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Uploaded byDr. Sudhadevi Sadanandan
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Physiology flow chart for NSG students

Detailed exploration of human physiological processes including hearing, taste, reproduction, cardiac cycle, blood circulation, cell division, nerve impulse transmission, blood clotting, urine formation, skin functions, digestion, and menstrual cycle.

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1. PHYSIOLOGY OF HEARING The pinna collects sound waves from the surroundings. ā†“ The auditory canal directs these sound waves toward the eardrum. ā†“ The tympanic membrane (eardrum) vibrates when the sound waves strike it. ā†“ The ear ossicles ā€“ malleus, incus, and stapes ā€“ amplify this vibration. ā†“ The vibrations pass into the cochlea, a fluid-filled spiral structure. ā†“ Movement of the fluid stimulates the hair cells, which generate electrical signals. ā†“ These electrical signals travel through the auditory nerve to the brain. ā†“ The auditory cortex interprets these signals, and this is how we perceive the sense of hearing.
2. PHYSIOLOGY OF TASTE Food entering the mouth mixes with saliva. ā†“ The dissolved food particles stimulate the taste buds on the tongue. ā†“ This stimulation is carried to the brain through three cranial nerves ā€“ the Facial (VII), Glossopharyngeal (IX), and Vagus (X) nerves. ā†“ The impulses first reach the medulla oblongata in the brainstem. ā†“ From there, they pass to the thalamus, which acts as a relay centre. ā†“ Finally, the impulses reach the gustatory cortex, where the brain identifies the taste as sweet, sour, salty, bitter, or umami. ā†“ This gives rise to the perception of taste.
3. PHYSIOLOGY OF OOGENESIS Oogonia (2n) multiply and develop into primary oocytes (2n). ā†“ Each primary oocyte undergoes Meiosis I. ā†“ This division is unequal, forming a secondary oocyte (n) along with the first polar body. ā†“ If fertilization occurs, the secondary oocyte completes Meiosis II. ā†“ This results in a mature ovum (n) and a second polar body. ā†“ The ovum then fuses with the sperm nucleus to form the zygote (2n).
4. SPERMATOGENESIS Spermatogonia (2n) divide by mitosis and develop into primary spermatocytes (2n). ā†“ Each primary spermatocyte undergoes Meiosis I to form two secondary spermatocytes (n). ā†“ Each secondary spermatocyte then undergoes Meiosis II, producing four spermatids (n) in total. ā†“ The spermatids undergo spermiogenesis, transforming into mature spermatozoa. ā†“ Finally, spermiation occurs, and the mature spermatozoa are released into the lumen of the seminiferous tubules.
5. CARDIAC CYCLE The atria fill with blood during atrial diastole. ā†“ The atria then contract, pushing blood into the ventricles. ā†“ The ventricles contract, pumping blood into the lungs and the rest of the body. ā†“ The semilunar valves close, and the heart relaxes. ā†“ The atria fill with blood again, and the next heartbeat begins.
6. BLOOD CIRCULATION Deoxygenated blood from the body tissues collects in the right atrium. ā†“ From the right atrium, blood passes into the right ventricle. ā†“ The right ventricle pumps this blood through the pulmonary artery to the lungs. ā†“ In the lungs, the blood is oxygenated ā€“ carbon dioxide is removed and oxygen is added. ā†“ The oxygenated blood returns through the pulmonary veins to the left atrium, and then to the left ventricle. ā†“ The left ventricle pumps this oxygenated blood through the aorta to the whole body. ā†“ After delivering oxygen to the tissues, the blood returns to the right atrium, and the cycle repeats.
7. MEIOSIS The parent diploid cell (2n) undergoes DNA replication during interphase. ā†“ In Meiosis I, crossing over occurs during Prophase I, and the homologous chromosome pairs align at the equator during Metaphase I. ā†“ During Anaphase I the homologous chromosomes move to opposite poles, and by Telophase I two haploid cells are formed. ā†“ In Meiosis II, new spindle fibres form during Prophase II and the chromosomes line up at the equator during Metaphase II. ā†“ During Anaphase II the sister chromatids separate, and by Telophase II four haploid daughter cells are formed. ā†“ The final result is four genetically different haploid (n) cells.
