Ch25 Endocrine
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Ch25 Endocrine






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    Ch25 Endocrine Ch25 Endocrine Presentation Transcript

    • The Endocrine System Chapter 25
    • The Endocrine System
      • A system of ductless glands that secrete hormones (‘messenger’) molecules
      • - secrete hormones directly into the blood or lymph
      • - hormones trigger physiological changes in target cells
      • Controls and integrates the functions of other body systems
      • - closely interacts with the nervous system
      • Endrocrinology
      • - the study of hormones and endocrine glands
      • Nervous System
      • Controls homeostsis rapidly
      • Anatomically continuous:
      • nerve impluse conducted along axons from one neuron to the next
      • Neurotransmitters (NTs)
      • Brief effect (muscle contraction)
      • Endocrine System
      • Controls growth and metabolism slowly
      • Scattered:
      • messenger molecules released into the EC space will immediately enter adjacent capillaries
      • Hormones (‘to excite’)
      • Longer lasting effect with feedback loops
      Together these systems interact to coordinate and integrate activity of our cells
    • Endocrine Organs
      • Series of ductless glands
      • - small and scattered throughout the body
      • - some may be both endocrine and exocrine
      • ‘ Pure’ endocrine glands
      • - pituitary, pineal, thyroid, parathyroid, and adrenal
      • Organs containing endocrine cells
      • - pancreas, thymus, gonads, and hypothalamus
      • Most endocrine cells are of epithelial origin
      • - others include hormone-secreting neurons, muscle cells, and fibroblast-like cells
      • Highly vascularized – blood and lymph vessels
    • Location of the Major Endocrine Glands
      • Endocrine cells also
      • occur in the heart,
      • alimentary canal,
      • kidney, skin, placenta,
      • and elsewhere
      Fig 25.1
    • Endocrine System Overview
      • Endocrine glands may be stimulated by the nervous system or chemical changes in the body
      • - respond by secreting hormones into the circulation
      • Hormones travel through the bloodstream but affect only specific tissues called target tissues
      • Hormones secreted by cells regulate the metabolic function of other cells in the body
      • - effects result from pre-programmed responses of target cells
    • Endocrine Functions
      • Regulation of:
      • - Internal environment (adjust fluid/volume ratio): aldosterone
      • - Metabolism and energy balance: thyroid hormones
      • - Cardiac and smooth muscle contraction: epinephrine and norepinephrine
      • - Immune system: cytokines
      • - Glandular secretions: hypothalamus and pituitary hormones
      • Maintainance and assistance of:
      • - Homeostasis despite disruptions: pancreatic hormones
      • - Growth and development: growth hormones
      • - Reproduction: hormones that influence oogenesis and spermatogenesis
    • Classes of Hormones
      • The body produces many different kinds of hormones with distinct chemical structures
      • Two broad molecular categories:
      • 1. Amino acid-based hormones - modified amino acids (amines), peptides (short chains of amino acids), and proteins (long chains of amino acids)
      • 2. Steroid hormones - lipid molecules derived from cholesterol
    • Basic Hormone Action
      • Hormones circulate throughout the body in BVs
      • - leave the bloodstream at capillaries encountering all body tissues
      • - influences only specific tissue cells or target cells
      • - same hormone can have different effects on different target cells
      • - similar molecular structures can have very different functions
      • Cells have receptors on their surface that bind only specific types of hormones
      • - receptor binding initiates a response/reaction
      • - hormones are just molecular triggers and do not carry any coded information
    • Control of Hormone Secretion
      • Secretion is triggered by three major types of stimuli: humoral, neural, and hormonal stimuli
      • Humoral (‘body fluids’) - simplest of endocrine control mechanisms
      • - secretion is in direct response to changing critical ion or nutrient levels in the blood
      • - parathyroid monitors calcium: responds to decline be secreting hormone to reverse decline
      • Neural
      • - a few glands secrete their hormones in response to stimuli by the nervous system to induce physiological changes
