Pituitary Gland, Pineal Body and Pancreas | Biology Class 11 - NEET PDF Download

Pituitary Gland

• On the basis of development, pituitary gland is completely Ectodermal.
• It is situated in the sella–turcica of sphenoid bone.
• This gland is attached to the hypothalamus through a stalk which is called as infundibulum.
• The upper terminal end of infundibulum which is attached to the hypothalamus is called as tubercinerium/ Median eminence.
• The lower terminal end of infundibulum is bulging type which is called as posterior lobe or pars nervosa.
• Tubercinerium, infundibulum & pars nervosa are collectively called as Neurohypophysis.
• A small & fine tube is developed in the foetus which is called as gut. This gut is developed into alimentary canal. Anterior part of gut is called as stomodaeum (developed from ectoderm).
• A small projection is developed from dorsal surface of stomodaeum (the anterior part of gut) this part is separated from stomodaeum and forms the Rathke’s pouch.
• Upper surface of Rathke’s pouch is developed into mid–lobe which is also known as pars intermedia.
• The upper margin of R.pouch, which surrounds the infundibulum & forms a collar like structure is called as parstuberalis.
• Remaining part of R.pouch. is developed into anterior lobe which is also called as pars distalis.
• Pars distalis, pars tuberalis & pars intermedia are collectively called as adenohypophysis.
• Neurohypophysis + Adenohypophysis is called as hypophysis cerebri or pituitary body.
• A remaining & vestigeal cavity of R.pouch is found in the anterior lobe which is called as Hypophysis recess.
• Superior branch of hypophyseal artery supplies blood to the hypothalamus.
• Inferior branch of hypophyseal artery supplies blood to the pituitary gland.

Hypophyseal portal vein collects the blood from hypothalamus and supplies to the pituitary gland.

• Branch of hypophyseal artery & hypophyseal portal vein form a network of blood capillaries which is called as circle of Willis.
• In human, mid lobe is ill developed or membrane like, while mid lobe is absent in elephants & Whales.
• Three types of glandular cells are found in Adenohypophysis.

1. Basophils → They are large cells & found in the peripheral part of gland. They are more in number.

2. Acidophil → They are small in size & found in the central part of pituitary gland.

3. Neutrophils → They are smallest in size and are found in scattered form. They are minimum in number.

• STH & LTH are secreted by acidophils.
• Remaining hormone of adenohypophysis are secreted by basophils.
• All hormones of pituitary gland are protein Hormones.

Hormones Secreted by Adenohypophysis

All these hormones are of proteinaceous nature:

1. Growth Hormone/Somatotropic Hormone/Somatotropin Hormone [GH or STH]: By Somatotroph Cells

Functions: 

Major effect: On metabolism.

Major effect: On growth.

Effect on Growth:

(1) On bone : It increases the longitudinal length of bone.

(2) On soft tissue : 
(i) GH promotes mitosis & increases number of cells in many organs & tissues. e.g. liver.

(ii) GH stimulates growth of muscle and cartilage due to increase synthesis of collagen, muscle grow in bulk.

Effect on Metabolism:

(i) Fat: Increases lipolysis so that free fatty acid level of plasma rises. Under the influence of growth hormone, fat is used for energy in preference to carbohydrate and protein, due to this protein deposition increases.

(ii) Carbohydrate: Hyperglycemia develops due to decreased uptake of glucose in the cells, so it is also called diabetogenic hormone.

(iii) Protein: GH increases amino acid uptake by the cells of the liver & muscles & helps in protein synthesis. 

In the presence of thyroxine and insulin, growth hormones become more active and help in body growth. 

In this way this hormone is important for the growth of body.

Diseases due to hyposecretion or hypersecretion of somatotropin hormone:
(a) Hyposecretion of STH :– Due to deficiency of STH in childhood or adolescence, dwarfism is observed. Dwarfism due to the defect of pituitary is called Ateliosis. Clowns of circus are such dwarfs, they are called midgets. This midget is physically & mentally normal while sexual maturation is delayed. 

(b) Hypersecretion of STH :– Due to hypersecretion in childhood and adolescence, a higher quantity of aminoacids is supplied to the body cells. 

(i) Epiphyseal cartilage present on the edges of bones does not convert into bone for a long time.  Thus the bones of legs & hands become very long and height of that person increases very much. Body becomes imbalanced. This disease is called Gigantism.

(ii) Acromegaly :– Due to hypersecretion of STH in adulthood, jaw bones of the affected person become long, cheek bones buldge out, broad hands, legs & fingers of person becomes gorilla like. These symptoms are observed as a result of acromegaly.

