Comprehensive Notes on Chemical Coordination & Integration

Chemical Coordination & Integration

Overview

  • Chemical Coordination & Integration is crucial for the proper functioning of the body.
  • Hormones act as intercellular messengers and are non-nutrient chemicals, produced in trace amounts.

Endocrine Glands

  • Endocrine glands lack ducts and secrete hormones directly into the blood for transport.
  • Exocrine glands secrete through ducts (e.g., salivary glands).
  • Heterocrine glands have both exocrine and endocrine functions.
Major Endocrine Glands and Their Locations
  • Pituitary gland
  • Hypothalamus
  • Thyroid and Parathyroid glands
  • Thymus
  • Pancreas
  • Adrenal glands
  • Ovaries (in females)
  • Testes (in males)

Hypothalamus

  • Considered the master controller, influencing the pituitary gland.
  • Contains neurosecretory cells that secrete releasing and inhibiting hormones.
  • These hormones regulate the secretion of pituitary hormones.
  • Examples: GnRH (Gonadotropin-Releasing Hormone).

Pituitary Gland

  • Located in Sella Turcica and connected to the hypothalamus by a stalk.
  • Also called the master gland.
  • Divided into:
    • Adenohypophysis (Anterior pituitary): Pars distalis, Pars intermedia
    • Neurohypophysis (Posterior pituitary): Pars nervosa
  • Stores and releases hormones synthesized by the hypothalamus (oxytocin, vasopressin).
Hormones of the Adenohypophysis (Anterior Pituitary)
  • GH (Growth Hormone)
  • PRL (Prolactin)
  • TSH (Thyroid Stimulating Hormone)
  • ACTH (Adrenocorticotrophic Hormone)
  • LH (Luteinizing Hormone)
  • FSH (Follicle Stimulating Hormone)
  • MSH (Melanocyte Stimulating Hormone)
Hormones of the Neurohypophysis (Posterior Pituitary)
  • Oxytocin
  • Vasopressin (ADH - Antidiuretic Hormone)

Functions of Pituitary Hormones

  • Growth Hormone (GH): Increases body growth.
  • Prolactin (PRL): Develops mammary glands and stimulates milk production.
  • Thyroid Stimulating Hormone (TSH): Stimulates the thyroid gland to synthesize and secrete thyroid hormones.
  • Adrenocorticotrophic Hormone (ACTH): Stimulates the adrenal cortex to synthesize and secrete glucocorticoids.
  • Follicle Stimulating Hormone (FSH):
    • Male: With androgens, stimulates spermatogenesis.
    • Female: Stimulates growth of ovarian follicles.
  • Luteinizing Hormone (LH):
    • Male: Acts on Leydig cells to secrete testosterone.
    • Female: Induces ovulation and maintains the corpus luteum.
  • Melanocyte Stimulating Hormone (MSH): Stimulates melanocytes in the skin, causing skin pigmentation.
  • Oxytocin: Causes uterine contractions during childbirth and milk ejection.
  • Vasopressin (Antidiuretic Hormone): Promotes reabsorption of water by the kidneys, reducing urine output (diuresis).

Disorders Related to Pituitary Hormone Imbalance

  • Dwarfism: Caused by hyposecretion of GH.
  • Gigantism: Caused by hypersecretion of GH (before epiphyseal closure).
  • Acromegaly: Caused by hypersecretion of GH (after epiphyseal closure).
  • Diabetes Insipidus: Caused by hyposecretion of ADH, leading to excessive water loss.

Pineal Gland

  • Located on the dorsal side of the forebrain.
  • Secretes melatonin, derived from tryptophan.
Functions of Melatonin
  • Regulates the diurnal (24-hour) rhythm and sleep-wake cycle.
  • Influences metabolism, pigmentation, and the menstrual cycle.
  • Defense capability.

Thyroid Gland

  • Located in the neck region, composed of two lobes connected by the isthmus.
  • Composed of follicles and stromal tissues.
  • Follicular cells synthesize Tetraiodothyronine or Thyroxine (T<em>4T<em>4) and Triiodothyronine (T</em>3T</em>3).
  • Requires iodine for hormone synthesis.
Functions of Thyroid Hormones
  • Regulation of the basal metabolic rate.
  • Red blood cell formation.
  • Control of carbohydrate, protein, and fat metabolism.
  • Maintenance of water and electrolyte balance.
  • Secrete thyrocalcitonin (TCT), which lowers blood calcium levels.
Disorders of the Thyroid Gland
  • Goiter: Enlargement of the thyroid gland due to iodine deficiency.
  • Hypothyroidism: Underactive thyroid gland.
    • Cretinism: In children, causes stunted growth, mental retardation, etc.
    • Myxedema: In adults, causes swelling, weight gain, etc.
  • Hyperthyroidism: Overactive thyroid gland.
    • Increased metabolic rate, weight loss, and exophthalmic goiter (bulging eyes).

