Download Chapter 13: The Endocrine System

Chapter 13: The Endocrine System
Communication and Coordination
 2 communicating and coordinating systems in the body: Nervous and endocrine
systems
 Nervous system communicates using short term nerve impulses (electrical
signals)
 Endocrine system communicates using longer lasting hormones (chemical
signals)
o Regulate metabolic processes (carbohydrates, proteins and fats)
o Role in growth and reproduction
o Regulate water and electrolyte balance
o Hunger, thirst and temperature responses
o Deal with infection, trauma and stress
Endocrine Glands
 Secrete hormones directly into capillaries and not into ducts
Hormones
 Chemical messengers that influence or control the activities of other tissues or
organs
 Most are transported to areas of the body far from their release site
 Two classes
o Steroids (from the adrenal cortex and sex glands)
o Proteins (all other hormones)
Hormone Targets
 Each hormone only binds to its target tissue or target organ
 Some have many target tissues (insulin)
o Widespread, generalized effects
 Others have fewer target tissues
o Specific effects
2 Types of Receptors
 Membrane receptors located on the outer surface of the cell membrane
o Protein hormones bind to receptor sites and a second messenger (cAMP)
is produced
o cAMP helps activate cellular enzymes
 Intracellular receptors located within the cell
o Steroid hormones (lipid soluable) pass through cell membrane and bind to
receptor sites in the nucleus
o Steroid-receptor complex stimulates protein synthesis
Hormone Control
 3 mechanisms to control secretion of hormones
o Negative feedback control
o Biorhythms
o Central nervous system
Negative Feedback
 Information about a hormone of its effects and fed back to the gland that secretes
the hormone
 Insulin production
Biorhythms
 A rhythmic alteration in a hormone’s rate of secretion
 Female menstrual cycle
 Circadian rhythm is a 24-hour rhythm
o Cortisol levels highest in the morning (peak 8 am)
o Lowest levels in the evening (lowest at midnight)
 Travel and alterations in sleep patterns can disturb these biorhythms
Control by The CNS
 The CNS activates the hypothalamus and stimulates the sympathetic nervous
system
 Stress can cause changes in hormone levels and cause changes in menstrual cycles
Pituitary Gland
 Also called the hypophysis
 Located under the hypothalamus
 Attached to the hypothalamus by the infundibulum
 2 main parts
o Anterior pituitary gland
o Posterior pituitary gland
Hypothalamus
 Secretes several hormones and is considered an endocrine gland
 Secretes releasing hormones and release-inhibiting hormones
 These hormones stimulate or inhibit secretion of specific anterior pituitary
hormones
 Hypothalamic hormones reach the anterior pituitary gland through the
hypothalamic-hypophyseal portal system (network of capillaries)
Anterior Pituitary
 Composed of glandular epithelial tissue
 Called the adenohypophysis
 Secretes six major hormones
 Often called the master gland because the hormones it releases affect so many
other glands and organ systems
Growth Hormone (GH)
 Also called somatotropin or somatotropic hormone (STH)
 Effects
o Growth of skeletal muscles and long bones of the body
 Determines a persons height and size
o Causes amino acids to be built into proteins and fats to be broken down
and used for energy
o Stimulates conversion of protein to glucose, especially between meals
 Causes blood glucose to rise
 Secreted during exercise, sleep and hypoglycemia
 Hypersecretion as a child leads to gigantism
o Growth very tall, often 8 or 9 feet
 Hypersecretion as an adult leads to acromegaly
o Enlarged jaw, eyebrow ridges, nose, hands and feet
 Deficiency in childhood leads to pituitary dwarfism
o normal body proportions but short height (4 feet or less)
Prolactin (PRL)
 Also called lactogenic hormone
 Promotes milk production in women
 Target tissue is breast tissue
 Stimulates growth of the mammary glands and stimulates them to produce milk
after childbirth
 Role of PRL in males is unknown
Tropic Hormones
 Hormones that are aimed at and control other glands
 Thyrotrophin or Thyroid-stimulating hormone (TSH)
o Stimulates thyroid to secrete two thyroid hormones
