Chemical Coordination and Integration Study Guide

CHEMICAL COORDINATION AND INTEGRATION

1. Overview of Coordination Systems

  • The neural system provides point-to-point rapid coordination among organs.

  • Neural coordination is:
      - Fast
      - Short-lived

  • Neural fibers do not innervate all body cells, hence a special kind of coordination is provided by hormones.

  • The neural and endocrine systems work together to coordinate and regulate physiological functions in the body.

2. Endocrine Glands and Hormones

2.1 Definition of Endocrine Glands

  • Endocrine glands are known as ductless glands.

  • Their secretions are called hormones.

  • Classical Definition of Hormone: A chemical produced by endocrine glands, released into the blood, and transported to a distant target organ.

  • Current Scientific Definition of Hormone: Non-nutrient chemicals acting as intercellular messengers, produced in trace amounts.

  • Invertebrates have simple endocrine systems with fewer hormones, while vertebrates exhibit a complex array of hormones.

2.2 Structure of the Human Endocrine System

  • The human endocrine system includes:
      - Pituitary
      - Pineal
      - Thyroid
      - Adrenal
      - Pancreas
      - Parathyroid
      - Thymus
      - Gonads (testis in males, ovary in females)

  • Other organs such as the gastrointestinal tract, liver, kidney, and heart also produce hormones.

3. Human Endocrine System

3.1 The Hypothalamus

  • The hypothalamus is located at the basal part of the diencephalon in the forebrain.

  • It regulates wide body functions with groups of neurosecretory cells called nuclei, which produce:
      - Releasing hormones (stimulate secretion of pituitary hormones)
      - Inhibiting hormones (inhibit secretion of pituitary hormones)

  • Example: Gonadotrophin releasing hormone (GnRH) stimulates pituitary release of gonadotrophins.

  • Hormones from Hypothalamus:
      - Released through axons into a portal circulatory system, affecting anterior pituitary functions.
      - The posterior pituitary is under direct neural control from the hypothalamus.

3.2 The Pituitary Gland

  • Located in the sella turcica, attached to the hypothalamus by a stalk.

  • Divided into:
      - Adenohypophysis (Anterior Pituitary):
        - Pars distalis:
          - Produces:
            - Growth hormone (GH)
            - Prolactin (PRL)
            - Thyroid stimulating hormone (TSH)
            - Adrenocorticotrophic hormone (ACTH)
            - Luteinizing hormone (LH)
            - Follicle stimulating hormone (FSH)
        - Pars intermedia:
          - Secretes melanocyte stimulating hormone (MSH).
      - Neurohypophysis (Posterior Pituitary):
        - Stores and releases oxytocin and vasopressin, synthesized in hypothalamus.

3.3 Functions of Pituitary Hormones

  • Growth Hormone (GH): Abnormal secretion can lead to gigantism (oversupply) or dwarfism (undersupply).

  • Prolactin (PRL): Regulates mammary gland growth and milk formation.

  • TSH: Stimulates thyroid hormone synthesis and secretion.

  • ACTH: Stimulates glucocorticoid hormone secretion from adrenal cortex.

  • LH and FSH: Activate gonadal activity (gonadotrophins).

  • MSH: Affects skin pigmentation.

  • Oxytocin: Stimulates muscle contractions during childbirth and milk ejection.

  • Vasopressin (ADH): Promotes water reabsorption in kidneys; deficiency leads to diabetes insipidus.

3.4 The Pineal Gland

  • Located on the forebrain's dorsal side.

  • Secretes melatonin, which regulates:
      - Sleep-wake cycles (diurnal rhythm)
      - Body temperature
      - Metabolism
      - Pigmentation
      - Menstrual cycle
      - Defense capabilities.

3.5 The Thyroid Gland

  • Composed of two lobes on either side of the trachea, connected by the isthmus.

  • Follicular Cells: Synthesize:
      - Thyroxine (T4)
      - Triiodothyronine (T3)

  • Importance of Iodine: Essential for thyroid hormone synthesis; deficiency leads to hypothyroidism and goitre.

  • Consequences of Hypothyroidism: Defective development in fetuses (cretinism) and irregular menstruation in adults.

  • Hyperthyroidism: Results from excessive hormone production, leading to exophthalmic goitre (Graves’ disease).

  • Thyroid hormones regulate basal metabolic rate and affect metabolism of nutrients.

3.6 The Parathyroid Gland

  • Comprises four glands located behind the thyroid.

  • Secretes parathyroid hormone (PTH), which regulates:
      - Increases blood calcium levels by bone resorption.
      - Stimulates renal tubules for Ca2+ reabsorption.
      - Enhances calcium absorption from diet.

3.7 The Thymus

  • Located between the lungs, behind the sternum.

  • Secretes thymosins which:
      - Aid in differentiation of T-lymphocytes for cell-mediated immunity.
      - Promote antibody production for humoral immunity.

  • Degeneration of thymus with age reduces thymosin production and weakens the immune response.

3.8 The Adrenal Gland

  • Situated above each kidney.

  • Adrenal Medulla: Secretes epinephrine (adrenaline) and norepinephrine (noradrenaline), known as catecholamines, which:
      - Enhance alertness and physical performance during stress (fight-or-flight response).
      - Increase heart rate and respiration.

  • Adrenal Cortex: Contains three layers, secreting corticoids:
      - Glucocorticoids: (e.g., cortisol)
        - Involved in carbohydrate metabolism.
        - Stimulate gluconeogenesis, lipolysis, affect blood pressure.
      - Mineralocorticoids: (e.g., aldosterone)
        - Regulate sodium and water reabsorption in kidneys, affecting blood pressure.
      - Androgens: Influence development of secondary sexual characteristics.

