ISC 11> STRUCTURE AND FUNCTION OF ANIMALS> 6. ENDOCRINE SYSTEM
SCOPE OF SYLLABUS
ENDOCRINE SYSTEM
Location of endocrine glands,
Tropic hormones of pituitary and their functions;
Feedback control of tropic hormones with examples; mechanism of hormone action.
Role of hypothalamus;
Hormones secreted by different lobes of pituitary and their functions; hypophysectomy,
Hormones of thyroid, parathyroid, pancreas, adrenal and gonads; Effects of hypo secretion and hyper secretion of various hormones; Differences between mineralocorticoids and glucocorticoids.
Location of endocrine glands,
Tropic hormones of pituitary and their functions;
Feedback control of tropic hormones with examples; mechanism of hormone action.
Role of hypothalamus;
Hormones secreted by different lobes of pituitary and their functions; hypophysectomy,
Hormones of thyroid, parathyroid, pancreas, adrenal and gonads; Effects of hypo secretion and hyper secretion of various hormones; Differences between mineralocorticoids and glucocorticoids.
ENDOCRINE SYSTEM
The system that brings about chemical coordination by complex organic compounds called hormones is the endocrine system.
It consists of different endocrine glands that secrete different hormones. Hormones are chemical messengers that regulate the biological processes in the organisms. These are also called information molecules. Characteristics of hormones
They may be proteinaceous or non-proteinaceous (amino acids or steroids) They are secreted as per need and not stored, only excreted Their secretion may be regulated by nerves or by feedback effect They are transported by blood They mostly cause long-term effects like growth, change in behaviour, etc. They function by stimulating or inhibiting specific target organs. |
Competitive focus: Mechanism of hormone action
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HYPOTHALAMUS
LOCATION -The hypothalamus is a small part of the brain located just below the thalamus on both sides of the third ventricle.
These secretions or hormones are called ‘releasing factors, releasing hormones or neurohormones’. Some of the hypothalamic hormones inhibit the secretion of some pituitary hormones these are called ‘inhibitory hormones or inhibitory factors’ |
RELEASING AND INHIBITING HORMONES/FACTORS
- Thyrotropin-Releasing Hormone (TRH): Stimulates cells in the anterior pituitary gland to produce and release thyroid stimulating hormone (TSH).
- Adrenocorticotropin Releasing Hormone (A-RH/CRH)-Stimulates release of adrenocorticotropin hormone (ACTH)
- Follicle Stimulating Hormone Releasing Hormone (FSH-RH)- stimulates release of follicle stimulating hormone (FSH).
- Lutenising Hormone Releasing Hormone (LH-RH)- stimulates pituitary to release lutenising hormone (LH).
- Growth hormone or Somatotropin Releasing Hormone (GH-RH/ S-RH): Stimulates the release of growth hormone or somatotropin.
- Growth hormone release- Inhibiting Hormone (GH-RIH) or Somatostatin: Inhibits the secretion of growth hormone.
- Prolactin- Releasing Hormone (P-RH): Stimulate secretion of prolactin or luteotropic hormone (LTH).
- Prolactin Release- Inhibiting Hormone (PR-IH): Inhibits the secretion of prolactin from pituitary.
- Melanocyte Stimulating Hormone- Releasing Hormone (MSH-RH): Stimulates the intermediate lobe to release Melanocyte Stimulating Hormone (MSH)
- Melanocyte Stimulating Hormone- Release- Inhibiting Hormone (MSH-RIH): Inhibits the secretion of Melanocyte Stimulating Hormone (MSH).
PITUITARY GLAND
Location- It sits
in the sella turcica which is a depression
of the sphenoid bone at the base of the skull and lies behind the sphenoid
sinus.