 Adrenocorticotropic hormone (ACTH)
o Stimulates adrenal cortex to secrete three steroids, particularly cortisol
 Gonadotropic hormones
o Target glands are the gonads (overies or testes)
o 2 gonadotropins
 Follicle-stimulating hormone (FSH)
 Stimulates production of ova or sperm
 Luteinizing hormone (LH)
 Causes ovulation and secretion of sex hormones
 Also called interstitial cell-stimulating hormone (ICSH) in
males because it stimulates interstitial cells to synthesize
and secrete testosterone
Posterior Pituitary
 An extension of the hypothalamus
 Composed of nervous tissue
 Called the neurohypophysis
 Hormones produced in the hypothalamus and transported to the posterior pituitary
where they are stored
 Nerve impulses from the hypothalamus stimulates secretion of hormones
 2 hormones
o Antidiuretic hormone (ADH)
o Oxytocin
Antidiuretic hormone (ADH)
 Released in an attempt to conserve water
 Target organ is the kidney
 Stimulates kidney to reabsorb water
 Stimulates blood vessel constriction causing elevated blood pressure
o Also called vasopressin for this effect
 Released in response to concentrated plasma (dehydration)
 Also released in response to stress, trauma, drugs (morphine and nicotine)
 Alcohol inhibits ADH secretion
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Diabetes insipidus
o Lack of ADH causes profound diuresis
o Excretion of up to 25 liters of urine per day
Oxytocin
 Target organs are the uterus and the mammary glands
 Stimulates muscles of the uterus to contract
o Helps in initiation of labor and delivery of a baby
 Released in response to breastfeeding
 Stimulates the contraction of smooth muscles around the mammary ducts in the
breasts releasing breast milk
o Called the milk let-down reflex
Pituitary Gland and MSH
 Small third lobe of the pituitary gland secretes melanocyte-stimulating hormone
(MSH)
 MSH stimulates melanocytes to increase pigmentation of the skin
 Structure of MSH is similar to ACTH
 Hypersecretion of ACTH causes skin to darken and become bronzed
Thyroid gland
 Located in the anterior neck on the front and sides of the trachea just below the
larynx
 Two lobes connected by the isthmus
 2 types of cells
o Follicular cells
 Located within the thyroid follicle
o Parafollicular cells
 Located between the follicles
Thyroid Follicle
 Thyroid gland is composed of secretory units called follicles
 Follicular cavity lined with cuboidal cells and filled with clear viscous substance
called colloid
 Secretes triiodothyronine (T3) and tetraiodothyronine (T4 or thyroxine)
T3 and T4
 Regulate the metabolism of carbohydrates, proteins and fats
 Increase the rate of metabolism of most cells
 Needed for normal maturation of the nervous system and normal growth and
development
Hypothyroidism
 Infants born with no thyroid can develop cretinism
o Infant fails to develop physically and mentally
o Short and stocky with abnormal skeletal development and severe mental
retardation
o Early diagnosis (in first 2 months) and treatment with T3 can prevent
further developmental delays
 In an adult low thyroid function leads to myxedema, a slowed metabolic state
o Slow heart rate
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Sluggish peristalsis resulting in constipation
Low body temperature
Low energy
Loss of hair
Weight gain
Skin becomes thick and puffy from thick fluid accumulating under the
skin
Hyperthyroidism
 Over production of thyroid hormones leads to a sped-up metabolic state
 Common type is Grave’s disease
o Increased heart rate
o Increase in peristalsis resulting in diarrhea
o Elevation in body temperature
o Hyperactivity
o Weight loss
o Wide emotional swings
o Bulging eyes called exophthalmia due to enlarged fat pads behind the
eyeballs
Regulation of Thyroid Gland
 Hypothalamus secretes ad releasing hormone
 This hormone stimulates the anterior pituitary to secrete TSH
 TSH stimulates thyroid gland to release T3 and T4
 When T3 and T4 increase sufficiently negative feedback stops production of TSH
Iodine and Thyroid
 Tetraiodothyronine or thyroxine contains four iodine atoms (T4)
 Triiodothyronine contains three iodine atoms (T3)
 Iodine comes from dietary sources and is actively pumped into the follicular cells
