Vertebral Column – Superior Articular Processes, Inferior Articular Processes and Articular Facet

The vertebral column (spine or backbone) extends from the skull to the pelvis and forms a somewhat flexible but sturdy longitudinal support for the trunk. It is formed of 24 slightly movable vertebrae, the sacrum, and the coccyx. The vertebrae […]

Divisions of The Nervous System

Although the nervous system functions as a coordinated whole, it is divided into anatomical and functional divisions as an aid in understanding this complex organ system. Anatomical Divisions The nervous system has two major anatomical divisions. The central nervous system […]

Epidermis And Accessory Structure Formed By The Epidermis And Their Functions

The epidermis is a keratinized stratified squamous epithelium. An epithelium is avascular, meaning it lacks blood vessels. Since the epidermis is prone to injury, the lack of blood vessels prevents unnecessary found only in areas subjected to high levels of […]

Pelvic Girdle – Coxal Bones

The pelvic (pel’-vik) girdle consists of two coxal (kok’sal) bones, or hip bones, that support the attachment of the lower limbs. The coxal bones articulate with the sacrum posteriorly and with each other anteriorly to form an almost rigid, bony […]

Nervous Tissue

The nervous system consists of organs composed primarily of nervous tissue supported and protected by connective tissues. There are two types of cells that compose nervous tissue: neurons and neuroglia. Neurons Neurons, or nerve cells, are the structural and functional […]

Cells And Layers of The Epidermis

The epidermis is composed of five types of cells Stem cells are undifferentiated cells that divide and give rise to the keratinocytes described next. They are found only in the deepest layer of the epidermis, called the stratum basale. Keratinocytes […]

Articulations – Immovable, Slightly Movable, or Freely Movable Joints

The junction between two bones or between a bone and a tooth forms an articulation, or joint. Joints allow varying degrees of movement and are categorised as immovable, slightly movable, or freely movable. Immovable Joints Bones forming an immovable joint, […]

What Is The Mechanism of Synaptic Transmission?

A synapse is a junction of an axon with either another neuron or an effector cell. At a synapse, the terminal bouton of the presynaptic neuron fits into a small depression on the postsynaptic neuron’s dendrite or cell body or […]

The Life History of A Keratinocyte

Dead cells constantly flake off the skin surface. They float around as tiny white specks in the air, settling on household surfaces and forming much of the house dust that accumulates there. Because we constantly lose these epidermal cells, they […]

Disorders of The Skeletal System, Bones and Joints

Common disorders of the skeletal system may be categorised as disorders of bones or disorders of joints. Orthopaedics (or-tho-pe-diks) is the branch of medicine that specialises in treating diseases and abnormalities of the skeletal system.   Disorders of Bones Fractures […]


The meninges consist of three membranes arranged in layers. From deepest to most superficial they are the pia mater, arachnoid mater, and dura mater. The pia mater is the very thin, deepest membrane. It tightly envelops both the brain and […]

Thermoregulation -Temperature Regulation In Skin – Hypothermia And Hyperthermia

Body temperature is maintained at 37°C as a result of balance between heat generation and heat loss processes. This balance involves autonomic nervous system, metabolism, and behavioral responses. According to a 1992 study published in the Journal of the American […]

Muscle Tissue And Types of Muscle Tissue

MUSCLE TISSUE is the only tissue in the body that is specialised for contraction (shortening). The body contains three types of muscle tissue: skeletal, smooth, and cardiac. Each type of muscle tissue exhibits unique structural and functional characteristics. Contraction of […]

Cerebrum – Structure, Functions and Hemisphere Specialization

The cerebrum is the largest portion of the brain. It performs the higher brain functions involved with sensations, voluntary actions, reasoning, planning, and problem solving. Structure The cerebrum consists of the left and right cerebral hemispheres, which are joined by […]

Infectious And Non infectious Disorders of The Skin

Because the skin is in contact with the environment, it is especially susceptible to injuries, such as abrasions (scraping), contusions (bruises), and cuts. Other common disorders of the skin may be subdivided into infectious and noninfectious disorders. Some inflammatory disorders […]

Structure of Skeletal Muscle

Skeletal muscles are the organs of the muscular system. They are called skeletal muscles because most of them are attached to bones. A skeletal muscle is composed mainly of skeletal muscle tissue bound together and electrically insulated by connective tissue […]

Brainstem – Midbrain and Medulla Oblongata

The brainstem is the stalklike portion of the brain that joins higher brain centers to the spinal cord. It contains several nuclei that are surrounded by white matter. Ascending (sensory) and descending (motor) axons between higher brain centers and the […]

Skeletal System And Its Functions

THE SKELETAL SYSTEM SERVES as the supporting framework of the body and performs several other important functions as well. The body shape, mechanisms of movement, and erect posture observed in humans would be impossible without the skeletal system. Two very strong […]

Excitation – Contraction Coupling

The action potential generated at the motor end plate region spreads along the membrane of skeletal muscle cell and into the T tubules. The T tubules contain dihydropyridine receptors that connect to the Ca++ channels of sarcoplasmic reticulum. Depolarization of […]

Spinal Cord -The Structure And Function of The Spinal Cord.

