mechanism of hormonal Action| types of hormones| function| structure|

    Mechanism of Hormonal Action    

The function of different hormones is to control the activity of level of target tissues. To achieve this, the hormones may alter either the permeability of the cells or they may activate some other specific cellular mechanism. Although the exact site of action of any hormone is not established, five general sites have been proposed: -

 (A.) Hormonal action at cyclic nucleotides level: -Many hormones exert their effect on cells in the first causing the formation of a substance, cyclic 3', 5'-adenosine monophosphate (Figure)in the cell. Once formed, the cycle AMP causes the hormonal effects inside the cell. Thus, cyclic AMP acts as intracellular hormonal mediator. It is also frequently referred to the second to messenger for hormone mediation; the first messenger being hormone the original hormone itself.

The effects of cyclic AMP on the action of a hormone were first described by Earl W. Sutherland and T.W. Rall in 1960. They found that the effect of epinephrine on hepatic glycogenolysis (breakdown of glycogen) is a result of the conversion of inactive phosphorylase by into an active form by cyclic AMP. Epinephrine was found to activate the enzyme, adenyl cyclase which, in turn, converts ATP to cAMP. Besides epinephrine, other hormones like glucagon, parathormone, ACTH, TSH, ICSH, LH, a-MSH and vasopressin are now known to have a stimulatory effect on cAMP levels. Several hormones, on the contrary, decrease cAMP levels and thus produce an opposite effect. These include insulin, melatonin and the prostaglandins. From the many names of hormones given above, it appears that hormone action not mediated by cAMP may be an exception rather than the rule. 

The following Figure depicts, in a schematic way, the effect of cAMP on hormone action. The stimulating hormone acts at the plasma membrane of the target cell and combines with a specific receptor for that particular type of hormone. The specificity of the receptor determines which hormone will affect the target cell. The combination of the hormone with its receptor leads to the activation of the enzyme, adenyl cyclase, which is also bound to the plasma membrane. The portion of the adenyl cyclase that is exposed to the cytoplasm causes 1mmediate conversion of cytoplasmic ATP into cAMP. The reaction representing cAMP synthesis may, thus, be written as: -

The reaction is slightly endergonic and has G°" value of about 1.6 kcal/mol. The then acts inside the cell to initiate a number destroyed. The various functions of cellular functions before it itself is initiated include: 

(a) activating the enzymes 

(b) altering the cell permeability 

(c) synthesizing the intracellular proteins 

(d) contracting or relaxing the muscles

(e) releasing other hormones (third messengers)

It should, however, be emphasized that what cAMP does in a particular affecter. cell is determined by the cell itself, rather than by cAMP. Cyclic AMP is however, destroyed (or inactivated) by a specific enzyme called phosphodiesterase, which hydrolyzes it to AMP. Like adenyl cyclase, the phosphodiesterase is present in practically all tissues.

This reaction is highly exergonic, having G°" value of about -12 kcal/mol. Cyclic. AMP is a very stable compound unless hydrolyzed by a specific phosphodiesterase. An important feature of the second messenger model is that the hormone need not enter the cell and its impact is made at the cell membrane. The biological effects of the hormone are mediated inside the cell by cAMP rather than by the hormone itself.

(B) Induction of enzyme synthesis at the nuclear level: - A second major mechanism by which the hormones, especially, the steroidal and thyroidal ones, act is to cause synthesis of proteins in the target cell. These proteins are presumably the enzymes which, in turn, activate other functions of the cells. The mechanism behind the steroidal hormones is depicted in other functions of the cells. The sequence of events is as follows: 

1). The steroidal hormone enters the cytoplasm of the target cell where it binds with a specific. high-affinity receptor protein.

Fig.: Mechanism of action of protein; [The dissimilar steroidal hormones: ST=steroid; R=specific receptor shapes of Rare intended to represent different conformations a

2). The receptor protein-hormone complex, so formed, then diffuses into (or is 2. transported into) the nucleus, where it reacts with the nuclear chromatin. 

3). Somewhere along this route, the receptor protein is structurally altered to form a smaller protein with. Low molecular weight, or else the steroid hormone is transferred to a second smaller protein.

4). The combination of the small protein and hormone is now the active factor that stimulates the specific genes to form messenger RNA (mRNA) in the nucleus. 

