A&p Ch 18 Lecture

Front 1

Endocrine System

Back 1

chemicals secreted into body fluids to regulate physiology

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Cellular Communication

Back 2

Cells must communicate to maintain homeostasis

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Nervous system

Back 3

provides rapid, but short-lived communication using nerve impulses (action potentials)

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Endocrine System

Back 4

–Chemicals secreted into body fluids, provide a slower type of communication

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Types of Cellular Communication
•Paracrine Communication

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–Paracrine Factors produce mostly local effects in surrounding tissue cells
–Prostaglandins, leukotrienes and histamine are examples
–Produce their local effects mostly through interstitial (tissue) fluids

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Types of Cellular Communication
•Endocrine Communication

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–Hormones secreted by glands or tissues
–Reach target cells in the blood
–Usually produce effects at a distance from where they are secreted
–We will restrict our studies to endocrine communication

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Endocrine System

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Composed of glands and tissues that secrete chemical regulators called hormones

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Study of endocrine system is

Back 8

endocrinology

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What do you call a doctor who specializes in diseases of the endocrine system?

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Endocrinologists

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Endocrine System

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•Hormones are chemical regulators
•Secreted into blood by endocrine glands or tissues
•Regulate physiology of other cells/tissues called targets

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Hormones

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function by binding to specific receptors of target cells

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Hormones that cannot enter cell, bind to

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membrane receptors

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Hormones that can enter cell, bind to

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intracellular receptors

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Targets range from

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specific tissues to widespread tissues

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Hormones Regulate

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•Growth
•Metabolism
•Fluid, electrolyte, and acid-base balance
•Reproduction
•Blood pressure
•And other processes such as heart rate, digestion, etc.

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Negative feed back

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–Hormone secretion/actions inhibit stimulus
•As hormone secretion increases, inhibition occurs
•After hormone levels decline, inhibition of stimulus stops and hormone secretion continues again
•Produces on/off effect
•Homeostasis maintained
•Most common control method
–Attempts to maintain homeostasis
–Thermostat analogy (A&P1)

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Positive feed back

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–Stimulus enhances action rather than inhibiting it
–Called positive feedback loop
–Endocrine controlled processes such as:
•Labor
•Beast feeding
–Blood Clotting

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Endocrine Glands and Tissues

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•Examples
–Pituitary gland (hypophysis)
–Thyroid gland
–Parathyroid glands
–Adrenal glands
–Pancreas
–Gonads
–Endocrine tissues within other organs

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Pituitary Gland (Hypophysis)

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•Small gland connected to hypothalamus
•Two parts
–Anterior pituitary (adenohypophysis)
–Posterior pituitary (neurohypophysis)
–Infundibulum – a funnel-shaped structure connecting the pituitary to the hypothalamus

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Anterior pituitary

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adenohypophysis

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Posterior pituitary

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neurohypophysis

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Infundibulum

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a funnel-shaped structure connecting the pituitary to the hypothalamus

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Pituitary Gland

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Hypophysis

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Anterior pituitary largest part

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–Produces and secretes most
of the hormones
–Under indirect control of hypothalamus

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Hypothalamus

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secretes releasing hormones (RH) and some inhibiting hormones (IH)
–Reach anterior pituitary through hypophyseal portal circulation
–Control synthesis and secretion of hormones

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Anterior pituitary Hormones

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secreted (hGH, TSH, PRL, ACTH, FSH and LH)

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Hormones of Anterior Pituitary
•Human Growth Hormone (hGH or GH)

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–Targets most cells especially skeletal and muscle tissue
–Actions-causes growth by:
•↑ rate of cell division for growth
•↑ protein synthesis provides structure needed for growth
•↑ use of fat for energy, especially during prolonged exercise
•↑ rate of bone growth

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Growth Hormone

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–Results in growth to adulthood and maintenance of skeleton and muscles in adults

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–Three disorders caused by imbalances in hGH secretion

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•Pituitary dwarfism
•Gigantism
•Acromegaly

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Pituitary dwarfism

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–Caused by hyposecretion in children
–Results in small body

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Gigantism

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caused by hypersecretion in infants and children resulting in height of 7 to 8 feet

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Acromegaly

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caused by hypersecretion in adults resulting in distorted features

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Thyroid stimulating hormone (TSH)

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–Targets thyroid gland
–Stimulates secretion of most thyroid hormones

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Adrenocorticotropic Hormone (ACTH)

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–Targets suprarenal (adrenal) cortex
–Stimulates secretion of most steroids from suprarenal glands

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Prolactin (PRL)

