CHAPTER 45 CHEMICAL SIGNALS IN ANIMALS Egg Larva Pupa Adult
Introduction • Nervous and endocrine systems are the main internal communication and regulation systems. • The animal hormone-secreting cells constitute the endocrine system. • Hormone secreting organs are called Endocrine Glands (ductless glandsالغدد الصماء). • Hormone is a chemical signal secreted into blood stream and regulates communicating messages within the body. • Target cell is the site that reached by the hormone to which it responds. • Complete changes in the body is regulated by hormones (e.g. metamorphosis in insects). • Types of hormones are [Polypeptide H., Amino acid derivatives H or Steroid H.].
Tropic hormones:الهرمونات المحفزة (المنبهة)target other endocrine glands and are important to understanding chemical coordination. • Many endocrine organs contain specialized nerve cells called neurosecretory cells that secret hormones. • The hormone epinephrine has two functions: • As a hormone of the endocrine system. • As a signal in the nervous system. • Feedback is common in regulation the activity of both endocrine and nervous systems (homeostasis) (Fig. 45.1, page 956): • Calcitonin and parathyroid hormones play an important role in maintaining the concentration of the blood calcium constant. • They are secreted from thyroid and parathyroid glands respictively. • Hormones regulate the development of invertebrates (e.g. insects) See Fig. 45.2, Page 957
Most chemical signals bind to plasma-membrane proteins, initiating signal-transduction pathways. Mechanism of chemical signaling: The chemical signals secreted by a cell either: I): Protein hormones: Bind to a receptor protein on the surface of the target cell whichwill trigger signal transduction pathway. Fig. 45.3a, Page 959
II) Steroid hormones: Penetrate the cell and bind to a receptor protein inside the target cell. This also will trigger signal transduction pathway (for triggering mRNA transcription for synthesizing a specific protein). • Estrogen, progesterone, vitamin D and NO. • Usually, the intracellular receptor activated by a hormone is a transcription factor. Fig. 45.3b, Page 959
الصنوبرية النخامية الدرقية الكظرية The Vertebrate Endocrine System • Tropic hormones (الهرمون المنبه للغدد) • Target other endocrineglands and areimportant to understandingchemical coordination. • Human has 9 endocrine glands. Fig. 45.5, Page 960
The hypothalamus and pituitary integrate many functions of the vertebrate endocrine system • The hypothalamus integrates endocrine and nervous function. • Neurosecretory cells of the hypothalamus produce hormones. • Releasing hormones stimulate the anterior pituitary (adenohypophysis) to secrete hormones. • Inhibiting hormones prevent the anterior pituitary from secreting hormones. 1)- Pituitary gland:secrets 9 hormones( 7 hormones by the anterior part and 2 hormones by the posterior part).
A)- Anterior pituitary hormones. • Growth hormone (GH): a protein. • Stimulates growth and metabolism. • Secretion regulated by hypothalamic hormones. • Acts directly on tissues or acts viagrowth factors. • Gigantism:العملقة excessive GH during development. • Acromegaly: excessive GH production during adulthood. • Hypopituitary dwarfism القزمية: childhood GH deficiency. • Prolactin (PRL): a protein. • Stimulates milk production and secretion from mammary glandالغدد اللبنية. This secretion regulated by hypothalamic hormones. • Gonadotropins (Gonotropic محفز للمناسل): glyocoproteins. • Follicle-stimulating hormone (FSH). • Stimulates production of sperms and ova. • Secretion regulated by hypothalamic hormones. • Luteinizing hormone (LH) المُحفز لتكوين الجسم الأصفر. • Stimulates ovaries and testes. • Secretion regulated by hypothalamic hormones.
Thyroid-stimulating hormone (TSH): a glycoprotein. • Stimulates thyroid gland. • Secretion regulated by thyroxine in blood. • Secretion regulated by hypothalamic hormones. • Adrenocorticotropic hormone (ACTH): a peptide • Stimulates adrenal cortex secretion of glucocorticoids • Secretion regulated by glucocorticoids and hypothalamic hormones. • Melanocyte-stimulating hormone (MSH): a peptide. • May play a role in fat metabolism. • Endorphins: peptides. • Inhibit pain perception. • Effects mimicked by heroin and other opiate drugs.
Melanocyte-stimulating H. Adrenocorticotropic Also called gonadotropine hormones هرمونات المناسل The anterior pituitary gland hormones Fig. 45.6b, Page 963
B)- Posterior pituitary hormones. • Oxytocin: a peptide. • Stimulates contraction of the uterus and mammary glands. • Secretion regulated by the nervous system. • Antidiuretic hormone (ADH):مُضاد لإدرار البول a peptide. • Promotes retention of water by the kidneys (in Kidney tubules). • High level decreases urination and viceversa. • Secretion regulated by water/salt balance. • 2- Pineal gland:الغدة الصنوبرية is a small mass of tissue near the center of the mammalian brain and involved in biorhythms. • The pineal gland secretes the hormone, melatonin, an amine. • Involved in biological rhythms associated with reproduction. • Secretion regulated by light/dark cycles.
Antidiuretic H • Posterior pituitary(neurohypophysis)stores and secretes hormones produced by the hypothalamus. Fig. 45.6a, Page 963