5). The mRNA diffuses into the cytoplasm where it accelerates the translation process at the ribosome to synthesize new proteins. It is, however, noteworthy that a direct chemical reaction of the hormone with DNA or RNA polynucleotide is not likely. Instead, the hormone must first combine with a specific receptor protein, and it is this combination that acts on DNA chromatin. It is possible that the chromatin proteins may influence hormonal activity by modifying the ability of the receptor complex to bind with DNA.

The thyroidal hormones act similarly to enhance RNA and enzyme synthesis but may do so by directly binding with the specific receptor proteins present in the nuclear chromatin. The receptors present in the cytoplasm are less effective in this regard.

(C). Stimulation of enzyme synthesis at ribosomal level: - In the case of some hormones, the activity is at the level of translation of information carried by the mRNA on the ribosomes to' the production of enzyme protein. For example, the ribosomes taken from animals, which have been given growth hormone, have a capacity for protein synthesis in the presence of normal mRNA.

(D). Direct activation at the enzyme level: -It has been experimentally observed that treatment of the intact animal (or of isolated tissue) with some hormones results in a change in enzyme behavior which is not related to de novo synthesis. The cell membrane is usually required for such activity. Henceforth, it is possible that activation of a membrane receptor might be an initial step in hormone action.

(E). Hormone action at the membrane level: - Many hormones appear to transport a variety of substances, including carbohydrates, amino acids and nucleotides, across cell membranes. These hormones, in fact, bind to cell membranes and cause rapid metabolic changes in the tissue. Catecholamines (epinephrine and norepinephrine) and many protein hormones stimulate different membrane enzyme systems by direct binding to specific receptors on cell membrane rather than in the cytoplasm.

respiratory Quotient (RQ)| respiratory Quotient of carbohydrates| RQ of Fat| RQ of proteins| RQ of organic acids|

     RESPIRATORY OTIENT (RQ)    

Respiratory quotient (R.Q.) is the ratio of the volume of carbon dioxide released to the volume of oxygen taken in respiration in the given period of time at standard temperature and pressure.

                              RQ= Volume of CO2 evolved by Volume of O2 absorbed 

Value of RQ varies with the respiratory substrates and their oxidation. Thus, the measurement of RQ may give some guide as to the nature of the substrate being respired by a particular tissue. The value of RQ in the oxidation of different substrates is given below: -

1. RQ of carbohydrates: -. When carbohydrates, such as hexose sugars (i.e., glucose or fructose), Sucrose, or starch, are respired in presence of oxygen (i.e., aerobic respiration), the volume of CO2, evolved during the process is equal to the volume of O2 absorbed. Thus, the value of RQ is equal to one or unity, as shown by the following chemical reaction: - 

C6H12O6 + 6O2 ------> 6CO2 + 6H2O +Energy

RQ = Vol. of CO2 by the Vol. of O2 = 6/6 = 1 or unity 

for example, leaves of many plants, rose petals, germinating seeds of cereal grains (Such as wheat), potato tubers, etc., show their RO value more nearly equal to unity. The germinating seeds of all those plants which contain starch as the main reserve food, also exhibit RQ equal to unity. 

(2) RQ of fats: -. When fats are respiratory substrates, as in case during germination or fatty seeds (e.g. ground nut, mustard, flax, castor, etc.), the fats are hydrolysed to glycerol and fatty acids. 1he complete Oxidation of glycerol results in the RO of 0-86. The fatty acids, being poorer in oxygen, require more O2 for complete oxidation as compared to CO2. Therefore, O2 absorption is more and CO2 absorption is less and the RQ becomes less than unity. For example: -

(i)RQ is 0-7 during oxidative breakdown of glycerol tripalmitate: -

2C51H98O6 (Tripalmitin) + 145O2 ----> 102 CO2 + 98 H2O + ENERGY 

RQ = Vol. of CO2 by the Vol. of O2 =  102/145 = 0.7(less than unity)

(ii) RQ is 0-69 during oxidative breakdown of glycerol trioleate: - 

C57H104O6 (Triolein ) + 83O2 -----> C12H22O11 + 4CO2 + 5H2O + Energy  

RQ= vol. of CO2 by the Vol. of O2 = 57/83 = 0.69(less than unity) 

(iii) RQ is 0.36 during conservation of palmitic acid to sucrose in the endosperm tissue of germinating fatty seeds: -

C16H32O2(Palmitic acid)  + 11O2 ----> C12H22O11 + 4CO2 + 5H2O 

RQ = Vol. of CO2 by the Vol. of O2 = 4/11= 0.36(less than unity)

3). RQ of proteins: -. As in case of fats, the protein also have RQ of less than unity. First of all the proteins are hydrolysed into amino acids. The hydrolytic products of proteins have lower proportion of oxygen as compared to carbohydrates. They required more O, and evolve less CO, during their complete oxidation. Thus, the value of RQ becomes less than unity. Example, germinating seeds of buckwheat (RQ is 0.5). 