3.9 The Pancreas

  • Functions as an endocrine and exocrine gland.

  • Islets of Langerhans: contain α-cells (secrete glucagon) and β-cells (secrete insulin).

  • Glucagon: Increases blood glucose levels by stimulating glycogenolysis and gluconeogenesis; classified as a hyperglycemic hormone.

  • Insulin: Lowers blood glucose by enhancing cellular uptake and stimulating glycogenesis; classified as a hypoglycemic hormone.

  • Diabetes Mellitus: Results from deficiencies in insulin action or production.

3.10 The Testis

  • Primary male sex organ, located in the scrotal sac.

  • Contains seminiferous tubules and Leydig cells, producing:
      - Androgens (e.g., testosterone).

  • Functions include:
      - Regulation of male accessory sex organs growth and maturation.
      - Influence on secondary sexual characteristics and spermatogenesis.

3.11 The Ovary

  • Primary female sex organ located in the abdomen.

  • Produces one ovum each cycle and secretes:
      - Estrogens: Promote growth of female sex organs and secondary characteristics.
      - Progesterone: Supports pregnancy and stimulates mammary gland formation and activity.

4. Hormonal Functions in Other Organs

4.1 Heart

  • Atrial wall secretes atrial natriuretic factor (ANF), which decreases blood pressure via blood vessel dilation.

4.2 Kidney

  • Juxtaglomerular cells produce erythropoietin, which stimulates erythropoiesis (red blood cell formation).

4.3 Gastrointestinal Tract

  • Secretes several peptide hormones:
      - Gastrin: Stimulates gastric acid secretion.
      - Secretin: Stimulates pancreatic secretion of bicarbonate.
      - Cholecystokinin (CCK): Stimulates pancreatic enzyme and bile secretion.
      - Gastric inhibitory peptide (GIP): Inhibits gastric secretions and motility.

4.4 Growth Factors

  • Secreted by non-endocrine tissues essential for normal growth and tissue repair/regeneration.

5. Mechanism of Hormone Action

  • Hormones interact with specific hormone receptors located on target tissues:
      - Membrane-bound Receptors: Interact with peptide hormones, generating second messengers (e.g., cyclic AMP, IP3, Ca++), influencing cellular metabolism.
      - Intracellular Receptors: Interact with steroid hormones, regulating gene expression through hormone-receptor complex action on the genome.

  • Each receptor is specific to one hormone, and hormone-receptor complex formation triggers biochemical changes in target tissues.

6. Summary of Endocrine Glands and Their Hormones

  • Hypothalamus: Produces releasing and inhibiting hormones.

  • Pituitary Gland: Divided into pars distalis (6 trophic hormones), pars intermedia (1 hormone), and pars nervosa (oxytocin, vasopressin).

  • Pineal Gland: Secretes melatonin, regulating diurnal rhythms.

  • Thyroid Gland: Regulates basal metabolic rate and metabolism of nutrients. Secretes T4, T3, and thyrocalcitonin (calcium regulation).

  • Parathyroid Gland: Secretes parathyroid hormone (PTH) which regulates calcium levels.

  • Thymus Gland: Produces thymosins for T-lymphocyte differentiation and immune response.

  • Adrenal Gland: Contains adrenal medulla (epinephrine, norepinephrine) and cortex (glucocorticoids, mineralocorticoids).

  • Pancreas: Secretes glucagon (hyperglycemic) and insulin (hypoglycemic).

  • Testis: Produces androgens for male characteristics and spermatogenesis.

  • Ovary: Produces estrogens and progesterone for female characteristics, menstruation, and pregnancy support.

  • Heart: Produces ANF, lowering blood pressure.

  • Kidney: Produces erythropoietin for red blood cell formation.

  • Gastrointestinal Tract: Secretes hormones regulating digestive functions.

7. Exercises

  1. Define the following:
       (a) Exocrine gland
       (b) Endocrine gland
       (c) Hormone

  2. Diagrammatically depict endocrine glands' locations in the body.

  3. List hormones secreted by:
       (a) Hypothalamus
       (b) Pituitary
       (c) Thyroid
       (d) Parathyroid
       (e) Adrenal
       (f) Pancreas
       (g) Testis
       (h) Ovary
       (i) Thymus
       (j) Atrium
       (k) Kidney
       (l) Gastro-intestinal tract

  4. Fill in the blanks regarding hormones and target glands.

  5. Write short notes on functions of:
       (a) Parathyroid hormone (PTH)
       (b) Thyroid hormones
       (c) Thymosins
       (d) Androgens
       (e) Estrogens
       (f) Insulin and glucagon.

  6. Provide examples for:
       (a) Hyperglycemic and hypoglycemic hormones
       (b) Hypercalcemic hormone
       (c) Gonadotrophic hormones
       (d) Progestational hormone
       (e) Blood pressure lowering hormone
       (f) Androgens and estrogens.

  7. Identify hormonal deficiencies associated with:
       (a) Diabetes mellitus
       (b) Goitre
       (c) Cretinism.

  8. Discuss the mechanism of FSH action.

  9. Match the following hormones with their respective glands.

NOTE

  • This document is a comprehensive study guide about chemical coordination and integration in humans, specifically focusing on the endocrine system and its hormones, mechanisms, and functions. It captures all essential details necessary for thorough understanding and study.