of the thyroid gland
Iodine Deficiency
 When iodine is deficient in the diet T3 and T4 production decreases
 Secretion of TSH is continuous because there isn’t a high enough concentration of
T3 and T4 in the blood to shut it off
 Persistent stimulation of the thyroid gland by TSH causes thyroid to enlarge
(goiter)
Calcitonin
 Secreted by the parafollicular cells
 Works with parathyroid hormone to help regulate the plasma levels of calcium
Parathyroid Glands
 Four tiny parathyroid glands lie on the posterior surface of the thyroid gland
 Secretes parathyroid hormone (PTH)
 Secretion stimulated by low plasma level of calcium
 3 target organs
o Bone
o Digestive system
o kidneys
Calcium Regulation
 Low calcium
o PTH released
o PTH increases release of calcium from bone tissue
o PTH stimulates kidneys to reabsorb calcium form urine and excrete
phosphate
o PTH (with vitamin D) increases absorption of calcium by the digestive
tract
 High calcium
o Calcitonin released
o Calcitonin stimulates bone production
o Calcitonin increases excretion of calcium in the urine
Adrenal Glands
 Two small glands located above the kidneys
 Also called the suprarenal glands
 2 regions
o Inner medulla
 Hormones secreted not essential for life
o Outer cortex
 Hormones secreted are essential for life
Adrenal Medulla
 Inner region of the adrenal gland
 An extension of the sympathetic nervous system
 Secretes epinephrine (adrenaline) and norepinephrine
 Exert effects similar to the sympathetic nervous system so they are called
sympathomimetic hormones
Epinephrine & Norepinephrine
 Secreted in emergency or stress situations
 Elevate blood pressure
 Increase heart rate
 Convert glycogen to glucose
 Increase metabolic rate of most cells
 Cause bronchodilation
 Cause dilation of blood vessels to the heart and muscles
 Constrict blood vessels to the digestive tract
Adrenal Cortex
 Outer region of the adrenal gland
 Secretes 3 steroids
o Glucocorticoids
o Mineralocorticoids
o Sex hormones
Glucocorticoids
 Converts amino acids into glucose and help maintain blood glucose levels
between meals
 Also cause protein and fat to be utilized for energy production
 Essential for life
 Death will occur if adrenal cortex function is lost unless steroid are administered
Cortisol
 Chief glucocorticoid
 A stress hormone secreted in greater amounts during times of physiological stress
o Disease, physical injury, hemorrhage, infection, pregnancy, extreme
temperature and emotional stress (anger or rage)
 Has an anti-inflammatory effect
 Used as a drug to prevent inflammation in the treatment of arthritis, sever allergic
responses and swelling associated with head trauma
Cortisol Secretion
 Hypothalamus secretes a releasing hormone
 Anterior pituitary stimulated to release adrenocorticotropic hormone (ACTH)
 ACTH stimulates adrenal cortex to secrete cortisol
 Cortisol inhibits further secretion of ACTH through negative feedback loop
Mineralocorticoids
 Chief mineralocorticoid is aldosterone
 Important role in regulation of blood volume and blood pressure and in
concentration of electrolytes in the blood
 Target organ is the kidney
 Causes conservation of sodium and water and elimination of potassium
Sex Hormones
 Estrogens and androgens secreted in small amounts from the adrenal cortex
 In females the sex hormones secreted by the ovaries usually mask the effects of
adrenal sex hormones
 After menopause adrenal androgens can cause increased body hair and other
affects once production of estrogens from the ovaries decreases
Hyposecretion of Cortical Hormones
 Insufficient production of adrenal cortical hormones
 Called Addison’s disease
o General weakness
o Muscle atrophy
o Bronzing of the skin
o Severe loss of fluids and electrolytes
 Is life threatening and must be treated with steroids and replacement of fluids and
electrolytes
Hypersecretion of Cortical Hormones
 Oversecretion of adrenal cortical hormones
 Caused by oversecretion of either ACTH (anterior pituitary) or cortisol (adrenal
cortex)
 Often caused by administration of steroids as drugs
o Must taper off dosage
o Can’t just stop taking them all at once
 Causes Cushing’s syndrome
o Obesity
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Rounded facial apperance (moon face)
