Zoology 109 Laboratory note - KSU

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1 Prepared by: Amaal A Alharbi

King Saud University

Faculty of Science

Zoology department

Zoology 109

Laboratory note

Prepared by:

Amaal Awad Al-Harbi

Supervision:

Dr.Maha H. Daghastani

Dr.Afrah F. Al-Khuriji

Dr. Sherifa S. Hamed

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Laboratory Sessions

(1) A. The Microscope and its use.

B. Cell structure:

- Prokaryotes: Bacteria.

- Eukaryotes: animal and plant cells.

C. Types of eukaryotic animal cells.

(2) Histology:

A. Connective tissue.

1- Areolar connective tissue. 2- Hyaline cartilage.

B. Nervous tissue.

1- Neurons. 2- Spinal cord.

(3) Histology:

Muscular tissue.

1- Striated muscles.

2- Cardiac muscles.

3- Smooth muscles.

(4) Histology:

A. Blood vessels.

B. Kidney.

(5) Histology:

The digestive system.

1- Oesophagus. 2- Stomach.

(6) Histology:

1- Liver. 2- Testis.

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(7) Cell division.

1- Mitosis. 2- Meiosis.

(8) Revision.

(9) First final exam.

(10) The Rat:

1- External features.

2- General viscera.

3- Endocrine system.

(11) The Rat:

1- Urogenital system.

2- Nervous system.

(12) A. Human genetics:

1- Blood Groups.

2- Other human traits.

B. Revision.

(13) Second final exam.

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MICROSCOPY

The Compound Microscope:

The compound light microscope is one of the most important and useful tools of the

biologist.

It is used to study the structure of developing embryos, organization of tissues, cells

and its organelles, along with many other important applications.

Since many of the exercises in this course will require the use of the compound

microscope, it is important to review some aspects of its construction, use and care.

There are numerous models of compound microscopes , the microscope assigned for

your use may differ from the one illustrated but the operating principles and

procedures will be similar.

A microscope must be carried with both hands. Grasp the arm of the microscope

firmly with one hand and support the base with the other hand.

Place it gently on your desk with the arm facing you.

Always remember that this expensive scientific instrument is assigned to you for your

use and safe-keeping. Be sure that you use the microscope properly and carefully,

and that you keep it in good condition.

Promptly notify your laboratory instructor if you observe any malfunction or

if you have any difficulty in the use of your microscope.

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Parts of the Microscope:

They can be grouped in three systems:

1- The mounting and movement system.

2- The magnification system.

3- The illumination system.

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1-The mounting and movement system:

Part Function

The base Supporting stand.

The arm Supports the upper part of the microscope.

The stage The horizontal platform upon which the slide rests.

The coarse

focusing knob To rise and lower the stage from the objective lenses.

The fine focusing

knob Focusing for the sharpest image.

The body tube Carry the ocular lenses at one end and the objective

lenses at the other end.

The revolving

nose-piece

Attached to the objective lenses and moves the different

objective lenses into position over the stage aperture.

2-The magnification system:

The objective lenses There are three or four lenses, each one gives a

different magnification. According to their power

of magnification, they are known as:

a) The scanning objective lens which has a

power of magnification 3.5x,4x or 5x.

b) The low power objective lens which has a

power of magnification 10x or 20x.

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c) The high power objective lens which has a

power of magnification 40x.

d) The oil immersion objective lens which

magnifies the object 100x.

The ocular lenses or

the eye-piece

They are used to examine and magnify the image

produced by the objective lens. They vary in their

power, the commonly used ones are 5x to 10x and

15x.

3-The illumination system:

The part The function

The illuminator Source of light.

The condenser Collect and concentrate the light towards the slide.

The iris diaphragm Control the amount of light.

How to use the microscope?

Magnification:

The magnification of an object is determined by multiplying the power of the objective lens

by the power of the ocular lens.

Example: 10x ocular × 40x objective = 400x total magnification.

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THE CELL STRUCTURE

Cells are the basic units of biological structure and function. They possess the following

three essential features:

I-The cell membrane (plasma membrane):

-The cell membrane is an outer membrane which separates the cell from the external

environment.

II- The genetic material:

-The genetic material is composed of DNA.

- It directs and controls all the cell activities, and enables it to reproduce passing on its

characteristics to its offspring.

III- The cytoplasm:

- The cytoplasm contains a large variety of molecules as well as formed bodies called

organelles.

Cell types:

-Two major types of cells are known according to the arrangement of the genetic material

and the contents of the cytoplasm.

1- Prokaryotes.

2-Eukaryotes.

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Prokaryotes Eukaryotes

name Pro=before, karyon=nucleus Eu=true, karyon=nucleus

nucleus Not present.

The genetic material is in the

form of a large, single,

circular molecule of DNA

found diffuse in the

cytoplasm. The region where

the DNA is found is known as

the nucleiod.

Present.

DNA is associated with proteins in a

complex structure known as the

chromatin, which is surrounded by a

double membrane called the nuclear

envelope, this envelope separates the

chromatin from the cytoplasm in a

distinct nucleus.

-Eukaryotic cells vary greatly in size and shape.

There are two types of eukaryotic cells:

1-Animal cells: which have a cell membrane and no cell wall.

2-Plant cell: which have a cell membrane and cell wall.

Characteristics of the different cell types:

1-Prokaryotes (Bacteria):

Type of cells Description of the shape Location

Bascillus Rod shaped, occur in

strands.

Free living or found in other

organism.

Coccus Round shaped, occur in

colonies and strands.

Free living or found in other

organism.

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Bacteria

Bascillus Coccus

Draw a labeled diagram in the space provided, notice their magnification:

Prokaryotes (Bacteria):

Bascillus coccus

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2-Eukaryotes:

Type of cells Description of the shape Location

a)Plant cells:

e.g. Onion cells.

Rectangular-with

eccentric nucleus. Cell

wall clearly seen.

Onion-leaves in onion

bulb.

b)Animal cells:

e.g. epithelial cells.

1-squamous epithelium.

2-cuboidal epithelium.

3-columnar epithelium.

Flat cells having an

irregular border with

flattened nuclei.

Cuboidal in shape with

large central spherical

nuclei.

Tall(rectangular),

column-like cells with

oval or elongated nucleus

basal in position.

1-Endothelium.

2-Bowman,s capsules.

3-Lung alveoli.

1-Thyroid gland.

2-Ovary

3-Large collecting tubule

in the kidney.

1-Stomach.

2-Intestine.

