L5 - Endocrine System PDF

Endocrine system H U M A N A N AT O M Y & P H Y SI O LO G Y – B I O L - 1 1 1 2 W I N T E R 2 02 5 R E A DI N G S: C H A P T E R 1 8 , PA G E S 6 47 – 6 5 5 Thyroid gland Parathyroid Pineal gland...

Endocrine system H U M A N A N AT O M Y & P H Y SI O LO G Y – B I O L - 1 1 1 2 W I N T E R 2 02 5 R E A DI N G S: C H A P T E R 1 8 , PA G E S 6 47 – 6 5 5 Thyroid gland Parathyroid Pineal gland Hypothalamus Pituitary gland Endocrinology glands (behind Trachea thyroid glands) Thyroid gland Endocrinology Trachea ◦ Study of chemical messengers (hormones) & tissues Skin Thymus or glands from which they are secreted Lung Heart Hormones Liver Stomach ◦ Produced by neuronal or non-neuronal cells Supraenal Kidney ◦ Most are carried by circulatory system to target glands Uterus Pancreas tissues away from (local or distant) site of production Small Ovary ◦ Bind a receptor in a target tissue intestine Female ◦ Affect activities of cells or organs to regulate function Scrotum ◦ Exert their effects at extremely low concentrations Testes Male OpenStax 17.1 Tortora Fig. 18.1 Tortora 18.1  Endocrine system vs. nervous system Similarities to nervous system ◦ Regulatory system in the body to maintain homeostasis ◦ Chemical messengers & receptors Differences from nervous system ◦ Infrastructure (neurons vs. circulatory system) ◦ Effective concentration of chemical messenger ◦ Speed of onset & duration of action OpenStax 17.1 Sherwood et al. 2013 Fig. 3-16 Tortora 18.1  Pineal gland Pituitary gland Endocrine glands Ductless & release hormones through diffusion directly into the vascular or lymphatic systems Thyroid gland Parathyroid glands May be organized as: Discrete organ Adrenal glands ◦ E.g., pituitary, thyroid, parathyroid, adrenal, & pineal glands Pancreas Group of cells within another organ ◦ E.g., hypothalamus, pancreas, gonads (testes & ovaries) Ovaries Individual cells within another organ Testes ◦ E.g., enteroendocrine cells in GI tract; kidney (erythropoietin) OpenStax 17.1 OpenStax Fig. 17.2 Tortora 18.1  Glandular hormones Hormones Classic glandular hormones ◦ Released by endocrine glands & secreted into bloodstream ◦ E.g., insulin, thyroid hormones, estrogen, testosterone Neurohormones Neurohormones ◦ Produced from “modified” neurons by neurosecretions ◦ E.g., oxytocin, antidiuretic hormone Autocrine & paracrine signaling Paracrine ◦ Locally produced, local acting ◦ E.g., eicosanoids – derived from arachidonic acid (e.g., prostaglandins) OpenStax 17.1 Sherwood et al. 2013 Fig. 3-16 Tortora 18.1  Classification of hormones Hormones are classified by their: Building blocks & method of synthesis ◦ Peptide/proteins ◦ Biogenic amines ◦ Steroids ◦ Eicosanoids Chemical properties – affects solubility & thus mode of transport in blood, half-life, & receptor type ◦ Water soluble ◦ Lipid soluble OpenStax 17.1 Moyes & Shulte 2015 Fig. 4.8, 4.11, 4.18, 5.36 Tortora 18.1  Thyrotropin-releasing hormone (TRH) pyroglutamyl-histidyl-proline Peptide/protein Polypeptide chains of amino acids Synthesized using protein synthesis machinery ◦ Ribosomes of rough ER for synthesis & sorting/packaging in Golgi Peptides – less than 50 amino acid chains ◦ E.g., TRH (tripeptide), antidiuretic hormone, & Growth hormone oxytocin (GH) Proteins – longer amino acid chains ◦ E.g., growth hormone (191 a.a.), insulin OpenStax 17.1 Tortora Fig. Tortora 18.1  Biogenic amines Amino acid derivatives ◦ Have amine (–NH2) group attached to a carbon atom ◦ Synthesized through various enzymatic steps E.g., tyrosine ◦ Catecholamines (NE, E, dopamine) ◦ Iodothyronines (thyroid hormones) E.g., tryptophan ◦ Serotonin, melatonin Note – these are NOT proteins, instead, they are made from a single amino acid OpenStax 17.1 Hill 2022 Fig. 16.5 Tortora 18.1  Steroids Cholesterol derivatives ◦ Synthesized by steroidogenic enzymes found in smooth ER or mitochondria Gonads – e.g., testosterone, estrogen Adrenal cortex – e.g., cortisol (glucocorticoid), aldosterone (mineralocorticoid) Moyes & Shulte 2015 Fig 4.8 OpenStax 17.1 Tortora 18.1  Eicosanoids Derived from arachidonic acid (fatty acid common in plasma membrane phospholipids) Paracrine chemical messenger Modulate inflammation & immune regulation E.g., prostaglandins OpenStax 17.1 Moyes & Shulte 2015 Fig 4.11 Tortora 18.1  Mechanism of action Hormones bind to receptors Receptors ◦ Protein whose function is regulated by ligands (hormones) ◦ Intracellular (cytosolic or nuclear), or plasma membrane-bound Hormone-receptor binding ◦ Highly specific ◦ Elicits cellular response ◦ Causes signal amplification OpenStax 17.1 Moyes & Shulte 2015 Fig 4.11 Tortora 18.1  Water soluble hormones Dissolve easily in plasma but unable to diffuse through plasma membrane ◦ Peptides/proteins ◦ Catecholamines (biogenic amine) ◦ Most eicosanoids Cell surface (membrane-bound) receptors ◦ G protein-coupled receptors ◦ Signaling cascades ◦ Use second messenger (e.g., cAMP) & effector proteins (e.g., protein kinases) to activate/inhibit cellular pathways Rapid, shorter-lasting effect OpenStax 17.1 Moyes & Shulte 2015 Fig 4.27 Tortora 18.1  Lipid soluble hormones Do not easily dissolve in plasma but diffuse through plasma membrane ◦ Steroids ◦ Thyroid hormones (biogenic amine) Bind intracellular receptors ◦ Transcription factors ◦ Activate specific region of DNA (promoter region upstream of a gene) ◦ Initiate production of mRNA & thus influence protein synthesis Slower, longer-lasting effect Moyes & Shulte 2015 Fig 4.19 OpenStax 17.1 Tortora 18.1  Lipid soluble hormones Lipophilic hormones – mostly bound to transport/carrier proteins ◦ Only a small amount of “free” hormone is biologically active Equilibrium between free & bound ◦ As unbound hormone enters targets cells, bound hormone dissociates from carrier proteins & becomes “free” Slows degradation E.g., albumin (generalized); cortisol binding globulin (specific) OpenStax 17.1 Moyes & Shulte 2015 Fig 4. 9 Tortora 18.1 Control processes Hormones circulate at basal (tonic) levels that can be regulated by: Humoral stimuli – changes in blood ion or nutrient levels ◦ E.g., ↓ blood [Ca2+] stimulates parathyroid gland Neural stimuli – nerve impulses ◦ E.g., SNS stimulates adrenal medulla cells to release epinephrine during stress Hormonal stimuli – tropic hormones ◦ E.g., anterior pituitary hormones regulated by releasing/inhibiting hypothalamic hormones OpenStax 17.1 Tortora 18.1  Integrative control mechanisms Feedforward systems Diurnal (circadian) or other biological rhythms Anticipatory changes E.g., plasma cortisol increases at night in anticipation of stresses associated with waking up (i.e., initiating activity, finding food) OpenStax 17.1 Sherwood et al. 2013 Fig. 7-6 Tortora 18.1  Positive feedback Negative feedback Feedback control of Glucose endocrine systems Positive feedback ◦ Stimulatory effect on hormone Pancreas secretion ◦ Rapid response that pushes farter away from set point Insulin ◦ E.g., oxytocin Negative feedback Lower ◦ Inhibitory effect on hormone blood secretion glucose ◦ Dampens hormonal response to maintain a constant level ◦ E.g., insulin OpenStax 17.1 Fig. 4.30; Sherwood et al. 2013 Fig. 1-8 Tortora 18.1  Antagonistic hormonal control Precise control over physiological processes via antagonistic pairs of hormones E.g., blood glucose regulation ◦ ↑ blood glucose – insulin secretion ◦ ↓ blood glucose – glucagon secretion OpenStax 17.1 Moyes & Shulte 2015 Fig 4.35 Tortora 18.1  Other actions of hormones Additive – sum of individual hormonal effects ◦ E.g., blood glucose regulation by glucagon & epinephrine Synergism – greater than sum of hormonal effects ◦ E.g., blood glucose regulation by cortisol, glucagon, & epinephrine Permissive – full effects of one hormone dependent on another hormone ◦ E.g., maturation of reproductive system by gonadotropins requires presence of thyroid hormones OpenStax 17.1 Moyes & Shulte 2015 Fig 4.36 Tortora 18.1 Check your knowledge Indicate important differences between hormonal and neural controls of body functioning. Distinguish between classic glandular hormones, neurohormones, paracrines, and autocrines. Describe how hormones are classified based on their building blocks & methods of synthesis. Describe the two major mechanisms by which hormones affect their target tissues. What control processes are involved in regulating hormone levels? Describe the difference amongst feedforward, positive, & negative feedback control and provide an example of each. Describe how hormones can interact to elicit their actions. Check your knowledge True OR false – the endocrine system has a quicker onset but longer duration of response compared to the nervous system. True OR false – peptide and protein hormones are synthesized using protein synthetic machinery. True OR false – catecholamines are an example of biogenic amine, which is derived from cholesterol. True OR false – cortisol is a steroid hormone that acts on G protein-coupled receptors found in the plasma membrane. True OR false – lipid soluble hormones diffuse through the plasma membrane and act on intracellular receptors, which are transcription factors. True OR false – transport proteins, such as albumin, facilitate the movement of hormones in the blood that are not able to easily dissolve in plasma. Check your knowledge True OR false – feedforward systems alter basal hormone levels in anticipation of change, not in response to a change. True OR false – negative feedback systems are stimulatory, whereas positive feedback systems are in inhibitory. True OR false – the presence of thyroid hormone is required for maturation of the reproductive system by gonadotropin hormones – this is an example of synergism.