      • - sympathetic nerve fibers stimulate cells in the adrenal medulla
      • - induces release of epinephrine and norepinephrine
    • Control of Hormone Secretion
      • Hormonal
      • - many endocrine glands secrete their hormones in response to hormonal stimuli received from other endocrine glands
      • - certain hormones signal secretion of other hormones
      • - the hypothalamus secretes hormones  stimulates the pituitary  stimulates other glands (the thyroid, adrenal cortex, and the gonads)
      • Note: the hypothalamus is called the master gland
      • - controls many functions of the endocrine system, through hormonal and other mechanisms
    • Control of Hormone Release: 3 Mechanisms Fig 25.2
    • Control of Hormone Secretion
      • Always controlled by feedback loops
      • - ensures that hormone concentrations stay within a narrow ‘desirable’ range in the blood
      • Negative feedback loop:
      • - Hormonal blood concentration declines below a minimum set point more hormone is secreted
      • - Blood concentration exceeds a maximum set point hormone production is halted
      • Positive feedback loop:
      • - as blood concentrations of a certain hormone increase the response of the effector organ stimulates further secretion
      • - progression of labor in childbirth by oxytocin
    • The Pituitary Gland (Hypophysis)
      • The pituitary gland (hypophysis - undergrowth):
      • - secretes 9 major hormone
      • - sits in the hypophyseal fossa of the sella turcica
      • - resembles a golf club: the gland forms the head of the club, and the stalk, called the infundibulum (funnel), forms the shaft
      • - the infundibulum connects superiorly to the hypothalamus
      • 2 basic divisions of the pituitary gland:
      • - Anterior adenohypophysis (adeno = glandular)
      • - Posterior neurohypophysis (neuro = neural)
      • Blood supply: 2 branches of the internal carotid artery
      • - superior hypophyseal artery supplies the adenohypophysis
      • - inferior hypophyseal artery supplies the pars nervosa
    • The Pituitary Gland Figure 25.3a–c
    • The Adenohypophysis
      • Hormone release is controlled by the hypothalamus
      • - stimulated and inhibited by releasing and inhibiting hormones
      • 3 subdivisions: pars distalis, pars intermedia, pars tuberalis
      • - pars distalis the largest division has 5 different endocrine cell types
      • - secrete protein hormones, have many secretory granules and a well-developed RER and Golgi apparatus
      • Somatotropic cells
      • - secrete growth hormone (GH)
      • Mammotropic cells
      • - secrete prolactin (PRL)
    • Pars Distalis Endocrine Cells
      • Thyrotropic cells
      • - secrete thyroid-stimulating hormone (TSH)
      • Corticotropic cells
      • - secrete adrenocorticotropic hormone (ACTH) and melanocyte-stimulating hormone (MSH)
      • Gonadotropic cells
      • - secrete follicle-stimulating hormone (FSH), luteinizing hormone (LH)
      • Tropic (‘changing’) hormones – TSH, ACTH, FSH, LH
      • - regulate secretion of hormones by other endocrine glands
      • - GH, PRL, and MSH act directly on nonendocrine target tissues
      • 5 cell types group into 3 categories when stained: acidophils, basophils, chromophobes
      • GH or somatotropin - stimulates growth of body tissues, especially in muscle and skeleton
      • TSH - stimulates the thyroid to produce and release T4 and T3 (influences metabolism)
      • PRL – initiates and maintains milk production (lactation) by mammary glands in the breasts
      • ACTH – influences production and secretion of hormones by the adrenal cortex (helps us deal with stress)
      • MSH - stimulates melanocytes of the epidermis to produce more melanin, thus darkening the skin
      • FSH - stimulates ova maturation and estrogen production in ovaries and sperm production in the testes
      • LH or ICSH – stimulates ovulation and progesterone secretion in ovaries and testosterone secretion in the testes
    • Hypothalamic Control of Hormone Secretion from the Adenohypophysis
      • The hypothalamus have neurons that produce and release hormones much like NTs are released
      • - secretes releasing factors to release hormones
      • - secretes inhibiting hormones to turn off hormone secretion
      • - travels through the hypophyseal portal system into the anterior pituitary to stimulate its hormone secretion
      • - the hypophysial portal system involves two beds of capillaries connected by a vein
      • - allows a high level of hormone concentration within a small region
