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Chapter 16 – The Endocrine System

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Chapter 16 – The Endocrine System . Endocrine system . Along with the nervous system, is responsible for homeostasis Nervous system – fast-acting; short-term effects Endocrine system – slow-acting; long-term effects Utilizes chemical messengers called hormones Gland types

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endocrine system
Endocrine system
  • Along with the nervous system, is responsible for homeostasis
    • Nervous system – fast-acting; short-term effects
    • Endocrine system – slow-acting; long-term effects
  • Utilizes chemical messengers called hormones
  • Gland types
    • Exocrine – have ducts
    • Endocrine – ductless when mature
      • Secrete into surrounding fluid and then enters bloodstream
      • Carried body-wide; affects distant tissues
structural classification of hormones
Structural classification of hormones
  • Amino acid derivatives
    • Hydrophilic
  • Peptide
    • Hydrophilic
  • Lipid derivatives
    • Hydrophobic
    • Steroids; sex hormones
    • Synthesized from cholesterol
hydrophilic hormone receptors
Hydrophilic hormone receptors
  • Water soluble hormones can no diffuse through plasma membrane; receptors are on cell surface
    • Transmembrane proteins – span entire membrane
  • Hormone binds to receptor; receptor changes shape
  • Shape change activates G protein
    • Converts to an active form
    • Starts chain reaction that ultimately activates kinases
      • Kinases attach phosphate groups to molecules
        • This either activates the molecule or inactivates it, depending on the specific molecule
hydrophobic hormone receptors
Hydrophobic hormone receptors
  • Fat soluble hormones can diffuse through plasma membrane
    • Receptors are located in cell’s interior (the cytoplasm)
  • Hormone-receptor complex enters nucleus and binds to DNA to affect gene expression
control of hormone release
Control of hormone release
  • Endocrine reflexes
    • Humoral
      • Detects and responds to change in concentration of certain molecules
    • Neural
      • Signal from nervous system stimulates secretion
    • Hormonal
      • Some hormones target other endocrine glands
        • Tropic hormones (sometimes called trophic hormones)
  • All can be modified by nervous system
pituitary gland hypophysis
Pituitary gland (hypophysis)
  • Located in the sellaturcica of the sphenoid bone
  • Attached to the hypothalamus by a stalk called the infundibulum
  • 2 lobes
    • Posterior (neurohypophysis)
    • Anterior (adenohypophysis)
posterior pituitary neurohypophysis
Posterior pituitary (neurohypophysis)
  • Composed of neural tissue; stores and releases hormones produced by the hypothalamus
  • Antidiuretic hormone (ADH)
    • Increases water reabsorption
      • Aquaporins placed in the collecting ducts of the kidneys
      • Increases blood volume/pressure
  • Oxytocin (OXT)
    • Stimulates smooth muscle contractions
      • Uterine contractions during childbirth
      • Milk letdown in lactating females
      • Durng sexual arousal in males and females
anterior pituitary adenohypophysis
Anterior pituitary (adenohypophysis)
  • Release or inhibition is controlled by hypothalamus
  • Growth hormone (GH)
    • Bones and skeletal muscles the major target tissues
  • Prolactin (PRL)
    • Stimulates milk production
  • Melanocyte-stimulating hormone (MSH)
    • Stimulates melanocytes in skin; contributes to skin pigmentation
anterior pituitary adenohypophysis1
Anterior pituitary (adenohypophysis)
  • Tropic hormones
    • Thyroid-stimulating hormone (TSH)
      • Thyroid gland
    • Adrenocorticotropic hormone (ACTH)
      • Adrenal cortex
    • Follicle-stimulating hormone (FSH)
      • Gonads to produce gametes
    • Leutinizing hormone (LH)
      • Stimulation of gonadal hormones
thyroid gland
Thyroid gland
  • On trachea, inferior to larynx
  • Butterfly-shaped
    • 2 lobes connected by isthmus
thyroid gland microscopic anatomy
Thyroid gland microscopic anatomy
  • Follicle cells produce thyroglobin (a glycoprotein)
