Endocrine System

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Endocrine System

• Chapter 16

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Overview

• Overall goal of endocrine system maintain a
  stable internal environment (homeostasis)
• Endocrine glands are ductless glands
• Endocrine glands secrete hormones which travel
  through the blood to a target cell
• Receptor must be present on target cell
• Glands of the endocrine system are present
  throughout the body
• Most cells are regulated by the endocrine system

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Endocrine vs Nervous System

• Both systems function to maintain homeostasis
• Main differences

Feature Endocrine System Nervous System
Effector cells Target cells throughout the body Postsynaptic cells in muscle and glandular tissue only
Chemical messenger Hormone Neurotransmitter
Distance traveled by messenger Long in blood Short across synaptic cleft
Regulatory effects Slow to appear long-lasting Appear rapidly short
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Endocrine vs Nervous System
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Major Endocrine Glands
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Classification of Hormones

• Classified by Function
• Tropic hormones target other endocrine glands
  and stimulate their growth secretion
• Sex hormones target reproductive tissues
• Anabolic hormones stimulate anabolism in their
  target cell

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Classification of Hormones

• Classified by Chemical Structure
• Steroid Hormones
• Derived from cholesterol
• Lipid soluble can pass through phospholipid
  bilayer
• Nonsteriod Hormones
• Synthesized from amino acids
• Proteins, Glycoproteins, peptides, amino acid
  derivatives (Fig 16-3)

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Chemical Classifications of Hormones
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How Hormones Work

• Hormones bind to receptors on target cells
• Lock key
• Hormone-receptor interactions produce regulatory
  changes within the target cell
• Ex initiating protein synthesis
  activation/inactivation of enzymes
  opening/closing of ion channels
• Endocrine glands produce more hormone molecules
  than necessary to hit the target cells
• Excess hormones are excreted in urine or broken
  down by metabolic processes

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How Hormones Work

• Synergism combinations of hormones have a
  greater effect on the target cell compared to a
  single hormone acting alone
• Permissiveness a small amount of one hormone
  allows a second hormone to exhibit its full
  effect on the target cell
• Antagonism two hormones produce opposite effects

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Mechanisms of Steroid Hormone Action

• Steroids are lipids ? not soluble in blood plasma
  (mostly H2O)
• In blood steroids attach to plasma proteins
• Steroid reaches a target cell ? dissociates from
  plasma protein ? diffuses into target cell
• In the nucleus a hormone-receptor complex is
  formed
• Hormone-receptor complexes in the nucleus trigger
  protein synthesis (transcription translation)
• Increase steroid increase response (protein
  synthesis)
• Regulatory effects of hormones are slow to appear

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Mechanisms of Steroid Hormone Action
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Mechanisms of Nonsteriod Hormone Action

• Nonsteroid hormones operate according to the
  second messenger hypothesis
• Nonsteroid hormone is the 1st messenger and
  binds to a receptor on the plasma membrane of the
  target cell
• The message is relayed inside the cell to a
  2nd messenger which triggers the appropriate
  cellular response

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Second Messenger Mechanism

1. Nonsteroid hormone (1st messenger) binds with
   receptor on plasma membrane
2. Hormone-receptor complex activates a membrane
   protein called the G protein
3. G protein activates guanosine triphosphate (GTP)
   which also activates another membrane protein
   (adenyl cyclase)

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Second Messenger Mechanism

• Adenyl cyclase removes 2 phosphate groups from
  ATP creating cyclic adenosine monophosphate
  (cAMP) (second mesenger)
• cAMP activates or inactivates protein kinases
• Protein kinases activate specific intracellular
  enzymes

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Second Messenger Mechanism

• Enzymes influence specific cellular reactions
  (target cells response to hormone)

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Second Messenger Mechanism

• Summary
• Hormone or 1st messenger binds to plasma membrane
  receptor
• Triggers formation of intracellular 2nd messenger
• 2nd messenger activates cascade of chemical
  reactions
• Target cells response to the hormone is produced

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Another Second Messenger

• Some hormones produce effects in target cells by
  triggering opening of calcium channels
• Hormone binds to receptor on plasma membrane
• Ca2 channels open
• Ca2 binds with calmodulin
• Ca2/Calmodulin complex acts as 2nd messenger
• Enzymes are activated/inactivated
• Target cells response is produced