Also called hypophysis. It is Pear shaped. Divided into three lobes
The pars anterior and the pars intermedia are together called adenohypophysis. Connected to the hypothalamus by a stalk called INFUNDIBULUM. It is connected by the hypothalamo-hypophysial portal system and axons of hypothalamic neurons. |
A. Hormones of the anterior pituitary
TROPIC HORMONES
These are hormones that activate other endocrine glands to release their hormones. 1. Somatotrophic hormone or Somatotrophin or growth hormone -enhances metabolic process -leads to body growth -influences growth of long bones. |
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Hyposecretion of STH
During childhood causes Dwarfism called ateleiosis and dwarfs are called midgets In adult-persons are weak, reduced development of genital organs and reduced fertility called Pituitary myxoedema |
Hypersecretion of STH
During childhood-causes Gigantism - produces healthy giant size persons called pituitary giants. In adults-causes Acromegaly - disproportionate giants, thickening of facial bones and protruding forehead. Development of hump in some- Kyphiosis |
2. Thyroid stimulating hormone(TSH) or Thyrotropin
Stimulates thyroid to secrete thyroxin Hyposecretion-causes thyroid atropy Hypersecretion – produces excess thyroxin |
3. Adrenocorticotropic hormone (ACTH)
Normal functioning of adrenal cortex or release of mineralocorticoids and glucocorticoids Hyposecretion- atropy of adrenal gland Hypersecretion- excessive growth of adrenal cortex. |
GONADOTROPINS
Controls normal functioning of gonads and other reproductive organs.
Secretion of these hormones start during puberty.
1. Follicle stimulating hormone (FSH)
Female – stimulates growth of graffian follicle & secretion of estrogens by follicle cells.
Males – controls formation of spermatozoa.
2. Lutenizing hormone (LH) –in female. Interstitial cell stimulating hormone (ICSH)- in male
LH stimulates ovulation
Formation of CL
Secretion of progesterone & estrogen from CL
ICSH- causes Secretion of testosterone
3. Prolactin or Lactogenic or Luteotropic hormone
Controls secretion of milk after delivery
During pregnancy promotes breast development.
With LH maintains CL in the postovulatory phase.
Controls normal functioning of gonads and other reproductive organs.
Secretion of these hormones start during puberty.
1. Follicle stimulating hormone (FSH)
Female – stimulates growth of graffian follicle & secretion of estrogens by follicle cells.
Males – controls formation of spermatozoa.
2. Lutenizing hormone (LH) –in female. Interstitial cell stimulating hormone (ICSH)- in male
LH stimulates ovulation
Formation of CL
Secretion of progesterone & estrogen from CL
ICSH- causes Secretion of testosterone
3. Prolactin or Lactogenic or Luteotropic hormone
Controls secretion of milk after delivery
During pregnancy promotes breast development.
With LH maintains CL in the postovulatory phase.
B. Hormones of Intermediate lobe
C. Hormones of posterior pituitary
1. Antidiureic hormone (ADH) or vasopressin
Water retaining hormone Regulates electrolyte balance Hyposecretion- Diuresis (abnormally large urine volume) causes Diabetes insipidus Hypersecretion- Anti Diuresis (small urine volume) 2. Oxytocin or Pitocin
In Females - contraction of uterine muscles during child birth. ejection of milk during lactation In Males- helps in sperm transport and ejection |
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HYPOPHYSECTOMY
Hypophysectomy is the removal of pituitary.
It was first performed by Ashner. The pituitary lies directly behind the nose, and access through the nose or the sinuses is often the best approach. Opening the skull and lifting the frontal lobe of the brain will expose the delicate neck of the pituitary gland. This approach works best if tumors have extended above the pituitary fossa (the cavity in which the gland lies). |
Feedback control of tropic hormones
Feedback control by hormones: (hormonal stimuli)
Tropic hormones are secreted by pituitary Pituitary is controlled by releasing hormones from hypothalamus Hypothalamus in response to stimuli secrete, releasing hormone. Releasing hormones stimulate anterior pituitary to release tropic hormones. The tropic hormones act on the target gland. The target gland secretes hormones in the blood. The increase or decrease in level of these hormones stimulates the negative and |
Feedback control by metabolites: (humoral stimuli)
Level of metabolites like glucose affects secretion of hormones. After a meal, the blood glucose levels increases. Rise in glucose stimulates secretion of insulin by the cells of the pancreas. This increases the uptake of glucose by the cells and thus brings the blood sugar level down. If there is a drop in the blood sugar level from normal levels then it stimulates the release of glucagon from the pancreas. Glucagon acts on the glycogen reserves in the liver and convert it to glucose. |
Feedback control by nerves: (neural stimuli)
Emotional stress stimulates sympathetic nervous system. Sympathetic nerves of the adrenal stimulate secretion of adrenaline. This increases the heart beat and blood pressure. When emotional stress is over, sympathetic nerves signal to stop adrenaline release. |
In case of TSH-
Thyrotropin or TSH stimulates thyroid to produce and release thyroxin When thyroxin level in the blood increases it exerts a negative feedback on the hypothalamus. Hypothalamus secrets less of the releasing hormone. Thus pituitary secretes less TSH. If thyroxin level in the blood is less then normal Stimulates hypothalamus to produce more releasing hormone. This causes the pituitary to produce more TSH In turn thyroid will now produce more thyroxin This is called positive feedback mechanism |
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THYROID GLAND
Location- In the neck below the larynx
Made up mostly of thyroid follicles Wall of each follicle contains: Parafollicular cells Produce thyrocalcitonin (TCT) Reduces blood calcium by inhibiting osteoclasts Follicular cells They become secretory under influence of TSH (from anterior pituitary) Produce: –Thyroxin (tetra-iodothyronine; T4) –Triiodothyronine (T3) |