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Eukaryotes

(A) Plant cells:


- Onion leaf epidermis (plant cell): (mag. ……….X)

(B) Animal cells:

(1) Squamous epithelium:

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Mouth mucosa. (Top view) Bowman's capsule. (Side view)


1- Mouth mucosa: Squamous cells (top view) (mag. ……….X).

2- Bowman's capsule: Squamous cells (Side view) (mag. ……….X).

(2) Cuboidal epithelium:

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Collecting tubules in the kidney Thyroid gland


1- Cuboidal epithelium: Collecting tubules in the kidney. (mag. ………X)

2- Cuboidal epithelium: Thyroid gland. (mag. ……….X)

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(3) Columnar epithelium:


- Columnar epithelium: (Section in Stomach) (mag. ……….X)

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THE CONNECTIVE TISSUE

General characteristics :

The connective tissue, connects, holds and supports body tissues and organs together.

It is characterized by the presence of several types of cells widely separated and

immersed in an abundant intercellular component formed by these cells.

Present almost in all parts of the body.

Constituents of connective tissue

I- Connective tissue fibers

II- Amorphus extracellular substance or matrix

III-Connective tissue cells

I-There are two types of connective tissue fibers

a-Collagen fibers

-The most numerous fibers in connective tissue.

- Fresh collagen fibers which are colorless but when Present in great number they

are white.

-They are inelastic, flexible and have a great tensile strength.

-The individual fibers do not branch while the bundles of fibers often do.

b--Elastic fibers :

-Fresh elastic fibers are yellow and branched.

-They are capable of stretching to 1.5 times their length.

-Elastic fibers are abundant in large blood vessels e.g.aorta.

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II-Amorphous ground substance which is:

a) soft as in the connective tissue proper.

b) liquid as in blood and lymph.

c) semisolid and solid as in cartilage and bone, respectively, which make the

skeletal tissue.

- Classification of Connective tissue according to the structural

characteristic of the tissue:

1-Areolar Connective Tissue

Areolar connective tissue is the most widespread connective tissue of the body.

-Areolar connective tissue is flexible, richly vascular and support epithelial

tissue.

- All types of cells are represented with predominance of fibroblast and

macrophages in areolar connective tissue.

-All types of fibers (collagen and elastic) are arranged in no particular

pattern, run in all directions and form a loose network in the intercellular

material in areolar connective tissue .

- Areolar connective tissue has a good amount of ground substance.

Areolar connective tissue surrounds and supports the blood vessels.

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Areolar connective tissue


- Areolar connective tissue. (mag. ……….X)

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- Areolar connective tissue. (mag. ……….X)

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2-Cartilage

- Cartilage is a specialized type of connective tissue which is firm.

- The firm matrix allows the tissue to bear mechanical stress.

- Cartilage support soft tissue.

- It acts as a shock absorbant and it also provides sliding surfaces for bones inside joint

cavities, facilitating bone movement.

- It also keeps the patency of the respiratory tract.

Cartilage of the body is classified according to:

1.The nature of the matrix.

2.The type of its fibers.

The hyaline cartilage:(example :trachea of rabbit)

- Components of hyaline cartilage:

1- It is called hyaline

(hyalos=gloss) because of

its glossy, whitish blue

appearance in the fresh

state and semi-solid .

2- Cartilage cells are

named chondroblasts and

chondrocytes.

3- Collagen fibers are

embedded in the matrix.

4- Hyaline Cartilage is usually covered by a vascular fibro-cellular membrane called

perichondrium which is essential for growth and maintenance of cartilage.

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The Hyaline cartilage (T.S. in costal cartilage).


T.S. of a hyaline cartilage. (mag. ……….X).

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THE NERVOUS TISSUE

The nervous system is divided anatomically into:

1- The central nervous system (CNS), consisting of the brain and the spinal cord.

2- The peripheral nervous system (PNS), composed of nerve fibers forming the

cranial and spinal nerves and the ganglia.

The nervous tissue consists of two cell classes:

1- The neurons, which are the functional units transmitting the nerve impulses.

2- The supporting cells (glial cell or neuroglia), which support, nourish and insulate

the neurons and perform the defense processes in the nervous system. They are

mainly of two types:

a) Neuroglia cells inside the CNS.

b) Schwann cells outside the CNS (in the PNS).

Structure of the neuron:

Neurons have diverse sizes and shapes, but each typically consists of the cell body,

an axon and dendrites:

1- The cell body:

It is also called the perikaryon or

soma. It contains the nucleus

,cytoplsmic organelle

(mitochondria, Golgi complexes,

endoplasmic reticulum ) and

cytoplasmic inclusions (Nissl bodies).

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2- The dendrites:

- Dendrites are multiple cytoplasmic processes specialized in receiving stimuli

and transmitting them to the cell body.

3- The axon:

-Axon is a single long process specialized in conducting nerve impulses to other

cells. The distal part of the axon is usually branched and constitutes the terminal

arborization forming synapses with other nerve cells. The axon emerges from the

cell body at the axon hillock.

The spinal cord:

It is a cylindrical tissue in the form of a hollow tube lying within the spinal cavity of

the vertebral column and is surrounded closely by a loose connective tissue layer

called the pia matter.

In the center, there is a central canal lined by simple epithelial cells.

In cross section, the spinal cord appears to be more or less oval with two deep dorsal

and ventral grooves known as the dorsal fissure and the ventral fissure,

respectively. These fissures divide the cord into right and left symmetrical halves.

The ventral fissure is deeper and wider than the dorsal fissure.

According to its color in the fresh condition, the spinal cord in cross section is

differentiated into:

a) A central zone called the gray matter, shaped like the letter H and contains the

nerve cell bodies and glial (neuroglia) cells.

b) A peripheral zone called the white matter composed entirely of myelinated nerve

fibers and neuroglia cells.

The two dorsal limbs of the H-shaped gray matter are called the dorsal horns and the

two shorter and broader limbs are called the ventral horns. The two central bars of the

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H, passing transversely above and below the central canal, are called the dorsal and

ventral commissures.

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T.S. of Spinal cord

T.S. of the Spinal cord

Enlarged part of White matter

(Nerve fibers)

T.S. of the Spinal cord

Enlarged part of Gray matter

(Cell body of the neuron and Glial

cell nucleus)

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- T.S. of Spinal cord. (mag. ……….X).

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THE MUSCULAR TISSUE

General characteristics of the muscular tissues:

The cells of the muscular tissues are elongated elements, named muscle fibers.

1- The cytoplasm of the muscle fiber, the sarcoplasm, contains myofibrils. These

myofibrils are made up of the proteins actin and myosin.