The spinal cord is continuous with the brain. It descends from the medulla oblongata through the foramen magnum into the vertebral canal and extends to the second lumbar vertebra. Beyond this point, only the roots of the inferior spinal nerves […]

The Gross and Microscopic structure of a Long and a Flat Bone

There are approximately 206 bones in an adult and each bone is an organ composed of a number of tissues. Bone tissue forms the bulk of each bone and consists of both living cells and a nonliving matrix formed primarily […]

Physiology of Skeletal Muscle Contraction

Contraction of a muscle fiber is a complex process that involves a number of rapid structural and chemical changes within the muscle fiber. The molecular mechanism of contraction is explained by the sliding-filament model. Mechanism of Contraction In order for […]

Ventricles And Cerebrospinal Fluid

There are four interconnecting ventricles, or cavities, within the brain. Each ventricle is lined by ependymal cells and is filled with cerebrospinal fluid (CSF). The largest ventricles are the two lateral ventricles (first and second ventricles), which are located within […]

Ossification – Intramembranous and Endochondral Ossification and Their Functions

The process of bone formation is called ossification (os-i-fi-ka’-shun). It begins during the sixth or seventh week of embryonic development. Bones are formed by the replacement of existing connective tissues with bone. There are two types of bone formation: intramembranous […]

Major Skeletal Muscles

There are more than 600 muscles in the body, but only a few of the major muscles are considered here. Muscles of Facial Expression And Mastication Muscles of the face and scalp produce the facial expressions that help communicate feelings, […]

Cranium – What Bones Form The Cranium?

The cranium is formed of one frontal bone, two parietal bones, one sphenoid, two temporal bones, one occipital bone, and one ethmoid. The frontal bone forms the anterior part of the cranium, including the superior portion of the orbits (eye […]

Muscular Disorders

Cramps involve involuntary, painful tetany. The precise cause is unknown, but a cramp seems to result from chemical changes in the muscle, such as ionic imbalances or ATP deficiencies. Sometimes a severe blow to a muscle can produce a cramp. […]

Facial Bones – What Bones Form The Face?

The paired bones of the face are the maxillae, palatine bones, zygomatic bones, lacrimal bones, nasal bones, and inferior nasal conchae. The single bones are the vomer and mandible. The maxillae (mak-sil’-e) form the upper jaw. Each maxilla is formed […]

Neurological Disorders Affecting Muscles

Botulism poisoning is caused by a neurotoxin produced by the bacterium Clostridium botulinum. The toxin prevents release of ACh from the terminal boutons of somatic motor axons. Without prompt treatment with an antitoxin, death may result from paralysis of breathing […]

Nucleus – Structure, Components and Functions

Nucleus is the most popular and the biggest cellular organelle. It has a size of 10 g to 22 g and inhabits about 10% of overall volume of the cell. Nucleus exists in all the cells in the body other […]

Skin Color Determination And Skin’s Protection From Ultraviolet Radiation

Skin color results from the interaction of three different pigments: hemoglobin, carotene, and melanin. Hemoglobin (hemo-glo “-bin) is the red pigmented protein in red blood cells that is used to carry oxygen and carbon dioxide in the blood. Carotenes (kair-o-tens) […]

DNA Structure and Function

DNA is a long threadlike molecule with a uniform diameter of 2 nm, although its length varies greatly from the smallest to the largest chromosomes. Most human cells have 46 molecules of DNA totaling 2 m in length. This makes […]

Mitosis and Its Phases

Cells divide by two mechanisms called mitosis and meiosis. Meiosis, however, is restricted to one purpose, the production of eggs and sperm, and is therefore not discussed here thoroughly. Mitosis serves all the other functions of cell division: development of […]

Structure of Cell – Membrane, Cytoplasm, and Organelles

All the living things are made up ofcells The human body is made up of about 75 trillion cells, the tiniest living systems that exist. Body cells can be categorized into about 300 types, such as neurons, epithelial cells, muscle […]

Chromatin And Chromosomes

DNA does not exist as a naked double helix in the nucleus of a cell, however, is complexed with proteins to form a great filamentous material called chromatin. In many cells, the chromatin takes place as 46 long filaments called […]

Stem Cells Types and Advantages

Stem cells are the primary cells capable of reforming themselves through mitotic division and differentiating into specialized cells. These cells serve as repair system of the body and are present in all multicellular organisms.   Types of Stem Cells Stem […]

Selectively Permeable Membrane Methods and Example

The plasma membrane is both a barrier and entrance in between the cytoplasm and ECF. It is selectively permeable– it permits some things through, such as nutrients and wastes, however generally avoids other things, such as proteins and phosphates, from […]

RNA Structure, Function, Synthesis, Types and Interference

There many types of RNA in a cell Nevertheless, we will focus on the three that are straight related to producing proteins: messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA). DNA can not produce proteins without their help. […]

Epithelial Tissues – Simple And Stratified: Functions, Locations And Difference

Epithelial tissues, or epithelia (singular, epithelium), may be composed of one or more layers of cells. The number of cell layers and the shape of the cells provide the basis for classifying epithelial tissues. Epithelial tissues are distinguished by the […]

Simple & Facilitated Diffusion, Osmosis – Across Plasma Membranes

A cell keeps its homeostasis mainly by managing the movement of substances across the selectively permeable plasma membrane. Some substances pass across the plasma membrane by passive transport, which needs no expense of ATP by the cell. Other substances move […]

Difference Between DNA And RNA

Feature DNA RNA Sugar Types of nitrogenous bases Variety of nitrogenous bases Variety of nucleotide chains Site of action Function Deoxyribose A, T, C, G Balances 108 base sets 2 (double helix) Functions in nucleus; can not leave Codes for synthesis […]

Action Potential

Action potentials are the principal mechanism of nerve impulse propagation and transmission, and they allow depolarization at a single region of skeletal and cardiac muscle cells to spread across the entire cell.Action potentials require a stimulus that depolarizes the cell […]

Passive Transport – Simple and Facilitated Diffusion and Osmosis

Passive transport describes the mechanism of transport of substances along the gradient without expense of any energy It relies on the physical aspects like concentration gradient, electrical gradient and pressure gradient. Given that the transport of substances takes place along […]

Gene Regulation

Genes do not just produce their products at a constant, relentless speed, like a 24- hour continuously manufacturing plant. They are switched on and off from day to day, even hour to hour, as their products are required or not, […]

