the endocrine system dr. anderson gcit. endocrine system a collection of glands that work together...
TRANSCRIPT
The Endocrine System
Dr. Anderson GCIT
Endocrine System
• A collection of glands that work together to maintain the homeostasis of the body by:
• Coordinating ____________________________and activity via chemical communication
The Theory of Communication
• All communication has at least three parts
• Sender – entity that releases information• Message – the forms of the information itself• Receiver – the entity that collects and
interprets the information contained in the message
Hormones
• Hormones are chemicals released by glands that control the function/activity of cells generally far from the source of production
Body Communication
• Sender?
• Message?
• Receiver?
Tissue that creates the hormone
The hormone itself
The target tissue
Autocrines vs. Paracrines
Autocrines – cells produce hormones that effect themselves
Paracrines – cells produce hormones that effect other nearby cells
How can chemicals alter cellular function?
Hormones can…
• 1. Alter cell membrane permeability• 2. Stimulate synthesis of proteins or enzymes• 3. Activates or deactivates enzymes• 4. Induces exocytosis• 5. Stimulates mitosis
Human Growth Hormone – Normal Amounts
Examples – HGHAbnormally High Amounts
Testosterone – Normal Amounts
Testosterone – Abnormal Amounts/ Gender Differences
Hormone Classification
• 3 Chemical classes– Amino acid based– Steroid-based (sterols)– Eicosanoid (lipid-based)
• What is the most important functional difference between these molecules?
Amino acid-Based Hormones
• Water soluble, so can diffuse through blood and body fluids easily
• However, they are generally fat-insoluble• How do they enter and affect cells?
Receptor Proteins
• Target cells have receptors for each hormone– Not every cell has all receptors
• Receptors bind with hormones to start a series of events, ultimately changing cell function
Water Soluble (Amino acid-based) Hormones
Fat-Soluble Hormones
• Can go right through the cell membrane!
• Bond with receptor proteins in the cytoplasm instead of the cell membrane
• Receptor-hormone complex can bond to DNA to initiate gene expression
Fat-Soluble Hormones
Hormone Life (Half-life)
• Presence of a hormone in the blood is limited by:
1.
2.
3.
Hormone Release• What controls the release/retention of
hormones?
1. Humoral Stimulus – Blood levels of certain ions/nutrients
2. Neural Stimulus- Nerve fibers stimulate hormone release
3. Hormonal Stimuli – hormones tell glands to release/retain hormones
Regulation
• Hypothalamus – regulates most hormonal release in the body– Monitors body
homeostasis (blood sugar, wastes, hormone levels)
– Direct link to pituitary gland
Pituitary gland
Hypothalamus Hormones
• The hypothalamus makes two hormones that are stored in the posterior pituitary gland– ADH– Oxytocin
• These hormones travel down the infundibulum ( nerve extensions) into the posterior pituitary where they are stored
Pituitary Gland• Bi-lobed structure that stores and produces
hormone• Under the direct control of the hypothalamus!
Pituitary Gland (Hypophysis)
Posterior Pituitary
• Does not create, but rather stores hormones that are made in the hypothalamus
• Derived from nervous tissue– Anti-diuretic hormone (ADH) -
– Oxytocin
Anterior vs. Posterior Pituitary
Anterior Pituitary• Derived from epithelial tissue (secretory cells)
• Creates MANY hormones de novo– Human growth hormone (HGH)– Thyroid Stimulating Hormone (TSH)– Adrenocorticotropic Hormone– Prolactin– Leutinizing Hormone– Follicle Stimulating Hormone
• Released or inhibited as directed by hormones from hypothalamus (stimulates or inhibits AP hormone production and release)
Pituitary Perfusion (Posterior)
• Posterior Pituitary (PP) is perfused with one major artery and vein
• Carries PP hormones out to body
Pituitary Perfusion (Anterior)
• Capillaries are “split” (form plexi) twice!– Primary capillary
plexus– Secondary capillary
plexus
• Why???
Primary plexus
Secondary plexus
Thyroid Gland• Surrounds the
trachea (bilateral lobes)
• Produces the hormone thyroxin
• Why is this not considered to be an exocrine gland?