2- The plasma membrane of the muscle fiber is called the sarcolemma.

3- Muscle fibers are called striated or smooth (non-striated) according to the presence or

absence of striations.

4- Muscle fibers may be voluntary (when their contraction is under the control of will),

or involuntary (when it is beyond the control of will).

5- There are three types of muscle fibers:

a) Skeletal muscles, which are striated and voluntary.

b) Smooth muscles, which are unstriated and involuntary.

c) Cardiac muscles, which are striated and involuntary.

A) The skeletal muscles (striated)

The skeletal muscles are voluntary and attached to the skeleton.

The skeletal muscle fibers are striated.

Each muscle fiber is elongated, unbranched, cylindrical cell, with numerous

peripheral flattened nuclei.

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T.S of skeletal muscle:

- Each individual muscle fiber is surrounded by a delicate connective tissue, the

endomysium.

- Bundles or groups of fibers are wrapped by a dense connective tissue called the

perimysium.

- The whole muscle (formed of several bundles) is covered by a dense connective tissue

sheath, the epimysium.

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L.S. of Skeletal muscle T.S. of Skeletal muscle


1- L.S. of Skeletal muscle. (mag. ……….X).

2- T.S. of Skeletal muscle. (mag. ……….X).

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B) The Smooth Muscle (unstriated)

The smooth muscle fibers are unstriated and contract under the control of the

autonomic nervous system, i.e. involuntary.

The smooth muscle fibers are elongated, spindle- shaped cells.

The nucleus is elongated or rod-shaped and centrally located in the cytoplasm at the

widest part of the cell.

These muscles are present in the wall of blood vessels, digestive, respiratory,

urinary and reproduction systems.

L.S. of Smooth muscle


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C) The Cardiac Muscles

These muscles are present only in the heart.

The cardiac muscle fibers are striated and involuntary.

Cardiac muscle fibers are elongated, branched and mononucleated.

The nuclei are oval and centrally located.

There are darkly-stained, transversely oriented bands scattered through cardiac

muscle fibers; points of end-to-end contact between contiguous myocardial fibers

which are known as intercalated discs.

L.S. of Cardiac muscle

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L.S of Cardiac muscle. (mag. ……….X).

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Types of muscle fibers

Skeletal (Striated

muscle)

Smooth (Unstriated

muscle) Cardiac muscle

Shape

An elongated,

unbranched, cylindrical

cell, with numerous

peripheral flattened

nuclei.

An elongated, spindle-

shaped cells with

pointed ends.

An elongated,

branched,

mononucleate or

binucleate.

Nucleus

shape

An elongated or rod-

shaped.

An elongated or rod-

shaped. Oval.

Nucleus

location Peripheral.

Centrally located in

the cytoplasm at the

widest part of the cell.

Centrally located.

Striation Transversely striated.

unstriated and contract

under the control of

the autonomic nervous

system.

Striated.

Voluntariness Voluntary. Involuntary. Involuntary.

Location Attached to the skeleton.

In the blood vessels,

digestive, respiratory,

urinary and

reproduction system.

In the heart.

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THE BLOOD VESSELS

The circulatory system consists of the blood and lymphatic vascular system.

The vascular system is composed of:

1- The heart which pumps the blood.

2- The arteries which carry oxygenated blood and nutrients to the tissues. They

becomes thinner as they branch forming arterioles.

3- The capillaries which consists of a diffuse network of thin tubules through which

gas exchange between blood and tissues takes place.

4- The veins which carry deoxygenated blood, rich in carbon dioxide and other

metabolic products from the tissues to the heart.

Histological structure of the blood vessels:

All blood vessels have a number of structural features in common. They are composed of

three layers called tunica intima, tunica media and tunica adventitia.

Tunica intima:(This is the innermost layer that faces the blood stream)

o This layer consists of 2 components:

1. A layer of simple squamous epithelium cells (endothelium) lines the vessel

with its basal lamina .

2. A subendothelial layer ( a very thin layer of fibrocollagenous support tissue) .

Tunica media :

o It is consists of layers of circular smooth muscle cells with elastic and

collagen fibers interposed among them.

Tunica adventitia:

o It is a connective tissue layer consisting of longitudinally collagen and

elastic fibers.

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o This layer gradually becomes continuous with the enveloping connective tissue of

the organ through which the vessel is running.

The Artery

o Tunica intima: The flattened endothelium is separated from the media by a well

developed layer of elastic connective tissues, called the internal elastic lamina.

o Tunica media: This layer is the thickest layer of the vessel wall. It consists mainly of

circular smooth muscle cells , elastic and collagen fibers.

o Tunica adventitia: The areolar connective tissue with loosely arranged cells and

fibers is especially rich in elastic fibers.

The Vein

o Tunica intima: The endothelial layer is not separated from the media by the internal

elastic lamina.

o Tunica media: This

layer is much thinner

than that of the artery

and contains more

collagen than elastic

fibers.

o Tunica adventitia:

This is the thickest

layer of the vein wall

and contains mainly

collagen fibers.

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Under microscope:

T.S of Blood Vessels (Artery & Vein)

T.S of the Artery T.S of the Vein

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Draw and label all slides you have studied in this lab, notice their magnification.

1- T.S of an artery. (mag. ……….X).

2- T.S of a vein. (mag. ……….X).

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THE URINARY SYSTEM

The kidney is bean-shaped with a concave medial border, the hilum

(where nerves enter, blood and lymph vessels enter and exit and the ureter

exits) and a convex lateral surface.

The kidney is surrounded by a mass of collagenous capsule and a mass of

adipose tissue.

The kidney tissue surrounds a cavity, the renal pelvis. This pelvis is the

expanded upper end of the ureter.

The kidney can be divided into an outer dark cortex and an inner paler

medulla.

• The human medulla, has 10-18 medullary pyramids.

• The pyramids tips are called the renal papillae and each is perforated by

10-25 orifices, the opening of the collecting ducts. From the bases of each

medullary pyramid, parallel medullary rays penetrate the cortex. Each ray

consists of one or more collecting tubules together with the straight

portions of several nephrons.

• Surrounding each medullary ray in the cortical region are the renal

corpuscles and convoluted portions of the nephron.

The functional unit of the kidney is the uriniferous tubule which consists

of the nephron and the collecting duct in which the renal tubule empties its

contents.

The Nephron:

Each kidney contains 1-4 million nephrons, the filtering units.

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Each nephron consists of:

1- A dilated portion, the renal or Malpighian corpuscle.

