Header Ads

Organs and Organ Systems of the Human Body

Organs and Organ Systems of the Human Body

Musculoskeletal system

Human skeleton
  • 270 bones at birth, 206 in adults.
  • Longest bone – Femur (thighbone).
  • Smallest bone – Stapes (in the ear).
  • Other bones – Humerus (upper arm), Fibula (lower leg), Tibia (shinbone).
Joints
  • Connection between bones in the body.
Ligaments
  • Connective tissue between bones.
  • Made of collagen.
Muscular system
  • Skeletal, smooth and cardiac muscles.
  • Largest muscle – Gluteus Maximus (buttock).
  • Smallest muscle – Stapedius (in the ear).
Tendons
  • Connective tissue between muscle and bone.
  • Made of collagen.
Digestive system
Mouth
  • Lower Jawbone is called mandible, upper is called maxilla.
  • First portion of the alimentary canal.
Teeth
  • 20 baby (or milk) teeth, 32 adult (permanent) teeth.
  • Incisors (8), Canines (4), Premolars or Bicuspids (8), Molars (12).
  • Made of enamel.
Salivary glands
  • Exocrine glands (glands with ducts).
  • Produce saliva from amylase etc.
  • Parotid glands, Submandibular glands, Sublingual glands, Von Ibner glands etc.
Pharynx
  • Nasopharynx, Oropharynx, Laryngopharynx.
  • Important part of Digestive system, Respiratory System, Vocalization
Esophagus
  • Aka Food pipe or gullet.
  • During swallowing, epiglottis tilts backwards to prevent food from going into lungs.
Stomach
  • Secretes digestive enzymes.
  • Pyloric Sphincter controls passage of partially digested food into duodenum.
Small intestine
  • Three parts – Duodenum, Jejunum, Ileum
  • Duodenum receives bile and pancreatic juice.
  • Average length in adult human male is 6.9 m.
Large intestine
  • Also known as bowels.
  • Average length is about 1.5 m.
  • Parts – Cecum, Ascending Colon, Transverse Colon, Descending Colon, Sigmoid Colon, Rectum, Anal Canal.
Liver
  • Largest internal organ in human body.
  • Largest gland in human body.
  • Secretes the enzyme – bile.
  • Located in upper right quadrant of abdominal cavity.
  • Has four lobes.
  • Can be fractured. Can be regenerated from part.
Gallbladder
  • Stores bile before being released into small intestine.
  • Can survive without gall bladder.
  • Three parts – fundus, body, neck.
Pancreas
  • An endocrine gland that produces several important hormones.
  • Chief among these hormones are insulin, glucagon, somatostatin, pancreatic polypeptide.
  • It also secretes digestive enzymes called pancreatic juices.
  • Insulin is produced from near the area called Islets of Langerhans).
Respiratory system
Nasal cavity
  • Aka nasal fossa.
  • Divided into two by vertical fin called nasal septum.
Larynx
  • Commonly called Voice box.
  • Involved in protecting trachea, manipulating pitch and volume of sound.
  • Thyroid Cartilage is called Adam’s apple.
Trachea
  • Aka Windpipe.
  • Cartilaginous tube that connects larynx and pharynx to the lungs.
Bronchi
  • Airway in respiratory tract that allows air into lungs.
  • Primary bronchus – right and left.
  • These branch into smaller secondary and tertiary bronchi.
  • No gas exchange takes place in bronchi.
Lungs
  • Primary respiratory organs.
  • Two lungs (left and right) – each divided into two lobes.
  • They extract oxygen from atmosphere and transfer to the bloodstream. They release carbon dioxide from bloodstream into atmosphere.
  • Right lung is bigger than left lung.
  • Protected by the ribcage.
Diaphragm
  • Primary muscle that drives breathing.
  • Separates thoracic cavity (containing heart and lungs) from abdominal cavity.
Urinary system
Kidneys
  • Regulates balance of electrolytes in blood.
  • Also maintains pH homeostasis.
  • Also removes excessive organic molecules from blood. Thus it removes waste products of metabolism.
  • Also produce hormones – renin, calcitriol and erythropoietin.
  • Two bean shaped organs made up of cells called nephrons.
Ureters
  • Tubes that take urine from kidneys to bladder.
Bladder
  • Hollow muscle that collects urine from kidneys before urination.
  • Typical capacity of bladder is between 300 and 500 ml.
Urethra
  • Tube that connects urinary bladder to urinary meatus.
  • It helps in removal of fluids from the body.
Reproductive organs – Female reproductive system
Ovaries
  • Produces and periodically releases eggs in the female body.