(4). RQ of organic acids: -. When organic acids are respired (as in succulents), the RQ is always more than unity. These acids are rich in O2, and, therefore, require less O2, and evolve more CO with the result the value of RQ becomes more. For example: - 

(i) RQ of oxalic acid is 4 as shown in the following reaction: -

2 (COOH)2 + O2 -----> 4CO2 +2 H2O+ 602 K cal. 

RQ =Vol. of CO2 by the Vol. of O2 = 4/1 = 4 (more than unity) 

(ii) RQ of citric acid is 1.33 

2C6H807 + 902 ----> 12 CO2+8 H2O 

RQ = Vol. of CO2 by the Vol. of O2 = 12/9 = 1.33 (more than unity) 

(iii) RQ of tartaric acid is 1.6 

C4H606 + 5O2 ----> 8C02 +6 H20 

RQ = Vol. of CO2 by the Vol. of O2 (more than unity)

(5) Anaerobic respiration: - If glucose molecule is broken down anaerobically into CO, and ethyl alcohol, the value of RQ is always more than unity. Though the numerical value of 2/4 is infinity but practically RQ will be more than unity.

Significance of RQ : -

The significance of determining RQ of plants is that it provides important information regarding the chemical nature of the respiratory substrate being respired. RQ less than unity indicates that respiratory Substrate has low O2 content, such as fats and proteins. The substrates having more O2 content, such as organic acids, show RQ more than unity. The carbohydrates, which have C and O2 in equal proportion, generally show unity (1) RQ. 

physiology of excretion| function| types| structure| DCT| PCT|

     PHYSIOLOGY OF EXCRETION    

Man is ureotelic. Urea is formed mainly in the liver and in small amounts in the brain and kidneys, is released to the blood stream, and is removed by Kidneys in urine. The excretory proses may, thus, be divided into two men. Events urea formation and urine formation.

Urea Formation: -

Urea is formed in the liver by a cyclic process called urea cycle, or ornithine cycle, or Krebs-Henselelt cycle.

The amino acids not needed in the body are deaminated by an enzyme oxidase, producing ammonia, NH3. Ammonia, being toxic, is quickly changed to urea. Three amino acids participate in the process -

(i) Ornithine combines with ammonia and carbon dioxide to form citrulline and water. 

(ii) Citrulline combines with more ammonia to form arginine and water. 

(iii) Arginine then decomposes to form urea and ornithine in the presence of enzyme arginase and water. Ornithine is set free for reuse in the urea cycle.

Urine Formation (Uropoiesis):- 

 Urine formation occurs in the kidneys. It involves three processes: glomerular filtration, tubular reabsorption and tubular secretion 

1. Glomerular Filtration (Fig. 20.16). Walls of glomerular capillaries and Bowman's capsule are very thin and are semipermeable due to the presence of pores in the former and slit pores in the latter. They Allow water and small molecule in the blood to pass through them. Fluid containing these materials is forced out of the glomerular capillaries into the Bowman's capsule by the high pressure of the blood in the Glomerular capillaries. The pressure is high because the glomerular capillaries are narrower than the afferent artery this pressure is about 75 mm. Hg. in man, the fluid tends to move in the reverse direction osmotic pressure of plasma proteins in the glomerular capillary and hydrostatic pressure Or the Fluid in the urinary tubule. These pressures in man are about 30 mm. Hg. and 20 mm. H8. Respectively. The net force moving the fluid from the glomerular capillaries. called the filtration pressure, is />0+20) or mm. Hg. The separation of small molecules and ions from large molecules and cells in the blood is entered ultrafiltration. The filtered-out fluid is known as glomerular filtrate. or capsular nitrate, or ultrafiltrate.