2- The renal tubule.

The Malpighian corpuscle consists of:

1. A capsule known as Bowman’s capsule which is lined by squamous cells.

2. The Bowman’s capsule surrounds a net work of capillaries known as

glomerulus.

3. The glomerulus is formed of a network of capillaries, branching from the

afferent arteriole entering the capsule and form the efferent arteriole leaving

the capsule.

The renal tubule consists of the following three parts respectively:

1- The proximal convoluted

tubule.

2- The descending and

ascending limbs of loops of

Henle.

3- The distal convoluted tubule.

The urine produced by the

nephron is collected into the

collecting tubule and then

conducted to the renal

pelvis.

The collecting tubule is lined

with cuboidal epithilum.

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Note:

In the cortex, which is the outer part of the kidney, the following structures are

present:

1- The Malpighian corpuscles.

2- Parts of the proximal convoluted tubule.

3- Parts of the distal convoluted tubule.

4- Parts of the collecting tubules.

In the medulla, which is the inner part of the kidney, the following structures are

present:

1- The loop of Henle.(thin and thick).

2- The terminal parts

of the collecting

tubules.

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Adipose tissue

capsule

Cortex

Medulla

Bowman’s capsule Glomerulus

The Malpighian corpuscle

Collecting tubules

T.S of a Mammalian Kidney

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T.S of the kidney. (mag. ……..x).

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1- T.S of the oesophagus. (40X).

2- T.S of the oesophagus. (mag. ……….X).

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1- T.S of the stomach. (40X).

2- T.S of the stomach. (mag. ……….X).

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THE LIVER

The liver is the largest gland associated with the alimentary tract.

It is situated in the abdominal cavity beneath the diaphragm.

It receives blood from 2 sources:

a) The portal vein that carries oxygen-poor, nutrient-rich blood from the

abdominal viscera.

b) The hepatic artery that supplies oxygen- rich blood.

In the liver, transformation of the metabolites and detoxification of toxic

substances take place.

The liver is covered by a thin connective tissue capsule.

The portal vein and the hepatic artery enter the liver, and the right and the

left hepatic (bile) ducts and lymphatics exit from it. These vessels and

ducts terminate in the portal spaces between the liver lobules.

The liver consists of compartments known as the hepatic lobules.

The Classic Hepatic Lobule:

The lobule is formed of a polygonal mass of tissue.

The main cellular components of the hepatic lobule are the hepatocytes.

Which form cords radially arranged around the central vein. The spaces

between these cords are known as the liver sinusoids.

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The hepatocytes are large polygonal cells with one or two rounded nuclei,

each containing a large nucleolus.

The liver sinusoids are irregularly-dilated vessels the wall of which is

composed only of a discontinuous layer of fenestrated (with opening for

exchange of macromolecules) endothelial cells, with no basal lamina.

The lobules are separated from each other by a layer of connective tissue

which contains the bile ducts, lymphatics, blood vessels and nerves. The

region containing these structures in the connective tissue layer is called

the portal area or portal space (the venule is usually the largest of the

structures in this space).

The bile ducts is lined by cuboidal epithelium and carries bile from the

hepatocytes and empties it eventually into the hepatic duct.

Portal veins and hepatic arterioles deliver blood into the sinusoids at the

periphery of the lobule. This mixed blood in the sinusoids run toward the

lobule center where they drain into the central vein.

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1- T.S of a mammalian liver. (mag. ………… x).

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THE TESTIS

The male reproductive system is composed of two testis, the genital ducts,

the accessory glands and the penis.

The testis are primary sex organs forming the sperm.

The Structure of The Testis:

Each testis is surrounded by

collagenous connective tissue

known as tunica albugenia.

Each testis is sub-divided by

fibrous septa into about 250

compartments called testicular

lobule.

Each testicular lobule consists of

1-4 tightly coiled seminiferous

tubules.

The seminiferous tubules:

In cross section, it appears to consist of spermatogenic cells arranged in 4-8

layers.

These cells consist of the following types:

Spermatogonia, which are diploid cells situated in thr tubule next to the basal

lamina, and are of two types:

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a) Type-A spermatogonia with lightly stained cytoplasm and a large

darkly stained nucleus. These cells divide mitotically and are a

continuous source of spermatogonia.

b) Type-B spermatogonia with lightly stained cytoplasm and nucleus.

They grow large in size and give rise to primary spermatocytes.

1- Primary spermatocytes, which are the largest diploid cells in the

seminiferous tubule and are arranged in 2-3 layers. They are characterized

by their rounded shape, extensive cytoplasm and clear chromatin in the

nucleus. They undergo the first meiotic division and each produces two

small cells known as the secondary spermatocytes.

2- Secondary spermatocytes, which are small rounded haploid cells which

undergo the second meiotic division and give rise to spermatids.

3- Spermatids, which are small haploid cells with condensed chromatin. They

are the nearest to the tubule lumen. They undergo a process of

differentiation known as spermeiogenesis and give rise to mature

spermatozoa.

4- Mature spermatozoa are specialized haploid cells with head and tail, and

are found in the lumen of the seminiferous tubule.

5- Sertoli cells, these are elongated pyramidal cells found between the

spermatogonial cells. Their basal lamina and their tip extent to the tubule

lumen. Sertoli cells acts as “nurse cells” by providing structural and

metabolic support for the developing spermatozoa. They also secrete a

peptide hormone called inhibin which suppresses the synthesis and release

of FSH by the anterior pituitary gland. They also phagocytize excess

cytoplasm shed by spermatids during spermeiogensis.

6- Interstitial cells (Lydig cells); these are rounded or polygonal cells with a

central nucleus and are rich in lipid droplets. These are found embedded in

the connective tissue filling the spaces between the seminiferous tubules.

The cells secrete the male hormone testosterone.

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Note:

The connective tissue found in between the seminiferous tubules also contains

other cells such as fibroblasts, mast cells and macrophages. Also it provided

with nerves and blood and lymphatic vessels.

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1- T.S of testis of the rabbit. (mag. ………… x).

2- T.S of seminiferous tubule of the rabbit. . (mag. ………… x).

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THE CELL DIVISION

Mitosis and Meiosis

Cell division is a process by which the cellular material is divided between 2 new daughter

cells.

Types of cell division:

There are 2 major types of cell division, these are mitosis and meiosis.

1- Mitosis (indirect division):

This type occurs in somatic cells of higher organisms, and is the means of population

growth in unicellular organisms.

This cell division results in two daughter cells, each having the same number of

chromosomes of the mother cell.