2. Thyrotrophic/ Thyroid Stimulating Hormone  [TTH OR TSH]

• T.S.H is secreted by basophil cells (Thyrotroph cell).
• It is glycoprotein in nature.
• T.S.H stimulates thyroid gland to secrete thyroxine. TSH helps in almost all step of the thyroid hormone synthesis & it causes growth of thyroid gland.
• Secretion of TSH is stimulated by Thyrotrophin releasing factor & inhibited by somatostatin of hypothalamus.

3. Adrenocorticotrophic/ Corticotropine [ACTH]

• ACTH is secreted by basophil (corticotroph) cells.
• In the ACTH of man, valine and tyrosine aminoacids are more in quantity.
• It accelerates the cortex part of adrenal gland to secretes hormones. 

4. Follicle Stimulating Hormone [FSH]

• It is also secreted by basophils. (Gonadotroph cell)
• It is a glycoprotein in nature.
• This is secreted in male and female both.
• In males, it stimulates spermatogenesis and normal functioning of seminiferous tubules.
• In females, it stimulates oogenesis and development of Graafian follicles in ovary.
• FSH is also known as Gametokinetic factor.
• Estrogen hormone that is secreted by Graafian follicles is also affected by FSH. 

 5. Luteinizing Hormone/ Interstitial Cell Stimulating Hormone [LH OR ICSH]

• It is also secreted by basophil (Gonadotroph) cells. It is also a glycoprotein in nature.
• It stimulates ovulation in female as a result of this corpus luteum is formed.
• Hormone progesterone which is secreted by corpus luteum is also stimulated by L.H.
• In men LH is called ICSH. It affects the Leydig's cells or Interstitial cells of testes and stimulates the secretion of male hormone " Testosterone".
• L.H. is also called " gamete releasing factor".
• FSH and LH both are called gonadotrophic hormone GTH.
• FSH and LH act in combined form so these are called synergesic hormone.
• Gonadotrophic hormones (FSH & LH) secretion start secreting during puberty. Their secretion is regulated by hypothalamus. It is supposed that there a biological clock present to control all this. 

6. Luteotrophic/Prolactin/Lactogenic/ Mammotropic Hormone [PRL]

It is secreted by acidophil (Lactotroph) cells.

Function of prolactin hormone:

Lactation (Galactopoiesis) :- Prolactin is responsible for lactation in postpartum (after delivery) women. 

• Regulation of Prolactin secretion by Hypothalamus :- Hypothalamus mainly stimulate the production of all pituitary hormone, but it mainly inhibits prolactin production because normally hypothalamus prolactin inhibitory hormone (Dopamine) is greater than the releasing hormone.
• Breast is prepared for lactation by oestrogen (duct growth) and progesterone (lobule growth) but both of these hormone inhibit the actual secretion of milk.
• Dopamine is a catecholamine (Biologically active amine) and neurotransmitter in the hypothalamus. It inhibits lactation.
• During pregnancy :- Prolactin hormone steadily increase until term but due to high level of oestrogen and progesterone (secreted by placenta) lactation is inhibited.
• After expulsion of the placenta at parturition, there is an abrupt decline in circulating estrogen and progesterone.
• The drop of circulating estrogen initiate lactation.
• Nursing stimulates prolactin secretion.
• Prolactin inhibits the action of GnRH on the pituitary and antagonize the action of gonadotrophin on the ovaries. Ovulation is inhibited and the ovaries gets inactive.
• Nursing is important and effective method of birth control. 

Hormones secreted ny Posterior Lobe of Pituitary or Neurohypophysis

Posterior lobe of pituitary gland is 1/4th part of total gland. It is just like nervous tissue, because in it, the terminal ends of the axons of neurosecretory cells of hypothalamus are swollen. These swollen ends are called " Herring bodies". Hormones are released in these bodies.

1. Vasopressin or Pitressin or Anti Diuretic Hormone [ADH]

Main functions of ADH :– Its main function is to increase the reabsorption of water in collecting duct and in distal convoluted part of uriniferous tubules. Due to this, amount of urine is reduced. So it is also called ADH.

•  The hormone increases the blood pressure by constriction of blood vessels of tissues.
• Due to hyposecretion of ADH or vasopressin, the amount of urine increases, this process is called Diuresis.
• Patient feels thirsty, Dehydration starts in the body. This disease is called Diabetes insipidus (taste less urine, polyuria).
• Due to hyposecretion of ADH, deficiency of water starts in Extra cellular fluid (ECF), Blood pressure reduces, urine becomes dilute and blood becomes thick or concentrate.
• Intake of coffee, tea and excess alcohol etc decrease the secretion of ADH.
• Secretion
• Kangaroo – Rat (Dipodomys) also shows hypersecretion of ADH. Kangaroo - Rat never drinks water in its life- time. Hypersecretion of ADH causes dilution of blood and increases concentration of urine and thus blood pressure increases.