Signal Transduction – Membrane And Lipid-Soluble

Membrane Receptor Signal Transduction Proteins, peptides, and charged molecules do not easily diffuse across the cell membrane. Consequently, the cell membrane can serve as a barrier to cell-to-cell communication when such agents are used as neurotransmitters and hormones. This communication […]

Radial Nerve

The radial nerve is a continuation of posterior cord of brachial plexus in the axilla. It is the largest nerve of the brachial plexus. It carries fibres from all the roots (C5, C6, C7, C8, and Tl) of brachial plexus […]

Active Transport – Primary and Secondary Processes

Active transport describes the mechanism of transport of substances versus the chemical and/or electrical gradient. Active transport includes expense of energy which is freed by breakdown of high energy substances like adenosine triphosphate (ATP). Considering that the transport of substances […]

Protein Synthesis Process and Role of DNA And RNA In It

Proteins play an important role in the body. Structural proteins make up substantial parts of all cells, and practical proteins, such as enzymes and hormones, straight manage cellular activities. Bear in mind that a protein is formed of a long […]

Cell-To-Cell Communication

Normally the cell membrane isolates a cell from the adjacent tissue. As a consequence, any cell-to-cell message must first transit the cell membrane. One exception to that arrangement is a feature found in cardiac and smooth muscle cells: the gap […]

Carrier-Mediated Transport and Kind of Carriers

The processes of membrane transport explained approximately this point do not always need a cell membrane; they can take place simply as well through artificial membranes Now. nevertheless, we concern processes for which a cell membrane is vital, since they […]

Mitotic Cell Division And Mitotic Phases

Cells replicate themselves through a process called cell division. Two types of cell division occur in the body: mitotic cell division and meiotic cell division. Somatic cells (cells other than sex cells) divide by mitotic cell division, during which a […]

Loose Connective Tissue

Loose connective tissues help to bind together other tissues and form the basic supporting framework for organs. Their matrix consists of a semifluid or jelly-like ground substance in which fibers and cells are embedded. The word “loose” describes how the […]

Vesicular Transport – Endocytosis and Exocytosis

Vesicular transport mechanisms are associated with the transport of macromolecules such as big protein molecules which can neither travel through the membrane by diffusion nor by active transport mechanisms The vesicular transport mechanisms consist of endocytosis, exocytosis and transcytosis. Endocytosis […]

DNA Replication

The law of complementary base pairing shows that we can forecast the base series of one DNA strand if we understand the series of the other. More notably, it allows a cell to reproduce one strand based upon info in […]

Dense Connective Tissue

Like loose connective tissues, dense connective tissues help binding tissues together and offering assistance fororgans Nevertheless, dense connective tissue has far less cells and ground substance and more various, thicker, and “denser” protein fibers. These tissues likewise include far less […]

Factors Affecting Net Rate of Diffusion

The diffusion of the substance can happen in any case, i.e. extracellular fluid (ECF) to intracellular fluid (ICF) or vice versa relying on the dominating environment The elements which impact the net rate of diffusion in the wanted direction are: […]

The Cell Cycle

Most cells periodically divide into two daughter cells, so a cell has a life cycle extending from one division to the next. This cell cycle is divided into four main phases: G1, S, G2, and M (fig. 4.15). G1 is […]

Homeostasis – Role and Component

‘Homeostasis’ refers to the maintenance of a constant internal environment of the body (homeo = same; stasis = standing). The importance of internal environment was notified by the great biologist of 19th century Claude Bernard. He enlightened the fact that […]

Molecular Motors Functions and Types

Molecular motors are the molecular makers based of protein that carry out intracellular movements in response to particular stimuli. Functions of Molecular Motors Transport of synaptic vesicles including neurotransmitters from the afferent neuron body to synaptic terminal Role in cell […]

Cell Death

Cell death occurs by two distinct processes: Apoptosis Necrosis. Apoptosis Apoptosis is defined as the natural or programmed death of the cell under genetic control. Originally, apoptosis refers to the process by which the leaves fall from trees in autumn […]

Function And Structure of Skin And Subcutaneous Tissue

THE SKIN AND THE STRUCTURES that develop from it-hair, glands, and nails-form the integumentary system. The skin, or integument, is also known as the cutaneous membrane, one of the three types of epithelial membranes. The skin is a pliable, tough, […]

Cellular Respiration and Its Importance

Cells need a consistent supply of energy to power the chain reaction of life. This energy is straight provided by ATP molecules Due to the fact that cells have a minimal supply, ATP molecules should continuously be produced by cellular […]

Cell Adaptation And Growth: Hypertrophy And Hyperplasia

Cell growth includes one of 2 processes– hypertrophy and hyperplasia. Although both processes will increase the size of a tissue, they are basically and functionally various. Cell adaptation describes the modifications taking place in a cell in response to environmental […]

Urinary Acid-Base Regulation

Renal acid/base excretion complements pulmonary CO2 elimination to regulate body acid-base balance. Normally, there is a net acid production by the body, and urine pH is slightly acidic to keep the body in pH balance. Acids excreted in the urine […]

Alimentary Canal: Characteristics and Layers Composing, it’s Wall and their Functions.