2- Meiosis (reduction division):

This type occurs in the diploid germ cells of animals and results in 4 daughter cells

each having a haploid number of chromosomes (i.e. half the number of chromosomes

of the original cell).

It involves exchange of the chromosomal segments between homologous (identical)

chromosomes.

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The Phases of Mitosis:

(A) Prophase:

1. The chromosomal threads become tightly coiled, thus become shorter and denser

and could be seen as chromosomes, each is formed of 2 sister chromatids

(replicated chromosome) attached together at the centromere.

2. The nuclear envelope dissolves.

3. The nucleolus disappears.

4. In the cytoplasm of animal cells, the centrioles, with a surrounding fan of astral

rays, start to migrate toward opposite poles of the cell.

5. The spindle fibers begin to form.

(B) Metaphase:

1. The spindle fibers are fully formed and astral rays appear around the centrioles at

the cell poles (in animal cells).

2. The chromosome are arranged in the equatorial plane and their centromeres

appear attached to the spindle fibers at their kinetochores. These kinetochores are

2 disk-shaped structure in each centromere.

(C) Anaphase:

The centromeres split and the 2 chromatids of each chromosome become

separated and pulled toward the corresponding cell pole (centriole in animal

cells). Now each chromatid is a chromosome.

(D) Telophase:

1. The chromosome have reached the opposite poles.

2. The spindle disperses.

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3. The chromosome become diffuse.

4. The nucleolus reappears.

5. A nuclear envelope forms around each chromosome set, thus a nucleus is formed.

Cytokinesis:

This involves the division of the cytoplasm into 2 nearly equal cells.

The process usually begins during telophase and sometimes during anaphase.

The cytoplasm gradually constrict at the equatorial plane (along the midline of the

spindle).

This process is not part of mitosis.

In plant cells, cytokinesis involves formation of a cell plate between the 2 daughter

cells. This plate is formed as a result of fusion of vesicles arranged at the equatorial

plane. A membrane bound space, i.e. the cell plate, is formed. This space is then

filled with pectin thus forming the middle lamella. Each daughter cell secretes its

own cell wall on the sides of this lamella.

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Draw the phases of the mitotic cell division as see them under the microscope and

label the different structures:

Prophase. (mag. ………… x). Metaphase. (mag. ………… x).

Anaphase. (mag. ………… x). Telophase. (mag. ………… x).

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Draw the phases of the mitotic cell division as see them under the microscope and


Prophase. (mag. ………… x) Metaphase. (mag. ………… x).

Anaphase. (mag. ………… x). Telophase. (mag. ………… x).

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The Phases of Meiosis:

Meiosis includes 2 successive nuclear divisions:

1. Meiosis I: during which homologus chromosomes separate.

2. Meiosis II: during which sister chromatids of each chromosome separate.

Interphase:

Meiosis I:

(A) Prophase:

1. The homologus chromosomes pair together so that they align along their length

precisely and thus form a tetrad (4 chromatids).

2. The aligned chromatids of the 2 chromosomes interchange segments in a process

called crossing over.

3. The chromatin threads condense.

4. The nuclear envelope dissolves.

5. The nucleolus disappears.

6. The spindle begins to form.

(B) Metaphase:

1. The spindle is fully formed.

2. Homologus pair of chromosomes line up in the equatorial plane (as tetrads).

3. The spindle fibers attach to each homologus at its kinetochore (centromere).

4. In animal cells, centriols and astral rays are also present at the opposite poles of

the cell.

(C) Anaphase:

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The homologus chromosomes separate; each chromosome (consisting of 2 sister

chromatids) of the homologus pair move toward one pole of the cell.

(D) Telophase:

1. Homologus chromosomes have reached the opposite poles where only half

(haploid = 1 n) the number of chromosomes can be seem.

2. A nuclear envelope may form around the chromosomes.

3. Cytokinesis may take place (depending on the species).

Meiosis II:

It resembles mitosis except that it is not preced by DNA replication, since this has

already taken place before meiosis I.

(A) Prophase:

1. The chromosomes condense fully again.

2. The nuclear envelope breaks down.

3. The spindle fibers begin to appear.

(B) Metaphase:

1. The spindle is fully formed.

2. The chromosomes (1 n), each of 2 sister chromatids, line up in the equatorial

plane.

3. The spindle appear attached to the kinetochore of each of the chromosome.

(C) Anaphase:

1. Sister chromatids separate as the centromers split up.

2. Each chromatid, now is a chromosome, moves towards one of the opposite

poles,

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(D) Telophase:

1. The chromosomes have reached the poles.

2. The spindle disappears.

3. A nuclear envelope forms around each set of chromosomes.

4. The chromosomes disperse into chromatin threads.

Cytokinesis:

This process proceeds during telophase to separate the 2 daughter cells, and to

separate the 4 daughter cells (if it has not occurred after telophase I).

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Draw the phases of the meiotic cell division as see them under the microscope and


Prophase I. (mag. ………… x). Metaphase I. (mag. ………… x).

Anaphase I. (mag. ………… x). Telophase I. (mag. ………… x).

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Draw the phases of the meiotic cell division as see them under the microscope and


Prophase II. (mag. ………… x). Metaphase II. (mag. ………… x).

Anaphase II. (mag. ………… x). Telophase II. (mag. ………… x).

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86 Photo by Jamilah Al-Shammarey Prepared by: Amaal A Alharbi

THE HUMAN BLOOD GROUPS

In humans, about 15 major blood group system have been recognized, but we will be studying

only two blood group systems, the ABO and the Rh blood group systems.

The ABO and the Rh blood group systems:

The human ABO blood groups are an example of the multiple allelic series.

There are three alleles: allele A (IA) which produces antigen A, allele B (I

B) which

produces antigen B and allele I (Ii) which cannot produce any antigen. Allele I is

recessive to both alleles A and B, but allele A and B are codominant to each other, i.e.

both are expressed.

Antigens are large molecules (often proteinacous. at least partly) present on the cell

membrane of the red blood cells.

Human blood also carries naturally occurring antibodies (large protein molecules)

specific for antigen A and B in the serum.

Detection of the blood group types depends on the antigen-antibody reaction

(agglutination) occurring between the antigens on the red blood cells and the antibodies

in the serum.

Since each individual carries only a pair of alleles, four phenotypes of ABO blood groups

are present in the population. Table (1) gives the blood type (phenotype), the possible

genotype and the antigens and antibodies present in the blood of the different individuals

of the population.

