Plus One Zoology Notes Chapter 11 Chemical Coordination and integration is part of Plus One Zoology Notes. Here we have given Kerala Plus One Zoology Notes Chapter 11 Chemical Coordination and integration.
|Text Book||NCERT Based|
|Chapter Name||Chemical Coordination|
|Category||Kerala Plus One|
Kerala Plus One Zoology Notes Chapter 11 Chemical Coordination and integration
The endocrine system includes endocrine glands and their secretions called hormones. The endocrine system operates as a chemical communication system. They work closely in association with the nervous system.
Endocrine glands and Hormones
- Endocrine glands secrete a chemical substance called Hormones.
- Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts,
- Hormones coordinate the activities that take place within cells and between the cells.
- They release their secretion directly into the blood.
- The endocrine gland has no ducts. Hence they are ductless glands.
- Invertebrates possess very simple endocrine systems with few hormones, whereas a large number of chemicals act as hormones and provide coordination in the vertebrates.
Human Endocrine System
- The endocrine system is a chemical coordination system in the body.
- Endocrine glands and hormone-producing diffused tissues or cells located in different parts of our body constitute the endocrine system.
- The major endocrine glands that make up the endocrine system are a pituitary gland, hypothalamus, thyroid glands, parathyroid glands, adrenal gland, pineal body and the reproductive gland that include testis in male and ovaries in a female.
- The organs like gastrointestinal tract, liver, kidney and heart also produce hormones.
- It is located in the basal part of diencephalon of the forebrain.
- It has several groups of neurosecretory cells called nuclei that produce hormones.
- The synthesis and secretion of pituitary hormones are regulated by these hormones.
- Hormones originate from hypothalamic neurons, pass through axons and are released from their nerve endings.
- These hormones reach pituitary gland through the portal circulatory system and regulate the functioning of the anterior pituitary.
- The posterior pituitary is under the direct neural regulation of the hypothalamus.
- Hormones from hypothalamus are of 2 types.
i. Releasing hormone It stimulates the secretion of pituitary hormones.
Eg., Gonadotropin-releasing hormone (GnRH) Stimulates release of gonadotropins from the pituitary.
ii. Inhibiting hormone It inhibits the secretion of pituitary hormones.
Eg., Somatostatin Inhibits the release of growth hormone from the anterior pituitary
2. Pituitary Gland
- It is the smallest endocrine gland.
- It is located in a body cavity called Sella Corsica and is attached to the hypothalamus by a stalk.
- Anatomically, it is divided into two
It is further divided into two portions.
A. Pars distalis commonly called anterior pituitary. It produces hormones like.
a. Growth hormone (GH)/ somatotropic hormone
b. Prolactin (PRL)
c. Thyroid stimulating hormone (TSH)
d. Adrenocorticotrophic hormone (ACTH)
e. Luteinizing hormone (LH)
f. Follicle Stimulating Hormone (FSH)
a. Growth hormone (GH)
- It promotes the growth and development of the body.
- Hyposecretion (low secretion) of GH leads to Dwarfism, results in stunted growth.
- Hypersecretion (over secretion) of GH leads to Gigantism, results in the abnormal growth of the body.
b. Prolactin (PRL)
It regulates the growth of mammary glands and the formation of milk.
c. Thyroid stimulating hormone (TSH)
It stimulates the secretion of thyroid hormones from the thyroid gland.
d. Adrenocorticotrophic hormone (ACTH)
Stimulates the synthesis and secretion of steroid hormones called glucocorticoids from the adrenal cortex.
(e) Gonadotrophic hormone
Gonadotropic hormones regulate .thegrowth and functioning of gonads, so they are called gonadotrophins.
In males, it stimulates synthesis and secretion of androgens from testis. In females, it induces ovulation and maintains the development of corpus luteum.
It stimulates gonadal activity. In males, FSH and androgen stimulate spermatogenesis. In females, it stimulates the growth and development of the ovarian follicles and ovum.
B. Pars intermedia
- In humans, it is almost merged with pars distalis.
