Human Physiology

Different phases of digestion take place including the cephalic phase, gastric phase and intestinal phase. The cephalic phase occurs at the sight, thought and smell of food, which stimulate the cerebral cortex. Taste and smell stimuli are sent to the hypothalamus and medulla oblongata.

Water and lipids are absorbed by passive diffusion throughout the small intestine.

Pancreatic amylase digests all the remaining starch in the duodenum. Amylase digests starch molecules from the ends of the chains in two-glucose units, forming the disaccharide maltose. Glycogen is also digested here.

Lungs filter gas micro-bubbles occurring in the venous blood stream such as those created during decompression after underwater diving. They also filter out small blood clots formed in veins.

The lower respiratory tract or lower airway, consists of the trachea, bronchi (primary, secondary and tertiary), bronchioles (including terminal and respiratory) and lungs.

Just behind the cornea is a dark coloured muscular diaphragm which has a small circular opening in the middle. The iris regulates the amount of light entering the eye. It regulates the light by adjusting the size of the pupil.

The cricoid cartilage is the only complete ring of cartilage around the trachea.

Sound is generated in the larynx and that is where pitch and volume are manipulated. The strength of expiration from the lungs also contributes to loudness.

The cells lining the proximal convoluted tubule are well adapted for reabsorption of materials from the filtrate. They have abundant mitochondria and bear numerous microvilli on the free side thus giving brush border appearance.

Angiotensinogen is an a-globulin protein produced by liver. Renin serves as an enzyme in the conversion of the plasma protein angiotensinogen into angiotensin. This protein stimulates the adrenal cortex to produce aldosterone which acts on the cells of the ascending limb of the loop of Henle and increases the rate of reabsorption of Na+.

The terminal sulcus is a groove in the right atrium of the heart. The terminal sulcus marks the separation of the right atrial pectinate muscle from the sinus venarum. The terminal sulcus extends from the front of the superior vena cava to the front of the inferior vena cava

The renal cortex is the outer portion of the kidney between the renal capsule and the renal medulla. It is the part of the kidney where ultrafiltration occurs. Erythropoietin is produced in the renal cortex.

They are produced in the bone marrow. They have a large kidney-shaped nucleus. The cytoplasm is more than in lymphocytes. They number 100 to 700 per cubic mm. They function as tissue macrophages feeding on damaged tissues.

Intercalated cells come in α and β varieties and participate in acid-base homeostasis.

Innervation of the penis comes from the pudendal nerve which is made up of the 2nd, 3rd and 4th sacral nerves. The penile nerve (also known as the dorsal nerve of the penis) is the deepest branch of the pudendal nerve.

The kidneys are covered by the peritoneum in the front and on the side and they rest against the abdominal muscles. Their position is slightly asymmetrical, the left kidney being a little higher than the right.

Primary haemostasis initially involves vasoconstriction in response to vascular damage which limits blood loss, and subsequent platelet adhesion to the damaged area and activation due to exposure of subendothelial matrix.

The nasal cavity conditions the air to be received by the other areas of the respiratory tract. Owing to the large surface area provided by the nasal conchae, the air passing through the nasal cavity is warmed or cooled to within 1 degree of body temperature.

The oesophagus lies posteriorly to the trachea. Circular bands of fibrous connective tissue called the annular ligaments of trachea join the tracheal rings together.

This forms the Adam's apple. It is usually larger in males than in females. The thyrohyoid membrane is a ligament associated with the thyroid cartilage that connects the thyroid cartilage with the hyoid bone.

The brainstem includes the midbrain, pons and medulla. It acts as a relay center connecting the cerebrum and cerebellum to the spinal cord. It performs many automatic functions such as breathing, heart rate, body temperature, wake and sleep cycles, digestion, sneezing, coughing, vomiting, and swallowing. Ten of the twelve cranial nerves originate in the brainstem.

Ventilatory rate (minute volume) is strictly controlled and determined primarily by blood levels of carbon dioxide as determined by metabolic rate. Blood levels of oxygen become important in hypoxia. These levels are sensed by chemoreceptors in the medulla oblongata for pH, and the carotid and aortic bodies for oxygen and carbon dioxide.

Some amount of air remains in the various parts of the respiratory tract also. The air in the trachea and bronchi (where no diffusion occurs) is called dead space air (350ml). The air remaining in the alveoli or air sacs is alveolar air (150mL).

