07 Animal Physiology - Endocrine System

Principles of Animal PhysiologyEndocrine System


Introduction▪ All cells secrete material into their environment for three main functions▸Protection▸Communication▸Feeding


Introduction▪ Types and functions of Secretions▸Autocrine - secreted substance affects the secreting cell itself▸Paracrine - substance affects neighboring cells▸Endocrine - substance released into blood stream and affects distal target tissue▸Exocrine - substance that is released onto the surface of the animal and other internalized structures


▪ Cell communication through various pathwaysIntroduction


▪ It brings about changes via chemical messengers, hormones, released into the blood stream or hemolymph and carried to target organs.▸Endocrinology - the study of hormones and the endocrine organs they control.▸Endoceine system - all of the glands that secrete hormones♦ Endocrine and exocrine glands

▸Exocrine glands - have ducts through which their nonhormonal products travel to the membrene

Introduction


Introduction▪Endocrine glands - release their substances into the surrounding fluid (ductless glands)▪They include the pituitary, thyroid, parathyroid, adrenal, pineal, and the thymus glands. Also included are the pancreas and gonads. They hypothalamus is called a neuroendocrine organ.

▸Know Table 7.1


▪ Endocrine organsIntroduction


▸Hormones - chemical messengers carried by the blood from endocrine glands to the cell upon which they act.♦ Are chemical messengers

♦ Secreted into the blood by endocrine cells or neurons

♦ Affect distal targets

▸Affect target cells by controlling♦ Rate of enzymatic reactions

♦ Transport of molecules across cell membrane

♦ Gene expression and protein synthesis

♦ Stimulation of mitosis

Introduction


Introduction▪ Tropic hormones▸ Its primary function is to regulate the production and release of other hormones▸ Stimulate and maintain their endocrine target tissue▸Eg., TSH maintains the structural integrity of the thyroid gland, but also cause it to secrete its hormones


Introduction▪ Nontropic hormone▸Exerts its effects on nonendocrine target tissues▸Thyroid hormone increases the metabolic activity of almost every cell


▪ Complexity of Endocrine Function♦A single endocrine gland may produce multiple hormones

♦A single hormone may be secreted by more than one endocrine gland

♦A single hormone may have more than one type of target cell and may induce more than one effect

♦Secretory rate may vary considerably over time

♦A single target cell may be affected by more than one hormone

♦A single chemical messenger may be a hormone or a neurotransmitter

♦Some organ are purely endocrine while other may have nonendocrine functions

Introduction


▪ Classification of hormones▸Peptide hormones - 3 or more amino acids

♦ Hydrophilic

▸ Steroid hormones - derived from cholesterol♦ Lipophilic

▸Amine hormones - single amino acids♦ Hydrophilic

▸Endocrine-disrupting chemicals (EDCs)♦ Nonnative hormonelike substances

♦ By-products of manufactured organic compounds

Introduction


▪ Peptide hormone - eg: Insulin▸ Synthesis - RER, preprohormone▸Packaged in vescicles▸ In Golgi apparatus, pre to pro hormone then to hormone and fragments▸Released into ECF when cell is signaled to do so▸Transported in blood, half-life - minutes▸Mechanism of action - bind to cell surface receptors. Many use cAMP and some use tyrosine kinase▸Action - open or close membrane channels or modulate metabolic enzymatic activity or transport

Introduction


▪ Peptide hormone synthesis, packaging, and release

Introduction


Introduction▪ Steroid hormones, eg: estradiol▸ Synthesis - SER, lipophilic, sythesized as needed▸Found bound (inactive) to protein carriers in blood▸Half-life - hours▸Mechanism - diffuses across cell membrane to cytoplasmic and nuclear receptors. Interact with DNA▸ Slow response by cells - hours


▪ Action of Steroid HormonesIntroduction


▪ Steroidogenic pathwaysIntroduction


▪ Amine hormones▸Nitrogen-containing▸Most derived from tryptophan or tyrosine▸ like peptide hormones (catecholamines) or like steroid hormones (thyroid hormones)▸ Thyroid hormones: produced by thyroid gland found in the lower part of the neck. It secretes 3 hormones:♦ Thyroxine - T4

♦ Triiodothyromine - T3

♦ Calcitonin

▸ The first two are collectively known as thyroid hormones (TH) and contain iodine

Introduction


Introduction▪ Amine hormone, Adrenal medullary hormones▸The adrenal gland consists of a medullary and cortical section. The cortex secretes steroid hormones.▸The adrenal medulla secretes two hormones♦ Epinephrine (E) and

♦ Norepinephrine (NE)

▸These are also called catecholamines


Introduction▪ Mechanism of action of lipophilic hormones


▪ Second messenger mechanisms of amino acid-based hormones

Introduction


Introduction▪ Hormonal Specificity▸All major hormones circulate to virtually all tissues (target cells), but for these cells to respond to a hormone, they must have a specific protein receptor on their plasma membrane or in their interior.

