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Chapter: Structural Organisation in Animals
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1 Cells:
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Cells are the basic structural and functional units of life
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Examples include nerve cells, muscle cells, and epithelial cells
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They are microscopic in nature and can only be seen under a microscope
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The main types of cells are prokaryotic cells (such as bacteria) and eukaryotic cells (found in
plants, animals, fungi, and protists)
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The nucleus is the control center of the cell, containing DNA, which carries genetic
information
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Examples
include mitochondria, responsible for energy production, and chloroplasts, involved in
photosynthesis in plant cells
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Cells can reproduce through cell division, either by mitosis (for growth and tissue repair) or
meiosis (for the production of gametes in sexual reproduction)
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Different types of tissues are found in animals, including epithelial, connective,
muscular, and nervous tissues
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Connective tissue provides support, protection, and connects body parts
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Nervous tissue controls and coordinates body activities
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There are four primary types of tissues in the human body: epithelial tissue, connective
tissue, muscle tissue, and nervous tissue
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It
provides protection, secretion, absorption, and sensation
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It includes various
types such as bone, cartilage, adipose (fat), blood, and fibrous connective tissue
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Nervous tissue is composed of specialized cells called neurons that transmit electrical
signals
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Tissues can have different levels of organization, ranging from simple to complex
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Tissues are arranged into higher levels of organization called organs, which work together
to perform specific functions in the body
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Examples include the stomach, heart, and lungs
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About Organs:
An organ is a structure composed of different types of tissues that work together to
perform specific functions in the body
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Examples of organs in the human body include the heart, lungs, liver, kidneys, brain, and
skin
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Organs often have a characteristic shape and organization that is suited to their function
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Organs are typically composed of several types of tissues, such as epithelial, connective,
muscle, and nervous tissues
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For example, the liver is composed of hepatocytes (liver cells) arranged in lobules,
allowing it to perform functions such as detoxification and nutrient processing
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Examples of organ systems include the circulatory
system, respiratory system, digestive system, and nervous system
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Organs can vary in size, shape, and complexity across different organisms and species
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4 Organ Systems:
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Organ systems are groups of organs that work together to perform specific functions
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Each organ system has specialized structures and functions that contribute to the
overall survival and functioning of the organism
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The human body has several organ systems, including the circulatory system, respiratory
system, digestive system, nervous system, skeletal system, muscular system, endocrine
system, urinary system, reproductive system, and integumentary system
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Organ systems are interconnected and often rely on each other to carry out complex
physiological processes necessary for life
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The respiratory system, composed of the lungs and airways, facilitates the exchange of
oxygen and carbon dioxide, enabling the body to obtain oxygen and eliminate waste gases
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The nervous system, consisting of the brain, spinal cord, and nerves, coordinates and
controls bodily functions and enables communication between different parts of the body
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Imbalances or disorders within organ systems can lead to various diseases and medical
conditions, highlighting the importance of their proper functioning
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Animal Tissues: 2
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It protects the underlying tissues, regulates the exchange of substances, and secretes
various substances
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About Animal Tissues:
Animal tissue refers to the specialized groups of cells that make up the structural
components of animals
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Epithelial tissue covers surfaces and lines body cavities and organs
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Connective tissue provides support, structure, and connection between different tissues
and organs
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Muscle tissue is responsible for movement and can be categorized into three types: skeletal
muscle, smooth muscle, and cardiac muscle
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Smooth muscle is
found in the walls of organs and facilitates involuntary movements
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Nervous tissue is composed of specialized cells called neurons that transmit electrical
signals
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Animal tissues can vary in structure and function depending on the specific needs and
adaptations of different organisms
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The study of animal tissue is crucial for understanding the structure, function, and overall
biology of animals, as well as for diagnosing and treating diseases and injuries
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Connective Tissue:

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Connective tissue provides support, protection, and connects different body parts
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Examples of connective tissues include bone, cartilage, blood, and adipose
tissue
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It is characterized by a matrix composed of protein fibers, ground substance, and cells
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Connective tissue is widely distributed throughout the body and plays a crucial role in
maintaining the overall integrity and function of organs and tissues
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Loose connective tissue is found beneath the skin and around organs, providing support
and flexibility
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Adipose tissue, also known as fat tissue, stores energy, cushions organs, and insulates the
body
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Bone is a hard connective tissue that forms the skeleton, providing support, protection, and
allowing for movement
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Lymphoid tissue, including lymph nodes, tonsils, and spleen, plays a role in the immune
response and defense against pathogens
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Connective tissue can undergo repair and regeneration in response to injury or damage
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It consists of cells called muscle fibers that contract and generate force