The alimentary canal is a muscular tube about 5 m (20 ft) in length that extends from the esophagus to the anus. Various portions of the alimentary canal are specialized to perform different digestive functions. The hollow space within the […]

Tubuloglomerular Feedback and Glomerulotubular Balance

Intrarenal control of renal function is by tubuloglomerular feedback and by glomerulotubular balance. In tubu- loglomerular feedback, Na/Cl delivery to the distal tubule serves as a signal to provide negative feedback control of GFR. In glomerulotubular balance, filtration at the […]

Deciduous And Permanent Teeth and Structure of a Tooth

Teeth are important accessory digestive structures that mechanically break food into smaller pieces during mastication (mas-ti-ka’-shun), or chewing. Humans develop two sets of teeth: deciduous and permanent teeth. The deciduous teeth, the first set, start to erupt through the gums […]

The Structure and Blood Supply of the Kidney and Functions of Nephron

The kidneys are reddish brown, bean-shaped organs located bilateral to the vertebral column in the retroperitoneal space posterior to the abdominal cavity. They lie posterior to the parietal peritoneum, which covers their anterior surfaces. The kidneys are located between the […]

The Location and Function of Pharynx and Esophagus

The pharynx (fayr’-inks) is the passageway that connects the nasal and oral cavities with the larynx and esophagus. It is part of both the respiratory and the digestive systems. Its digestive function is the transport of food from the mouth […]

Urine Formation, Components, Glomerular Filtration, Tubular Reabsorption and Secretion

The formation of urine is a homeostatic mechanism that maintains the composition and volume of blood plasma within normal limits. In the production of urine, nephrons perform three basic functions: (1) They regulate the con centration of solutes, such as […]

Structure and Functions of the Stomach and Control of Gastric Secretions

The J-shaped stomach is a pouchlike portion of the alimentary canal. It lies just inferior to the diaphragm in the left upper quadrant of the abdominopelvic cavity. The basic functions of the stomach are temporary storage of food, mixing food […]

Excretion of Urine and Control of Micturition – Ureters, Urinary Bladder and Urethra

The term urinary tract refers collectively to the renal pelvis, the ureters, the urinary bladder, and the urethra. These structures function to carry urine from the kidneys to the external environment. Urine passes from the renal pelvis into the ureter […]

Sources and Uses of Carbohydrates, Lipids, Proteins, Vitamins, And Major Minerals

Nutrients are chemicals in foods that provide energy for powering life processes; chemicals aiding or enabling life processes; or materials to construct molecules for the normal development, growth, and maintenance of the body. There are six groups of nutrients: carbohydrates, […]

Maintenance of Blood Plasma Composition

The composition and volume of blood plasma are affected by diet, cellular metabolism, and urine production. The intake of food and liquids provides the body with water and a variety of nutrients, including minerals, that are absorbed into the blood. […]

Digestive System

It can be helpful to think of the digestive system as a tube running through the body with an opening at each end, the mouth at the top and the anus at the bottom. The tube isn’t a neat, constant […]

Disorders of The Digestive System

Inflammatory Disorders Appendicitis is an acute inflammation of the appendix. First symptoms include referred pain in the umbilical region and nausea. Later, pain is localized in the right lower quadrant of the abdominal wall. Surgical removal of the appendix is […]

Disorders of The Urinary System

Inflammatory Disorders Cystitis is the inflammation of the urinary bladder. It is often caused by bacterial infection. Females are more prone to cystitis because their shorter urethra makes it easier for bacteria to reach the urinary bladder. Glomerulonephritis is the […]

Urinary And Renal System: Anatomy, Physiology, Structure and Function

The renal system consists of the kidneys, ureters, bladder, and urethra. The kidney contains the nephron, the functional unit of the renal system. The nephron consists of the glomerular and peritubular capillaries and the associated tubular segments. The glomerular tuft […]

Male Reproductive System – Locations and Functions of the Male Reproductive Organs

The primary functions of the male reproductive system are the production of male sex hormones, the formation of sperm, and the placement of sperm in the female reproductive tract, where one sperm can unite with a female sex cell. The […]

Proximal Convoluted Tubule

  The proximal convoluted tubule reabsorbs 65% of the filtered water, Na+, Cl–, and K+. The epithelia of the proximal tubule have “leaky” tight junctions and can maintain only a small transepithelial membrane potential. Most of the energy consumed by […]

Male Sexual Response

In the absence of sexual stimulation, the vascular sinusoids in the erectile tissue of the penis contain a small amount of blood and the penis is flaccid (flak’-sid), or soft. Sexual stimulation initiates parasympathetic nerve impulses that cause the dilation […]

Loop of Henle

The loop of Henle carries filtrate from the proximal tubule to the renal medulla and back to the renal cortex. There are three functional divisions: the thin descending limb, thin ascending limb, and thick ascending limb. The thin descending limb […]

Hormonal Control of Reproduction in Males

The onset of male sexual development begins around the ages of 11 or 12 and is completed by ages 15 to 17. The mechanisms initiating the onset of puberty are not well understood, but the sequence of events is known. […]

Urinary Concentration and Dilution

The balance of water and solute reabsorption rates determines urine osmolarity. Water reabsorption is driven by an osmotic gradient, particularly evident as filtrate passes through tubule segments of the hypertonic renal medulla. Reabsorption and secretion characteristics are specific for each […]

The Neural Control of Breathing And Respiratory Centers

The normal rhythmic cycle of breathing is involuntary- we don’t have to think about it. It continues when we are sleeping or even unconscious. However, we can voluntarily override the normal pattern and take deep breaths and breathe faster or […]

Factors Influencing Breathing

The respiratory areas of the medulla oblongata and pons are influenced by a number of factors that cause modifications in the rate and depth of breathing. Factors involved in involuntary control are detected by sensory receptors, which forward nerve impulses […]

The Mechanisms of Gas Exchange in the Lungs and the Body Tissues

Alveolar Gas Exchange During alveolar gas exchange, respiratory gases are exchanged between the air in the alveoli and the blood in the capillaries that surround them. Oxygen and carbon dioxide must diffuse through the respiratory membrane, which is composed of […]

Transport of Respiratory Gases – Oxygen And Carbon Dioxide Transportation By The Blood

The RBCs play a major role in the transport of both oxygen and carbon dioxide. Oxygen Transport In the lungs, oxygen diffuses from the air in alveoli into the blood of surrounding capillaries. Most of the oxygen enters RBCs and […]