Each body cell releases carbon dioxide into nearby capillaries by diffusion, because the level of carbon dioxide is higher in the body cells than in the blood. In the capillaries, some of the carbon dioxide is dissolved in plasma and some is taken by the haemoglobin, but most enters the red blood cells where it binds with water to form carbonic acid.

Eosinophils have a bilobed nucleus (two lobes connected by a narrow strand of chromatin). Their granules are considered to be lysosomes. Eosinophils actively phagocytize complexes formed by the action of antibodies on antigens (foreign substances).

Atrial natriuretic peptide (ANP), a hormone secreted by the atria of the heart, lowers blood pressure by causing vasodilation and by stimulating the kidneys to excrete more water and Na+(lowering blood pressure by reducing blood volume).

Blood is sometimes considered to be a fluid connective tissue because of the mesenchymal origin of its cells and a low ratio of cells to liquid intercellular substance, the blood plasma.

During rest, the vagal tone is the dominant. There is continuous parasympathetic activity that has a negative chronotropic character.

The atrioventricular node, located in the wall between the right atrium and the right ventricle. Here, the impulses are delayed for about 0.1s before spreading to the walls of the ventricle.

Lining mucosa is made up of nonkeratinised stratified squamous epithelium. It is found almost everywhere else in the oral cavity.

The muscularis externa consists of an inner circular layer and a longitudinal outer muscular layer. The circular muscle layer prevents food from traveling backward and the longitudinal layer shortens the tract.

Third heart sound is physiologic in children but pathological in adults. The four heart sound is a result of the atrial systole and vibration of the AV valves, due to blood rush during atrial systole. It is inaudible neither in adults nor in children.

Pepsin (in gastric juice) digests proteins to peptides, 6-12 amino acids long. Pepsin is an endopeptidase, which means it hydrolyses peptide bonds in the middle of a polypeptide chain. It is unusual in that it has an optimum pH of about 2 and stops working at neutral pH.

After passing through the small intestine, food passes into the large intestine. In the large intestine, some of the water and electrolytes (chemicals like sodium) are removed from the food. Many microbes (bacteria like Bacteroides, Lactobacillus acidophilus, Escherichia coli, and Klebsiella) in the large intestine help in the digestion process.

Interphase occurs just prior to cell division. Prepubertal male primordial germ cells are reactivated from interphase at puberty and enter rounds of mitoses followed by meiosis 1 and 2 to produce unique haploid sperm.

This is due to protein deficiency and not food calories intake. In developing countries like India it is common in infants below one year of age. The causal factor may be due to early replacement of mother's milk by other foods of low protein and calorific value. This may happen if the mother has a second pregnancy when the older infant is still too young.

After passing through the small intestine, food passes into the large intestine. In the large intestine, some of the water and electrolytes (chemicals like sodium) are removed from the food. Many microbes (bacteria like Bacteroides, Lactobacillus acidophilus, Escherichia coli, and Klebsiella) in the large intestine help in the digestion process.

Pellagra is a vitamin deficiency disease most frequently caused by a chronic lack of niacin (vitamin B3 in the diet. It can be caused by decreased intake of niacin or tryptophan, and possibly by excessive intake of leucine.

It is a conical extension of the right ventricle in the heart of mammals, from which the pulmonary artery originates.

Progesterone secretion increases after an ovary releases an egg (ovulation) at the middle of the cycle. This helps the estrogen keep the lining thick and ready for a fertilised egg.

Vitamin E deficiency causes nerve problems due to poor conduction of electrical impulses along nerves due to changes in nerve membrane structure and function.

Protein should be supplied only for anabolic purposes. The catabolic needs should be satisfied with carbohydrate and fat. Protein catabolism involves the urea cycle, which is located in the liver and can easily overwhelm the capacity of an already damaged organ.

The secretion of this gland is more serous in dogs and more mucous in bulls. It serves to promote the movement of spermatozoa in all the mammals and to form a vaginal plug.

Antonie Philips van Leeuwenhoek is commonly known as the Father of Microbiology.Sperm cells were first observed by him.

Medulla oblongata is the connection between the spinal cord and the brain. It is important for essential reflexes, e.g. breathing, heart rate and regulation of blood vessels, and other reflexes, e.g. swallowing, salivation, blinking, coughing, sneezing.