1) Glomerular Filtration Rate. :-

About 1100-2000 litters of blood flows through the human kidney each day. This is about 275 times the total volumes of blood in the body. The glomerular filtration rate in a normal adult human being is about 125 ml. per minute, and some 180 litters of filtrate is produced daily. This is about four and a half times the amount of fluid in the whole body. Kidneys excrete only about 1.5 litters of urine in a day. The ultrafiltrate contains sodium. potassium. and chloride 1ons. glucose. amino acids. along with urea, uric acid, creatinine*, ketone bodies, and a large amount of water. The blood is left with only corpuscles, and plasma proteins (albumen. globulins). The concentrations of various materials in the glomerular filtrate are nearly equal to their respective concentrations in the plasma The filtrate. therefore, almost resembles the protein-free and cell-free plasma in composition and osmotic pressure.

2.) Tubular Reabsorption.

 From the Bowman's capsule, the glomerular filtrate passes in ten. Tubule and flows through it to the collecting duct. During this course, its composition, osmotic pressure and pH Change due to selective reabsorption of materials from it and secretion of more waste materials into it. 

  i)Proximal convoluted tubule: - The cells lining the PCT are well adapted for reabsorption of materials from the filtrate. They have abundant mitochondria and bear numerous microvilli on the free side. Mitochondria power the active transport of nutrient molecules back into the blood. Microvilli increase the Surface for reabsorption. The cells reabsorb entire glucose. amino acids, most of the inorganic 1ons (Na*, C, much of the water as well as some urea from the filtrate. Reabsorption takes place as under.

A) Glucose, amino acids and Na+, K+, ions are reabsorbed by active transport. Glucose reabsorption is so efficient that appearance of only a trace of glucose in urine suggests a possible presence of a disease named diabetes mellitus. 

(B) Cl- are reabsorbed by passive transport following the positively charged ions. 

(C) Active uptake of ions reduces the concentration of the filtrate, and an equivalent amount of water passes into the peritubular capillaries by osmosis. 

(D) Most of the important buffer bicarbonate (HCO;) is also reabsorbed from the filtrate. 

(E) Some urea is reabsorbed by diffusion. The rest remains in the filtrate for removal in the urine. 

(ii) Henle's Loop. The following events occur in the Henle's loop.

(a) The first wide part of the descending limb is impermeable to ions, urea and water. It merely transfers the nearly isotonic filtrate from the PCT to the narrow region of the descending limb. 

(b) The second (narrow) part of the descending limb is around freely permeable to water. The interstitial fluid it has a high osmotic Therefore, water pressure due to a high concentration of sodium chloride and urea in it. is drawn out of the filtrate by osmosis. 

(c) The exit of water makes the filtrate hypertonic by the time il reaches the turn of the loop the ascending limb.

(d) The ascending limb is impermeable to water along its entire length Its first (narrow part is permeable to inorganic ions (Na", K", U) and urea. lons leave the filtrate by diffusion and the urea enters the filtrate by diffusion (secretion). 

 (e) The cells of the second (wide) region of the ascending limb pass inorganic ions out of the filtrate by active transport into the renal medulla whicn Decomes concentrated. This helps the process given in (b)

(f) The filtrate becomes hypotonic to plasma due to loss of inorganic ions and passes into the DCT. 

(iii) Distal Convoluted Tubule, Collecting Tubule and Collecting Duct. Following events occur in these regions. 

(a) When the level of plasma waterfalls, the posterior pituitary lobe releases the antidiuretic hormone (ADH) which increases the permeability of the distal convoluted tubule, collecting tubule and the collecting duct to water. Water is reabsorbed from the filtrate by osmosis, and a reduced amount of concentrated urine is produced. When the level of plasma water becomes normal, ADH is not secreted, permeability of DCT collecting tubule and collecting duct to water decreases, less water is reabsorbed, and abundant dilute urine is produced. 

(b) The distal convoluted tubule, collecting tubule and the collecting duct actively reabsorb sodium from the filtrate under the influence of the adrenal hormone aldosterone which makes their walls permeable to ions. The reabsorption of sodium brings about the uptake of an osmotically equivalent amount of water. Lack of aldosterone makes the DCT, collecting tubule and he collectingg duct impermeable to ions. 