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Calcium-Calmodulin as 2nd Messenger
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Regulation of Hormone Secretion

• Hormone secretion is controlled by a negative
  feedback loop
• Ex parathyroid hormone (PTH) and blood calcium
  levels (fig 16-10)
• Ex insulin and blood glucose levels

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Endocrine Feedback Loop
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Hyper vs Hyposecretion

• Tumors or abnormalities of the endocrine glands
  cause secretion of too much or too little hormone
• Hypersecretion production of too much hormone
• Hyposecretion production of too little hormone
• Results in lack of target cell response
• Also caused by target cell insensitivity

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Regulation of Target Cell Sensitivity

• Sensitivity of target cell depends on number of
  receptors it has for a specific hormone
• Receptors are constantly begin broken down and
  re-synthesized by the cell
• Up-regulation synthesis of new receptors gt
  degeneration of old receptors
• Increase target cell sensitivity to that
  particular hormone
• Down-regulation synthesis of new receptors lt
  degeneration of old receptors
• Decrease target cell sensitivity

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Pituitary Gland

• Also called hypophysis
• Located on ventral surface of brain, inferior to
  the hypothalamus
• Master gland because functions are crucial to
  life
• Composed of two parts Anterior Pituitary and
  Posterior Pituitary

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Anterior Pituitary

• Hormones secreted from Anterior Pituitary
• Growth Hormone
• Prolactin
• Trophic hormones
• Thyroid-stimulating hormone (TSH)
• Adrenocorticotropic hormone (ACTH)
• Gonadotropic hormones
• Follicle-stimulating hormone (FSH)
• Luteinizing hormone (LH)

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Growth Hormone

• Growth Hormone (GH) promotes growth by
  stimulating protein anabolism
• Increased protein anabolism allows increased
  growth rate
• Target cells
• Promotes growth of bone and muscle
• GH has a hyperglycemic effect antagonist of
  insulin
• Hyperglycemic effect because GH stimulates fat
  metabolism
• Interaction vital to maintaining homeostasis of
  blood glucose levels

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Growth Hormone Abnormalities

• Hypersecretion
• Prior to ossification of the epiphyseal plates
  hypersections of GH results in rapid skeletal
  growth ? Gigantism
• After closure of epiphyseal plates hypersecretion
  causes cartilage to continue to form new bone ?
  Acromegaly
• Distorted appearance enlarged hands, feet, face,
  jaw thickened skin

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Growth Hormone Abnormalities

• Hyposecretion
• Results in stunted body growth ? pituitary
  dwarfism
• Treated with genetically engineered growth
  hormone

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Prolactin (PRL)

• Also called lactogenic hormone
• Initiates milk secretion (lactation)
• Target cells Mammary glands
• During pregnancy PRL promotes development of
  breasts
• At birth PRL stimulates milk production

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Prolactin Abnormalities

• Hypersecretion
• Lactation in non-nursing women
• Disruption of menstrual cycle
• Impotence in men
• Hyposecretion
• Insignificant unless mother wishes to breastfeed

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Trophic Hormones

• Review a trophic hormone stimulate effects of
  other endocrine glands
• Trophic hormones released from anterior pituitary
  gland
• Thyroid-stimulating hormone (TSH)
• Adrenocorticotropic hormone (ACTH)
• Gonadotrophic hormones
• Follicle-stimulating hormone (FSH)
• Luteinizing hormone (LH)

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Thyroid-stimulating hormone (TSH)

• Promotes and maintains growth and development of
  thyroid gland
• Required for thyroid gland to secrete its hormones

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Adrenocorticotropic hormone (ACTH)

• Promotes and maintains normal growth and
  development of the cortex (outer portion) of the
  adrenal gland
• Required for adrenal cortex to secrete its hormone

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Gonadotrophic hormones

• Target cells gonads (testes ovaries)
• Follicle-stimulating hormone (FSH)
• Females
• Stimulates growth development of an ovum that
  is released each month during ovulation
• Stimulate estrogen release from the ovaries
• Males
• Stimulates development of seminiferous tubules
  and maintains sperm production in the testes

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Gonadotrophic hormones

• Luteinizing hormone (LH)
• Females
• Triggers ovulation
• Promotes development of corpus luteum which
  secretes progesterone and estrogen these
  hormones help maintain pregnancy
• Males
• Stimulates cells of the testes to synthesize and
  secrete testosterone

