Endocrine SystemGlands and Hormones

Definitions

• Hormones are chemicals regulators, secreted into the blood, that affect the functioning of other cells

• These “other cells” are called target cells • Hormones are specific for certain targets because

hormones bind to specific receptors of target cells

Hormones Regulate

• Growth• Metabolism• Fluid and electrolyte• Acid-base balance• Reproduction• Blood pressure

Endocrine Glands and Tissues• Secrete hormones

Examples – Pituitary gland

(hypophysis)– Thyroid gland– Parathyroid glands– Adrenal glands– Pancreas– Gonads– Endocrine tissues within

other organs

Chemistry of hormones • Compounds that act as hormones are:

– Steroids (derived from cholesterol)– Amines (derived from a single amino acid)– Peptides (smaller chains of amino acids)– Proteins (polypeptide chains of amino acids)– Glycoproteins (protein/carbohydrate complex)

Hormone SecretionStimulus

Gland

Target cell

Hormone secretion

Action

Blood

Receptor------------

----------------Hormone

Control of Secretion

• Negative feed back – Stimulus is decreased or inhibited by some factor

such as concentration of hormone – Attempts to maintain normal levels of secretion

• Positive feed back – Stimulus for secretion is increased or exaggerated

Specific Glands

Pituitary Gland (Hypophysis)• Small gland connected

to hypothalamus • Two parts

– Anterior pituitary (adenohypophysis)

– Posterior pituitary (neurohypophysis)

posterior pituitary---------

-------anterior pituitary

hypothalamus

---------infundibulum

Pituitary Gland

• Posterior pituitary derived from neural brain tissue and connects to hypothalamus by the stalk-like hypothalamic hypophyseal tract

• Anterior pituitary from ectodermal tissue in the roof of embryonic mouth.

-----------------------infundibulum

Pituitary Gland

• Posterior pituitary secretes two hormones – Hormones produced by hypothalamus and

placed in posterior pituitary for secretion• Anterior pituitary largest part

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

• Hypothalamus secretes releasing and inhibiting hormones that reach anterior pituitary through hypophyseal portal circulation.

Hormones of the Posterior Pituitary

• Oxytocin (OT)– Target tissues are smooth muscles of reproductive

system of both sexes– Actions in female

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

– Actions in male• Contraction of smooth muscle in reproductive tissue

Hormones of Posterior Pituitary

• Antidiuretic Hormone (ADH) (vasopressin)– Target tissues are kidneys, sweat glands and

arterioles– Actions

• Causes kidneys and sweat glands to conserve water• Causes vasoconstriction of arterioles

Hormones of Anterior Pituitary • Human Growth Hormone (hGH)

– Targets all cells especially skeletal and muscle tissue – Actions

• Promotes secretion of insulin-like growth factors (IGFs) within target tissues

• IGFs increase: -rate of cell division for growth -protein synthesis needed for

growth

-use of fat for energy • Results in growth to adulthood and maintenance of

skeleton and muscles in adults

Hormones of the Anterior Pituitary

Human Growth Hormone Imbalances • Pituitary dwarfism caused by hyposecretion in

children and adolescents resulting in small body• Giantism caused by hypersecretion in infants and

children resulting in height of over 8 feet• Acromegaly caused by hypersecretion in adults

resulting in distorted facial features

Giantism

Acromegaly

Hormones of Anterior Pituitary

• Thyroid stimulating hormone (TSH)– Targets thyroid gland– Stimulates secretion of the thyroid hormones

• Adrenocorticotropic Hormone (ACTH) – Targets Adrenal cortex– Stimulates secretion of glucocorticoids from

adrenal glands

Hormones of Anterior Pituitary

• Prolactin (PRL)– Targets mammary glands – Stimulates milk production in mammary glands in

concert with other hormones• Gonadotropins

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

• Secretion Stimulated by releasing hormones (RH’s) from hypothalamus through hypophyseal portal system