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–Targets mammary glands
–Stimulates mammary gland development in concert with other hormones
–Stimulates milk production

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Gonadotropins

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–Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH) target the ovaries and testes (gonads) and control female and male reproductive physiology

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Posterior pituitary

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–Hormones produced by hypothalamus and placed in posterior pituitary by neurons

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Posterior pituitary
–Secretes two hormones

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•Oxytocin (OXT or OT)
•Antidiuretic hormone (ADH)

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Oxytocin (OXT)

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–Mostly targets smooth muscles of reproductive system of both sexes

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Oxytocin (OXT)
–Actions in female

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•Labor (uterine) contractions
•Release of milk from mammary glands (milk- letdown)

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Oxytocin (OXT)
–Actions in male

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•Contraction of smooth muscle in reproductive tissue

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Antidiuretic Hormone (ADH) (vasopressin)

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–Targets kidneys, sweat glands and arterioles

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Antidiuretic Hormone (ADH) (vasopressin)

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–Actions
•Causes kidneys and sweat glands to conserve water
•Constricts arterioles

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Thyroid Gland

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Large shield-shaped gland in neck below voice box (larynx)

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Thyroid Gland

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Has two lobes connected by an isthmus

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Histology of Thyroid

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Composed of many follicles filled with jelly-like (colloidal) thyroglobulin protein

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Histology of Thyroid

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Thyroid hormones synthesized by follicle cells and stored in combination with thyroglobulin

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Thyroid Hormones Synthesis

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•Synthesis and secretion stimulated by TSH (thyrotropin)
•Thyroglobulin protein made by follicular cells
•Hormones formed by addition of iodine to the thyroglobulin protein
–3 or 4 iodine atoms added to thyroglobulin
•T3 (triiodothyronine) if 3 iodine atoms added
•T4 (tetraiodothyronine or thyroxine) if 4 iodine atoms added
•Thyroglobulin with hormones stored inside follicle

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Thyroid Hormones Secretion

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•Some thyroglobulin with T3 & T4 taken out of storage by endocytosis
•T3 & T4 harvested from thyroglobulin
• T3 & T4 secreted into blood
•Binds to carrier proteins such as thyroid binding globulins and albumin
•Circulates through body to produces actions

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Target Tissues and Actions of T3 & T4

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•Targets most tissues, but not all
•Actions
–ATP production and use of ATP for energy
–Normal growth
•Control by negative feedback

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Imbalances of T3 & T4

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Thyroid dwarfism (cretinism)
–Too little from birth
–Severe form

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Hyperthyroidism

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–Too much T3 & T4
–Grave’s disease most common form
–Symptoms
•metabolic rate (MR)
•tachycardia
•body temperature (BT)
•anxiety & irritability
•goiter
•Exophthalmos (exophthalmia)
•heat intolerance
•weight loss

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Hypothyroidism

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–Too little T3 & T4
–Symptoms
•metabolic rate (MR)
•bradycardia
•body temperature (BT)
•lethargy
•goiter
•weight gain
•cold intolerance
•swollen face (Myxedema)

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Thyroid Disorders

Back 54

Goiter
Exophthalmos

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Suprarenal (adrenal) Glands

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•Located on top of kidneys
•Hormones adjust metabolism and affect
–Use of nutrients
–Fluid and electrolyte balance
–Energy consumption
•Help maintain homeostasis against stress

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Suprarenal Layers

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•Capsule
•Cortex – outer layer
•Medulla – inner layer
–Secretes catecholamines such
as epinephrine (adrenaline)

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•Capsule

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–Outer CT covering

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•Cortex – outer layer

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–Threes zones
–Secretes steroids

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•Medulla – inner layer

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–Secretes catecholamines such
as epinephrine (adrenaline)

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Cortex

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–Secrete steroid hormones called corticoids
–Three Zones

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Cortex Three Zones

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•Zona Glomerulosa (outer zone)
•Zona Fasciculata (middle zone)
• Zona Reticularis (inner zone)

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Zona Glomerulosa (outer zone)

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–Cells in globular clusters
–Secretes mineralocorticoids such as aldosterone

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Zona Fasciculata (middle zone)

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–Cells form vertical elongated bundles
–Secrete glucocorticoids such as cortisol

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Zona Reticularis (inner zone)

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–Cells form irregular, net-like pattern
–Secrete some sex steroids in both sexes

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Suprarenal Layers

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•Capsule
•Cortical Zones
–Zona Glomerulosa
–Zona Fasciculata
–Zona Reticularis
•Medulla

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Mineralocorticoids from glomerular zone