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Control of Anterior Pituitary Secretion

• The hypothalamus releases chemical called
  releasing hormones which influence hormone
  secretion from the anterior pituitary gland
• This regulatory mechanism is a negative feedback
  loop

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Posterior Pituitary

• Hormones secreted from Posterior Pituitary
• Antidiuretic Hormone (ADH)
• Oxytocin (OH)

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Antidiuretic Hormone (ADH)

• Target cells kidney
• Prevents formation of large volumes of dilute
  urine
• Antidiuresis
• Helps conserve water balance
• Example
• Blood is hypertonic ? change detected by
  osmoreceptors ? ADH is released ? water
  reabsorbed in kidneys and returned to blood

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ADH Abnormalities

• Hyposecretion
• Diabetes insipidus
• Increased urine output of dilute urine
• high and dry
• Na levels are increased ICF dehydrated
• Hypersecretion
• Syndrome of inappropriate antidiuretic hormone
  (SIADH)
• Decreased urine output
• Fluid overload low Na levels

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Oxytocin (OT)

• Target cells mammary glands uterine smooth
  muscle
• Operates on a positive feedback loop
• Stimulates uterine smooth muscle contractions
• During childbirth stretching of receptors causes
  continued release of oxytocin until after
  delivery of the placenta
• Ejection of milk into ducts of the breast of
  lactating women
• When breastfeeding the suckling action of the
  baby causes secretion of additional oxytocin
  increasing milk production
• Breastfeeding also helps the uterus continue to
  contract back to normal size during the
  postpartum period

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Project Reminders

• Make sure your illustrations shows both the
  anterior and posterior pituitary.
• Show ovaries and testes (only testes)
• Remember that trophic hormones will be a double
  pathway
• Plan ahead we have not learned about all of the
  hormones yet so make sure you leave room for
  future information
• You will be adding additional organs to represent
  target cells
• Questions??

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Pineal Body

• Regulates the bodys biological clock
• Patterns of eating
• Sleeping
• Female reproductive cycle
• Behavior
• Secretes melatonin
• Induces sleep
• Secretion is inhibited by sunlight
• Target cell in humans is unknown

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Melatonin Seasonal Affective Disorder

• Also know as winter depression
• During shorter days, melatonin secretion
  increases causes a depressed feeling in affected
  patients
• Treatment
• Exposure to high-intensity lights to inhibit
  melatonin secretion

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Thyroid Gland

• The thyroid gland is composed of two lateral
  lobes connected by an isthmus
• Located on the anterior and lateral surfaces of
  the trachea, below the larynx

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Thyroid Hormones

• Tetraiodothyronine or thyroxine (T4)
• Most abundant thyroid hormone
• Contains 4 iodine atoms
• May have effect on target cells, but mostly serve
  as precursor to T3
• Triodothyronine (T3)
• principal thyroid hormone
• Contains 3 iodine atoms

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Thyroid Hormones

• Both hormone bind to plasma proteins once
  secreted into the bloodstream
• Function
• Regulate metabolic rate of all cells
• Regulate cell growth
• Regulate tissue differentiation
• Target cells general because thyroid hormones
  can potentially interact with all cells of the
  body

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Hypersection

• Graves Disease
• Autoimmune condition (thyroid stimulating
  antibodies causes abnormal secretion)
• Weight loss
• Increases basal metabolic rate
• Increased heart and respiratory rate
• exophthalmos

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Exophthalmos
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Hyposecretion of Thyroid Hormone

• Cretinism develops during the growth years due
  to hypothyroidism
• Low metabolic rate
• Retarded growth and sexual development
• Mental retardation (possibly)
• Hypothyroidism later in life
• Decreased metabolic rate
• Loss of mental physical vigor
• Weight gain
• Loss of hair
• Yellow discoloration of the skin
• myxedema

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Goiter

• Caused by lack of iodine in the diet
• Iodine is needed to synthesize thyroid hormone
• Lack of iodine causes drop in thyroid hormone
  production/secretion
• Negative feedback loop informs hypothalamus and
  anterior pituitary to release releasing hormones
  and TSH
• Lack of iodine causes enlargement of thyroid gland