      • - designed so that the hormones released by the hypothalamus travel directly to the anterior pituitary
      • - in turn the anterior pituitary releases hormones into systemic circulation
    • Hypothalamic Control of Hormone Secretion from the Adenohypophysis Fig 25.4
    • The Neurohypophysis
      • Stores and releases hormones produced by the hypothalamus
      • - structurally part of the brain
      • - composed of nervous tissue (unmyelinated axons and neuroglial cells)
      • Hormones made in the neuron cell bodies, transported along the axons, and stored in dilated axon terminals ( Herring bodies ) – secrete 2 hormones
      • - antidiuretic hormone (ADH) or vasopressin (‘vessel constrictor’): targets the kidney to resorb more water from the urine and return it to the blood
      • - secretes oxytocin induces contractions of smooth muscle of reproductive organs
    • The Neurohypophysis
      • When the neurons
      • fire, they release
      • stored hormones
      • into a capillary bed
      • in the pars nervosa
      • for distribution
      Fig 25.5
    • Table 25.1
    • The Thyroid Gland
      • Largest pure endocrine gland
      • - located in the anterior neck
      • Internally, is composed of hollow follicles
      • - separated by areolar CT rich in capillaries
      • - walls are formed of cuboidal or squamous epithelial cells (follicular cells)
      • - lying within the epithelium are parafollicular (C) cells
      • - central lumen filled with colloid (‘gluelike’) consisting of thyroglobulin (protein precursor to thyroid hormone)
      • Produces 2 hormones: amino-based and protein
      • - Thyroid hormone (TH): thyroxine (T 3 ); tri-iodothyronine (T 4 )
      • - Calcitonin: lowers blood levels of Ca 2+ , mostly during childhood
    • The Thyroid Gland
      • T4 and T3, consists of 2 amino acids and iodine
      • Main function is to increase metabolic rate
      Fig 25.6
    • Histology of the Thyroid Gland
      • Follicle cells continuously synthesize thyroglobulin and secrete it into the follicle lumen for iodination and storage
      • TSH (pituitary gland) signals the follicle cells to release TH
      Fig 25.6
    • The Parathyroid Glands
      • Lie on the posterior surface of the thyroid gland surrounded by CT capsules (number varies)
      • Contains thick branching cords composed of 2 types of endocrine cells
      • - small abundant chief cells and rare larger oxyphil cells
      • Chief cells produce a small protein hormone, PTH
      • - PTH increases calcium levels and is essential to life:
      • 1) stimulates osteoclasts to release calcium from bones
      • 2) decreases secretion of calcium by the kidney
      • 3) activates vit D, which stimulates uptake of Ca by the intestine
    • The Parathyroid Glands
      • Posterior view of the pharynx a
      • and trachea showing the location
      • of the parathyroid glands on the
      • posterior aspect of the thyroid
      Fig 25.7
    • Histology of the Parathyroid Gland
      • The function of oxyphil (‘acid-loving’) cells is unknown
      • PTH is essential to life - low Ca 2+ levels lead to lethal neuromuscular disorders
      • What is the antagonist of PTH?
      Fig 25.7
    • The Adrenal (Suprarenal) Glands
      • Paired pyramidal organs on the superior surface of the kidneys – highly vascularized
      • 3 groups of 60 small suprarenal arteries supply each gland
      • - the superior suprarenal arteries from the inferior phrenic artery;
      • - middle suprarenal arteries from the aorta;
      • - inferior suprarenal arteries from the renal artery
      • Veins
      • - left suprarenal vein drains into the renal vein and the right suprarenal vein drains into the inferior vena cava
      • Nerve supply is almost entirely sympathetic fibers
      • 2 endocrine glands in one - internal and external:
      • - Adrenal medulla: a cluster of neurons derived from the neural crest, acts as part of the sympathetic NS
      • - Adrenal cortex: bulk of the adrenal gland derived from mesoderm
      The Adrenal (Suprarenal) Glands
    • The Adrenal Medulla
      • Part of the autonomic nervous system (Ch 15)
      • Chromaffin (‘affinity for chromium’) cells
      • - arranged in spherical clusters with some branching cords
      • - modified ganglionic sympathetic neurons
      • - secrete catecholamines: the amine hormones epinephrine and norepinephrine
      • - active in the ‘fight, flight, and fright’ (fight or flight) response
      • - hormones stored in secretory vesicles
    • The Adrenal Cortex
      • Secretes a variety of corticosteroid hormones
