, where these microorganisms help process food.

• Caeca increase surface area and can be found in different parts of animal digestive tracts.

• However, since most digestion happens in the small intestine, having a caecum at its end is not ideal for breaking down cellulose.

Perch: Digestive System

• The type of teeth a mammal has reflects its diet.

• Molars have flat surfaces for crushing and milling = HERBIVORES

• Premolars are used for shearing, cutting, and slicing EXCEPT in advanced herbivores where they function like molars.
  

Perch: Digestive System

• Incisors: chisel-shaped teeth in the front, are useful for biting.

• Premolars and incisors are found in herbivores, carnivores and omnivores.

• Pointed teeth (canine teeth) are characteristic of carnivores and are useful for tearing flesh and catching and holding prey

• Perch are carnivores

Perch Esophagus

• the esophagus is a short, straight tube leading from the oropharynx to the stomach.

Perch Stomach

• In the perch, breakdown of the food by mechanical and chemical means begins in the stomach.

• The size of the stomach varies according to how much food it contains

Perch Pyloric Caecum

• (singular, caecum)

• the junction of the stomach and the intestine is
  marked by the presence of three pyloric caeca.

• These are blind-ended tubes extending from the gut that serve secretory and absorptive functions

Perch Intestine

• Originating at the stomach, the intestine forms an S-shaped loop.

• At the end of the loop, the intestine constricts and straightens.

• The intestine extends directly to the anus.

Perch Liver

• Situated just anterior to the stomach.

• On the undersurface of the liver is the gall bladder.

• The gall bladder drains bile from the liver, and opens into the intestine.

• Bile is necessary for the proper digestion of fats

Perch Pancreas

• The pancreas is a digestive gland, usually found along the ventral border of the intestine.

• In some fish, the pancreas is embedded in the liver.

• The pancreas secretes digestive enzymes into the intestine, and hormones (insulin and glucagon) into the blood.

Perch Spleen

• lying on the posterior dorsal surface of the stomach, the spleen is a football shaped organ.

• It functions in the production and maintenance of blood cells.

• It might be hard to find on some specimens.
  

Perch Excretory System

• The perch urinary system includes the kidneys, which are located above the swim bladder.

• At the back of the kidneys, two small ducts join to form one ureter.

• The ureter and the gonoduct (which carries reproductive products from the gonad to the outside) both open through a common urogenital opening.

Perch Excretory System

• The urinary bladder is a small sac at the most posterior, ventral end of the body cavity.

• It is a separate structure in the male, but in females, it is incorporated into the oviducts to form the urogenital sinus.

Male Perch

• In the male, the testes are a pair of white elongated bodies lying just below the air bladder to which they are joined by a thin sheet of tissue, the mesentery.

• They fuse together toward the posterior end, and the sperm are passed to the outside through the urogenital opening

Female Perch

• In the female, the ovary lies between the intestine and the air bladder It is an epithelial sac filled with eggs.

• The posterior end of the ovary is tapered, and the eggs pass to the outside through the urogenital opening just behind the anus.

• The ovaries are paired in early stages, as they are in other vertebrates, but during development, they fuse into a single organ.

Perch Respiratory System

• The gills are attached to each of the four pairs of branchial arches

• On the anterior surface of the arches are the gill rakers.

• Each gill has two sets of filaments, one extending anteriorly, and the other posteriorly.

• Gills with double sets of filaments like these are known as holobranchs

Perch Counter Current System

• counter-current system to maximize oxygen uptake from water.

• Water enters through the mouth and passes over the gills while the opercula (gill covers) regulate flow.

• As the oral cavity contracts, water is forced over the gill filaments, where oxygen diffuses into the blood and carbon dioxide diffuses out.

• The blood in the gill capillaries flows in the opposite direction to the water, ensuring a continuous concentration gradient that enhances oxygen absorption.

Perch Circulatory System

• The closed circulatory system of vertebrates consists of the heart, arteries, veins, capillaries, and blood.

• Arteries carry blood away from the heart to the sites of exchange in the tissues, in the capillaries.

• Veins carry blood from tissue capillaries back to the heart

Perch Circulatory System - Single Type System

• A perch has a simple, low-pressure circulatory system with a single loop.

• The heart pumps deoxygenated blood to the gills, where it picks up oxygen.

• The oxygenated blood then flows directly to the rest of the body before returning to the heart.

• Unlike humans, the heart only handles deoxygenated blood, making this a single-circuit system

The Perch Heart

• The transverse septum is a heavy membrane separating the pericardial and abdominal cavities.