2. Oxytocin or Pitocin

It is the main parturition hormone. It stimulates the fast/ rapid contractions and expansions of non- striated muscles of the uterine wall at the last moment of gestation period (pregnancy). Due to this uterine constrictions, labour pains start just before child birth.

• This hormone is secreted by pituitary glands of mother at the time of parturition.
• This hormone also initiates the contractions in uterine wall muscles during copulation/ coitus as a  result of that semen of man is sweeped out in the fallopian tubes of woman.
• After parturition, this hormone constricts the uterine wall and thus brings back to the normal position.
• Oxytocin hormone contracts the myoepithelial cells present at all the sides of alveoli of mammary glands. Thus it helps in milk ejection so it is also called milk let down hormone. 
• In female, this hormone related with emotion.
• Even thought, cry or sound of baby can bring about release of this hormone in lactating mother.

This hormone helps during egg laying in birds.

Injection of oxytocin are initiates cows and buffaloes for instant milk release.

Hormones Secreted by Middle Lobe of Pituitary Gland

• The part of adenohypophysis of pituitary gland, which is very close to neurohypophysis is a very thin portion, it is called pars intermedia or middle lobe of pituitary gland.
• In men, it is in the form of a thin membrane only. It is inactive in men.  

1. Melanocytes Stimulating Hormone [MSH] 

• It is secreted by middle lobe (By corticotroph cell).
• MSH is also called Intermedin.
• In man, MSH is secreted by anterior lobe, because middle lobe is ill- developed.
• It stimulates the melanocytes to synthesize melanin in mammals.
• This hormone is related with change in the colour of skin in Amphibian and Reptiles. This phenomenon of colour changing is known as metachrosis.
• It darkens the complexion of skin by distributing melanin pigment evenly under the skin.
• Just opposite to it, melatonin secreted by pineal body, collects the melanin pigments at one place thus fairing the complexion of skin.
• MSH is found in all the vertebrates, but it is functional in poikilothermic animals e.g. fishes, amphibians, reptiles etc.
• The importance of MSH in man has not been evaluated. 

Hormone Releasing Factors of Hypothalamus

Hormones secreted by adenohypophysis of pituitary gland are under the control of neuro- secretory cells of hypothalamus. These neuro-secretory cells produce some substances in very small amount which are called releasing factors.

(1) Growth Hormone Releasing Factor [GHRF]:- It stimulates the secretion of growth hormone.

(2) Thyrotropin Releasing Factor [TRF]:- It stimulates the secretion of TSH.

     GnRH Follicle stimulating hormone releasing factor [FSHRF] :– It stimulates the secretion of FSH.

     GnRH Luteinising hormone releasing factor [LHRF] :– It stimulates the secretion of LH.

(4) Growth Hormone Inhibitory Factor [GHIF] (Somatostatin) :– It inhibits the secretion of GH.

(5) Prolactin Release Factor [PRF] :– It stimulates the secretion of Prolactin.

(6) Prolactin Inhibitory Factor [PIF] (Dopamine) :– It inhibits the secretion of Prolactin.

(7) Melanocyte Release Factor [MRF] :– It stimulates the secretion of MSH.

(8) Melanocyte Inhibitory Factor [MIF] :– It inhibits the secretion of MSH.

(9) Adrenocorticotropic Releasing Hormone (CRH) :– It stimulates secretion of Adrenal cortex hormone.

Pineal Body

Position

• It is situated at the dorsal side of diencephalon of anterior part of brain i.e. prosencephalon. It is also known as Epiphysis cerebri. Pineal body is a part of brain. It is ectodermal in origin.
• There are pinealocyte cells (formed by the modification of nerve cells) and supporting interstitial cells or neuroglial cells in pineal body.
• Pineal body called as third eye in frog.

Hormone & Functions 

• Pineal body secretes a hormone melatonin, which is an amino acid.
• Melatonin is functional in lower vertebrates only.
• In amphibians and reptiles, this hormone is related with metachrosis (change in the colour of skin). It affects the Melanophores of skin, thus acts antagonistically to the MSH of pituitary i.e. it fairs the complexion of skin.
• Mid part of gland secretes antigonadial hormone.
• This hormone controls the sexual behaviour in mammals. It inhibits the sexual irritation, and also inhibits the development of genitalia and their functions.
• If pineal body is removed from rat, these will attain premature adolescence.
• The gland probably controls the sexual behaviour according to light differentiation, thus it acts as a biological clock.
• It is proved that the level of melatonin rises during periods of darkness and falls during periods of light.
• Children blind from birth attain puberty earlier than normal.
• Maximum development of pineal body upto 7 years & then it undergoes involution & at the age of 14 years interstitial tissue and crystals of CaCO3 or Ca3PO4 are deposited in it, these are called "Brain sand" or "Acervuli"

Pancreas

Position 

These are exocrine in nature. There are found numerous small endocrine glands scattered in between the acini, these small endocrine glands, are called Islets of Langerhans. They form only 1% part of the gland. These were discovered by Langerhans.