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Table (1)

The phenotypes, possible genotypes, antigens and antibodies characterizing the ABO

blood group system

blood type

(phenotype)

possible

genotypes

Antigens on

RBCs

Antibodies in

serum

Type-A IAI

A or I

A I

i A B

Type-B IBI

B or I

B I

i B A

Type-AB IAI

B A & B absent

Type-O IiI

i absent A & B

The Rh blood groups:

This is Rhesus blood group (Rh factor) also commonly called the D antigen.

This blood group is determined by only two alleles. The dominant allele Rh+ (D)

produces the Rh antigens, while the recessive allele Rh- (d) dose not produce the Rh

antigen.

There are no naturally occurring antibodies for Rh antigen in the blood.

In the population, tow phenotypes are recognized, one is known as +ve and the other

are –ve.

Table (2) gives the blood types (phenotypes), the possible genotypes and the antigens

present on the RBCs.

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Table (2)

The phenotypes, possible genotypes and antigens present in the Rh blood group system

blood type

(phenotype)

possible

genotypes

Rh antigen on

RBCs

Rh+

(positive)

Rh+ Rh

+ (DD)

or Rh+ Rh

-

(Dd)

Present

Rh-

(negative) Rh

- Rh

- (dd) Absent

Blood group typing:

Procedure:

1. Sterilize the tip of your figure with an alcohol swab and prick it with a blood

lancet.

2. Place three drops of blood on the slide provided to you.

3. Add a drop of anti-A to the first drop, anti-B to the second drop and anti-D to

the third drop.

4. Mix well each of the three groups with a separate tooth pick or lancet. Observe

the agglutination in each of the three reactions and record your blood type and

possible genotype for both the ABO and Rh groups in table (3).

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Table (3)

The blood type of the student

Blood group

type

(phenotype)

Possible

genotypes

ABO

Rh

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Iiiustrate diagrammatically your observations on the agglutination

reactions of the different blood groups you have examined:

Blood types

(phenotype)

Anti-

A

Anti-

B

Anti-

D Possible genotypes

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HUMAN TRAITS

In any group or population of organisms, unless breeding is controlled experimentally or

by self-fertilization mechanisms as in plants, it is unusual to fine two individuals exactly

alike. Among humans except for identical twins, it is highly improbable that two

persons would be genetically identical (alike). The purpose of this exercise (lab) is to

demonstrate the genetic variation among humans within a relatively small group. And to

calculate the frequencies of particular genes among the individuals within this group

(class/section).

Human traits (characteristics):

There are large numbers of human characteristics which may be used in studying human

variations. However, some are more easily observed and distinguished than others. Six

of such as traits are described below so that you can determine the particular phenotype

you possess for each trait. Place a check mark before the possible genotype responsible

for your phenotype in table (4).

Widow’s Peak:

This trait is due to a dominant allele (W) in which the forehead hair line forms a point in

the center of the forehead. The

recessive allele (w) dose not produce

the Widow’s Peak, and the individual

homozygous for this allele (with

,,ww,,) has a straight hair line in the forehead.

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Ear lobes:

Earlobes that do not join the side of the head are known as free earlobes, a trait

produced by the dominant allele (F). Attached earlobes are the result of the presence of

the recessive allele (f) in the homozygous condition (ff).

Free earlobes Attached earlobes

Handedness:

When a person is asked to cross fold the hands, if the right hand comes over the left

hand this is known as right handedness. This trait is inherited as a dominant allele (R).

Left Handedness is inherited as a recessive allele (r) present in the homozygous

condition (rr).

Right hand Left Handedness

Hair shape:

Hair shape is controlled by 2 alleles, the dominant allele (C) which produces curly

hair, and the recessive allele (c) which produces straight hair. However in this trait the

(C) allele exhibit incomplete dominance.

Therefore, 3 phenotypes are present in the population

1. The homozygous condition (CC) produces curly hair.

2. The homozygous condition (cc) produces straight hair.

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3. The heterozygous condition (Cc) produces wavy hair due to interaction between

the two alleles.

straight hair wavy hair curly hair

Tongue curling or rolling:

Some individuals are able to roll their tongue at the sides

forming a V-shape. Tongue curling is produced by a

dominant allele (R). persons unable to roll their tongue have the

recessive allele (r) in homozygous condition (rr).

Tongue folding:

Some persons are able to fold their tongue backwards or fold

it front to back. This is also produced by a dominant allele

(F). Individuals unable to fold their tongue possess the

recessive allele (f) in homozygous condition (ff).

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THE RAT

EXTERNAL FEATURE, GENERAL VISCERA

The rat has a long cylindrical body, a long, thin tail and very short legs. This shape is

well suited to running on narrow burrows or squeezing through small holes.

External Features:

* The outer surface of the body is almost completely covered with hair, which is devoid

of pigmentation in the albino rat.

* The body is divided into the head, neck , trunk, with two pairs of limbs, and the tail.

The head:

* The head has a pointed mobile nose (a characteristic of mammals), with 2 slit-like

nostrils at the edge of a hairless zone called the rhinarium.

* The mouth is anterior, narrow, with a short lower jaw, and bounded by two mobile soft

lips (a characteristic of mammals). The upper lip is divided by a median cleft.

* The two small beady eyes are set so that they look diagonally forwards and sideways.

* On the anterior region of the head are numerous long whiskers or vibrissae.

* The two ear pinnae are rounded, and freely movable ( a mammalian characteristic).

The neck:

* The neck is short and connects the head with the trunk.

The Trunk:

* The trunk is very little wider than the head, and consists of the thorax and abdomen.

There is considerable flexibility of the spine so that the body can be bent well over to

either side or backwards when.

* The thorax is strengthened by the ribs and stemum, and the abdomen is large.

* At the base of the tail is the anus, and in front of it is the urogenital aperture.

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* In the male the common urogenital

aperture is at the tip of a retractile organ

called the penis, surrounded by a free

fold of skin called the prepuce. Behind

the called the Behind the peris are two

very large scrotal sacs in which the two

testes lie outside the body cavity.

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* In the female, the urinary and genital

apertures are separate and anterior to the anus

on the ventral surface of the hind end of the

abdomen. The urethra opens at the base of the

clitoris which is a small projecting

homologue of the penis enclosed in a little

prepuce. The vagina lies between the clitoris

and the anus-nearer to the former, and is

closed by a membrane during the first ten

weeks of life, that is, until puberty.

* In the female, along the ventral surface of the

thorax and abdomen there are usually 6 pairs of teats on the tips of which open the ducts

of the mammary glands, Theses teats include three thoracic, one abdominal and two

inguinal pairs. Sometimes one of the second thoracic teats may be lacking.