• The fish heart consists of four distinct parts.

• Posterior to anterior (in the same direction as blood flow) these are the sinus venosus, atrium, ventricle, and bulbus arteriosus
  

The Perch Heart

• These parts are not arranged in a straight line, but have folded over one another to produce an S-shaped organ.

• The top of the S, the sinus venosus, receives blood from two common cardinal veins and the hepatic sinus.

• The sinus venosus is thin walled and opens directly into the atrium.

The Perch Heart

• The ventricle itself is a thick muscular structure.

• Like the atrium, it has a single internal chamber.

• Backflow of blood from the ventricle during contraction is prevented by a valve.

• The last portion of the perch heart is the bulbus arteriosus.

• The bulbus arteriosus is really an enlarged, very
  muscular portion of the ventral aorta, the vessel in which blood flows away from the heart and toward the gills.

• Backflow of blood from the bulbus arteriosus is also prevented by the presence of valves

General Features of the Rat

• The rat is a tetrapod with digitigrade locomotion, meaning the animal walks on the digits only, with the remainder of the foot elevated.

• The principle covering of the body is hair, which is derived from the epidermis of the skin.

• The scales covering the tail in the rat are also epidermal in origin as are the rat’s claws.

• The body of the rat is divided into four general regions: head, neck, trunk, and tail,

Rat Head and Neck

• The head is large and separated from the trunk by the neck.

• The mouth is bounded by well-developed upper and lower lips. The upper lip is cleft in the rat.

• Has incisor teeth

• External nares are situated on a more or less flexible nose.

• The eyes are protected by upper and lower eyelids.

• The ear has an external fold called the pinna, which directs sound waves into the ear canal (external auditory meatus).

• A tympanic membrane lies out of sight at the base of this canal.

• The rat, and many other mammals, have special long sensory hairs called vibrissae which grow out from the snout, upper eyelid, cheek, and chin of the rat

Rat Trunk

• The trunk is divided into an anterior thorax and a posterior abdomen.

• Teats or nipples (the external openings of the mammary glands) can also be located in two rows on the ventral surface of the trunk

• There are usually twelve teats in the rat, evenly distributed between the thoracic and abdominal regions

Rat - separate urogenital and anal openings

• In female rats, the urinary and genital openings are separate.

• The urethral opening (urinary opening) is the most anterior with the vaginal orifice (reproductive opening) just posterior to it.

• The anus is located at the base of the tail, posterior to the vaginal orifice

• In males, the urethra serves both urinary and reproductive functions and opens at the tip of the penis.

• at the base of the tail, is the scrotum containing the testes

• The tail of the rat has only a few scattered hairs, which are distributed between reptile-like scales of epidermal origin.
  

Rat - body cavity

• The coelom is the body cavity within which the viscera (internal organs, such as liver, stomach, intestines, etc.) are suspended.

• The abdominal cavity and viscera are covered by a peritoneum, which is formed from mesoderm.

Rat - Mesentry Proper

• A double layer of peritoneal membrane extending from the dorsal body wall to the viscera (internal organs)

Rat Falciform Ligament

• 
  A layer of tissue extending from the ventral body wall and diaphragm to the liver

Rat Parietal Peritoneum

• This is the shiny membrane which lines the body wall of the abdominal cavity

Visceral Peritoneum

• This is the shiny membrane which covers the
  internal organs (viscera) within the abdominal cavity
  

Rat - Greater Momentum

• This is a double walled peritoneal sac which extends from the greater curvature of the stomach to the spleen

Rat - Lesser Omentum

• This membrane joins the lesser curvature of the stomach to the liver

Rat Stomach

• The stomach is comprised of three areas.

• These are the cardiac portion (entrance from the esophagus), the fundic portion (large middle area) and the pyloric portion (constricted posterior portion).

• The stomach opens to the duodenum through the pyloric sphincter
  

Rat Small Intestine

• The small intestine is comprised of three regions:

• The anterior portion (the duodenum) receives the ducts from the digestive glands, pancreas, and liver.

• The second portion is the jejunum and the most posterior is the ileum.

• The small intestine is the site of most chemical digestion and the absorption of nutrients.

• Digestive enzymes from the pancreas and the intestine itself are secreted into the lumen of the small intestine where the chemical breakdown of food occurs

Rat Large Intestine

• The ileum opens to the large intestine via the ileocolic valve.

• The large intestine consists of four areas: a large caecum or blind sac near the ileocolic valve; an ascending colon on the right side; a short transverse colon; and a descending colon heading posteriorly.

