Topic: Circulatory System
The circulatory system transports oxygen, carbon dioxide, nutrients, hormones, and waste materials throughout the body. It also helps maintain body temperature, pH, and internal balance.
| Type | Meaning | Example |
|---|---|---|
| Open circulatory system | Blood or haemolymph is not always confined to vessels; it directly bathes organs. | Arthropods, most molluscs |
| Closed circulatory system | Blood always flows inside vessels. | Vertebrates, annelids |
| Vertebrate group | Circulation type | Notes |
|---|---|---|
| Fishes | Single circulation | Blood passes through the heart once in a complete cycle. |
| Amphibians | Double circulation | Heart is three-chambered; incomplete separation of blood. |
| Most reptiles | Double circulation | Incomplete septum in heart in many reptiles. |
| Birds | Complete double circulation | Four-chambered heart. |
| Mammals | Complete double circulation | Four-chambered heart. |
The heart pumps blood into arteries, arteries divide into arterioles, arterioles end in capillaries, capillaries join to form venules, and venules join to form veins. This network allows efficient exchange of materials.
Blood is a fluid connective tissue that circulates through the body and performs transport, defense, clotting, and regulation. It is made up of plasma and formed elements such as RBCs, WBCs, and platelets.
| Component | Approximate percentage | Role |
|---|---|---|
| Plasma | About 55% | Transport of substances, maintains osmotic balance |
| Formed elements | About 45% | RBCs, WBCs, platelets |
Plasma is the liquid part of blood. It is mainly water and contains proteins, salts, nutrients, hormones, enzymes, gases, and waste products.
| Protein | Function |
|---|---|
| Albumin | Maintains osmotic pressure and blood volume |
| Globulins | Help in immunity and transport |
| Fibrinogen | Essential for blood clotting |
Red blood cells are the most abundant cells in blood. They contain haemoglobin and transport oxygen from lungs to tissues.
| Feature | Details |
|---|---|
| Formation | Red bone marrow |
| Destruction | Spleen and liver |
| Lifespan | About 120 days |
| Shape | Biconcave, flexible, non-nucleated in mammals |
| Normal count | About 5 million per mm3 in males, slightly less in females |
Haemoglobin is an iron-containing pigment present in RBCs. It binds oxygen reversibly and forms oxyhaemoglobin. It also helps in the transport of some carbon dioxide.
White blood cells defend the body against pathogens. They are fewer in number than RBCs but are vital for immunity.
| Type | Examples | Main function |
|---|---|---|
| Granulocytes | Neutrophils, eosinophils, basophils | Defense, inflammation, allergy, phagocytosis |
| Agranulocytes | Lymphocytes, monocytes | Immunity, antibody production, phagocytosis |
Platelets are small cell fragments formed in the bone marrow from megakaryocytes. They help in blood clotting and prevent excessive blood loss.
| Feature | Details |
|---|---|
| Normal count | About 1.5 to 4 lakh per mm3 of blood |
| Function | Clot formation |
Blood clotting is a protective mechanism that stops bleeding when a blood vessel is damaged. It involves platelets, clotting factors, calcium ions, and fibrin formation.
According to the cascade theory, clotting occurs through a sequence of enzymatic reactions. One factor activates the next, ultimately converting prothrombin into thrombin and fibrinogen into fibrin.
| Step | Event |
|---|---|
| 1 | Damage to blood vessel |
| 2 | Platelets release clotting factors |
| 3 | Prothrombin is converted into thrombin |
| 4 | Fibrinogen is converted into fibrin |
| 5 | Fibrin forms a mesh and traps blood cells |
| Blood group | Antigen on RBC | Antibody in plasma |
|---|---|---|
| A | A antigen | Anti-B |
| B | B antigen | Anti-A |
| AB | A and B antigens | None |
| O | None | Anti-A and Anti-B |
Rh factor is an antigen found on RBCs. If it is present, the blood group is Rh positive; if absent, it is Rh negative.
The heart is a muscular pumping organ located slightly to the left in the thoracic cavity. It keeps blood moving continuously through pulmonary and systemic circulation.
| Chamber | Function |
|---|---|
| Right atrium | Receives deoxygenated blood from the body |
| Right ventricle | Pumps deoxygenated blood to the lungs |
| Left atrium | Receives oxygenated blood from the lungs |
| Left ventricle | Pumps oxygenated blood to the whole body |
The heart is enclosed by a double-layered membrane called the pericardium. The pericardial fluid reduces friction during beating.
| Part | Function |
|---|---|
| SA node | Natural pacemaker; starts heartbeat |
| AV node | Delays impulse and passes it to bundle of His |
| Bundle of His and Purkinje fibers | Carry impulse through ventricles |
The first sound, lub, is caused by closure of atrioventricular valves. The second sound, dub, is caused by closure of semilunar valves.