Male Female

* The limbs are built up on the same plan as in the other tetrapods. In the fore-limb are the

upper arm, fore-arm and fore-foot (hand), while in the hind-limb are the thigh, shank

and hind-foot. The fore-limbs are shorter than the hind-limbs. But both pairs are well

flexed so that the body is only slightly raised off the ground.

* Each of the hands has 4 clawed digits and a small nodule which represents the pollex

(thumb). The hairless sole of the fore-foot has a number of pads, a digital pad at the apex

of each digit and five larger footpads on the palm.

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* Each hind-foot has 5 clawed digits, but the first hallux is much shorter than the others.

The hairless surface of the sole extends to the tarsal joint. This joint corresponds to the

ankle of man. There are 6 footpads on the sole.

* The tail is almost as long or longer than the trunk. It is very narrow and tapers

gradually toward the hind end. The entire surface of the tail is covered by rows of scales

which overlap like roof-tiles. Three short bristles project from under the edge of each

scale. The surface of the tail is covered with orange-yellow-waxy grease.

GENERAL VISCERA

Dissection I:

1- Take a rat killed by an overdose of an anesthetic chemical, such as chloroform or ether,

and lay it on its back on the dissecting board. Fix it by tying the four limbs with the strings

attached to nails on the dissection board.

2- Wet the whole ventral surface of the rat with Dettol solution.

3- Make a median longitudinal incision in the skin only, from the chin to the root of the tail,

i.e. the full length of the ventral surface. Then cut at right angles to this along the fore limbs

as far as the elbows, Make similar incisions along the hind limbs to about the level of the

knee joint.

4- With the help of your fingers or the handle of the scalpel (not its sharp edge). Separate

the skin from the muscular body wall (note that the two are connected together by loose

subcutaneous connective tissue). In doing this avoid damaging the superficial nerves and

blood vessels, Reflect the skin flaps and nail them down on the dissection board.

Observations:

* Through the relatively thin abdominal musculature, the abdominal viscera can be seen.

The most obvious of these are the liver, stomach, caecum and small intestine.

* In the female, the mammary glands can be seen intimately attached to the reflected skin.

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The mammary tissue consists of anterior and posterior portions. The anterior mass extends

as far as the chin, and up the sides of the neck and the thorax. The posterior part is separated

from the anterior by a space just behind the ribs. The tissues of the abdominal and inguinal

glands are confluent. The mammary tissues appear red-brown in color but, if it is full of

milk it appears paler and mottled with white.

* In the throat region, the salivary glands can be seen. The most obvious from the ventral

aspect are the sub maxillary glands, which are in contact along the mid-ventral line, and

cover most of the ventral surface of the neck. The major sublingual gland is closely applied

to the anterior- lateral surface of the sum maxillary gland. The parotid gland is a less

compact structure which extends from the ventral surface behind the jaw to the ear.

Dissection II:

* In the mid-line of the neck dissect away

the glands and muscles to expose the length

of the trachea, the larynx and the thyroid.

Observations:

* The trachea appears as a tubular

structure supplied with a series of

cartilaginous rings.

* The larynx consists of a number of

cartilaginous plates which forms the voice

box.

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THE GENERAL VISCERA OF THE RAT

The Digestive System :

The digestive system consists of the buccal cavity, pharynx, oesophagus, stomach,

small intestine and large intestine. The associated glands are the salivary glands, the

pancreas and the liver.

Dissection I:

Open the buccal cavity by cutting through the muscles on each side. Turn the lower jaw

through about 180 degrees and examine the structures of the buccal cavity, which is the

region between the mouth and the pharynx.

Observations:

* The jaws are long and narrow. The upper jaw is fixed but the lower jaw is movable by

articulation to the skull, just anterior to the ears.

* In each jaw there are one pair of incisors, no canines, no premolars and 3 pairs of

molars. Thus the dental formula is: I 1/1, c0/0, pm 0/0, m 3/3=16.

* The tongue is very muscular and has a ridged and roughened surface. On the surface of

the tongue are taste buds.

* At the posterior end of the buccal cavity appears the pharynx which joins the buccal

cavity with the oesophagus. It also forms the passage between the nasal cavities and the

windpipe. The opening to the windpipe lies on the ventral side of the pharynx and is

called the glottis, this opening can be closed and covered by the epiglottis so that food

cannot pass through it during swallowing.

Dissection II:

* Remove the lower jaw, taking with it the oesophagus, the larynx and the trachea.

* Displace the above structures together with stomach and the small and large intestines

to one side. Unravel the coils of the intestine leaving the duodenal loop and the rectum

with their mesenteries untouched. Spread the intestine on the dissecting board so as to

show the proportions of its several parts.

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Observations:

* The oesophagus appears as straight tube extending from the pharynx to the stomach. It

lies partly in the neck, dorsal to the trachea and partly in the thorax diaphragm before

reaching the stomach.

* The stomach is large and saccular. It shows extremely its division into a cardiac part,

which is translucent with white lining, and a pyloric part which has an opaque thicker

wall.

* The small intestine is about 6 times the length of the body from snout to anus. It is

approximately uniform in diameter and is supported in the abdominal cavity (before

unraveling) by an extensive mesentery.

* The first part of the small intestine forms a U-shaped loop known as the duodenum.

The bile duct from the liver opens into this region. This duct is joined by numerous

pancreatic ducts from the pancreas. The remainder of the small intestine is known as the

ileum.

* The large intestine is about one-sixth the length of the small intestine. It is also

supported by mesentery (before unraveling). It is divided into a short colon and a longer

rectum which opens by the anus. The lining of the colon has the colon and the ileum there

is a diverticulum called the caecum, the blind end of the presence of a mass of lymphoid

tissue in its lateral wall.

* The liver is suspended from the posterior surface of the diaphragm by the falciform

ligament, it has 4 lobes. The right lobe is large and partially divided the left lobe is also

large but undivided, the median or cystic lobe has a deep fissure for the hepatic ligament,

and the caudal lobe is a small portion of the liver tissue wrapped around the oesophagus.

The bile duct receives tributes from each of the lobes and has a muscular sphincter art its

duodenal end, but the rat has no gall bladder.

* The pancreas is very diffuse with small lobules scattered in the mesentery of the

duodenal loop and in the fold called the gastro-splenic omentum. It has many ducts

opening into the bile duct.