(c) Some urea diffuses from the last part of collecting duct into the interstitial fluid to raise latter's density for further uptake of water into collecting duct and bottom of Henle's loop

 (d) Bicarbonate ions (HCOG) are also reabsorbed in DCT.

3)Tubular Secretion.: -

 It occurs as under-

(a) Creatinine, hippuric acid and foreign substances (pigments, drugs including penicillin) are actively secreted into the filtrate in the PCT from the interstitial fluid. Hydrogen ions and ammonia (NH3) are also secreted into the PCT.

(b) Potassium, hydrogen, NH* and HCO; ions are secreted by ctive transport, into the filtrate in the DCT. 

(c) Urea enters the filtrate by diffusion in the thin region of the ascending limb of Henle's loop. Removal of H* and NH* from the blood in the PCT and DCT helps to maintain the pH of the blood between 6 to 8. Any variation from this range is dangerous.

Tubular secretion probably plays only a minor role in the function of human kidneys, but in animals, such as marine fish and desert amphibians which lack glomeruli and Bowman's capsules, tubular secretion is the only mode of excretion. When the blood pressure, and consequently the filtration pressure, drop below a certain level, filtration stops, and urine is formed by tubular secretion only 

Modified Glomerular Filtrate: - 

The glomerular filtrate reaching the end of the collecting duct, after being modified by reabsorption of certain substances and addition of others, is called final urine. The volume of urine is far less than the violone of glomerular filtrate, and its composition is quite different from that of the glomerular filtrate due to loss and gain of many substances in the nephron. The composition of urine does not change beyond the collecting ducts, except that it may acquire some mucus and epithelial cells in the ureters, bladder and urethra.

thyroid gland| hormone| types| function| structure| example|

 Thyroid Gland  

Thyroid Gland is a dumbbell shaped, bilobed gland located in the thoracic. region at the root of the throat. The two lobes are almost symmetrical and lie one on either side of the tracheal tube. Each lobe measures about 5x 2x 2 cm. The two lobes are Joined together by a narrow strip of tissue. called isthmus or middle lobe, which crosses the 2- 4th tracheal rings. In some cases, the right lobe is bigger than the left lobe. A pyramidal lobe varying in size extends from the isthmus upward in the neck. Accession thyroid bodies are located beneath the main thyroid gland.

Morphology 

The weight of the thyroid gland of the adult varies between 20 to 25 gm and is influenced by diet, age, sex and reproductive state of the individual Thyroid gland is highly vascular. Blood is supplied by the paired superior and inferior thyroid arteries and directly from the aorta. Venous blood is collected by internal jugular and innominate veins. Blood flows at the rate of 4 6 ml per gland per minute. This high rate of blood flow ensures adequate supply of inorganic iodine to the gland. Thyroid gland is innervated by sympathetic fibers derived from the superior, middle and inferior cervical ganglia and parasympathetic fibers derived from the superior and inferior laryngeal branches of the vague nerve. These nerves control the blood supply to the gland. 

Development 

Thyroid gland is endodermal in origin arising from the primitive foregut During embryonic development, the primitive thyroid gland arises as out pushing from the middle of the neck Infront of the thyroid cartilages Thyroid gland is derived from the fourth pharyngeal pouch, which gives reset the lateral lobes of the gland. During intra-uterine development, thyroid gland can be recognized in the seventh week. The follicular structure of the gland is evident by 12 -14th week of the fetus. Gradually, with the development of the gland, it auguries the capacity of concentrating iodine from the circulating blood and other functions of synthesis and secretion follows. 

Histology: -

Microscopic examination of the sections of the thyroid gland reveals the presence of numerous acini or follicles about 200 u in diameter. The number of the follicles in a normal gland is about 100, 000.The size of the follicles also varies. Large follicles are found near the periphery of the gland while smaller follicles are arranged at the center. Each follicle is made up of a Cuboidal follicular epithelium. In the resting condition, the epithelium is low, but the height is dependent upon Under the extent of stimulation of the gland. stimulation by thyroid stimulating hormone the low cuboidal epithelium becomes converted into tall columnar epithelium. The thyroid follicles are usually spherical or oval in shape and measure about 20- 150 diameter. A single layer of cubical follicular epithelial cells lines each follicle. The follicular cells are surrounded by a basement membrane consisting of fine connective tissue fibers on which rest the bases of the follicular cells. Follicles are surrounded by a highly vascular stroma containing Channels and nerve endings. The follicular lumen is filled with a colloidal material, the thyroglobulin. Thyroglobulin constitutes about 75% of the colloid material, which is the main storage form of the thyroid hormones.