Effect of thyroid hormone
1. General Metabolism- Controls metabolic activities and growth.
2. Carbohydrate metabolism -Absorption of glucose and Synthesis of glucose from non-carbohydrate sources.
3. Protein metabolism- increases protein synthesis
4. Lipid metabolism- increases lipid synthesis
5. Thyroxine level increases- there is weight loses and decreases obesity
6. Heart rate – Accelerates heart beat
7. Growth & differentiation –Controls functioning of adrenal and gonads
8. Metamorphosis – Accelerates metamorphosis
1. General Metabolism- Controls metabolic activities and growth.
2. Carbohydrate metabolism -Absorption of glucose and Synthesis of glucose from non-carbohydrate sources.
3. Protein metabolism- increases protein synthesis
4. Lipid metabolism- increases lipid synthesis
5. Thyroxine level increases- there is weight loses and decreases obesity
6. Heart rate – Accelerates heart beat
7. Growth & differentiation –Controls functioning of adrenal and gonads
8. Metamorphosis – Accelerates metamorphosis
Hypothyroidism
1. Cretinism in children Retarded mental & physical growth Immature sexuality &retarded sexual characters 2. Myxoderma or Gull’s disease in adults Low BMR,body temperature & BP Mental,physical dullness &loss of memory Degenerated sex organs 3. Simple Goitre Enlargement of thyroid due to deficiency of iodine in food. |
Hyperthyroidism
Increased BMR, High body temperature, increased heart rate, damage to heart, muscles, leading to heart failure mental restlessness & increased irritability. 1. Osteoporosis- due to excessive loss of calcium and phosphorous ions from bones. 2. Exopthalmic goiter or Grave’s disease- protruded and wide open eyes with less twinkling of eyelids and increase in size of thyroid. |
PARATHYROID GLAND
Location- behind/on the posterior surface of the thyroid gland or embedded in the dorsal surface of the thyroid gland.
Secretes- Parathyroid hormone or Parathormone · Regulates Ca-P balance in blood · Increases blood Ca – taking from bones · Lowers blood phosphate- eliminates in urine · Increases absorption of Ca by cells of intestine · Controls muscle contraction |
COMPETITIVE FOCUS: THYMUS GLAND
PINEAL GLAND (EPIPHYSIS)
LOCATION : situated between the cerebral hemispheres, attached to the third ventricle.