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* The spleen, which is not a part of the digestive system, is a bright red body lying close

to the greater curvature of the stomach.

pancreas spleen

ileum

cecum

liver

stomach

duodenum

appendix

rectum

colon

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THE UROGENITAL AND NERVOUS SYSTEMS

* The excretory system of mammals consists of 2 kidneys, 2 ureters, a bladder and a

urethra.

* In the female rat the excretory system is separate, while in the male it is joined with the

genital system.

Dissection:

1. Dissect and open an anaesthetized rat as you did in the last laboratory cession.

2. Remove the alimentary tract leaving only the stump of the rectum.

3. Cut the bones of the sides of the public symphysis and remove the cut pieces away.

So as to expose the posterior part of the urogenital system.

4. Examine carefully all parts of the urogenital system, then with a sharp scalpel slit

One kidney opens from its outer edge, and turns the ventral half inwards, so as to expose

the cut surface.

Observations:

The Excretory System:

* The two kidneys are dark red in color, bean-shaped and are enveloped within a fibrous

capsule. The right kidney lies more interiorly than the left. Anterior to each kidney, a

small yellowish rounded body, the adrenal gland is present. Each kidney has a notch

called the hilum where the renal artery enters and the renal vein and ureter emerge.

* The two ureters extend from the concavity of the kidney to open into the posterior

wall of the urinary bladder.

* The urinary bladder is an ovoid sac which narrows posteriorly. In the female it receives

only the ureters at this narrow end, the neck which extends as a tubular urethra bladder.

* The urinary bladder is an ovoid sac which narrows posteriorly. In the female it

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receives only the ureters at this narrow end, the neck, which extends as a tubular urethra

in the pelvis to open by the urethral opening at the tip of the clitoris in the pelvis as a

urogenital passage before opening by a common urogenital opening at the tip of the

penis.

* In the cut kidney, the substance of the kidney can be differentiated into an outer cortex

with a dotted appearance due to the presence of the Malpighian bodies which are

confined to this part. The inner part is the medulla. It appears radially striated and

consists mainly of the renal and collecting tubules. The inner surface of the medulla

projects into the renal pelvis of the kidney forming the pyramids on which the colleting

tubules open.

The Male Genital System:

* This consists of two testes, each with an epididymis and a vas deferens, 2 seminal

vesicles and a number of associated glands.

* The testes lie in the scrotal sacs and each remains connected with its original position

in the abdominal cavity by a spermatic cord. The spermatic cord consists of a spermatic

artery, a spermatic vein-

and a spermatic nerve,

all bound in connective

tissue.

* Along the side of each

testis lies the epididymis

which is enlarged

interiorly forming the

caput epididymis and

posteriorly forming the

cauda epididymis.

The spermatic cord is connected to the caput epididymis.

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* The 2 vasa deferentia are connected to the cauda epididymis and each passes forwards

out of the scrotal sac to open into the dorsal wall of the narrow neck of the bladder.

* Associated with each vas deferens is a vesicular seminalis which is relatively enormous

in size, curved and sacculated and is closely connected with a large coagulating gland.

* There is a pair of prostate glands, each of which is subdivided so that they appear as 2

pair of prostate glands, each pair being attached by a stalk to the neek of the bladder.

* The pair of Cowper or bulbo-urethral glands open into the urethra at the flexure where

it emerges from the pelvis.

* Around the neck of the bladder lies another gland called the gland of vas deferens.

* The urogenital canal, the urethra, opens at the tip of the protrusible penis which has a

fold of skin called the prepuce.

* Two preputial glands lie under the skin of the prepuce and open at the base of this fold

into the area between the prepuce and the penis. The secretions of these glands identify

the individuals within the rat community. These glands are not part of the reproductive

system.

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The Female Genital System:

* This consists of the paired ovaries and oviducts and the unpaired vagina.

* The ovaries are much smaller than the testes and lie in the abdominal cavity ventro-

lateral to the kidneys, enclosed within a very walled periovarial sac.

* The oviducts are tubular and each has a minute opening close to the corresponding

ovary. The oviducts are suspended from the wall of the abdomen by peritoneal folds

called the mesovaria. Each oviduct is divided into 2 regions. The first region is narrow

and coiled and is called the Fallopian tube, while the other region is wide and usually

called the uterine horns or uterine cornua.

* The two uterine horns open separately into the vagina which extends backwards lying

dorsal to the urethra but ventral to the rectum and anal passage. The external opening of

the vagina is immediately posterior to the opening of the urethra.

* Two prepucial glands lie under the skin on the sides of the urethra but open into the

vagina. They are not part of the reproductive system.

* In young rats the opening of the vagina is partially covered by a membrane called the

hymen.

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The Nervous System:

* This consists of the central nervous system and the peripheral nervous system.

* The central nervous system consists of the brain, which is enclosed by the skull, and

the spinal cord which extends within the spinal column.

* The peripheral nervous system consists of the cranial nerves, which originate from the

brain, and the spinal nerves, which originate from the spinal cord and innervate all parts

of the body.

To study the brain and the cranial nerves, the skull has to be dissected open. The spinal

nerves can be studied in the dissected rat after removing all the viscera.

Dissection of The Head :

1 .Remove the skin of the head with the help of the scalpel. Separate with a bone- Cutter

the two halves of the lower jaw.

2 .Remove the upper and side walls of the cranium. Cut the roots of the cranial nerves on

both sides, and very gently take the brain out, put it in the dissecting dish examine it.

3 .Examine also the roots of the cranial nerves.

Observations :

* The brain is ensheathed by the Dura (outer) and Pia (inner) mater.

* In the dorsal side, the following parts are, clearly seen:

1 .Two large cerebral hemispheres, separated by the median fissure, which form the

major part of the brain.

2 .The olfactory lobes which are found in front the cerebral hemispheres.

3 .The cerebellum which consists of a median lobe or vermis and two lobes lateral to the

vermis, each is called the flocculus and carries laterally a small lobe called the

paraflocculus.

4 .The cerebral hemispheres are separated from the cerebellum by the venous sinus, in

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which projects the pineal body (at the tip of a pineal stalk) which lies at the end of the

median fissure.

* The medulla oblongata merges backwards from the brain and connects it with the spinal

cord.

* In the ventral surface, the olfactory lobes, the cerebral hemispheres, the flocculus, the

paraflocculus and medulla oblongata are clearly seen. In addition, the pituitary body, just

anterior to the medulla oblongata, and the optic chiasma are observed.

olfactory lobes

cerebral hemispheres

pineal body

flocculus

paraflocculus

vermis

medulla oblongata

Spinal cord

Dorsal view of the brain

Documents

Zoology 109 Laboratory note - KSU