GRADE 11 CHAPTER: CHEMICAL COORDINATION
ENDOCRINE GLANDS AND HORMONES
• Endocrine glands lack ducts and are hence, called ductless glands.
• Their secretions are called hormones
HORMONES
• hormones produced and released into the blood and transported to a distantly located target
organ
• Hormones are intercellular messengers
• Produced in trace amounts
HUMAN ENDOCRINE SYSTEM
1. Hypothalamus
2. Pituitary,
3. Pineal,
4. Thymus
5. Thyroid,
6. Parathyroid,
7. Adrenal,
8. Pancreas,
9. gonads (testis in males and ovary in females)
In addition to these, some other organs, e.g., the gastrointestinal tract, liver, kidney, and heart also
produce hormones.
THE HYPOTHALAMUS
• Located in the basal part of forebrain
• It contains neurosecretory cells called nuclei which produce hormones.
• These hormones regulate the synthesis and secretion of pituitary hormones.
HORMONES OF HYPOTHALAMUS
• Releasing hormones - stimulate secretion of pituitary hormones
• Inhibiting hormones - inhibit secretions of pituitary hormones Eg:- Somatostatin
• Oxytocin
• Vasopressin
These hormones originating in the hypothalamic neurons, pass through axons and are released
from their nerve endings.
1. RELEASING HORMONES
➢ Eg:-Thyrotrophin releasing hormone (TRH) stimulates the pitutary gland for the synthesis and
secretion of thyroid stimulating hormone (TSH)
➢ Eg:-Gonadotrophin releasing hormone (GnRH) stimulates the pituitarygland for the synthesis and
release of gonadotrophins
2.INHIBITING HORMONES
Somatostatin from the hypothalamus inhibits the release of growth hormone from the pituitary
3. OXYTOCIN
Stimulates a vigorous contraction of uterus at the time of child birth,
Stimulates milk ejection from the mammary gland
4.VASOPRESSIN
Stimulates reabsorption of water by the distal tubules and thereby reduces loss of water through
urine (diuresis). Hence, it is also called as anti-diuretic hormone (ADH).
2. THE PITUITARY GLAND
▪ Growth hormone (GH),
▪ Prolactin (PRL),
▪ Thyroid stimulating hormone (TSH),
▪ Adrenocorticotrophic hormone (ACTH),
▪ Luteinizing hormone (LH) and
▪ Follicle stimulating hormone (FSH)
▪ Melanocyte stimulating hormone (MSH)
1. GROWTH HORMONE (GH)- Growth of the body
GIGANTISM-Over-secretion of GH stimulates abnormal growth of the body leading to gigantism
DWARFISM-Low secretion of GH results in stunted growth resulting in pituitary dwarfism
2. PROLACTIN
Prolactin regulates the growth of the mammary glands and production of milk in them
3. THYROID STIMULATING HORMONE (TSH)
TSH stimulates the synthesis and secretion of thyroid hormones from the thyroid gland
4. ADRENOCORTICOTROPHIC HORMONE (ACTH)
ACTH stimulates the synthesis and secretion of steroid hormones called glucocorticoids from the
adrenal cortex.
5. GONADOTROPHINS
Luteinizing hormone (LH) and Follicle stimulating hormone (FSH) stimulate gonadal activity and
hence are called gonadotrophins.
6. MELANOCYTE STIMULATING HORMONE (MSH) -MSH acts on the melanocytes (melanin
containing cells) ®ulates pigmentation of skin
THE PINEAL GLAND
▪ Located on the dorsal side of forebrain.
▪ Pineal secretes a hormone called melatonin
MELATONIN
▪ Regulates a 24-hour (diurnal) rhythm of our body.
▪ melatonin also influences
▪ metabolism
▪ pigmentation
▪ the menstrual cycle
▪ defense capability
THYROID GLAND
❖ Located on either side of the trachea.
❖ Composed of two lobes
❖ Both are interconnected with isthmus.
❖ synthesize 3 hormones,
1.Tetraiodothyronine or thyroxine (T4)
2. Triiodothyronine (T3)
3. Thyrocalcitonin
GOITRE
• Iodine is essential for the synthesis of thyroid hormones.
• Deficiency of iodine results in hypothyroidism and enlargement of the thyroid gland, commonly
called goitre.
HYPOTHYROIDISM-Hypothyroidism during pregnancy causes defective development and
maturation of the growing baby leading to
• Stunted growth (cretinism),
• mental retardation,
• low intelligence quotient,
• abnormal skin, deaf-mutism, etc.
• HYPERTHYROIDISM-Due to cancer of the thyroid glands, the secretion of the thyroid hormones
is increased to high levels leads to hyperthyroidism which adversely affects the body physiology.
FUNCTIONS OF THYROID HORMONES
• Regulates the basal metabolism
• Support the process of red blood cell formation.