Disorders of The Respiratory System

Inflammatory Disorders Chronic obstructive pulmonary disease (COPD) is a group of disorders in which there is a long-term obstruction that reduces airflow to and from the lungs. The two most important COPDs are chronic bronchitis and emphysema. Bronchitis is inflammation […]

Immunity Or Specific Resistance – Cell-Mediated Immunity And Antibody-Mediated Immunity

In contrast to nonspecific resistance, immunity (i-mu- ni-te), or specific resistance, is directed at specific antigens. An immune response involves the production of specific cells and substances to attack a specific antigen. Immunity has “memory,” that is, if the same […]

Immune Responses – Primary And Secondary Immune Responses

When an antigen is encountered for the first time, it stimulates T cells and B cells to become activated and proliferate, producing clones that attack and destroy the invading antigen. This is the primary immune response, and it also produces […]

Rejection of Organ Transplants

Organ transplants are viable treatment options for persons with terminal disease of certain organs such as the heart, kidneys, and liver. Except for the surgery, the major problem encountered is that the patient’s lymphoid system recognizes the transplanted organ as […]

The Cell Theory Development and History

Cytology, the clinical study of cells, was born in 1665 when Robert Hooke observed the empty cell walls of cork and created the word cellulae (” little cells”) to explain them. Soon he studied thin pieces of fresh wood and […]

Mechanism of Blood Circulation – Blood Flow

Blood circulates because of differences in blood pressure. Blood flows from areas of higher pressure to areas of lower pressure. Blood pressure is greatest in the ventricles and lowest in the atria. Contraction of the ventricles creates the blood pressure […]

Disorders of The Lymphoid System

Infectious Disorders Acquired immunodeficiency syndrome (AIDS) is a viral disease that is approaching epidemic proportions. It is caused by the human immunodeficiency virus (HIV), which attacks and kills helper T cells and invades macrophages, which serve as a reservoir for […]

Cell Membrane (Plasma Membrane) – Structure Function and Composition

The cell membrane is a phospholipid bilayer into which proteins, glycoproteins, and glycolipids are ingrained. It is likewise called plasma membrane or plasmalemma. This membrane separates the fluid outside the cell called extracellular fluid (ECF) and the fluid inside the […]

Blood Pressure – Systolic And Diastolic Blood Pressure And Its Regulation

The term blood pressure, the force of blood against the wall of the blood vessels, usually refers to arterial blood pressure in the systemic circuit-in the aorta and its branches. Arterial blood pressure is greatest during ventricular contraction (systole) as […]

Structures and Functions of the Respiratory System

THE PRIMARY ROLE of the respiratory system is to make oxygen available to cells for cellular respiration and to remove carbon dioxide, the main byproduct of that metabolism. The entire process of respiration encompasses five unique and sequential processes: Breathing […]

Endoplasmic Reticulum – Types and Functions

Endoplasmic reticulum is a network of tubular and microsomal vesicular structures which are adjoined with one another. It is covered by a restricting membrane which is formed by proteins and bilayered lipids. The lumen of endoplasmic reticulum consists of a […]

Circulation Pathways- Systemic And Pulmonary Circuits.

The heart is a double pump that serves two distinct circulation pathways: the pulmonary and systemic circuits. Pulmonary Circuit The pulmonary circuit carries deoxygenated blood to the lungs, where oxygen and carbon dioxide are exchanged between the blood and the […]

Respiratory Volumes their Capacities and their Significance

Healthy adults average 12 to 15 quiet breathing cycles per minute. A breathing cycle is one inspiration followed by one expiration. The volume of air inhaled and exhaled in a quiet or forceful breathing cycle varies with size, sex, age, […]

Golgi Apparatus and Its Functions

The Golgi apparatus is a packaging center Golgi apparatus or Golgi body or Golgi complex is a membrane-bound organelle, associated with the processing of proteins It exists in all the cells other than red blood cells It is called after […]

Systemic Arteries And The Arterial Pathway of Blood To Various Organs

The systemic veins receive deoxygenated blood from capillaries and return the blood to the heart. Ultimately, all systemic veins merge to form two major veins, the superior and inferior venae cavae, that empty into the right atrium of the heart. […]

Lysosomes – Types and Functions

Lysosomes are the membrane-bound vesicular organelles discovered throughout the cytoplasm. The lysosomes are formed by Golgi apparatus The enzymes manufactured in rough endoplasmic reticulum are processed and crammed in the form of little vesicles in the Golgi apparatus Then, these […]

Disorders of the Heart and Blood Vessels

These disorders are grouped according to whether they affect primarily the heart or the blood vessels. In some cases, the underlying cause of a heart ailment is a blood vessel disorder. Heart Disorders Arrhythmia, or dysrhythmia, refers to an abnormal […]

Peroxisomes and Its Functions

Peroxisomes or microbodies are the membrane minimal vesicles like the lysosomes. Unlike lysosomes, peroxisomes are pinched off from endoplasmic reticulum and not from the Golgi apparatus Peroxisomes consist of some oxidative enzymes such as catalase, urate oxidase and D-amino acid […]

Lymph Formation and Pathway of Lymph & Lymphatic Vessels

The lymphatic network of vessels begins with the microscopic lymphatic capillaries. Lymphatic capillaries are closed-ended tubes that form vast networks in the interstitial spaces within most vascular tissues. Notably, these capillaries are not found in the CNS. Instead the CNS […]

Mitochondrion – Structure and Function

The mitochondria are called the “powerhouses” of the cell. Without them, cells would not be able to draw out adequate energy from the nutrients, and basically all cellular functions would stop. All cells in the body, with the exception of […]

Lymphoid Organs – Locations And Functions – Red Bone Marrow, Thymus, Lymph Nodes, And Spleen.