• Secretion suppressed by inhibiting hormones (IH’s) from hypothalamus through hypophyseal portal system

• All controlled by negative feedback

Control of Secretion of Anterior Pituitary Hormones

Thyroid Gland

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

• Has Two lobes connected by an isthmus

right lobe----- --------left lobe------------isthmus

thyroid follicle-----

Histology of Thyroid• Composed of many

follicles filled with jelly-like (colloidal) thyroglobulin protein

• Thyroid hormones T3 and T4 synthesized by follicle cells and stored in combination with thyroglobulin

Thyroglobulin with T3 and T4

Thyroid Hormones

• T3 short for triiodothyronine

• T4 short for tetraiodothyronine (thyroxine)

Thyroid Hormones

• Formed by addition of iodine to the thryroglobulin

• 3 & 4 stands for number of iodines

Secretion of T3 & T4

• Synthesis and secretion stimulated by anterior pituitary hormone TSH

• Portion of stored thyroglobulin taken in from colloid by follicles cells

• Colloid digested by lysosomes releasing T3 & T4

• T3 & T4 enter blood, combine with transport proteins and are transported to target cells

Synthesis and Secretion of T3 & T4

Figure 18.11 in text

Target Cells and Actions of T3 & T4

• Actions ATP production by mitochondria

(aerobic cell respiration)– Normal growth

• Control by negative feedback

Thyroid and Negative Feedback

• Increase in blood levels of T3 & T4 etc.

• Release of thyrotropin releasing hormone (TRH) inhibited

• Release of thyroid stimulating hormone (TSH) inhibited

• Secretion of T3 & T4

decreases

Imbalances of T3 & T4

• Thyroid dwarfism (Cretinism)– Too little secretion of thyroid hormones

during fetal development and infancy.– Severe forms of mental and physical

retardation in the newborn.– Retardation is reversible if hormonal

replacement therapy is started during the first four months of life.

Imbalances of T3 & T4

• Hypothyroidism (in adults)– Too little T3 & T4 – Symptoms

MR• bradycardiaBT• lethargy• goiter• weight gain• cold intolerance• myxedema

Imbalances of T3 & T4

• Hyperthyroidism (in adults)– Too much T3 & T4

– Grave’s disease most common form– Symptoms

MR• tachycardiaBT• anxiety & irritability• goiter• Exophthalmia (exophthalmos)• heat intolerance• weight loss

Imbalances of T3 & T4

• Endemic goiter and iodine deficiency – Insufficient dietary iodine to make T3 & T4

– Endemic means localized or regional– Lack of negative feedback from T3 & T4

causes over stimulation and overgrowth of the thyroid gland.

– Goiter results (enlarged thyroid gland)

Thyroid Disorders

Endemic Goiter Exophthalmia

Control of Blood Calcium

• Calcitonin (CT) from thyroid lowers blood calcium by adding it to bones

• Parathyroid hormone from parathyroid glands (small pea-shaped gland embedded in back of thyroid) increases blood calcium by removing it from bones

Adrenal Glands

• Located on top of kidneys

• Gross Anatomy– Enclosed by

capsule– Outer cortex– Inner medulla

Structure of Adrenal Gland

Histology of Adrenal Glands

• Cortex with three zones– Secrete steroid hormones called corticoids– Outer (glomerular) zone

• Cells in globular clusters• Secretes mineralocorticoids

– Middle (fascicular) zone• Cells form vertical elongated bundles • Secrete glucocorticoids

Histology of Adrenal Glands

– Inner (reticular) zone • Cells form irregular, net-like pattern• Secrete some sex steroids in both sexes• More important in females

– Affects female sex drive– Produces some estrogens

• Secretion stimulated by ACTH

Corticoids

• Mineralocorticoids: glomerular zone– Aldosterone most important– Regulates blood sodium, potassium and

acid– Regulation affects fluid & electrolyte

homeostasis

Corticoids• Glucocorticoids from fascicular zone• Principle one is cortisol• Actions include