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About Muscular Tissue:
Muscular tissue is a type of animal tissue responsible for movement, stability, and
generating force
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Skeletal muscle is attached to bones and allows for voluntary movement, such as walking,
running, and lifting objects
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It facilitates involuntary movements, such as the contractions of the digestive system or
blood vessel constriction
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It contracts rhythmically to pump blood
throughout the body and has properties intermediate between skeletal and smooth
muscle
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Muscle fibers contain specialized proteins called actin and myosin, which interact to
generate muscle contractions
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Muscular tissue has the ability to contract and relax, enabling it to generate force, produce
movement, and maintain posture
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Regular exercise and physical activity help maintain and strengthen muscular tissue
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Muscular tissue is highly vascularized, meaning it has a rich blood supply, which provides
the necessary oxygen and nutrients for muscle function
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Muscular tissue has a high metabolic rate and can generate heat, contributing to body
temperature regulation
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4 Nervous Tissue:
Nervous tissue is a specialized type of animal tissue that forms the communication network
within the body
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Nervous tissue is primarily found in the brain, spinal cord, and nerves
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Neurons consist of a cell body, dendrites (which receive signals), and an axon (which
transmits signals)
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Nervous tissue is responsible for coordinating and controlling bodily functions, including
sensory perception, motor control, memory, and cognition
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Nervous tissue allows for rapid signaling and responses to stimuli
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Nerves composed of nervous tissue extend from the CNS to different parts of the body,
forming the peripheral nervous system (PNS)
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Disorders of the nervous tissue can result in neurological conditions, such as Alzheimer's
disease, Parkinson's disease, multiple sclerosis, and stroke
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Nervous tissue enables sensory perception, coordination of movement, regulation of
internal organs, and higher cognitive functions
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Animal Organs and Organ Systems:

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It includes organs such as the mouth, esophagus, stomach, small intestine, and large
intestine
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2 Respiratory System:
The respiratory system is a complex network of organs and tissues responsible for the
exchange of oxygen and carbon dioxide in the body
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The main organs of the respiratory system include the nose, nasal cavity, pharynx, larynx,
trachea, bronchi, bronchioles, and lungs
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The respiratory system works in coordination with the cardiovascular system, as
oxygenated blood is transported to body tissues and deoxygenated blood is returned to the
lungs for oxygenation
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The pharynx serves as a common pathway for both air and food, branching into the trachea
(windpipe) and esophagus (food pipe)
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The trachea divides into two bronchi, which further branch into smaller bronchioles that
lead to the alveoli
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Oxygen diffuses across the walls of the alveoli into the bloodstream, while carbon dioxide
moves in the opposite direction, from the bloodstream into the alveoli
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The diaphragm, a dome-shaped muscle located below the lungs, plays a crucial role in the
breathing process by contracting and relaxing to facilitate inhalation and exhalation
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The respiratory system also helps regulate pH levels in the body by controlling the
concentration of carbon dioxide, which affects blood acidity
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3 Circulatory System:
The circulatory system, also known as the cardiovascular system, is a network of organs,
vessels, and blood that transports substances throughout the body
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The main organs of the circulatory system are the heart, blood vessels (arteries, veins, and
capillaries), and blood
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Arteries carry oxygenated blood away from the heart to the body's tissues, while veins
return deoxygenated blood back to the heart
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Blood is a specialized fluid that consists of plasma (a liquid portion) and various types of
cells, including red blood cells, white blood cells, and platelets
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White blood cells are part of the body's immune system, defending against pathogens and
foreign substances
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The circulatory system also plays a role in maintaining body temperature and pH balance
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The cardiac cycle involves the alternating contraction (systole) and relaxation (diastole) of
the heart chambers, ensuring blood is pumped efficiently
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Cardiovascular diseases, such as heart disease, stroke, and hypertension, are common
conditions that can affect the circulatory system and overall health
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4 Excretory System:
The excretory system, also known as the urinary system, is responsible for eliminating
waste products and regulating the balance of fluids and electrolytes in the body
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The kidneys are two bean-shaped organs located on either side of the spine
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Urine produced in the kidneys travels through the ureters, which are tubes that connect the
kidneys to the bladder
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The excretory system helps maintain the body's fluid balance by regulating the volume and
composition of urine produced
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They also produce and release hormones that influence red blood cell production and
blood pressure regulation, such as erythropoietin and renin
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The process of urine formation involves filtration, reabsorption, and secretion in the
nephrons, the functional units of the kidneys
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Maintaining proper hydration is important for the optimal functioning of the excretory
system and the elimination of waste products
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Proper functioning of the excretory system is vital for the overall health and balance of the
body
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Its primary functions include receiving sensory information, processing and integrating that
information, and initiating appropriate responses
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The CNS consists of the brain and spinal cord, which serve as the control center for
processing and coordinating information
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Neurons are the specialized cells of the nervous system that transmit electrical signals or
impulses
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Glial cells, also known as neuroglia, support and protect neurons, provide nutrients, and
maintain the overall function and environment of the nervous tissue