Each follicular cell is loaded with of granular cytoplasm containing large mitochondria and distinct Golgi apparatus. The luminal end of each follicular cell facing the colloidal material is thrown into a number of microvilli. The nucleus is situated at the bases of the follicular cell and its cytoplasm is filled with well-developed rough endoplasmic reticulum Golgi complex. In addition to these, large number of cytoplasmic vesicles filled with the colloid material are also found in the cytoplasm. Based the staining properties, the cytoplasmic vesicles can be distinguished by three types, eosinophile or acidophilic, basophilic and mixed tow type of follicular epithelial cells have been distinguished on the basis of electron microscopic and histochemical studies. The first are the principal cells present in large number and contain small number of mitochondria, and different proteases and oxidases required for the synthesis of thyroid hormones. The second type of cells occurs in small number but contain large number of mitochondria and these are scattered in between the principal cells. These cells are known as parafollicular cells or C-cells those secrete thyrocalcitonin.

endocrine gland| function| types| structure|

  Endocrine Gland   

Master of endocrine gland is Pituitary gland, which is even the smallest gland of body. Pituitary gland is regulated by hypothalamus and is located at base of hypothalamus. Pituitary gland is made up of covering called durometer. It is divided into 3 regions called Pars distalis, Pars intermedia and Pars neurosa . Depression in pituitary gland is called as Sella turcica which is made up of sphenoid bone. Pituitary gland can also be divided on basis of development into 2 regions Adenohypophysis, which develops from the roof of mouth cavity. It consists of 3 components called Pars distalis, Pars intermedia and Pars tuberalis . Other region is called neuro hypophysis and it consist of 2 components called Pars neurosa and Infundibulum (region that joins pituitary to hypothalamus). Matured pituitary gland consist of anterior lobe. Pars distalis make up 75% of anterior lobe of pituitary gland. It consists of two types of cells called chromophils and chromophobes. Chromophils stain with both acidic and basic stains while chromophobes do not stain at all.

Chromophils are further divided into; -

i)Acidophils

ii)Basophils

Acidophil consist of somatotrophs that secrete somatotrophic growth hormones and lactotrophs that secrete lactogenic hormone prolactin. 

Basophil consists of corticotropes that secrete adrenocorticoids hormones, thymotrophs that secrete thyroid stimulating hormone and gonadotrophs that secrete gonadotrophic hormones such as luteinizing stimulating hormone, follicle stimulating hormone. These hormones produced are tropic hormones, which target another endocrine hormone production. Pars intermedia, present between Pars distalis and Pars neurosa, is a narrow strip of tissues which is separated by Pars distalis by interglandular deft. In case of humans, it is poorly developed but in lower eukaryotes it is well developed. It secretes melanocyte stimulating hormone. Pars tuberalis is a tube-like structure surrounding infundibulum and it produces no hormone. Infundibulum is composed of neuroglial cells. Pars neurosa consist of pituicytes, herring bodies, most cells and non-myelinated fibers. Pituicytes are large branching spindle shaped neuroglial cells also called supporting cells. Herring bodies contain an accumulation of neurosecretory cells. They produce neurosecretory hormone on activation of nerve fibers, which secrete them and store them in Pars neurosa. Neurosecretory hormones are vasopressin and oxytocin. Secretion of neurosecretory hormone occurs by nerve fibers present in hypothalamus cells such as supra optic cells which Secrete vasopressin and other one paraventricular cell which secrete oxytocin.

Hormones secreted by pituitary gland:- 

i )Growth Hormones: -It is a protein of 191amino acids. It increases rate of metabolism and cell division. Its production is regulated by hypothalamus, which produces growth hormone-releasing hormone (GHRH) and growth hormone inhibitory factor (GHIF). On low glucose level of body, GHRH is activated that leads to activation of somatotrophs to Trelease growth hormone. In high glucose levels, GHIH/F is activated that leads to low production of growth hormone. 