8. PHYSIOLOGY OF NEURON ā€“ TRANSMISSION OF NERVE IMPULSE At rest, the neuron maintains a resting membrane potential of ā€“70 mV, with the inside negative and the outside positive. ā†“ When a stimulus is received, sodium channels open and depolarization begins ā€“ sodium ions rush in, making the inside positive. ā†“ Next, potassium channels open and repolarization occurs ā€“ potassium ions move out, making the inside negative again. ā†“ This is briefly followed by hyperpolarization, where the membrane becomes slightly more negative than normal. ā†“ The membrane returns to its resting state, while the sodiumā€“potassium pump maintains the normal ion gradients. ā†“ The impulse travels along the axon and reaches the axon terminal. ā†“ At the synapse, a neurotransmitter such as acetylcholine is released, crosses the synaptic cleft, and stimulates the next neuron. ā†“ In this way, the impulse travels in one direction ā€“ from dendrite to cell body to axon to axon terminal to the next neuron.
9. MITOSIS The cell passes through interphase, where it grows and replicates its DNA. ā†“ It then enters prophase, metaphase, anaphase, and telophase in sequence, as the chromosomes condense, align, separate, and reach opposite poles. ā†“ Cytokinesis then divides the cytoplasm. ā†“ This results in two identical daughter cells, each with the same chromosome number as the parent cell.
10. BLOOD CLOTTING FACTORS (Iā€“XIII) Factor I, fibrinogen, is converted into fibrin to form the clot. ā†“ Factor II, prothrombin, is converted into thrombin, the key enzyme of clotting. ā†“ Factor III, thromboplastin, is released from damaged tissue and starts the extrinsic pathway. ā†“ Factor IV, calcium ions, act as an important cofactor in several steps of coagulation. ā†“ Factor V, proaccelerin, works with Factor X to form the prothrombin activator. ā†“ Factor VI is no longer used ā€“ it was the old name for activated Factor V. ā†“ Factor VII, proconvertin, helps activate Factor X in the extrinsic pathway. ā†“ Factor VIII, the anti-haemophilic factor, works with Factor IX to activate Factor X; its deficiency causes Haemophilia A. ā†“ Factor IX, the Christmas factor, works with Factor VIII; its deficiency causes Haemophilia B. ā†“ Factor X, the Stuartā€“Prower factor, is the meeting point of both pathways and forms the prothrombin activator. ā†“ Factor XI helps activate Factor IX; its deficiency causes Haemophilia C. ā†“ Factor XII, the Hageman factor, starts the intrinsic pathway on contact with a damaged surface. ā†“ Factor XIII strengthens and stabilizes the fibrin mesh to form a firm, stable clot.
11. BLOOD COAGULATION ā€“ MECHANISM OF BLOOD CLOTTING When a blood vessel is injured, the vessel wall is damaged. ā†“ Platelets become activated and stick to the injured area. ā†“ Damaged tissue releases tissue factor, while the activated platelets provide phospholipids and release clotting mediators. ā†“ Together with Factor X, Factor V, and calcium, these form the prothrombin activator. ā†“ Prothrombin is then converted into thrombin in the presence of calcium ions. ā†“ Thrombin converts fibrinogen into fibrin threads. ā†“ The fibrin threads form a meshwork that traps red blood cells and platelets. ā†“ Factor XIII strengthens and stabilizes this fibrin mesh, forming a stable clot. ā†“ Bleeding stops, and healing begins.