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–Aldosterone most important
–Regulates plasma sodium, potassium and acid – increases plasma sodium and decreases plasma potassium
–Regulation affects fluid & electrolyte homeostasis

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Glucocorticoids

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–Include cortisol, and lesser amounts of cortisone and corticosterone
–Regulate carbohydrate, proteins and fat metabolism
•Create and store glucose
•Spare glucose by increasing use of fat for energy
•Regulate protein metabolism

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Additional Glucocorticoid Functions

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•Reduce inflammation
•Help maintain blood pressure
•Most of cortisol’s actions help us resist stress

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Imbalances of Cortisol

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Addison’s disease

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Addison’s disease

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–Insufficient cortisol
•Usually caused by own antibodies attacking suprarenal cortex
–Symptoms
•Lack of energy
•Weight loss
•Inability to resist stress
•John F. Kennedy had it

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Imbalances of Glucocorticoids

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Cushing’s Disease

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Cushing’s Disease

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–Excessive cortisol secretion
•Usually caused by tumors in adrenals or elsewhere
–Muscle wasting
•Spindly arms & legs
–Fat redistribution
•Large abdomen with stretch marks
•Rounded face
•Fatty hump between shoulders

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Hormones of Suprarenal Medulla

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Catecholamines - epinephrine (adrenaline) and norepinephrine (noradrenaline)

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Catecholamines - epinephrine (adrenaline) and norepinephrine (noradrenaline)

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–Targets – most cells
–React quickly to stress by:
•heart rate and strength
•blood flow to skeletal muscles, heart and brain
• dilation of airways (bronchodilation)
•fuel for energy-release of glucose from glycogen
•blood pressure

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Suprarenal medulla receives direct innervation from

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sympathetic nervous system

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Suprarenal medulla

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–Develops from same tissue as Autonomic neurons
–Effects mimic those of sympathetic NS
–Cause fight-flight behavior (alarm reaction)

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Sympathetic stimulation increases hormone secretion by

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suprarenal medulla

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Pancreas

Back 78

Large, leaf-shaped organ/gland

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Pancreas

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Located behind stomach, fits into curve of small intestine

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Pancreas

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Both endocrine and exocrine
–Endocrine part controls mostly blood sugar
–Exocrine part secretes digestive enzymes

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Anatomy of Pancreas

Back 81

•Five inches long
•Consists of head, neck, body & tail
•Most of pancreas is exocrine and secretes digestive enzymes
•Endocrine cells produce hormones that control blood sugar and affect metabolism and digestion

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Histology of Pancreas

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•Exocrine acinar cells surround a small duct
•Endocrine cells form Pancreatic Islets (Islets of
Langerhans)
•1 to 2 million Islets
•Contain four types of cells

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Cell Types in the Pancreatic Islets

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•Alpha cells (20%) produce glucagon
•Beta cells (70%) produce insulin
•Delta cells (5%)
•F cells (5%)

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Actions of Insulin
•Insulin lowers blood glucose by:

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– uptake and utilization of glucose by cells
–synthesis of liver and muscle glycogen for storage
–Insulin also protein & fat synthesis

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Actions of Glucagon
•Glucagon increases blood glucose by:

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–breakdown of liver glycogen into glucose
–fat break-down (catabolism) to fatty acids in adipose tissue
–Synthesis of glucose from amino acids in liver
–release of glucose from liver into blood

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Regulation of Glucagon & Insulin Secretion

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•Rising blood glucose after meal stimulates secretion of insulin and inhibition of glucagon
•Falling blood glucose when fasting stimulates release of glucagon and inhibition of insulin

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Diabetes Mellitus

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•Beta cells destroyed or cells do not respond to insulin
–Decreased uptake of glucose into cells
•Blood glucose becomes elevated – hyperglycemia

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Diabetes Mellitus
•Two Types:

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–Type I (IDDM) or juvenile DM
–Type II (NIDDM) or maturity onset DM

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–Type I (IDDM) or juvenile DM

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•Beta cells destroyed by own immune system
•Insulin levels low
•Insulin injections required
•Usually develops in people younger than 20

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–Type II (NIDDM) or maturity onset DM

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•Most common type (90%)
•Insulin secreted but cells become less sensitive to it
•Insulin injections may not be required
•Mostly in people over 35 who are over weight
•May be controlled by diet

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Three Signs (P’s) of DM

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•Polyuria
•Polydipsia
•Polyphagia

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Complications of DM

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•Cardiovascular disease
•Loss of vision
•Kidney disease
•Diabetic Coma
•Most complications linked to high glucose and acidosis
•Acidosis caused by excessive use of fat for energy instead of glucose