▪ Hormone-target interaction depends on:▸ Blood levels of the hormone▸ The relative number of receptors for that hormone▸ The affinity of the bond between the hormone and the receptor

▪ Up-regulation and down-regulation


Introduction▪ Onset, Duration, and Half-life▸Onset varies greatly, from almost immediately to hours or days▸Duration can range from several minutes to several hours▸Half-life is the length of time the hormone concentration takes to drop by half♦ From a fraction of a minute to several hours

▸Concentration determined by its rate of release and the speed of deactivation and removal


▪ Endocrine glands are stimulated by humoral, neural and hormonal means.▸Humoral stimuli - changing levels of blood ions and nutrients. Example:- ↓calcium →↑parathyroid hormone▸Neural stimuli - nerve fiber stimulates hormonal release. Example:-↑nervous input to adrenal medulla → release of catecholamines▸Hormonal stimuli (tropic hormones) - endocrine glands release their hormones in response to hormones produced by other endocrine organs. Example:- hypothalamic hormones → anterior pituitary to release hormones → other endocrine glands to produce even more hormones

Introduction


▪ Hormone action in invertebrates▸Prothoracicotropic hormone♦ Produced by neurosecretory cells of the brain

▸ Juvenile hormone♦ Produced by non-neural cells near the brain

▸Ecdysone♦ Steroid-like hormone produced by glands in the thorax

▸Eclosion hormone♦ A peptide hormone produced by cells near the brain

▸Bursicon♦ Produced by neurosecretory cells of the brain and

Invertebrate Endocrinology


Invertebrate Endocrinology▪ Hormone production in an insect


Invertebrate Endocrinology▪ Development sequence in the cecropia moth


Invertebrate Endocrinology▪ Developmental hormones in insects


▪ Hypothalamic-Pituitary system▸Pituitary gland (hypophysis) - lies just below hypothalamus, in pocket of bone at base of brain. Consists of two adjacent lobes - the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis)▸Posterior pituitary hormones♦ Oxytocin and vasopressin are released

♦ Made in hypothalamus, move down the neural axons and accumulate in the axon terminals in the posterior pituitary

♦ Vasopressin - blood pressure and kidney function

Vertebrate Endocrinology


Vertebrate Endocrinology▪ Hypothalamus▸The hypothalamus also secretes hormones that control the secretion of ALL the anterior pituitary hormones. The basic pattern is as follows:♦ Secretion of a hypothalamic hormone, which controls secretion of

♦ An anterior pitiutary hormone, which controls the secretion of

♦ A hormone from some other endocrine organ/gland

▸Anterior Pituitary Hormones♦ At least eight secreted, six with well-established functions


▪ Anatomy of the Pituitary glandVertebrate Endocrinology


▪ Hypothalamic-Pituitary systemVertebrate Endocrinology


Vertebrate Endocrinology▪ The Intermediate Lobe▸Rudimentary after birth in human fetus▸ Secretes melanocyte-stimulating hormone (MSH)▸ Secretion inhibited by hypothalamic dopamine▸MSH controls skin coloration via melanin▸MSH may help regulate food intake and suppress the immune system


▪ Hypothalamus and the Posterior PituitaryVertebrate Endocrinology


Vertebrate Endocrinology▪ Posterior Pituitary▸Receives input from supraoptic and paraventricularnuclei▸ Stores and releases vasopressin and oxytocin▸A single neuron produces a single hormone


▪ Posterior Pituitary▸Vasopressin♦ Antidiuretic hormone (ADH); arginine vasotocin (AVT) in lower vertebrates

♦ Enhances water retention

♦ Stimulates arteriolar smooth muscle contractions

♦ Releases due to increased plasma osmolarity

▸Oxytocin♦ Stimulates uterine contraction in mammals

♦ Promotes milk ejection from mammary glands

♦ In nonmammals it is called mesotocin (MT)– Influences blood flow



▪ Hypothalamic Releasing Hormones (Table 7-2)▸Corticotropin Releasing Hormone (CRH)▸Thyrotropin Releasing Hormone (TRH)▸Growth Hormone Releasing Hormone (GHRH)▸ Somatostatin (SS) also called Growth hormone releasing Inhibitin Hormone (GIH)▸Gonadotropin Releasing Hormone (GnRH)▸Prolactin Releasing Hormone (PRH)▸Prolactin releasing Inhibiting Hormone (PIH)

M l t Sti l ti H (MSH)



Vertebrate Endocrinology▪ Anterior Pituitary Hormones▸Gonadotropic Hormones♦ Follicle-Stimulating Hormone (FSH)

♦ Luteinizing Hormone (LH)

▸Growth Hormone (GH)▸Thyroid-Stimulating Hormone (TSH)▸Prolactin (PRL)▸AdrenoCorticoTropic Hormone (ACTH)▸Tropic hormones

– TSH, ACTH, FSH, AND LH


▪ Functions of Anterior Pituitary HormonesVertebrate Endocrinology


▪ Feedback control in the Endocrine SystemVertebrate Endocrinology


▪ Vascular link between the hypothalamus and anterior pituitary



▪ Physiological Effects of Four Major Categories▸Metabolic and Developmental Hormones♦ Glucocorticoids and catecholamines

♦ Thyroid hormones

♦ Growth hormone

♦ Insulin and glucagon

▸Hormones that Regulate Water and Electrolyte Balance♦ Vasopressin - prevents water loss

♦ Aldosterone - prevents sodium (and water) loss

♦ Atrial Natriuretic Peptide - increases sodium (and water) loss

♦ ParaThyroid Hormone - increases plasma Ca++ levels



Vertebrate Endocrinology▪ Physiological Effects of Four Major Categories▸Reproductive Hormones♦ Estrogens - female characteristics and secretions

♦ Androgens - male characteristics and secretions

♦ Progesterone - supports estrogens

▸Prostoglandins♦ May be paracrine or endocrine in nature

♦ Act on smooth muscles of many tissues


▪ Hormonal action of Parathyroid hormoneVertebrate Endocrinology


▪ Hormonal action of Insulin and GlucagonVertebrate Endocrinology


Vertebrate Endocrinology▪ Amine hormone, Adrenal medullary hormones▸The adrenal gland consists of a medullary and cortical section. The cortex secretes steroid hormones.▸The adrenal medulla secretes two hormones♦ Epinephrine (E) and











Date post:	24-Oct-2014
Category:	Documents
Upload:	jerome-ysrael-e
View:	74 times
Download:	0 times

07 Animal Physiology - Endocrine System

Documents