Lymphoid structures can be found throughout the body. While all lymphoid structures are capable of lymphocyte production, the red bone marrow and thymus are considered primary lymphoid organs because all WBCs, especially lymphocytes, originate in these organs. After production in […]

Cytoskeleton – Filaments, Structure and Functions

The latticework of microfilaments and microtubules is stated to operate as a cytoskeleton. Cytoskeleton is the cellular organelle present throughout the cytoplasm. It identifies the shape of the cell and provides assistance to the cell. It is a complex network […]

Lymphoid Tissues – Locations And Functions of The Tonsils And Mucosa Associated Lymphoid Tissues

The tonsils and mucosa associated lymphoid tissues are not structurally organs; however, they function as secondary lymphoid organs because they are sites of immune responses. Tonsils Tonsils (ton’-sils) are clusters of lymphoid tissue located just deep to the mucous membrane […]

Circulation in Specific Vascular Beds

Blood flow serves multiple functions. Matching of blood flow to metabolic needs is complex in organs that have variable metabolic rates, such as skeletal muscle. Local regulation of blood flow is well developed in tissues that have a low tolerance […]


Hematopoiesis is the synthesis of blood cells. Pluripotent hematopoietic stem cells in the bone marrow divide and differentiate into erythrocytes, leukocytes, or megakaryocytes. Replication and differentiation are regulated by hormones, cytokines, and growth factors. The aggregate weight of adult bone […]

Colonic Motility

The colon reabsorbs salts and water. About 1500 mL of fluid enters the colon each day, but only 50 to 100 mL of fluid is excreted in feces. Anatomically, the colon is divided into the cecum, ascending colon, transverse colon, […]

Pulmonary Circulation

The lungs receive the entire output of the right ventricle. Consequently, pulmonary blood flow is equal to cardiac output, about 5 L/min. The normal transit time for blood through the pulmonary capillaries is about 0.75 seconds. Gas equilibration between the […]

Red Blood Cells – Appearance, Normal Concentration Production, Life Span And Destruction

Red blood cells, or erythrocytes are tiny, biconcave discs that are involved in respiratory gas transport throughout the body. The biconcave shape creates maximal surface area of the cell for the diffusion of these gases through the plasma membrane. Mature […]

Myocardial Physiology

Myocardial cells have distinctive anatomic and physiologic characteristics. Under a microscope, striations are visible owing to the arrangement of actin and myosin as in skeletal muscle. T tubules increase the contact area of the cell membrane and extracellular fluid space. […]

Types of Blood Vessels – Structure And Function of Arteries, Arte¬rioles, Capillaries, Venules, And Veins

There are three basic types of blood vessels: arteries, capillaries, and veins. They form a closed system of tubes that carry blood from the heart to the tissue cells and back to the heart. Comparison of Arteries, Capillaries, And Veins […]

White Blood Cells – Production, Types, Structure, Concentration And Functions

White blood cells, or leukocytes are so named because pus and the buffy coat are white. These spherical cells are the only formed elements with nuclei and other organelles. A healthy person’s WBC count is typically 4,500 to 10,000 per […]

Disorders of The Blood – Rbc, Wbc And Hemostasis

Blood disorders may be grouped as red blood cell disorders, white blood cell disorders, and disorders of hemostasis. Normal values for common blood tests are located on the inside back cover. Blood tests are valuable in diagnosing a variety of […]

Plasma – Importance of The Normal Components of Plasma

Plasma is the fluid portion of the blood and consists of over 90% water. Water is the liquid carrier of plasma solutes (dissolved substances) and formed elements, in addition to being the solvent of all living systems. Plasma contains a […]

Heart Anatomy – The Parts of The Heart And Their Functions Flow of Blood And Blood Supply

The heart is a four-chambered muscular pump that is located within the mediastinum in the thoracic cavity. It lies between the lungs and just superior to the diaphragm. The apex of the heart is the inferior pointed end, which extends […]

Hemostasis – The Sequence of Events That Occurs During Hemostasis.

Whenever blood vessels are damaged, the loss of blood poses a considerable threat to homeostasis. Hemostasis is a positive-feedback mechanism initiated after vascular injury to stop or limit blood loss. There are three separate but interrelated processes involved in hemostasis: […]

Cardiac Cycle – Events and Sound of Heartbeat

The cardiac cycle refers to the sequence of events that occur during one heartbeat. The contraction phase of a cardiac cycle is known as systole (sis ‘-to-le); the relaxation phase is called diastole (di ‘-as-to-le). Note that the ventricles are […]

Fibrinolysis and Anticoagulants

The ability to create clots to limit blood loss from sites of vascular injury is balanced by systems designed to limit clot formation and to dissolve existing clots. The blood contains natural anticoagulants that act continuously to inhibit clot formation. […]

Parathyroid Hormone and Calcitonin

Plasma calcium levels are regulated by the polypeptides parathyroid hormone and calcitonin. Parathyroid hormone, secreted by the parathyroid glands embedded in the thyroid, acts to increase plasma calcium levels. Parathyroid hormone also decreases plasma PO4. Calcitonin, secreted from the parafollicular […]

Human Blood Types – Importance And Blood Typing Antigens & Antibodies In Abo & Rh Blood Type.