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Calcitonin

• The 3rd hormone secreted from the thyroid gland
• Target cells bone
• Function regulates calcium levels in the blood
  by decreasing blood calcium levels
• Increases action of osteoblasts (build bone) and
  inhibits action of osteoclasts (breakdown bone)
• Antagonist to parathyroid hormone

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Parathyroid Glands

• Parathyroid glands are embedded in the posterior
  aspect of the thyroid glands
• Usually 4 or 5 parathyroid glands

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Parathyroid Hormone

• Secreted from Parathyroid glands
• Target cells bone and kidney
• Action maintains calcium homeostasis
• Increases osteoclast activity decrease
  osteoblast activity
• Calcium absorbed in kidneys and returned to the
  bloodstream
• Activates vitamin D in the kidneys which
  increases intestinal absorption of calcium
• Parathyroid hormone is an antagonist to calcitonin

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Adrenal Glands

• Located on top of both of the kidneys
• Composed of two parts
• Outer portion ? adrenal cortex
• Inner portion ? adrenal medulla
• Both parts of the adrenal glands are structurally
  and functionally different often treated as two
  different glands

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Adrenal Cortex

• Composed of three distinct layers or zones
• Outer zone ? secrete mineralocorticoids
• Middle zone ? secrete glucocorticoids
• Inner zone ? secrete glucocorticoids and
  gonadocorticoids

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Mineralocorticoids

• Mineralocorticoids regulate electrolytes in the
  body
• In humans the most important mineralcorticoid is
  aldosterone
• Target cell kidneys
• Function maintaining sodium homeostasis in the
  blood
• In the kidneys, sodium ions are reabsorbed from
  the urine back to the blood
• Sodium ions are exchanged for potassium or
  hydrogen ions
• Aldoesterone also promotes water retention
  because re-absorption of sodium ions also causes
  water to be reabsorbed

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Regulation of Aldosterone Secretion

• Aldosterone secretion is controlled by the
  renin-angiotensin mechanism
• This mechanism is a negative feedback loop that
  helps maintain homeostasis of blood pressure
• Blood pressure drops in the kidneys ? renin (an
  enzyme) is secreted
• Renin converts angiotensinogen to angiotensin I
• Angiotensin I travels to the lungs where enzymes
  split the molecule forming angiotensin II
• Angiotensin II travels to the kidneys where it
  simulates the secretion of aldosterone
• Aldosterone causes reabsorption of sodium ions ?
  followed by water reabsorption ? increase in
  blood pressure

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Glucocorticoids

• Main glucocorticoid secreted from the adrenal
  cortex is cortisol (also hydrocortisone)
• Target cells general affect every cell in the
  body

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Cortisol - Functions

• Accelerate protein breakdown into amino acids
• Amino acids travel to liver and are converted to
  glucose (gluconeogenesis)
• Increased glucocorticoids (cortisol) ? increased
  breakdown of proteins in tissue (tissue wasting)
  ? hyperglycemia
• Shift cells from carbohydrate catabolism to lipid
  catabolism for energy sources
• Further causes hyperglycemia

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Cortisol Functions cont

• Help maintain blood pressure
• Permissiveness relationship with epinephrine and
  norepinephrine
• Epi and NE cause vasoconstriction of blood
  vessels
• Suppression of immune system responses

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Glucocorticoid Hypersecretion

• Cushing Syndrome
• Too much cortisol is being secreted
• Causes
• Could be caused by hypersecretion of ACTH from
  anterior pituitary (tumor)
• Cirrhosis of liver or liver failure ? cant
  breakdown hormones
• Signs/Symptoms
• Abnormal hair growth
• buffalo hump
• muscle wasting
• skin breakdown (thin skin)
• striae across abdomen and thighs
• truncal obesity
• Susceptible to infection

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Adrenal Insufficiency

• Hyposecretion of mineralcorticoids
  glucocorticoids ? Addison Disease
• Signs/Symptoms
• Drop in blood sodium
• Hypoglycemia
• Increase in blood potassium
• Dehydration
• Weight loss

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Adrenal Medulla

• Secretes two nonsteroids in the catecholamine
  class
• Epinephrine and norepinephrine
• Bind to sympathetic effectors and enhance the
  effects of the fight or flight response of the
  autonomic nervous system