- It secretes only one hormone, melanocyte stimulating hormone (WISH)
- MSH acts on melanocytes to regulate pigmentation of the skin.
Also known as posterior pituitory. It stores and releases two hormones, namely
ii. Vasopressin (ADH)
- It acts on the smooth muscles of mammary glands and uterus and stimulates their contraction.
- In females, contraction of the uterus at the time of child birth and milk ejection from the mammary glands is aided by oxytocin.
- Also called Anti diuretic hormone (ADH).
- It stimulates the reabsorption of water and electrolytes by the DCT and there by reducing the loss of water through urine (diuresis).
- Hyposecretion of ADH causes Diabetes insipidus.
- Caused due to decreased reab sorption of H2O from the col lecting tubules.
- Characterised by diuresis
3. Pineal Gland
It is located on the dorsal side of the forebrain and secretes a hormone called Melatonin.
Functions of Melatonin
- It regulates the diurnal ie 24-hour rhythm of the body. Eg Maintenance of sleep wake cycle, body temperature.
- Influences metabolism, pigmentation, menstrual cycle, as well as our defence capability
4. Thyroid Gland
- It is the largest endocrine gland.
- It includes 2 lobes located on either side of the trachea.
- The lobes are interconnected with a connective tissue called isthmus.
- The thyroid gland is composed of follicles and stromal tissues.
- Each thyroid follicle is composed of follicular cells, enclosing a cavity.
- Follicular cells synthesise two hormones.
a. Tetraiodothyronine or thyroxine (T4).
b. Triiodothyronine (T3).
- hyroid gland also secretes a protein hormone called thyrocalcitonin (TCT) which regulates the blood calcium level.
Functions of Thyroid hormone (T3 and T4)
- They help in the regulation of basal metabolic rate (BMR).
- They support RBC formation.
- They control the metabolism of carbohydrates, proteins and fats.
- They help in the maintenance of H2O and electrolyte balance.
- Decreased secretion of thyroxin from the thyroid gland. It leads to,
i. Goitre Enlargement of the thyroid gland due to deficiency of iodine. Hypothyroidism during pregnancy affects the infants and causes
– Stunted growth (cretinism)
– Mental retardation.
– Low intelligence Quotient.
– Abnormal Skin.
– Deaf Mutism.
Hypothyroidism may cause the menstrual cycle to become irregular.
- The condition in which rate of synthesis ’ and secretion of the thyroid hormone is increased to high levels,
- It is due to cancer of thyroid gland or due to the development of nodules of the thyroid glands.
Eg., Grave’s disease or exophthalmic goitre.
- Enlargement of the thyroid gland
- Increased BMR.
- Increased heart rate and pulse rate.
- Reduced body weight.
- Bulging of the eyeball.
5. Parathyroid Gland
- In humans, four parathyroid glands are present on the back side of the thyroid gland,
- One pair each in the two lobes of the thyroid gland.
- They secrete parathyroid hormone (PTH) which is a peptide hormone.
- The secretion of PTH is regulated by the circulating levels of calicum ions.
Functions of PTH
- Increases the Ca2+ levels in the blood(Hence called hypercalcemic hormones).
- It Stimulates the process bone re sorption [demineralisation],
- It stimulates the reabsorption of Ca2+by the renal tubules and increases Ca2+ absorption from the digested food.
- Along with TCT, It helps in Ca2+ balance In the body.
6. Thymus Gland
- It is a lobular structure located on the dorsal side of the heart and aorta.
- It secretes a peptide hormone called “Thymosin”.
- The thymus is degenerated in old individuals resulting in a decreased production of thy mosins.
- As a result, the immune responses of old persons become weak.
Functions of Thymosin
- It helps in the differentiation of TLym J phocytes which provide cell medl 1 ated immunity
- It promotes the production of antibodies 1 for humoral immunity.
7. Adrenal Gland
- The adrenal gland is a pair of glands, located at the top of each kidney.