    • Simple cuboidal epithelium
    • Central cavity of follicles is filled with colloid – thyroglobulin with iodine atoms
      • Forms T3 and T3 hormones
  • Parathyroid cells (C cells) produce calcitonin
thyroid hormones
Thyroid hormones
  • Thyroxine (T4) and Triiodothyronine (T3)
    • #4 and #3 refer to number of iodine atoms attached
    • Affects most cell in body
      • Increases basal metabolic rate and heat production
      • Aids in maintenance of blood pressure
      • Helps regulate growth and development
  • Calcitonin
    • Lowers blood calcium levels
      • Inhibits osteoclasts
parathyroid glands
Parathyroid glands
  • Usually 4 on posterior thryoid
  • Parathyroid hormone
    • Produced by chief cells
    • Increases blood calcium levels
      • Antagonistic to calcitonin
      • Stimulates osteoclasts
      • Increases reabsorption of calcium by kidneys
        • Kidney also converts vitamin D to its active form, which aids in calcium absorption in digestive system
adrenal glands
Adrenal glands
  • Also called suprarenal glands due to their location
  • Adrenal cortex (superficial) and adrenal medulla (deep)
adrenal cortex microscopic anatomy
Adrenal cortex microscopic anatomy
  • 3 layers/zones (superficial to deep)
    • Zonaglomerulosa
      • Produces mineralcorticoids
    • Zonafasciculata
      • Produces mainly glucocorticoids, some gonadocorticoids
    • Zonareticularis
      • Produces mainly gonadocortcoids, some glucocorticoids
adrenal cortex hormones
Adrenal cortex hormones
  • Mineralcorticoids
    • Regulation of electrolytes in extracellular fluid
    • Aldosterone
      • Stimulates sodium reabsorption in distal convoluted tubules of kidneys
  • Glucocorticoids
    • Influence energy metabolism
    • Regulates blood glucose and blood pressure levels
    • Cortisol (hydrocortisone)
      • Gluconeogenesis – formation of glucose from non-carbohydrate sources
    • Excess of glucocorticoids results in oversuppression of inflammatory and anti-immune responses
  • Gonadocorticoids
    • Androgens
      • Male sex hormones
      • Converted to testosterone in males; estrogen in females
    • Estrogens
adrenal medulla hormones
Adrenal medulla hormones
  • Autonomic nervous system
  • Epinephrine and norepinephrine
    • “Fight or flight” response
    • Blood glucose levels rise, increases heart rate, blood directed to cardiac and skeletal muscles
    • Epinephrine serves as a blood vessel contrictor and a bronchiole dilator
pineal gland
Pineal gland
  • Located at roof of third ventricle in brain
  • Melatonin
    • Concentration rises and falls within a 24 hour time period
      • Peaks at night – causes sleepiness
    • Affects biological clock/circadian rhythms
pancreas
Pancreas
  • Posterior to stomach
  • Microscopic anatomy
    • Acinar cells
      • Produce pancreatic secretions for digestive system
    • Islets of Langerhans
      • Alpha cells – produce glucagon
      • Beta cells – produce insulin
pancreatic hormones
Pancreatic hormones
  • Glucagon
    • Increases blood glucose levels
      • Glycogenolysis
        • Breaks down glycogen to glucose
      • Gluconeogenesis
        • Synthesizes glucose from non-carbohydrate sources
      • Releases glucose from the liver
  • Insulin
    • Decreases blood glucose levels (antagonistic to glucagon)
      • Increases glucose transport into cells (primarily adipose and muscle)
        • Uses glucose for ATP production
        • Stores as glycogen
        • Excess stored as fat
thymus
Thymus
  • Overlays heart
  • Produces several peptide hormones
    • Thymosin, thymopoetin, thymic factor
    • Development/maturation of T lymphocytes
gonadal hormones
Gonadal hormones
  • Hormones are steroids (fat-soluble)
  • Ovaries (female)
    • Estrogen
      • Secondary sex characteristics
      • Maturation of reproductive organs
    • Progesterone
      • Along with estrogen:
        • Breast development and menstrual cycle regulation
  • Testes (male)
    • Testosterone
      • Secondary sex characteristics
      • Maturation of reproductive organs
      • Production of sperm
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