Thyroid Structure• Principal (Follicle)
Cells – produce thyroglobulin
• Colloid – stores thyroglobulin and iodine molecules
• Parafollicular cells – produce calcitonin
Thyroid Synthesis1. Thyroglobulin made by follicular cells and goes
into follicle2. Iodine trapped from the blood (active
transport)3. Iodide converted to iodine4. Iodine attached to tyrosine5. Iodinated tyrosines are linked6. Thyroglobulin is endocytosed7. Thyroid hormone is processed by enzymes
and diffuse from the cell into the blood stream
Thyroid Production
Calcitonin• Produced by the
parafollicular cells in the thyroid
• Release of calcitonin results in lowered blood Calcium– 1. Inhibits osteoclast activity– 2. Enhances bone absorption
of Ca.
The Parathyroid Glands
• Paired glands located on the posterior aspect of the thyroid
• They produce parathyroid hormone which control Calcium levels in the blood– Antagonist of calcitonin (inhibited by rising Ca
levels)
The Adrenal Glands
• Divided into two sections– Adrenal Medulla (the
core of the gland)
– Adrenal Cortex (the outermost layer of tissue)• Zona glomerulosa• Zona fasciculate• Zona reticularis
Adrenal Cortex
• Produces corticosteroids (derived from cholesterol!)
• Each zone of the cortex produces its own suite of hormones that are functionally specific
Adrenal Cortex – Zona glomerulosa
• Produce mineralocorticoids– Regulate ion concentration in blood and interstitial
fluid
– Aldosterone reduces excretion of Na + from the body and enhances resorption • Production triggered by low blood volume, low blood
pressure and increases in K+ ion concentration.
• Why is this important?
Glucocorticoids
• Synthesized in zona fasciculata
• Cortisol – steroid-based hormone– Release of cortisol promoted
by ACTH release– Depresses inflammation,
increases blood sugar by provoking gluconeogenesis
Gluconeogenesis
• Where do sugars normally come from?
• Gluconeogenesis -
Gonadocorticoids
• Secreted in the zona fascicularis/reticularis
• Most are weak androgens (precursors to testosterone and estrogen)– Not really (anabolic) steroids?
• Play a large role during puberty (both sexes) and female sex drive
The Adrenal Medulla• Chromaffin cells produce
catecholamines – Epinephrine– Norepinephine
• Released during fight-or-flight stress– Increases heart rate,
constricts blood vessels (increasing blood pressure) for a short time
Pineal Gland
• Located in the diencephalon
• Produces melatonin, which causes drowsiness
• Decreased light, received by the eyes (to brain) stimulate the release of melatonin
Pancreas
• Organ most directly related in regulating blood sugar
• Two hormones produced– Glucagon – produced by alpha cells when blood
sugar is low (hypoglycemia)– Insulin – produced when blood sugar is high
(hyperglycemia)
Pancreas
Glucagon
• When released from the pancreas, 1. causes the breakdown of glycogen (liver starch)
into sugar2. Gluconeogenesis3. Release of glucose from liver cells into the blood
Insulin
• When released from the pancreas, insulin…
1. Enhances cellular uptake of blood glucose2. Inhibits gluconeogenesis3. Inhibits the breakdown of glycogen to
glucose
Diabetes mellitus• Due to low or non-functional insulin
• Since sugar cannot be absorbed into body cells:– Blood sugar levels rise (hyperglycemia)– This stress causes the body to release MORE
glucose into the blood!• Gluconeogenesis from fat and protein conversion, the
waste products of which lead to ketoacidosis (nail polish breath)
Diabetes Symptoms
• In the kidneys, sugar lost in urine pulls water from the blood at excessive rates (polyuria)
• Dehydration leads to excessive thirst (polydipsia)
• Excessive hunger (polyphagia) results as fat stores are used in a effort to get sugar into body cells
Ovaries
• Ovaries – produce estrogen and progesterone
– Estrogen – regulates monthly menstrual cycle
– Progesterone – support pregnancy and menstruation
Menstrual Cycle
Testes
• Produce testosterone leading to puberty (secondary sex characteristics), aggression, muscle growth