- The gland is composed of two types of tissues
i. Adrenal medulla
ii. Adrenal Cortex
♦ Adrenal Medulla
- Central Part of the adrenal gland
- It secretes two hormones.
(a) Adrenaline (Epinephrine)
(b) Noradrenaline (Norepinephrine)
- Adrenaline and noradrenaline are collectively called Catecholamines.
Functions of Adrenaline
- It increases the rate of heart beat.
- It increases alertness, pupilary dilation, piloerection (raising of hairs), sweating, heart beat, heart contraction and rate of respiration.
- They increase the blood sugar level by stimulating glycogenoly sis in the liver and muscles.
- These hormones are rapidly secreted in response to any stress and emergency situations and are called emergency hormones [hormones of fight or flight].
♦ Adrenal Cortex
- It lies outside the adrenal medulla.
- It can be divided into 3 layers,
- Zona reticularis (inner layer)
- Zona fasciculata (middle layer)
- Zona glomerulosa (outer layer)
- Adrenal Cortex secretes many hormones commonly called as Corticoids.
- It lies outside the adrenal medulla. They include glucocorticoids and mineralocorticoids.
It includes mainly cortisol and cortisone, secreted by Zona fasciculata of the adrenal cortex
- Involved in carbohydrate metabolism and stimulates gluconeogenesis, lipolysis and proteolysis.
- It inhibits cellular uptake and utilisation of amino acids.
- Cortisol maintains the cardiovascular system as well as kidney functions.
- Cortisol stimulates RBC production.
- It produce antiinflammatory reactions and suppresses immune response.
Secreted by the adrenal cortex in small amounts.
- It plays a role in the growth of axial hair, pubic hair and facial hair during puberty.
It includes mainly Aldosterone, secreted by the zona glomerulosa of the adrenal cortex. Functions It regulates the balance of water and electrolyte, body fluid volume, osmotic pressure and blood pressure. It stimulates the reabsorption of Na’ and water from renal tubules and excretion of K+ and phosphate ions.
- The endocrine pancreas consists of ‘ Islets of Langerhans’.
- It is a composite gland which acts as both endocrine (with duct) and exocrine (without duct) gland.
- Endocrine part is formed of about 1 2 million Islets of Langerhans.
- The islets of langerhans have two types of cells, alpha (a ) cells and beta (p )cells.
- Alpha cells secrete glucagon, s Beta cells secrete insulin.
Glucagon is a peptide hormone secreted by alpha cells. Secretion is stimulated by low blood sugar level.
- It maintains blood glucose level.
- It acts on hepatocytes and stimulates glycogenolysis resulting in increased blood sugar (hyperglycemia).
- It stimulates gluconeogenesis
- Itreducescellularglucoseuptakeand utilization. Thus, glucagon is a hyperglycemic hormone
It is a hypoglycemic factor, secreted by beta cells. Secretion is stimulated by higher glucose level in blood than the normal level.
- It stimulates the utilization of glucose as respiratory fuel in body cells.
- It stimulates glycogenesis(conversion of glucose to glycogen). The rapid conversion of glucose from the blood to glycogen in hepatocytes and adipo cytes results into a deceased glucose level.
- Prolonged hyperglycemia leads to Dia betes mellitus.
♦ Diabetes mellitus
The abnormal high glucose level in the blood due to hyposecretion or lack of insulin in blood This leads to loss of glucose through urine and formation of harmful compounds known as ketone bodies. Treated with insulin ther apy.
- A pair of the testis is present in the scrotal sac (outside the abdomen ) of male individuals.
- Testis performs dual functions as a primary sex organ as well as an endocrine gland.
- It is composed of seminiferous tubules and interstitial or stromal tissue.
- The leydig cells in the intertubular spaces are stimulated to secrete male sex hormone called androgens, mainly testosterone.
Functions of androgens
- They regulate the development, maturation and functions of accessory sex organs like epididymis, vas deferens, seminal vesicles, prostate gland, urethra etc.
- It stimulates spermatogenesis.