Several different blood types occur in humans. The most familiar ones involve the ABO blood group (types A, B, AB, and O) and the Rh blood group (Rh+ and Rh-). Blood types are classified by the presence or absence of […]

Renin-Angiotensin System And Atrial Natriuretic Peptides

Angiotensin and atrial natriuretic peptides generally act to oppose each other. Angiotensin II has strong acute vascular effects and is an important mediator of renal Na+ retention. Atrial natriuretic peptides are released from the atria of the heart by distention […]

Mechanisms of Hormone Action And Control of Hormone Production

A hormone produces its effect by binding to a target cell’s receptors for that hormone. The more receptors it binds to, the greater is the effect on the target cell. All hormones affect target cells by altering their metabolic activities. […]

Cardiac Electrophysiology

Cardiac tissue has distinctive electrical characteristics. Intercalated disks allow action potentials to pass to adjacent cells. Myocardial cells can spontaneously depolarize, a process called automaticity. This spontaneous depolarization generates a pacemaker potential or prepotential and is caused by decreasing K+ […]

Autonomic Regulation- Neural And Hormonal Regulation of The Heart

Heart rate regulation is primarily under the control of the cardiac control center located within the medulla oblongata of the brain. It receives sensory information about the level of blood pressure from baroreceptors located in the aortic arch and the […]

Pituitary Gland – Control And Hormones of Anterior And Posterior Lobe

The pituitary gland, or hypophysis, is attached to the hypothalamus by a short stalk. It rests in a depression of the sphenoid bone, the sella turcica, which provides protection. The pituitary gland consists of two major parts that have different […]

Mouth and Esophageal Motility

Mastication, or chewing, mixes food with salivary mucus. This action subdivides food and exposes ingested starch to salivary amylase to begin the digestive process. Mastication is not essential for normal GI function but facilitates the process. Swallowing propels food from […]

Blood Vessel Histology

Blood vessels have structural characteristics that allow them to be classified as arteries, arterioles, capillaries, venules, and veins. The structure of a blood vessel contributes to its functional characteristics. The anatomic identification of blood vessels is based on the presence […]

Thyroid Hormones – Production Control, List The Actions And Major Disorders

The thyroid gland is located just inferior to the larynx. It consists of two lobes, each one lateral to the trachea, that are connected by an anterior isthmus. Hormones of the Thyroid Gland Hormone Control Action Disorders Thyroxine (T4) and […]

Gastric Motility

Stomach The stomach is anatomically and functionally divided into the fundus, body, and antrum. The fundus and body are highly distensible and act as reservoir for the ingested meal. A 1.5 L volume increase causes only a small increase in […]

Vascular Segments

As blood exits the left ventricle, it passes progressively through the aorta, arteries, arterioles, capillaries, venules, veins, and vena cava before returning to the right atrium. These vascular segments have significant functional differences. Arteries And Arterioles An extensive network of […]

Adrenal Glands – Production Control, List The Actions And Major Disorders

There are two adrenal glands; one is located on top of each kidney. Each adrenal gland consists of two portions that are distinct endocrine glands: the deep adrenal medulla and the superficial adrenal cortex. Hormones of The Adrenal Glands Hormone […]

Small Intestinal Motility

The small intestine is divided into duodenum, jejunum, and ileum, with the duodenum and jejunum being the major site of digestion and absorption. Chyme takes 2 to 4 hours to move through the 5 m of the small intestine. Segmentation, […]

Disorders of The Nervous System – Inflammatory and Non Inflammatory

Inflammatory Disorders Meningitis (men-in-ji ‘-tis) results from a bacterial, fungal, or viral infection of the meninges. Bacterial meningitis cases are the most serious, with about 20% being fatal. If the brain is also involved, the disease is called encephalitis. Some […]

Abdominopelvic Quadrants And Regions

The abdominopelvic cavity is subdivided into either four quadrants or nine regions as an aid in locating organs. The four quadrants are right upper left upper right lower left lower The nine regions are epigastric right flank left hypochondriac hypogastric […]

Thermoregulation of Human Body

The anterior hypothalamic “thermostat” adjusts heat balance to maintain body core temperature. Heat exchange is determined by convection, conduction, evaporation, and radiation. Radiation, conduction, and convection are determined by the difference between the skin temperature and the environmental temperature. Behavioral […]

Homeostasis Regulation – Positive and Negative Feedback Mechanism

Homeostasis, a term presented by W. B. Cannon, describes the mechanism by which the constancy of the internal environment is maintained and ensured Homeostasis is the maintenance of a fairly steady internal environment by self-regulating physiological processes Homeostasis keeps body […]

The Structures, Locations, and Functions of the Sensory Receptors

Sensory receptors for the general senses are widely distributed in the skin, muscles, tendons, ligaments, and visceral organs. Temperature Two types of thermoreceptors are located in the skin. Warm receptors are free nerve endings, which are sensory neuron dendrites, in […]

The Location, Structure and Function of Olfactory and Taste Receptors

The sensory receptors for special senses are localized rather than widely distributed, and they, like all sensory receptors, are specialized to respond to only certain types of stimuli. There are three different kinds of sensory receptors for the special senses. […]

The Location, Structure and functions of the Sensory Receptors involved in Hearing

The ear is the organ of hearing. It is also the organ of equilibrium. The ear is subdivided into three major parts: the external ear, middle ear, and internal ear. External Ear The external ear consists of two parts: the […]

Sensory Receptors involved in Static Equilibrium and Dynamic Equilibrium

Several types of sensory receptors provide information to the brain for the maintenance of equilibrium. The eyes and proprioceptors in joints, tendons, and muscles are important in informing the brain about equilibrium and the position and movement of body parts. […]

The Structure of the Eye and the Functions of these Accessory Structures.