      • - all are lipid-based steroids
      • Cortex is composed of 3 layers or zones:
      • - Zona glomerulosa (‘ball of yarn’): cell clusters
      • - Zona fasciculata: cells arranged in bundles
      • - Zona reticularis (‘network’): cells arranged in a branching network
    • The Adrenal Gland Figure 25.8a, b
    • Adrenal Corticosteroids
      • 2 main classes: mineralocorticoid & glucocorticoid
      • Main mineralocorticoid is aldosterone
      • - secreted by the zona glomerulosa
      • - in response to a decline in blood volume or BP
      • - prompts kidney to resorb more sodium into the blood; water passively follows, increasing blood volume
      • Glucocorticoids: cortisol is the main type
      • - secreted by zona fasciculata and zona reticularis
      • - helps the body deal with stressful situations by keeping glucose levels high to support the brain
      • - body cells switch to fats and amino acids as energy sources
      • - high amounts depress the inflammatory response
      Adrenal Corticosteroids
    • Adrenal Corticosteroids
      • Hormonal pathway of stress:
      • - hypothalamus sends corticotropin-releasing hormone (CRH)
      • to the adenohypophysis, which secretes ACTH
      • - ATCH travels to the adrenal cortex to signal glucocorticoid secretions
      • - the sympathetic NS can also stimulate glucocorticoid secretions
      • Zona reticularis secretes an androgen hormone, dehydroepiandrosterone (DHEA)
      • - DHEA is converted to testosterone and estrogens in peripheral tissues
      • - proposed beneficial effects include counteracting stress, boosting immunity, and mood
      Adrenal Corticosteroids
    • Structure of Steroid-Secreting Cells
      • Steroid-secreting cells have distinctive features
      • - abundant SER and no secretory granules
      • - mitochondria have unusual cristae shaped like tubes
      • - lipid droplets are abundant in cytoplasm (lipids = raw material of steroids)
      • Characterize cells of the adrenal cortex
      • - also testicular and ovarian cells which secrete steroid sex hormones: the interstitial cells, theca folliculi cells, and cells of the corpus luteum
    • Interstitial cell in the testis Fig 25.9
    • The Pineal Gland
      • Small, pine cone shaped structure at the end of a short stalk on the roof of the diencephalon
      • Pinealocytes are arranged in both spherical clusters and branching cords
      • - star-shaped cells with long, branching cell process
      • - dense particles of calcium lie between the cell clusters, forming the ‘pineal sand’ (which is radiopaque)
      • - in Xrays used as a landmark to identify brain structures
      • - secretes melatonin: a hormone that regulates circadian rhythms (hypothalamus responds to a lack of visual input)
    • The Pineal Gland
    • The Pancreas
      • Located in the posterior abdominal wall
      • Contains endocrine and exocrine cells
      • Exocrine acinar cells, form most of the gland
      • - secrete digestive enzymes into the small intestine
      • Endocrine cells are contained in spherical bodies
      • - pancreatic islets or islets of Langerhans
      • - about 1 million scattered among the exocrine acini
      • Main endocrine cell types:
      • - Alpha cells ( α cells): secrete glucagon signals liver to release glucose from glycogen; raises blood sugar
      • - Beta cells ( β cells): secrete insulin signals most body cells to take up glucose from the blood; promotes glucose storage as glycogen in liver; lowers blood sugar
      The Pancreas
    • Figure 25.10 A Pancreatic Islet
    • The Thymus
      • Located in the lower neck and anterior thorax
      • Important immune organ
      • Site at which T-lymphocytes arise from lymphocyte-precursor cells
      • - transformation stimulated by thymic hormones, secreted by the thymus epithelial reticular cells
      • Thymic hormones – a family of peptide molecules, including thymopoietin and thymosin
    • The Gonads
      • Main sources of sex hormone – testes and ovaries
      • Male testes
      • - interstitial cells secrete androgens (primarily testosterone)
      • - promotes the formation of sperm
      • - maintains secondary sex characteristics
      • Female ovaries
      • - androgens secreted by the theca folliculi directly converted into estrogens by the follicular granulosa cells & progesterone
      • - estrogens and progesterone secreted by the corpus luteum
      • - estrogens maintain reproductive organs and secondary sex characteristics
      • - progesterone signals uterus to prepare for pregnancy
      The Gonads
      • Endocrine cells occur within