Abnormalities: -

In children, growth hormone hyposecretion leads to dwarfism and its hypersecretion leads to a giant. In adults, growth Hormone hyposecretion lead to Simon's disease and its hypersecretion led to Acromegaly 

• Prolactin is a protein of 198 amino acids. It is produced on activation through prolactin releasing factor secreted by hypothalamus. Low level of estrogen and progesterone levels inhibit prolactin production and vice versa.
• Adrenocortico tropic hormones, are proteinaceous in nature with 39 amino acids. Its product is even regulated by corticotropic releasing hormone secreted by hypothalamus. Adrencortico tropic hormones are secreted on detecting. Low levels of cortical and indirectly affect adrenal glands.
• Thyroid stimulating hormone is glycoprotein in nature and is also under control of thyroxine releasing factor secreted by hypothalamus. It affects thyroid gland cells to secrete thyroxin.
• Follicle stimulating hormone (glycoprotein in nature) is also. Under control of hypothalamus - mediated secretion of follicle stimulating releasing hormone, which gets activated in low levels of progesterone and estrogen. It plays role in gametogenesis.
• Luteinizing hormone is glycoprotein in nature and is even under control of luteinizing hormone releasing factor secreted by hypothalamus and is secreted when there are low levels of progesterone and estrogen in females and low level of testosterone in male.
• Melanocytes stimulate hormones consist of a form of alpha and beta form of 13 amino acid and 22 amino acid and is regulated by Melanocyte stimulating hormone releasing factor release by hypothalamus and in case of fishes are activated in low intensity of light environment leading to pigmentation.
• Vasopressin which is also called antidiuretic hormone (ADH) is a protein of 10 amino acids sequence. It leads to water reabsorption from distal convoluted tube and collecting tube of nephrons. ADH enter kidney and form aquaporins through which water reabsorption occurs. ADH also inhibits sweat glands. Vasopressin production is inhibited when blood content rise, blood pressure rises and even on stretching of heart muscles that leads to production of atrial natriuretic hormone ANP that inhibit vasopressin production.
• Oxytocin is proteinaceous of 10 aa sequences, and it function in contraction of smooth muscles of uterus during time of parturition.
• High prolactin levels in blood are responsible for the initiation of maternal behavior in the first-time pregnant rats after parturition.

Thyroid gland It is largest gland of body. It is only gland which stores its own secretion. It is located close to larynx anteroventral side of trachea. It is bilobed structure. Its size depends on age, sex and physiological conditions. Fack lobe consists of thyroid follicles. Thyroid follicles are lined by simple cuboidal follicular epithelium and inside its follicle cavity, hormone is stored.

Formation of Thyroxine: -

• Iodine trapping Active transportation of iodide in epithelium occurs from blood circulating in thyroid gland.

• Formation of thyroglobulin Rough endoplasmic reticulum of follicular epithelium cells which are rich in tyrosine secretes thyroglobulin through exocytosis and reach the lumen of thyroid follicles. 

• Oxidation of iodide: - I + I = I2 molecule.

• Iodination of thyroglobulin: - If 1 molecule of iodine (l,) is added it forms monoiodotyrosine (T1) and if 2 molecules of iodine (I) is added it forms diiodotyrosine (T2). 
•  Coupling of T and T2: - Two molecules of T, combine to form mono-iodotyrosine which is formed but not active. One abundantly T1 and one T2 molecule combine to form T3 which is biological active form.
• Pinocytosis: - is mechanism through which T4 and T3 enter follicular epithelium cells and gets digested by lysozyme and then enter blood.

Function of Thyroxine: -

It increases metabolic rate, increase use of glucose and oxygen for ATP synthesis, increase body temperature stimulating protein synthesis, accelerate tissue growth and decrease body weight.

• Calcitonin: - is a protein hormone that is synthesized and secreted by humans and other mammals primarily by the parafollicular cells (C cells) in the thyroid gland. The overall effect of calcitonin is to lower the concentration of calcium in the blood when it rises above the normal value. It also lowers the concentration of phosphorus in the blood when levels exceed normal. 
•  Parathyroid Gland: - It is present at the back of thyroid gland. It is small oval yellowish brown and is present in 4 pairs. Upper pair is known as superior parathyroid and lower pair is known as inferior parathyroid. Parathyroid glands consist of 2 type of cells called principal cells which are smaller in size with large nucleus and no granules. Parathyroid hormone is also called collapse's hormone which deals with regulation of calcium and phosphorus balance. It increases blood calcium due to dissociation of calcium from bones.
  