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Pancreas

• Located in the LUQ
• Contains both endocrine and exocrine tissue
• Endocrine portion is made up of tiny islands of
  cells called pancreatic islets (also islets of
  Langerhans)
• Alpha cells secrete glucagon
• Beta cells secrete insulin

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Pancreatic Hormones

• Glucagon
• Increases blood glucose levels
• Converts glycogen to glucose in liver cells
• Stimulates gluconeogenesis
• Target cells ? liver
• Insulin
• Decreases blood glucose levels
• Promotes movement of glucose, amino acids, fatty
  acids into cells
• Promotes metabolism of these molecules once by
  cells
• Target cells ? general (all cells)
• Glucagon and Insulin produce antagonistic effects
  (fig 16-27, page 512)

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Diabetes

• Results from either
• 1) inadequate or absence of insulin production
• 2) Insulin resistance decreased insulin
  receptors results in decreased effectiveness of
  glucose uptake

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Diabetes Signs Symptoms

• Hyperglycemia elevated amounts of glucose in
  the blood
• Results glucose not entering the cells properly
• Glycosuria glucose present in the urine
• Elevated glucose levels in the blood exceeds
  kidneys abilities to reabsorb glucose glucose
  spills over into the urine
• Polyuria increased urine production
• Water follows glucose lost in urine

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Diabetes Signs Symptoms

• Polydipsia excessive thirst
• Polyuria causes dehydration
• Polyphagia excessive and continuous hunger
• Although blood sugar is high cells are starving
  because cells cannot uptake glucose
• 3 Ps polyuria, polydipsia, polyphagia

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Diabetic Ketoacidosis

• Diabetics are unable to utilize glucose for
  energy cells must use protein and fat
• Large quantities of fat metabolism results in
  build up of acidic metabolites called ketone
  bodies
• Signs/Symptoms
• Acidosis
• Abdominal pain
• Nausea/vomiting
• Fruity breath
• Decreased LOC
• Coma
• death

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Type 1 Diabetes

• Absolute deficiency of insulin production
• Cause of beta cell destruction is unknown
• Requires insulin injections or an insulin pump

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Type 2 Diabetes

• Previously called non-insulin-dependent diabetes
  (NIDDM) or adult onset diabetes
• Beta cell produce reduced amounts of insulin
• Loss of insulin receptors on target cells leads
  to insulin resistance
• Treated with insulin injections, oral diabetic
  medication and lifestyle modifications

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Complications of Diabetes

• Untreated or poorly controlled diabetes can lead
  to many complications that affect almost every
  system in the body
• Atherosclerosis build up of fatty materials in
  the blood vessls
• Lead to heart attack, stroke, reduced circulation
• Diabetic retinopathy can lead to blindless

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Complications of Diabetes

• Neuropathy nerve damage
• Amputations
• Kidney disease
• May require dialysis

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Gonads Testes Ovaries

• Testes
• Composed mainly of coils of seminiferous tubules
  interstitial cells
• Interstitial cells secrete testosterone
• Target cells general
• Function
• Growth maintenance of male sexual
  characteristics
• Sperm production
• Testosterone secretion is regulated by the
  gonadotropin ? leutinizing hormone (LH)

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Gonads Testes Ovaries

• Ovaries
• Estrogen
• Secreted by cells of the ovarian follicles
• Target cells general
• Functions
• Promote development maintenance of female
  sexual characteristics
• Breast development
• Regulation of menstrual cycle

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Gonads Testes Ovaries

• Ovaries
• Progesterone (pregnancy-promoting hormone)
• Secreted by corpus luteum
• Target cells general
• Functions (with estrogen)
• Maintains the lining of the uterus to maintain a
  pregnancy
• Remember Estrogen Progresterone secretion is
  regulated by FSH and LH (gonadotropic hormones)

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Placenta

• Tissue that forms along the lining of the uterus
• Serves as the connection between the circulatory
  systems of the mother and developing fetus
• Secretes human chorionic gonadotropin (hCG)
• Target cells ovaries

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Placenta

• Function
• Stimulates hormone (estrogen progesterone)
  secretion from the ovaries
• High levels of estrogen progesterone help
  maintain uterine lining for pregnancy
• hCG is high during the 1st trimester
• A high hCG level is used to confirm a pregnancy