Download Endocrine System

Endocrine System
Glands 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
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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:
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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 Secretion
Stimulus
Gland
----------------Hormone
Hormone secretion
Blood
Receptor-----------Target
cell
Action
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)
hypothalamus
---------infundibulum
posterior
pituitary---------
-------anterior pituitary
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
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Follicle Stimulating Hormone (FSH) and
Luteinizing Hormone (LH)
Target the ovaries and testes (gonads)
Control female and male reproductive physiology
Control of Secretion of Anterior
Pituitary Hormones
• 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
Thyroid Gland
• Large butterflyshaped 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 jellylike (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
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MR
bradycardia
BT
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
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MR
tachycardia
BT
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 by
• Glucose formation from fats and protein
• Conversion of excess glucose to glycogen for
storage in liver
• use 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
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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 Treatment
During 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 strength
• blood flow to skeletal muscles, heart and brain
• Dilation of airways
• fuel for energy
• blood 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
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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