The pineal gland is a common gland shared by most mammals, its function is clearly understood only in some organisms. In humans, however, its function remains somewhat misunderstood. It is known to administer melatonin. It has been proven to adhere to rhythmical patterns of day and night and adapt to seasonal changes. It is unclear what melatonin provides for humans. It has been determined that melatonin directly affects the hypothalamus and encourage the release of some releasing agents. Others have speculated that melatonin directly impacts the sleep cycle. While there is some evidence supporting melatonin’s probably role in sexual development, the evidence has not yet been proven beyond theory. Too much melatonin has been proven to delay the initial onset of puberty. |
ADRENAL GLAND
Location-on top of each kidney
The adrenal gland has two distinct parts the outer adrenal cortex and the inner adrenal medulla. THE ADRENAL CORTEX The adrenal cortex is composed of 3 zones: the zona glomerulosa (outer zone), the zona fasciculata (middle zone), and the zona reticularis (inner zone). The zona glomerulosa is responsible for the production of mineralocorticoids, mainly aldosterone, which regulates blood pressure and electrolyte balance. The zona fasciculata, is responsible for the production of glucocorticoids, predominantly cortisol, which increases blood sugar levels via gluconeogenesis, suppresses the immune system, and aids in metabolism. This zone secretes cortisol both at a basal level and as a response to the release of adrenocorticotropic hormone (ACTH) from the pituitary gland. The zona reticularis produces gonadocorticoids and is responsible for administering these hormones to the reproductive regions of the body. Most of the hormones released by this layer are androgens. Hormones of adrenal cortex 1. Glucocorticoids Regulates the metabolism of carbohydrates, fats &protein Helps in constriction of blood vessels during excessive bleeding 2. Mineralocorticoids Regulates metabolism of Na & K and maintains water balance. Aldosterone reduces removal of Na but increases K dimination Helps in retention of Na in blood increases absorption of water & increases blood volume. 3. Sex steroids Helps in proper functioning of sex organs & development of sex character. |
MINERALOCORTICOIDS
1. Secreted by the zona glomerulosa of adrenal cortex.
2. Secretion is stimulated by blood electrolyte levels. 3. Regulates the Na/K levels. 4. Increases the blood levels of Na and water, and decreases potassium level. 5. Target tissue is kidney. 6. Main mineralocorticoid is aldosterone. 7. Excess aldosterone causes- aldosteronism. |
GLUCOCORTICOIDS
1. Secreted by the zona faciculata of adrenal cortex.
2. Secretion is stimulated by blood glucose levels. 3. Regulates carbohydrate metabolism. 4. Increases the sugar level of blood and promotes liver glycogen formation. 5. Target tissue is liver. 6. Main glucocorticoid is cortisol. 7. Excess cortisol causes Cushing's syndrome. |
THE ADRENAL MEDULLA
The adrenal medulla produce epinephrine (also known as adrenaline) and norepinephrine. These hormones prepare the body for the fight-or-flight response by increasing the heart rate, constricting blood vessels, increasing the metabolic rate, heightening cognitive awareness, and increasing the respiratory rate. Hormones of Adrenal Medulla
Two hormones 1. Non adrenalin- (non epinephrine) Regulates BP, transmits nerve impulse 2. Adrenalin (Epinephrine) Secreted during emergency like emotional stress, anger, fear & grief. It is a vasconstrictor Carbohydrate metabolism Bronchodicating effect- used treatment of asthma |
Disorders related to the adrenal gland
Hypersecretion
Excessive Aldosterone
Aldosteronism/conn’s syndrome
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Excessive Adrenal androgens
Adrenal virilism / adrenogential syndrome
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PANCREAS
Location- between the stomach and intestine in the abdominal cavity.
The pancreas is a narrow, flat organ about six inches long, with a head, middle, and tail section. It is located below the liver, between the stomach and the spine, and its head section connects to the duodenum. It consists of two types of tissues-
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THE ENDOCRINE PANCREAS
The endocrine portion of the pancreas takes the form of many small clusters of cells called islets of Langerhans or, more simply, islets. Humans have roughly one million islets.
Pancreatic islets house three major cell types, each of which produces a different endocrine product:
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HORMONES OF THE PANCREAS
Secretes two hormones
1. Insulin Lowers blood glucose Induces protein synthesis Induces synthesis of enzymes converting glucose – glycogen Deficiency of Insulin Diabetes mellitus Hyperglycemia Diuresis 2. Glucagon changes liver glycogen-glucose forms glucose from amino acid Increases blood glucose level |
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INSULIN AND DIABETES
HYPOSECRETION OF INSULIN.
Hyposecretion of insulin causes Diabetes mellitus. symptoms of Diabetes-
1. Insulin dependent Diabetes mellitus (type 1 diabetes) Blurred vision, fatigue and being underweight are other symptoms. 2.Type 2 diabetes, non insulin dependent or adult onset diabetes. |
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GONADS
Hormones of ovaries
1. Estrogens These are produced by the granulosa cells. It helps in development of female reproductive tract and differentiation of ovum in ovary. It also causes puberty changes. 2.Progesterone suspends ovulation during pregnancy Fixes foetus to uterine wall. Promotes placental formation. Promotes development of mammary glands. 3.Relaxin Relaxes pelvic ligament and cervix for easy growth of young ones. |
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