Each Islet of Langerhans has 4 types of cells. They are:

(A) Alpha cells (α - cells) : These are the largest cells present in peripheral region these are approximately 25% of the total cells. They secrete glucagon hormone.

(B) Beta cells (β- cells) : These are the small cells present in central region. These are about 60–65% part of total cells. They secrete Insulin hormone.

(C) Delta cells (d - cells) OR Gamma cells (g - cells) : These cells are found in middle region. These are about 10% part of total cells .They secrete somatostatin hormone which regulates the activities of α-cells and β - cells.

(D) F cell or PP– cells : Along with above mentioned cells, some other cells are also found in islet of Langerhans, these are called PP - cells which secrete pancreatic polypeptide hormone.

(1) Insulin 

• It was first prepared/found by Banting and Best.
• Molecular structure of insulin was given by A.F. Sanger (with the help of cow's insulin) The term insulin was also given by A.F. Sanger.
• Insulin is the first protein that is artificially synthesized in lab and is crystallized.
• Human insulin was synthesized by "Tsan"
• One molecule of Insulin is made up of 51 - amino acids that has 2 chains.
  (i) α - chain - It is made up of 21 aminoacids
  (ii) β - chain - It is made up of 30 amino acids. Both the branches or chains are bind together with cross bonds of disulphide bonds.
•  "A.F. Sanger"  was awarded by Noble Prize for it.

Functions of Insulin Hormone 

(I) Actions on cell membrane permeability.

(II) Actions on metabolism of : Carbohydrate, Protein, Fat, Nucleic acid, Mineral.

Hyposecretion of Insulin 

• Due to hyposecretion of insulin, body cells cannot use the sugar stored in blood. 
• So amount of sugar is increased in blood and this disease is called "Diabetes mellitus" or sugar disease. 
• In this disease, concentration of glucose in blood is increased from normal concentration.
• World diabetes day - 14 November

• Glucose is excreted through urine, if amount of glucose is in excess in the blood, this is known as "Glycosuria".
• In this stage. amount of glucose in blood increases upto > 180 mg./dl. of blood.
• The amount of water increased (in this stage) in the urine, so intervals of urination gets reduced, it is called polyuria.
• Polydipsia :- Due to excess excretion of urine (Urination at short intervals) probability of dehydration is enhanced.
• The patient feels thirsty, and there is a continuous loss of electrolytes from the body. 
• Polyphagia : excessive hunger.
• Due to active and incomplete decomposition of fats in fatty tissues, ketone bodies are formed. These ketone bodies are acetone, aceto acetic acid and beta hydroxy butyrate. Due to increased amount of these ketone bodies ketoacidosis starts in the body. These bodies are poisonous.
• The combined effect of ketoacidosis, dehydration and hyperglycemia may cause diabetic comma to the patient, patient becomes unconscious and even may die.
• Insulin hormone is given to the patient by injection in this disease, Insulin given orally is not effective, because it digests in the alimentary canal like protein.
• Now a days, oral insulin is used in following states :-
  (A) IZS - Insulin Zinc Suspension.
  (B) PZI - Protamine Zinc Insulin.

Hypersecretion of Insulin

• Due to hypersecretion of insulin, amount of glucose decreases in blood. It is called hypoglycemia.
• In hypoglycemia stage, body cells take more and more glucose from blood. So need of glucose for nervous system, retina of eye, genital epithelium is not fulfilled, as a result of that patient looses its reproductive power and sight. Due to excess irritation in brain cells, patient feels exhausted, unconsciousness, Cramps, and at last patient may die.
• "Insulin shock" - At the time of physical labour or fasting, if a diabetic patient takes an insulin injection, sugar level in blood reduces quickly up to 40 mg/100ml of blood. It is called insulin shock. The patient may be unconscious or even may die. 

(2) Glucagon

• This is secreted by α-cells.
• It was discovered by "Kimball and Murlin." 
• Glucagon is a hyperglycemia factor.
• It is made up of chain of polypeptide 29 amino acids.
• It is antagonistic to insulin. It is secreted by the gland, when sugar level of blood reduces.
• Glucagon hormone increase the amount of sugar (glucose) in blood.
• It stimulates gluconeogenesis in liver, as a result of that amount of glucose in the blood increases.
• It stimulates lipolysis of fats in fatty tissues.
• It decomposes the glycogen into glucose in liver i.e. it stimulates "glycogenolysis" in liver.
• The secretion of insulin and glucagon is controlled by a limit control feed back. When amount of sugar is increased in blood, then insulin is secreted by β-cells. As a result of it, when amount of glucose is reduced in blood, then glucagon is secreted by-cells. 

(3) Somatostatin

(4) Pancreatic Polypeptide (PP)