As a consequence of stimulation with luteinizing hormone the interstitial cells (Leydig) secrete testosterone into the intertubular tissue, where it is absorbed by blood vessels, lymphatics, and the seminiferous tubules.

Somatic nervous system is a subdivision of the PNS that controls voluntary activities such as the activation of skeletal muscles.

A complex material formed of protein and phospholipid (fat) that is laid down as a sheath around the axons of certain neurons. It iIncreases the rate of transmission of nerve impulses.

Paracoel are the second ventricles.

This nerve innervates the muscles of the tongue.

Vitamin B12 deficiency can lead to vitamin B12 deficiency anemia and neurologic dysfunction. A mild deficiency may not cause any discernible symptoms, but as the deficiency becomes more significant symptoms of anemia may result.

Sympathetic nervous system stimulation causes vasoconstriction of most blood vessels, including those of the skeletal muscle.

In a neuron, the dendrite receives a signal from an axon terminal of a neuron through a synapse.

Limbic lobe of the brain governs the emotions and memory of an individual.

Ependyma is the thin epithelium-like lining of the ventricular system of the brain and the central canal of the spinal cord. Ependyma is one of the four types of neuroglia in the central nervous system (CNS). It is involved in the production of cerebrospinal fluid (CSF).

The axolemma is the cell membrane surrounding an axon. It is responsible for maintaining the membrane potential of the neuron, and it contains ion channels through which ions can flow.

A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. There are 31 pairs of spinal nerves, one on each side of the human vertebral column.

They are circulating immature macrophages or dendritic cells.

The left ventricle is the pumping chamber for the systemic circulation. Because a greater blood pressure is required to pump blood through the much more extensive systemic circulation than through the pulmonary circulation, the left ventricle is larger and its walls are thicker than those of the right ventricle.

During contraction of the ventricular myocardium (systole), the subendocardial coronary vessels (the vessels that enter the myocardium) are compressed due to the high intraventricular pressures.

A pseudounipolar neuron is a kind of sensory neuron in the peripheral nervous system. This neuron contains an axon that has split into two branches; one branch runs to the periphery and the other to the spinal cord.

It is a trilobed valve, present at the opening of aorta into the left ventricle.

Plasma cells secrete large amounts of antibody and therefore require well developed ER in order to make sufficient amounts of this protein.

The hilum of the lung is a triangular part which allows the other structures forming the root of the lung to enter and exit. It permits arteries, veins, nerves, bronchi, and other structures to enter and exit.

Mesenchyme arising beneath the germinal epithelium in the testes is the precursor to testicular interstitial cells, or Leydig cells, while in the ovaries it is the precursor to ovarian stroma or thecal cells.

Follicle-stimulating hormone (FSH) causes maturation of a cohort of early-stage ovarian follicles; one of these will ultimately become the dominant, or Graafian follicle.

A Sertoli cell is a 'nurse' cell of the testes. The MIS glycoprotein is produced by Sertoli cells of the testes during fetal and neo-natal life in males.

Primordial germ cells are maintained against the basement membrane of the seminiferous tubules; Sertoli cells do not appear to have a role in this process.

Testosterone is a main male sex hormone. It is produced by the male testes and influences men physically, emotionally and sexually.

Once the Mullerian ducts have reached the urogenital sinus and the vaginal plate has formed the ducts will begin to fuse centrally. This forms the body of the uterus.

Mullerian inhibiting substance (MIS) is responsible for causing the mullerian ducts to degenerate, accounting for the sole development of male internal genitalia in a fetus with a functional testis. If it is absent during fetal development, female internal genitalia would develop by default

The internal pudendal arteries serve as the penile blood supply by entering the penis dorsally and running deep into the tissues of the corpora cavernosa. The internal pudendal artery becomes the penile artery.

The right testicular vein drains into the inferior vena cava at an acute angle.

The ejaculatory duct in males is formed by a union of the ampulla of the ductus deferens and the duct of the seminal vesicle. This duct receives secretions from the seminal vesicle and prostate gland and penetrates the prostate gland where it empties into the urethra.

During the act of expiration the diaphragm potentially relaxes and the elastic recoil of the lungs, chest wall, and abductor muscles compress the lungs.