  • They are both gonads and endocrine glands.
  • They secrete estrogen, testosterone, progesterone.
Fallopian tubes
  • Aka Uterine tubes.
  • They allow passage of eggs from the ovaries to the uterus.
Uterus
  • Aka womb.
  • It is a hormone-responsive reproductive sex organ in females.
  • One end connects to the fallopian tubes. The other end, the cervix, opens into the vagina.
  • It is within the uterus that the egg is fertilized, and the fetus is developed.
Vagina
  • It is the opening of the female genital tract.
  • It allows for sexual intercourse, childbirth and channels menstrual flow.
Vulva
  • This is the external genital organ of the woman.
Clitoris
  • It is a female sex organ.
Placenta
  • Aka afterbirth.
  • Organ that connects developing foetus to the uterine wall.
  • It allows for nutrient uptake, thermoregulation to the foetus, waste elimination and gas exchange via mother’s blood supply.
Reproductive organs – Male reproductive system
Testes
  • They are the male gonads producing sperms.
  • They are also endocrine glands producing androgens, primarily testosterone.
  • Typically there are two.
Prostate
  • It is an exocrine gland in males.
  • It produces a white fluid that constitutes 30% of the seminal fluid.
Penis
  • It is the external male sexual organ.
  • It also serves as the urinal duct.
Scrotum
  • It is the male reproductive organ.
  • It consists of a pair of suspended sacs.
Endocrine glands
Pituitary gland
  • Aka hypophysis.
  • It is an endocrine gland, the size of a pea.
  • It is found at the base of the brain.
  • It secretes hormones that regulate growth, blood pressure, certain functions of sex organs, thyroid glands, temperature regulation, pain relief, metabolism, and some aspects of pregnancy, childbirth nursing etc.
Pineal gland
  • Aka conarium or epiphysis cerebri.
  • Small endocrine gland found near the center of the brain, between the two hemispheres.
  • It resembles a tiny pine cone.
Thyroid gland
  • One of the largest endocrine glands in the body.
  • It consists of two connected lobes.
  • It is found in the neck.
  • Controls rate of use of energy sources, protein synthesis, and controls body’s sensitivity to other hormones.
  • They help regulate growth and rate of function of many other systems in the body.
  • T3 and T4 are synthesized from iodine and tyrosine.
  • It also produces calcitonin which plays a role in calcium homeostasis.
  • Hormonal output is regulated by thyroid stimulating hormone (TSH).
Parathyroid glands
  • Small endocrine glands in the neck.
  • It produces parathyroid hormone.
Adrenal glands
  • Aka suprarenal glands.
  • Endocrine glands that produce many hormones.
  • These include adrenaline and the steroids cortisol and aldosterone.
  • They are found above the kidneys.
Circulatory system – Cardiovascular system
Heart
  • Muscular organ that pumps blood through blood vessels to entire body.
  • Divided into 4 chambers – Left atrium (top), right atrium (top), left ventricle (bottom), right ventricle (bottom).
  • In healthy heart, blood flows one way through heart due to heart valves, which prevent backflow.
  • Enclosed by a protective sac called pericardium.
  • Wall of heart made up of – epicardium, myocardium, endocardium.
  • Blood low in oxygen enters right atrium from superior and inferior venae cavae.
  • From here it passes to right ventricle.
  • From here it is sent to the lungs, where it receives oxygen and gives off CO2.
  • Oxygenated blood returns to left atrium and passes to left ventricle.
  • From here it leaves heart through aorta.
  • Heart is a fist-sized organ that is placed in the middle of the chest cavity.
  • It is slightly offset to the left. The left heart is stronger so heartbeats felt more strongly on the left.
Arteries
  • Blood vessels that carry blood away from heart.
  • Most carry oxygenated blood.
  • Exceptions are pulmonary and umbilical arteries.
Veins
  • Blood vessels that carry blood towards the heart.
  • Most carry deoxygenated blood from tissues.
  • Exceptions are pulmonary and umbilical veins.
  • Less muscular than arteries and closer to skin.
  • Valves in veins prevent backflow.
Capillaries
  • Smallest blood vessels in the human body.
  • Make up microcirculation.
  • They connect arterioles and venules.
  • Help enable exchange of O2, CO2, other nutrients and waste substances between blood and tissues.
  • Lymph capillaries drain lymph from lymph vessels.
Circulatory system – Lymphatic system
Lymphatic vessel
  • Thin walled, valved structures that carry lymph.
  • Lymph is a fluid that lies between body tissues.
Lymph node
  • Oval or kidney shaped organ.
