Endocrine Glands

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Chapter 18

• Endocrine Glands

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Endocrine System Functions

• Metabolism and tissue maturation
• Ion regulation
• Water balance
• Immune system regulation
• Heart rate and blood pressure regulation
• Control of blood glucose and other nutrients
• Control of reproductive functions
• Uterine contractions and milk release

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Pituitary Gland and Hypothalamus

• Where nervous and endocrine systems interact
• Pituitary gland/hypophysis
• Secretes 9 major hormones
• Hypothalamus
• Regulates secretory activity of pituitary gland
  through neurohormones and action potentials
• Posterior pituitary is an extension of

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Pituitary Gland Structure

• Posterior or neurohypophysis
• Continuous with the brain
• Secretes neurohormones
• Anterior or adenohypophysis
• Consists of three areas with indistinct
  boundaries pars distalis, pars intermedia, pars
  tuberalis

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Relationship of Pituitary to Brain
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Hypothalamus, Anterior Pituitary and Target
Tissues
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Pituitary Gland Hormones

• Posterior
• Antidiuretic hormone (ADH)
• Oxytocin

• Anterior
• Growth hormone (GH) or somatotropin
• Thyroid-stimulating hormone (TSH)
• Adrenocorticotropic hormone (ACTH)
• Melanocyte-stimulating hormone (MSH)
• Luteinizing hormone (LH)
• Follicle-stimulating hormone (FSH)
• Prolactin

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Antidiuretic Hormone

• Also called vasopressin
• Promotes water retention by kidneys
• Secretion rate changes in response to alterations
  in blood osmolality and blood volume
• Lack of ADH secretion is a cause of diabetes
  insipidus

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Oxytocin

• Promotes uterine contractions during delivery
• Causes milk ejection in lactating women

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Growth Hormone (GH)

• Stimulates uptake of amino acids and conversion
  into proteins
• Stimulates breakdown of fats and glycogen
• Promotes bone and cartilage growth
• Increased secretion in response to increase amino
  acids, low blood glucose, or stress
• Regulated by GHRH and GHIH or somatostatin

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TSH, ACTH, MSH

• ACTH
• Stimulates cortisol secretion from adrenal cortex
• MSH
• Increases skin pigmentation

• TSH or thyrotropin
• Causes release of thyroid hormones from thyroid
  gland

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LH, FSH, Prolactin

• LH and FSH
• Both hormones regulate production of gametes and
  reproductive hormones
• Testosterone in males
• Estrogen and progesterone in females
• GnRH from hypothalamus stimulates LH and FSH
  secretion

• Prolactin
• Stimulates milk production in lactating females

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Thyroid Gland

• One of largest endocrine glands
• Highly vascular
• Histology
• Composed of follicles
• Parafollicular cells
• Secrete calcitonin which reduces calcium
  concentration in body fluids when levels elevated

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Biosynthesis of Thyroid Hormones
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Thyroid Hormones

• Include
• Triiodothryronine or T3
• Tetraiodothyronine or T4 or thyroxine
• Transported in blood
• Bind with intracellular receptor molecules and
  initiate new protein synthesis
• Increase rate of glucose, fat, protein metabolism
  in many tissues thus increasing body temperature
• Normal growth of many tissues dependent on

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Regulation of T3 and T4 Secretion
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Thyroid Hormone Hyposecretion and Hypersecretion

• Hypothyroidism
• Decreased metabolic rate
• Weight gain, reduced appetite
• Dry and cold skin
• Weak, flabby skeletal muscles, sluggish
• Myxedema
• Apathetic, somnolent
• Coarse hair, rough dry skin
• Decreased iodide uptake
• Possible goiter

• Hyperthyroidism
• Increased metabolic rate
• Weight loss, increased appetite
• Warm flushed skin
• Weak muscles that exhibit tremors
• Exophthalmos
• Hyperactivity, insomnia
• Soft smooth hair and skin
• Increased iodide uptake
• Almost always develops goiter

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Parathyroid Glands

• Embedded in thyroid
• Secrete PTH
• Increases blood calcium levels
• Stimulates osteoclasts
• Promotes calcium reabsorption by kidneys

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Regulation of PTH Secretion
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Adrenal Glands

• Functions as part of sympathetic nervous system
• Composed of medulla and cortex (3 layers)
• Hormones
• Medulla secretes epinephrine and norepinephrine
• Cortex secretes mineralocorticoids,
  glucocorticoids, androgens

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Hormones of Adrenal Cortex

• Mineralocorticoids
• Zona glomerulosa
• Aldosterone produced in greatest amounts
• Increases rate of sodium reabsorption by kidneys
  increasing sodium blood levels
• Glucocorticoids
• Zona fasciculata
• Cortisol is major hormone
• Increases fat and protein breakdown, increases
  glucose synthesis, decreases inflammatory
  response
• Androgens
• Zona reticularis
• Converted to androgen and testosterone

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Pancreas

• Located along small intestine and stomach
• Exocrine gland
• Produces pancreatic digestive juices
• Endocrine gland
• Consists of pancreatic islets
• Composed of
• Alpha cells secrete glucagon
• Beta cells secrete insulin
• Delta cells secrete somatostatin

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Insulin and Glucagon

• Insulin
• Target tissues liver, adipose tissue, muscle,
  and satiety center of hypothalamus
• Increases uptake of glucose and amino acids by
  cells

• Glucagon
• Target tissue is liver
• Causes breakdown of glycogen and fats for energy

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Regulation of Insulin Secretion
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Regulation of Blood Nutrient Levels After a Meal
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Regulation of Blood Nutrient Levels During
Exercise
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Hormones of the Reproductive System

• Female Ovaries
• Estrogen and Progesterone
• Uterine and mammary gland development and
  function, external genitalia structure, secondary
  sex characteristics, menstrual cycle
• Inhibin
• Inhibits FSH secretion
• Relaxin
• Increases flexibility of symphysis pubis

• Male Testes
• Testosterone
• Regulates production of sperm cells and
  development and maintenance of male reproductive
  organs and secondary sex characteristics
• Inhibin
• Inhibits FSH secretion

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Pineal Body

• In epithalamus
• Produces
• Melatonin
• Enhances sleep
• Arginine vasotocin
• Regulates function of reproductive system in some
  animals

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Effects of Aging on Endocrine System

• Gradual decrease in secretory activity of some
  glands
• GH as people age
• Melatonin
• Thyroid hormones
• Kidneys secrete less renin
• Familial tendency to develop type II diabetes

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Diabetes Mellitus

• Results from inadequate secretion of insulin or
  inability of tissues to respond to insulin
• Types
• Type I or IDDM (Insulin-dependent)
• Develops in young people
• Type II or NIDDM (Non-insulin dependent)
• Develops in people older than 40-45
• More common