Endocrine System PDF

Endocrine System Karen Gil MD, MHSN Objectives 1. Provide an overview of what the endocrine system, his components, and its role in maintaining homeostasis 2. Explain the function of hormones in the body, including how they are produced, released, and their target organs or tissues 3. Discuss the ma...

Endocrine System Karen Gil MD, MHSN Objectives 1. Provide an overview of what the endocrine system, his components, and its role in maintaining homeostasis 2. Explain the function of hormones in the body, including how they are produced, released, and their target organs or tissues 3. Discuss the major endocrine glands, detailing their structure and primary hormones 4. Describe the mechanisms of hormonal regulation, including feedback loops and the role of hypothalamus-pituitary axis 5. Discuss common disorders of the endocrine system, specifically at the anterior pituitary gland and their association with eye diseases and treatment Endocrine System The nervous and endocrine systems act together to coordinate functions of all body systems The endocrine system controls body activities by releasing mediator molecules called hormones Hormones are released in one part of the body but regulates the activity of cells in other parts of the body Nervous and Endocrine System Nervous system Endocrine system Neurotransmitter are the mediator molecules Locally released in response to nerve impulses Site of action close to the site of released Target cells are muscle, cells, glands, neurons Time of onset of action milliseconds Duration of action milliseconds Hormones are the mediator molecules Delivered to tissues throughout the body by the blood Site of action far from site of released Target cells are cells throughout the body Time to onset of action seconds to hours or days Duration of action seconds to days Endocrine Glands Function Help regulate– – – – Chemical composition and volume of interstitial fluid Metabolism and energy balance Contraction of smooth and cardiac muscle fibers Glandular secretions and some immune system activities – Control growth and development – Regulate operation of reproductive systems – Help establish circadian rhythms Endocrine System Two kinds of glands – Exocrine glands Secrete their products into ducts that carry the secretions into body cavities, into the lumen of an organ or to an outer surface of the body – – – – Sudoriferous glands Sebaceous glands Mucous glands Digestive glands – Endocrine glands Secrete their products into the interstitial fluid surrounding the secretory cells rather than into ducts Circulating blood delivers the hormones to target tissues Endocrine System Endocrine Glands: – – – – – Pituitary Thyroid Parathyroid Adrenal Pineal glands Organs that contain cells that secrete hormones – – – – – – – – – – – – – Hypothalamus Thymus Pancreas Ovaries Testes Kidneys Stomach Liver Small intestine Skin Heart Adipose tissue Placenta All endocrine glands and hormonesecreting cells constitute the endocrine system Hormone 50 hormones Affect only target cells binding to specific receptors Endocrine secretion alters the physiologic activity of target cells Powerful effect even at low concentrations Target cells can have 5,000 to 100,000 receptor for a particular hormone Functional Types Endocrine Circulating Autocrine Paracrine Local Types of local hormones Paracrines Act on neighboring cells Autocrines Act on the same cell that produce them Hormone Interactions Responsiveness of a target cell to a hormone depends on: 1. Hormone concentration 2. Abundance of the target cell’s hormone receptors 3. Influences exerted by other hormones Control of Hormone Secretion Regulated by: 1. Signals from CNS 2. Chemical changes in blood 3. Other hormones Most systems that regulate secretion of hormones work by – Feedback mechanism positive (stimulating secretion) negative (inhibiting secretion) most common Feedback Mechanism Hormone level low or hormone required Negative feedback mechanism – Works when high levels of a hormone in question turns off its own secretion – Controlled by hypothalamus or pituitary gland Hormone released Blood hormone levels become high Hypothalamus releases inhibitory hormone or hypothalamus and/or pituitary secretions stopped Feedback Mechanisms Positive