      • The heart - the atria contains atrial natriuretic peptide (ANP)
      • - hormone that stimulates the kidneys to produce more urine containing salt
      • - getting rid of the excess fluid and salt reduces excess blood volume and salt levels; reduces blood pressure
      • The GI tract has scattered enteroendocrine cells
      • - release amino acid/peptide hormones chemically similar to neurotransmitters
      • - affect functions related to regulating digestion, blood chemistry, and blood flow
      Other Endocrine Structures
    • Other Endocrine Structures
      • The placenta is produced when conception occurs
      • - secretes hormones that prevent the uterus from getting rid of the nutrient layer to which it is attached
      • - produces other steroid protein hormones: estrogen, progesterone, corticotropin-releasing hormone, and human chorionic gonadotropin
      • The kidneys
      • - cells of the juxtaglomerular apparatus (JGA) secrete rennin which regulates blood pressure
      • - endothelial cells and interstitial CT secrete erythropoietin which stimulates erythrocyte production
      • The skin
      • - when exposed to UV rays produces a steroid hormone precursor to vitamin D essential for calcium metabolism
      Other Endocrine Structures
    • Pituitary Disorders
      • Gigantism
      • - hypersecretion of GH in children
      • Acromegaly
      • - hypersecretion in adults causes
      • Pituitary dwarfism
      • - hyposecretion of GH
      • Diabetes insipidus
      • - pars nervosa does not make enough ADH
    • A Closer Look Potential Uses for Growth Hormone
    • Disorders of the Pancreas
      • Diabetes Mellitus
      • - caused by insufficient secretion of insulin
      • - or resistance of body cells to the effects of insulin
      • Type 1 diabetes
      • - develop suddenly, usually before age 15
      • - T cell-mediated autoimmune response destroys β cells
    • Diabetes Mellitus
      • Type 2 diabetes
      • - Adult onset
      • - Usually occurs after age 40
      • - Cells have lowered sensitivity to insulin
      • - Controlled by dietary changes and regular exercise
    • Disorders of the Thyroid Gland
      • Grave’s Disease
      • - most common type of hyperthyroidism
      • - immune system makes abnormal antibodies
      • - stimulates the oversecretion of TH by follicle cells
      • - leads to nervousness, weight loss, sweating, and rapid heart rate
      • Myxedema
      • - adult hypothyroidism
      • - antibodies attack and destroy thyroid tissue
      • - common symptoms include low metabolic rate and weight gain
    • Disorders of the Thyroid Gland
      • Endemic goiter
      • - due to lack of iodine in the diet
      • Cretinism
      • - hypothyroidism in children
      • - short, disproportionate body, thick tongue and mental retardation
    • Thyroid Disorders Figure 25.11
    • Disorders of the Adrenal Cortex
      • Cushing’s syndrome
      • - caused by hypersecretion of glucocorticoid hormones usually due to a pituitary tumor
      • Addison’s disease
      • - hyposecretory disorder of the adrenal cortex
      • - deficiencies of both mineralocorticoids and glucocorticoids
    • Thyroid Disorders Figure 25.12
    • The Endocrine System Throughout Life
      • Endocrine organs operate effectively until old age
      • Adenohypophysis
      • - increase in CT and lipofuscin
      • - decrease in vascularization and number of hormone-secreting cells
      • Adrenal cortex
      • - normal rates of glucocorticoid secretion continue
      • Adrenal medulla
      • - no age-related changes in catecholamines
      • Pituitary gland – dual origin
      • - adenohypophysis originates from the roof of the mouth
      • - neurohypophysis grows inferiorly from the floor of the brain
      • Thyroid hormones
      • - decrease slightly with age
      • Parathyroid glands
      • - little change with aging
      • GH, DHEA, and the sex hormones
      • - marked drops in secretion with age
      The Endocrine System Throughout Life
    • Embryological Origin of Endocrine Organs
      • Thyroid gland
      • - forms from a thickening of endoderm on the floor of the pharynx
      • Parathyroids and the thymus gland
      • - from endoderm lining the pharyngeal pouches
      • Pineal gland
      • - originates from ependymal cells
      • Adrenal gland – dual origin gland
      • - adrenal medulla from neural crest cells of nearby sympathetic trunk ganglis
      • - adrenal cortex from mesoderm lining the coelom
    • Embryonic Development Figure 25.13
    • Figure 25.b–d