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The brain, as the central organ of the nervous system, controls and coordinates most bodily
functions, and is responsible for higher cognitive processes
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The PNS includes the somatic nervous system, which controls voluntary movements, and
the autonomic nervous system, which regulates involuntary functions like heart rate,
digestion, and respiration
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Disorders of the nervous system can lead to various conditions, such as neurological
disorders, neurodegenerative diseases (e
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, Alzheimer's, Parkinson's), stroke, and spinal
cord injuries
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It consists of bones, joints, ligaments, and tendons
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There are 206 bones in the adult human body
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The skeletal system is divided into two main parts: the axial skeleton and the appendicular
skeleton
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The appendicular skeleton includes the bones of the limbs (arms and legs), shoulders, and
hips, which facilitate movement and support the body's weight
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Ligaments are strong, fibrous connective tissues that connect bones to each other,
providing stability and preventing excessive movement
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The skeletal system is essential for the production of red and white blood cells in the bone
marrow
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Regular exercise and weight-bearing activities are important for maintaining bone health
and strength
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It is composed of three types of muscles: skeletal muscles, smooth muscles, and cardiac
muscles
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Smooth muscles are found in the walls of internal organs, blood vessels, and the digestive
system, and are responsible for involuntary movements, such as digestion and blood flow
regulation
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Muscles are made up of muscle fibers, which contract and relax to produce movement
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Muscles work in pairs or groups, with one muscle contracting (agonist) to produce a
movement and its opposing muscle relaxing (antagonist)
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The muscular system also helps maintain posture and stability, supporting the body's
framework and allowing for balance
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Muscular disorders and conditions include muscle strains, sprains, muscular dystrophy,
myasthenia gravis, and fibromyalgia
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Muscles require a constant supply of oxygen and nutrients from the circulatory system to
function properly
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It differs between males and females, with specific organs and structures dedicated to the
production and transport of gametes (reproductive cells) and the development of the
embryo
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The testes produce sperm cells and male sex hormones, primarily testosterone
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The seminal vesicles, prostate gland, and bulbourethral glands produce seminal fluid, which
nourishes and helps transport sperm during ejaculation
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The female reproductive system includes the ovaries, fallopian tubes, uterus, cervix, and
vagina
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The fallopian tubes transport eggs from the ovaries to the uterus, where fertilization can
occur
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The cervix is the lower part of the uterus that connects to the vagina and acts as a
passageway for sperm during intercourse and as the birth canal during delivery
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The menstrual cycle is a recurring monthly process in females, characterized by the
shedding of the uterine lining and the release of an egg
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Hormones are chemical messengers that travel through the bloodstream and bind to
specific target cells or organs to initiate a response
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The pituitary gland, often called the "master gland," is located at the base of the brain and
controls the functions of other endocrine glands
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The parathyroid glands secrete hormones that regulate calcium levels in the body
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The pancreas produces insulin and glucagon, which regulate blood sugar levels
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In males, the testes produce testosterone, which is involved in reproductive functions and
development of secondary sexual characteristics
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Hormones released by the endocrine system can have both short-term and long-term
effects on target cells or organs
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The endocrine system interacts closely with the nervous system, and both systems work
together to maintain proper bodily functions and respond to internal and external stimuli
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Asymmetry: Some animals have no definite body shape or symmetry, such as
sponges
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Bilateral Symmetry: Animals have a body that can be divided into two similar halves,
as seen in humans
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Bilateral symmetry is the most common type of body symmetry in animals, where the body
can be divided into two equal halves along a sagittal plane
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Body symmetry is an important characteristic for the overall appearance and functionality
of an organism
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Many animals, including humans, exhibit bilateral symmetry, with a distinct left and right
side
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Radially symmetrical organisms, such as jellyfish and starfish, can be divided into equal
parts along multiple planes passing through the central axis
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Asymmetry is a rare occurrence in animals and is often associated with specialized
adaptations or evolutionary traits
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Human perception tends to favor symmetrical bodies and faces, considering them more
attractive and aesthetically pleasing
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Developmental processes, such as cell division and growth, play a role in establishing and
maintaining body symmetry during embryonic development
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Acoelomates: Animals that lack a body cavity, such as flatworms
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Coelomates: Animals with a true body cavity, which is completely lined by
mesoderm, as seen in humans
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It is derived from the embryonic mesoderm and is lined by a thin membrane called the
peritoneum
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It acts as a shock absorber, cushioning organs from mechanical forces and impacts
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In animals with a coelom, the body wall muscles can contract and relax without directly
affecting the internal organs
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It enables organ systems to work together and coordinate their functions more effectively
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Animals with a true coelom are known as coelomates, which include most of the complex
animal groups, such as mammals, birds, reptiles, and insects
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The presence of a coelom allows for greater flexibility and mobility in animals, facilitating
complex movements and behaviors
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The absence of a true coelom limits the complexity and organization of internal organs in
acoelomates and pseudocoelomates
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