Thin skin that bruises easily
Bone loss
Muscle weakness
Salt and water retention cause blood volume and blood pressure to
increase
Pancreas
 Long slender organ that lies transversely across the upper abdomen from the
curve of the duodenum to the spleen
 Exocrine and endocrine gland
o Exocrine function
 concerned with digestion of food
o Endocrine function
 secretes insulin and glucagon
 Hormone-secreting cell called the islets of Langerhans
Pancreas
 Hormone-secreting cell called the islets of Langerhans
 Two types of cells
o Alpha cells
 Secrete glucagon (increase blood glucose)
o Beta cells
 Secrete insulin (lower blood glucose)
Insulin
 Secreted by the beta cells of the islet of Langerhans
 Released in response to increased blood glucose levels
 Secretion decreases as blood glucose levels decrease
 Has many target tissues (liver, skeletal muscle, adipose tissue)
 2 main effects
o Helps transport glucose into cells
o Helps control carbohydrate, protein and fat metabolism in the cell
 Stimulates the breakdown of glucose for energy
 Increases the transport of amino acids into cells and then stimulates
the synthesis of proteins
 Promotes the synthesis of fats from fatty acids
 Insulin deficiency – diabetes mellitus
Glucagon
 Secreted by the alpha cells of the islet of Langerhans
 Released in response to decreased blood glucose levels
 Increases blood glucose levels
 Stimulates conversion of glycogen to glucose in the liver
 Stimulates the conversion of proteins into glucose
Diabetes Mellitus
 Hyperglycemia
o Excess glucose in the blood
 Glucosuria or glycosuria
o Glucose in the urine
o Kidneys can’t reabsorb excess glucose and it is excreted in the urine
 Polyuria
o Excretion of large amounts of urine
o Caused by glucosuria
 Acidosis
o Excess of acidic substances in the blood
o Cells can’t utilize glucose as fuel so they fatty acids instead
o Rapid, incomplete breakdown of fatty acids produces strong acids called
ketoacids
o Causes diabetic ketoacidosis
 Fruity odor to the breath
o Acetone (ketone) produced by fatty acid breakdown
o Acetone smells like bananas and makes the patient’s breath smell fruity
o Fruity odor is a sign of ketoacidosis
Gonads
 Sex glands
 Ovaries
o Produce ova (eggs)
 Testis
o Produce sperm
 Also secrete hormones making them glands
Ovaries
 Located in the pelvic cavity on each side of the uterus
 Secrete estrogen and progesterone
 Help development and functioning of the female reproductive organs and
expression of female sex characteristics
o Breast development
o Fat in hips, thighs, and breasts
o Body hair growth
o Maturation of reproductive organs
o Closure of the epiphyseal discs of long bones
 Excretion controlled by hypothalamic-releasing hormones and the gonadotropins
(FSH and LH)
Testes
 Located in the scrotum
 Interstitial cells of the testes secrete testosterone
 Stimulated by anterior pituitary hormone LH
 Testosterone helps in maturation of sperm and is responsible for male sex
characteristics
o Growth and development of the male reproductive organs
o Musculoskeletal growth
o Body and facial hair growth
o Enlargement of the larynx and voice changes
Thymus Gland
 Lies in the thoracic cavity behind the sternum
 Much larger in children than in adults
 Involutes, gets smaller, as a child enters puberty
 Secretes thymosins which play a role in the immune system
Pineal Gland
 Cone shaped gland located close to the thalamus in the brain
 Called the bodies “biological clock” because it controls many of the bodies
biorhythms
 Secretes melatonin
Melatonin
 Affects the reproductive cycle by influencing the secretion of hypothalamicreleasing hormones
 Plays important role in sexual maturation
 Plays a role in sleep/wake cycle
o Lowest secretion during daylight hours
o Highest secretion at night
o Elevated levels in people with seasonal affective disorder (SAD)
Prostaglandins
 Hormones derived from the fatty acid arachidonic acid
 Produced by many tissues and generally act near their site of secretion
 Important role in regulation of smooth muscle contraction and the inflammatory
response
 Increases the sensitivity of pain nerve endings
 Aspirin, ibuprofen and acetaminophen block synthesis of prostaglandins