Vision is one of the most important senses supplying information to the brain. The sensory receptors for light stimuli are located within the eyes (or eyeballs), the organs of vision. The eyes are located within the orbits, where they are […]

The Functions And Characteristics Of Living Things and Life

The world around us includes a variety of living organisms with various looks and lifestyles Despite this variety, all living things carry out the very same standard functions:  Living things respond to modifications in their instant environment–Plants orient to the […]

Difference Between Anatomy And Physiology

Difference between Anatomy and Physiology is this that Anatomy is the study of structure while on the other hand Physiology is the study of Functions. Anatomy is the study of structure: Anatomy, which suggests “a cutting open” is the study […]

Human Body System Anatomy, Functions, Facts And Relation

The human body is complex, so it is not unexpected that there are numerous levels of structural organisation for the benefit of description, the human body can be thought about to be functionally arranged into different systems The levels of […]

Peripheral Nervous System (PNS) – Cranial Nerves and it’s Reflexes

The peripheral nervous system (PNS) consists of cranial and spinal nerves that connect the CNS to other portions of the body, along with sensory receptors and ganglia. A nerve consists of axons that are bound together by connective tissue. Motor […]

Body Planes And Sections

Many views of the body are based on real or imaginary “slices” called sections or planes. In studying the body or organs, you often will be observing the flat surface of a section that has been produced by a cut […]

Autonomic Nervous System (ANS)

The ANS is a major mechanism for neural control of physiologic functions. The autonomic nervous system (ANS) consists of portions of the central and peripheral nervous systems and functions without conscious control. Discussions of ANS usually take one of three […]

Major Body Cavities, Their Subdivisions And Membranes.

Body cavities are spaces inside the body which contain, protect, separate, and support internal organs. There are two major cavities of the body which contain internal organs: the dorsal (posterior) and ventral (anterior) cavities. The body cavities protect as well […]

Hormonal Control of Reproduction in Females – The Ovarian and Menstrual Cycles

Reproduction in females is controlled by hormones produced by the hypothalamus, anterior lobe of the pituitary gland, and ovaries. Female Sex Hormones The ovaries produce the two major groups of female sex hormones-estrogens and progesterone-plus inhibin, which aids estrogens in […]

Disorders of Pregnancy, Prenatal Development, And Postnatal Development

Pregnancy Disorders Eclampsia (e-klamp’-se-ah), or toxemia of pregnancy, is a disorder that occurs in two forms. Preeclampsia of late pregnancy is characterized by increased blood pressure, edema, and proteinuria (protein in the urine). The cause is unknown. If unsuccessfully treated, […]

Structure of Mammary Glands and Breasts

Both males and females possess mammary glands. The mammary glands of males and immature females are similar. At puberty, estrogens and progesterone stimulate the development of female mammary glands. Estrogens start breast and mammary gland development, and progesterone stimulates the […]

Roles of DNA, Genes, And Chromosomes in Inheritance

Genetics is the study of heredity, the passing of inherited traits from one generation to the next. The determiners of hereditary traits are located on chromosomes, consisting of DNA and proteins. It is the DNA that controls inheritance and directs […]

Various Methods of Birth Control Work

Birth control methods may be categorized into several groups based on their mode of action: hormonal, chemical and behavioral contraceptive methods, anti-implantation devices, sterilization, and induced abortion. Contraception Contraception is the prevention of conception, which is the union of sperm […]

The Inheritance of the More Common Inherited Disorders

Inherited, or genetic, diseases are caused by either chromosome abnormalities or specific alleles. The development of advanced techniques and new knowledge makes an understanding of genetic disease increasingly important. Chromosome Abnormalities Some genetic diseases are related to the presence of […]

Disorders of the Reproductive Systems

Male Disorders Prostatitis is acute or chronic inflammation of the prostate gland and is often associated with tenderness and enlargement of the prostate. It is usually caused by bacteria in connection with urinary tract infections or sexually transmitted diseases. It […]

Acid Base Disorders – Acid Base Tutorial

Acid-base disturbances are first characterized by the initial change in pH. There are four major classes of acid-base disturbances: respiratory acidosis, respiratory alkalosis, metabolic acidosis, and metabolic alkalosis. The acid-base disturbances are further categorized as compensated or uncompensated. Compensation attenuates […]

The Processes of Fertilization, Preembryonic Development and Implantation

Each primary oocyte undergoes the first meiotic division while still in the ovarian follicle. This division forms a secondary oocyte and the first polar body, each containing 23 chromosomes. At ovulation, the secondary oocyte and first polar body, still enclosed […]

Embryonic Development – Germ Layers, Extraembryonic Membranes and Placenta

The embryonic stage of development begins at the start of the third week of development and is completed at the end of the eighth week. During this time, the embryo undergoes rapid development, forming the rudiments of all body organs, […]

Fetal Development Stages

At the beginning of the ninth week of development, the developing offspring has a distinctively human appearance and is now referred to as a fetus. Weeks of Development Changes 5-8 Weeks Recognizable human shape; head as large as the body; […]

Hormonal Control of Pregnancy

Without the formation of a preembryo, the corpus luteum degenerates about two weeks after ovulation as a result of the decline in luteinizing hormone from the anterior lobe of the pituitary gland. The resulting decline in blood levels of estrogens […]

Neuroendocrine Positive-Feedback Mechanism Controlling Labor

During the latter stages of pregnancy, the blood concentration of estrogens become increasingly greater than that of progesterone, as noted earlier. Whereas progesterone inhibits uterine contractions, estrogens promote them. Therefore, there is an increasing tendency toward the onset of uterine […]

Cardiovascular Adaptations – Fetal Cardiovascular Adaptations and Postnatal Cardiovascular Changes

Fetal circulation is quite different from adult circulation because the digestive tract, lungs, and kidneys are not functioning. Oxygen and nutrients are obtained from the maternal blood in the placenta, while carbon dioxide and other metabolic wastes are removed via […]

Lactation – The Control of Lactation and Milk Ejection

High blood levels of estrogens and progesterone during pregnancy stimulate the development of the mammary glands and enlargement of the breasts in preparation for milk secretion, or lactation (lak-ta’-shun). Although the mammary glands are capable of secreting milk, the high […]

Female Reproductive System – Locations and Functions of the Female Reproductive Organs

The female reproductive system produces female sex hormones and female sex cells and transports the sex cells to a site where they may unite with sperm. In addition, the female reproductive system provides a suitable environment for the development of […]
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