These are pea-sized structures located on the sides of the urethra. These glands produces transparent, slippery fluid which serves to lubricate the urethra and to neutralize the acidity being present due to the drops of urine in the urethra.

These glands are located beside the vaginal opening and produce a fluid secretion. It is a one of the important parts among the main external structures of the female reproductive system.

Colostrum is a form of milk produced by the mammary glands in late pregnancy and the few days after delivery in all the mammals. Human colostrum is thick, sticky and yellowish.

The epithalamus is a dorsal part of the diencephalon and connects the limbic system to other parts of the brain.

It is a V shaped groove diffentiating the anterior two thirds of the tongue from the posterior third and containing the circumvallate papillae.

The cerebral cortex is the portion of the brain that provides remarkable distinctions between humans and other animals. It enables humans not only to receive and interpret all kinds of sensory information, such as color, odor, taste, and sound, but also to remember, analyze, interpret, make decisions, and perform a host of other higher brain functions.

It is a conical extension of the right ventricle in the heart of mammals, from which the pulmonary artery originates.

It is a V shaped groove diffentiating the anterior two thirds of the tongue from the posterior third and containing the circumvallate papillae.

It refers to the wall at the back of the pericardial sac. It acts as a collection reservoir to isolate oxygenated haemolymph entering the heart.

The acrosome is the part of the sperm containing proteolytic enzymes to digest the zona pellucida. It is exposed by the process of capacitation. Then, under the influence of substances released by corona radiata cells, it releases its proteolytic enzymes and penetrates the oocyte.

The iris is a highly vascularised organ which needs to contract and relax.

The abducens innervates the lateral rectus muscles of the eye.

The caruncula lacrimalis is the small, pink, globular nodule at the inner corner (the medial angle) of the eye. It is made of skin covering sebaceous (oil) and sudoriferous (sweat) glands.

Choroid is layer of the eye behind the retina, contains blood vessels that nourish the retina.

The stomach has a priority to destroy the bacteria and viruses using its highly acidic environment but also has a duty to protect its own lining from its acid. The way that the stomach achieves this is by secreting mucin and bicarbonate via its mucous cells, and also by having a rapid cell turn-over.

The pancreas is also the main source of enzymes for digesting fats (lipids) and proteins. The enzymes that digest polysaccharides, by contrast, are primarily produced by the walls of the intestines.

Amylases are used in breadmaking and to break down complex sugars, such as starch (found in flour), into simple sugars. Yeast then feeds on these simple sugars and converts it into the waste products of alcohol and CO2. This imparts flavour and causes the bread to rise.

This is a significant brush border enzyme.This enzyme decreases with age, and as such lactose intolerance is often a common abdominal complaint in the older population, manifesting with bloating, abdominal pain, and osmotic diarrhea.

Peyer's patches are covered by specialized epithelium (follicle-associated epithelium). Some of these epithelial cells have surfaces, which seem folded under the scanning electron microscope. These microfold, or M, cells sample and actively transport particulate antigens from the lumen into the dome area, where priming of both T and B lymphocytes occurs.

A uriniferous tubule/nephron is a long tubule differentiated into four regions: Bowman's capsule, proximal convoluted tubule, loop of Henle and distal convoluted tubule. Collecting ducts are the larger tubes, each receiving the collecting tubules of several nephrons. Collecting duct does not form a part of the uriniferous tubule.

The excretory system in man is formed of one pair of kidneys, a pair of ureters, a urinary bladder and a urethra. The gall bladder is a pear-shaped, hollow structure located under the liver and on the right side of the abdomen.

It extends from the base of the skull to the upper surface of the soft palate. It includes the space between the internal nares and the soft palate, and lies above the oral cavity. The adenoids are lymphoid tissue structures located in the posterior wall of the nasopharynx.

Elimination of uric acid as the main nitrogenous waste material is called uricotelism. Animals showing uricotelism are called uricotelic animals. It is a common method seen in birds, land reptiles, insects, land snails and some land crustaceans.

The spleen breaks down both red and white blood cells that are spent. This is why, it is sometimes known as the 'graveyard of red blood cells'. A product of this digestion is the pigment bilirubin which is sent to the liver and secreted in the bile.

The sinoatrial (SA) node is a section of nodal tissue that is located in the upper wall of the right atrium. The SA node is also referred to as the pacemaker of the heart.