Feedback – results in amplification of the stimulus and increased release of the hormone involved until a particular process is complete Hormone required and released Process stimulated and hormone release continues Process complete Hormone release stop Hypothalamus Important regulatory center for the Nervous and Endocrine Systems Hormones secreted by the hypothalamus and the Pituitary Gland regulate: – virtually all aspects of growth, development, metabolism and homeostasis Hypothalamic Hormones GHRH – Growth hormone releasing hormone GHIH – Growth hormone inhibiting hormone) TRH – Thyrotropin releasing hormone GnRH – Gonadotropin releasing hormone PRH – Prolactin releasing hormone PIH – Prolactin inhibiting hormone CRH – Corticotropin releasing hormon Pituitary Gland Anatomically rest on the sphenoid bone (sella turcica) in the cranial vault 1-1.5 cm Connected by the infundibulum to the hypothalamus Histologically is divided into three lobes but functionally into two lobes 1. 2. 3. Adenohypophysis (anterior lobe) 75 % Pars intermedia (intermediate lobe) Neurohypophysis (posterior lobe) Pituitary Gland Adenohypophysis Produces 7 hormones: hGH - human Growth Hormone ACTH - Adrenocorticotropic hormone TSH -Thyroid-stimulating hormone PRL - Prolactin MSH - Melanocyte-stimulating hormone Gonadotropins ▪ FSH - Follicle-stimulating hormone ▪ LH - Luteinizing hormone Pituitary Gland Neurohypophysis Produce 2 hormones ADH - Antidiuretic hormone or vasopressin Oxytocin Histology of the Adenohypophysis Somatotrophs – Produce human growth hormone (hGH) – stimulating general body growth and regulating aspects of metabolism Thyrotrophs – Produce thyroid stimulating hormone (TSH) – involved in control of secretion and other activities of the thyroid gland Histology of the Adenohypophysis Gonadotrophs – Produce and release follicule stimulating hormone (FSH) and lutenizing hormone (LH) Together stimulate secretion of estrogen and progesterone stimulating oocyte maturation in the ovaries and production of sperm in the testes Histology of the Adenohypophysis Lactotrophs – Synthesize prolactin (PRL) – initiates milk production by mammary glands Corticotrophs – Produce adrenocorticotropic hormone (ACTH) and melanocyte-stimulating hormone – which stimulates the adrenal gland to secrete glucocorticoids Control of secretion by the Anterior Pituitary Regulated in two ways 1. Neurosecretory cells in the hypothalamus secrete releasing and inhibiting hormones 2. Negative feedback – Rising blood levels of hormones released by target glands decrease secretions of some anterior pituitary cells http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter20/ani mation__hormonal_communication.html Control of secretion by the Anterior Pituitary Hormone Secreted by Releasing hormone Inhibiting hormone hGH Somatotrophs GHRH GHIH TSH Thyrotrophs TRH GHIH FSH Gonadotrophs GnRH - LH Gonadotrophs GnRH - PRL Lactotrophs PRH PIH ACTH Corticotrophs CRH - MSH Corticotrophs CRH Dopamine Control of secretion by the Anterior Pituitary Human Growth Hormone (hGH or Somatotropin) Most abundant hormone of the anterior lobe It is released every 2 hours It promotes cell growth and regulates metabolism Human Growth Hormone (hGH or Somatotropin) DIRECT ACTION Stimulates protein synthesis Promotes synthesis of small proteins that are powerful insulin-like growth factors (IGF’s or somatomedins) – Mainly produced by the liver Human Growth Hormone (hGH or Somatotropin) INDIRECT ACTION Stimulates lipolysis (breakdown of triglycerides into fatty acids and glycerol) – for ATP production through fatty acids oxidation Also stimulates glucose release from the liver (insulin antagonist or diabetogenic effect) Human Growth Hormone (hGH or Somatotropin) REGULATION MECHANISM Mainly controlled by 2 hypophysiotropic hormones – GHRH (growth hormone releasing hormone) – GHIH (growth hormone inhibiting hormone) Major regulator of GHRH and GHIH secretion is blood glucose level Other factors which promote secretion includes – – – – – Decreased fatty acids increased amino acids deep sleep stress or vigorous exercise other hormones as glucagon, estrogen, cortisol and insulin Hypothalamus is stimulated to secret GHRH during hypoglycemia and GHIH during hyperglycemia Follicle Stimulating Hormone (FSH) Women Stimulates development of follicles for secretion of estrogen - ovulation Men Stimulates production of sperms Luteinizing Hormone LH In females together with FSH stimulates secretion of estrogen and bring about ovulation Also stimulates the formation of the corpus luteum (structure formed after ovulation) in females – in the ovary and produces progesterone – This help in the preparation of the uterus for implantation of a fertilized ovum as well as mammary gland for milk secretion In males stimulates the interstitial cells to secret large amounts of testosterone Regulation mechanism GnRH release is under a negative feedback http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter20/animation__posi tive_and_negative_feedback__quiz_1_.html Gonadotropins FSH and LH Prolactin Together with other hormones initiate and maintain milk secretion by the mammary gland Ejection of milk depends on oxytocin raise during pregnancy Sucking of the infant reduces the hypothalamic secretion of PIH – Increase prolactin secretion (PRH elevated) Prolactin Regulation – The hypothalamus secretes Stimulating hormone - PRH (prolactin-releasing hormone) inhibitory hormones – PIH (prolactin-inhibiting hormone) PIH diminish before menstruation and prolactin rises, as the menstrual cycle begins new PIH increase and prolactin decrease Prolactin levels Endocrine Disorders Disorders results form – Dysfunction originating in the peripheral endocrine gland itself (primary disorders) – Understimulation or overstimulation by the pituitary (secondary disorders) Overproduction (hyperfunction) Underproduction (hypofunction) HYPERSECRETION – Functional Adenoma HYPOSECRETION – – – – Ischemic damage Inflammation Radiation Non-functional adenomas Pituitary Adenoma Pituitary Adenomas Prolactinoma Most common type of benign tumors Lactotroph cells secrete prolactin – High prolactin levels (hyperprolactinemia) Characterized by – – – – – – – Headaches Amenorrhea Galactorrhea Loss of libido or impotence Infertility Visual disturbances Visual field defect Lab test – High Prolactin levels – Low FSH and LH Pituitary Adenomas Pituitary Adenomas Head MRI Visual Field Pituitary Adenomas Treatment – Macroadenomas >10mm Surgery – Microadenomas < 10 mm Dopamine agonists control prolactin release Cabergoline 0.5mg (Dostinex) – QD or BID Bromocriptine 2.5mg (Parlodel) – BID or TID Pituitary Adenomas Growth-hormone-producing adenoma Elevated growth hormone (GH) Elevated somatomedin C or IGF-1 – GIGANTISM – ACROMEGALY Pituitary Adenomas Gigantism Occurs in children and adolescent's prior fusion of the growth plates Hypersecretion of GH Characterized – symmetrical increase in stature and visceral enlargement Dx. – GH quantification Pituitary Adenomas Acromegaly Functional adenoma – Hypersecretion of GH during adulthood Physical findings – – – – – – Coarse facial features Prominent jaw Flat, broad forehead Enlarged hands and feet Broad fingers and toes Headache and visual field defects (bitemporal hemianopsias) Enlarged sella turcica Internal organs enlarged Most common cause of death is cardiac failure Dx: – GH quantification Tx. – Surgery Pituitary Adenomas Acromegaly Pituitary Adenomas Hypopituitarism Destructive lesion of Pituitary gland (75% of parenchyma) result in panhypopituitarism Characterized – Thyroid, adrenal gland and reproductive organs abnormalities Common causes 1. Adult Pan-hypopituitarism – Expansile pituitary tumors 2. Sheehan’s Syndrome – Postpartum necrosis of the pituitary gland Pituitary Adenomas Panhypopituitarism Tx. Hormone replacement Pituitary Insufficiency in Children In most cases no lesions are identified Other causes is a Craniopharingioma – Most common manifestation is dwarfism – Rare – Characteristics Headache 60-80 % Vomiting (projectile vomiting) 35-70 % Vision loss – 20-60 % – Anterior extension to the optic chiasm result in bitemporal hemianopsia, unilateral temporal hemianopsia, papilledema or decrease in visual acuity unilateral or bilateral Endocrine dysfunction – Tx. Surgery Pituitary Adenomas Carcinoma Pituitary Carcinoma Exceedingly rare tumors only diagnosed after metastasis has occur – mostly from breast, lung, renal, prostate, and colon cancers Surgical Removal of Pituitary Tumors Endoscopic skull base surgery Open Craniotomy