12. PHYSIOLOGY OF FORMATION OF URINE Blood reaches the glomerulus inside Bowman's capsule through the afferent arteriole. ā†“ Here, glomerular filtration takes place ā€“ water, glucose, salts, and urea filter out, while large proteins and blood cells remain in the blood. ā†“ This filtrate, called primary urine, passes along the tubule for tubular reabsorption, where useful substances like glucose, amino acids, sodium, and water are reabsorbed back into the blood. ā†“ At the same time, tubular secretion adds extra wastes such as hydrogen ions, potassium ions, ammonia, and drugs into the tubule. ā†“ The Loop of Henle and vasa recta help maintain the medullary concentration gradient, while ADH regulates water reabsorption and aldosterone regulates sodium reabsorption in the distal tubule and collecting duct. ā†“ What remains ā€“ urea, uric acid, creatinine, salts, and water ā€“ becomes the final urine. ā†“ This passes through the collecting duct, renal pelvis, ureter, and urinary bladder, and is finally excreted through the urethra.
13. PHYSIOLOGY OF THE SKIN The skin protects the body against injury, harmful chemicals, ultraviolet rays, and microorganisms. ā†“ It helps regulate body temperature through sweating, vasodilation, and vasoconstriction. ā†“ It senses touch, pressure, pain, and temperature through its receptors. ā†“ It assists in excretion by releasing small amounts of water, salts, and waste products through sweat. ā†“ It synthesizes vitamin D when exposed to sunlight. ā†“ It supports immunity through Langerhans cells and antimicrobial secretions. ā†“ It heals and regenerates itself after injury. ā†“ It secretes sebum and sweat to lubricate the skin and cool the body. ā†“ It stores a portion of the body's blood volume, while the underlying subcutaneous tissue stores fat as an energy reserve. ā†“ It also reflects emotions and health status through visible changes in colour and expression.
14. PHYSIOLOGY OF DIGESTIVE SYSTEM Digestion begins in the mouth, where food is chewed and mixed with saliva, and salivary amylase starts breaking down starch into maltose. ā†“ The pharynx and oesophagus carry the food down by swallowing and peristaltic movement toward the stomach. ā†“ In the stomach, gastric juice containing hydrochloric acid and pepsin breaks proteins into peptones, converting the food into semi-liquid chyme. ā†“ In the small intestine, bile from the liver emulsifies fats, while pancreatic enzymes act ā€“ amylase converts starch to maltose, trypsin breaks proteins into smaller peptides, and lipase breaks fats into fatty acids and glycerol. ā†“ Intestinal enzymes complete digestion into absorbable nutrients, which are absorbed through the villi into the blood and lymph. ā†“ In the large intestine, water and electrolytes are absorbed, and the remaining waste is formed into feces. ā†“ Finally, the rectum and anus store and expel the feces through defecation.
15. PHYSIOLOGY OF MENSTRUAL CYCLE The hypothalamus releases GnRH, which stimulates the pituitary to secrete FSH and LH. ā†“ Under FSH and LH influence, the ovarian follicle grows and secretes rising levels of estrogen, which repairs and thickens the endometrium. ā†“ A sudden LH surge then triggers ovulation, releasing the secondary oocyte, and the ruptured follicle becomes the corpus luteum, which secretes progesterone. ā†“ The endometrium is now ready to receive a fertilized ovum. ā†“ If fertilization does not occur, hormone levels fall, menstruation begins, and a new cycle starts.
16. PULMONARY VENTILATION ā€“ MECHANICS OF RESPIRATION During inhalation, the diaphragm and external intercostal muscles contract, the ribs move upward and outward, and the diaphragm flattens and descends. ā†“ As the thoracic cavity expands, intrapleural pressure and alveolar pressure fall, drawing air into the lungs. ā†“ During exhalation, the diaphragm and external intercostal muscles relax, and the diaphragm returns to its dome shape as the ribs move downward and inward. ā†“ As the thoracic cavity shrinks, intrapleural pressure and alveolar pressure rise, pushing air out of the lungs.