  • Present at multiple locations throughout body including armpits, neck and groin.
  • Important for proper functioning of immune system.
  • Act as filters for foreign particles and cancer cells.
Bone marrow
  • Flexible tissue in the interior of bones.
  • Red blood cells produced by bone marrow in heads of long bones.
  • Bone marrow is a key component of the lymphatic system.
  • It produces lymphocytes that supports the body’s immune system.
Thymus
  • Specialized primary lymphoid organ of immune system.
  • Within thymus, T cells or T lymphocytes mature.
  • These are key to adaptive immune system.
  • Consists of two identical lobes located in front of the heart.
Spleen
  • Similar in structure to large lymph node.
  • Acts as a blood filter.
  • Removes old red blood cells and holds a reserve of blood.
  • It recycles iron.
  • It also synthesizes antibodies in its white pulp.
Nervous system
Brain
  • Main organ of human central nervous system and the human body.
  • Located in head, protected by skull.
  • Composed neurons, glial cells and blood vessels.
  • Divided into three parts – forebrain, midbrain and hindbrain.
  • Dominant feature of human brain is the wrinkling of the cerebral cortex. The cerebral cortex is so large that it overshadows all other parts of the human brain.
  • Three parts of cerebral cortex – cerebrum (forebrain), cerebellum (hindbrain), and brainstem.
  • There are two hemispheres in the brain – left and right.
  • The mind is an emergent property of the brain.
The brainstem
  • Posterior part of the brain.
  • Consists of – Midbrain, Pons, and Medulla Oblongata.
  • Medulla Oblongata is responsible for involuntary functions like sneezing, breathing, heart rate, blood pressure etc.
  • Pons has a role in sleep and dreams. Also deals with swallowing, bladder control, equilibrium, hearing, taste, eye movement, facial expressions and posture.
  • Midbrain is associated with vision, hearing, motor control, sleep/wake, alertness, temperature regulation.
Cerebellum
  • Important in motor control, cognitive functions like language and attention.
  • Also regulates fear and pleasure responses.
Spinal cord
  • Long, thin, tubular bundle of nervous tissue and support cells.
  • Extends from brainstem to pelvis.
  • Brain and spinal cord together make up central nervous system.
Nerves
  • Enclosed, cable-like bundles of axons (nerve fibres).
  • Part of the peripheral nervous system.
  • Provides pathway for electrochemical nerve impulses to and from peripheral organs.
  • Categorized in three groups based on direction of signals – afferent nerves (from sensory neurons to central nervous system), efferent nerves (from CNS to muscle and glands) and mixed nerves (contains both signals).
  • Categorized in two groups based on where they connect to CNS – spinal nerves (connect to spinal cord), and cranial nerves (connect directly to brain).
Sensory organs
Eye
  • Eye is a sense organ.
  • Contains rod cells (for light perception) and cone cells (for colour perception).
  • Made of three coats enclosing three transparent structures.
  • Outermost layer composed of cornea and sclera.
  • Middle layer consists of choroid, ciliary body and iris.
  • Innermost layer is the retina, a light sensitive layer of tissue.
  • Within these coats are the aqueous humour (clear fluid), the vitreous body (clear jelly), and the flexible lens.
  • The lens is suspended to the ciliary body by the suspensory ligament (Zonule of Zinn).
  • The cornea is the transparent front part of the eye that covers the iris and pupil. It refracts light.
  • The iris controls the size and diameter of the pupil, which is a hole that lets light in.
Ear
  • Ear is an organ for hearing and balance.
  • Consists of three parts – outer ear, middle ear and inner ear.
  • Outer ear consists of auricle (visible part of the ear) and ear canal. It gathers and focusses sound energy on to the eardrum.
  • Ear drum is a membrane that separates external ear from middle ear.
  • Middle ear contains three ossicles which transfer vibrations from ear drum to inner ear.
  • Inner ear is a bony labyrinth. It has two main functional parts – cochlea and vestibular system.
Olfactory epithelium
  • Specialized epithelial tissue in the nasal cavity.
  • Involved in smell and detecting odors.
Tongue
  • Taste receptors or taste buds on different parts of the tongue.
  • Taste buds are also found in the soft palate, upper esophagus, cheek and epiglottis.
  • They are involved in detecting five elements of taste perception – salty, sour, bitter, sweet and umami.
Integumentary system
Mammary glands
  • It is an exocrine gland that produces milk.
Skin
  • Largest organ of the integumentary system.
  • Contains pigment melanin that gives skin its colour.
  • Composed of three primary layers – epidermis, dermis and hypodermis.