• Feces are stored in the rectum (the terminal portion of the colon) until eliminated through the anus
  

Rat Rectum

• The rectum is the continuation of the descending colon through the pelvic region.

• It terminates with the anus, which opens externally

Rat Liver

• It is divided into several lobes.

• The bile produced in the liver passes directly to the duodenum, via the bile ducts.

• The gall bladder, which stores the bile in most mammals, is not present in the rat.

• Bile is needed for proper digestion of fats.

• The liver has many functions such as detoxification of certain chemicals and production of glycogen

Rat Spleen

• The spleen and the liver remove old red blood
  cells from circulation and break them down.

Rat Pancreas

• The pancreas is a diffuse gland which is embedded in the mesentery proper and greater omentum and is found along the anterior edge of the duodenum, just after the stomach.

• The pancreas secretes many digestive enzymes into the small intestine as well as hormones (insulin and glucagon) into the blood

Rat Osmoregulation System

• The osmoregulatory system helps regulate water and waste in the body.

• The kidneys, found in fat for protection, filter waste and produce urine.

• Ureters carry urine from the kidneys to the bladder, where it is stored before exiting through the urethra.

• In males, the urethra also carries sperm, while in females, it is only for urine. A pig kidney dissection shows two main parts: the outer cortex and the inner medulla

Male Rat

• The scrotum contains the testes

• Sperm are made in the seminiferous tubules of the testes and move into the epididymis, where they mature.

• From there, they travel through the vas deferens, a tube that carries sperm to the urethra inside the penis

• The accessory sex glands: the prostate glands are located next to the urinary bladder, along with the vesicular and coagulating glands.

• Their secretions create seminal fluid, which carries sperm, provides nutrients, and helps neutralize acidity in the vagina to support fertilization.

Female Rat

• The ovaries, located behind the kidneys, contain developing eggs and are often surrounded by protective fat.

• The oviducts are small, coiled tubes that connect the ovaries to the uterus, which has two horns (cornua) that unite to form the vagina.

• The vagina opens to the outside separately from the urethra

Rat Respiratory System

• To expose the lungs and heart, an incision is made along the rib cage.

• The heart is in the center of the chest, with the lungs on either side.

• The left lung has one lobe, while the right lung has four.

• The pleura are membranes lining the thoracic cavity (parietal pleura) and covering the lungs (visceral pleura).

• Below the lungs is the diaphragm, a thin muscle that helps with breathing.

Rat Respiratory System

• The trachea has cartilage rings that keep it open for airflow.

• It branches into a right and left bronchus, which lead to the lungs and further divide into bronchioles.

• At the upper part of the trachea is the larynx, a box-like structure that allows mammals to produce sounds, from bat squeaks to human speech.

Rat Circulatory System

• Rats have a double circulatory system, meaning their heart pumps blood twice—once through the pulmonary circuit (to the lungs for oxygenation) and once through the systemic circuit (to deliver oxygen to the body).

• The heart handles both oxygenated and deoxygenated blood, ensuring efficient circulation.

Rat Heart

• Locate the thymus gland, which overlies the anterior portion of the heart

• The heart of the rat consists of four chambers.

• There is a right ventricle, and a left ventricle, which are not easy to distinguish externally.

• Locate the easily distinguishable right atrium and left atrium which are dark, ear-shaped structures on each side of the anterior portion of the hear

Rat Heart

• Three main veins bring deoxygenated blood back to the right atrium of the heart:

1. Right superior vena cava – Returns blood from the right side of the head and neck.

2. Left superior vena cava – Returns blood from the left side of the head and neck.

3. Inferior vena cava – A large vein that carries blood from the lower body to the heart. It can be found by lifting the heart and separating the lung lobes.

These veins ensure that blood from all parts of the body flows back to the heart for oxygenation.

• The thoracic cavity is drained by the azygous vein which empties into the left superior vena cava near its entry into the atrium. It is found only on the left side of the thoracic cavity

Rat Heart Blood Flow

• 1) Deoxygenated blood from the body enters the right atrium.

• 2) It flows into the right ventricle through the tricuspid valve.

• 3) The right ventricle pumps blood through the pulmonary semilunar valve into the pulmonary trunk, which splits into right and left pulmonary arteries that carry blood to the lungs for oxygenation.

• 4) Oxygenated blood returns to the left atrium via the right and left pulmonary veins.

• 5) Blood then moves into the left ventricle through the bicuspid valve before being pumped to the rest of the body.