– Response to stress byGlucose formation from fats and protein• Conversion of excess glucose to glycogen for

storage in liveruse of fat for energy assures glucose availability

for brain

Corticoids

• Glucocorticoid actions• Reduce inflammation• Various steroids including cortisol,

cortisone, and synthetic steroids used medically to reduce inflammation

• Control is by negative feedback

Imbalances of Glucocorticoids

• Addison’s disease– Insufficient glucocorticoids– Lack of energy– Weight loss– Inability to resist stress– John F. Kennedy had it

Imbalances of Glucocorticoids

• Cushing’s Disease– Excessive glucocorticoids– Muscle wasting– Fat redistribution– Spindly arms & legs– Large abdomen with stretch marks– Rounded face– Fatty hump between shoulders

Addison’s Disease – President Kennedy

Before Steroid TreatmentDuring Steroid Treatment

Cushing’s Syndrome

Before After

Adrenal Medulla• Develop from same tissue as the sympathetic

nervous system• Chromaffin cells receive direct innervation

from sympathetic nervous system• Sympathetic stimulation increases hormone

secretion by adrenal medulla• Hormones are sympathomimetic

– effects mimic those of sympathetic NS– cause fight-flight behavior

Hormones of Adrenal Medulla• Catecholamines • epinephrine and norepinephrine • (adrenaline & noradrenaline)

– Targets – most cells– React quickly to stress by:

heart rate and strengthblood flow to skeletal muscles, heart and brain• Dilation of airwaysfuel for energyblood pressure

Pancreas• Large leaf-shaped gland• Located in the curve of small intestine and

extend to the spleen• Both endocrine and exocrine

– Endocrine part secretes hormones– Exocrine part secretes digestive enzymes

Anatomy of Pancreas

• Five inches long, consists of head, body & tail• Most cells produce digestive enzymes• Endocrine cells in pancreatic islets produce hormones

Cell Organization in Pancreas

• Exocrine acinar cells surround a small duct• Endocrine cells secrete near a capillary

Histology of the Pancreas

• 1 to 2 million pancreatic islets• Contains 4 types of endocrine cells

Cell Types in the Pancreatic Islets

• Alpha cells (20%) produce glucagon• Beta cells (70%) produce insulin• Delta cells (5%) produce somatostatin• PP cells (5%) produce pancreatic

polypeptide

Actions of Insulin

• Insulin decreases blood glucose by: uptake of glucose into cells synthesis of liver glycogen for storage

• Insulin also protein & fat synthesis

Actions of Glucagon

• Glucagon increases blood glucose by: Synthesis of glucose from amino acids in the

liver breakdown of liver glycogen into glucose release of glucose from liver into blood

Regulation of Glucagon & Insulin Secretion

• High blood glucose after a meal stimulates secretion of insulin and inhibits secretion of glucagon

• Low blood glucose when fasting stimulates release of glucagon and inhibits secretion of insulin

FED STATE

FASTING STATE

Diabetes Mellitus

• Insulin is unavailable for uptake of glucose into the cells

• Or the cells are not responding to insulin• Blood glucose levels becomes elevated –

hyperglycemia

Diabetes Mellitus

• Two Types:– Type I (IDDM) or juvenile DM

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

Diabetes Mellitus

– Type II (NIDDM) or maturity onset DM• Most common type (90%)• Insulin may still be secreted but cells may be

less sensitive to its actions• Insulin injections may not be required• Mostly in people over 35 who are obese• May be controlled by diet

Three Signs (P’s) of DM

• Polyuria- Excessive urination

• Polydypsia- Excessive water drinking

• Polyphagia- Excessive eating

Complications of DM

• Cardivascular disease• Loss of vision• Kidney disease

- Most complications linked to high glucose and acidosis

- Acidosis caused by excessive use of fat for energy instead of glucose