• Control the metabolism of carbohydrates, proteins and fats.
• Maintenance of water and electrolyte balance
THYROCALCITONIN
Thyrocalcitonin (TCT) -regulates the blood calcium levels. (Decreases the calcium level in blood)
PARATHYROID GLAND
• Four parathyroid glands are present on the back side of the thyroid gland, one pair each in the
two lobes of the thyroid gland
• Secrete a peptide hormone called parathyroid hormone (PTH).
• Parathyroid hormone (PTH) increases the Ca2+ levels in the blood by three ways.
1.Stimulates the process of bone reasorption (dissolution/demineralisation).
2.Stimulates reabsorption of Ca2+ by the renal tubules
3. Increases Ca absorption from the digested food.
• Along with TCT, PTH plays a significant role in calcium balance in the body.
THYMUS GLAND
• Secretes the peptide hormones called Thymosins.
• A lobular structure located on the dorsal side of the heart and the aorta.
• Function in immunity
• Helps in the differentiation of T lymphocytes, which provide cell-mediated immunity.
• Increase the production of antibodies to provide humoral immunity.
• Degenerates with aged individuals resulting in a decreased production of thymosins. As a result,
the immune responses of old persons become weak
ADRENAL GLAND
• One pair of adrenal glands, one at the anterior part of each kidney.
• Two PARTS
Adrenal medulla & Adrenal cortex
ADRENAL medulla
▪ Secretes 2 hormones
▪ 1.Adrenaline or Epinephrine
▪ 2,Noradrenaline or Norepinephrine.
▪ Commonly called as Catecholamines
▪ Called as emergency hormones or hormones of Fight or Flight. Because they secreted in stress
of any kind and during emergency situations
Effects of catecholamines - Adrenaline & Noradrenaline
▪ Increase alertness,
▪ Pupilary dilation,
▪ Piloerection (raising of hairs),
▪ Sweating etc.
▪ Increase the heartbeat, and the rate of respiration.
▪ Stimulate the breakdown of glycogen. stimulate the breakdown of lipids and proteins
ADRENAL cortex
▪ The adrenal cortex secretes many hormones, commonly called as corticoids.
CORTICOID HORMONES
▪ The corticoids, which are involved in carbohydrate metabolism and also maintain water and
electrolyte balance.
▪ In our body, cortisol is the main glucocorticoid.
PANCREAS
▪ Pancreas is a mixed (composite) gland which acts as both exocrine and endocrine gland.
▪ The endocrine pancreas consists of Islets of Langerhans.
▪ The two main types of cells in the Islet of Langerhans α-cells and β-cells.
▪ The α-cells secrete glucagon,
▪ the β-cells secrete insulin.
Glucagon is a hyperglycemic hormone
▪ Stimulates glycogenolysis (breakdown of glycogen into glucose) resulting hyperglycemia.
INSULIN
▪ Insulin is a peptide hormone,
▪ Plays a major role in the regulation of glucose homeostasis.
▪ Insulin stimulates conversion of glucose to glycogen (glycogenesis) in the target cells.
▪ The glucose homeostasis in blood is thus maintained jointly by the two – insulin and glucagon.
TESTIS
▪ A pair of testis is present in the scrotal sac (outside abdomen) of male
▪ Primary sex organ
▪ Endocrine gland
Composed of
1.Seminiferous tubules -Production of male gametes.
2. Leydig cells or interstitial cells. The Leydig cells or interstitial cells, produce male hormones
called androgens mainly testosterone.
OVARY
▪ Females have a pair of ovaries located in the abdomen
▪ Ovary is composed of ovarian follicles and stromal tissues.
▪ Ovary produces two groups of steroid hormones and female gametes.
1.Estrogen and
2.Progesterone
HORMONES OF HEART
Arial Natriuretic Factor (ANF)
▪ Decreases blood pressure.
▪ When blood pressure is increased, ANF is secreted which causes dilation of the blood
vessels. This reduces the blood pressure.
HORMONES OF KIDNEY
The juxtaglomerular cells of kidney produce a peptide hormone called erythropoietin which
stimulates erythropoiesis (formation of RBC).
Hormones produced bind with a specific hormone receptor present in the target cells and form a
hormone-receptor complex. Hormone receptors are two types
1. Membrane-bound receptors 2. Intracellular receptors
Membrane-bound receptors-Action: Hormones do not enter the cell and interact with
receptors present in the cell membrane Generate a second messenger(cyclic AMP, IP3 Ca++).
2nd messenger regulates cellular metabolism. Eg. Protein hormones
Intracellular receptors-action:
Hormones interact with intracellular receptors and interact with chromosome and gene
expression. Resulting in biochemical actions. e.g., steroid hormones, iodothyronines, etc (refer
ppt flow chart)