Blood pressure is the pressure exerted by blood on the walls of arteries. It is measured as systolic pressure over diastolic pressure. Normal adult blood pressure is about 120/80 mmHg.
| Vessel | Direction of flow | Wall structure | Special feature |
|---|---|---|---|
| Arteries | Carry blood away from heart | Thick, elastic, muscular | Usually carry oxygenated blood |
| Veins | Carry blood toward heart | Thin, less muscular | Have valves to prevent backflow |
| Capillaries | Connect arteries and veins | One-cell thick | Site of exchange |
The excretory system removes metabolic wastes from the body and maintains water, salt, and acid-base balance. The main nitrogenous waste in humans is urea.
| Waste product | Source | Example |
|---|---|---|
| Ammonia | Highly toxic nitrogen waste | Found in aquatic animals |
| Urea | Less toxic, major human waste | Humans, mammals |
| Uric acid | Least soluble, conserved water | Birds, reptiles |
| Organ | Role |
|---|---|
| Kidneys | Filter blood and form urine |
| Lungs | Remove carbon dioxide and water vapour |
| Skin | Removes water, salts, and a little urea through sweat |
| Sweat glands | Produce sweat for cooling and excretion |
| Sebaceous glands | Secrete sebum that protects skin and hair |
The urinary system includes two kidneys, two ureters, one urinary bladder, and one urethra. It removes wastes and helps regulate body fluid balance.
| Part | Description |
|---|---|
| Cortex | Outer region of kidney |
| Medulla | Inner region, contains renal pyramids |
| Renal pelvis | Collects urine and leads to ureter |
The nephron is the structural and functional unit of the kidney. Each kidney has about one million nephrons.
| Part of nephron | Function |
|---|---|
| Glomerulus | Ultrafiltration of blood |
| Bowman's capsule | Collects filtered fluid |
| PCT | Maximum reabsorption of useful substances |
| Loop of Henle | Concentrates urine and maintains salt gradient |
| DCT | Selective reabsorption and secretion |
| Collecting duct | Final urine concentration |
Blood is filtered under pressure in the glomerulus. Water, ions, glucose, amino acids, and small molecules pass into Bowman’s capsule.
Useful substances such as glucose, amino acids, sodium ions, bicarbonate, and water are reabsorbed back into blood.
Extra ions and wastes such as hydrogen ions, potassium ions, ammonia, and certain drugs are actively secreted into the tubule.
Micturition is the process of expelling urine from the urinary bladder through the urethra. It is controlled by reflex action and voluntary control.
| Component | Presence in urine |
|---|---|
| Water | Major component |
| Urea | Main nitrogenous waste |
| Uric acid, creatinine, salts | Present in small amount |
| Glucose, protein | Normally absent |
Antidiuretic hormone increases water reabsorption in the kidneys. When ADH level is high, urine becomes concentrated; when low, urine becomes dilute.
Osmoregulation is the maintenance of water and salt balance in body fluids. It is controlled by kidneys, ADH, thirst, and osmotic regulation mechanisms.
Kidney failure occurs when kidneys cannot properly filter blood. It may lead to accumulation of wastes, fluid imbalance, and dangerous changes in electrolytes.
The nervous system controls and coordinates body activities. It receives stimuli, processes information, and sends commands to different organs. It works rapidly and is responsible for quick responses.
| Feature | Nervous control | Endocrine control |
|---|---|---|
| Signal | Nerve impulses | Hormones |
| Speed | Very fast | Slower |
| Duration | Short-lived | Long-lasting |
| Path | Through neurons | Through blood |
| Main division | Subdivisions | Function |
|---|---|---|
| CNS | Brain and spinal cord | Control center |
| PNS | Sensory and motor divisions | Connects CNS with body |
| Motor nervous system | Somatic and autonomic | Controls movement |
| Autonomic nervous system | Sympathetic and parasympathetic | Controls involuntary actions |
Nervous System
├── Central Nervous System
│ ├── Brain
│ └── Spinal Cord
└── Peripheral Nervous System
├── Sensory Division
└── Motor Division
├── Somatic Nervous System
└── Autonomic Nervous System
├── Sympathetic Division
└── Parasympathetic Division
A neuron is the structural and functional unit of the nervous system. It carries nerve impulses from one part of the body to another.
| Part | Function |
|---|---|
| Cell body | Contains nucleus and controls cell activities |
| Dendrites | Receive impulses |
| Axon | Carries impulses away from cell body |
A synapse is the junction between two neurons or between a neuron and an effector. Nerve impulses cross the synapse chemically through neurotransmitters.