  
  
  

ABNORMALITIES: - 

1. Hypersecretion 

2.Parathyroid tetany i.e., Ca+ increases 

3.Hypersecretion 

4.Ca++ dissolve in irregular manner, bone porous and osteoporosis. 

nephron, types of nephrons, Structure of nephrons, Short notes of nephron,

  Nephron  

A nephron is a unit of structure and function in a kidney. Number and Size. A kidney contains about a million nephrons, each approximately 3 cm. long There is, thus, an enormous surface area for the exchange of materials in a kidney.

Types of Nephrons: -

Nephrons are of two types: - Cortical and Juxtamedullary, with regard to their location in the kidney. The cortical nephrons form about 80% of the total nephrons. They lie in the renal cortex and have very short loops of Henle that extend only a little into the medulla. The juxtamedullary nephrons have their Bowman's capsules close to (juxta) the junction of the cortex and the medulla, and have very long loops of Henle, extending deep into the medulla The cortical nephrons control the plasma volume when water supply is normal. The juxtamedullary nephrons regulate the plasma volume when water is in short supply.

Structure of Nephron: -

A nephron 1s a long tubule differentiated into four regions having different anatomical features and physiological role: Bowman's capsule. proximal convoluted tubule (PCT), loop of Henle, and distal convoluted tubule (DCT). The latter opens into one of the collecting ducts.

(i) Bowman's Capsule.: - The Bowman's capsule is a large, double-walled cup. It lies in the renal cortex and forms the beginning of the nephron. It contains a glomerulus in it. Inner wall of the Bowmans capsule, called the visceral wall is in close contact with the glomerular capillaries its outer wall is continuous with the rest of the nephron. The space between the two walls of the Bowman's capsule is continuous with the lumen (Cavity) of the next part of the nephron The Bowman's capsule and the glomerulus (a group of about 50 capillaries) together form a globular body called renal corpuscle, or Malpighian body. The endothelial cells forming the wall of the glomerular capillaries have pores between them called fenestrae. The cells rest on a basement membrane. The podocytes forming the inner wall of the Bowman's capsule have gaps, the stilt-pores, between them. Thus, the basement membrane of the capillary wall is the only continuous layer between the blood in the glomerular capillaries and the lumen of the Bowman's capsule. This facilitates the process of ultrafiltration. The outer wall of the Bowman's capsule consists of unspecialized squamous epithelium.

ii) Proximal Convoluted Tubule (PCT).: - I starts from the neck of the Bowman's capsule and i greatly twisted. It also lies in the renal cortex. Its wall consists of a single layer of columnar cells bearing microvilli on the free surface and resting on a basement membrane (hg 20.14)

iii)Loop of Henle.: - It is a U-shaped segment of the nephron located in the renal medulla. It consists of two straight parallel limbs: a descending limb which is aa continuation of PCT into the renal medulla and an ascending limb which reenters the renal cortex and joins the DCT Each limb has a thick region toward the cortex and a thin region on the other side. The thick regions are walled by columnar cells, and the thin regions by flat cell.

iv)Distal Convoluted Tubule (DCT).: -Like the PCT. it is greatly twisted and lies in the renal cortex into A short a terminal relatively straight part of the DCT is called collecting tubule. The 1a DT hag collecting duct. The cells forming the wall of the DCT are similar to those in the PCT wall. The D JUxtaglomerular apparatus (JGA). It is a special sensitive region formed by cellular modifications in distal cOnvoluted tubule and the afferent arteriole at the location of their contact. This mechanisim playo role in the regulation of glomerular filtration rate. Collecting Ducts. These are larger tubes, each receiving the collecting tubules of several Deprons. They pass into the renal medulla and join each other, forming still larger ducts of Bellini. Tnese ru through the medullary pyramids and open into calyces, which lead into the pelvis. The collecting ducts are lined by cuboidal and columnar cells in different regions. At intervals, the cuboidal cells are ciliated.

amino acid, amino acid classification and properties, type of amino acid, what are amino acid,

  Amino acids are organic compounds containing amine [- NH2] carboxyl [-COOH] side chain [R group] The major key elements if amino acids are carbon, hydrogen, nitrogen, oxygen. About 500 amino acids are known (though only 20 appear in the genetic code) and can be classified in many ways.

  AMINO ACID  

BASIC STRUCTURE [SKELETON] OF AMINO ACID: -