- These hormones stimulate male sexual behaviour (libido), a growth of muscles, hairs, aggressiveness, low pitch voice etc.
- These hormones produce anabolic effects on protein and carbohydrate metabolism.
- A pair of ovaries are located in the abdomen of females.
- An ovary is the primary female sex organ formed of ovarian follicles and stromal tissues.
- After ovulation, the ruptured follicleis converted to a structure called corpus luteum.
- Ovarian follicle secrete Estrogen while corpus luteum secretes Progesterone.
Functions of Estrogen
- Estrogen stimulates the growth and activi ties of female secondary sex organs, de velopment of ovarian follicles.
- It as a role in the appearance of female secondary sex characters (high pitch voice), Mammary gland development.
- It also regulates female sexual behaviour.
Functions of Progesterone
- It supports pregnancy.
- It acts on mammary glands to stimulate the formation of alveoli sacs (sac to store milk) and milk secretion.
Hormones of Heart, Kidney and Gastrointestinal tract
- The atrial walls of the heart secretion hormone called atrial natriuretic factor (ANF).
- When blood pressure increases, ANF is secreted and causes dilation of blood vessels which reduce the blood pressure.
- The juxtaglomerular cells of kidneys produce a peptide hormone called Erythropoietin.
- Stimulates erythropoiesis (formation of RBC).
♦ Gastrointestinal tract
Endocrine cells of Gl tract, secrete four peptide hormones.
- Cholecystokinin (CCK)
- Gastric inhibitory peptide (GIP)
Acts on the gastric glands and stimulate the secretion of hydrochloric acid and pepsinogen.
Act on the exocrine pancreas & stimulate the secretion of water and bicarbonate ions.
It acts on both pancreas and gall bladder and stimulates the secretion of pancreatic enzyme and bile juice.
Gastric inhibitory peptide (GIP)
It inhibits gastric secretion and motility.
Hormones secreted by other non endocrine tissues are called growth factors. These factors are essential for the normal growth of the tissues and their repairing and regeneration.
Mechanism of Hormone Action
- Hormones produce their effects on target tissues by binding to specific proteins called hormone receptors.
- Binding of a hormone to it’s receptor leads to the formation of the hormone receptor complex.
- Each receptor is specific to one hormone only.
- ormone receptor includes, membrane bound receptors and intracellular receptors.
- Membranebound receptors Receptors present on the cell membrane of the target cells.
- Intracellular receptors Receptors present inside the target cells.
- Hormone receptor complex formation leads to biochemical changes in the target tissue, and regulates metabolism and physiological changes.
- On the basis of chemical nature, hormones can be divided into groups.
- Peptide, Polypeptide, Protein hormones.
Eg., Insulin, glucagon, pituitary hormon I es, hypothalamic hormones etc.
Eg., Cortisol, testosterone, estra j diol and progesterone.
- lodothyronens (Thyroid hormones)
- Amino acid derivatives.
Diagrammatic presentation of the mechanism of hormone action of a protein hormone
- Peptide, Polypeptide, Protein hormones.
- Hormones which interact with membrane bound receptors normally do not enter the target cell, but generate second messengers (eg..cyclic AMP, IP3, Ca++), which inturn regulate cellular metabolism.
- Hormones which interact with intracellular receptors (eg..steroid hormones, iodothy ronines) mostly regulate gene expression or chromosome function by the interaction of hormone receptor complex with the genome.
- Cumulative biochemical actions results in physiological and developmental effects.
- Gigantism Over secretion of growth hormone in children.
- Dwarfism Low secretion of growth hormone in children.
- Acromegaly Over secretion of growth hormone in adults.
- Diabetes insipidus Low secretion of ADH.
- Cretinism Due to hypothyroidism during pregnancy affects the infants growth.
- Goitre Iodine deficiency cause enlargment of the thyroid gland.
- Exophthalmic goitre Bulging of eye ball due to hyperthyroidism.
- Diabetes mellitus Low secretion of insulin.
- Hypoglycemia High secretion of insulin.
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