The brain is the main control organ of the nervous system. It is protected by the skull, meninges, and cerebrospinal fluid.
| Division | Main parts | Function |
|---|---|---|
| Forebrain | Cerebrum, thalamus, hypothalamus | Higher mental activities, sensory processing, homeostasis |
| Midbrain | Midbrain region | Reflexes related to vision and hearing |
| Hindbrain | Cerebellum, pons, medulla oblongata | Balance, coordination, vital functions |
The cerebrum is the largest part of the brain. It controls intelligence, memory, thinking, learning, emotions, speech, voluntary actions, and interpretation of sensory input.
The thalamus acts as a relay station for sensory impulses, except smell, before they reach the cerebrum.
The hypothalamus maintains internal balance. It regulates body temperature, hunger, thirst, sleep, and controls the pituitary gland.
The midbrain is involved in visual and auditory reflexes. It helps coordinate eye movement and head movement.
The cerebellum coordinates voluntary muscular activity, maintains posture, and keeps body balance.
The pons acts as a bridge between different parts of the brain. It also helps regulate breathing.
The medulla oblongata controls involuntary functions such as heartbeat, breathing, swallowing, and blood pressure.
The spinal cord is the continuation of the medulla oblongata and is protected by the vertebral column. It conducts impulses between brain and body and also controls reflex actions.
Reflex action is a quick, automatic, involuntary response to a stimulus. It is controlled mainly by the spinal cord or brainstem.
| Type | Example |
|---|---|
| Spinal reflex | Withdrawal of hand from hot object |
| Cranial reflex | Blinking of eyes, salivation |
The reflex arc is the pathway followed by a nerve impulse during a reflex action.
Sense organs receive information from the environment and convert it into nerve impulses. The main sense organs are eyes, ears, nose, tongue, and skin.
The eye is the organ of vision. It detects light and helps us perceive shape, color, distance, and movement.
| Part | Function |
|---|---|
| Orbit | Bony socket that protects the eye |
| Eyelids | Protect eye and spread tears |
| Eyebrows | Prevent sweat from entering eyes |
| Tear gland | Produces tears for lubrication and cleaning |
| Meibomian gland | Secretes oily fluid that prevents tear evaporation |
| Conjunctiva | Thin protective membrane |
| Part | Role |
|---|---|
| Cornea | Transparent front part; major refraction occurs here |
| Sclera | White outer tough layer |
| Choroid | Vascular pigmented middle layer |
| Iris | Controls pupil size and light entry |
| Retina | Light-sensitive layer with rods and cones |
| Yellow spot / fovea | Point of sharpest vision |
| Blind spot | No photoreceptors; optic nerve leaves eye |
| Lens | Focuses light on retina |
| Aqueous chamber | Filled with aqueous humour; maintains pressure |
| Vitreous chamber | Filled with vitreous humour; maintains shape |
| Cell | Function |
|---|---|
| Rod cells | Vision in dim light; black-and-white vision |
| Cone cells | Color vision and sharp vision in bright light |
Light enters through the cornea, passes through aqueous humour, pupil, lens, and vitreous humour, and forms an inverted image on the retina. Photoreceptors convert the light stimulus into nerve impulses, which are carried by the optic nerve to the brain.
| Defect | Cause | Correction |
|---|---|---|
| Myopia | Image forms in front of retina | Concave lens |
| Hypermetropia | Image forms behind retina | Convex lens |
| Presbyopia | Age-related reduced accommodation | Bifocal or convex lens |
| Astigmatism | Unequal curvature of cornea or lens | Cylindrical lens |
| Cataract | Lens becomes opaque | Surgery |
The ear is the organ of hearing and balance. It has three main parts: outer ear, middle ear, and inner ear.
| Part | Components | Function |
|---|---|---|
| Outer ear | Pinna, ear canal | Collects sound waves |
| Middle ear | Eardrum, ossicles | Transmits and amplifies vibrations |
| Inner ear | Cochlea, semicircular canals | Hearing and balance |
The cochlea is the hearing part of the inner ear. It contains receptor cells that convert sound vibrations into nerve impulses.