Parathyroid Gland

  • Located on the dorsal side of the thyroid gland (four glands in total).
  • Secretes parathyroid hormone (PTH), also known as Collip's hormone.
Functions of Parathyroid Hormone (PTH)
  • Increases calcium levels in the blood.
  • Acts on bones to stimulate bone resorption.
  • Stimulates reabsorption of calcium by the renal tubules.
  • Increases calcium absorption from digested food.
  • PTH is antagonistic to TCT (Thyrocalcitonin).

Thymus Gland

  • Located in the thoracic region, beneath the sternum.
  • Lobed structure that decreases in size with age.
  • Secretes thymosins.
Functions of Thymosins
  • Differentiation of T-lymphocytes, providing cell-mediated immunity.
  • Promotes the production of antibodies, providing humoral immunity.

Adrenal Gland

  • Located on top of the kidneys.
  • Composed of the adrenal cortex and adrenal medulla.
Adrenal Cortex
  • Outer region that secretes steroid hormones.
    • Glucocorticoids (e.g., cortisol)
    • Mineralocorticoids (e.g., aldosterone)
    • Sex corticoids
Functions of Glucocorticoids (Cortisol)
  • Involved in carbohydrate metabolism.
  • Stimulate Gluconeogenesis
  • Anti-inflammatory effects.
  • Immunosuppressant - affects lymphoid tissue.
  • Also involved in maintenance of cardiovascular system and kidney functions
Functions of Mineralocorticoids (Aldosterone)
  • Act on renal tubules to cause reabsorption of sodium and water.
  • Cause excretion of potassium and phosphate ions.
  • Maintain electrolyte, fluid, osmotic balance, body fluid volume, osmotic pressure and blood pressure.
Adrenal Medulla
  • Inner region that secretes epinephrine (adrenaline) and norepinephrine (noradrenaline).
  • These are catecholamines.
Functions of Epinephrine and Norepinephrine
  • Increase alertness, pupil dilation, sweating, heart rate, and respiratory rate.
  • Stimulate glycogen breakdown.
  • Increase blood glucose levels.
  • Vasoconstriction.
Disorders of the Adrenal Cortex
  • Addison’s Disease: Caused by hyposecretion of adrenocortical hormones.
    • Symptoms include fatigue, weight loss, low blood sugar, and electrolyte imbalance.

Pancreas

  • Heterocrine gland with both exocrine and endocrine portions.
Endocrine Pancreas
  • Consists of Islets of Langerhans.
    • α-cells: Secrete glucagon.
    • β-cells: Secrete insulin.
Functions of Insulin and Glucagon
  • Insulin: Decreases blood glucose levels by stimulating glucose uptake and utilization by cells, glycogenesis.
  • Glucagon: Increases blood glucose levels by stimulating glycogenolysis and gluconeogenesis.
Disorders of the Pancreas
  • Diabetes Mellitus: Caused by hyposecretion or deficiency of insulin.

Testes (Male)

  • Located in the scrotal sac outside the abdomen.
Functions of Testes
  • Primary sex organ and endocrine gland.
  • Composed of seminiferous tubules and interstitial tissue.
  • Leydig cells produce androgens (mainly testosterone).
Functions of Testosterone
  • Regulates the development, maturation, and function of male secondary sex organs.
  • Stimulates spermatogenesis.
  • Influences libido.
  • Anabolic effects on protein and carbohydrate metabolism.

Ovaries (Female)

  • Located in the abdomen.
Functions of Ovaries
  • Primary female sex organ that produces one ovum during each menstrual cycle.
  • Produces estrogen and progesterone.
Functions of Estrogen
  • Growth and activities of female secondary sex organs.
  • Appearance of female secondary sex characteristics.
Functions of Progesterone
  • Supports pregnancy.
  • Stimulates formation of alveoli in mammary glands.

Hormones of Heart, Kidney, and Gastrointestinal Tract

Heart
  • ANF (Atrial Natriuretic Factor): Decreases blood pressure by dilating blood vessels.
Kidney
  • Erythropoietin: Stimulates erythropoiesis (RBC production).
Gastrointestinal Tract
  • Gastrin: Stimulates secretion of HCl and pepsinogen.
  • GIP (Gastric Inhibitory Peptide): Inhibits gastric secretions and motility.
  • Cholecystokinin (CCK): Stimulates secretion of pancreatic enzymes and bile juice.
  • Secretin: Stimulates secretion of water and bicarbonate from the pancreas.
  • Growth factors: Essential for normal growth, repair, and regeneration of tissue.

Types of Hormones

  • Peptide, polypeptide, protein hormones: (e.g., insulin, glucagon, pituitary hormones, hypothalamic hormones).
  • Steroids: (e.g., cortisol, testosterone, estradiol, progesterone).
  • Iodothyronines (thyroid hormones): (Need iodine).
  • Amino-acid derivatives: (e.g., epinephrine).

Mechanism of Hormone Action

  • Hormones bind to receptors on or inside target cells.
  • Membrane-bound receptors: Hormones do not enter cells but generate second messengers (cAMPcAMP, IP3IP_3, Ca2+Ca^{2+}) to regulate cellular metabolism (e.g., FSH).
  • Intracellular receptors: Hormones regulate gene expression or chromosome function (e.g., steroid hormones, iodothyronines).