17. RESPIRATORY GAS TRANSPORT Inhaled air reaches the alveoli of the lungs, where oxygen diffuses into the pulmonary capillaries and combines with haemoglobin to form oxyhaemoglobin. ā†“ This oxygenated blood travels through the pulmonary veins to the left atrium and left ventricle, and out through the aorta to the tissues. ā†“ At the tissues, oxyhaemoglobin releases oxygen, which diffuses into the cells and is used for cellular respiration. ā†“ The now-deoxygenated blood travels through the veins to the right side of the heart and is sent back to the lungs for oxygenation. ā†“ Meanwhile, carbon dioxide produced by cellular metabolism diffuses into the capillary blood, where seventy percent is carried as bicarbonate, twenty-three percent binds to haemoglobin as carbaminohaemoglobin, and the remaining seven percent dissolves in plasma. ā†“ This deoxygenated blood travels through the veins to the right atrium, right ventricle, and pulmonary artery to reach the lungs. ā†“ In the lungs, bicarbonate is converted back into carbon dioxide and water, and the carbon dioxide diffuses into the alveoli to be exhaled from the body.
18. PHYSIOLOGY OF PAIN Tissue injury releases pain-producing substances such as bradykinin and prostaglandins. ā†“ These substances activate the nociceptors, the free nerve endings that sense pain. ā†“ The signal is transmitted through A-delta and C fibres to the dorsal horn of the spinal cord, where neurotransmitters like Substance P and glutamate pass it to the next neuron. ā†“ This signal crosses to the opposite side and ascends through the spinothalamic tract to the thalamus, which relays it to the cerebral cortex. ā†“ Here the brain perceives the pain, while descending pathways release endorphins and enkephalins that help modulate and control it.
19. PHYSIOLOGY OF VISION Light rays from an object enter the eye through the cornea and pass through the aqueous humour, pupil, and lens, while the iris controls how much light enters. ā†“ The cornea and lens refract and focus the light rays exactly on the retina, forming a small, real, inverted image, especially at the fovea centralis for sharp vision. ā†“ The photoreceptors ā€“ rods and cones ā€“ detect this light and convert it into electrical impulses through phototransduction. ā†“ These impulses pass through the bipolar cells and ganglion cells, whose axons join to form the optic nerve. ā†“ The optic nerve carries the impulses to the optic chiasma, where some fibres cross over to form the optic tract, and the signal reaches the thalamus. ā†“ From the thalamus, the impulses travel to the visual cortex of the occipital lobe, where the brain interprets them into a meaningful visual perception.
20. PHYSIOLOGY OF CEREBROSPINAL FLUID (CSF) The choroid plexus produces cerebrospinal fluid by actively secreting sodium, chloride, and bicarbonate ions, with water following osmotically. ā†“ This fluid enters the lateral ventricles, flows through the interventricular foramen into the third ventricle, and passes via the cerebral aqueduct into the fourth ventricle. ā†“ It then exits through the median and lateral apertures and circulates in the subarachnoid space around the brain and spinal cord. ā†“ Here it provides mechanical protection, supplies nutrients, removes waste, and helps regulate temperature. ā†“ Finally, the fluid is reabsorbed by the arachnoid villi into the dural venous sinuses and venous blood, keeping the CSF volume and intracranial pressure constant.
21. PHYSIOLOGY OF JOINTS ā€“ MOVEMENTS AND FUNCTIONS Muscle contraction produces movement at the joint. ā†“ These movements may be gliding, angular movements such as flexion, extension, abduction, adduction, and circumduction, rotational movements, or special movements like supination, inversion, and elevation. ā†“ Together, these movements provide mobility, support, locomotion, shock absorption, and protection to the body.