The organ of Corti is present inside the cochlea and contains hair cells that act as auditory receptors.
Receptors are specialized cells that detect stimuli. Examples include photoreceptors in eye, phonoreceptors in ear, and mechanoreceptors in skin.
The endocrine system consists of ductless glands that release hormones directly into the blood. Hormones regulate growth, metabolism, reproduction, water balance, and many body functions.
| Feature | Endocrine gland | Exocrine gland |
|---|---|---|
| Duct | Absent | Present |
| Secretion | Hormones | Enzymes, mucus, sweat, etc. |
| Mode | Released into blood | Released through ducts |
| Gland | Shape / appearance | Location |
|---|---|---|
| Pituitary | Small oval pea-like gland | Below hypothalamus in brain |
| Thyroid | Butterfly-shaped | Front of neck |
| Parathyroid | Small oval nodules | Behind thyroid |
| Adrenal | Triangular / cap-like | On top of kidneys |
| Pancreas | Elongated gland | Behind stomach |
| Gonads | Ovaries and testes | Pelvic cavity / scrotum |
| Pineal | Small cone-like | Brain |
The pituitary gland is called the master gland because it controls several other endocrine glands. It is connected to the hypothalamus.
| Hormone | Function |
|---|---|
| Growth hormone (GH) | Controls growth of bones and body tissues |
| TSH | Stimulates thyroid gland |
| ACTH | Stimulates adrenal cortex |
| FSH | Stimulates gamete formation |
| LH | Triggers ovulation and testosterone secretion |
| Prolactin | Stimulates milk secretion |
| Hormone | Function |
|---|---|
| ADH / vasopressin | Increases water reabsorption in kidneys |
| Oxytocin | Stimulates uterine contraction and milk ejection |
| Condition | Cause |
|---|---|
| Gigantism | Hypersecretion of GH in childhood |
| Dwarfism | Hyposecretion of GH in childhood |
| Acromegaly | Excess GH in adults |
The thyroid gland secretes thyroxine, triiodothyronine, and calcitonin. Thyroxine regulates metabolism, growth, and development.
| Condition | Cause |
|---|---|
| Hyperthyroidism | Excess secretion of thyroxine |
| Hypothyroidism | Deficiency of thyroxine |
| Goitre | Enlargement of thyroid, often due to iodine deficiency |
| Myxedema | Adult hypothyroidism |
| Cretinism | Childhood hypothyroidism |
Pancreas is both exocrine and endocrine gland. Its exocrine part secretes digestive enzymes, while the endocrine part secretes hormones through islets of Langerhans.
| Cell type | Hormone | Function |
|---|---|---|
| Beta cells | Insulin | Reduces blood glucose |
| Alpha cells | Glucagon | Increases blood glucose |
Diabetes mellitus is a condition in which blood glucose level remains high due to insufficient insulin secretion or poor response to insulin.
Adrenal glands are located on top of the kidneys and have an outer cortex and inner medulla.
| Zone | Hormone | Function |
|---|---|---|
| Zona glomerulosa | Aldosterone | Regulates salt and water balance |
| Zona fasciculata | Cortisol | Regulates metabolism and stress response |
| Zona reticularis | Androgens | Produces small amount of sex hormones |
| Hormone | Also called | Function |
|---|---|---|
| Adrenaline | Epinephrine | Fight-or-flight response |
| Noradrenaline | Norepinephrine | Supports stress response |
Hormone levels are controlled by feedback mechanisms. In a negative feedback loop, if the hormone level becomes too high, secretion stops or decreases. If the level becomes too low, secretion increases.
| Topic | One-line revision |
|---|---|
| Circulatory system | Heart, blood, and vessels transport materials throughout the body. |
| Blood | Plasma + formed elements. |
| RBCs | Carry oxygen using haemoglobin. |
| WBCs | Provide immunity. |
| Platelets | Help in clotting. |
| Heart | Muscular pump with four chambers. |
| Kidney | Forms urine and regulates water-salt balance. |
| Neuron | Structural and functional unit of nervous system. |
| Brain | Main control organ of the body. |
| Eye | Organ of vision. |
| Ear | Organ of hearing and balance. |
| Pituitary | Master gland. |
| Thyroid | Controls metabolism. |
| Pancreas | Secretes insulin and glucagon. |
| Adrenal | Produces stress hormones. |