22. PHYSIOLOGY OF BONE ā€“ OSSIFICATION Intramembranous ossification occurs directly in membranous tissue and forms mainly the flat bones of the skull, along with parts of the clavicle and mandible. ā†“ Mesenchymal cells differentiate into osteoblasts, which secrete the bone matrix, or osteoid; this calcifies to form trabeculae that develop into spongy bone with an outer layer of compact bone, and the osteoblasts become osteocytes trapped within lacunae. ā†“ Endochondral ossification occurs within a pre-existing cartilage model and forms long bones such as the femur, humerus, and tibia. ā†“ A primary ossification centre appears in the diaphysis as blood vessels invade and osteoblasts deposit bone matrix, while secondary ossification centres later appear in the epiphyses. ā†“ An epiphyseal growth plate remains between the diaphysis and epiphysis, allowing the bone to lengthen, until growth stops and the plate is finally replaced by bone.
23. REGULATION OF BLOOD PRESSURE When blood pressure falls, the baroreceptors become less active. ā†“ This increases sympathetic activity, causing vasoconstriction and a faster heart rate, which raises blood pressure. ā†“ The kidneys also release renin, activating angiotensin II and aldosterone, which promotes sodium reabsorption with water following, further raising blood pressure, while ADH secretion adds to this by increasing water reabsorption. ā†“ When blood pressure rises, the baroreceptors become more active. ā†“ Parasympathetic activity increases and sympathetic activity decreases; the heart rate decreases, while reduced sympathetic activity causes vasodilation and decreases vascular resistance, thereby lowering blood pressure. ā†“ ANP is also secreted, promoting water and sodium excretion to bring blood pressure back down.
24. PHYSIOLOGY OF TISSUE FORMATION AND REPAIR Following tissue injury, hemostasis occurs first, forming a clot to stop bleeding. ā†“ This is followed by the inflammation phase, where white blood cells clean the area of debris and pathogens. ā†“ During the proliferation phase, fibroblasts produce collagen and new capillaries form, helping to rebuild the tissue. ā†“ Finally, the maturation phase remodels the collagen and forms scar tissue, resulting in healed tissue with restoration of tissue strength and function.
25. PHYSIOLOGY OF ERYTHROPOIESIS The haemocytoblast, or stem cell, develops into a proerythroblast. ā†“ This matures into a basophilic erythroblast, then a polychromatic erythroblast, as haemoglobin synthesis increases. ā†“ It continues to mature into an orthochromatic erythroblast, or normoblast, whose nucleus is expelled. ā†“ This becomes a reticulocyte, which is released into circulation and matures into a fully functional erythrocyte, or red blood cell.
26. PHYSIOLOGY OF MUSCLE CONTRACTION A nerve impulse triggers the release of acetylcholine at the neuromuscular junction. ā†“ This produces an action potential on the sarcolemma, causing calcium ions to be released from the sarcoplasmic reticulum. ā†“ The calcium ions enable actin and myosin to interact, forming cross-bridges. ā†“ These cross-bridges pull the filaments to slide over each other, shortening the sarcomere and producing muscle contraction. ā†“ Once the stimulus stops, the muscle relaxes.
27. PHYSIOLOGY OF THE CELL The cell performs several essential functions to sustain life. ā†“ It transports substances across its membrane, produces energy in the mitochondria, synthesizes proteins in the rough endoplasmic reticulum and ribosomes, and removes waste through the lysosomes. ā†“ It also communicates through chemical signals, grows and divides through mitosis, and maintains homeostasis. ā†“ Together, these functions keep the cell's life processes running smoothly.
28. PHYSIOLOGY OF HEMOSTASIS ā€“ PROCESS OF BLOOD CLOTTING When a blood vessel is injured, it first undergoes vasoconstriction, or vascular spasm, to reduce blood flow. ā†“ Platelets then adhere to the injured site and form a temporary plug. ā†“ Damaged tissue releases tissue factor, leading to the formation of the prothrombin activator. ā†“ In the presence of calcium ions, prothrombin is converted into thrombin, which converts fibrinogen into fibrin. ā†“ This forms a fibrin mesh, which Factor XIII strengthens and stabilizes into a stable blood clot. ā†“ Finally, the clot retracts, and once healing begins, fibrinolysis dissolves the clot.